Skip to content
Elisabeth C. Miller Library

Keyword: Pests

About diatomaceous earth and slugs

Someone suggested that I could use diatomaceous earth to get rid of slugs in the garden. Is this a good idea? Any drawbacks I should consider?

 

First, here is a definition of what diatomaceous earth is, from the National Pesticide Information Center: “Diatomaceous earth is made from the remains of diatoms, which are tiny organisms that lived in rivers, streams, lakes and oceans. Diatom skeletons are made up of silicon dioxide, a combination of silica and oxygen. Silica is very common in nature and it makes up 26% of the earth’s crust. Diatomaceous earth is very abrasive to an insect’s exoskeleton, causing them to dry out and die.”

Slugs are not killed by diatomaceous earth, though it may slow them down. It is mainly used to control insects with hard exoskeletons. According to the book Mason Bee Revolution (Dave Hunter and Jill Lightner, Skipstone Press, 2016), the abrasive dust can damage the bodies of butterflies, spiders, and some bees by causing severe dehydration; it can also kill beneficial hard-shelled bugs. It is considered a relatively low toxicity method of pest control, usually sold as a dust. However, it is not entirely risk-free: wearing a respirator is recommended. Prolonged exposure can cause serious problems like silicosis).

Using submerged saucers of beer will take care of slugs without adverse consequences for non-target species. A potential alternative slug and snail control method that has yet to be researched thoroughly is using wool as a compost or in pelletized form.  Excerpt: “Wool may also be included in mulch or mats where it has been shown to reduce predation by slugs and snails, eliminate weed growth, and reduce soil temperature variation.”

, , ,

Amaryllis and syrphid flies

My Amaryllis bulbs are infected with syrphid flies. I have dug them but don’t know what to do with the bulbs. What can I do to save them?

 

Until receiving your question, I had always known of syrphid flies as beneficial insects in the garden, so I considered the possibility that the bulbs might be infested with bulb mites, or mealybugs, which are fairly common pests of Amaryllis. That being said, in my research to answer your question, I came across an article by Whatcom County Washington State University Extension agent Todd Murray which describes the Narcissus bulb fly, which is indeed a syrphid fly, and does sometimes infest Amaryllis bulbs. Excerpt:

Monitoring and Management: There are no pesticide recommendations available for these bulb flies. But that’s O.K.; we have many alternatives that we can use to avoid mushy bulbs. You should be thinking about trying these practices if you have a problem with bulb flies.

  • In May, on sunny days look for large bumblebee-like flies hovering around your flowers. Bumblebees will have two pairs of wings while bulb flies will have one. Grab your handy insect net (you all have one, right???) and catch the critters before they can do too much egg laying. This sounds tedious, but is very effective for protecting small plantings of susceptible bulbs. Remember, each female fly can lay up to 100 eggs! Plus, if it is a nice sunny day, you should be outside admiring and tending your garden anyway.
  • Adult flies use visual cues and smell to locate your delicious bulbs. After you have enjoyed your flowers, cover the bulb bed with a floating row cover, like Reemay*. Another recommendation given suggests that you mow down the vegetative portions of your plant and gently cover the tops with soil. Female flies will be unable to locate the bulb. Once no new foliage is sprouting, remove and store
    the bulb through the off-season. If you do this, I do not know the impacts this will have on next year’s flower. That vegetation produces the bulb’s energy reserve that is needed for next year’s growth. Regardless, the earlier you can pull your bulbs out, the better chance that you will avoid bulb flies.
  • Bulb flies are less active in open, windy areas. Plant your beds in exposed windy places, if your landscape provides this type of climate.
  • Avoid any damage to the bulbs when handling and planting. The lesser bulb fly prefers damaged goods to healthy bulbs. Establishment of maggots is much easier if there are already rot producing organisms in the bulb.
  • Plant your bulbs deep, if they can tolerate it. Bulbs planted 25cm (or about 10″) deep in the soil will evade attack by adult flies. I am unaware if planting this deep is practical.
  • When the time comes to pull up the bulbs, check the basal plate of each bulb. When you purchase new bulbs, check the plate for any signs of squishiness and rot. If you find some rot there, do not plant them and discard the rotten bulbs.
  • Infested or suspicious bulbs can be cleaned of maggots by soaking bulbs in hot water (43-44 C) for at least 40 minutes. Care must be taken to not exceed this temperature, because you will damage the bulb. This is a great way to kill other pests of bulbs, too.
  • Finally, if the problem persists, the sure-fire way to avoid bulb flies is to buy your flowers at the store like all the non-gardeners and black-thumbers out there. If you don’t plant it, they won’t come. This option is the one that I’m going to take now.

