Barley thrips are dark brown to black in colour, have a long, narrow body shape and are between 1-1.8 mm in length. Adult thrips cause damage by feeding on plant tissue. Feeding results in the bleached appearance of tissue and intense feeding on the head results in small, shriveled kernels. When feeding is severe on the flag leaf, kernels will not fill properly, and kernel weight will be reduced.
One adult thrips per stem results in yield loss of 0.4 bu/ac. To determine if chemical control is economical, the following formula can be used:
Threshold (thrips/stem) = (Cost of control/Expected $ value per bu)/0.4
This often results in about 7-8 thrips per stem, but doing the math is recommended to determine an accurate threshold for your situation. Insecticide treatments should only be applied prior to the completion of heading.
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