Integrated pest management is a multipronged approach. IPM combines various mechanical, cultural, biological, and chemical treatments to help control pests and reduce crop loss. To effectively control pests, we need to understand their lifecycle.
Western flower thrips as an example pest
The western flower thrips begin their life as eggs embedded in plant tissue. Once hatched, the thrips live as nymphs, typically with four instars, or development stages. The first 2 instars, the larval stage, is characterized by thrips actively feeding on plants. The last 2 instars, the prepupal and pupal stages, occur in the soil and are characterized by thrips no longer actively feeding. Pupas eventually mature into adults with wings; the whole lifecycle takes approximately 2 weeks to complete.
Knowing this, we can target specific stages in the growth of thrips.
Thrip control
Horticultural sprays and oils, typically applied as a plant drench, will target the nymph-larval stages. Thorough coverage is important, as most drenches work by smothering the pest.
Plant drenches may not effectively target nymph-pupal stages burrowed in the soil. The surviving pupas will mature into adults who will lay eggs, and then the cycle will begin again. In this case, treating only one life stage results in ineffective control. How can we improve the effectiveness of our control?
We can target the nymph-pupal stage using entomopathogenic fungi, bacteria, and nematodes. Nematodes can reduce the number of nymph-pupal stage that mature into adults, but what about the nymph-pupal stages that escape our control?
We can add sticky trap cards to our grow room. Sticky trap cards do a good job of helping to control adult thrips (and other flying insects) and will help reduce the amount of new larva added. In addition to targeting all life stages, we are also targeting pests in different locations. We have foliar coverage, soil drench, and peripheral coverage for flying insects.
After the initial treatment, it is best to reapply treatments about every 10-14 days. This will help ensure that any surviving thrips are controlled. Continued use of sticky cards, regular scouting and preventative treatment can help keep thrips under control all season. A shutdown period at the end of the season is also recommended, going just 14 days without plants can starve pests.
Why targeting multiple life stages works
There is an entire branch of ecology dedicated to studying populations, population ecology. One concept in population ecology that is invaluable to growers is life tables. Life tables describe the population age make up, number of males and females, chances of surviving to next instar, and fecundity (offspring contribution to next generation).
This allows us to see what life stages are most important to control to best reduce population numbers. Because these tables need to be made through experimentation and measurement, it is not always feasible for us to use them. Instead, we can target multiple life stages and reduce population numbers to an insignificant amount.
This is just one example of how the ideas of IPM and ecology can come together to effectively control pest populations.
