Chemicals -- The Last Resort


Chemical applications are either organic or synthetic, contact or systemic. Herbicides, pesticides, fungicides, miticides are used to kill. "Cide" means "kill." Most “cides” are contact-type chemicals that are sprayed or applied on to the plant or into the air. Systemic pest controls are applied to leaves, stems or through the soil for the plants absorption into its system. One should not eat any plants, leaves flowers or vegetables that have taken in systemic insecticides. Likewise, one should not eat plants, leaves, flowers or vegetables that have been sprayed with chemicals. Be on the safe side (read the label carefully for full instructions).

Organic Chemicals

Organic “cides” are made from natural substances and break down quickly. Repeat applications may need to be made. Organic pesticide examples are insecticidal soaps, horticultural oils, and botanicals such as neem oil, sabadilla, rotenone, ryania, and pyrethrum (sometimes spelled pyrethrin).

Insecticidal soaps, such as Safer, are contact controls that work on soft-bodied insects like aphids and mites by drying their outer layer. They have minimal impact on beneficial insects.

Horticultural oils, or dormant oils, are generally applied in late winter and act by smothering the insects breathing pores, killing both the active and over wintering stages. Horticultural oils are contact controls and will also kill beneficial insects. Horticultural oils have been developed for summer use, called superior oils, are lighter oil concentrations. To avoid premature leaf drop due to burn, do not apply oils and soaps often when temperatures are above 80º; that is, more than twice within a 7 day period. As with all substances designed to kill, follow label instructions carefully. Follow these don'ts from Washington State University on how not to use horticultural oil:

  • Don't overuse oils. Like any other pesticide, natural or synthetic, overuse can damage non-target species and ecosystems.
  • Do not use oils on unregistered insects, arachnids, or diseases.
  • Don't use unregistered vegetable or petroleum-based oils for pest control.
  • Do not use oils as soil drenches.
  • Don't mix with sulfur-containing pesticides. This effectively decreases the UR number and can cause phytotoxicity.
  • Do not apply oils to wilted plants.
  • Do not use oils on seedlings or other tender plant tissues.
  • Do not use oils on conifers or other species with a waxy, bluish cast to their foliage.
  • Don't apply when rain is expected, or when humidity is high (over 90% RH).
  • Do not let oil drift onto water surfaces; it will inhibit oxygen transfer and possibly harm aquatic organisms.

Twenty percent vinegar solution is a non-specific organic herbicide. There are other organic herbicides on the market as well; one new product introduced to the market recently is AllDown (, with more products introduced in the market every year. Some products are available locally. If you’re not able to find them, ask for them or search the Internet (peruse

Before you turn to synthetic chemicals, consider using natural pest remedies. Study up on them, there are many books available today and many naturally based products (,, for example). Because many people are now choosing to live healthier lifestyles in their home and garden, the “Green Industry” is emerging, offering products that claim to be ecologically, environmentally friendly, previously referred to as organic. As with anything, the possibility for fraud exists. But there are sources consumers can access to help them in making informed, earth-friendly choices.

The Organic Materials Review Institute (OMRI) is a 501(c)(3) nonprofit organization that specializes in the review of substances for use in organic production, processing, and handling. OMRI conducts materials review according to the standards established with the implementation of the USDA National Organic Program (NOP) in October 2002. Brand name review is conducted as a transparent, third party review of products intended for use in certified organic production, handling, and processing. After review by OMRI staff, applications are submitted to an independent Review Panel of experts who evaluate a product’s compliance with the NOP National List. Products that have passed review are included on the OMRI Brand Name Product List. The OMRI Listed™ seal, which these products can display on labels and in advertising and promotions, assures their suitability for use in certified organic production. ( Consumers and gardeners alike can access their website for additional information.

Keep in mind that natural or organic remedies also kill beneficial insects along with the problem insects or weeds. Follow directions carefully and in recommended concentrations only. The label is the law. The users of these products are responsible for any damage, including drift damage. Use hand held spray bottles to spot treat the area to minimize toxic effect. Spray only on calm, windless days. A small, disposable sponge craft brush comes in handy in painting on “cides” (organic or synthetic) among ornamentals and even vegetables in close quarters.

Synthetic Chemicals

Use synthetic pesticides, herbicides, miticides or fungicides as the last resort. Synthetic “cides” are made from chemical compounds not found in nature. Many have long-lasting residual effect; some have a shorter residual life. Over time, pests develop resistance to these synthetic substances and rebound even stronger. In addition, these synthetic compounds contribute or cause unintended and harmful environmental effects.

