Part 2, Section 1: Pest Management
Successful insect pest management must be based on knowing: 1) what insect species are likely to be pests; 2) when these species are usually active; 3) whether these insect species are present in your fields; and 4) whether these insects are occurring in economically damaging populations. The first two items can be learned from variety of sources, including this guide, other extension publications, fellow agricultural workers, and on-farm experience. The latter two items, however, can only be learned by walking fields, inspecting crop plants, and sampling for insects and/or their damage.
Scouting for insect pests and their damage is an important part of an integrated pest management (IPM) program and is the very best way to determine whether an economically damaging population of an insect pest species is present. A primary goal of IPM is keeping pest populations below an economically important level (see Fig. 2.1-3 and associated text); therefore, failing to regularly assess pest levels could cause one to miss an opportunity to treat an infestation and keep it below the economic injury level. Conversely, basing treatments on a calendar, gut feeling, or the potential of a threat could lead to unnecessary treatments.
Besides wasting time and money, unnecessary insecticide applications can have detrimental side effects, particularly the killing of beneficial insect species. Pollinators of different types (e.g., honey bees, bumblebees, butterflies, flower-visiting flies, etc.) can be abundant in agricultural fields, particularly when soybean, alfalfa, and clover are in bloom, but generally speaking also any time pollen is available. Unfortunately, these flowering-visiting insect species tend to be more sensitive to many insecticides than the insect pest species themselves and are easily killed by unnecessary or poorly timed insecticide applications. (Most insecticides are highly toxic to bees and this is stated on the label, but other beneficial insects are often similarly susceptible.)
Unnecessary applications, such as insurance sprays or unjustified tank-mixes of insecticides with other agricultural chemicals can be particularly hard on insect predators and parasitoids, which can provide important levels of natural control. Killing these valuable natural enemies can lead to outbreaks of secondary pests, which are typically kept in check by these natural control agents, or even promote a resurgence of the target pest species because populations of plant-feeding insects tend to recover from insecticide applications more quickly than natural enemy populations.
Some crop species (e.g., soybean and alfalfa) can harbor large populations of natural enemies, but predators and parasitoids can also be promoted in agricultural settings using a variety of tactics. Woodlots, meadows, conservation lands, and field borders with a diversity of plant species can support large natural enemy populations that will move into adjacent agricultural fields. Of course, these areas can also harbor pest species (e.g., bean leaf beetles, cutworms, groundhogs) so their benefits need to be evaluated, but university-based research has documented that on-balance these habitats are beneficial. Similarly, research in England has shown that strips of natural vegetation in agricultural fields (i.e., ‘beetle banks’) can significantly contribute to natural enemy populations, which can kill plant-feeding insects and even consume weed seeds. Natural enemy-populations can also be bolstered by agronomic practices such as reduced tillage and cover crops, which minimize disturbance and provide hospitable habitats for predators and parasitoids.
Natural enemies can also be conserved by insecticide selection and usage. Some insecticides can have a small negative influence on predators and parasitoids when compared to the target pest (e.g., Bt, seed treatments, insect growth regulators, azadirachtin, spinosad, etc.). Using lower rates of insecticides can also be useful, decreasing the impact the chemicals have on ‘good’ insects. Lastly, timing of applications can reduce their severity. For example, many pollinators and natural enemies are often more active in the morning. Therefore, applications later in the day can help conserve these beneficial insect species.