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California Statewide IPM Project IPM fact sheets

Sustainable Agriculture Information Service

UC Davis IPM Online Guide to Healthy Lawns

National Sustainable Agriculture Information Service— pest management

Missouri Botanical Garden IPM List of Pests by Plant Host

WSU Extension Hortsense

Information Resources for Organic Gardening

Pacific Northwest Nursery IPM

Information Resources for Pests and Diseases

Integrated Pest Management

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Plant Answer Line Question

Keywords: Plant diseases--Control, Fungicides, Powdery mildew diseases, Integrated pest management, Dahlia

What can I do about powdery mildew on my dahlias? Should I throw the bulbs away, or does it only contaminate the plant above the ground? I have heard both too much water and not enough water cause this problem. Is either true?


The main thing you will need to do is destroy all the foliage affected by the mildew. The mildew can survive the winter on infected foliage, and then spread to new foliage.

Powdery mildew thrives where plants are crowded and there isn't enough air circulation, so give your plants space, a sunny site, and try watering in the morning, and watering from beneath the plants (not over the leaves) so they are able to dry off during the course of the day. As you indicated, too little water can also be a problem.

Here are two websites with additional information:
Univ. of California IPM Online Guide
Washington State University Extension Garden Tips

I did not come across any information specifically saying that powdery mildew will affect bulbs or tubers. I spoke to an experienced dahlia and begonia grower here who said that it should be all right to store and replant your tubers, as long as you thoroughly get rid of all the diseased foliage aboveground.

Some sources (such as The Organic Gardener's Handbook of Natural Insect and Disease Control, edited by Barbara Ellis, Rodale Press, 1996) suggest that a baking soda spray (1 tsp. per 1 quart of warm water, with a bit of dish soap) is protective or preventive, but Washington State University Extension professor Linda Chalker Scott disputes the efficacy of this method. She says that other methods work better:
"Other treatments have been more successful in powdery mildew control, including horticultural oils, potassium bicarbonate, potassium phosphate, sulfur, milk, and even water sprays. Probably the most field success has been found in combining SBC [sodium bicarbonate] with horticultural oils, including mineral and vegetable oils (see the Fall 2008 MasterGardener magazine). The mixtures are so effective that they've been successful even on serious powdery mildew epidemics."

Date 2017-08-08
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Plant Answer Line Question

Keywords: Weed control, Integrated pest management

I have a smaller lawn, in a slightly shady area and have been having problems with dandelion and white clover. I don't mind a few weeds, but it is getting to be too many. Children and pets play on this lawn so I don't want to put anything that would be toxic to them on the lawn. What would you suggest I do?


Given that you are concerned for your children and pets, it makes sense to hand-weed your lawn. A little pocket knife is a great tool for doing this quickly and tidily. If you just spend a little bit of time at it a few days a week, it will go faster than you might imagine. Try to live with the clover; it is extremely difficult to eradicate, and it is great for honeybees.

Small dandelions are easier to pull out. The City of Seattle has excellent information about caring for lawns without pesticides, including hints about controlling dandelions. Look in the right-hand menu for additional links to lawn care information.

This Mother Earth News article (June 2, 2011) describes several types of dandelion weeding tools.

Date 2017-08-08
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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: Aphids, Integrated pest management, Viburnum

I have a small snowball bush that I planted three years ago. Each spring this plant is inundated with more and more ants and aphids. I try to garden organically and could use Safer Soap on it, but it is large and the leaves are all curled under and withering from the insects. Is there anything other than Safer Soap that I could use to help the plant, either systemic or otherwise?


Following are the best sources I have found about environmentally friendly control of aphids.

Aphids (order Homoptera)

Almost all plants have an aphid species that may occasionally feed on them. Many aphid species attack several plants rather than having only one host. Trees (esp. birch, beech, maple, apple, peach, apple, plum, cherry, spruce, dogwood, willow); annuals (esp. nasturtium, snapdragon); perennials (esp. lupine, roses, lilies, begonias, columbine); vegetables (esp. peas, beans, brassicas, lettuce, spinach); fruit (esp. apple, peach, cherry).

