EB1880

SNOW MOLD DISEASES OF WINTER WHEAT IN WASHINGTON

Timothy Murray1, Stephen Jones2, and Ed Adams1 Department of Plant Pathology1 and Crop and Soil Sciences2 Washington State University

Snow mold diseases of wheat over a much wider area of the growers increased substantially are some of the most dramatic and state in 1997 due to snow cover during the 1940s. Research into devastating diseases of plants. In that lasted for 150 days in some control began in Washington state the Pacific Northwest (PNW), the areas. This bulletin describes when Drs. Charles S. Holton, with snow molds are important in areas occurrence of the snow mold the U.S. Department of Agricul- where snow falls on unfrozen or diseases in the PNW, their symp- ture, and Roderick Sprague, with lightly frozen soil and persists for toms, and methods of control. Washington State College, (now 100 days or more. Snow mold was Washington State University), prevalent in Washington from the Snow mold was first recog- began to search for a control. 1940s through the 1970s, but nized as a disease problem in the occurred infrequently during the PNW in 1923 from wheat grown Four different snow mold 1980s. In 1995, we converted a in Fremont and Teton counties of diseases, all caused by soil-borne disease observation nursery on southern Idaho. Prior to this time, fungi, occur in Washington: pink the farm of Adelbert Jacobsen near the disease was thought to be a snow mold (Microdochium Mansfield, to yield trials so we form of winterkill. In 1924 and [Fusarium] nivale), speckled snow would have a more accurate way 1929, respectively, snow molds mold (Typhula idahoensis, T. of evaluating varieties and breed- were observed on wheat grown ishikariensis, and T. incarnata), ing lines for resistance to snow near Chelan, Washington, and in snow scald (Myriosclerotinia mold. Significant losses due to Gallatin County, Montana. Al- borealis), and snow rot (Pythium snow mold occurred in parts of though work describing the iwayami and P. okanoganense). In Douglas and Okanogan counties pathogens and diseases they addition to speckled snow mold, T. in both 1995 and 1996. Snow cause was conducted during the incarnata is often found causing a mold was a significant problem 1920s and 1930s, the perceived root and crown rot of wheat and importance of snow molds by barley in the absence of snow COOPERATIVE EXTENSION cover. Pink snow mold is the most usually cause significant losses of visible over the surface of infected widespread of these diseases, wheat. Snow scald and snow rot plants (Fig. 2). Sclerotia of T. occurring on wild grasses, lawns, are limited in distribution and their idahoensis and T. ishikariensis are and winter wheat throughout the overall impact on winter wheat more or less round and dark PNW. On wheat, however, pink production is minimal. This brown to black, whereas those of snow mold is less destructive than bulletin will focus on speckled T. incarnata are irregularly shaped, speckled snow mold (primarily T. snow mold and pink snow mold. reddish brown, and more abun- idahoensis and T. ishikariensis), dant on roots and between which is restricted to higher sheaths in the crown than T. elevation areas in Washington Symptoms idahoensis and T. ishikariensis. (Douglas, Okanogan, Lincoln, Chelan, Grant, and Spokane Snow mold diseases destroy Immediately following snow- counties), Idaho (Teton, Fremont, the leaves and crowns of host melt, plants with pink snow mold Bonneville, and Caribou counties), grasses under snow. Following have a whitish fungal growth and Montana (Gallatin County). snowmelt, the leaves of plants covering the leaves. The fungal In addition to the PNW, both with speckled snow mold are growth soon turns a characteristic speckled and pink snow molds matted to the soil and covered salmon color, resulting in the occur in Alaska, Canada, Japan, with a whitish gray fungal growth name “pink” snow mold (Fig. 3). Scandinavia, Central and Eastern (Fig. 1). Leaves and leaf sheaths with pink Europe, and parts of the former snow mold remain intact and turn U.S.S.R. The fungal growth disappears a light to dark brown color, as after a few days of dry, sunny opposed to the disintegration that Speckled snow mold on turf weather, and numerous dark- occurs with speckled snow mold. and crown, and root rot of wheat colored bodies the size of radish Disease severity ranges from and barley (both caused by T. seeds known as sclerotia become relatively small lesions on leaves incarnata) are widespread through- to complete destruction of the out much of the PNW, but do not foliage and dead plants.

Figure 1. Figure 2. Figure 3. Damage to winter wheat by speckled Sclerotia of the snow mold pathogens Symptoms of pink snow mold snow mold is apparent following are visible on infected plants soon following snowmelt. snowmelt. after snowmelt.

