16.3: Pesticides Applied to Food Crops

When we grow food, other plants (“weeds”) compete for the space, and we provide a tempting buffet for deer, birds, insects, fungi, and other earth creatures. We call these competitors “pests” (to them, we are the pests), and use fences, nets, and scarecrows against big ones, and pesticides (pest killers) against small ones.

The FDA monitors pesticides in food, and safe levels are decided by our own experts and by expert committees of the United Nations. They generally regard the scant amount of pesticide residues in our food supply as safe (accidental overdoses of pesticides among farm workers are another matter). There are, of course, broader concerns. Crop pesticides aren’t restricted to pests alone and can upset the natural ecology of the field. Accidental spills and incorrect application of pesticides create hazards to farm workers.

An alternative solution is to use a pest’s natural predators. Natural predators can arrive too slowly on their own (it took 3 years for seagulls to come to Utah to rescue crops from the locust plague in the 1850s), so we sometimes import natural enemies, e.g., collecting parasitic wasps in Iran and releasing them on California crops to combat olive scale (a pest to olives, plums, apricots, and other plants).

Another age-old alternative that’s still used is crossbreeding to make crops more pest-resistant. A new alternative is to use biotech to directly transfer into plants specific genes that make natural pesticides (Chap. 10)—a more precise and confined application of pesticide. For example, the pesticide can be localized to the non-edible part of the plant and also wouldn’t be dispersed as it would be if sprayed on the plant.

Integrated Pest Management (IPM)

Integrated Pest Management (IPM) is a customized ecological approach to minimize pesticide use by using what’s needed in the safest and most effective way possible. IPM integrates strategies based on the biology of the pests and their predators, the specific crop, local soil and weather conditions, etc. IPM includes careful monitoring of pests (to decide if control is needed), using weather information to predict when the pests will be at the most susceptible stage of their life cycle (so less pesticide will do the job), controlling weeds to reduce pest reservoirs, etc.

IPM relies on an extensive base of knowledge. Even if you know that predator mites can control spider mites, you must know how to get the predators to where they are needed (e.g., mix predator mites with corncob grit, then blow the mixture on the crop with a leaf blower). IPM for certain grape crops includes removing leaves around grape clusters, to reduce bunch rot and the number of pesticide applications needed to control powdery mildew.

IPM requires a lot of research, education, and training. Even after databases (e.g., Database of Alternatives to Targeted Pesticides) and publications (e.g., IPM for Apples and Pears) are used to customize a plan, hands-on workshops for growers and farm workers are needed (e.g., how to distinguish between spider mites and predatory mites). The University of California system has been a leader in IPM research and implementation, supported mainly by state and federal funds.

Environmental Contaminants

Experts don’t worry much about residues from food pesticides, but do worry about environmental contaminants. In fact, this is second—right below microbial hazards—on their worry list. Pesticides are used to control mosquitoes, weeds along highways, etc. Some of these pesticides find their way into our food, both plant and animal.

When cars use leaded gas, lead is released into the air and taken up by crops grown along highways. Wines (representing grape crops) from many years and locales are still around and can be used to measure changes in environmental pollution. Another concern is contamination from environmental disasters, such as the Gulf oil spill in 2010 and Japan’s radiation leak in 2011 from tsunami-damaged nuclear power plants.

Plants’ ability to take up substances in air, soil, and water can be useful. As discussed in Chapter 13, the iodine content of foods— and the distribution of goiter caused by iodine deficiency—varied according to soil iodine content. Plants don’t need iodine; they simply take it up if it happens to be there. Plants are used in this way for environmental clean‑up, to remove toxic metals from polluted soil and ground water; the plants are then discarded as toxic waste.