June 15, 2012

In a previous article I discussed the impact that our dry spring was having on increasing brown grass mites in wheat. Our dryness continues in the Panhandle and, according to our state climatologist, it is likely to remain dry through most of our growing season this year. This will mean continued issues with grasshoppers, thrips, and mites.

Grasshoppers

Our growing season is ahead of schedule and with poor rainfall, our rangeland and pastures are drying down quickly. This means that grasshoppers will be moving from pastures to field crops sooner than usual.

Scouting your young crops for grasshoppers is critical in the Panhandle. Grasshoppers will invade border rows first and move into the field so apply border treatments to protect crops from grasshopper feeding. Border treatments might be especially important for fields bordering rangeland; however, a recent survey of a potato production field revealed that grasshoppers had skipped through the outmost border rows into the field to the first row of potatoes with adequate moisture (about 15 rows in). This is a very large field and the outmost rows had not received adequate moisture for good plant growth. At 15 rows into the field the grasshopper damage was very high. This just reinforces the need to scout entire fields to fully assess an insect infestation.

For more information on grasshopper management see the UNL Department of Entomology resource: http://entomology.unl.edu/grasshoppers/

Currently, grasshopper densities of 16-20 per square yard can be found throughout the northern two-thirds of the Panhandle. Many of these grasshoppers are 1st-2nd instar stage from our second hatch. If environmental conditions remain hot and dry, it is likely that some of these species will move into field crops.

Thrips

Thrips thrive in warm, dry weather. In western Nebraska, onion thrips are found earlier in the growing season, while western flower thrips appear later in the season. Onion thrips are abundant in some alfalfa fields right now. This should not be an issue for established alfalfa stands; however, new, spring-planted alfalfa may require an insecticide application if leaves are cupping as a result of severe thrip infestation. There are no treatment thresholds for thrips in Nebraska and a low number of western flower thrips can be beneficial as they feed on spider mites. So, growers and scouts should carefully evaluate the causative agent for their particular problem before applying any chemical treatments.

Mites

Over the last couple weeks there have been several reports of serious infestations of mites in Panhandle corn fields. So far, most of our mite populations have been Bank’s grass mites. These mites have benefitted from the recent warm, dry weather. If these conditions continue throughout the season, they may continue to be a problem. Additionally, as we approach late July, growers need to also keep twospotted spider mites on their radar in corn. Both of these mites are likely to remain in high numbers this year and because of the advanced pace of the season, may flare up earlier than normal. Twospotted spider mites will attack many of our crops in the Panhandle and, similarly to grasshoppers, will invade from field edges first.

I will keep you posted as we get further into the season to provide scouting details and treatment recommendations.

Jeff Bradshaw
Extension Entomologist, Panhandle REC, Scottsbluff