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Purdue lab sees increase in wheat disease and tree dieback

April 26, 2011

The Purdue University Plant and Pest Diagnostic Laboratory is busy this spring identifying wheat diseases for Indiana farmers and helping homeowners understand why needles on their spruce and confers are discolored or dropping.



And coming up yet this year, the lab is expecting to see more of a new pest to Indiana: the brown marmorated stink bug.



Indiana wheat fields are showing signs of diseases that infect plants in the fall. The PDDL has confirmed the presence of soil-borne wheat mosaic virus and wheat spindle streak mosaic virus, among other viral diseases, said Director Tom Creswell.



"We are seeing more samples with wheat viral diseases this year," Creswell said. "The severity of symptom development depends on variety and weather. The prolonged cool temperatures this spring have increased symptoms in infected fields."



Both viruses often are transmitted to wheat roots by a soil-borne fungus, which infects wheat roots and transmits the viruses to wheat plants. Symptoms of infection, including yellowing and stunted areas of wheat, do not show up until spring. Severe or widespread infections can cause yield loss.



Although no control methods are available to reduce symptoms in infected plants, getting an accurate diagnosis will help farmers manage future crops by planting resistant varieties in areas with a previous history of the diseases.



The PPDL, part of the Department of Botany and Plant Pathology, provides accurate and timely assistance with plant problems. Commercial growers, agricultural consultants, gardeners, homeowners and landscapers are among those who send physical or digital samples to the PPDL for examination.



Homeowners are learning that a condition causing discoloration or dropping of spruce and conifer needles can be traced to last fallís drought.



"Weíre seeing more samples come in related to drought stress, and calls from Purdue Extension county educators on this are on the increase as well," Creswell said.



The problem may have started as much as a year or two earlier when heavy spring rains resulted in drowning of some roots.



"In the hot, dry weather in August the affected trees have fewer roots for water uptake, resulting in the dieback we see now," he said.



With symptoms similar to dieback, the PPDL is seeing an increase in needlecast disease, another condition that began last year. Needles on new growth become infected with this fungus in May and June, but the damage often is not visible until the following spring.



One pest that Creswell expects to see more of this year is brown marmorated stink bug; the PPDL confirmed the first record of the insect in Indiana last October.



"The stink bug has been a significant problem in the eastern United States and itís moving west," he said. A nuisance to homeowners, the bug has the potential to become a serious pest for most fruit crops, some vegetables, corn, soybeans and various ornamental plants.



The PPDL will continue to see an increase in activity as more than 70 percent of samples arrive between June and September. "The number of samples are running a bit ahead of this time last year so we expect to see as many samples, or even more, as last year."



In 2010 the lab diagnosed 3,864 problems on 2,250 samples. Infectious diseases, noninfectious disorders and arthropod-related problems were the most common pest categories. Ornamentals were the most common commodities submitted - nearly half of all plant samples - followed by agronomic crops.



The departments of Botany and Plant Pathology, Entomology, Agronomy, Horticulture and Forestry and Natural Resources collaborate to diagnose plant diseases, identify pests and recommend control and management solutions. Training is offered for plant- and pest-related concerns as well.



After initial examination, additional tests such as isolation, biochemical testing, DNA extraction and rapid serological analysis may be used to look for specific pathogens. Fees for sample submission and additional testing vary.



Extension specialists encounter a wide range of issues beyond diseases, bacteria and fungi. They also address unknown plant identity, plant nutrition, soil conditions, weeds and insects on plants, inside buildings or in stored food products. Additionally, the PPDL is the plant diagnostic facility for the Indiana Department of Natural Resources and also serves the Office of the State Chemist.