In the event that there are other pests present on your bulbs, this information from University of Florida Extension may be of interest. Excerpt:

“Spider mites are tiny animals (1/50 inch or 0.5 mm long) that cause injury similar to that of sucking insects as they feed on the leaves of amaryllis during warm, dry periods. Bulb mites attack rotting bulbs and tunnel into healthy bulbs, transmitting organisms that produce bulb rot.
Bulb mites are particularly damaging to bulbs of amaryllis.
Mealybugs are soft-bodied insects covered with a white, waxy material. When mature, they vary from 1/50 to 1/3 inch (0.5 to 8.5 mm) in length. They damage plant foliage by sucking plant fluids and may invade stored bulbs. Some control can be obtained by frequent syringing with a hose.”

In case you are curious, here is information on the beneficial properties of syrphid flies, from University of California, Davis Integrated Pest Management.

,

keeping cats out of flower beds

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. This page from the ASPCA (now archived) 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 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 or hardware cloth 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.

insect pests that affect bamboo

I have a “fence” of golden bamboo that is approximately 8 years old. It has a black coating on the leaves as well as small white flying insects that scatter when I move the branches. Any ideas as what has invaded my yard?

While we cannot diagnose plant problems remotely, what you describe sounds a bit like aphids or whitefly.

This page (now archived) from the American Bamboo Society  website also has information on insect pests that affect bamboo. Here is an excerpt, about aphids:
“Aphids love bamboo! There are over 50 species of Asian aphids known to feed on Asian bamboos. A good example is Astegopteryx bambusifoliae, which sucks sap from the leaves of Bambusa, Phyllostachys, and Dendrocalamus throughout Southeast Asia. It over-winters on the bamboo plant, where it sucks sap from the leaf undersides and culms. It is most common during the winter and spring, and disappears during hot summers. It is controlled by ladybeetles. In general, aphids aren’t a major problem since there are so many organisms that prey on them, but they can appear in an occasional outbreak that causes wilting of the leaves and shoots, a reduction in vigor, and stunted growth. They can also transmit fungal diseases, such as black mildew.” Bamboo mites are also common in our area.

University of California at Davis “Giant Whitefly” page mentions a black mold that forms during whitefly infestations.

To determine which insect is invading your bamboo, you may want to take a bagged sample to a Master Gardener Clinic for identification. For information about Clinic hours see their website (Plant Clinic Schedule).

snail and slug control

I have a big snail population in my yard. I don’t use pesticides and I want to avoid Sluggo or other iron phosphate type baits.

I have read online that decollate snails (Rumina decollata) eat brown garden snails (Helix aspersa). I’m thinking about ordering some of these as they say the decollate snails don’t eat your plants. Also I’ve read that garter snakes will eat the slugs and snails.

 

Decollate snails may not be imported into the Pacific Northwest. See this information from Oregon State University on nursery pests, excerpted here:
“Decollate snails, Rumina decollata, have been reared and released as biological control agents to control brown garden and other snails. They are native to the Mediterranean and have been in the US since the 1820s and in southern California since the 1950s. They are commercially available and have been used rather commonly in citrus orchards in California. They can harm native snails and are also plant feeders themselves. Decollate snails are prohibited from shipment to the Pacific Northwest but have managed to slip in at times.”

