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Take an IPM approach to preventing wheat disease

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Written Tuesday, February 12, 2008  

As spring approaches, along with the subsequent "green-up" of Ohio's wheat crop, growers are looking to prevent the development and spread of barley yellow dwarf virus.

The virus, which is transmitted by several aphid species in either the fall or early spring, was found in relatively high levels in some wheat fields across Ohio last year, with as much as 20 percent of the plants showing symptoms of the disease in some cases.

Pierce Paul, an Ohio State University plant pathologist with the Ohio Agricultural Research and Development Center, said that growers are tempted to use insecticides this spring to control aphid populations and prevent the development and spread of the disease. OSU Extension specialists, however, are recommending an Integrated Pest Management approach, and indicate that spraying insecticides to control aphids may not be cost-effective.

"Any aphids present prior to spraying may have already transmitted the virus, while other aphids may continue to arrive in the field after the spraying. When spraying insecticides to control aphids early, growers should know that the residual effect of the insecticide may not last long enough to protect against later aphid population buildup nor virus transmission," said Ron Hammond, an Ohio State University Extension entomologist. "Though insecticides applied after infection will reduce the aphid population, it will not prevent the disease from developing once the plants have been infected."

Paul said that growers should be aware of the fact that barley yellow dwarf virus development and the success of insecticide treatments to manage the disease are affected by several factors including the efficiency of aphid transmission of the virus, the source and strain of the virus being transmitted, the difference in aphid mobility and feeding habits, the age and susceptibility of plants when infected, and weather conditions.

Hammond added that spraying insecticides in the spring might not be cost-effective since yield reduction due to barley yellow dwarf virus is generally greater when infections occur in the fall rather than in the spring.

“Fields planted before the Hessian fly-free date are at greater risk for barley yellow dwarf virus development in the spring,” said Paul, who also holds an OSU Extension appointment. "Barley yellow dwarf virus tends to be most severe in fields planted before the Hessian fly-free date at a time when aphid populations are high and aphids are still actively feeding or in years such as last year when warmer than usual fall and winter conditions occur."

Recommended management tactics to prevent and control barley yellow dwarf virus include:

* Planting varieties less susceptible to barley yellow dwarf virus.

* Delaying planting until after the Hessian fly-free date to avoid fall infections.

* Implementing a balanced fertility program.

* Controlling volunteer wheat, barley and oats. For aphids to successfully transmit the virus, they normally need between 12 and 30 hours feeding to acquire the virus, and then four or more hours of feeding to transmit it. However, aphids are capable of acquiring the virus after feeding on infected plants for only 30 minutes and once they acquire the virus, they can transmit it to healthy plants for the rest of their life.

There are acceptable situations where spraying for aphids might be warranted. They include:

* Spraying when wheat is under drought stress with aphids present.

* Growing a variety known to be susceptible to barley yellow dwarf virus with aphids present.

* Growing wheat for seed.

* Intensively managing wheat for a 100-plus bushel per acre yield potential.

* Planting wheat before the Hessian fly-free date.

If using insecticides is warranted, log on to http://bugs.osu.edu/ag/545/sgiap.pdf for a list of labeled materials. For more information on wheat management, log on to http://agcrops.osu.edu .

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