Insect Management

A successful insect management program can best be accomplished by combining IPM techniques, such as accurate pest identification, scouting, monitoring and action thresholds, with biological and alternative (preventative) control practices and selective insecticide applications if needed.

Use scouting and monitoring techniques to help assess and quantify insect populations over time.

Insecticides should be used only when action thresholds have been exceeded or damaging insect populations are present. Action thresholds help minimize insecticide use and crop damage. Avoid making routine insecticide applications to crops without evidence of insect activity and damage. All insects have natural enemies which, if conserved, can help regulate pest populations. Whenever possible, use selective insecticides that spare beneficial organisms and target the pest you wish to control. Broad-spectrum insecticides should be used as a last resort. All insecticide applications should be made with ample water and with nozzles directed so that they provide thorough coverage of the plant parts where insects hide. Alternate between insecticide classes or families to help manage insect resistance and extend the life of available products.

Insect Identification

Become familiar with the biology and life-cycle of the major insect pests that attack crops on an annual basis. Understanding some basic insect biology often reveals when the pest is most vulnerable to control measures and helps lead to successful management efforts. Insects usually have either a simple life-cycle, where they grow from egg to nymph to adult, or a slightly more complex cycle, where they mature from egg to larva and then go through metamorphosis in the pupal stage before becoming adults. Insects damage plants either as nymphs/larvae or as adults, or in both immature and adult stages. Learn to recognize the important life-stages of major insect pests, and to  recognize the crop injury or damage they produce to help determine when control efforts are needed. You should also be able to identify common beneficial insects and their immature stages (i.e., lady bug larvae) to avoid accidentally targeting natural enemies with insecticides. There are dozens of minor and secondary insect pests that may attack crops on a less frequent basis. Growers should have unknown insects and minor pests identified (see Diagnostics section) when they are suspected of causing crop damage. Misidentification often leads to the application of an ineffective pesticide and extensive or chronic crop damage. The application of ineffective or unnecessary pesticides can often reduce the populations of beneficial organisms or natural enemies and lead to secondary insect or mite outbreaks. An accurate diagnosis of the problem early on can often avoid years of frustration and needless expense. See the photo supplement section for help with identification.

Scouting and Monitoring

Crops should be inspected or scouted for insects or damage in a systematic fashion, on a regular basis throughout the growing season. For many crops and pests, this may mean walking fields weekly, or even more frequently, especially during critical or vulnerable plant development stages. Crops should be scouted in a systematic fashion by walking in an "M" or "W" pattern as you crisscross the field. Select plants (i.e., 25 or 50) at random and quantify the pest damage or count the individual insects. Record the average number of insects or damage per plant for each field. Scouting crops always saves money in the long run by allowing for early pest detection, by reducing crop damage and by helping to maintain consistent quality. Sometimes scouting duties can be performed by other farm members or by hired consultants.

Monitoring insect populations with various types of traps (black light, pheromone, sticky, baited) can supplement or sometimes substitute for information normally gathered during crop scouting. Insect traps can help you quantify pest pressure that is difficult to see, such as the number of night flying (i.e., corn earworm) moths present. The number of insects captured in traps is often used to time scouting activities, predict future pest levels, or is used in conjunction with action thresholds to time sprays and help avoid crop damage.

Action Thresholds

Action thresholds tell you when to spray to prevent economic damage to the crop. They also help you avoid applying insecticides to crops when insect populations are low or no pests are present. Thresholds can be based on the number of insects found per plant, the amount of injury or damage per plant, or the number of insects captured in a trap. Using action thresholds helps improve insecticide timing and effectiveness, helps minimize the number of applications and associated costs, and helps reduce crop damage and resistance problems. Use action thresholds whenever possible to help you decide if and when a spray is needed. Some insect thresholds are provided in this publication. See your state's Extension IPM personnel for local action thresholds for specific pests.

Preventative Controls

As mentioned in the introduction to the general Pest Management section, there are many preventative management options, such as cultural, mechanical, physical, genetic and biological controls. These should be used whenever possible to help prevent insect pest problems. Preventative insect control options can be used alone or in combination to provide a complete management program. For example, plant inspections, eliminating weeds in the greenhouse, using screens, avoiding excess nitrogen applications, using plastic mulch and preserving natural enemies can combine to produce a very effective aphid management program. If the distance between fields is great enough, crop rotation (alone) for Colorado potato beetle and cucumber beetles can often keep these tough pests from reaching damaging levels for the entire season. However, if only nearby fields are available, CPB can be effectively controlled by the use of a combination of two or more alternative controls, such as short-distance crop rotation, intervening trap crops or plastic-lined trenches, row covers, organic mulches, flaming, and microbial controls. Many preventative controls are mentioned in crop-specific IPM manuals, individual pest fact sheets and on IPM web sites.

