ISSUE 5 June 7, 2007
INSECT SCOUTING TIPS:
CUTWORMS STILL ACTIVE ON FIELD CROPS
Cutworms continue their feeding frenzy on many crops, especially in the northern regions of North Dakota. Continue to scout for feeding injury (cut plants) and economic threshold levels.
CRUCIFER FLEA BEETLES ACTIVE WITH WARMER WEATHER
With the warmer weather and break from the rain, flea beetle feeding injury increased this week primarily in the northern tier of North Dakota. Check canola field to ensure insecticide seed treatments are still efficacious.
SOYBEAN APHIDS PRESENT IN NEIGHBORING STATES
Low numbers of soybean aphid (<20 aphids per plant) have been detected in early planted soybeans (V1 and V2 stage) in southern Minnesota, South Dakota, Wisconsin, and Indiana. This is the earliest documented report of aphids in these states. No soybean aphids have been detected in soybean fields in North Dakota. Stay tuned for more scouting reports.
ALFALFA WEEVIL DEVELOPMENT - DEGREE DAY (DD) UPDATE
200-300 DD - Scout soon
300-400 DD - Scout now
400-500+ DD - Scout & Treatment Decision
MIGRATORY INSECTS ON THE MOVE
Recent southernly wind patterns indicate the need to get out and start scouting fields for migratory insects that may have been blown into North Dakota (see map). These include our cereal aphids on small grains, potato leafhoppers on alfalfa/potato/dry beans/soybeans, and diamondback moths on canola. Based on the Insect Migration Risk Forecast from Northern Illinois University, North Dakota’s risk is low to moderate in the eastern half of the state. It’s important to remember that migratory insects can be blown 100s of miles and quickly infest fields, sometimes in large numbers. Scout frequently, weekly if possible.
Cereal Aphids: In North Dakota, low numbers of cereal aphids (<20% plants infested) were detected by the NDSU IPM scouts in Cass, Griggs, Steele, and Traill counties this past week. Reports from southern states (Kansas, Nebraska, South Dakota) indicate high populations of cereal aphids with barley yellow dwarf virus being prevalent. See last week’s Crop & Pest Reports for scouting tips and thresholds on cereal aphids. Remember, the current aphid thresholds do NOT take into account the negative effects of barley yellow dwarf virus.
Potato leafhoppers: Potato leafhoppers have arrived in high numbers in the southern Minnesota. Potato leafhoppers are small ( inch), wedge-shaped, yellowish-green insects with inconspicuous white spot on head (see photo). Nymphs are similar to adults but smaller and wingless. Adults and nymphs are usually found on the underside of leaves, and hop, crawl rapidly and move backward or sideward when disturbed. Leafhoppers feed by inserting their piercing sucking mouthparts and injecting saliva into plants. Injury symptoms first appear as discolored spots, and later as distorted leaf veins and curling of leaves. Potato leafhoppers infest alfalfa , dry beans, soybeans, and potatoes in North Dakota.
Potato leafhopper (photo by S. Brown, Univ. of GA)
Fortunately, most of our alfalfa is close to being cut within the next week. Later in the season, economic populations of potato leafhopper represent a threat to newly seed alfalfa fields. Dr. D. Meyer indicates that regrowth alfalfa (after cutting) is typically not damaged by potato leafhoppers in North Dakota. Potato leafhopper treatments need to be preventative rather than curative. Once the yellowing tips called "hopper burn" is apparent throughout the field, damage is already done and treatment is not recommended. Scout for increasing leafhopper populations. Economic thresholds are:
Dry bean = 1 leafhopper per trifoliate leaf;
Alfalfa = 1-2 leafhopper per sweep when alfalfa is 8-14 inches high;
Soybeans = 5 leafhoppers per plant in vegetative stage & 9 leafhoppers per plant in early bloom stages
Potatoes = 10-20 adults per 20 sweeps or 1 nymph per 10 leaves
Diamondback moths: Pheromone traps for Diamondback moths will be set out by IPM Scouts in the next two weeks. Diamondback moth represents a threat to canola in the flowering stages causing aborted flowers. Stay tuned for future trap reports.
SUGARBEET ROOT MAGGOT: MOST FIELDS TO PEAK BY SATURDAY, BUT FLIES WILL PERSIST
Sugarbeet root maggot fly activity has increased significantly during the past few days. Hotspots in North Dakota include central and southern Pembina county, as well as central and southeastern Walsh and northern Grand Forks counties. Moderate to high activity has also occurred in central Clay county of Minnesota. Fly activity maps are updated Mondays, Wednesdays, and Fridays, and can be viewed at the following web page:
Actual peaks in activity usually occur on the first warm (about 80 degrees Fahrenheit or above) day following the accumulation of sufficient heat units (600 air degree days) for adults to become active and infest/lay eggs in beet fields. Recent cool, windy, and rainy weather is likely to cause many flies to be less active and remain in grain fields, field margins, and shelterbelts. Therefore, a sharp one-day peak is NOT likely this year. Moderate activity is likely to persist for a few more days (through Sunday or Monday). Based on current air DD accumulations and the extended forecast, the NDSU predictive model projects the following for peak activity:
Table 1. Predicted accumulation of 600 degree day (DD) units and peak fly activity, June 5, 2007.
Date to reach 600 DD
*Prediction of actual peak fly activity is based on extended forecast to estimate best flight weather after reaching 600 DD.
CONTROL: Unprotected fields (or those treated with a low rate of an at-plant insecticide) in areas of moderate to high activity should be treated as soon as possible. The anticipated broad window of fly activity will probably justify insecticide applications in most high-risk areas through about June 12 or 13, although treating sooner is preferred. Liquid insecticides will probably be the best option for postemergence control at this time because most infestations have either reached peak or will do so soon. Applying liquid materials on or slightly before peak fly activity usually provides the best control.
Two "split applications" (a low to moderate rate, applied on or before peak fly, then repeated 5 to 8 days later) should also be effective this year due to gradual fly buildups.
For further guidance on anticipated populations in the region or for specific information on sugarbeet root maggot management, please refer to the "Insect Control" section of the 2007 Sugarbeet Production Guide for more detail and specific recommendations. An online version of this publication is at:
Research & Extension Entomologist