Elisabeth C. Miller Library

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Search Results for: Insect pests--Control | Search the catalog for: Insect pests--Control

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Washington Toxics Coalition

Northwest Coalition for Alternatives to Pesticides

Natural Pesticides

Virginia Tech Insect ID

Information Resources for Pests and Diseases

National Sustainable Agriculture Information Service— pest management

Integrated Pest Management Information

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Plant Answer Line Question

Keywords: Insect pests--Control, Trees--Diseases and pests, Pesticides

What is the latest method of eradication for the mountain pine beetle, Dendroctonus ponderosae, that is rampant in western Canada?


In the northwestern U.S., Washington State University's Forest Health Notes (page 9) states that the focus has shifted from using pesticides to taking preventive measures:
Control methods have shifted away from direct control (e.g. spraying, felling, burning) and towards prevention of outbreaks. This course of action was chosen after thoroughly exploring direct control measures for nearly a century and arriving at a simple conclusion: They don't work. It is possible to prevent infestation with penetrating sprays on individual, high value trees such as those in campgrounds and near houses, but they need to be applied before the tree is infected and the cost of such treatments is prohibitive for any large-scale application.
Once a mountain pine beetle outbreak begins to spread, it can be stopped by thinning the stand ahead of the edge of the outbreak. This is because outbreaks expand on a tree to tree basis where the incoming beetles switch their attacks from a recently attacked-stem to the next largest tree. More importantly, infestations can be prevented by thinning stands before crown closure, an operation that not only increases the vigor of the residual stand, but also prevents the spread of an outbreak if individual trees have been attacked.
Mountain pine beetles are a natural part of western ecosystems, and for this reason will never be completely eradicated (nor should they be, as they serve to create small stand openings which are important for biodiversity of both flora and fauna). As such, the death of a few trees on your property doesn't necessarily mean an epidemic is getting started; check your trees for root disease symptoms. To maintain mountain pine beetles at their normal levels, predisposing factors for outbreak must be removed. Some of these, such as environmental stresses, are not possible to control. However, many stresses are related to stand management practices. First and foremost, two situations need to be addressed: root disease centers and overstocked stands. More details about treatment for root disease centers have been given in other WSU Cooperative Extension "Forest Health Notes;" in summary, they need to be identified and planted with resistant species. Overstocking causes trees to compete for water, light and nutrients, and thus weakens their defenses against bark beetle attack. To minimize stand stresses and maintain vigorous growing conditions, stand managers should: (adapted from Berryman: Forest Insects, 1986).

Natural Resources Canada has a task force on the mountain pine beetle. You might want to contact them for the latest update. Go to their mountain pine beetle website and follow the links for additional information, including how to contact CCoFI.

Date 2018-04-21
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Plant Answer Line Question

Keywords: Insect pests--Control, Wildlife pests, Moles

I live in Seattle and have, for the first time this fall, noticed dirt mounds on my property. These mounds tend to be located near patios/driveways, and are not in the sod. They are loamy, with no apparent holes, and are about three to five inches high. I wouldn't call them conical. There are no mole tunnels, and, as far as I can see, no bugs. The mounds are bigger than the little fine-grain mounds I have noticed in years past with small black ants crawling in them. Is there someone I can ask about what is causing these mounds, and if it is something to be concerned about? Could it be ants or mice?


From your description of the dirt mounds, it sounds as though the critter in your yard may be either a mole or a gopher. The easiest way to tell the difference is by the type of mound you have. Here is information on moles and pocket gophers from Washington Department of Fish and Wildlife's Living with Wildlife website.

Below is additional information from "Of Bugs and Blights" (in Balls and Burlaps, February 1988, pp. 4 and 14):

A gopher mound fans out from a hole near one edge of the mound. This hole remains plugged while the gopher is on the runway system. The gopher mound is relatively flat compared to the mole mound. Gopher mounds vary from 1 to 3 feet in diameter...several mounds often will be found together. They are not regularly found in a line as are mole mounds. The mole mound is somewhat conical and not much over a foot in diameter. The hole is not evident when you look at the mound. Push the soil aside and you will find it under the center of the mound. Each mound is connected with the other in a line by the moles' runway system.

According to the article quoted above, moles are more likely to be found in gardens in Western Washington than are gophers. We have the journal Balls and Burlaps in the Miller Library. The article discusses the problems and benefits of moles, as well as control methods.

I also consulted the Western Garden Problem Solver (Sunset Books, 1998) to see if I could identify your mound-maker. Ground squirrels leave their burrows open, so if your mounds show no opening, you probably don't have squirrels. Mole mounds appear volcano-like, with signs of soil excavation.

Here is a link to information on ants and their nests which you might look at to see if the images resemble the mounds of soil you are seeing.

Date 2018-09-12
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Plant Answer Line Question

Keywords: Insect pests--Control, Arctostaphylos, Aphids

My Arctostaphylos uva-ursi has suffered from galls caused by aphids. What approach would be best to combat the aphids and when is the best time in their life cycle to attack?


Kinnikinnick or Arctostaphylos uva-ursi sometimes suffers from galls caused by aphids, and is also susceptible to fungal diseases. If your plant has galls, you would see distorted, thickened, and often reddish leaves which almost don't seem leaf-like. The aphids may also secrete honeydew which can then turn blackish with mold.

