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Posted 27 April 2015. PMN Crop News.


Should You Spray Cereal Leaf Beetle?


Source: North Carolina State University Press Release. harvest.cals.ncsu.edu


Raleigh, North Carolina (April 20, 2015)--How many insects are there? Our established threshold is one larva or egg per four tillers, with more larvae than eggs present to justify a spray. Note that scouting should be done away from the field edge, since they tend to clump in fields and near edges. Dirty pant legs and windshield scouting will not work for this insect. Your eye tends to be drawn to damage; when you pull random tillers, rather than scanning the field, there are fewer insects than you think. Note that I am only aware of a handful of fields in a single northern NC county that have exceeded threshold. We are in a very light beetle year.

 

Did you spray an insecticide already? If you sprayed an insecticide a month ago, consider it gone. Residual from pyrethroids for cereal leaf beetle is phenomenal. However, at its best, it will last a month. See this previous article for a discussion on tank mixing an insecticide for cereal leaf beetle.

Stage of the wheat. Wheat is most sensitive to cereal leaf beetle at flag leaf emergence, followed by the boot stage. Wheat is much less sensitive to cereal leaf beetle after heading, with only small yield reductions caused by cereal leaf beetle during grain fill (Webster et al. 1972, Buntin et al. 2004). So consider wheat planted in October to be safer from loss than wheat planted in November.

How are you going to apply the spray? Keep in mind that yield loss solely due to drive-down after jointing is 3.3% (assuming a 90 foot boom with 18-inch tires).

What is the yield potential of the wheat? Based on current prices, thresholds should only be raised by 6% when the yield potential moves from 60 bushel to 40 bushel wheat. So the insect should be treated, even on low yield potential wheat, but ONLY if it exceeds the threshold of one larvae or egg per four tillers.