Small (2 mm long), pear-shaped, softbodied insects in a range of colors (green, brown, red, yellow, black). Most are wingless, but winged aphids appear at certain times, especially when populations are high or during spring or fall. A few species appear waxy or woolly. A magnifying glass will reveal the long, slender mouth parts used to suck plant fluids. Aphids are usually found in clusters, especially on new growth. Signs of aphid infestations include sticky honeydew on leaves or under plants, distortion of leaves, stunting of shoots, or large numbers of ants on the plant.

Life Cycle:
Overwintered eggs of some common garden species hatch in spring. These wingless females reproduce asexually, bearing live young (up to 80 per week) that already have the next generation developing inside. Young aphids, called nymphs, molt four times before becoming adults. There is no pupal stage. This simple, rapid reproduction allows for very large population increases in a short time. Late in fall, males and females are produced, mate, and the females subsequently lay eggs. Winged aphids may appear at certain times, allowing the colony to move to other locations. Not all aphid types have this reproductive pattern, but many do.

Natural Enemies:
Aphids have many natural enemies, including birds, spiders, ladybird beetles, lacewings, syrphid fly larvae, and braconid wasps. A naturally occurring fungal disease can also kill aphids when conditions are right. Ants have a symbiotic relationship with aphids: ants milk the aphids for honeydew while protecting the aphids from natural enemies.

Check plants often, since aphid populations can rise rapidly. Inspect growing tips and undersides of leaves. On trees, clip off leaves from several parts of the tree to look for aphids. If you see large numbers of ants on tree trunks, check for aphids on limbs and leaves. Look also for associated signs, such as yellowed leaves, stunted or distorted growth, or dripping honeydew. Sticky traps can be used to monitor for winged aphids. Check for signs of predators (named under Natural Enemies above), aphids that have been parasitized (look for a small exit hole on a dead, brown aphid body), or that have been killed by disease. Substantial numbers of any of these natural control factors can mean that population numbers will fall rapidly without the need for treatment. Because of the rapid changes that can occur in aphid populations, it is important to record monitoring data to detect changes due to predators or treatments.

Action Threshold:
Due to the incredibly high numbers that may be present, counting individual aphids is usually not practical. Action thresholds can be based on general descriptions of aphid density, plant damage such as stunted or distorted growth, or unacceptable amounts of honeydew beneath trees. Treatment should be triggered by rapidly rising numbers, unacceptable plant damage, or by honeydew falling on structures and people. Aphids seldom kill a plant, but they can cause defoliation. They also carry diseases from one plant to another. It is usually not necessary or even desirable to treat at the first sign of aphids, since low populations are needed to sustain predators.

Cultural/Physical Controls:
Plant selection: If possible, avoid or consider replacing varieties such as birch that have ongoing, serious aphid problems. Check transplants for aphids and remove them before planting.

Water spray: A strong blast of water knocks aphids from the plant, and most will not return. Water also helps rinse off the honeydew. Do this early in the day to allow leaves to dry and minimize fungal diseases.

Pruning: Where high aphid populations are localized on a few curled leaves or new shoots, prune these areas out and drop in soapy water to kill the aphids.

Fertilization control: High nitrogen levels favor aphid reproduction. Avoid over-fertilization and use slow-release rather than highly soluble fertilizers.

Sticky or teflon barriers: If you see ants crawling up the trunk of trees or other woody plants, place a band of sticky material (such as Tanglefoot or Stik-Em) around the trunk. Place a protective band of fabric tree wrap or duct tape underneath the barrier first. Teflon tape barriers may also be effective. Prune out branches touching the ground, buildings, or other plants.

Biological Controls:
Since aphids have many natural enemies, biological control usually means protecting these enemies from ants and avoiding broadspectrum pesticides that kill beneficial insects. Recognize that predator populations usually lag behind aphid populations in time. A number of aphid enemies can be purchased for introduction into landscapes. Ladybird beetles, lacewings, and parasitic wasps and flies are all available. Although such introduced predators may not remain where released, some benefit is likely, especially if releases are staggered in time. Many of the natural predators of the aphid are especially attracted to a garden with plants in the Umbelliferae family, such as angelica, sweet cicely, dill, and Queen Anne's lace. The flowers of these plants provide a good food source for insects, especially parasitic wasps, who may stay to prey on some aphids as well.

