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Extension Folder 571-1981 11 . Common blight Crop Pest Management Series symptoms on navy bean Agricultural Extension Service University of Minnesota Edible Bean Disease ancl Disorder Identification R. A. Meronuck, extension plant pathologist and L. L. Hardman, extension agronomist 12. Common blight symptoms on pods 8. Bean rust, summer spore 1. White mold, cottony 4. White mold, germinating stage (urediospore) on growth on adzuki bean sclerotia pinto bean

9. Rust pustules (spore 5. White mold, initial clusters) on pods of pinto infection on pod bean

2. White mold, cottony growth on pinto bean

3. White mold, sclerotia, close up 10. Bean rust, overwinter spore stage (teliospore) on pinto bean ~-----

slides continued on page 4 WHITE MOLD symptoms appear 10 to 15 days after infection. The earlier these symptoms appear The characteristic symptom of white the greater the potential for crop yield mold is a white cottony growth near the reductions. stem base (1, 2).* The fungus also produces Cultural practices are important in sclerotia, which are black, hard mats of slowing initial infection by this fungus. Three mycelium in or near the cot~ony growt~~ (3). to four year rotations are recommended for Sclerotia survive adverse (winter) cond1t1ons control of this disease. Following bean in the field. The disease starts when the harvest all refuse should be plowed under as plant growth covers the space between the completely as possible, because refuse is a rows and when the soil surface is cool and primary source of inoculum for the next moist enough for sclerotia to germinate (4). growing season. Chemical con~rol of early Initially the fungus colonizes plant debri~ and rust infection is easily accomplished when then spreads to plants in the row. Infection the disease is identified in the early stages. will kill some plants and severely reduce the Fungicides such as coppers, manebs, a~d yield of those plants with only pod infections zinebs will control the disease. For details (5, 6). see Agriculture Extension Service Plant White mold is caused by the fungus Pathology Fact Sheet No. 20 (1975), Pinto Sclerotinia sclerotiorum. High humidity and Bean Rust Control with Fungicides. temperatures between 60° and 70° F. favor the growth of this fungus. Crop rotation helps prevent the build up of enough inoculum to cause white mold in COMMON AND HALO BLIGHT edible beans. A rotation of three to four Common blight first appears as small years between beans and other susceptible translucent water-soaked spots on the leaf. crops is recommended. Sunflowers, potatoes, As these spots enlarge, the tissue within sugar beets, and soybeans should not be each dies and forms brown lesions with a grown in close rotations with edible beans narrow yellow margin (11 ). In some cases, a since they are susceptible to white mold. yellow bacterial discharge may be seen. Small grains, corn, or forages are Water-soaked sunken lesions are also found recommended in a rotation with edible beans on the pods (12). These lesions turn to prevent increase of white mold inoculum. brownish-red with age. The bacteria may One to two applications of the fungicide also infect the vascular system, destroying Benlate has provided good control of white the node and killing branches. Infected seed mold. When applying this fungicide, it is is discolored and shriveled. very important that the first application be Halo blight may have symptoms similar made when the field is in 10 to 25 percent to common blight, but a distinguishing bloom, and the second application should be characteristic of halo blight lesions is a large made after the full bloom stage or during yellow halo around the individual spots (13, late bloom. Benlate applications should be 14). This chlorotic zone or halo may be as considered if white mold has been a large as one-half inch in diameter. The problem on the field in previous years, or discharge found in these lesions will be a when cool conditions are forecast for the last cream or silver color. Systemic plant month of the growing season. infection with these bacteria causes stunted plants with small, chlorotic trifoliolate leaves. RUST Common blight is caused by Xanthomonas phaseoli, and halo blight is Rust appears first as small chlorotic pale caused by Pseudomonas phaseolico/a. These spots (lesions), usually slightly yellow with a bacteria are introduced to a new area by small dark center (7). As the disease infected seed. Organisms overwinter in seed progresses, these spots enlarge and are or plant debris left in the field. Common covered with brick-red rust (summer) spores, blight development is favored by relatively which spread the disease (8, 9). With cooler high temperatures; halo blight infection is weather these lesions will develop black favored by relatively cool conditions. Damp (overwintering) spores (10). weather favors the spread and development Bean rust is caused by the fungus of both diseases. Uromyces phaseoli var. typica, and Disease free seed can prevent these diseases. A three to four year rotation *numbers refer to photos on pages 1 and 4 provides ample time for any pathogenic bacteria in plant debris to die. Seed the rows. This disease is caused by several treatment with streptomycin has not proven types of soil fungi. effective in eliminating these bacterial blights, Good quality seed is very important in but it may reduce the incidence of disease preventing damping off. Cracks in the seed resulting from surface contamination of the coat permit soil borne pathogens to enter. seed. Copper fungicides have been used for Poor quality, weathered seed may rot in the controlling bacterial blights, however, soil before germination. Seed treatment is research has not shown these fungicides to available to protect against many fungi be effective against the bacterial blights in known to cause damping off. Seed should Minnesota. always be treated with fungicide to help An additional bacterial blight caused by prevent this particular disease. Pseudomonas syringae (brown spot) can also attack edible beans, but it has distinctly different symptoms (15). The same control COMMON BEAN MOSAIC VIRUS measures used for halo and common blight Common bean mosaic virus stunts the are recommended. plant and causes mottling and leaf malformations (18). Trifoliolate leaves affected with mosaic usually have irregular shaped, ROOT ROTS light yellow and green patches and may also Root rotting fungi present in the soil live show considerable puckering (19). Infected on decomposing vegetation. These fungi leaves are narrower and longer than normal, attack bean plants whenever the fungus with downward cupping. Bean plants population is large and soil and weather attacked early in the season are yellowish, conditions are favorable. Fusarium solani and dwarfed and spindly. Dark necrotic lesions Rhizoctonia solani commonly cause root rots are sometimes found on the roots, petioles, in Minnesota edible beans. and leaf veins. The virus can be spread by The Fusarium root rot may be identified direct contact, by insects, and by seed. by reddish colored lesions on the taproot, The only satisfactory methods of control which later turn brown (16). This are use of resistant varieties and good discoloration may extend up to the soil line. quality seed. Removing infected plants from Plants seriously infected are stunted and will the field reduces the amount of secondary have yellow leaves, and branch roots that spread but may be costly on large acreages. develop from the taproot are killed. Rhizoctonia root rot may cause the seedlings BRONZING to be twisted and stunted. Reddish-brown cankers appear on the roots partially below Bronzing of leaves can be caused by sun or at the soil line and often girdle the stem scalding or by ozone. Sun scalding is caused (17). Plants infected with Rhizoctonia may be by the concentration of the sun's heat on stunted and have yellow leaves. leaf tissue. Ozone damage is caused by an Rotation is very important in controlling air pollutant that originates from large cities the root rots. Rotation of three to four years and power plants. Polluted air can travel between bean crops is effective in preventing long distances at high altitudes and follow the build up of these soil pathogens. Other down drafts into bean fields. crops such as sunflowers and potatoes, Damage from ozone usually appears as which are susceptible to these fungi, should small sunken necrotic lesions on the upper not be used in a close rotation with edible leaf surface. The leaves then develop a beans. Corn, alfalfa, and small grains are bronzed appearance as the lesions enlarge and extend deeper into the leaf interior. generally considered good rotation choices. Older leaves appear to bronze more readily than younger leaves. Severely bronzed leaves drop off prematurely, causing yield reduction. DAMPING OFF Sun-scald bronzing is most apparent on Severely infected plants die shortly after the side of the row receiving the most direct germination or emergence, but damping off rays from the sun. Bronzing symptoms (20) is also suspected when there are occasional are usually most obvious during the later spaces in a row where plants have not part of the growing season. emerged, or when plants wilt shortly after There is no control for bronzing, and no emergence. These wilting plants soon die data are available in Minnesota showing the and dry up, leaving additional bare spaces in extent of yield reduction. 14. Halo blight symptoms on llllll~lilii1!1~1ii1~~11l1[111~1i1~1i1il[i~~~IIIII leaf and pod of edible 17. Rhizoctonia sp. rot on 3 1951 D01 921 083 9 bean edible bean

15. Brown spot 18. Bean common mosaic (Pseudomonas sp.) on virus symptom on edible edible bean bean

19. Bean common mosaic virus symptom on trifoliolate leaves

16. Fusarium sp. rot on edible bean

Funds for the development and printing of this folder were provided by the Red River Edible Bean Growers Association, Rural Route 3, Box 102, Frazee, MN 56544. 20. Bronzed versus healthy leaves

Editor: Sheila Wistad Fugina Designer: Rose Mauch

The information given in this publication is for educational purposes only. Reference to commercial products or trade names is made with the understanding that no discrimination is intended and no endorse· ment by the Minnesota Agricultural Extension Service is implied. 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. Norman A. Brown, Director of Agricultural Extension Service, University of Minnesota, St. Paul, Min­ nesota 55108. The University of Minnesota, including the Agricultural Extension Service, is committed to the policy that all persons shall have equal access to its programs, facilities, and employment without regard to race, creed, color, sex, national origin, or handicap. 20 cents