It’s a different form of “scouting” for cutworms, but it works.
More than a few Dakota sunflower growers could be seen driving spray boom-equipped ATVs through emerging sunflower fields near nightfall last spring. They were spraying for cutworm —but only in a narrow strip. Coming back the next morning, they looked to see whether there were dead cutworms in the swath. If so, and if the counts were high enough to justify treatment, they likely sprayed more or all of the field. If not, they saved money by not applying insecticide unnecessarily to the bulk of their acreage.
The increased number of sunflower acres under a minimum- or no-till management system has, along with its benefits, brought along at least one downside for a number of producers: a higher threat of cutworm damage. Plant residue from the prior crop serves as a welcome host for cutworm. If not controlled, this insect can wreak havoc on early season plant stands, contributing to poorer weed control and, ultimately, lower seed yields at harvest.
The sobering news, according to North Dakota State University extension entomologist Janet Knodel, is that there exist, in North Dakota alone, about 150 different species of cutworms — 26 of which are considered “economic insect pests.” The good news is that only a few are of significant concern for sunflower producers — and, those few can be managed through timely scouting and prompt treatment.
Here’s a summary of description, life cycle, damage and management for the three most prominent species of cutworm found in sunflower fields — darksided, redbacked and dingy.*
• Description — Adult forewings of the darksided cutworm are light and grayish brown with indistinct markings. Larvae are the destructive life stage sunflower growers need to deal with in the spring. For darksided cutworm, larvae are pale brown dorsally and white on their ventral areas. At maturity, the larvae are about 1.25 to 1.5” in length and 0.25” wide.
Adult redbacked cutworm forewings are reddish brown with bean-shaped markings. The redbacked larvae are dull gray to brown in color and measure 1.0 to 1.25” long when mature. These larvae can be distinguished from other species by two dull reddish stripes along their back.
Adult dingy cutworm forewings are dark brown with bean-shaped markings similar to those of adult redbacked cutworms. Larvae have a dull, dingy brown body mottled with cream color. There is a thin light line running down the middle of the back, with a series of diagonal markings on either side.
• Life Cycle — Female darksided and redbacked cutworm moths deposit eggs in the soil in late July and early August. The eggs remain dormant until the onset of warm weather the following spring. Larvae of both species emerge from late May to early June, continuing to feed and grow until about the end of June. When mature, the larvae pupate in earthen cells near the soil surface. This period lasts for about three weeks.
The adult dingy cutworms emerge in August and are active until mid-October. Eggs are deposited on plants of the Asteraceae family (which includes sunflower) during the fall. After developing to the second or third instar stage, the larvae overwinter in the soil. Larval feeding resumes in the spring, with pupation occurring in spring to early summer.
• Damage — Cutworm damage is caused by larval feeding. It normally consists of seedlings being cut off from 1.0” below the soil surface to as high as 1.0 to 2.0” above the soil surface. Young leaves also may be severely chewed by cutworms climbing up on the foliage to feed.
Most cutworms feed at night. During the daytime, they usually are found just beneath the soil surface near the base of recently damaged plants. Wilted or dead plants often indicate the presence of cutworms, and bare field patches are evidence of cutworm infestations.
• Pest Management — Sampling for cutworm should begin as soon as sunflower plants emerge, with fields checked at least twice weekly until roughly mid-June. This is particularly important in areas where cutworms have caused problems in past years. A trowel or similar tool can be used to dig around damaged plants to determine whether cutworms are present, since gaps within a row could be due to another cause.
The size of cutworm larvae also should be estimated. Small larvae (< 0.5”) pose the greatest potential for damage since they still have to feed and grow.
The economic threshold is one larva per square foot, or a 25-30% stand reduction. If using the “Z” scouting pattern, examine five one-square-foot soil samples per site (within the row), for a total of 25.
A number of insecticides are registered for cutworm control in sunflower. Most are restricted use pesticides. Currently labeled products include:
• Baythroid XL (0.81.6 fl oz/ac)
• Sevin 20% Bait (20-40 lbs/ac)
• Sevin XLR (1.5 qts/ac)
• Chlorpyrifos 4E AG (PPI @ 2-4 pts/a)
• Lorsban 4E (PPI @ 2-4 pts/ac)
• Lorsban Advanced (PPI @ 2-4 pts/ac)
• Warhawk (foliar (@ 2 pts/ac)
• Yuma 4E (foliar @ 2 pts/ac)
• Lorsban 15G (8 oz/1,000 ft. row, banded at planting)
• Cobalt (19-38 fl oz/ac)
• Tombstone (0.8-1.6 fl oz/ac)
• Tombstone Helios (0.8-1.6 fl oz/ac)
• Delta Gold (1.0-1.5 fl oz/ac)
• Adjourn (5.8-9.6 fl oz/ac)
• Asana XL (5.8-9.5 fl oz/ac)
• Proaxis (1.92-3.2 fl oz/ac)
• Lambda-Cy (1.92-3.2 fl oz)
• Silencer (1.92-3.2 fl oz)
• Grizzly Z (1.92-3.2 fl oz)
• Kaiso 24 WG (1.0-1.67 oz/ac)
• Warrior II (0.96-1.60 fl oz/ac)
• Mustang Max EC (2.24-4.0 fl oz/ac)
• Pending for 2010 is Mustang Max applied in a 5-7” T-band at 5.0 gal/ac over the seed furrow.
* These details are excerpted from the new North Dakota State University Extension Bulletin E-1457, “Integrated Pest Management of Sunflower Insect Pests in the North Dakota Plains.” The bulletin is authored by Janet Knodel, extension entomologist with North Dakota State University; Larry Charlet, research entomologist with USDA-ARS, Fargo, N.D.; and John Gavloski, extension entomologist with Manitoba Agriculture, Carman, Man. Bulletin E-1457 is available online at: www.ag.ndsu.edu/pubs/bugcrops.html.
NDSU and KSU Insect Guides
The 2010 North Dakota “Field Crop Insect Management Guide” carries extensive details on the control of all significant sunflower insects, including listings of all currently labeled insecticides. To view it online, go to www.ag.ndsu.edu/ pubs/plantsci/pests/e1143w1.htm.
To access Kansas State University’s guide, “Sunflower Insect Management 2010,” go to www.ksre.ksu.edu/library. Click on “Publications,” “Crops” and then “Sunflower.” (Click here to take you to that page.)
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