Use specific remedies for the problem in the most vulnerable stage of growth to the pest or invasive weed. Using these products require specific knowledge of the pest and/or pathogens. Some chemicals are broad spectrum; others target specific pathogens, pests or weeds. As with organic “cides”, follow directions carefully and in recommended concentrations only. The label is the law. The users of these products are responsible for any damage, including drift damage. Use hand held spray bottles to spot treat the area to minimize toxic effect. Spray only on calm, windless days. A small, disposable sponge craft brush comes in handy in painting on “cides” (organic or synthetic) among ornamentals and even vegetables in close quarters.

Beneficial insects, organisms and plants are affected adversely along with the bad. Removing the bad insect, fungus and/or weed at the same time as beneficials sometimes will give room for secondary problems to move in and multiply, thereby exchanging one problem for another.

Resistant insects develop as a result of an incomplete kill. For some reason, 100% eradication is never achieved. Some of the pests that remain have some resistant quality that prevents them from being killed. When these pests multiply, the chemical resistance is passed on to the young. Soon, a new pesticide resistant strain of pest is present, and without the normal predators to keep them in check.

In the rebound effect, pests usually recover quicker than the predators. Plant-feeding insects are at the bottom of the food chain and are therefore more numerous than their predators. Naturally this makes sense. It'll take many aphids to satisfy the hunger of an aphid predator, such as a lady beetle. If pesticides killed all aphids, this guaranteed meal to lady beetles would cease. But pesticides do not wipe out all aphids (or lady beetles either, although a good many of both are destroyed at the same time). The remaining aphids multiply faster than the lady beetles. Being lower on the food chain, aphids multiply faster and stronger and may even become genetically resistant. They now face fewer enemies. The use of pesticides, instead of using the less harmful method, such as spraying with a jet of water, thus creates a greater problem.

Insect interactions with other insects, both insect predators and plant predators are within the natural order of things. One feeds on the next, that feeds on the next, that feeds on the next and so on. Disruption by chemicals sets the community off balance.

Herbicide Carryover – Killer or Contaminated Compost

Farmers and home gardeners across the United States have reported damage to vegetable, flower and fruit crops after applying composted manure (whether from cows or horses) or composted hay, straw or grass clippings to the soil. Shortly after these applications as soil amendments or mulch, they noticed stunted growth, poor germination, death of plants, deformed plants and fruit. In most cases, the damage was caused by a group of synthetic chemicals known as pyridine carboxylic acids, sometimes referred to as pyralids, namely, aminopyralid, clopyralid, fluroxypyr, picloram, triclopyr and/or aminicyclopyrachlor. Products containing these chemicals include Curtail, Forefront, Grazon Next, Grazon P+D, Milestone, Redeem R&P, Surmount, Confront, Lontrel, Millennium Ultra Plus and Plus2, Clopyr AG, Stinger and Imprelis. In September, 2009, Mother Earth News reported that a previously considered organic product, Grab 'n Grow, contained one of the above chemicals and caused damage to a vegetable garden of Grab 'n Grows manager, Don Liepold. Subsequently “I have been testing  and detecting herbicide residues and thus rejecting cow manure, horse manure, turkey mulch, rice hulls, mushroom compost and yard trimmings,” says Grab n’ Grow manager Don Liepold. “I spent $20,000 in lab fees in 2008, and am on the same track for 2009,” he says.”

The Mother Earth News article continues “It is extremely difficult to keep contaminated materials out of commercial compost. “One load of contaminated grass clippings can ruin a batch of compost,” says Eric Philip of Anatek Labs in Moscow, Idaho. Philip has seen so many positive tests for clopyralid residues in compost that he would not use untested compost in his own garden.

“When folks have plants die in their home gardens, their first assumption is that they did something wrong,” Philip says. But with pyralid-laced commercial compost becoming more common, contaminated soil amendments are often to blame.

The effects of contaminated compost and composted manure might be transferred to foliar sprays as well, although I have not read any reports mentioning them specifically.

The source of pyralid pollution can be impossible to trace. For example, a horse stable may use hay brought in from a neighboring state, without knowing that it is laced with pyralid herbicides. If the horse’s manure or stable litter ends up in a garden, disaster is ready to strike. It’s better to be safe than sorry. Liepold stopped making one of Grab n’ Grow’s most popular products, Mango Mulch, for more than a year because he could not find an uncontaminated manure supply. Now he’s getting it from two local organic dairies.”