2 Disease Development Development of snow mold is Statewide, it is estimated that favored by rain during the autumn about 200,000 acres are chroni- The fungi causing speckled and snow falling on unfrozen or cally affected by the snow molds. snow mold survive between crops lightly frozen soil that persists for Although precise estimates for as sclerotia in soil and infested approximately 100 days or more. dollar loss do not exist, in 1953, host debris. Although sclerotia Deep snow cover insulates plants Sprague estimated annual losses can germinate in the fall and and soil, maintaining temperatures due to speckled snow mold at produce airborne spores, most close to 32° F with relative humid- about $300,000 and for pink snow infections are the result of fungal ity near saturation, both of which mold, up to $1 million (1953 strands (hyphae) growing from are favorable to growth of these dollars). In 1953, Dr. Hugh C. sclerotia in soil under the snow. fungi. Deep snow also ensures McKay and John M. Raeder esti- Germination of sclerotia and contact between leaves and soil, mated annual losses due to infection of plants begin within thus allowing an entry point for speckled snow mold in southern one month after snowfall and the fungi, while at the same time Idaho from $50,000 to $800,000. continue as long as snow cover preventing photosynthesis, which persists. Invasion of crowns and is thought to make plants more death of plants occur after about susceptible to infection due to a Control three months of snow cover; depletion of carbohydrates in the consequently, damage from crown. Frozen soil, intermittent Early research focused on speckled snow mold increases snow cover, or less persistent cultural practices including seed- with longer snow cover. snow cover reduce the severity ing date, crop rotation, fertilizer of snow mold. application, residue management, The fungus causing pink snow fall fungicide application, and the mold survives between crops application of blackeners to snow primarily in residue from previ- Economic Importance to hasten snowmelt. Later, dis- ously infected plants. Infection of ease resistance was sought as a leaves occurs during cool, wet Occurrence of snow molds is control. weather in the fall before and after sporadic. In years when disease is snowfall. Fungal filaments grow- severe, entire fields may be killed ing from infested residue near the and require reseeding, whereas in Cultural practices. soil surface penetrate leaves and other years the diseases do not An association between early continue to grow in infected plants occur or are insignificant. In seeding and improved spring as long as the snow persists. The Douglas County from 1947 to recovery of snow mold infected pink snow mold fungus also 1966 (19 crop years), speckled plants was made soon after the produces airborne spores, but snow mold was severe in four disease was recognized. Two most of these spores are released years, moderate in eight years, schools of thought emerged on during spring or summer and are, light in three years, and not how best to manage seeding therefore, not important for present in four years. In other dates. Early seeding (early to late development of snow mold. These words, snow mold caused signifi- August) results in large, well- spores can be important, however, cant losses more than half of this tillered plants that tolerate the for the development of head scab time period. disease and recover in the spring in areas with warm and moist better than late seeded plants. environmental conditions during In contrast, late seeding (October flowering. 1-15) results in small plants that

