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Gardening Answers Knowledgebase

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

Plant Answer Line Question

Keywords: soil contamination, Wood preservatives, Pesticides and the environment

We are thinking about putting in a retaining wall and a fence on our property, which is near a lake. Should we avoid using pressure treated wood? If so, what are some alternatives?


There are many reasons not to use treated wood for your fences and/or retaining walls. The chemicals most used to preserve wood---creosote (on railroad ties, among other things) and penta---were banned by the EPA in 1986 for indoor use and for many outdoor uses. The chemical used to pre-treat wood (CCA, a mixture of copper, chromium, and arsenic called chromated copper arsenate) has been shown to leach into the soil and to transfer to human skin through contact.

There are safe paints and preservatives for coating wood; there are safe types of pre-treated wood; some people use stone, cement blocks, or other materials instead of wood.

Below is lots of info about treated wood and alternatives.

Start with the page on the EPA site, which is full of information on treated wood. It includes a section on alternatives and some questions and answers about studies.

If you find this too technical, try the next two links below.
The Natural Handyman website has good information.

Toxic-Free Future (formerly known as Washington Toxics Coalition) has a fact sheet about safe and unsafe paints and wood preservatives. Lots of background information on the toxicity of treated wood is included as well.

Date 2017-08-04
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Plant Answer Line Question

Keywords: Snails, Slugs, Pesticides and the environment

Is there any scientific reason to not use the iron phosphate based slug baits (Sluggo etc.) near bodies of water (streams, ponds, lakes)? I did some preliminary (not exhaustive) Google research and did not find anything to suggest they cause increased algae growth. Please let me know what you can find on this subject. Are other water-borne organisms harmed?


The Material Safety Data Sheet for Sluggo indicates that one should avoid disposal of this product near bodies of water (see Section 13), though there is not definitive information in Section 12 on the ecological impacts of the product on algae and other life forms. Here is a link to the PDF document.

See also "Grow Smart" from King County Hazardous Waste Management on dealing with slugs in gardens.

It does not list Sluggo, Escar-go, or any of the other iron phosphate products as water pollution hazards, but the MSDS sheet makes me think there is a potential problem with dumping large quantities. It seems not enough information is out there, perhaps because the research has not been done. Here is the page from the Pesticide Action Network database, where you can see that iron phosphate's eco-toxicity has not been established.

Here is what the Environmental Protection Agency has to say about iron phosphate slug baits:

Ecological Effects Hazard Assessment

"A number of ecological effects toxicology data requirements were waived based on the known lack of toxicity of iron phosphate to birds, fish and non-target insects, its low solubility in water, conversion to less soluble form in the environment (soil), and its use pattern (soil application). An acute oral toxicity study in Bobwhite quail (NOEL & LD50 greater than 2000 mg/kg) indicated that iron phosphate was practically nontoxic to avian species. Based on these factors, the data requirements for the toxicity studies in Mallard duck, rainbow trout, freshwater invertebrates, and non-target insect/honeybees are waived. It is likely that there will be exposure to ground-feeding non-target insects and earthworms. Submitted studies involving ground beetles, rove beetles and earthworms demonstrated that the product will not affect these organisms at up to two times the maximum application rate.

Environmental Fate and Ground Water Data

Exposure assessments on this type of product (biochemical pesticide) are not performed unless human health or ecological effects issues arise in the toxicity studies for either of these disciplines. Since no endpoints of concern were identified, there is no requirement for environmental fate data.

Ecological Exposure and Risk Characterization

Exposure to daphnids and other aquatic invertebrates would not occur based on current label use directions. Exposure to honeybees is also not expected to occur, due to the composition and particle size of the end-use product and its use pattern (soil application). Non-target insects, such as ground beetles and earthworms, could encounter the end-use product; however, in tests of rove beetles, ground beetles and earthworms, no effects were observed at up to twice the maximum application rate. Thus, the acute risk to aquatic invertebrates, non-target insects, and earthworms is considered minimal to nonexistent."

United Nations Environment Programme has information on the impact of Phosphorus on aquatic life, a process called eutrophication. However, the iron phosphate in Sluggo and similar products binds with Phosphorus, which may mitigate the effects in water.

Date 2017-05-12
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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: Rosa, Fungal diseases of plants, Pesticides and the environment

I heard somewhere that the fungicide Rose Pride was less toxic to beneficial insects than plain baking soda. Is this true? I'd like to continue to use it in my garden.


Rose Pride is the chemical Triforine. I was not able to find any articles which suggest it is safer for beneficial insects than baking soda. Pesticides Action Network's Pesticides Database indicates it is toxic in varying degrees to some forms of aquatic life. It is on the PAN List of "Bad Actor" pesticides, which means it belongs to a group of pesticides classified as most toxic (because they are known or probable carcinogens, reproductive or developmental toxicants, etc.). The Extension Toxicology Network also has a profile for this pesticide. Here are excerpts:
"In the United States, triforine is marketed for use on almonds, apples, asparagus, blueberries, cherries, hops, ornamentals, peaches and roses. Triforine is a 'restricted use' pesticide (RUP) with an EPA toxicity classification of I (highly toxic). Check with specific state regulations for local restrictions which may apply. Products containing triforine must bear the Signal Word 'Danger' on their label.
Triforine and the formulated product Saprol are considered of low hazard to honeybees and to the predatory mite Typhlodromus pyrii. It is also of low hazard to earthworms at recommended dose rates."

My comment would be that "low hazard" is not the same as no hazard, and since there are many other areas of concern with this highly toxic product, it would be best to find an alternative. Locally, the Woodland Park Rose Garden converted a pesticide-dependent landscape to an organic one, and the roses look better than ever. (See an article about the garden from the Seattle Times.) Many gardeners are learning to live with a bit of black spot on their roses, and manage the disease by maintaining good garden hygiene. Don't leave fallen leaves on the ground. Give your roses good air circulation, and keep the leaves dry when you water your plants. Mulching with wood chips can help, too, since they may prevent water from splashing up onto the leaves.

When deciding whether to treat a garden problem with pesticides, the "Precautionary Principle" provides an important perspective:
"When an activity raises threats of harm to human health or the environment, precautionary measures should be taken even if some cause and effect relationships are not fully established scientifically."

Date 2017-08-24
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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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May 31 2018 13:14:08