Crop & Pest Report


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Insect Degree-Days Running Behind (05/16/19)

Day-degree accumulations have been slow this spring due to the mostly cool weather.

Day-degree accumulations have been slow this spring due to the mostly cool weather. Insect development is temperature dependent, so degree-day models are useful for predicting their development. Degree-day models are commonly used in Integrated Pest Management (IPM) to help forecast insect emergence, peak emergence and insect growth stages. They are important IPM tools for managing insect pests and are used for timing of scouting activities and control measures.

Alfalfa weevil is a good example of an insect pest whose development is temperature dependent. Adults overwinter in sheltered areas and under plant debris in ND. The degree-day model for alfalfa weevil uses a base of 48°F (Table 1). Accumulated degree-days will help you time when to begin scouting (early larval instars), when heavy plant feeding might occur in the 3rd and 4th larval instars, and when control action might be necessary.

To assess the DD model, go to the 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.

The current map (next page) indicates that no egg hatch is occurring in ND yet. At 200 degree-days accumulation, adult weevils will just be emerging, as shown in southwest and northwest ND. NDAWN indicates that our current ND weather is running about -50 to -140 degree-days behind the 5-year average for alfalfa weevil development!

For more information, see the NDSU Extension publication:

 Integrated Pest Management of Alfalfa Weevil in North Dakota E1676.






Janet J. Knodel

Extension Entomologist

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