Questions About Gardening and Pesticides

Some of the most frequenlty asked questions about home gardening and the use of pesticides:

Home gardens are usually labor intensive. In addition to producing fruits, vegetables or ornamentals, people often garden for enjoyment and exercise. If a pest invades your garden patch, you can pick it off, pull it up, or do nothing and hope it will go away. Commercial agriculture is a for profit business. Chemical pest control plays a major role in modern agriculture, and has contributed to dramatic increases in crop yields over the past four decades for most field, fruit and vegetable crops. Pesticides have enabled some growers to produce some crops profitably in otherwise unsuitable locations, extend growing seasons, maintain product quality and extend shelf life.

Most gardeners purchase pesticides at retail stores. These stores often have information on what pesticide to use to control a pest, but rarely have information on safe use, storage or disposal. In addition, sales personnel are rarely knowledgeable of pesticide safety, but frequently provide advice when asked. The best source of information on the safe use of pesticides in gardens, and around the home, is the county Extension office. In addition, most states have a Master Gardeners program supported through the Extension Service. Master Gardeners are volunteers that have training in all aspects of gardening, including the safe use, storage, and disposal of pesticides.

There is no information in the scientific literature that would indicate any change in nutrient value of food produced with the use of pesticides. Occasionally, pesticides may impart an off flavor to some fruits and vegetables.

Yes, some plants will take up some pesticides. A pesticide that is designed to be taken up by plants, and then transported to other parts of the plant to control pests, is called systemic. For example, a systemic pesticide applied to the soil may be active in controlling leaf feeding insects. Most pesticides used in the garden are not systemic. To determine if a pesticide is systemic, carefully read the use directions or consult your county Extension office. Some pesticides that are not designed to be systemic can be taken up to a lesser degree by some plants. It is less likely that these pesticides will be transported to the edible portion of the plant at concentrations that are of concern. Pay close attention to root crops planted in soil where pesticides have been used recently. Also, pesticides that break down rapidly in soil are less likely to be present in the soil at the time of replanting. Consult your county Extension office for advise on replanting into soil where pesticides have been previously used.

First, know the history of your garden soil. Where did the soil come from? What pesticides were used in the past? Has the site always been a garden or was it once used for commercial agriculture? Is the area downhill from a commercial operation, such as a nursery or farm, where pesticides are used and subject to runoff? If you are concerned about excess herbicide residues and have the opportunity, before planting, pot sensitive plants in the soil and observe plant health. Finally, consult your county Extension office and consider having your soil tested if there is sufficient evidence of past pesticide use that may be problematic. Testing soil for pesticides is expensive (usually more than $100/sample) if you know what you are looking for, and really expensive if you don’t.

Generally, pesticides do not concentrate in fruits and vegetables, but there is the rare exception. Trace amounts of organochlorine pesticides, such as DDT, chlordane, and dieldrin, no longer used but still present in some garden soils, can concentrate in the oily parts (usually the seeds) of some vegetables. Organochlorine levels found in these soils are usually very low, on the order of a few parts per billion. Even when concentrated in seeds, levels are not generally considered a health risk, but exposure should be avoided if possible.

Buy in small quantities and only what you need. The safest way to dispose of a pesticide is to use it for the intended purpose. If disposal is necessary, follow the directions on the label. For some pesticide products it is recommended to triple rinse the container, putting the rinsate in the spray tank, before disposal of the container. Some landfills will not knowingly accept any pesticide containers. Also, look for pesticide collection days sponsored by your county Extension office or state department of agriculture. Pesticides may also be deposed of at home hazardous waste collection days. Some pesticides deteriorate with age and containers may leak, so early disposal of unused chemicals is a good idea.

There are no universally effective procedures for soil decontamination except time or removing the soil. Some suggest that activated charcoal is effective in adsorbing unwanted contaminants, but pesticide contaminants are often adsorbed to the soil and not available for immediate adsorption by charcoal. Another commonly recommended treatment is to add some form of manure to the soil with the hope that this will stimulate the microbial activity resulting in rapid break down of pesticide residues. If the pesticide is water soluble it may be leached from the root zone with excessive water. However, this practice should be evaluated for its potential impact on groundwater. For pesticides that are volatile, frequently turning moist soil on a warm day, as to maximize exposure of the soil surface to the atmosphere, may help reduce soil residue levels.

When constructing a raised bed, treated wood is often used as it is resistant to rot. The most commonly available treated wood is impregnated with a CCA (chromated copper arsenate), often known as Wolmanized wood. To treat wood throughout, CCA is applied under very high pressure. This treatment fixes the CCA inside the wood, greatly reducing to potential for loss at the surface. However, with time, small amounts of arsenic, chromium, and copper will leach out to the surrounding soil. Soil migration is limited, however, depending on the soil type. Although arsenic, chromium, and copper are commonly found in all soils, the levels surrounding treated wood, up to a distance of approximately 6 inches away, will likely exceed normal background levels of these elements. Therefore, because some garden plants will accumulate these elements, do not plant close to treated wood. Alternatives to CCA treated wood include the heartwood of cedar or redwood. These woods will not last as long and are more expensive.

Here are some very informative internal and external links that pertain to gardening and pesticides:

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This Page prepared by the EXTOXNET FAQ Team. , January 1998