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ISSUE 6   June 8, 2006

BEAN LEAF BEETLE ON SOYBEANS & DRY BEANS

Bean leaf beetle have been observed in soybeans and dry beans in SE North Dakota. This beetle has rarely caused economic losses to crops grown in North Dakota in the past. Adult beetles vary in color from yellow to reddish brown and have 3-4 black spots with a black margin on wing covers (see photo). Feeding injury appears as round holes between the veins (see photo). For food grade and seed bean producers, the main concern is the second generation (we presume) that emerges during the pod stage. Bean leaf beetles vector the bean pod mottle virus and can cause direct feeding injury to pods. Little is known about its biology in North Dakota since it has not been a major insect pest - how many generations a year? Hopefully, this will not become a new insect pests on beans in North Dakota.

Adult bean leaf beetle
Adult bean leaf beetle

Bean leaf beetle feeding injury
Bean leaf beetle feeding injury

 

POTATO LEAFHOPPER

Potato leafhopper has been observed on dry beans, alfalfa and other crops in the Red River Valley. Reports indicate high populations of potato leafhoppers in southwest Minnesota. Adult potato leafhopper is small ( inch), wedge-shaped and pale green in color 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. Severely injured leaves may turn from green to yellow to brown called "hopperburn." Watch for increasing leafhopper populations that may cause economic injury to crops. 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 and 9 leafhoppers per plant in early bloom stages

Potatoes = 10-20 adults per 20 sweeps or 1 nymph per 10 leaves

Adult potato leafhopper
Adult potato leafhopper
(Steve L. Brown, University of Georgia,
http://www..insectimages.org)

 

SUNFLOWER BEETLE EMERGENCE UNDERWAY

Begin scouting for adult sunflower beetles. The adult is ¼ to ½ inch long and looks like a Colorado potato beetle except for a reddish-brown head and patch on thorax and exclamation point on the side of the wing cover (see photo). Adults overwinter in the upper 2 to 4 inches of soil and emerge from the previous sunflower fields in late May to early June. Beetles overwinter throughout the field and exhibit no preference for field edges or shelterbelts. Research indicates that a degree day (DD) model and calendar dates are equally accurate in predicting the onset and 50 percent emergence of the sunflower beetle population. The DD model is initiated on March 1st and is based on soil temperature at a depth of 2 inches and a base of 32oF. Sunflower beetles begin to emerge at a mean of 416 DD or Julian date 120, and 50 percent of the adult emergence occurs by 710 DD or Julian date 131. Early planted sunflower fields will attract newly emerged adult sunflower beetles first and have higher populations than later planted sunflower fields (late May to June). In the seedling stage, one-two adults per seedling is the recommended economic threshold. A foliar broadcast insecticide spray will control adult sunflower beetles. Most sunflower insecticides can be tank mixed with sunflower herbicides. Check label for specifics. If Cruiser Seed Treatment was used, it will also control adult sunflower beetles early in the season. Insecticides registered in sunflower in North Dakota include: Asana XL, Baythroid, carbaryl (Sevin), Decis, Furadan, Lorsban, Warhawk, Yuma, Proaxis, Warrior, and Taiga Z. 

Adult sunflower beetle
Adult sunflower beetle

Janet Knodel
Extension Entomologist
janet.knodel@ndsu.edu

 

SUGARBEET ROOT MAGGOT: MANY HOT SPOTS OF FLY ACTIVITY IN VALLEY

Sugarbeet root maggot fly counts at several Red River Valley monitoring sites are higher this year than in the past several years. Degree-day unit accumulations in all sugarbeet growing areas of the Valley have exceeded the minimum needed for peak fly activity to occur. Accordingly, fly activity was extremely high at several reporting sites during the past weekend and earlier this week, despite a few pop-up showers and windy days that made it less than optimal for fly activity.

The most severe infestations are occurring in the following areas: 1) Pembina County, ND - Hamilton, Glasston, Hensel, Crystal, and St. Thomas; 2) Walsh Co., ND - Hoople, Nash, and Grafton; 3) Wilkin, Co., MN - Baker and Sabin. Moderate activity is occurring in southern Walsh Co. (Forest River and Minto), and is mostly moderate to low into Grand Forks and Traill Counties of ND and western Polk County in MN. Moderately high activity has also been detected in the Casselton/Amenia area of central Cass County, ND. Fly counts this year are being carried out through a cooperative effort between NDSU, the American Crystal Sugar Cooperative, and the Sugarbeet Research & Education Board of MN and ND.

Fields at Risk. Fields at greatest risk in the above-listed areas are those that received a low to moderate rate (10 lb product/ac or less) of a granular insecticide at planting, a liquid material at planting, or a banded application of soil insecticide at planting. Rainfall has been insufficient this year to adequately activate banded applications of these materials. Fields at risk should be treated with a liquid insecticide immediately if a postemergence application has not yet been made.

Postemergence Options for Root Maggot Control. Postemergence insecticides are needed to protect many fields this year. Soil conditions are dry in most areas at risk for damaging root maggot infestations. Because granular insecticides require moisture for optimal activation, they will be less likely to provide the desired levels of control in this year’s dry soils. Liquid insecticides are definitely a good choice for postemergence control of root maggots this year. Lorsban 4E (or a generic equivalent containing 4 lb/gallon of chlorpyrifos active ingredient) or Asana XL should perform well in controlling adult flies; however, the chlorpyrifos-containing materials like Lorsban will kill flies and also be soil-active to kill root maggot larvae.

Fields that receive a postemergence insecticide treatment should be re-checked in 4 to 5 days to determine if another application is needed. A second application may be justified in fields that have at least 1 live root maggot fly per plant. Close monitoring of individual fields is critical during the next 10 days in case a resurgence of fly activity develops.

Mixing Insecticides with Herbicides. Postemergence liquid insecticides can be tank-mixed with micro-rate herbicide combinations. This is an attractive cost-saving option because the herbicides are often being applied on a schedule basis at this time of year. Most liquid insecticides applied for postemergence control of root maggots are formulated with a petroleum-based carrier, so adding the insecticide contributes "oil" to the mixture. To save on costs of the application, the volume of methylated seed oil (MSO) in the mix can be reduced to 1% of total spray volume. Crop injury is not likely to occur when combining an insecticide with the micro-rates; however, growers should avoid reducing the MSO volume to less than 1% because weed control performance may otherwise be diminished. Tank-mixing oil-based insecticides with conventional herbicide treatments is NOT advised due to the risk for crop injury.

For more specific information on sugarbeet root maggot management, please refer to the "Insect Control" section of the 2006 Sugarbeet Production Guide or the "Sugarbeet Insects" section of the 2006 Field Crop Insect Management Recommendations for more detail and specific product recommendations. The respective WWW locations for online versions of these publications are:

http://www.sbreb.org/Production/production.htm

and

http://www.ext.nodak.edu/extpubs/plantsci/pests/e1143w1.htm

Mark Boetel
Research & Extension Entomologist
mark.boetel@ndsu.edu


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