Chemical Controls:
Insecticidal soap is widely recognized as the least-toxic chemical aphid control. Although its effect is temporary, it can help to bring aphid numbers down so that natural enemies can take care of them. Repeat applications within a few days may be necessary. Soap works only by direct contact with the insects. Be sure to cover both sides of the leaves. Although readily biodegradable, soaps are highly toxic to fish, so avoid runoff or direct application to water. Avoid using when temperature exceeds 90 degrees F.

Oil sprays:
Supreme or superior-type oils will help to kill overwintering aphid eggs on fruit trees if applied as a delayed dormant application in early spring. Although perhaps not justified for aphid control alone, oils can also control other overwintering fruit pests. Oils may, however, kill some beneficial species. Summer weight oils are also available, but they can burn tender leaves when applied in hot sun.

Conventional chemical control:
Foliar applied insecticides (malathion, diazinon, carbaryl, pyrethrin) are broad spectrum and will kill beneficial insects. They should be avoided, especially in home gardens and landscapes. Remember that allowing some aphid population in the garden helps to keep predators available.

ProIPM Integrated Pest Management Solutions for the Landscaping Professional
The Green Gardening Program is a collaborative effort of Seattle Tilth, Washington Toxics Coalition, and WSU Cooperative Extension, King County.
Sponsored by the Seattle Public Utilities in an effort to promote alternatives to lawn and garden chemicals.
Funded by the Local Hazardous Waste Management Program in King County.
Written by Philip Dickey, Graphic Design by Cath Carine, CC Design

Pest description and crop damage:
Aphids are soft-bodied insects that typically feed on leaves and succulent stems. They may vary in color from pale green or reddish to dark or black. Aphids are usually less than 1/8 inch in length.

Feeding damage to the plant is usually minor, although some leaf and shoot distortion can occur if populations are high. Aphids also produce honeydew, a sweet, sticky secretion that collects on plant tissues and encourages growth of a black sooty mold. This can interfere with photosynthesis of the plant. Honeydew is also a nuisance when it falls on decks, cars, or other landscape surfaces. They are a problem in early summer.

Biology and life history:
Most species of aphids have similar life cycles. Aphid females give birth to live offspring all year without mating. When other hosts are not available, aphids live on a wide variety of weeds. Aphids usually are found in colonies on new growth, the underside of leaves, and near flower and fruit clusters. In summer and fall, aphids may produce winged females and, later, winged males. They mate and produce eggs for overwintering, especially in colder climates. Otherwise, adult aphids overwinter on crops, weeds, or trees. There may be as few as 2 or as many as 16 generations each year, depending on the species and climate.

Management & biological control:
Aphids have many natural enemies, including lady beetles, syrphid fly larvae, and green lacewings. Avoid broad-spectrum insecticide applications that would disrupt these controls.

Management & cultural control:
Wash aphids from plants with a strong stream of water or by hand-wiping. Aphid populations tend to be higher in plants that are fertilized liberally with nitrogen and heavily watered, as this produces flushes of succulent growth. 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.

Management & chemical control (home):
It is important to cover foliage thoroughly, including lower leaf surfaces.
1. Beauveria bassiana
2. horticultural oil
3. insecticidal soap


Date 2018-04-05
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Plant Answer Line Question

Keywords: Integrated pest management, Acer

I have a wood boring beetle in a maple tree and I am wondering if there is a treatment for the tree or do I need to take the tree down?


Here is a link to University of Kentucky's entomology department website that describes a number of different species of insect borers affecting trees and shrubs, including maples.

I also consulted Pests of Landscape Trees and Shrubs: an Integrated Pest Management Guide, second edition, which suggests that prevention is best. If you can make sure the tree is protected from damage, and prune any damaged limbs and branches (should be done when adult borers are not present, Fall through February), this should help, since the borers are attracted to stressed, damaged, or diseased trees. Do not store cut wood near the tree. Insecticide is not considered effective against borers under the bark. If the tunnels are visible and there are not too many of them, you can try using a sharp wire to probe and kill the larvae, but it may be difficult to tell how far to insert the wire.

