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Alfalfa Weevil Emerging (05/19/16)

Based on May 17th degree day accumulations (see map below) for alfalfa weevils in North Dakota, adult weevils are emerging.

Alfalfa Weevil Emerging

Based on May 17th degree day accumulations (see map below)ent.3.weevil for alfalfa weevils in North Dakota, adult weevils are emerging. Adult alfalfa weevil have been observed at low densities in the Minot area by T.J. Prochaska (NCREC, NDSU). Adults are about ¼ inch long and brown-golden with a blunt snout and dark brown longitudinal stripe in the center of the back. Antennae are elbowed and clubbed. They overwinter in debris and alfalfa stubble. Eggs are laid inside the stems of alfalfa, and are small and cream colored. Mature larvae are about ⅜ inch long with a black head capsule and a green-wrinkled body.  A white stripe, running lengthwise, can be observed across the top. 

The degree days for alfalfa weevil use a base development temperature of 48F and show that adults are active mainly in the southeastern area with 200 accumulated degree days (DD). Egg hatch begins at 300 accumulated DD. To assess the DD model, go to theent.4.weevil NDSU’s NDAWN website and Applications – Insect DD. Then, click on the Map tab and select 48 F for your base temperature and Degree Days (DD) for your map type. Although adult weevils will feed on the foliage causing defoliation, most of the economic defoliation is caused by larval feeding. Peak feeding occurs about mid-June (or 504 - 595 accumulated DD) when larvae are in the 3rd to 4th instar. For alfalfa grown for hay, the most cost-efficient method is to cut the alfalfa early before feeding damage occurs. A treatment threshold of 40% tip feeding is recommended.

We will continue to follow alfalfa weevil degree day and discuss scouting & IPM in upcoming issues of Crop & Pest Report.

 ent.4.weevil.map

 

Janet J. Knodel                                                                                  Travis J. Prochaska

Extension Entomologist                                                                Area Extension Specialist / Crop Protection

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