Douglas Justice, University of British Columbia Botanical Garden Associate Director offers these comments on Arctostaphylos uva-ursi:

The Arctostaphylos uva-ursi cultivar 'Vancouver Jade' -- a UBC introduction and one of the most widely grown cultivars in temperate climates -- is adapted to wetter conditions than many other cultivars, as it was selected from the Pacific Northwest. Nevertheless, like all kinnikinnicks, it is not a plant for poorly drained, shaded or high traffic areas. And unfortunately, it appears to be rather more susceptible to manzanita pod gall aphid than other cultivars. Populations of that insect pest can build up during "warm winter" periods (such as we've been experiencing in Vancouver over the past several years) and disfigure plants significantly.
Source: UBC Botanical Garden Forums

Oregon State University has information about leaf gall on Arctostaphylos uva-ursi in their Plant Disease management handbook online.

The following, from Pacific Northwest Insect Management Handbook (WSU, OSU and U. of Idaho, 2005) provides more information about the aphids.

Kinnikinnick Arctostaphylos - Aphids

Manzanita leafgall aphid, Tamalia coweni:

Pest description and crop damage - Manzanita leafgall aphids are grayish or greenish in color and prefer new growth. They feed on the leaves of kinnikinnick and other manzanita species (Arctostaphylos spp.). Aphid feeding causes the leaves to thicken and form bright red galls. Older galls turn brown. Severe infestations may slow the growth of the plant.

Nongall-forming aphids also may be seen occasionally on kinnikinnick. They are greenish, soft-bodied insects that may feed on leaves or stems. Honeydew, a sweet, sticky material, may be associated with aphid feeding. It may attract ants or become covered with a growth of dark, sooty mold. Severe infestations may result in leaf and twig dieback.

Management-biological control: Syrphid fly larvae are important predators of leafgall aphids, and will feed on them inside the galls. Avoid use of broad-spectrum insecticides which kill these and other beneficial insects such as ladybird beetles and parasitic wasps.

Management-cultural control: Prune off and destroy galls where seen. Avoid frequent shearing and overfertilization, which encourages succulent new growth favored by aphids. Wash other aphid pests from plants with a strong stream of water or by hand-wiping. Avoid excessive watering, and use slow-release or organic sources of nitrogen. Control ants, which "farm" aphids and protect them from predators in order to harvest their honeydew.

Date 2018-08-23
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Plant Answer Line Question

Keywords: Whiteflies, Insect pests--Identification, Insect pests--Control, Root weevils, Rhododendrons--Diseases and pests, Dahlia

I have a line of Ward's ruby azaleas. The three weakest ones have a lot of tiny notches in the leaves. I seem to remember the notches from the root weevil as being larger than these. Are the tiny notches from something else?

I also noticed that some of my dahlias have splotched leaves and that when I disturb the leaves, white-looking insects fly off the leaves. These flies apparently have spread to tomatoes as well. Are these whitefly? Will they disappear after the winter or is there some control I should use to prevent them from taking over?


First you need to get an accurate diagnosis of your problems. If you are in King County, you can bring samples to a Master Gardener Clinic. For information about Clinic hours see their website (Plant Clinic Schedule).

Oregon State University offers this information about root weevils and Rhododendron (which includes Azaleas). It describes using beneficial nematodes as a control.

According to Washington State University Cooperative Extension's publication, How to Identify Rhododendron and Azalea Problems (1984), root weevil damage to foliage is not usually a serious problem. You can check for weevils with a flashlight at night to confirm that they are the source of the notches you are seeing. There are some Neem oil-based products that may be helpful, but they must be used at the correct times of year. See WSU's HortSense page.

As for the dahlias and tomatoes, it is important to determine exactly what the insects are before proceeding with treatment. If they are whiteflies, you can put yellow sticky traps around the plants to trap them. University of California, Davis's Integrated Pest Management site has other recommended control methods, including reflective mulch. You may not want to use insecticidal soap:
"Insecticides have only a limited effect on whiteflies. Most kill only those whiteflies that come in direct contact with them. For particularly troublesome situations, try insecticidal soap or an insecticidal oil such as neem oil or narrow-range oil. Because these products only kill whitefly nymphs that are directly sprayed, plants must be thoroughly covered with the spray solution. Be sure to cover undersides of all infested leaves; usually these are the lowest leaves and the most difficult to reach. Use soaps when plants are not drought-stressed and when temperatures are under 80 degrees F to prevent possible damage to plants. Avoid using other pesticides to control whiteflies; not only do most of them kill natural enemies, whiteflies quickly build up resistance to them, and most are not very effective in garden situations."

Date 2017-08-15
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Plant Answer Line Question

Keywords: Crassula, Insect pests--Identification, Insect pests--Control, House plants

My 100-year-old Jade plant is about 5 feet tall and recently has been producing a sap from its leaves. White and sticky. Is there anything I can do to help this? Is it normal? Or is it endangering the plant? It is in kind of a cool spot; should I move it to a warmer place? It is a succulent, right? I would also like some information about repotting if necessary.