If the infestation is not severe, you may be able to save the tree by improving its care and its growing environment.

Date 2018-03-15
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Plant Answer Line Question

Keywords: Prunus lusitanica, Plant diseases, Integrated pest management, Phytophthora

I have two Portuguese laurel shrubs. One has large reddish-purple leaf spots and the leaves on part of the shrub have dropped. It looks like the fungus is spreading to part of the other shrub. Do you have any suggestions? I have raked up as much of the dropped leaves as I can. Would Daconil be safe for Portuguese laurels? I also have Bonide multi-purpose fungicide (contains chlorothalonil), but wanted to see if you thought it would be safe for laurels. Thank you for any suggestions you may have.


While I cannot diagnose the problem remotely, I will offer several possibilities of what may be causing the leaf spots on your Prunus lusitanica (Portuguese laurel). The causes might be bacterial, fungal, or environmental. According to Oregon State University's Plant Disease database, English laurel (and other types of laurel) can suffer from leaf spots and shothole. (Search plant list under the letter P, for Prunus laurocerasus.) Excerpt:

Shothole symptoms are commonly observed on Prunus sp. and can be caused by a variety of factors. The bacterium Pseudomonas syringae pv. syringae and several fungi including Cercospora sp., Blumeriella sp., and Wilsonomyces carpophilum (Coryneum blight) can cause leaf spots and shothole on cherry laurel (English laurel, Otto Luyken, or 'Zabeliana'). Copper spray injury and boron toxicity can also cause leaf spotting and shothole. When symptoms are advanced, it is not possible to identify the cause specifically.

Cherry laurels (English laurel, Otto Luyken, or 'Zabeliana'), P. laurocerasus and sometimes other Prunus sp. including cherry and plum, commonly show shothole symptoms resulting from cultural or environmental stress. Research has failed to identify what specific stress is responsible. Both container- and field-grown laurel can develop symptoms.

Symptoms: Necrotic leaf spots with circular to irregular margins. Bacterial spots are brown surrounded by a reddish border with a yellow halo. Abscission layers develop around necrotic leaf spots causing the injured tissue to drop away, leaving holes and tattered areas in the leaf (as if someone fired a shotgun at the leaf-thus the name shothole). After tissues drop, most often it is difficult to determine specifically what caused the initial injury. Observations of early symptom development, signs, and symptoms on other areas of the plant may help make an accurate diagnosis. Note the holes in the leaves.

Cultural control: No management practices have been shown to help reduce physiological shothole. For disease-induced shothole, try the following cultural practices.

Avoid overhead irrigation.

Remove and destroy fallen leaves.

Do not plant near other flowering or fruiting Prunus sp.

If the problem is physiological shothole, this is an environmental disorder which cannot be controlled with chemicals, and infected parts of the plant should be removed and destroyed.

Your description does not sound like bacterial blight, which in laurels usually affects only the leaves, but this link, from University of California, Davis's Integrated Pest Management site, may help you see if the symptoms match your plant.

Prunus lusitanica can also suffer from Phytophthora, which may be seen in affected leaves as reddish or purplish discoloration.

It would be best to find out for certain what is causing the problem before attempting to treat it. I suggest bringing samples of the affected leaves to one of the Master Gardener Clinics in our area.

I cannot recommend using pesticides such as Daconil or Bonide (which both contain chlorothalonil), as I do not have a pesticide handler's license. Also, the information linked here, from Northwest Coalition for Alternatives to Pesticides, indicates that there are many more concerns (human health, environmental) about chlorothalonil than simply whether it will harm the Portuguese laurel. If you do choose to use pesticides, you must follow the directions to the letter. Another reason to find out the specific cause of the leaf spot and leaf loss is that it is against the law to use a pesticide on a pest or problem for which it was not intended.

