You go over your label instructions, mixing procedures, nozzle configuration and everything else you can think of. Everything checks out except your results. 

The problem in many cases is pest "resistance" to pesticides. In this instance, you are fortunate to have discovered the problem early. You have time to try a different pesticide. Many growers have not been as lucky, and the problem has gone unnoticed until long past the time to take corrective action. 

A resistant pest is one that suffers no ill effects after exposure to a pesticide that formerly killed it. This scenario has repeated itself over and over with all types of pests. Colorado potato beetle, numerous species of whiteflies, leafminers and spider mites share a demonstrated ability to overcome the effects of pesticides with such diseases as late blight of potato and fireblight. Resistant weed pests include goosegrass, cocklebur and annual ryegrass.

How resistance occurs

Insect, weed and disease pests have the ability to "learn" and pass their "schooling" down to their offspring. The learning takes place as a change in the inherited genetic material within the pest population. 

For example, year in and year out your neighbor has been spraying pesticide "A" to suppress aphids, his number one pest. Each time he sprays, 99 percent of the aphids are killed. 

The aphids are never entirely eradicated, and over the course of a season millions of new aphids are born. A small portion of those aphids have slight, accidental changes, or "mutations" in their genetic makeup. Most of the defective, mutant aphids don't live long enough to pass on the mutation to their offspring. 

However, one summer day, an accidental change in the genetic makeup of a single aphid turns the pest into a "super bug." The aphid is now no longer susceptible to a formerly toxic pesticide. Due to this highly beneficial mutation, this aphid leads a long and fruitful life, passing the genetic change onto thousands of offspring. 

Your neighbor notices more and more aphids, and increases his spraying frequency to every five days instead of every 10. By the end of the season, he's succeeded in killing off all of the susceptible aphids, leaving only the mutant "super bugs." If he doesn't make a change to a different, still effective insecticide, he's in for a huge pesticide bill and a poor return on an aphid-infested crop. Back to top

What can be done?

Here are some ideas to help delay the development of resistance.

• Rotate pesticides — Don't use the same material or class of material time after time. Choosing alternates that don't kill pests using the same mechanism prevents a mutant, resistant pest from surviving for more than a couple of treatments in a row. 
  Example: Organophosphate insecticides share the same mode of action. Alternate any one organophosphate with a pesticide from a different class, such as a Bacillus Thuringiensis, pyrethroid, soap, oil or insect growth regulator.
• Use mixtures — When permitted by label instructions and manufacturers' recommendations, use a tank mix of two or more materials with different modes of action. 
• Create "refugia" — Refugia are portions of a planting that are not treated with pesticides. These areas allow susceptible pests to escape a pesticide's toxic effects. These pests will reproduce and preserve susceptible genetic profiles in the pest population, ensuring that resistant pests won't take over. 
• IPM — By treating only when absolutely necessary instead of on a regular schedule, you limit pest exposure to pesticides and the development of resistance.
• Spot spraying — By treating border rows only (for pests that migrate into your planting from outside) and localized "hot spots" where pest numbers are over the action threshold. You leave large areas unsprayed for susceptible pests to survive. These areas can be treated at a later date, if thresholds are reached.
• Evaluate results — Always check treated areas to verify the results of your treatment. Keep detailed records on which materials have been applied and where, and what percent kill was achieved. 

Only by careful post-treatment monitoring and conscientious record keeping can you be sure to avoid an unpleasant surprise from resistant pests. Back to top

Resistance to pests

Resistance is a double-edged sword: pests become resistant to pesticides, and plants can develop resistance to pests. 

In general, however, plants need our help. For centuries, humans have "bred" or consciously selected individual plants with superior qualities for propagation. This has been accomplished through slower, traditional breeding programs, whereby seeds or other propagation materials are selected from superior plants, or by rapid, new genetic engineering technology which allows desirable traits to be "inserted" into plants. 

Examples include traditionally bred disease-resistant varieties of apples, including Liberty, Prima, Priscilla and Sir Prize. Genetically engineered plants including Bt cotton and corn are also products of genetic engineering. Back to top

IPM: Integrated Pest Management or Integrated Pesticide Management?

A complaint sometimes heard from IPM advocates is that much of what is called IPM is really just pesticide management. It is true that delaying resistance, sprayer calibration, choosing less toxic materials, treating only when economically justified and improving pesticide timing and targeting are essential components of IPM. 

At the same time, much more is being done. More than 50 percent of the new pesticides now being submitted for registration are "biologicals," pesticides of natural origin or identical to natural products. It has simply become much more cost-effective to register a biological material than to register traditional chemistry. 

Monsanto, a chemical giant, sold off its pesticide operations and is concentrating on "transgenic" plants, which are genetically engineered to include pest-preventive qualities. 

Many agchem dealers are refocusing their efforts on service. Precision or site-specific technologies, IPM scouting and training classes and seminars are tools of a trade formerly measured only in pounds of materials sold and applied. 

IPM is not just pesticide management. IPM is a philosophy of using our growing knowledge of pest and plant biology to prevent pests from causing economic damage. We would be foolish to make a 180° turn in practices, away from chemical pesticides without waiting for our support system of knowledge and technology to stand behind us. Back to top