The pests most likely to cause a white, sticky substance are aphids, whiteflies, scale or mealybugs. These are known to affect jade plant, or Crassula ovata, which is indeed a succulent. They won't destroy plants, but can weaken them and allow other problems to surface. If none of the pest descriptions below resemble what you are observing, you can take affected plant samples to a local county extension agent. Without knowing the specific pest, we can't suggest specific treatments. Northwest Center for Alternatives to Pesticides has general information on caring for houseplants. Note their description of mealybugs, which do produce a sticky substance:
"These insects look like little bits of cotton that are greasy or waxy. They are oval in shape, have a segmented body, and are about 1/4 inch long. You'll usually find them hidden between leaves and stems or under leaves. They move slowly. They make a sticky liquid called honeydew and also cause leaves to become distorted and spotted."

As for temperature and repotting, The New House Plant Expert (by D. Hessayon, 1991, p. 212), says that succulents like a difference between day and nighttime temperatures. They like to be kept cool in the winter, with 50-55 degrees F ideal, but as low as 40 is alright. Jade plants should only be repotted when essential. Repotting should occur in the spring; shallow pots rather than deep ones are preferable.

Extensive care information can be found on Succulent-plant.com. There is also excellent general information on indoor care of succulents and cacti from Brooklyn Botanic Garden.

Date 2018-06-14
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Plant Answer Line Question

Keywords: Mealybugs, Scale insects, Insecticidal soap, Crassula, Insect pests--Control, House plants

I have been nursing a Jade plant cutting that dropped off an overwatered and rotting larger plant. It has been thriving in my windowsill for 6 months or so, and has grown a lot already.

In the last week or so, I have noticed a strange white speckling on the upper surface of almost all of its leaves. Upon close inspection, it does not look like insects; it looks sort of like a detergent residue, and if I scrape my nail against the surface of the leaf, a lot of it will come off, albeit with effort.

Do you know whether this is something I need to treat?


I wouldn't assume the spots are a problem. As the following link to North Dakota State University Extension mentions, it might be salt crystals that you are seeing:
"Those dots are salt crystals and can be wiped off with a damp cloth or just ignored because they are not causing any harm to the plant. All water (except distilled) contains some salt. When fertilizer is added to the root system, the plant takes up the nutrient salts with the water. As the water moves through the leaf pores during transpiration, the salts often are left behind on the surface."

However, if you were to use a hand lens (not just the naked eye) and discover insects, there are resources with information on identifying and treating insect problems on indoor plants.

1. http://www.succulent-plant.com/pests.html

2. Washington State University's PestSense site lists several common houseplant pests, with information about treatment.

Always test any spray on one leaf before spraying the entire plant.Wait a few days after the test spray. Some plants are more sensitive to various soaps or oils.

3. The Northwest Center for Alternatives to Pesticides also has a guide to Growing Houseplants Without Using Pesticides.

Date 2018-06-14
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Plant Answer Line Question

Keywords: Insect pests--Control, Fuchsia

My fuchsias have gall mites. Will a horticultural oil control them? I would prefer not to use a more toxic pesticide.


Several resources I consulted confirm what you thought about using horticultural oil to control the gall mite problem. The Organic Gardener's Handbook of Natural Insect and Disease Control (ed. by Ellis and Bradley, 1996) says to spray dormant oil or lime-sulfur on dormant plants.

University of California, Davis's Integrated Pest Management site has a page about this gall mite, recommending that gardeners "plant only resistant fuchsias and consider replacing susceptible plants. Prune or pinch off and destroy infested terminals. If damage cannot be tolerated, pruning may be followed with two applications of a miticide, applied 2 to 3 weeks apart. Soap or oil sprays provide some control, but cannot kill fuchsia gall mites enclosed in distorted plant tissue."

According to a May 2004 article from the American Fuchsia Society, "to be effective, [horticultural oil] must come in contact with every live gall mite and smother every gall mite egg. The only way oil products can be effective in killing gall mites is for you to remove the leaves." Link to this article.

Date 2018-08-15
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Plant Answer Line Question

Keywords: Insect pests--Control, Integrated pest management

Is it normal to have many different insect pests in one garden? Is it a sign that I am not taking care of my plants well? Everything looks fine except for one infestation after another!


As far as I am concerned it is perfectly normal to have all of these pests (because I also have many)! But some gardeners are more ruthless than I am. They would rip out the plants. Others would assault their garden with chemicals. I prefer the middle ground of tolerance of some damage and using low-toxic controls.

The mantra these days is RIGHT PLANT RIGHT PLACE and HEALTHY SOIL = HEALTHY PLANTS. For further information (and support) go to the Seattle Public Utilities website, which has a number of great publications on Natural Lawn and Garden Care. There are lots of links to browse.

There is also information about Natural Pest, Weed, and Disease Control.

Other good resources are Toxic-Free Future (formerly known as Washington Toxics Coalition) and Northwest Center for Alternatives to Pesticides.

Date 2017-08-04
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Plant Answer Line Question

Keywords: Insect pests--Control

Is there really a plant that will ward off mosquitoes, and if so, what is the name and is it available in the Seattle area?


There is disagreement about the extent to which certain plants repel mosquitoes. Below, please find some web sites that highlight some plants that may work.

There are eleven plants generally thought to repel mosquitoes:

Citronella, Eucalyptus, Pennyroyal, Rosemary, Rue, and Wormwood. Milder ones (in our experience) include Basil, Bay, Lavender, Sage and Thyme. With even the smallest of herb gardens, or access to a supermarket selling freshly-cut herbs, the leaves of such plants can simply be rubbed on pets and people to temporarily ward off insect attacks.
(Source: Janette Grainger & Connie Moore. Natural Insect Repellents for Pets, People & Plants. 1991, p.11.)

