Protect Stands from Early Season Bugs
Tuesday, January 1, 2008
filed under: Insects
Life is good. You selected a high-yielding sunflower hybrid with strong resistance to key diseases, your planter was calibrated to perfection, seedbed conditions were excellent, and seed placement consistency was the best it’s ever been. The foundation has been laid for a superb sunflower crop.
But there could be one cloud hanging over this otherwise giddy scenario: bugs. Serious infestations of certain early season insects can poke holes in that otherwise-stellar plant stand and ultimately take a chunk out of your final yield. So well before you head out to the field, it’ll “pay to pay” some attention to those potential early season threats. Here are brief descriptions of three key culprits.
— Wireworm —
Wireworm larvae and adults overwinter anywhere from nine to 24 inches deep in the soil. At about the same time that planting gets under way (soil temperatures of 50-55°F), the larvae and adults move toward the soil surface. After mating, adult females burrow down to lay their eggs — sometimes re-emerging, moving to other sites and laying more eggs.
Wireworm larvae feed at around a 6” depth in the early spring, moving deeper as the topsoil warms up and/or becomes dry.
Field history is the best indicator of whether wireworm problems can be expected in a given year, though considerable population variation can occur between years, both within and between fields. The only insecticide currently labeled for wireworm is the seed treatment Cruiser. Since it is a seed treatment product, the decision whether to include Cruiser must be made at the time of hybrid selection.
FMC is expecting a label amendment in February for Mustang Max® to control wireworm and other early season insects with an at planting in-furrow treatment.
One point: Seeds treated with the earlier Cruiser formulation sometimes would sometimes stick to seed plates, creating seed flow problems and hurting seed placement consistency. The new CruiserMaxx is significantly better in that regard; also, some seed companies now use special polymers to minimize the problem even more.
— Cutworm —
There are three species of cutworm: the darksided, the redbacked and the dingy cutworm. The female darksided and redbacked cutworm moths deposit eggs in midsummer, with the eggs staying dormant until the onset of warm weather the following spring. Larvae emerge from late May to early June.
The adult dingy cutworm emerges anywhere from August to mid-October in the Northern Plains, with peak emergence in September. Eggs are deposited in plants of the Compositae family (e.g., sunflower) in the fall, and the larvae eventually overwinter in the soil.
Cutworm damage in sunflower fields typically consists of plants being cut off from 1” below the soil surface to 1 to 2” above the surface. Young leaves may be severely chewed as well, due to cutworms climbing up to feed on plant foliage.
Most feeding occurs at night. During the day, the cutworms reside just beneath the soil surface under recently damaged plants. Scouting for cutworms should start as soon as plants emerge, with monitoring continuing at least twice weekly until around mid-June. North Dakota State University says the sampling should encompasses 100 plants at each of five sites within the field. The economic threshold is one larva per square foot, or a stand reduction of 25 to 30%. (Kansas State University recommends treatment if cutworm feeding has caused a stand loss of more than 15%.)
Several insecticides are labeled for cutworm control in sunflower, including Asana XL, Baythroid XL, Lorsban 4E and 15G, Sevin, Mustang Max and Warrior. Except for Sevin, all are restricted use pesticides.
— Sunflower Beetle —
Though quite similar in appearance to the adult Colorado potato beetle, the sunflower beetle is a separate species associated exclusively with sunflower. It is much more common in the Northern Plains growing region than in the High Plains.
Adult beetles overwinter in the soil, emerging in late May to early June. They’ll start feeding on sunflower plants immediately following emergence. Damage can be very pronounced on the first true leaves (sometimes completely consumed), and fields can be severely defoliated if beetle populations are high enough. The adults feed mainly on leaf margins, while sunflower beetle larvae munch on the entire leaf surface. Most larval feeding occurs at night, while the adults feed during the day.
NDSU recommends counting beetles on 20 plants at each of five sampling sites in an X pattern. Sampling sites should be at least 75 to 100 feet from field margins. The larger the plant, the more damage it can tolerate. In the seedling stage, the recommended economic threshold is one to two adults per seedling. With beetle larvae, treatment is recommended when the population reaches 10 to 15 per plant, or when about 25% defoliation occurs on the upper eight to 12 leaves.
The sunflower beetle can be effectively controlled with insecticides such as Asana XL, Baythroid XL, Furadan 4F, Lorsban 4E, Mustang Max and Warrior — all of restricted-use pesticides.
Most of the above information is from the “Pest Management” chapter of the new edition of Sunflower Production (EB-25 Revised), published by the North Dakota State University Extension Service. This chapter was authored by NDSU extension entomologist Janet Knodel and USDA-ARS research entomologist Larry Charlet.
For more information on these early season pests or other sunflower insects, contact your university extension entomologist or visit one of these websites:
• North Dakota State University — www.ag.ndsu.edu/crops/guides.html
• Kansas State University — www.oznet.ksu.edu/library/entml2/MF814.pdf