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Commercial Horticulture > Comm Hort Blog > Posts > Microbial Control of Caterpillars in Crucifer Crops

xentari and pyganic on cabbage1.jpgSeveral species of caterpillars are common to leafy greens and brassica crops. Those include armyworms, diamondback moths, cabbage loopers, cabbage white butterfly (AKA imported cabbageworm), cross-striped cabbageworm, etc. The caterpillars come from eggs that are in clusters or singly on various parts of the plant, usually hidden from predators. Here are control recommendations to lesser the caterpillar load on your crop.

  • Small farms and urban gardens can use low-cost pest exclusion as the first defense strategy by using light weight insect barriers such as Super Light Insect Barrier or the AgriFabric Pro. With this system, the overall caterpillar numbers can be significantly reduced.
  • In terms of using microbial insecticides in organic or other situations, start with a Bacillus thuringiensis or Bt formulation like DiPel, Xentari., etc. There are also virus formulations like Spod-X that are specific to a species and also some newer products like Chromobacterium extracts like Grandevo. Remember to use these materials at low pest pressures to prevent outbreaks. 
  • Several years of testing with various summer and fall crops in Alabama has shown that Xentari (a Bt formulation) is very effective for controlling armyworms like the beet, cross-striped, and fall armyworms. Xentari also does well against other species. The Bt formulations are similarly priced, and come in a variety of formulations and packaging. Make sure you mix up a fresh batch of microbial insecticides and use quickly – don't store a spray solution for several days. Store the original containers away from direct sunlight, especially the living insecticides like Bts and viruses.
  • Spinosad-containing products like Entrust and Monterey Home and Garden Spray are effective at high pest pressure; however, those products are not living insecticides and insecticide resistance could be an issue if you live in an area known for insecticide failure.
  • Tests in Alabama have also shown that Bt can be tank-mixed with natural pyrethrin or Pyganic for a very good synergistic effect which can knockback a rising caterpillar pressure and improve crop quality (see image above). In other words, tank-mixes can work for mid-season caterpillar control in brassicas, but ensure thorough applications multiple times for best effect.
  • There are also insecticide pre-mixes that are available in organic and conventional production systems. Currently, we are testing several pre-mixes in Alabama such as Leap that has Bt and a fungicide for summer crops. With all the products, at least weekly sprays may be needed depending on caterpillar activity and abundance. Use insect pheromone traps for monitoring moth activity that can indicate upcoming problem.
  • When treating brassicas, it is easier to do a thorough spraying when the leaves are small and upright. With waxy leaves, remember to add an appropriate sticker-spreader to allow the leaf to wet and retain the insecticide. Spray from bottom to the top of the canopy during evening hours, targeting the underside of leaves and let the excess solution drop to the ground. In this way, producer can maximize insecticide efficacy, increase persistence, and reduce insecticide need.
  • Remember to stop using organic and conventional insecticides since natural enemies can be affected by continuous foliar applications. For example, lady beetle and lacewing larvae can be easily drowned with excessive leaf wetness due to over-applications of insecticides.

Related article:  Pest alert for high tunnel crop producers (basic scouting/pest identification)

Ayanava Majumdar, Extension Entomologist 

and State SARE Coordinator


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