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Potato Leafhopper Populations in Alfalfa
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Location: Blogs Wisconsin Crop ManagerInsects and Mites |
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| Posted by: WCM Staff |
6/15/2007 9:32 AM |
Potato leafhopper populations have increased over the last week, and nymph production is well underway. Many consultants and farmers have begun weekly sweep net sampling of alfalfa fields - this practice should continue for the remainder of the season. UPLOADTEMPLATE
Potato Leafhopper Populations in Alfalfa
Eileen Cullen, Extension Entomologist, UW Entomology Department
Potato leafhopper populations have increased over the last week, and nymph production is well underway. Many consultants and farmers have begun weekly sweep net sampling of alfalfa fields - this practice should continue for the remainder of the season. Potato leafhopper populations can build quickly and to high numbers under hot, dry weather conditions. It is important to scout second crop regrowth, and make sure fields are greening up. With warm, dry conditions moisture levels can influence crop regrowth rate, and just as critically – so can leafhopper populations.
For the current week, Charlie Hampton (Syngenta Crop Protection) reported that multiple alfalfa fields in Jefferson, Dodge and east to Sheboygan County had potato leafhoppers above threshold. One field in particular, along the Lake Michigan had a particularly high infestation. Potato leafhopper should be a concern statewide, as it is each year at this time. We are currently receiving reports of threshold populations in WI and regionally, so this is a reminder to begin monitoring alfalfa fields for potato leafhopper if you have not yet started.
Once reproduction has started, just 10 days are required for populations with overlapping generations to double in size. To obtain an accurate population estimate, sample for leafhoppers when alfalfa is dry, and avoid field edges. Cold, wet or windy conditions may temporarily knock adults and nymphs from plants, resulting in an inaccurate sweep count. Use a standard 15-inch diameter insect sweep net. A total of 100 sweeps should be taken throughout the field, in an approximate “M-shape” through the field to obtain 20 consecutive sweeps in each of 5 randomly selected areas.
Economic thresholds are based on average number of potato leafhoppers/sweep. Keep a running total of the number of leafhoppers caught and divide by 100. Nymphs are not generally recovered in the bottom of the sweep net with adults, but found along the collar of the net (along the wire hoop rim of the net). Nymphs move quickly, typically sideways, when disturbed.
The larger the alfalfa the more PLH it takes to cause economic damage. This occurs both because the older plant is more tolerant of damage and because the PLH will be on the plant less time before it is harvested.
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Alfalfa Height (inches)
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Potato leafhoppers per sweep
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Do not spray if you are within 7 days of your normal cutting schedule, in that case cut if possible*
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<3 inches
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0.2
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3to 6 inches
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0.5
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8 to 11 inches
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1.0
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12 inches or taller
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2.0
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Potato leafhopper has 3-4 generations per year in the Midwest, so this is an insect to continue monitoring for the remainder of this season. Natural predators and parasites of the potato leafhopper do not typically provide consistent economic suppression of leafhopper. Consult UW-Extension bulletin A3646 Pest Management in Wisconsin Field Crops for insecticide label information (potato leafhopper rates, pre-harvest interval, restricted entry intervals, and precautions to avoid honey bee kill).
Potato leafhoppers: small (1/8 inch), green, wedge-shaped. Adults and nymphs look similar except that adults have wings and nymphs have wing pads. Leafhopper nymphs move sideways when disturbed.
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Print issue files for 2007
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Crop Manager Vegetable Update
Clicking on these links will access the Wisconsin Crop Manager PDF files for 2008.
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Clicking on these links will access the Wisconsin Vegetable Crop Update PDF files for 2007.
- July 31, 2008>> Veg Update 2008-11
- July 24, 2008>> Veg Update 2008-10
- July 17, 2008 >> Veg Update2008-9
- July 10, 2008 >> Veg Update2008-8
- July 3, 2008 >> Veg Update2008-7
- June 26, 2008 >> Veg Update2008-6
- June 19, 2008>> Veg Update2008-5
- June 12, 2008>> Veg Update2008-4
- June 5, 2008>> Veg Update2008-3
- May 28, 2008>> Veg Update2008-2
- May 22 2008 >> Veg Update2008-1
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- August 22 >> Veg Update2007-11
- August 9 >> Veg Update2007-10
- July 26 >> Veg Update2007-9
- July 19 >> Veg Update2007-8
- July 11 >> Veg Update2007-7
- July 5 >> Veg Update2007-6
- June 28 >> Veg Update2007-5
- June 21 >> Veg Update2007-4
- June 14 >> Veg Update2007-3
- June 6 >> Veg Update2007-2
- May 30 >> Veg Update2007-1
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