According to Donald Lewis of the Department of Entomology at Iowa State University, citrosa, lemon thyme or citronella grass may help repel mosquitoes, but you have to crush the leaves and rub them on your skin to make them work.

According to the MadSci Network, citronella oil may be more effective at repelling mosquitoes than the plant itself.

Lastly, Colorado State Cooperative Extension recommends scented geranium, lemon grass and a host of other plants.

There are many local nurseries which may carry the plants mentioned above, but since inventory changes frequently and they do not list their inventory online, it is best to give them a call to find out if plants you are seeking are available.

Because of the ongoing concern about West Nile Virus, there is a lot of information available on ways to control mosquitoes. See King County Public Health's resources on this topic.

Date 2018-10-20
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Plant Answer Line Question

Keywords: Citrus limon, Insect pests--Control

I have a lemon tree that is actually not dead yet, but it's not looking good. I had to bring it in late last year as Florence [Italy] was due to have frost for a few days. Then we had horrendous winds and heavy rains. After a few weeks inside, (on a nice sunny indirect-light window sill) it started to drop everything: leaves, blossoms, tiny lemons, and now it is utterly bare. Maybe this is why? On clearing the leaves off the dirt I noticed little blister-like spots on some of the branches. I scraped them with my fingernail and they peeled off, but left sticky stuff behind. Is this a disease? Can I wash the stems? With what? I trimmed the tips of the tiny branches; they are green inside so not dead. I did fertilize with a high-nitrogen liquid, over the leaves and in the pot, a couple of times a month. I have a feeling that spider mites are doing the mischief. Is there hope?


Sorry to hear of your bare lemon tree! The loss of leaves could have been a reaction to the wind, and once the leaves are gone, the tree can become susceptible to waterlogging, pests, and diseases. It is good that you moved it inside, and that it has good light. The blister-like spots on the branches sound like a kind of scale insect, to which Meyer lemons can be prone: California red scale (Aonidiella aurantii). I do not think it would be spider mites, because they would cause stippled, yellowed leaves, and might leave telltale webs. Scale can defoliate and kill a tree. There are beneficial Aphytus wasps that can be used to control scale, but they have to released regularly to be effective and, of course, you would not do this while your tree is indoors. A good reference about scale insects and how to manage them is Pests of the Garden and Small Farm by Mary Louise Flint (University of California Division of Agriculture, 1990)

Here are two recommended books on growing citrus:
Citrus: Complete Guide to Selecting & Growing More than 100 Varieties by Lance Walheim (Ironwood Press, 1996)
Success with Citrus Fruit by Sigrid Hansen-Catania (Merehurst Ltd., London: 1998)

Date 2018-03-15
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Plant Answer Line Question

Keywords: Scale insects, Euonymus, Insect pests--Control

Have you heard about a problem with Burning Bush (Euonymus alatus) getting a mildew this year? The leaves have turned yellow green with small spots of lighter yellow discoloration.


Powdery mildew is a common and usually not life-threatening problem with Euonymus. Make sure the plant has good air circulation, and be sure to clean up and destroy fallen leaves which are infected. However, the symptoms of this fungal problem would be whitish coating on the leaves, rather than yellowed leaves. This makes me wonder if it is a different problem such as scale (which is actually an insect). Check and see if there are small bumps on the leaves or stems. Scale can cause yellowed leaves. If your plant has a small infestation, you can try scraping the scales off with your fingernail, prune out the most infested parts of the plant, and then apply dormant oil to the trunk and branches before growth starts next spring, or apply superior oil during the growing season. There are also other fungal and bacterial problems that could be causing the spots.

See this fact sheet from Penn State for more on Euonymus scale.

Here is a link to additional information, which comes from University of Illinois Extension. Excerpt:

Burning bush (also called Winged Euonymus): Euonymus alatus

Cold injury - Winter injury may be caused by very low temperatures as well as drought stress. With excessively low temperatures, the moisture in the cells freezes (due to chemical compounds in plants, moisture freezes at various degrees below freezing). Drought stress already has resulted in limited moisture in the plant cells. Dry, freezing winds during the winter reduces the moisture level even farther, often resulting in dead plant tissue. Diseases can help magnify or increase susceptibility to winter kill. Nectria canker kills the sapwood tissue thus reducing or even cutting off moisture to tissue further out on the plant. Winterkill also makes plants more prone to infectious diseases and insect problems.

Dieback/canker - See bridal wreath spirea. In addition Botryosphaeria dothidea will infect and kill for similar reasons.

Winged euonymus scale - Lepidosaphes yanagicola occasionally occurs in the southern half of Illinois on burning bush. It is an armored scale. And will attack several trees as well. This scale can cause premature leaf drop, branch die back and cause the plant to become more prone to winter injury. It is found between the "wings" - the bark ridges. It does not move to the plant's leaves. The scale over winters as an adult and lays its eggs in June. Eggs may be laid for up to a month. Mating occurs before frost.

Euonymus scale - Unaspis euonymi - females are black and males are white. The scale causes the foliage to develop yellowish green spots. Heavy infestation results in early foliage drop and often stems are killed. Eggs survive by over wintering in the female body. The eggs hatch about early June in Northern Illinois. Crawlers emerge and move onto new growth or can be blown by wind to other plants.

