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 Field Notes: Remember Insect Scouting on Alfalfa 2nd Crop Regrowth Minimize
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Posted by: WCM Staff 5/31/2007 12:59 PM
A reminder to watch 2nd crop alfalfa regrowth for remnant alfalfa weevil larvae and adults. UW-Extension Fond du Lac Crops/Soils Agent, Mike Rankin sent the featured pictures here on May 22nd. Mike reported significant alfalfa weevil larval feeding pressure along the east shore of Lake Winnebago.

Field Notes: Remember Insect Scouting on Alfalfa 2nd Crop Regrowth

Eileen Cullen, Extension Entomologist, UW-Madison Entomology Department

A reminder to watch 2nd crop alfalfa regrowth for remnant alfalfa weevil larvae and adults. UW-Extension Fond du Lac Crops/Soils Agent, Mike Rankin sent the featured pictures here on May 22nd. Mike reported significant alfalfa weevil larval feeding pressure along the east shore of Lake Winnebago. The field in which these two pictures were taken was in the process of first crop cutting on May 22nd. Alfalfa weevil IPM information has been featured in two previous Wisconsin Crop Manager articles, May 3rd and May 17th (see links in references section following this field note).

However, Mike Rankin’s photos are a good reminder to watch 2nd crop regrowth for presence of remnant late instar larvae and adults. Once second crop regrowth is successfully underway, and alfalfa defoliation remains below threshold – the alfalfa weevil chapter will be closed for 2007. (Second crop alfalfa weevil defoliation threshold is 50% of a 50-stem sample with any leaf feeding; and 2 or more larvae per stem).

Alfalfa first crop alfalfa weevil larval feeding damage
Fond du Lac County, Wisconsin
Photo: Mike Rankin, UWEX Fond du Lac
 
 

 

Late instar alfalfa weevil on leaf litter in alfalfa field at first crop cutting
Fond du Lac County, Wisconsin
Photo: Mike Rankin, UWEX Fond du Lac

Potato leafhopper migrants will be the next insect pest of note in alfalfa. Sweep net sampling should begin as soon as 2nd crop regrowth develops. Unlike alfalfa weevil, potato leafhopper does not overwinter in Wisconsin. Since it overwinters in the southeastern U.S. region, weather patterns assist potato leafhopper migrations in reaching WI. First crop typically escapes damage because potato leafhopper migrants have not yet arrived. The WI DATCP Pest Survey recorded its first capture of migrant potato leafhopper during the week of May 21st, although in very low numbers. Krista Hamilton, Entomologist, WI DATCP Pest Survey reported on May 25th the survey found low counts of 1-2 potato leafhopper adults per 10 sweeps in Adams, Dane, Columbia, Juneau, Marquette, Jefferson, Waukesha, and Walworth Counties.
 
There is no need or rationale to apply insecticide to alfalfa stubble in preparation for potato leafhopper migrations, and this is not an effective means of control. Regular scouting should commence with 2nd crop regrowth. WI DATCP pest survey updates and scouting/threshold information will be provided in Wisconsin Crop Manager articles as 2nd crop progresses.
 
References
 
Cullen, E. 2007. Alfalfa weevil larvae will be active soon. Wisconsin Crop Manager 14(9): 53-55 (May 3, 2007) http://ipcm.wisc.edu/WCMNews/tabid/53/EntryID/255/Default.aspx
 
Cullen E. 2007. Field Crop Alfalfa Alert: Threshold Alfalfa Weevil Populations Reported. Wisconsin Crop Manager 14(10): 65-66 (May 17,2007)
 
Wisconsin Pest Bulletin 52(7) May 25, 2007

 
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