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Gardening Answers Knowledgebase

Search Results for: Pesticides | Search the catalog for: Pesticides

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: Vegetable gardening, Pesticides and the environment, Pesticides

How soon I can plant my edibles after I've used weed and feed?


Do you know which weed and feed product was used? That would help in determining the chemical's half life (persistence) in the soil. Regardless of which chemical was used, my recommendation would be not to plant any edibles in a site which has been treated with weed and feed, but to find another location for your food plants (such as containers made of safe materials, or raised beds with a barrier between the bed and the chemically treated area of the garden).

Local garden writer Ann Lovejoy has discussed weed-and-feed products in her column. Here is a link.

Here is what retired Washington State University Extension agent Mary Robson had to say on this subject in one of her columns no longer available online:

Just one note of caution-be careful with all chemicals. Many pesticides ordinarily used in gardens are not allowed on edibles. An example is Lawn Weed and Feed which will harm any broadleaf plant whether lettuce or marigold or petunia. It's probably safest to keep pesticides out of the garden if you plan to eat the produce.

Formerly available from the website of Washington Toxics Coalition:
The Hazards of Weed and Feed
"Weed and feed is a mixture of lawn fertilizer with weed killer, usually 2,4-D and related compounds. The problem with weed and feed is that it is designed to be applied to the entire lawn regardless of whether or not weeds are actually present. This encourages over use. For example, if 30% of your lawn is covered in weeds, 70% of a weed and feed application will be wasted, since the herbicides have no residual action. Since many people do not realize that weed and feed is a pesticide, they may be less inclined to read an follow label instructions. For example, did you know that it is illegal to apply weed and feed more than twice per year on the same site?

"The herbicides in most weed and feed products are mobile in soils and are widely found as pollutants in local streams, according to the U.S. Geological Survey. In addition, 2,4-D is neurotoxic and may be a carcinogen according to some studies.

"Weed control should be practiced only as needed, not every time you fertilize. Mechanical controls are preferable to protect health and the environment. If chemical controls are used, spot treatment should be utilized to minimize product use and resultant risks from direct exposure and track-in to the home on shoes and feet."

Here are links to information on some common weed-and-feed type products and their hazards:

From the Pesticide Action Network North America

From the Winter 2005 (updated April 2006) article in Journal of Pesticide Reform

Date 2017-05-24
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Plant Answer Line Question

Keywords: Sod webworms, Pesticides

Our maintenance contractor has told us that our grass is infested with the dreaded sod webworm, and that we should attack it immediately with the insecticide Covert. A little research tells me that this product is very toxic. Question: true or false? What are some commercially available alternatives if this is a toxic product?


It would be best if you could avoid using pesticides to control sod webworm. If you can encourage natural predators in your garden (such as ants, ground and rove beetles, parasitic wasps, and particularly birds), this should cut down on the infestation, whereas pesticides may well have a deleterious effect on beneficial insects and wildlife. University of California, Davis Integrated Pest Management also suggest that reducing thatch, and proper irrigation and fertilization of lawns will cut down on infestations of sod webworm.

Covert is a synthetic pyrethroid (as opposed to a natural pyrethrin). You may have already looked at the Material Safety Data Sheet for this product, but in case you have not seen it, here is a link. This document lists the product as highly toxic to bees, extremely toxic to fish and aquatic life, and notes that it contains ethyl benzene, a confirmed animal carcinogen. The Northwest Coalition for Alternatives to Pesticides also has information about the toxicity of permethrin (an ingredient of Covert). Here is more on permethrin and pyrethroid insecticides. Essentially, synthetic pyrethroids last longer in the environment than pyrethrins. They may be less toxic than some pesticides, but they are not without health and environmental concerns. Since there are nonchemical methods of control, it does not make sense to take a chance using something which is potentially harmful.

Bt or Bacillus thuringiensis is registered for use on sod webworm, and you can find it as well as beneficial insects, Steinernema nematodes from some gardening suppliers and well-stocked nurseries. Peaceful Valley Farm & Garden Supply has a large inventory of organic pest control products:

Organic Pest Control

Safer Caterpillar Attack

Parasitic Nematodes, Steinernema carpocapsae

Moth Egg Parasite - Trichogramma Wasp

I encourage you to pursue these alternatives to using the toxic product suggested by the maintenance contractor. Toxic chemicals can harm birds and beneficial insects, and using such products starts a vicious cycle, since those creatures would actually help keep down the undesirable webworm population.

