|
|
Watch out for disease in winter canolaOklahoma Phoma blackleg or Phoma stem canker are the names of a new plant disease recently observed in winter canola fields near Cherokee and as far south as Hennssey, according to Gene Neuens, Producers Cooperative Oil Mill and the Plains Oilseed Products Cooperative. Located first in a field of canola in Alfalfa County by Heath Sanders, Oklahoma State University Extension assistant, symptoms of the new disease are beige-colored lesions or spots on the winter canola leaves and black pepper-like dots within the spots. Not previously confirmed in Oklahoma, the effect of the disease on canola yields is not known at this time, Sanders said. OSU Extension agronomists and specialists are working to determine the extent of the disease in the 2009-10 Oklahoma winter canola crop. Because the disease has been seen in several areas in the state, it is likely the disease, also known as blackleg, has been present at low levels for several years. The outbreak this year is most likely due to the cool, wet weather that helps plant diseases to development and spread. There are two species of the blackleg fungus. One, Leptosphaeria maculans, is more aggressive than the other one, L.biglabosa, Neuens said. The weaker version affects plants later in the season by causing stem cankers that have minimal affect on yield. L. maculans, the more aggressive variation, is the one discovered in Oklahoma canola fields according to laboratory tests made on specimens collected by OSU Extension specialists, Neuens said. L.maculans can attack plants at all ages and significantly affect yield, OSU Extension specialists said. Aggressive blackleg begins with lesions on the leaves, followed by infection of the stems near the soil-line. Stem infections can cause deep cankers, lodging, reduced plant vigor and in severe cases, kill the plant. In this early stage of the 2009-10 winter canola crop, with approximately 85,000 acres planted in Oklahoma, growers should take no action at this time besides scouting their fields for symptoms of blackleg, Neuens said. "If growers observe symptoms of the disease and want to have the disease confirmed, they should contact their local county OSU Extension office," Neuens said. "Samples can be taken and checked in the laboratory. Symptoms should not be confused with normal winter dormancy and dieback of canola leaves in cold weather. "Care should be taken to avoid introducing the blackleg fungus in uninfested fields. The spores can be carried on equipment, shoes and clothing so these items should be cleaned when leaving symptomatic fields." Blackleg fungus can affect a variety of Brassica crops including canola, rutabaga, oilseed turnip rape, turnip and cabbage. Volunteer canola is often affected with the disease, OSU Extension specialists say. It can also attack plants in other genera including white mustard, radish, tansymustard, flaxseed, rocket, pennycress and Shepherd's purse. Spores from blackleg fungus remain viable in plant debris at the end of the growing season and may continue to cause infections three to five years later. It may take large canola roots two to five years to break down and until stubble is completely decomposed, spores can be produced that infect new plants, the OSU Extension specialists said. Blackleg fungus can also produce another spore on infected debris. Formed when two strains of the aggressive fungus mate, the spores can discharge and be wind-blown to canola or weedy mustards in nearby fields to start new infections, Neuens said. Able to travel long distances on wind currents, most lesions land within one mile of the site where they were formed, he said. Research in other states on spring canola, not the winter canola grown in Oklahoma, has shown fungicides rarely provide control of blackleg on plants larger than the six leaf stage, OSU Extension specialists say. Fungicides may have some value if applied to young plants and are most valuable as seed treatments. Fungicide studies on winter canola have recently been established in northern and central Oklahoma to evaluate the ability of labeled products to control blackleg. Blackleg, they say, is best controlled by a variety of methods. These are using certified seed that declared blackleg-free. Canola seed should always be treated with a fungicide for blackleg control since, even with certified seed, a few infected seeds may slip through the testing process. Winter canola fields should be rotated ever three to five years. Longer rotations ensure infected stubble has sufficiently degraded and spores are no longer viable. Volunteer canola and weedy mustards should be eliminated. Unless these alternatives are removed, crop rotation will not be effective. The broad host range has not been well studied, but an effort should be made to eliminate weeds in the mustard family from infected fields, the border of the infected fields and fields in rotation out of canola. Clean equipment and machinery before moving from one field to another one, the OSU Extension specialists say. This is especially important if canola is being planted in fields or areas not previously planted to canola. If canola plants are infected with blackleg, bury canola stubble under five inches of soil. This will bury debris and fruiting bodies so they are not on the surface releasing spores that will blow to nearby host plants. Use shallow tillage or direct seeding to prevent bringing residue back to the soil surface at planting. Non-hosts like wheat should be planted during crop rotations. Growers should plant varieties that are less susceptible to blackleg. In locations where blackleg is established, the use of resistant or tolerant varieties is the main method of controlling blackleg. Tests of winter canola varieties commonly grown in Oklahoma that demonstrate resistance or a high tolerance against blackleg are HyClass115W, HyClass154W and Sumner. If growers have questions, they should contact their local county extension educator or Dr. Tom Peeper, Dept. of Plant and Soil Sciences, OSU, 1-405-744-6420. Since blackleg is new to Oklahoma, Neuens said, the information given here has been gathered from sources in other states and countries that grow canola. The effect of the fall blackleg infections on Oklahoma-grown canola has yet to be determined. Neuens said. OSU Extension specialists will continue to evaluate the situation as the current crop matures and present new information as it becomes available,. Neuens said.
Copyright/Privacy
Copyright 1995-2011. High Plains Publishers, Inc. All rights reserved. Any republishing of these pages, including electronic reproduction of the editorial archives or classified advertising, is strictly prohibited. If you have questions or comments you can reach us at High Plains Journal 1500 E. Wyatt Earp Blvd., P.O. Box 760, Dodge City, KS 67801 or call 1-800-452-7171. Email: webmaster@hpj.com |
|