Oregon also lists Rumina decollata on its 2003 Invasive Species Report Card, and states that it is polyphagous, eating both plants and other snails:
“decollate snail, Rumina decollata (a polyphagous species that consumes both plant material and other snails, promoted as a biological control agent in areas heavily infested with European brown garden snail in California, reported for sale in a Eugene garden center in 2003)”

The U.S. Department of Agriculture’s Animal and Plant Health Inspection Service (APHIS) also states that decollate snails cannot be permitted across state lines:
“Decollate snails (Rumina decollata) and aquatic snails in the family Ampullaridae (e.g., Pomacea canaliculata, channeled apple snail), with one exception, may not be imported or moved interstate except for research purposes into an APHIS inspected containment facility.”

I’m not sure I’d recommend importing garter snakes, though there may be natives already in your garden or surrounding areas. See the Washington Department of Fish and Wildlife’s information about our native species, which includes tips for attracting snakes.

There are much easier methods than the above for controlling destructive snails. The same traps that work for slugs–beer in saucers, upturned melon rinds, or copper barriers around plants–should help. A vigilant eye will catch lots of them, too, and they can be squished if you aren’t squeamish. More information from University of California, Davis Integrated Pest Management is here.

I understand your reluctance to use iron phosphate products like Sluggo. Although it is certified as acceptable for organic use by the Organic Materials Review Institute (OMRI), information published on the website of Oregon State University in May 2013 quotes recent research suggesting that even “less toxic” iron phosphate slug bait can cause iron toxicosis, and should be kept away from animals and children. Here is a fact sheet from the National Pesticide Information Center which explains the risks. Stormwater runoff may also be a concern, although one typically doesn’t use much of the stuff at a time. You might borrow a duck or two to come in and do some serious snail-eating!

managing rose slug and rose mosaic

My roses were diagnosed with both rose slug and rose mosaic. I would like to know your thoughts about treatment of these conditions, as it was suggested that I just remove affected leaves, and I am looking for a more effective solution.

 

I will summarize what Christine Allen’s Roses for the Pacific Northwest (Steller Press, 1999) says about these two problems:

Mosaic virus:
This disease infected the roots of your rose when the plant was grafted; the symptoms do no show up for a year or two. The problem is widespread anywhere that rootstocks are developed from cuttings (rather than seed). (In Canada, apparently, most rootstocks are grown from seed, so they have far less of a problem with the disease.) The disease is incurable, and affected plants will have yellow patterning on their foliage. Other plants in the garden cannot “catch” the disease. Sometimes the symptoms disappear by midsummer, but recur the following spring.

Rose slug:
The greenish-white worms are actually sawfly larvae, and they can skeletonize leaves. They aren’t caterpillars, so controls that are used for caterpillars (such as Bt) won’t help. Insecticidal soaps can kill them, but only by making contact, so this means repeated spraying. It is best to do this in early evening when the larvae are most active, and may be seen on the top surfaces of the leaves. Pyrethrins are effective, but they also are acutely toxic to aquatic life, moderately toxic to birds, and may kill beneficial insects such as honeybees [my comments, not the author’s], so they should be a choice of last resort. The Environmental Protection Agency has additional information on pyrethroids and pyrethrin.

To prevent or mitigate rose slugs, clean up leaf litter and other debris several times a season to eliminate pupae and interrupt the life cycle. Hoe the soil gently and not deeply, and apply annual mulch early in the year.

Garden Tip #39

The Northwest Center for Alternatives to Pesticides (NCAP) works on two fronts to find solutions for pest problems. The Oregon-based organization does research to find natural or non-toxic answers for managing home and garden pest insects, weed and fungus problems. NCAP also advocates for stricter safety regulations and full disclosure on pesticide labels. For $25 per year, members receive the bimonthly Journal of Pesticide Reform. Call 541-344-5044 (9:00-5:00 Pacific Time) for membership information, or go to their website and join online. Many fact sheets, brochures, and articles are available for free at their website www.pesticide.org