05-23-16 CSU Ext News: Lower population of grasshoppers predicted in 2016 still monitoring is required in Colorado…

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Lower population of grasshoppers predicted in 2016 still monitoring is required

grasshopper CSU ExtWritten by: Assefa Gebre-Amlak and Frank Peairs, Colorado State University

According to the 2015 USDA APHIS adult grasshopper counts, there were low to moderate population of grasshoppers in north eastern Colorado (Golden Plains Area) last year with the exception of a few spots with higher risk in some south eastern counties (USDA 2016 Rangeland Grasshopper Hazard map). Moderate population of grasshoppers reported from Adams and Weld counties in the Front Rage area.

We encourage ranchers and producers to monitor grasshopper situations in your area in those counties with moderate or higher risk of the hazard. The rest of Colorado had much lower counts of the insects and no risk of grasshopper infestations and damage expected in 2016. For details of grasshopper specific hazards maps for your areas/counties, please contact USDA APHIS Colorado office at: 303-371-3355.

Generally, grasshoppers have one generation per year. Eggs are deposited in the ground in the fall. The eggs hatch in the spring and summer (late May through early June) and hatch is dependent on soil temperature, which differs for different species.

Weather conditions will determine how much of the damage potential will be realized in those areas with light to moderate populations of grasshoppers. For example, the cool wet weather conditions our state has been enjoying may cause enough mortality in immature grasshoppers to prevent outbreak. Most grasshopper outbreaks are associated with drought conditions in previous years.

The simple economic threshold for grasshoppers in rangeland is 15-20 grasshopper nymphs per square yard. This number is equivalent eight to ten adult grasshoppers per square yard. However, the economic importance of an infestation is affected by such factors as range condition, cattle prices, and treatment costs. CARMA is a computer program that allows the landowners to include these factors in their treatment decisions. CARMA is available at the same website as the hazard map mentioned earlier.

Treatment options for grasshopper management are based on the Reduced Agent and Area Treatment (RAAT) strategy, which results in untreated swaths and swaths treated with reduced chemical rates. Using lower rates and leaving untreated areas reduces treatment costs by as much as 50% and preserves biological control. Grasshoppers move constantly, insuring that they will enter a treated swath and that levels of control will be similar to complete coverage applications. Large infestations can be treated aerially with malathion, carbaryl or diflubenzuron (Dimilin). Smaller infestations can be controlled with RAAT treatments applied aerially or with all-terrain vehicles appropriately equipped to apply carbaryl or diflubenzuron. These insecticides do not have grazing restrictions when used in the rangeland.

All-terrain vehicles also can be used for spot treatments of egg-laying sites such as pastures, ditches, and untilled field margins. Grasshopper nymphs tend to remain concentrated in their hatching areas for some time after they emerge, where the application of an approved insecticide can provide effective and economical control of localized infestations. 

Dimilin (diflubenzuron) treatment for grasshoppers should be applied in 2nd to 3rd instar stage because growth regulator will not control adults. This product has no grazing restrictions.

Strategies for managing grasshoppers in cropland are somewhat different. Recommendations for specific crops can be found in the High Plains Integrated Pest Management Guide, (www.highplainsipm.org).

Written by Frank Peairs and  Assefa Gebre-Amlak, (PhD) Extension Specialist, Pest Management at Colorado State University Extension.

Any questions can be directed to Assefa at 970-491-2666 or assefa.gebre-amlak@colostate.edu

Submitted by:

Dr. Wilma Trujillo

Area Agronomist

Logan and Morgan Counties

Colorado State University Extension

Email: Wilma.Trujillo@colostate.edu

Cell: (719) 688 – 9168