Timely Scouting, Timely Treatments
Friday, April 15, 2005
filed under: Insects
Timely Scouting, Timely Treatments
Predicting insect pressure from one year to another can be as uncertain as predicting the weather, so timely scouting and timely treatments remain the mantra. Much of the information about the following insects that can be a problem in sunflower is courtesy of the North Dakota State University Extension Service and Kansas State University. Labeled products, product use rates, and application restrictions may vary by state. Some treatment products are restricted-use insecticides. All products should be used with close adherence to label instructions.
The sunflower stem weevil is 3/16 inches in length, and grayish-brown with varying shaped white spots on the wing covers. The weevils emerge in mid-to-late May in the High Plains, and June in the Northern Plains. Eggs are deposited in epidermal tissue of the stem. Controls are directed at the adults in order to minimize egg laying, initiated about when plants are at the six to eight leaf stage. When about 25 to 30 or more larvae per stalk, it can become weakened, with breakage most likely to occur during drought stress or high winds.
Scouting is difficult due to their size, coloration, and habit of “playing dead.” NDSU advises to examine five plants each at five locations and keep record of the number of weevils found. Approach plants carefully to avoid alarming the weevils, causing them to drop to the ground. Scout from late June to mid-July.
Treatment: Treat for sunflower stem weevils when scouting determines that an average of one adult per three plants is found.
Colorado State University stem weevil fact sheet:
Longhorned Beetle (Dectes or Soybean Stem Borer)
The bluish gray adult stem borer is about 5/8 inches long with long banded antennae. In soybeans, adults lay eggs during July and August, and larvae tunnel through stems until September. Even if an insecticide for control was available (no sunflower insecticide labels include this insect), treatment would be difficult due to prolonged emergence of the adults. Early research indicates that timely harvest will help prevent lodging due to this insect. Avoid rotating soybeans after sunflower where this insect has been a problem. See fact sheet online: http://www.planthealth.info/borer_basics.htm
Most cutworm damage occurs when plants are in the early stage of development. Damage consists of young plants being chewed off slightly below or at ground level. Some cutworm feeding injury may occur on foliage. Cutworms primarily feed at night. When checking fields for cutworms during the day, dig down into soil an inch or two around recently damaged plants and look for the gray to gray-brown larva.
Treatment: Warranted when one cutworm or more is found per square foot or if there is a 25 to 30% stand reduction.
Wireworms join cutworms as crop pests that growers should watch for early in the growing season, particularly in a no-till system. Wireworms have a longer life cycle than cutworms, and usually feed on roots and germinating seedlings below ground. Wireworms prefer more moist, cooler soil temperatures (50-55 degrees F) and move deeper into the soil if soil gets too dry and when soil temperatures become too hot (>80 F). Currently the only insecticide registered for wireworm in sunflower that provides seedling protection is the new seed treatment Cruiser (thiamethoxam). Some producers who have applied Furadan 4F (Carbofuran) at planting for treating early-season insects have observed wireworm control. The systemic product can be mixed with water or liquid fertilizer, and producers have observed that applying it in-furrow with the seed doesn’t hurt seed germination or seedling development.
Banded Sunflower Moth
Banded sunflower moths begin to emerge from the soil about mid-July. Peak activity normally occurs about the last week of July or the first week of August. Moths fly from last year's field to the current year's field, congregating around field margins. The moths tend to move into sunflower fields during the bud stage, with a preference for the mid-bud stage. Eggs are laid on the back of the bud and the outside of bracts. Newly hatched larvae move from these sites to the face of the flower and begin feeding on bracts and florets.
Treatment: Consider an insecticide application when one moth is found for every two plants inspected. Because moths initially congregate around field margins prior to flowering, treatment of field margins can reduce the adult population.
A migratory insect that blows in from the south, this grayish-tan moth moves into fields in early bloom, depositing its eggs on the face of the flower, commonly at the base of newly opened florets. Damage is similar to that caused by the banded moth. The same monitoring strategies are recommended for sunflower moth as those for the banded moth. This insect traditionally does not move further north than Nebraska.
Treatment: When one to two moths are found for every five plants inspected, treatments should be considered.
The midge is a small tan-colored fly, 3/32 inch in length. It emerges in early July, preferring to lay eggs on developing buds, one to two inches in diameter. The cream to yellowish-orange larvae feed on bract tissue at first and later on the flowers and seeds. When feeding is confined to the bracts, damage results in little economic loss. At higher populations, seed production is reduced or prevented. This type of injury appears as twisted and gnarled flowers. Often, infestations will be limited to field margins. When populations are large, damage may extend into the field and significant field losses may be observed. Good soil moisture in the month of June may enhance survival and emergence of midge. This insect is seldom seen in the High Plains states.
