Heads Up! Pest Alerts

Soybean drills are now moving at a furious pace. Lots of beans will be up and out of the ground in a very short period of time. So, it is the time of the season to be on guard for the bean leaf beetle (BLB).

This beetle is generally an important pest of very young soybean plants. The most dangerous time is during the cotyledon stage (seed leaves) but is also important during the unifoliate stage. Generally speaking, if the growing season is good, by the time the soybean plants put out their first trifoliate leaves, they are growing so rapidly that they will out grow any beetle damage.

It is very important to prevent damage to the cotyledons. These plant parts provide nutrition required for the plant to get started growing. If the seed leaves are damage the plants will be less thrifty and more susceptible to all forms of pest activity. If the seed leaves are completely destroyed before the unifoliate leaves emerge the plant may die.

BLBs are abut 1/8 inch to 1/4 inch long. The body is slightly convex and the beetle is longer than wide. Color is variable, ranging from light brown to dark red, spots and or stripes may be present or absent. However, all beetles will have a black triangle pointing backward behind the head. BLBs feed on cotyledons, leaves and pods. Leaf feeding consists of very distinctive almost circular holes. Feeding on cotyledons and pods usually appears as scooped-out holes in the surface.

When scouting look for areas of stand reduction or heavily damaged cotyledons. If stand is reduced on average 30% or when feeding on leaves if the defoliation level reaches 30% then treatment is warranted. A more precise scouting method and economic threshold calculation can be found in IPM-3, KY ICM Manual for Field Crops 'Soybean' (You must obtain the free Adobe Acrobat reader to view this document).

If insecticidal controls are warranted you may find products labeled for control in ENT-13, In your County Extension office or on our Insect Management web site at: http://www.uky.edu/Agriculture/PAT/recs/rechome.htm.

(first published in Kentucky Pest News, Number 954, June 3, 2002)

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	Original document: 4 June 2002 Last updated: 4 June 2002