3 may escape the disease entirely. ing mercury effectively controlled Dry coal dust applied at 150 to Late seeding has not been recom- snow mold when applied in the 200 lbs per acre is adequate to mended in Washington because fall before snowfall; however, the cover snow and hasten melting. yield potential is less than with unpredictability of snow mold Coal milled larger than 200-mesh early seeding, especially in non- occurrence coupled with the high flowed well from hoppers and snow mold years, and although cost of $5 to $7 per acre (1950s’ settled well on the snow; however, small plants may escape disease, dollars) prevented them from finer materials present drifting most die when infected. being widely adopted by growers. problems. Slurries of blackeners Only growers in areas where snow work well, but the weight of the Planting method, that is, deep- mold was severe nearly every year water may increase the cost of furrow or double disc had no and who could not grow spring application. Low sun angles on effect on disease as long as plants wheat used fungicides. The steep north slopes prevent dusting emerged and became established economics of wheat production in from greatly accelerating snow- soon after seeding. Likewise, the chronic snow mold area have melt and the temptation should be clean tillage and stubble mulch not changed and there are no avoided. In addition, it may had no direct effect on disease as fungicides currently registered for require several farmers working long as plants were established snow mold control. together to obtain a cheap supply soon after seeding. Application of of blackeners. nitrogen and phosphorus fertiliz- ers had no direct effect on disease Snow blackeners. development, but were valuable Spreading dark colored mate- Disease resistance. for more rapid recovery of dis- rials such as coal dust, fly ash, or Although reports in the 1940s eased plants in the spring. lamp black to hasten snowmelt indicated some Japanese wheat has been used to control snow varieties were resistant to the Crop rotation provides time for mold. William R. Fischer and Dr. snow molds, none of the reports infested crop debris to decompose George W. Bruehl tested several were substantiated. A dedicated and for sclerotia to die. Fields in different materials, application search for disease resistance which spring cereals or legumes methods, and rates of application began in earnest in 1960 when were grown in place of winter in the early 1960s. Although they Sprague planted 5,200 wheat lines wheat, and not sown following a were able to hasten snowmelt by from the USDA world collection in crop destroyed by snow mold, had up to 20 days, they were unable to a plot near Mansfield. He planted less snow mold in subsequent demonstrate a clear economic another 4,000 lines the following years. Controlling weeds during return due to unpredictable year at the same location, but died the rotation is important, however, weather conditions after dusting. before seeing the results. Dr. since many grasses are suscep- In some cases, snow after dusting George W. Bruehl culminated the tible to snow mold and can pro- covered the blackeners and search for a snow mold resistant vide inoculum for subsequent prevented them from melting the variety adapted to the PNW in crops. snow. In others, the wheat did not 1972 with release of Sprague, respond to early snow removal which was named in honor of because of cold, wet weather Roderick Sprague. Only 15 of the Fungicides. afterwards. original 8,200 lines screened for Holton and Sprague tested resistance to snow mold were fungicides for control of snow considered promising sources of mold from 1944 until the late resistance and these have been 1950s. Several fungicides contain- used in breeding programs since.

4 The value of resistance for year. Under these harsh condi- Moro and Stephens (Table 1), but control of snow mold is both tions, the resistant variety Sprague equal to or slightly less than visually (Figs. 4 and 5) and eco- survived (Figure 6), but the sus- Edwin (formerly WA7834) and nomically dramatic (Table 1). ceptible variety Nugaines was Bruehl (formerly WA7833). As a Figure 4 illustrates recovery of a killed by snow mold (Figure 7). result of this work, the club wheat snow mold resistant variety about Snow mold was not as severe Edwin was released in 1998, and one month after snowmelt, com- in 1996 at the nursery near club wheat, Bruehl was released in pared with a susceptible variety. Mansfield, as at the Tetonia 1999. These lines have very good (Figure 5). The photographs in location; however, yield of the snow mold resistance and yields Figures 6 & 7 were taken at a resistant varieties Sprague and competitive with Sprague and nursery on the University of Idaho Eltan was significantly better than Eltan (Table 1). There has never Experiment Station in Tetonia, a been a club wheat released with high elevation site where snow snow mold resistance equal to or mold is very severe nearly every better than Sprague.

Figure 4. Figure 5. Recovery of a snow mold resistant Lack of vigorous regrowth by a snow variety following snowmelt is mold susceptible variety. characterized by vigorous growth.

Figure 6. Figure 7. Nearly complete recovery of a plot of Nearly complete destruction of a plot Sprague winter wheat by speckled of Nugaines winter wheat by speckled snow mold. snow mold.

5 Maturity date is an important varieties that will eventually afford Stress is rarely lessened when characteristic of snow mold growers in snow mold areas a the advice is to be patient. It takes resistance. Severe snow mold choice in variety and market class two to three weeks for the stressed delays maturity and is especially equal to other production areas of plants to show signs of recovery. apparent with susceptible variet- the state. It also takes about that long for ies. In 1997, maturation of Eltan, fields to dry enough to allow Moro, and Stephens was approxi- fieldwork. Although there has mately two weeks later than Replanting been little work comparing snow Sprague, Edwin, and Bruehl. mold damaged winter wheat As the snow cover retreats and stands and yields to replanted Growing resistant varieties is damage from snow mold becomes spring wheat, some data exists the most effective and affordable evident, the decision of whether or from winterkill research. There, control measure for snow mold. not to replant is difficult for the recommendation has been six Presently, Sprague and Eltan are growers. The wheat will look very live winter wheat plants per the predominate varieties grown in bad as the snow melts and may square foot would equal a re- the snow mold areas of Washing- even look worse for the first few planted spring wheat yield. This ton. Both varieties have short- days after the snow is gone. Cold is six plants per foot of row in 12- comings. Sprague is more resis- conditions after snowmelt can inch rows, more in wider spacing, tant than Eltan, but has weak further weaken the wheat plants. fewer in narrow row spacing. This straw and a tendency to lodge. Warm conditions hasten the is based, however, on research Eltan is less resistant and matures decomposition of the badly conducted before the advent of the later when injured by snow mold, affected leaves. In addition, one new, higher yielding spring but has excellent yield potential has to line up additional seed at wheats. Another confounding and end-use quality. A concen- the same time everyone else is factor is that rarely do whole fields trated effort is currently underway buying spring wheat seed. All of need to be replanted. Replanting to select resistant varieties with this leaves the grower anxious. partial fields can cause harvesting better snow mold resistance, difficulties due to differing maturi- stronger straw with less tendency ties. It is rarely advisable to for lodging, high yield potential, replant without destroying the and good end-use quality. We are remaining winter wheat. It is very optimistic that the two new important to break the green- lines in Table 1 will be effective bridge between crops so an replacements for the current snow additional 10 (minimal) to 21 mold resistant varieties. We see (preferred) days elapse before these as the first in a succession of replanting.

6 Table 1.

Snow mold ratings, yield and test weight for winter wheat varieties and breeding lines grown near Mansfield, WA, in 1995-1996 on the Jacobsen farm.

Market SM Ratingc Yield, bu/ac Test wt., lbs/bu

Varietya classb 1995 1996 1997 1995d 1996 1997 1995 1996 1997

Bruehl Club 5.0 5.7 5.0 - 89.9 67.9 - 57.9 58.1

Sprague SWW 5.3 5.5 5.8 - 77.2 52.9 - 60.6 61.7

Eltan SWW 3.6 3.5 3.8 - 66.2 64.2 - 58.3 55.7

Edwin Club nae 3.3 4.5 - 68.8 60.9 - 61.3 61.0

Moro Club 2.2 2.9 4.3 - 49.7 52.9 - 58.3 60.0

Stephens SWW Na 0 2.0 - 6.0 17.0 - 49.0 58.5

a Sprague, Eltan, and Moro are commercial varieties with varying degrees of resistance to snow mold. Edwin is a snow mold resistant club wheat released in 1998, and Bruehl is a snow mold resistant club wheat that was released in 1999. b SWW = soft white winter wheat; Club = soft white winter club wheat. c SM = snow mold rating is a visual estimate of growth approximately one month after snowmelts that is based on both the percent recovery and vigor. The scale ranges from 0 to 8, with 0 equaling no recovery and 8 equaling complete recovery. d Yield data were not collected in 1995. e na = data not available; Edwin was not grown at this location in 1995.

7 Recommendation • If there are more than eight plants per square foot on Severe snow mold years are average, it may not pay to generally good moisture years. replant. The season is delayed, warming up later than usual, hence the • Four to eight plants per square long snow cover. Wait two weeks foot require careful consider- after the snow has left most of the ation. How soon can you field, then carefully survey the work the field? What does the field. Small patches of dead wheat long-term weather look like, may not be worth replanting. and how well does spring Large acreage may require further wheat normally yield in the consideration. field? What seed can you get? What price will wheat bring? • If the wheat is totally dead, Then comes the balancing act.
Will the reduced yield from the then the replant decision is a little easier. There should damaged winter wheat cover be good moisture and fertilizer the costs already invested in remaining in the field, although the field? Or will the costs of starter fertilizer may help as replanting and the expected last year’s fertilizer may have increased harvest bring a leached a foot or two through better bottom line? the soil profile.

Prepared by Timothy Murray1, Stephen Jones2, and Ed Adams1 Department of Plant Pathology1 and Crop and Soil Sciences2 Washington State University

College of Agriculture and Home Economics, Pullman, Washington

Warning. Use pesticides with care. Apply them only to plants, animals, or sites listed on the label. When mixing and applying pesticides, follow all label precautions to protect yourself and others around you. It is a violation of the law to disregard label directions. If pesticides are spilled on skin or clothing, remove clothing and wash skin thoroughly. Store pesticides in their original containers and keep them out of the reach of children, pets, and livestock.

Issued by Washington State University Cooperative Extension and the U.S. Department of Agriculture in furtherance of the Acts of May 8 and June 30, 1914. Cooperative Extension programs and policies are consistent with federal and state laws and regulations on nondiscrimination regarding race, color, gender, national origin, religion, age, disability, and sexual orientation. Evidence of noncompliance may be reported through your local Cooperative Extension office. Trade names have been used to simplify information; no endorsement is intended. Published October 1999. Subject code 356. B. EB1880