Management: There are no effective chemical controls currently recognized for this pest. The best management strategy is crop rotation. Rotate to crops other than sunflower in the vicinity of large infestations. Staggering planting dates to promote different budding periods between fields aids in reducing risk of damage to fields in the same geographic areas. Some hybrids may have greater midge tolerance than others – ask your seed dealer for guidance.
Red Seed Weevil
The red sunflower seed weevil commonly begins to emerge in early July and can continue until mid-August, although actual dates can vary by latitude. Thus, it’s advised to time scoutings and treatments to plant development stages. For example, red seed weevil females need to feed on pollen before they lay eggs, so scouting should start at about R.5. Start counting adult seed weevils when the yellow ray petals are just beginning to show. Counts should continue until the economic threshold level has been reached or most plants have reached 70% pollen shed, when few seeds are still suitable for red seed weevil egg laying. At this point, fields should no longer be susceptible to damage. When sampling, use the X pattern and begin counting at least 70 to 100 feet into the field to avoid field margin effects. Count the number of weevils on five plants at each site for a total of 25 plants. Recommended plant stage for treatment is when three out of 10 plants are just beginning to shed pollen.
Treatment: For confection Sunflower, treatment is recommended when one to two weevils are found per plant. For oil sunflower, the economic threshold can be calculated using the following formula.
Threshold (weevils per head) =
Cost of Insecticide Treatment
(Market Price x 21.5) (0.000022 x Plant Population + 0.18)
Sunflower beetles begin feeding shortly after they emerge from overwintering. Emergence starts mid-May (again, this can be earlier further south, and later further north). Most feeding by adults is concentrated on the true leaves. When beetles are numerous, young plants may be severely defoliated by adults, although most damage usually results from larval feeding. Adults quickly begin laying pale yellow eggs on stems and the underside of leaves. Eggs hatch in about 8 days. The pale green humpbacked larvae begin feeding, eating holes throughout the leaf. Larvae do not feed during the day, resting in the plant tops where they are easily observed.
Treatment: Adults-Treatment is recommended when scouting determines that an average of one to two beetles per plant can be found throughout the field. Larvae-When an average of 10 to 15 larvae per plant is found, defoliation levels of 25 to 30% would be expected. Treatment is suggested when damage levels reach this point and most larvae are still 1/4 inch in size. When larvae become larger than this, most damage will already have occurred and little can be gained by treatment.
The palestriped flea beetle has a widespread presence in the U.S., but has been a localized early-season problem in sunflower the past few years, causing leaf injuries to sunflower seedlings in central S.D. counties. It is also known to feed on numerous field crops including potatoes and corn.
Adults are very small, about 3/16 of an inch long, dark brown to black in color, with two white stripes down its back. Like any flea beetle species, the palestriped flea beetle has enlarged hind legs enabling them to jump from plant to plant. Adults overwinter on the field under soil and plant debris. They then resume feeding in the spring of the following year. These overwintered beetles will then lay eggs in the soil near the base of host plants. Grubs feed on plant roots transform into pupae, then adult flea beetles in the summer. There is only one generation per year.
Flea beetles produce a characteristic injury known as “shot-holing.” The adults chew many small holes or pits in the leaves, which make them look as if they have been damaged by fine buckshot. Young plants and seedlings are particularly susceptible. The insecticide seed treatment Cruiser has demonstrated control of the palestriped flea beetle.
Colorado State University online fact sheet on flea beetles: http://www.ext.colostate.edu/pubs/insect/05592.html
SDSU fact sheet: http://plantsci.sdstate.edu/ent/entpubs/SEE_010702.htm
Lygus (Tarnished Plant Bug)
Sunflower is susceptible to Lygus damage during flowering, from anthesis through seed hardening. Lygus can be treated at the same time confection sunflower is treated for other insects, such as the seed weevil and banded sunflower moth. NDSU entomologists suggest two insecticide treatments for confection sunflower to adequately protect heads from insect feeding: One application at the onset of pollen shed, or about 10% bloom, followed by a second treatment seven days later.
Insect Info on the Internet
2005 N.D. Field Crop Insect Management Guide
NDSU Crop Insect Publications
North Dakota State University Entomology
Kansas State University Extension Entomology
2005 K-State Sunflower Management Bulletin
South Dakota State University Extension Entomology
University of Nebraska Insect Treatment Recommendations