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Horticulture and Home Pest News
Horticulture & Home Pest News is filled with articles on current horticulture, plant care, pest management, and common household pests written by Iowa State University Extension specialists in the Departments of Entomology, Horticulture and Plant Pathology.

To Spray or Not to Spray

This article was published originally on 8/25/2000

Your plant is showing signs of stress. The leaves may be curling, distorted, or have holes in them. What should you do? In a state of panic, you look for a chemical that will solve the problem. While pesticides and other chemicals can be helpful, they are often improperly and unnecessarily used. A small amount of energy spent researching the situation can save time, money, and reduce potential harm to the environment.

In fact, in many cases the symptoms seen are the result of environmental stresses. Poor growing conditions, such as wet, poorly drained soils, can contribute to the decline of a plant. Carefully consider the conditions in which the plant is growing. In addition, a plant growing in an environment that is not optimal may be more prone to injury from insects and disease.

Identify the Pest

The first step in remedying the situation is determining the cause of the problem. After ruling out poor growing conditions, look for signs of insects or disease. Knowing the exact cause will help determine the treatment and whether a chemical is necessary at all. Different pesticides control different problems. Herbicides treat weed problems. Insecticides treat insect problems. Fungicides treat disease problems. A fungicide won't control an insect problem and an insecticide won't control blight on your tomatoes.

If an insect is causing the problem, identification is of utmost importance. Insects are vulnerable at different stages in their life cycle. If you spray an adult insect that is only vulnerable in its larval stage, little or no control will be achieved. It is also important to know when the insects are causing the most damage. While white grubs are present in the soil in spring, they are not causing serious damage to the turf, so treatment in spring is a waste of time and money. The most appropriate time to treat them is late July, when there is the most potential for damage to the lawn.

Not all problems warrant chemical treatments. For example, the plant bug is an insect that attacks the honey locust tree. While it deforms the foliage in the spring, the bugs stop feeding early and the tree looks healthy by mid-July. Insecticides can also kill butterflies and beneficial insects such as ladybugs and bees.

Likewise, disease problems need to be treated at different stages of their development. Spraying for peach leaf curl after the buds break will not be effective. Peach trees must be sprayed while the buds are still closed in order to control this disease. There are some plant diseases for which there are no chemical controls. For example, there is no known cure for Pine Wilt, a disease that is fatal to Scotch Pines. Treating the plant when symptoms appear may be too little too late.

Know the Plant

The type of plant affected needs to be identified. You cannot treat a plant with a pesticide if it is not listed on the label. The insecticide that works well on roses may not be labeled for tomatoes. When treating weeds, it is important to know whether a weed is an annual or perennial. Because of their short growing season, annuals can usually be easily pulled or their seed heads can be removed to keep them from reproducing. Perennials, on the other hand tend to have a deeper and more persistent root system. Often chemicals are the most realistic form of control for perennial weeds. Lastly, certain plants are more susceptible to diseases and insects than others are. Planting disease resistant varieties can eliminate the need for some chemicals entirely.

Read and Understand the Label

The label is the law. "It is illegal to use this product inconsistent with label directions," is a statement commonly found on pesticide containers. It not only protects the manufacturer, but the applicator as well. The label contains directions for mixing, use, safety equipment, reentry times, storage, and which crops it can be applied to. Not using the product according to label directions removes liability from the company and retailer and places it with the consumer.

Finally, be realistic about what chemicals can accomplish. The damage did not occur overnight and likewise there is not a solution that will cure it overnight. It is dangerous to operate under the assumption that chemicals can solve all of our gardening woes. The saying, "An ounce of prevention is worth a pound of cure," applies to gardening as well. There are many practices you can employ to reduce the likelihood of pest problems in your yard and garden. Often the best pest control can be achieved by using sound gardening practices.



This article originally appeared in the August 25, 2000 issue, pp. 107-108.

Year of Publication: 
2000
Issue: 
IC-483(21) -- August 25, 2000