JoAnne Skelly: Is it time to use a pesticide?

There are many definitions of the word “pest,” and personal perceptions of pests can often be very different. A pest might be annoying (ants), damaging to plants (rabbits), a health concern (ticks) or a cause for fear (black widow spiders). However, relatively few pests cause significant injury to plants, so pesticides are rarely needed.

A pesticide is a substance that destroys, prevents or repels a pest. There are many types of pesticides. For example, herbicides kill plants, insecticides kill insects, fungicides kill fungal organisms, miticides kill mites and rodenticides kill rodents.

Often, plant problems in Northern Nevada result from non-living factors. These include weather, wind exposure, lack of water or excess water, soil type, soil compaction, poor drainage, improper plant selection for the site, restricted roots or poor cultural practices. Since many plant problems are not caused by living pests, it is important to determine the cause of the problem or symptoms before buying and using a pesticide.

First, identify the plant. Some plants are prone to certain insects, such as aphids on ash trees or roses. Some problems are actually nutrient deficiencies. Pin oaks are subject to iron deficiency, which causes the leaves to yellow but veins to stay green. Note the signs of damage. Do you see insects? Or could site conditions or gardening practices be causing the problem? What characterizes the microclimate, soil type or drainage near the plant? Consider sun, shade and wind exposure. Often, improper watering causes the damage. How do you water, how often, how much and how deeply? If you use a drip system, where are the emitters located, and how many are there for each plant? Is the plant watered all through the year, or just seasonally?

Factors people rarely consider when worrying about a plant are the kind of activities that may have occurred near it, such as construction, pesticide spraying, painting or fertilizing. Each may damage plants and cause signs similar to insects or disease.

Once you have identified that a pest is present, realize that some level of damage can be tolerated if it’s primarily aesthetic and not harming the plant, particularly if the plant is fairly healthy. Before using a pesticide, consider that the problem might go away without taking any action. Try other less-toxic methods of control, for example, spraying plants infested with aphids or spider mites with a strong jet of water.

For more information go to

JoAnne Skelly is Associate Professor & Extension Educator, Emerita at University of Nevada Cooperative Extension. She can be reached at


Use the comment form below to begin a discussion about this content.

Sign in to comment