Bean Leaf Beetle and Seed Corn Maggot: As the 2005 growing season begins to wind down for most vegetable crops, there are several key points that caught our attention and are noteworthy. Two insect pests that we worked with, the seed corn maggot (SCM) and bean leaf beetle (BLB) (see image, left), both overwinter in Minnesota and are highly attracted to specific crops or conditions. SCM is an early season pest attracted to high organic matter in the soil and causes higher levels of damage in areas with cool and poorly drained soils. BLB is primarily an early season pest and is attracted to legumes (soybean and snap bean). With both insects, we have limited ability to predict population levels for the following spring. However, growers can try to minimize the attraction of the crop to the pest by noting where you had infestations and problems with these pests in 2005 (and therefore where populations may spend the winter) so you can either move crops to new fields or adjust planting dates to delay infestations to minimize the risk of infestation in 2006. If these options aren’t viable the use of scouting and/or insecticide treatment can offer high levels of protection against both of these pests.

Potato Leafhopper and Cabbage Looper: Conversely, insect pests such as potato leafhopper (PLH) (see image, left) and cabbage looper (CL) do not overwinter in Minnesota and must migrate into the state from southern locations. With migrating insect pests there is much less predictability as to when and where they will occur. We have limited ability to use planting dates to avoid pest infestations and the primary pest management tactic must be to scout fields frequently, use treatment thresholds, and apply insecticides as needed. Particularly with insects like PLH, we have actively moving populations throughout the growing season and a given field may be over the treatment threshold one day and back under the threshold the next. With PLH, however, once the nymphs begin to hatch (on average ca. 9 days after egg-lay), the nymph population being less mobile, will create continuous feeding pressure, and if over threshold, requiring the need for intervention.

These pests illustrate the importance of scouting and record keeping for successful pest management in vegetable crops in the current year as well as the following year of production.

Research Updates: In 2005, we evaluated the use of a new yellow/attractant sticky card for SCM that worked very well (i.e., easy to use and catches lots of flies). However, further research will continue to assess how well these counts relate to nearby crop damage (e.g., snap beans), or as a possible control tactic (e.g., for organic growers). Snap bean seeds treated with Cruiser (thiamethoxam) again provided consistent and high levels of control against early-season BLB feeding on seedling stage snap beans. During the next few months, watch the VegEdge site for complete Research Update Reports of these and other projects at: http://www.vegedge.umn.edu/Research%20Reports/research.htm

Or go to the VegEdge site, scroll the left-hand column and click on “Research Updates.”