Since I cannot diagnose the problem remotely, it makes sense to take plant samples to a Master Gardener Clinic.

Date 2018-06-07
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Plant Answer Line Question

Keywords: Insect pests--Control, Camellia

My camellia is potted and lives on an urban deck. In the spring, it was full of beautiful blooms and lush foliage. This summer it has been plagued with aphids and mealy bugs. I have sprayed two different times, 3 times each. My bush appears to continue to fail. It is dropping perfectly healthy-looking leaves and getting new growth, but it has few new buds and looks very "naked." What is wrong with it? I have noticed small insects in the soil as well. I have added a watering of Safer-soap-with-water mixture but it seems to have had no improvement. Please help!


I wonder what kind of spray you have been using. Was it the Safer soap product? Aphids seldom cause the demise of a mature plant. Aphids are attracted to lots of leafy new growth, so it is best to avoid quick-release high-nitrogen fertilizer. The best way to keep aphids in check is to encourage natural predators like ladybugs, syrphid flies, lacewings, and parasitic wasps. Broad spectrum pesticides will harm the helpful insects as well, so I would avoid use of those. Mealy bugs are also a favorite of natural predators like those mentioned above. Usually, regularly spraying jets of water to knock the aphids and mealy bugs off the plant's leaves should keep the damage in check. If necessary, you can use insecticidal soap, but always test it on a small area of the plant to make sure it does not cause any damage to the leaves.

It is possible there is something else going on with your camellia. Here is a link to University of California, Davis's Integrated Pest Management website, with a list of problems affecting camellias. My own camellias do shed a certain number of healthy green leaves every year, but still manage to keep flowering. Excessive leaf drop may indicate overfertilizing, but it could also be a sign of too much or too little water. Did buds drop from the plant, or did they simply not form? Failure to form buds might be a result of cold injury (although since you had flowers in spring, this seems to not be the problem), or it could also be a sign of overfertilizing with a nitrogen-heavy product which encourages leafy growth at the expense of flowers.

You may want to bring samples of the insect-affected leaves and the insects in the soil to a Master Gardener Clinic for identification and diagnosis. You might also mention the excessive leaf drop, which can be a symptom of Sudden Oak Death (Phytophthora ramorum).

Date 2018-06-27
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Plant Answer Line Question

Keywords: Insect pests--Control, Root weevils, Heuchera, Bergenia

What is the pest that eats little notches around my Bergenia and Heuchera? What can I do to prevent this?


It is possible your Bergenia and Heuchera are being nibbled by black vine weevils or strawberry root weevils. Usually you would begin to notice the damage in mid-spring. The notches won't kill your plants, but if you have a lot of black vine weevils and plants appear to be wilting, you may want to attempt to control the larvae. Spraying beneficial nematodes (Steinernema) on the surrounding soil may also help.

Below are links to information about weevils:

Black Vine Weevil from UMass Extension

Black Vine Weevils from University of California's Integrated Pest Management site

Strawberry Root Weevil from the Pacific Northwest Insect Management Handbook

A document about Black Vine Weevil (and other root weevils) from Ohio State University Extension


"Adults that feed along leaf margins produce typical crescent shaped notches. Careful searches should be made to try and locate specimens since several other weevils and some caterpillars can produce this same type of notching. Moderate to light notching seems to have little effect on plant health.

"Black vine weevils are oblong oval in shape, about 1/2-inch long and have a short, broad snout with elbowed antennae. The body is slate grey to blackish brown and the wing covers have numerous small pits and short hairs. This pest is difficult to distinguish from other Otiorhynchus weevils. The strawberry root weevil is usually half the size of the black vine weevil, and more brown in color. The rough strawberry root weevil is only slightly smaller than the black vine weevil but the collar just behind the head, the pronotum, is heavily pitted.

"Female weevils emerge from soil pupation chambers late May to early July. These weevils must feed on plant material for 21 to 45 days before they are ready to lay eggs. After the preoviposition period has passed, the females place several eggs each day into the soil or leaf litter nearby suitable host plants. The weevils hide during the daytime at the base of plants or in mulch and leaf litter near food plants. Adults may live 90 to 100 days and usually lay 200 eggs during this time. The eggs hatch in two to three weeks and the small C-shaped, legless larvae feed on plant rootlets. The larvae grow slowly over the summer, molting five to six times. By late fall the larvae have matured and are about 5/8-inch long. The mature larvae enter a quiescent prepupal stage in an earthen cell and pupate the following spring. A single generation occurs each year.

"Strategy 1: Habitat Modification - Egg and larval survival is helped when soil moisture is moderate to high in July and August. Heavy mulches also help maintain critical moisture levels. Remove excessive mulch layers and do not water plants unless necessary. Excessively damp soils in the fall also force larvae to move up the base of the plant where girdling can occur. Properly maintain rain down spouts and provide for adequate drainage of soil around plants.

"Strategy 2: Biological Control Using Parasitic Nematodes - The entomopathogenic nematodes, Steinernema and Heterorhabditis spp., have been effective for controlling black vine weevil larvae, especially in potted plants. Sufficient water must be used during application to wash the infective nematodes into the soil and root zone. If the nematodes are to be used in landscape plantings, remove a much of the mulch as possible and thoroughly wet the remaining thatch and soil before and after the nematode application. Applications of the nematodes in landscapes has produced variable results."

