Insect Pest Management
Insects can truly make or break crop systems. Organic farms are home to a more balanced and sustainable community of beneficial insects than conventional ones, and there are quite a few cultural techniques that can improve within-field habitat to encourage natural pest suppression services. Still, herbivorous pests can be devastating, but they can also be managed effectively using Integrated Pest Management (IPM) strategies that promote regular monitoring, and proper pest identification. This will enable thoughtful choices of pest control tools that are the most affordable, specific, effective, and will reduce damage to the insect predator community. We'll provide several resources here to help implement sustainable organic IPM strategies.
The Vegetable Insects And Their Management website produced by Dr. Rick Foster and Purdue’s Entomology Extension contains photos you can use to identify vegetable pests and the types of damage they inflict for specific crops.
Predators and Parasitoids
Dr. Mary Gardiner at the Ohio State University produced an excellent natural enemy field guide. This guide will help to identify predatory insects, and describe the pests they commonly prey on.
This video by Rick Foster and John Obermeyer at Purdue University demonstrates the effectiveness of beneficial insects in controlling insect pests.
Another useful handout produced by OSU can help to identify bees and other important pollinators of vegetable crops is available at:
Organic Insecticide Use
Many insecticides are approved to control pests in organic systems, but organic approval certainly does not guarantee that products are safe for non-target insects like predators and pollinators. Scouting and correctly identifying pests can enable selection of pest-specific products like Bacillus thuringiensis (Bt) or Kaolin clay that will reduce risk and promote natural pest suppression by beneficial insects. If possible, minimize or eliminate use of broad-spectrum, highly toxic insecticides like Spinosad and pyrethrins. Before pest outbreaks occur, consider alternatives (see below), like pest-resistant varieties, modified planting times and cultural management strategies that can decrease outbreak risk. Finally, if outbreaks do occur (they always seem to, right?), familiarize yourself with the risks of particular pesticides, and try to select a product that minimizes exposure to non-targets. This factsheet produced by the Xerces Society describes the risks associated with various insecticides approved for organic production.
If use of a broad-spectrum insecticide is unavoidable, be sure to make applications at dusk, when most pollinators and predators are less active, reducing the risk of direct exposure.
For vulnerable seedlings and leafy greens, floating row covers are often more effective than prophylactic insecticide applications. Even minimal herbivore damage can kill a new seedling or render greens unmarketable, and the complete exclusion that row covers provide is a better strategy than pesticide applications that are only temporarily effective. Be sure to open row covers at the ends of rows if you are protecting a crop that requires pollination! For more information on using row covers to protect vegetables from insect damage, visit the following University of Massachusetts Extension webpage:
Trap Crops, Intercropping And Companion Planting
Strategic arrangement of various vegetable crops may repel, distract or disorient pest insects. While polycultures have long been utilized successfully by organic growers, surprisingly little research has been done in this area.
Trap crops are highly preferred varieties that pull pests away from marketable crops, making the ultimate sacrifice for the sake of crop protection. As an alternative to treating an entire field with insecticide, trap crops may be treated once they reach a certain pest-density threshold, reducing the area affect by pesticide. This tactic is particularly of interest for management of cucumber beetles. For more information on this, visit:
Intercropping species that are not closely related can disorient specialist pests that use plant volatiles to locate their host plants. Crop monocultures (even at a small scale) are more vulnerable to specialist herbivore attack because they produce a simple, strong, identifiable volatile signature.
Companion plants may be particularly aromatic (like dill, cilantro, basil and parsley) and attractive to natural enemies, or act as repellants (like garlic, leeks and onions) to certain pests. More information about these planting strategies can be found in this University of Tennessee extension bulletin:
The video below provides an example of one intercropping strategy, describing how intercropping flowers in lettuce can help reduce aphids.
Natural herbivore suppression is consistently greater in diverse farm systems. There are many ways to make a crop environment more diverse and hospitable to beneficial insects that perform critical ecosystem services like pest control and pollination.
- Cover crops and living mulches provide temporary habitat for colonizing predators and pollinators.
- Incorporating perennial native plant habitats into a crop environment can provide refuge and food resources that will promote and protect stable beneficial insect populations.
- Minimizing tillage or relying on more shallow tillage practices will reduce mortality of ground-nesting bees and the overwintering larvae of many important pest predators.
Read the Xerces Society's Invertebrate Conservation fact sheet for more cultural practices that can manage weeds and pests while minimizing damage to beneficial insects.
Here is a list of publications from various sources that provide information on plant selection, habitat placement and construction, and even government-sponsored technical assistance and cost-share programs for incorporating beneficial insect habitat into a farmscape. For specific details and assistance with applications for cost-share programs, contact your local NRCS field office.
Recent insect ecology research at Purdue:
The Xerces Society for Invertebrate Conservation has a comprehensive list of resources for maximizing the pest suppression services by beneficial insects.
Michican State University has an amazing website entirely devoted to harnessing ecosystem services using native plants. This website includes regional plant lists, step by step instructions for creating insectary plantings, and an identification guide for native bees and natural enemies they will attract.
Purdue Extension Publication on Organic Vegetable Production: