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Montana producers have dramatically increased their interest in
pulse crops (lentils, peas, chickpeas) and the acreage allotted to these
crops during recent years. Conversely, acreage in the primary producing
states, Washington and Idaho, has dropped. The Canadian provinces of Alberta,
Saskatchewan and Manitoba continue to be major producers with increasing
production levels.
There are good reasons for the increased interest in pulse crops. The latest farm bill allowed for expanded acreage of alternative crops. This, coupled with potentially favorable economics, an environment that in many areas is conducive to pulse crop production, plus the benefit of crop rotation in our cereal intensive systems explain the rapidly expanded acreages. Two MSU Extension publications, MT 9615, Growing Lentils in Montana, and MT 9520, Growing Peas in Montanaaddress agronomic variables associated with the production of these crops.
For Montana small grain producers, the benefits of using a rotational crop for pest management are obvious. The majority of diseases that affect wheat or barley do not affect pulse crops. Thus the survival of cereal pathogens is dramatically reduced during years when pulse crops are grown. Conversely, the pathogens attacking cereals are seldom an issue during the production of a pulse crop.
As with small grain, frequent pulse crop production will cause an increase in disease pressure. Canadian experts recommend that no single pulse crop be grown in the same field more often than once in four years. Producers planning a small grain-pulse rotation should rotate among chickpea, dry pea and lentil during the pulse crop year.
Whenever new crops are introduced into a region they should be relatively free of residue-borne diseases. Thus far, most pulse crop growing regions in Montana have not experienced any significant disease outbreaks. However, the potential for introduction via infected seed and subsequent spread does exist. Therefore producers need to take appropriate actions to avoid economic losses. This includes learning to recognize the common diseases, understanding how they are spread and learning about methods used to manage pulse crop diseases.
Based on the distribution of anthracnose, it is apparent that humid, wet environments, or environments with rainfall near the end of the production season are more susceptible to the disease. It could present a problem for Montana producers in wet production years. Varietal resistance to anthracnose is not currently an option for control. However, breeding programs at Saskatchewan's Crop Development Center (CDC) are evaluating intermediate levels of resistance.
Plants attacked by the anthracnose fungus exhibit grey to creamy brown lesions on leaves. Stem lesions also appear, ranging from tan to brown in color. Lower leaves are generally affected first and if the infection is severe, defoliation occurs. If environmental conditions favorable to the fungus exist--warm moist weather with frequent showers and a dense canopy--the disease can spread rapidly, resulting in premature plant death. Plants killed by this disease exhibit a dark brown discoloration. Microscopic examination of the lower stem may reveal small bristle-like fungal fruiting bodies characteristic of the pathogen.
The pathogen is transmitted in a number of ways including wind blown soil or crop residue and by seed. It generally survives at low levels from year to year on infested residue and in seed. Where anthracnose has limited lentil production, growers have adopted a four or five year rotation to minimize losses. No other susceptible crops, such as peas or faba beans, can be grown during the rotation if this control method is used. In Canada, chlorothalonil is effectively used for control but currently, no foliar fungicides are registered in the U.S.
Seed transmission currently represents the greatest potential for introducing anthracnose into Montana. Although the pathogen is not efficiently transmitted by seed, its movement by this method has been documented. In Saskatchewan, most seed samples that tested positive for anthracnose had less than 5 percent infection. A similar survey in Manitoba revealed only one seed lot that had a 0.3 percent infection. Because of potential introduction, and possible spread, all seed planted in Montana should test negative for anthracnose
Leaves, stems, pods and seeds all can be infected. Symptoms include light gray to tan spots that often have darkened borders. Within these lesions small, black fungal bodies can be easily observed with the naked eye. Spores are released from these bodies during moist periods and are spread by splashing rain to previously unaffected tissue. During wet periods the lesions may coalesce and result in premature leaf death. With severe disease pressure, stem tips may wilt, turn brown and cause the crop to appear blighted. Pod and seed infection can occur before or after swathing, resulting in brown to purple seed discoloration and shriveling. Wet conditions following swathing may result in significant loss in seed quality which can reduce the crop to feed value.
Since the pathogen survives on previous crop residue, rotation, preferably at least three years out of lentil, is an effective control measure when combined with other practices. Selection of more resistant varieties, especially in areas where the disease has become endemic, is a viable management option. Currently, 'Indianhead,' CDC 'Redwing' and CDC 'Matador' are considered to be resistant to Ascochyta. 'Laird,' a common variety, was formerly considered partially resistant to the disease but recent evidence from Canada suggests that a new, more aggressive strain of the fungus has developed. Now, 'Laird' has no better resistance than Common Chilean, 'Eston' or landrace Spanish Brown, all considered susceptible. New Ascochyta-resistant lines are being tested in Canada. These include CDC 'Glamis,' a new Laird variety, and CDC 'Milestone,' a new Eston line.
As Montana's lentil acreages increase so does the potential for Ascochyta
blight. To minimize this, potential producers should use seed that has
been tested for the presence of Ascochyta. Tests in Saskatchewan show that
a 1 percent seed-borne infection can cause epidemics in cool, wet years
while a 4 percent seed-borne infection results in no infections during
dry years. Seed treatments registered in the U.S. do not provide adequate
protection
against this disease. Currently, Ascochyta testing is conducted by
Canadian laboratories.
Seed treatments containing metalaxyl are available for lentils produced where Pythium is a recurring problem--generally, wet heavy soils. Captan is also registered for protection against seed decay, damping off and seedling blights and will provide protection against seed decay for 7-l0 days. Captan-treated seed should not be in contact with Rhizobium inoculum for over two hours as this reduces the efficacy of the inoculant. Granular inoculant formulations are more tolerant of Captan than liquid applied Rhizobia.
Lentils are known to be susceptible to several virus diseases including pea soil-borne mosaic, alfalfa mosaic, bean yellow mosaic and pea leaf roll. Thus far, none of these virus diseases have caused problems in the northern great plains or Canada.
A. pinodella and Mycosphaerella pinode, different states of the same fungus, cause a disease complex known as "foot rot and Mycosphaerella blight." Producers commonly refer to this as the "Ascochyta" disease. Where peas are grown year after year the disease complex becomes endemic, although varying in severity. In higher moisture regions of Manitoba, the foot rot stage has essentially eliminated pea production.
Foot rot symptoms begin with bluish-black discoloration starting at the seed and moving up to slightly above the soil line. Severe foot rot infections result in reduced harvestablity due to lodging. Blight symptoms appear as small purple lesions without definite margins. They can enlarge with age, eventually forming larger brown to black lesions with a target like appearance. Affected leaves dry prematurely but remain attached to the primary stem. Floral infections may occur resulting in blossom drop. Pod infections result in small purple lesions that can lead to seed infection with varying degrees of shrinkage and discoloration.
Fungi responsible for these diseases may be carried in seed. They also survive from year to year in infested crop debris. Resting stages of these fungi are known to survive in soil. Where the disease has grown to limit yield and quality, producers have used 4 to 5 year rotations to manage the disease. Seed produced in low rainfall areas reduces the risk of seed-borne infections. To assure low Ascochyta levels in seed, a laboratory analysis is recommended. These are routinely done in Canada. Seed treatments and foliar sprays, effective against these fungi, are not currently registered for use in Montana.
The fungus is transmitted by seed but seed produced in the semiarid western regions is nearly free of anthracnose. Pea anthracnose should present little threat to Montana pea growers, especially if good rotations are practiced.
When observed, the infections generally occur in small patches. Stems
become soft, particularly near nodes, and are soon covered with white cottony
fungal growth. Premature death will occur, leading to brown patches of
peas intermingled with healthy plants. Control is seldom warranted and
when peas are grown in rotation with cereals, the disease is rarely observed.
