Early season pest pressure a mixed bag

From South Carolina to Virginia many records were set for average high temperatures in January and February. How this will impact insect damage and diseases, especially those vectored by insects is beginning to play out.

In Virginia, the news isn't all bad. Cereal leaf beetle larvae began showing up in wheat fields in April, but pressure seems to be lower than in previous years. It appears growers should be in the clear with this insect.

Though aphids have shown up in some wheat fields, these insects typically cause more problems in the fall by spreading barley yellow dwarf virus. Again, the jury is out for the fall crop, but it appears 2006 wheat will not be severely impacted by insects or disease.

From northern South Carolina to central Virginia, researchers have recorded an increase in movement of cotton thrips. Growers who took advantage of warm late April weather to plant cotton are most susceptible to thrips damage. While there is no reliable way to predict how severe thrips pressure will become, most experts agree cotton producers should plan for the worst.

Early planted cotton will be at the greatest risk for thrips damage because slow growth early in the year exposed the plant to thrips longer than later planted cotton. It is critical for growers to watch these early planted cotton fields and make timely sprays.

Another troublesome cotton pest, green and brown stinkbugs also are showing up earlier than usual in the woods and weedy areas. Even in heavy stinkbug outbreaks, damage is usually sporadic and careful scouting is required to avoid over-use of insecticides.

Perhaps the most ominous threat from over-wintering diseases comes from tomato spotted wilt virus and soybean rust. Early signs for both are not promising for soybean, tobacco and peanut growers, especially in South Carolina and eastern North Carolina.

Four years ago, tomato spotted wilt virus caused severe problems on a number of crops, even potatoes, from Florida to Virginia. North Carolina Crop Consultant, Bruce Niederhauser, says TSWV has probably been around for 15 years or more, but it looks so much like other viruses it was misdiagnosed.

“Four years ago, we had a major disease problem in potato fields in eastern North Carolina, and it looked different enough from other viruses that I called George Kennedy, an entomologist at North Carolina State University and asked him to come down and look at our potato fields. He used a field ELISA test to diagnose the problem as TSWV,” Niederhauser explains.

This year, TSWV started showing up in potatoes in late April and in early transplanted tobacco in May. Though none of the outbreaks has been severe as of press time, the fact it is showing up early and in scattered areas in North and South Carolina is cause for concern, especially for peanuts, which are highly susceptible to the disease.

South Carolina Peanut Specialist Jay Chapin warns that although there are peanut varieties that have some resistance to TSWV, these are not widely used, leaving most peanuts susceptible to the disease. With so many new peanut growers in South Carolina, it is extremely important to know how to identify TSWV and to know the characteristics of the peanut variety planted.

TSWV is vectored by thrips and four years ago, when TSWV was so destructive in the Carolinas, there was a noticeable increase in thrips flights. As of mid-May, thrips flights have been sporadic, with heavier flights expected in late May and on into June.

Yellow mustard and wild pansy are ideal hosts for thrips and the warm winter and cool, dry spring provided ideal growing conditions for these and many other host plants. Warm winter and spring weather will impact the level of thrips damage. However, these tiny pests move on air currents, so prevailing winds will also play a part in the build up of thrips and subsequent vectoring of viruses on plants.

Virginia Tech Entomologist and State IPM Leader, Ames Herbert points out that thrips can have a triple negative impact on crops. The obvious damage is from direct contact with plants and vectoring disease causing viruses. However, over-spraying of thrips can cause flare-ups of aphids and spider mites, which can be more destructive than thrips.

Sentinel plots of soybeans have been planted throughout the Carolinas to help detect the movement of Asian soybean rust. Drought in the lower Southeast may have slowed the movement northward of soybean rust. Though no significant activity had been noted as of mid-May, sporadic but heavy rainfall throughout the Florida Panhandle and the southern parts of Georgia and Alabama in May have intensified scouting for soybean rust.

Warm winter conditions helped kudzu survive as far north as Montgomery, Ala., and kudzu is a known host for soybean rust. Similarly, rust over-wintered on kudzu in south Georgia and throughout the Panhandle of Florida. Despite its slow movement, rust watchers agree that changes in weather conditions could create movement of the disease-causing spores.

USDA's Risk Management Agency (RMA) recently reminded insured producers that Asian soybean rust remains a concern for the 2006 crop year in parts of the country. While crop loss due to soybean rust is a covered loss under the Federal crop insurance program, farmers must use good farming practices by seeking and following recommendations of agricultural experts to control soybean rust. While a loss caused by soybean rust is an insured peril under the Federal crop insurance program, damage due to the insufficient or improper application of available disease control measures is not.

To be eligible for crop insurance claims from soybean rust damage, growers should use good farming practices, defined as actions that will allow the crop to make normal progress toward maturity and produce at least the yield used to determine the production guarantee. Failure to purchase and apply adequate control measures due to economic reasons is not an insurable cause of loss.

Producers must be knowledgeable of any pending outbreaks and the control methods recommended by local agricultural experts, such as Extension agents and certified crop consultants, used in their area to combat the disease.

Appropriate treatment may vary from timing of application (pre- or post-discovery of the disease), frequency, and choice of chemical or other determining factors.

If crops become infected, RMA recommends that insured producers document the date of discovery of the disease, any recommendations received from agricultural experts, and actions taken regarding the application of appropriate control measures.

For the 2006 crop, the U.S. Department of Agriculture has expanded the scope of its public soybean rust Web site to include surveillance of another major crop pest, the soybean aphid (Aphis glycines Matsumuraare). The site <<a href="http://www.sbrusa.net" target="_blank">www.sbrusa.net has also been renamed the “USDA Public PIPE Mapping Web Site,” with PIPE standing for Pest Information Platform for Extension and Education.

As has been the case with Asian soybean rust, the facility will include mapping of aphid scouting efforts, on-going reports of fresh discoveries of the damaging insect pest, while providing individual state-by-state aphid commentary from local Extension experts.

As is historically the case, the success of the 2006 crop in the Southeast, from king cotton to minor crops, like potatoes, will be significantly impacted by weather. The warm, dry winter and early spring provided comfort to many people, but considerable anxiety among farmers.

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