Pinpointing ’03 Insect Potential
Tuesday, April 1, 2003
filed under: Insects
Keep your eye on sunflower insect developments this growing season, with particular attention to insects and fields that were problem areas last year.
Last year, sunflower midge and moth damage was reduced, but sunflower stem weevil and longhorned beetle (also called soybean stem borer and Dectes stem borer) activity occurred from Texas into the Dakotas. There was also some red sunflower seed weevil and banded sunflower moth activity in sunflower-producing states.
That’s according to an extensive survey of 477 oil and confection sunflower fields conducted last August and September by the National Sunflower Association in Texas, Missouri, Kansas, Nebraska, Colorado, Minnesota, and North and South Dakota.
Field evaluations at the time of the survey were made by examining visible damage to the heads from the sunflower midge, and webbing caused by both the sunflower moth and banded sunflower moth. In addition, stalks were split to determine the incidence of the sunflower stem weevil and long-horned beetle. Seed was collected from the fields at the time of the survey, and evaluated in the laboratory for sunflower
moth, banded sunflower moth, and red sunflower seed weevil damage. The impact of lygus bug feeding also was assessed from confection seed samples.
A summary of insect findings from last year’s survey follows. Complete survey results including mapped findings for weeds, diseases, bird damage, and other factors, can be found on the web site: http://18.104.22.168/sunflower.
Another comprehensive pest survey will be conducted next August and September. NSA production coordinator Max Dietrich says producer cooperation that enables volunteers to sample fields is vital to the success of the survey. Results of the survey help the NSA to evaluate pest problems and trends, he says, and this in turn helps the sunflower industry to develop sunflower research priorities. Dietrich says the survey results also help producers assess and manage production problems and trends in their area.
The maps of last year’s survey results can help pinpoint insect hot spots.
However, entomologists caution that last year’s problem insects may not necessarily
carry over to this year. As well, areas that weren’t pressured last year aren’t immune
from problems developing this year.
“If you had problems last year, sure that’s a red flag. But that doesn’t necessarily
mean you’re going to have them this year. There are so many things that can occur from
the time you saw them last year, to this year,” says Larry Chandler, entomologist and
director of the USDA-ARS Red River Valley Agricultural Research Center, Fargo, N.D.
A lack of insulating snow cover coupled by subzero cold that moves frost deeper
into the ground can increase mortality of overwintering insects. That occurred this past winter, but still should not be used as a barometer for predicting insect pressure this growing season.
“Every year I am asked to make predictions, but predictions don’t mean much.
We should assume that every year we’re going to be threatened by insect pests, so every year we should be scouting. And if numbers are there based on economic thresholds, then treat appropriately,” says Michael Catangui, South Dakota State University extension entomologist.—Tracy Sayler
For many sunflower producers, this was the biggest insect problem last year, with incidence high throughout the Plains. There was significant lodging in Kansas, and lodging was widespread even in N.D. The NSA survey found weevil larvae in about 70% of fields surveyed in Kansas and Nebraska, and nearly 60% of fields surveyed in South Dakota.
Adults are present in the fields in the Northern Plains until late August, with peak densities occurring in mid July. In the High Plains, weevil activity typically subsides by the end of July or early August.
Planting-time treatments should be considered if a sunflower crop will be planted before June 1, especially if sunflower stem weevil damage was evident in the area during the previous growing season. Carbofuran (Furadan 4F) can be applied at planting, mixed with water or liquid fertilizer, applied directly into the seed furrow. An in-furrow treatment at planting will also help control early-season insect problems, such as wireworms, sunflower beetles and early-season grasshoppers.
Banded foliar treatments are effective and economical for row-planted sunflower fields. Economic threshold for treatment is one adult weevil per two plants, or one adult weevil per three plants when stalks are small because of high plant populations or drought stress.
See a more detailed article on stem weevil control (and other insects) online at www.sunflowernsa.com. Click on the link, “especially for producers,” then “magazine,” and “the archives.” Go to the “insects” category.
Banded Sunflower Moth
Some activity could be found in the High Plains, even more so in the Northern Plains, but overall damage last year was minor. Adult: Small 0.25” straw-colored moth with brown triangular area on forewing. Occurrence: About mid July to mid August. Economic Threshold (ET) for treatment: One moth per two plants. Since the BSM congregate around field margins prior to flowering, treatment of field margins can reduce adult populations.