Several seed treatments, including PCNB, Thiram, and Captan are registered as general protectants. PCNB has historically provided good protection against Rhizoctonia. Thiram and Captan protection include Fusarium and some Pythium suppression. Seedling blights caused by Pythium sp. can reduce stands. Canadian researchers have observed that seed which was damaged or immature at harvest is particularly susceptible to this seedling blight. In general, round seeded field peas are less prone to infection than wrinkled processing peas. Where Pythium is the predominant problem, products containing metalaxyl give the best level of control.
Powdery mildew begins as small specks on leaves that enlarge and merge until the entire leaf becomes coated with a white, powdery growth in which small, dark fungal fruiting bodies are commonly observed. Rotation, residue destruction and early seeding minimize powdery mildew infections. Resistant lines are available should the disease become serious in Montana.
Downy mildew can be serious in cool, cloudy pea production areas or where the crop is irrigated. Infections are characterized by a fluffy bluish grey growth on the underside of infected leaves with the upper leaf surface exhibiting yellow blotches corresponding to the underside infection. Stems and pods may also be infected but these infections are rare in Montana.
Crop rotation reduces the risk of serious downy mildew infections. Seed produced in low rainfall areas also reduces the risk of introduction. If downy mildew becomes a problem, growers can select resistant varieties.
Plants infected with Ascochyta exhibit dark, sunken lesions that soon take on a concentric ring appearance. Eventually the stem is girdled and the plant dies above the point of infection. Cool, moist conditions favor the disease and splashing rain aids in spreading it.
Resulting pod infections lead to seed contamination and potential long distance spread. The pathogen also survives on infected residue. In Canada, the use of disease-free seed helps limit spread. Note, however, that even a very low infection level in seed is sufficient to introduce the pathogen into new areas. Pathogen-free seed, coupled with a minimum four year rotation will help to minimize the potential for Ascochyta blight outbreaks. In Canada, chlorothanil is registered for control but its use on chickpea is not registered in Montana.
Resistance to Ascochyta blight is now available. Montana producers must select only resistant lines to limit the potential development of this disease in our state. Currently available Ascochyta-resistant kabuli lines include 'Dwelley,' 'Evans' and 'Sanford' developed at Washington State University by the USDA. The Crop Development Center at the University of Saskatoon also recently released lines with resistance to Ascochyta including CDC 'Yuma,' CDC 'Xena' and CDC 'Chico.''B-90' is also resistant. For producers interested in the desi type, 'Myles,' and CDC 'Chino' have resistance.
Canadian research also verifies difficulty in establishing kabuli chickpea without appropriate seed treatments. Currently registered materials in the U.S. include metalaxyl for Pythium control and Captan as a general seed dressing. No kabuli seed should be planted in Montana without appropriate seed treatments.
Caution must be observed when using Captan seed treatments. This fungicide adversely affects Rhizobium if in contact with the seed for more than two hours. Canadian data suggests the granular inoculum is more tolerant than liquid.
Even though the risk of disease may presently be lower in Montana, it is still advisable to minimize risk by using a 3 to 5 year rotation between individual pulse crops. Finally, any seed planted in Montana should be tested by an accredited testing facility prior to purchase.
We encourage the use of this document for non-profit educational purposes. This document may be reprinted if no endorsement of a commercial product, service or company is stated or implied, and if appropriate credit is given to the author and the MSU Extension Service (or Experiment Station). To use these documents in electronic formats, permission must be sought from the Ag/Extension Communications Coordinator, Communications Services, 416 Culbertson Hall, Montana State University-Bozeman, Bozeman, MT 59717; (406) 994-5132; E-mail - APBTK@Montana.edu.
The programs of the MSU Extension Service are available to all people regardless of race, creed, color, sex, disability or national origin. Issued in furtherance of cooperative extension work in agriculture and home economics, acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture, David A. Bryant, Vice Provost and Director, Extension Service, Montana State University, Bozeman, MT 59717.
Issued March 1999 4782000399 MS