An alternative approach would be to prune the plants severely to rejuvenate them. Portuguese laurel is a good candidate for this type of renovation. Here is more information on how to do this type of pruning. Scroll down to the section on renovating evergreen shrubs. Excerpt, from the Royal Horticultural Society:

Aucuba, Buxus, Choisya, Euonymus, Ilex x altaclerensis, Ilex aquifolium, Prunus laurocerasus, Prunus lusitanica, Taxus, and Viburnum tinus all tolerate severe pruning. Many evergreens are best renovated over several years, removing one-third to half of shoots to ground level, and reducing all other shoots by one-third in the first year. Over the next couple of years remove half of the older shoots to ground level.

Date 2018-06-27
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Plant Answer Line Question

Keywords: Theobroma cacao, Integrated pest management, Pests

How can I keep cats out of my flower beds? They keep using them as a litter box. I've heard to use cocoa hull mulch or eggshells since cats don't like to step on them. Is that safe, and will it work?


One of the main results I found is that cats are unpredictable, so you might want to try a few possibilities. The most reliable approaches seem to revolve around creating smells, textures, or situations that cats dislike.

We don't recommend using cocoa beans or eggshells to prevent cats from going into your flowers. Cocoa bean mulch is toxic to dogs and possibly other pets. In fact, it has more concentrated theobromine per ounce than most chocolate products. The ASPCA has more information, and it is further confirmed at Snopes.com, a site that evaluates word-of-mouth knowledge and urban legends. Eggshells, on the other hand, are nontoxic, but seem likely to attract pests and thus create a new and different animal problem.

Instead, there are a number of other solutions you might try. One that a librarian here has had success with is spreading garlic and onions that are too old to be eaten. Other options include planting strong-smelling plant like lavender (Lavandula spp.) or other herbs (but NOT catmint, also known as Nepeta!).

Another tactic that might not offend your nose is to make the area unpleasant to use as a litter box. In particular, you can make it unpleasant for cats to walk through and dig in. Laying chicken wire out over the garden bed is said to be successful sometimes, though it would be difficult to do after plants were established. Another possibility would be making a ground-level lattice of thorny branches, like rose prunings, around established plants. Other possibilities include a stone mulch or some other kind of bristly mulch, such as prickly pinecones. This article discusses these and other cat repellents.

Please note, though, that we don't recommend all of the ideas you will find there, like scattering mothballs in your garden, which is just as likely to be toxic to you as to the cats. You don't want to harm yourself or anything else!

If you are looking for a long term solution with no toxicity and some fringe benefits like doing your watering for you, motion activated sprinklers are highly recommended as a cat repellent.

Date 2018-03-01
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Garden Tip

Keywords: Cutworms, Integrated pest management

Warm winter days above 50 degrees make gardeners eager to get back out working in the garden. The warm temperatures also trigger many over-wintering insects and caterpillars to hatch and begin their development. Practitioners of Integrated Pest Management use "degree days," or days above 50° to forecast when a garden pest might start doing damage and when management should begin. Some pests require more accumulated heat then others to complete their lifecycles. The variegate cutworm, for example, may start feeding as early as February during mild Northwest winters. Dedicated fruit and vegetable growers will want to download degree day calculators and spread sheets from Washington State University's Entomology department.
Colorado State Cooperative Extension published an interesting article on the strategies pests use to survive cold winter days.

Date: 2007-04-03
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Garden Tip

Keywords: Reference books, Woody plants--Diseases and pests, Integrated pest management, Trees--Diseases and pests

A reference book is available to help gardeners solve pest problems. Pests of Landscape Trees and Shrubs: An Integrated Pest Management Guide (University of California, $42.00) diagnoses common diseases, insects and environmental stresses with color photos and suggests appropriate solutions. This book also has a chapter on how to get your plants off to a healthy start with proper planting techniques.

The Integrated Pest Management approach tell us the most important fact to remember about plant problems is that poor growing conditions like soggy roots or bone-dry roots inevitably leads to pests and diseases. Select the right plant for the garden conditions to avoid problems later.

Date: 2007-04-03
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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: Integrated pest management, Beneficial insects

Yellowjackets are at their most aggressive in late summer so it is understandable that people want to destroy their nests. Before you pull out the can of pesticide, remember that wasps are considered beneficial insects that eat plant-eating bugs, and will only inhabit their nest for one season. This article from University of Minnesota Extension gives good advice on how to deal with these insects.

Date: 2007-03-26
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