Perimeter Trap Cropping utilizes a combination of control measures to concentrate and/or kill pests in the border area of the field. This technique involves planting one or more rows of an attractive plant species so that it completely encircles the less attractive main crop, and intercepts a migrating insect population. Often a chemical or microbial insecticide is used to spot-spray the perimeter trap crop (only), sparing beneficials on the main crop, and substantially reducing insecticide use. Perimeter trap cropping has been shown to be effective at controlling diamondback moth larvae on cabbage, using collards as the trap crop; pepper maggots on bell peppers or eggplant, using hot cherry peppers as the trap crop; and cucumber beetles on summer squash, winter squash, cucumbers, melons, and sometimes pumpkins, using Blue Hubbard squash or another Cucurbita maxima variety as the trap crop. This technique may prove useful on related crops and against additional pests in the future.

Insecticides

Follow the label specifications for application rates. If the rate suggested in this guide does not agree with the current label, follow the label recommendations. Amounts of pesticides are in lb/A (pounds per acre), oz/A (ounces per acre) or pt/A (pints per acre) of commercial formulation, not a.i. (active ingredient), unless otherwise stated. The percentage by weight or concentration of a.i. varies with different brands of pesticides. The label gives pounds of a.i. in each commercial preparation. For example, Lorsban 4E has 4 lb active ingredient/gallon of formulated material.

The amount of insecticide recommended per acre should not be changed when varying gallonage of water per acre. Make sure a pesticide is labeled for concentrate application before using a low volume sprayer, air or mist sprayer, aircraft or other concentrate application equipment.

Seed Treatments

Insecticide seed treatments may help protect your crop from soil insects and other early-season pests. Some of the seed treatments listed under various crops must be applied by a professional licensed seed coating applicator. In some cases the use or purchase of treated seed may be economical as it may result in a substantial reduction in pesticide use and increase the plant stand and yield in the field.

Resistance Management

Adult pests that survive an environmental hardship, such as the application of an insecticide, are likely to pass the trait that enabled them to survive on to their offspring. Repeat applications with the same type of pesticide will eventually remove almost all the susceptible individuals from a pest population and leave only those with the resistant gene. Because insects and mites go through generations quickly, resistance to an overused pesticide can develop in as little as three years.

To preserve the useful life of a pesticide, it is necessary to practice resistance management. The most effective way to extend the useful life of an effective product is to use it on a single pest generation only, and then on the next generation use a second pesticide with a different method of killing the pest (mode of action). On some pests particularly prone to developing resistance (i.e., Colorado potato beetle) it is best to use a product with a particular mode of action on one generation every second year only. To help select pesticides with a different mode of action, see chemical resistance groupings in Table 27. These resistence group numbers, or IRAC codes, were developed by the Insecticide Resistance Action Committee (IRAC). Products with the same code (number and letter) indicate products with a common mode of action. For multiple applications to the same crop, select products from different resistance groups.

Once a pest develops resistance to a group of pesticides with a particular mode of action, a higher rate of a similar chemical from the same group usually will not control the insect.

NOTE: There is no cross resistance between insecticides, herbicides and fungicides. For example, there is no problem when using material from the herbicide group 1 and an insecticide or fungicide from group 1.

There are many other techniques that can help delay the onset of resistance. Most resistance management techniques help minimize the use of pesticides, so that a lower proportion of each pest generation is exposed to the toxin.

  • Integrate chemical control with effective cultural, mechanical, physical, and genetic management options.
  • Use biological/microbial control agents or other selective pesticides to preserve natural enemies and help minimize the number of repeat applications.
  • Scout, monitor and use action thresholds to ensure that applications are necessary.
  • Good spray coverage helps do the job right the first time and avoids unnecessary repeat applications: use the proper size nozzles and the correct angle or orientation and an adequate amount of water per acre.
  • Time the application so that the most vulnerable insect life stage is exposed to the spray.
  • Use spot sprays, perimeter trap crop treatments, refuge plantings, and other methods that prevent the entire field or population from being treated to help preserve susceptible individuals.

Toxicity Rating of Insecticides

Insecticides vary greatly in their toxicity to humans and the environment. The toxicity of the insecticide is usually stated in the precaution on the label. For example, a skull and crossbones figure and the signal word "Danger" are always found on the label of highly toxic (Toxicity Class I) materials. Those of medium toxicity (Toxicity Class II) carry the signal word "Warning." The least toxic materials (Toxicity Class III) have the signal word "Caution." The toxicity of a pesticide is expressed in terms of oral and dermal LD50. LD50 is the dosage of poison that kills 50% of test animals (usually rats or rabbits) with a single application of the pure pesticide for a given weight of the animal (mg/kg of body weight). The lower the LD50 value, the more toxic the material. Oral LD50 is the measure of the toxicity of pure pesticide when administered internally to test animals. Dermal LD50 is the measure of the toxicity of pure pesticide applied to the skin of test animals. Generally, an oral exposure is more toxic than a dermal one.