I noticed a couple dogwoods blooming this morning, which reminded me to check local temperatures for cereal leaf beetle development. Insect growth can be tracked using fairly simple temperature-based models. Based on the temperatures in Plymouth, NC, tomorrow (March 30) should be the time of peak egg-lay for cereal leaf beetle.
Peak larval densities follow (on average) 17.7 days later, corresponding to April 17th. I ran the model for Statesville, and peak egg-lay should lag Plymouth by nearly two weeks. This tracks very similar (but a little behind) to the 30-year average.
Once peak egg-lay occurs, many fields will need only a single scouting for eggs and larvae. Wait about a week following the peak egg lay. If the proportion of eggs in the sample is 50% or greater then sample again in 5-7 days.
Insecticides are effective only on the larvae, not the eggs. Keep in mind rain and other weather events can kill eggs. It’s better to time your spray when a few small larvae have hatched. The threshold is 25 eggs plus larvae total per 100 tillers (this is an average of one per each four tillers or 0.25 eggs plus larvae per tiller).
Any insecticide sprayed prior to March 15 does not have an effect on cereal leaf beetle. Insecticide sprayed after this date might only slow the rate of infestation down. So it’s a good idea to scout your fields even if you’ve sprayed. Remember that cereal leaf beetle can still overwhelm your field if they invade in high densities. Insecticide residual for this insect runs out after about a month.
Cereal leaf beetle tend to be worse in thin stands. Contrary to common opinion, this is not because cereal leaf beetle prefer thin wheat (they actually prefer thick and healthy wheat), but because there are simply more beetles per tiller in thin stands compared to thick ones.