Date 2018-07-12
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Plant Answer Line Question

Keywords: Insect pests--Control, Potting soils

I need advice on how to rid my house of fungus gnats which were introduced in a bag of potting soil I used when repotting my houseplants. One plant is difficult to repot because it has long branches that cascade down the side of the pot in an intertwined mass.

I always let the soil dry out completely before potting, and also in between waterings. Recently I added a bunch of sand to the top of the soil. Would repotting again help? Is there a no-pest strip that is safe for use indoors for this insect? (I'm chemically sensitive and also concerned about the soil's fungus).


I'm sorry to hear of your struggle with fungus gnats. I consulted University of California, Davis Integrated Pest Management online, and here is a link to their page on this insect and methods of controlling it. Here are excerpts which may be relevant to your situation:

Purchase and use only pasteurized container mix or treat potting soil with heat or steam before using it; this will kill flies as well as the algae and microorganisms they feed on. Store pasteurized potting soil in closed containers to prevent it from becoming infested before use.

Commercially available Steinernema nematodes, Hypoaspis mites, or the biological insecticide Bacillus thuringiensis subspecies israelensis (Bti) can be applied to control fungus gnat larvae in container media.

North Carolina State University Extension also has suggestions on indoor control of this pest. Excerpt:

Potted plants and other types of interiorscaping are often the culprits. Check plants to see if the soil is excessively wet. Drain any excess water from the dish below the pot. If the weather permits, move the plants outdoors or allow the soil to dry down (not to the point where plants wilt). You can also drench the soil as mentioned previously. Then, increase the interval between regular watering and the problem should abate.

If you can possibly repot the plant(s) which had the infested soil, and use sterile potting soil, that should help. If this doesn't work, the Bacillus thuringiensis (Bt) or parasitic nematodes might be an option. I think the Bt might present problems for your chemical sensitivity, as you would need to avoid breathing it in, and prevent it from getting on your skin and clothing. However, the Steinernema feltiae nematodes should not be a problem at all. One example of a source for these is Peaceful Valley Farm Supply.

I don't think adding sand on top of the potting soil will be effective. It might actually create a kind of crust over the top of the soil, causing a drainage problem. If you are concerned about fungus in the soil, using sterilized or pasteurized potting soil is a good idea. You can try using yellow sticky traps to catch the gnats; it can't hurt, although it won't completely solve the problem unless you are willing to repot with new soil. Most garden centers sell these traps, or you can make your own as described by New Mexico State University Extension.

You can also employ trapping techniques using yellow sticky traps. These may be purchased, or you can make them from yellow surveyors tape or yellow plastic butter tubs, etc., coated with vegetable oil, Vaseline, or other sticky material. Put these traps in a window or other well-lighted location. The adult gnats are attracted to the yellow color and get stuck on the trap. This removes them from the home environment and reduces their ability to reproduce. (They die on the trap.) After you catch a lot of gnats, just discard the whole trap or wipe the insects off and reapply the sticky material mentioned above, and you are ready to catch more.

Date 2018-07-12
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Plant Answer Line Question

Keywords: Azadirachta indica, Horticultural oil, Laurus nobilis, Insect pests--Control

I have some insects on my bay laurel, which we use for seasoning. Someone told me to spray it with horticultural oil. I wondered, though, if it would still be safe to use the leaves in cooking. Is horticultural oil petroleum based?


As you suspected, horticultural oil is petroleum-based. U.C.Davis provides information on Integrated Pest Management for the plant I am assuming you mean, the usual source of culinary bay leaves, sometimes called sweetbay, or Laurus nobilis. (Just to be clear, I don't think you are referring to the plant known as California bay laurel, Umbellularia californica, which has leaves that are aromatic and reportedly edible, but not commonly used for seasoning.) They also note that horticultural oils are "...specially refined petroleum products, often called narrow-range, superior, or supreme oils. Some botanical (plant-derived) oils are also available."

When referring to plant-derived oils, I believe they are referring to Neem oil, as described in this information from U.C. Davis Integrated Pest Management. Additional information from the Cornell University Resource Guide for Organic Inesct and Disease Management about Neem and human health is excerpted here:

Studies of azadirachtin mutagenicity and acute toxicity have shown that it likely does not pose a significant risk to human health. However, some people have exhibited skin and mucous membrane irritation from neem seed dust (Weinzierl and Henn 1991). Note that most studies have been done on azadirachtin, and may not show the effects of a whole neem product. Neem is used in some commercial human hygiene products.

Another long excerpt on horticultural oil from Colorado State University Extension suggests the following:

Essentially all commercially available horticultural oils [...] are refined petroleum products also known as mineral oils. Impurities in the oil that are associated with plant injury, such as aromatic compounds and compounds containing sulfur, nitrogen or oxygen, are removed. Filtration, distillation and dewaxing complete the production of the finished base oil. Final formulations of horticultural oils are normally combined with an emulsifying agent that allows the oil to mix with water. This mixture usually is used at about a 2 percent dilution.

Vegetable oils also can be used as insecticides, although the type of oil can greatly affect its activity. Cottonseed oil is generally considered the most insecticidal of the vegetable oils. Soybean oil, the most commonly available vegetable oil used in cooking, has often provided fair to good control of some insects and mites.

