David Owens, Extension Entomologist, owensd@udel.edu; Bill Cissel, Extension Agent – Integrated Pest Management; bcissel@udel.edu
As mentioned in this week’s scouting report, we are starting to pick up cereal leaf beetle adults and the first eggs in a few fields in Sussex Co. Adults cause only cosmetic feeding scars, but the larvae are voracious and can strip the important flag leaf that contributes to yield.
When scouting small grains, look at 5-10 tillers per site, 10 sites per field at minimum. A treatment may be warranted if 25 eggs and small larvae are found per 100 stems. If only eggs are located, you may want to resample in one week because there can be significant egg mortality. The optimum timing for making an insecticide application if the threshold is reached is 50% egg hatch. Our recommendation guide for small grain insect pest management can be found here: https://cdn.extension.udel.edu/wp-content/uploads/2012/05/18063827/Insect-Control-in-Small-Grains-final-2017.pdf.
Adult feeding scar in barley last week
When scouting small grains, look at 5-10 tillers per site, 10 sites per field at minimum. A treatment may be warranted if 25 eggs and small larvae are found per 100 stems. If only eggs are located, you may want to resample in one week because there can be significant egg mortality. The optimum timing for making an insecticide application if the threshold is reached is 50% egg hatch. Our recommendation guide for small grain insect pest management can be found here: https://cdn.extension.udel.edu/wp-content/uploads/2012/05/18063827/Insect-Control-in-Small-Grains-final-2017.pdf.
Two cereal leaf beetle eggs laid in barley last week
In 2010 and 2011, Virginia Tech and North Carolina developed a simple degree day (DD) model that could predict peak egg lay in wheat to within 1 week. The model takes the high/low temperature for the day, subtracts a base insect development temp of 8°C (46°F), and sums up degree days since January 1. The target is 182 degree days (on the Celsius scale, Fahrenheit is going to be 328 DD). This helps really tighten their scouting window for cereal leaf beetle. And, it helps determine if a field may be at risk for insect loss despite prophylactic pyrethroid applications tank mixed with fungicides applied at flag leaf and/or flowering. If a field receives a pyrethroid before the adults are active and laying eggs, the pyrethroid is doing no good. If a field is treated well after peak egg lay, larvae may have an opportunity to injure yield.
We need your help to find out how this model works or might need to be adjusted. For example, according to the model, we will hit the egg degree day soon in Georgetown, yet CLB is just now showing up in fields. You have more eyes on more acres, and your data can help improve this model. Below is a link to a scouting form that you can enter your data in confidentially. By entering field location (or nearest crossroad, town or GPS) we can relate CLB back to temperature data from the nearest weather station. If the model can be improved to fit, this will help you predict when to focus scouting efforts for CLB!