Date 2018-06-27
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Plant Answer Line Question

Keywords: Plant diseases--Control, Prunus, Pesticides and the environment, Pesticides

We live in a heavily treed (fir and cedar mostly) condominium complex. Our shrubs are sprayed twice a year by a professional spraying company to protect against fungus and other problems. We are thinking of spraying every other year to save on expenses.

Would we be jeopardizing the health of our shrubs and small cherry trees by doing so?


Unless your shrubs and trees have a history of trouble with diseases, I can't think of any reason they should be sprayed at all. Even if the plants were susceptible to disease, a more sustainable approach than annually applying fungicides and other pesticides would be to select disease-resistant plants that will thrive in your garden's conditions without that sort of intervention.

Spraying, depending on what is being sprayed, can be a hazard to human health and the environment. You may be able to stop your spraying program entirely by instituting good garden practices, like cleaning up debris and providing good air circulation around the trees, and avoiding overhead irrigation.

Examples of nonchemical ways to manage fungal problems that may affect ornamental cherry are provided below, from Washington State University Extension's HortSense website:
"Brown rot is a fungal disease which initially infects the flowers. The petals turn light brown, develop water-soaked spots and may have tan or grayish areas of fungal spores. Infected flowers often remain attached to the plant, spreading the disease to small twigs and branches. Infected twigs and branches are often observed in the summer as flagged, dead leaves and twigs. Infected branches develop cankers which may produce gumming (leaking sap) or may girdle and kill the branch. Most brown rot cankers develop with a dead twig at the center where the initial branch infection occurred. Fruit can also be infected, dry out, and hang in the tree. Tan or gray fungal spores may be found on infected blossoms, fruit, or twig cankers. Ornamental and fruiting stone fruit trees are affected.
Select Non-chemical Management Options as Your First Choice!!

  • Avoid wounding trees.
  • Clean up and destroy fallen flowers and other debris beneath trees.
  • Remove and destroy all infected twigs and branches during the summer, making pruning cuts well below infected tissues."

Similarly, here are their recommendations for managing Coryneum blight or shothole:

  • Avoid overhead watering, as leaves must be moist for infection to occur.
  • Prune and destroy dead buds and cankered twigs if present.
  • Rake and destroy infected leaves.

Again, for cherry leaf spot:

  • Avoid overhead watering. If overhead irrigation is necessary, limit it to times when foliage can dry quickly.
  • Rake and destroy all fallen leaves and debris under trees.
  • Space plantings and prune to provide good air circulation.

Date 2017-05-26
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Plant Answer Line Question

Keywords: Lamium galeobdolon, Weed control--Pacific Northwest, Pesticides

Is it safe to use a product like RoundUp to get rid of invasive plants such as Yellow archangel in my yard? What do you suggest?


Do you have a large area covered with Lamium galeobdolon (Yellow archangel, formerly known as Lamiastrum)? I successfully eradicated this plant from my garden by hand-pulling persistently over a few months. This method is certainly safer than using herbicide, but if you have a vast area to tend, it may be harder to achieve. King County Noxious Weed Control has factsheets on this plant which mention various methods of control, including chemical. Because we are librarians and not licensed pesticide handlers, by law we can't actually recommend use of a particular pesticide. Note that the information linked here does say that RoundUp (glyphosate) isn't as effective as some other products. You may also want to take into account the costs of using pesticides in a home garden (where they may affect other non-target plants as well as wildlife, pets, and human inhabitants) against the perceived benefits (perhaps faster and easier than manual control).

The following information about eradicating Lamium galeobdolon is from the Washington State Noxious Weed Control Board:
"Response to Mechanical Methods: Viny plants are easily pulled out by hand during the fall through early spring; however, great care must be taken to remove all parts of plant, as rooted fragments will regenerate (Graham, 2003). It should be noted that L. galeobdolon is highly susceptible to trampling (Packham, 1983)."

If your question is about the safety of glyphosate (RoundUp active ingredient), you may want to read the Northwest Center for Alternatives to Pesticides page about it.

Date 2018-06-27
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Garden Tip

Keywords: Pests, Pesticides

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

Date: 2006-03-01
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Garden Tip

Keywords: Pesticide safety measures, Pesticides

The National Pesticide Information Center was created by a cooperative effort of Oregon State University and the Environmental Protection Agency to answer questions about pesticides. The public is encouraged to call 1-800-858-7378 to talk with an expert about general safety concerns or specific chemical risks. Fact sheets on over 40 common pesticides are available online at their website, npic.orst.edu/npicfact.htm.

Date: 2006-03-01
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May 31 2018 13:14:08