Longhorned Beetle (Dectes or Soybean Stem Borer)
Problems most evident in central South Dakota and Kansas. The bluish gray adult stem borer is about 5/8 inches long long with long banded antennae. In soybeans, adults lay eggs during July and August, and larvae tunnel through stems until September. Even if a chemical control was available (none is labeled), treatment would be difficult. Best remedy is rotation to non-host crop, such as small grains. Avoid rotating soybeans with sunflower. See fact sheet online: http://www.planthealth.info/stemborer/stemborer.htm
Sunflower Moth (Head Moth)
Some sporadic, minor damage, with numbers much less overall last year of this migratory insect compared to 2001. Grayish tan moth moves into sunflower fields early bloom. ET is 1 to 2 adults/5 plants at onset of bloom.
Red Seed Weevil
Damage from this insect was more extensive last year than in 2001. Peak emergence generally late July. Start counting adult seed weevils when yellow ray petals are just beginning to show. Continue counts until ET met or when most plants have reached 70% pollen shed. Ideal plant stage for treatment when most plants at 40% pollen shed, but consider treatment when 3 of 10 plants are just beginning to shed pollen.
The midge could be found sporadically in the Northern Plains, but generally in low levels. Still, there were some hot spots where there was severe damage. The midge emerges early July. Good soil moisture in June can encourage development. Infestation often limited to field margins. Larvae feed around head margin and at base of seeds, causing shrinkage and distortion of heads. There is no effective chemical treatment currently recognized for this pest; crop rotation, hybrid selection, and staggered planting dates are the best management strategies.
Lygus (Tarnished Plant Bug)
Kernel brown spot from lygus was still a problem last year, mostly in North Dakota, and severe in some northern parts of the state. 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 about 10% bloom, followed by a second treatment 7 days later. See more information about Lygus in the insects category of the Sunflower magazine online at www.sunflowernsa.com
Other bugs to watch
Cutworms and wireworms can be a crop pest 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).
Cutworms usually feed above ground on young plants at night. Cutworm damage consists of young plants chewed off slightly below or at ground level. When checking fields for cutworms during the day, dig down into the soil an inch or two around recently damaged plants, where larvae are likely to be found.
Early-season prevention and scouting is critical for managing both insects. Currently the only insecticide registered for wireworm in sunflower that provides effective suppression is Lindane, as a seed treatment. Several products are available for controlling cutworms: treatment is warranted when one cutworm or more is found per square foot, or when a stand reduction reaches 25 to 30%. More information on wireworms from NDSU can be found online at http://www.ext.nodak.edu/extpubs/plantsci/pests/e188-1.htm and on the army worm and army cutworms at http://www.ext.nodak.edu/extpubs/plantsci/pests/e830w.htm
The pale-striped flea beetle has been a minor problem in some areas of South Dakota. Very small at only 1/16”, it is dark brown with two broad white stripes down its back. 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. Colorado State University has a fact sheet on flea beetles online: http://www.ext.colostate.edu/pubs/insect/05592.html
The sunflower beetle is another insect to watch. Adults appear in early June, larvae shortly thereafter. Both adults and larvae chew large holes in leaves. Treatment is recommended when scouting determines that an average of 10 to 15 larvae per plant or 1 to 2 adult beetles per plant can be found throughout the field.
Grasshopper numbers are usually weather dependent, with the most severe infestations likely to occur during seasons when the weather is hot and dry. Scouting should begin in May and early June, and producers should be prepared to start management measures when young hopper populations reach threatening levels, suggests Phil Glogoza, NDSU extension entomologist.
Most grasshoppers emerge from eggs deposited in uncultivated ground. Sunflower growers should expect to find grasshopper feeding first along field margins adjacent to these sites. Later infestations may develop when grasshopper adults migrate from harvested small grain fields. Grasshopper control is advised whenever 20 or more adults per square yard are found in field margins or 8 to 14 adults per square yard are occurring in the crop.
Insect Info on the Internet
2003 N.D. Field Crop Insect Management Guide
NDSU Crop Insect Publications
North Dakota State University Entomology
Kansas State University Extension Entomology
South Dakota State University Extension Entomology
Colorado State University stem weevil fact sheet
University of Nebraska Insect Treatment Recommendations