Extracts from seeds of the neem tree, Azadirachta indica, have recently attracted attention as a source of pest management products. Several neem-derived insecticides have been developed. A number of compounds found in neem seeds, notably azadirachtin, have proven useful as insecticides. However, the oil fraction of neem seed extracts, which is mostly free of azadirachtin and related terpenoid compounds, also has demonstrated effects as a fungicide and insecticide. At least one product currently on the market, TrilogyR, consists of a largely azadirachtin-free oil fraction of neem seed extracts. It is formulated with an emulsifier and mixed with water at a concentration similar to horticultural oils (0.5 to 2.0 percent). Many over-the-counter products sold in nurseries that mention neem contain the oils of neem seed extracts.

If you know the insect on your bay tree, Peaceful Valley Farm Supply is one commercial supplier which carries less toxic, of not organic, products to control specific pests. That does not necessarily mean they are safe enough to spray on leaves which will be harvested for cooking.

Date 2018-09-29
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Plant Answer Line Question

Keywords: Cupressocyparis, Insect pests--Control, Trees--Diseases and pests--Washington

My Leyland Cypress is browning and has Cypress tip moth signs. I'm worried about the brown spots, and wonder if it can survive this attack? How can I control the pests, if it might survive?


From what I can determine, your Leyland cypress (x Cupressocyparis leylandii) trees are probably going to survive this attack unless they are weakened in some other way. x Cupressocyparis leylandii in California survive the Cypress tip moth, though they can be unsightly. Since California is a bit too dry for this tree, the conditions are not identical, but Natural Resources Canada does not indicate that infestations are fatal. Because you said you found evidence of tip moth (Cypress tip moth = Argyresthia cupressella), I will assume that is what the problem is, but a bit of browning, even in conifers, is not unusual right after trees are planted. Be sure that you are not overwatering, as one effect of that is the same as underwatering (i.e., tip die-back or yellowing) because too much water prevents the plant from taking water and oxygen into the roots.

The Organic Gardener's Handbook of Natural Insect and Disease Control (ed. by Ellis and Bradley, 1996, p.183) says about pine tip moth (Rhyacionia frustrana):

Handpicking works if only a few caterpillars are present. Pruning off and destroying infested tips in winter is a very effective control.

I would recommend a prune-and-wait-and-see approach. April is a bit late to prune (and puts root establishment in competition with shoot regrowth), but you may be able to slow the infestation down, so go ahead and do it. Watch the trees this season and then prune again in the winter next year. Be sure to destroy (burn or bag and put in the garbage) the debris so you don't reinfect your tree.

A good gardening resource is the UBC Botanical Garden Forum. Personal testimony/experience is valuable, especially if it's regional. (You might find it useful in the future.) Several people commenting about x Cupressocyparis leylandii note that it is not a very desirable tree; one of its parents, the Cupressus nootkatensis, also called Callitropsis nootkatensis or Chamaecyparis nootkatensis, or, for that matter, plain Nootka cypress) is better. One person recommended planting small trees in the beginning, since they grow very fast. This might save you some money, should you have to replace your trees. The site does not need a password; just click on "Search" in the upper right corner.

Below is some additional information from Oregon State University about cypress tip moth. This site recommends pesticides, but from everything I read, they are not effective without multiple treatments. Since this pest is generally not fatal to the trees, it is probably not worth it to use chemicals which would be dangerous and time-consuming to apply. If you know something about the life cycle of the pest, your observations will yield more information and any manual control attempts are more likely to be effective.

Date 2018-04-11
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Plant Answer Line Question

Keywords: Sawflies, Azadirachta indica, Rosa, Insect pests--Control

I think my rose leaves are being devoured by rose sawfly, and I was wondering if spraying 'Rose Defense' on them would help.


Rose Defense is a Scott's product that contains Neem (as well as other ingredients). There is some evidence that Neem is effective against sawfly larvae. As with any pesticide, you should follow the directions on the package carefully (and note that this product may be harmful to humans, domestic animals, bees, and the environment, depending on the route of exposure).

You might want to start out with the least toxic approach first, that is, handpicking and spraying with water. Once larvae are knocked off the roses, they will not climb up again. If this doesn't seem to be helping, then you could choose a Neem-based spray or insecticidal soap, keeping in mind that the Neem product is toxic to bees, and should not be applied when bees are active.

According to University of Minnesota Extension, sawflies are best controlled when young. You can simply pick them off by hand or dislodge them with a stick or a stream of water. If using water be sure to spray early enough in the day for the foliage to dry by sunset. This will prevent favorable conditions for fungal development. Horticultural oil, insecticidal soap and azadirachtin (sometimes called neem), are among the less toxic insecticides to treat young sawflies. Azadirachtin is slower acting. Bacillus thuringiensis (Bt) is effective on young lepidoptera caterpillars but NOT on larval sawflies.

