Crop, Chemical Rotation Criticial to Limiting Blight
BOZEMAN - Jan 17/13 - MSU -- Growers generally appreciate moisture, but wind-driven rain and hail have spread blight through Montana's lentil, chickpea and dry pea fields.
To protect their $1.2 billion industry from Ascochyta blight, growers should rotate their crops with at least three years between pulse crops, get accurate diagnoses of suspected problems, consider planting fungicide-treated seeds and be aware that pathogens can become resistant to fungicides, said Mary Burrows, associate professor in the Department of Plant Sciences and Plant Pathology at Montana State University and MSU Extension plant pathologist.
"As we get more pulse acres in the state, disease issues will increase in importance and vigilance is imperative," Burrows said. "The species of Ascochyta blight are different between the three pulse crops, and the fungus will not infect a plant it is not adapted to cause disease on."
Montanans grow 500,000 acres of pulse crops. The highest concentration is in northeast Montana, but pulse crops are grown elsewhere, and acreage is increasing in the "Golden Triangle" area in northcentral Montana, Burrows said. Pulse crops - mainly lentils, chickpeas and dry peas in Montana - provide nitrogen to the soil, don't use a lot of water, help control weeds and break cereal disease and insect cycles. They are eaten by humans and livestock alike.
Ascochyta blight is damaging those crops, however. Infected crops are edible, but they bring less money than uninfected crops because the blight reduces yield, quality and appearance, Burrows said. Growers can't sell their crops for seed if the seeds fall below a certain quality.
Blight and Anthracnose Prevalent
Ascochyta has been around as long as pulse crops, but the blight ran through Montana's chickpea fields this past summer, Burrows said. She also found low levels of Ascochyta in lentils, but more common in the Moccasin, Lewistown and Chester areas was a related and much more serious disease that affects pulse crops - Anthracnose. She received a "ton" of samples, emails and texts about bacterial blight in peas; the damage was all associated with hail.
Fungicides don't work on bacterial diseases, Burrows said.
Correctly identifying Ascochyta will help growers apply the best management practices, Burrows said. Growers can get their seed tested for Ascochyta blight right now by submitting a seed sample to the Montana State Seed Laboratory. During the growing season, they should bring plant samples to their local MSU Extension agents or send them directly to the Schutter Diagnostic Laboratory.
"We recommend getting seeds tested so if you have Ascochyta blight, you can plan to apply a seed treatment fungicide that is effective at reducing Ascochyta," Burrows said.
Crop and Chemical Rotations
To reduce the effects of Ascochyta blight, Burrows recommended both crop and chemical rotations. She suggested that growers let at least three years pass before planting the same pulse crop in a field. That will allow the residue where the pathogen lives to break down.
Burrows also recommended rotating the chemistry classes of fungicides growers use, so they can prevent strobilurin resistance in peas and lentils. Headline and Quadris are two of the most commonly used and inexpensive strobilurin products available. Stamina and Dynasty are strobilurin fungicides used as seed treatments.
Growers need to know that resistance can develop in pulse crops, Burrows said. Peas in Saskatchewan and Alberta, Canada have already become resistant to strobilurin fungicides. Chickpea growers in North Dakota sprayed multiple applications of strobilurin fungicides around 2005, and the Ascochyta blight did a major flip. Instead of being killed by the fungicide, it became entirely resistant. The Ascochyta blight in chickpeas in North Dakota and Montana, in general, is considered to be resistant to strobilurin fungicides. The Schutter Diagnostic Laboratory and North Dakota State University will begin monitoring this year for strobilurin resistance in Ascochyta species causing blight in peas and lentils.
Follow Labels to Limit Resistance
"Follow pesticide labels," Burrows said. "If we have resistance develop, we will lose these fungicides as tools for disease management in pulse crops. Once a fungus is resistant to one strobilurin, it is resistant to all strobilurins. Resistance is maintained in populations for years even without continued fungicide selection pressure."
The seed treatment product "Stamina" is currently as effective against Ascochyta as the former gold standard, Mertect, but it is not recommended for chickpeas in Montana and North Dakota because of the fungicide resistance problems in Ascochyta blight of chickpea, Burrows said. The fungicide Xemium (a component of Priaxor) and seed treatment product Systiva are effective against Ascochyta, but Systiva will be available on a very limited basis this year.
The Schutter Diagnostic laboratory is starting to monitor for strobilurin resistance, Burrows said. If it identifies strobilurin resistance in a seed lot, the lab will notify individual growers so they can plan appropriately and not use strobilurin fungicides.
If dry pea, lentil and chickpea growers want the Montana State Seed Lab and Schutter Diagnostic Laboratory to test seeds for quality, Ascochya and other diseases, they should clean the seeds before sending them to prevent delays in processing, Burrows said. The test for Ascochyta generally takes 10 days after planting, and it can take three to four weeks to get results.
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By Evelyn Boswell, Montana State University News Service
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