Mother Earth News first sounded the alarm on “killer compost” in 2008, and has continued to report as new information comes to light. In 2011, Dupont's Imprelis, an herbicide praised for being a “green alternative” because of its long residual, made headlines as it killed trees and shrubs in numerous states from New England across the Midwest into the northern Plains States. Currently, the EPA Stop Sale Order on Imprelis, but not on the other products by Dow AgroScience and Dupont.

Dupont did notice that Imprelis could create killer compost. From Page 7 of the 9 page label on Dupont's Imprelis: “Do not use grass clippings from treated areas for mulching or compost, or allow for collection to composting facilities. Grass clippings must either be left on the treated area or, if allowed by local yard waste regulations, disposed of in the trash. Applicators must give verbal or written notice to property owner/property managers/residents to not use grass clippings from treated turf for mulch or compost.”

It is well known that the “label is the law”. How many people do you imagine read the entire label when purchasing herbicides? Although Imprelis was sold only to licensed applicators, how many of them read the label or warned home or corporate owner/managers when they applied Imprelis of the long term effects regarding compost? In areas where community composting is practiced, it is easy to see how contamination of these resources can occur.

North Carolina University Cooperative Extension issued an excellent bulletin entitled “Herbicide Carryover in Hay, Manure, Compost and Grass clippings warning “farmers and home gardeners of reported damage to vegetable and flower crops after applying horse or livestock manure, compost, hay or grass clippings to the soil,” ( Although the above mentioned products were licensed for use in agriculture by licensed applicators, Imprelis was licensed for use on residential lawns by licensed applicators.

Just because many of these products were for agricultural use, doesn't mean home gardeners are safe from the herbicides long term effects. The warning for vegetable growers and home gardeners is to be aware of your source for hay, straw, manure or compost from hay, straw or manure. These herbicides can be active up to four years or more. The person you purchase or receive these products from may not even know this class of herbicides have been sprayed on them, or be aware of the longterm effects.

Here is an example of why it is difficult to find out. A friend of yours offers you horse manure that has been composted. You might ask him/her if herbicides were used, with the farmer replying the manure/compost is "safe" because the animal has not been effected. The horse or cattle were fed hay that was sprayed with one of these herbicides (it's reported not to be harmful to animals). The horse eats the hay, and the resulting horse manure contains active residues of the herbicide, even after it composts. You spread the manure in your vegetable garden and your vegetables are stunted and fail to thrive, or die outright.

You might think this couldn't happen to you, but a case very similar to what I described happened to a family member of mine. After he did some research, he went back to the neighbor where he got the manure and found out the man did indeed spray his hay with one of these chemicals.

Unless you are absolutely sure hay or straw does not have a history with these herbicides, I would not use them in compost or on your garden soil or ornamental beds.

The affected composted manure would be safe to spread on your turfgrass. To be safe, I would not compost the grass clippings or use the grass clippings in beds or borders. It would be safe to cut your turf with a mulching mow, returning the clippings to the soil if you had already used contaminated compost there. I'm unsure of the effects of these chemicals on trees (except for Imprelis). The North Carolina bulletin goes on to describe how to do tests to determine whether the compost or hay/straw contains residues of one of these herbicides.

The latest warning has come from Mother Earth News, published in the February/March 2013 issue. They noted that livestock feeds now contain the contaminated chemicals and are passed through the animal into the manure in this manner. Because of the growing contamination problem, Mother Earth News advises gardeners that “the time has come for the public to stop buying compost or manure products unless they come from suppliers that are able to afford testing and can screen feedstocks for herbicide residues.”

Once again, the buyer needs to be very aware.

Read More: a FAQ sheet from the US Composting Council on contaminated compost:

Read more:
Read more:


  • Ecology for Gardeners, Steven B. Carroll and Steve Salt, Timber Press, 2004.
  • Insects and Gardens, In Pursuit of a Garden Ecology, Eric Grissell, Timber Press, 2001.
  • IPM for Gardeners, A Guide to Integrated Pest Management, by Raymond A, Cloyd, Philip L. Nixon and Nancy R. Pataky, Timber Press, 2004.
  • Master Gardener Handbook, edited by Douglas F. Welch and Samuel D. Cotner, Texas A & M Press, 1995, third edition.
  • Silent Spring, Rachel Carson, Houghton Mifflin, 1962.

Angie Hanna