Cornell University's Resource Guide for Organic Insect and Disease Management (formerly available on the Cornell website) also discusses the uses of Neem. Here is an excerpt:
"Neem products are generally sold as emulsifiable concentrates. Neem oil soap is sold as a water-soluble liquid concentrate. While Copping (2001) reports no known incompatibilities with other crop protection agents, phytotoxicity may be a problem when combining neem oil or soap products. Read labels for specific application guidelines including determination of re-entry interval and pre-harvest interval. Range of efficacy will depend on the susceptibility of species in question and environmental conditions at time of application. However these are points to follow:
Make multiple applications. Frequent applications are more effective than single sprays because neem does not persist well on plant surfaces. Like most other botanically derived materials, it can be rapidly broken down by sunlight and washed away by rain (Thacker 2002).
Use against immature insects. Azadirachtin-based insecticides act on immature stages of insects more effectively than on eggs or adults. To reduce a build up of populations it is important to make treatments to crops targeting insects in an early stage of their life cycle. For instance, neem would likely have little effect on an infestation of striped cucumber beetle adults; however if applied to potato plants early in the season, it has been shown to greatly reduce larval activity of Colorado potato beetle.
Begin applications before pest levels are high. Antifeedant and egg-laying repellant effects show best results in low to moderate pest populations.
Neem is reported to work best under warm temperature conditions (Schmutterer 1990)."

There are quite a few different species of sawfly, and I would guess that the rose sawfly is so named because rose bushes are its primary feeding ground. If you aren't sure what is eating your roses, you may want to take samples of the affected leaves to your local county extension agent before you begin to treat the problem. You may find the images on the self-described Buggiest Rose Website helpful in comparing with the leaf damage you are seeing.

Date 2017-08-15
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Garden Tip

Keywords: Insect pests--Control, Root weevils, Slugs

A trip through the garden at night with a flashlight will reveal a surprising amount of animal and insect activity. Earthworms crawl across the ground looking for decomposing plants to consume while weevils, slugs and cutworms feed on our prized shrubs and perennials. Remember that the new non-toxic iron phosphate slug baits, such as Sluggo, must be reapplied about every two weeks. More slug-coping advice can be found online at www.ipm.ucdavis.edu/PMG/PESTNOTES/pn7427.html

Date: 2006-03-01
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Garden Tip

Keywords: Biological control, Insect pests--Control, Pesticides and wildlife, Trees--Diseases and pests

Gypsy moth is often in the news and with it comes the promise of aerial spraying of Btk by the department of agriculture. While the idea of the government spraying pesticides over an entire neighborhood may be frightening, a gypsy moth out-break would be devastating to the trees of the Emerald City or any city. Gypsy moths defoliate over 500 species of trees, both deciduous and evergreens.

Bacillus thuringiensis var. kurstakiis a bacterium that affects only caterpillars. It is considered an acceptable pesticide by organic gardeners, provided it used only when really needed. The major caterpillar pests in our area include:

  • the larvae stage of the gypsy moth;
  • cutworms that feed in winter and spring on primroses, chives and other perennials;
  • tent caterpillar often seen later in the spring on apple trees;
  • keep in mind that sawfly larvae which can strip a flowering red currant bare in a few weeks are not caterpillars, and Btk will not control them.

Btk will kill caterpillars of butterflies, which is why it must be used with caution only when pest populations are high or the potential damage is intolerable. Btk is typically sold as "caterpillar killer" where other pesticides are sold.

Date: 2007-04-20
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Garden Tip

Keywords: Insect pests--Control, Moths

Act in October to defeat the Winter moth (Operophtera brumata). These moths mate in autumn and then the wingless females climb up tree trunks to lay their eggs. In early spring the little green inch-worm like larvae eat flower and leaf buds from the inside out. The many host plants include maples, oaks, crabapples, apple, blueberry, and some spruces such as Sitka spruce. To detect female moths place a band of heavy paper covered with Tanglefoot (a sticky goo available at nurseries) around susceptible tree trunks. If females are found it may be a good idea to spray the tree (trunk and branches) with dormant oil to smoother the eggs for reliable control. If the little caterpillars start "ballooning" out of trees in high numbers spraying with Bt (caterpillar killer) will provide control. For more information go to this University of Massachusetts Extension publication

Date: 2007-03-20
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Garden Tip

Keywords: Insect pests--Control, Integrated pest management, Insects

To find pictures of insects go online to www.insectimages.org, Developed by Bugwood Network and the USDA Forest Service, this free database can be browsed by category of insect or keyword searched.

Once a mystery insect has been identified go to Plant Disease and Insect Identification Pests Leaflet Series from WSU for information on insects commonly found in western Washington or Insect and Pest Series Index from Ohio State University for general garden pest fact-sheets.

Date: 2007-04-03
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Garden Tip

Keywords: Plant care, Plant diseases--Control, Insect pests--Control, Attracting wildlife

By November Seattle has usually had a good hard frost and most of our herbaceous (non-woody) perennials have either turned to mush or look a bit tattered. Before you give in to the temptation to cut back everything in sight, consider the advice of natural gardening advocates James Van Sweden, author of Gardening with Nature (Random House, 1997) and Jackie Bennett, author of The Wildlife Garden (David & Charles, 1993):

  • Leaving seed heads and dead stems over the winter gives the garden winter interest, especially if we get some snow
  • Seed heads from Black Eyed Susans, Echinacea, Larkspur and Evening primrose provide bird food
  • Beneficial insects hibernate or over-winter as eggs on plant waste
  • Marginally hardy plants like some salvias and lavenders benefit from the little bit of frost protection from the desiccated stems

On the other hand, sanitation is critical if your apples suffered from codling moth or scab or your roses suffered from black spot. Rake up and dispose of every single diseased leaf or infected fruit. Insect and disease organisms also over-winter on plant debris, so if you had a problem this year, start the treatment now with a thorough clean-up.

Date: 2007-03-26
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