Management reference for white mold, soybean cyst nematode, and Phytophthora in Soybeans
1998

Bruce Potter - IPM Specialist SW MN, SW Experiment Station - Lamberton, MN

Ward Stienstra - Extension Plant Pathology, Department of Plant Pathology

White mold Soybean cyst nematode Phytophthora

When are symptoms and yield loss worse? Cool & wet during flowering. Early, heavy canopy formation. Conditions that cause poor root development. Moist early, Hot droughty mid- season Wet soils

Time of year problems occur Flowering to harvest Season long Seedling blight and mid-season plant death.

Do races of organism exist? Races or biotypes are suspected. YES, 16 known More suspected. Most SCN in MN are race 3 YES, 42 races known more suspected.

Are resistant varieties available? No true gene based resistance known. Some varieties more or less sensitive to white mold infection. Less susceptible varieties may still become severely diseased. Currently three genetic sources in MN production varieties & tolerance. SCN resistant varieties can still have nematode reproduction. Nematode race changes may occur if resistance sources are not rotated. Several genes (Rps) & tolerance in commercially available MN varieties. Failures of Rps 1a, 1b, 1c and possibly 1k have occurred in MN. New races develop if a resistance gene is continually used.

How does over-wintering occur? Sclerotia can persist many years Cysts and eggs can persist in soil Oospores

How are they spread? Wind born ascospores for short distances, infected soybean straw and manure, combine Tillage equipment, soil movement with wind and water Soil movement. New races develop within a field. Organism is widespread.

Seed spread? YES, If fungus on seed or sclerotia in seed lot. YES, Soil particles with seed NO

Does tillage help? MAYBE short term or under low disease pressure. NO YES, If tillage improves soil drainage and warmth.

Does rotation help? YES, May need more than one year of a non-host including weed hosts to reduce inoculum level. YES, May need more than one year of non-host when populations are high. A single year of SCN resistant soybeans may not reduce populations for susceptible varieties to yield well. NO

Does row spacing make a difference? YES, Drill beans tend to have higher incidence of white mold. NO NO, Drilled beans, however, eliminate the cultivation option.

Does seeding rate help? YES, Avoid excessive seeding rates. NO NO, Stand loss may lower population below intended if susceptible variety.

Does soil fertility make a difference? YES, Disease can be worse if canopy lodges. YES, Adequate fertility can counter root inefficiency caused by soybean cyst nematode NO

Do seed treatments help? TBZ fungicides on seed lots known to have white mold NO Metalaxyl (Ridomil and Apron) seed treatments can help reduce damping off in some conditions. Not season long control. Susceptible varieties only.

Are there post planting chemical treatments that work? MAYBE, Fungicides and some herbicides (e.g. Cobra) may reduce white mold losses. Economics, timings and rates not well worked out. NO, Nematicides may provide temporary supression of populations but not season long control. NO

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Created on 03/10/98 by M. Werner Last revised on 4/13/00.

	White mold	Soybean cyst nematode	*Phytophthora*
When are symptoms and yield loss worse?	Cool & wet during flowering. Early, heavy canopy formation.	Conditions that cause poor root development. Moist early, Hot droughty mid- season	Wet soils
Time of year problems occur	Flowering to harvest	Season long	Seedling blight and mid-season plant death.
Do races of organism exist?	Races or biotypes are suspected.	YES, 16 known More suspected. Most SCN in MN are race 3	YES, 42 races known more suspected.
Are resistant varieties available?	No true gene based resistance known. Some varieties more or less sensitive to white mold infection. Less susceptible varieties may still become severely diseased.	Currently three genetic sources in MN production varieties & tolerance. SCN resistant varieties can still have nematode reproduction. Nematode race changes may occur if resistance sources are not rotated.	Several genes (Rps) & tolerance in commercially available MN varieties. Failures of Rps 1a, 1b, 1c and possibly 1k have occurred in MN. New races develop if a resistance gene is continually used.
How does over-wintering occur?	Sclerotia can persist many years	Cysts and eggs can persist in soil	Oospores
How are they spread?	Wind born ascospores for short distances, infected soybean straw and manure, combine	Tillage equipment, soil movement with wind and water	Soil movement. New races develop within a field. Organism is widespread.
Seed spread?	YES, If fungus on seed or sclerotia in seed lot.	YES, Soil particles with seed	NO
Does tillage help?	MAYBE short term or under low disease pressure.	NO	YES, If tillage improves soil drainage and warmth.
Does rotation help?	YES, May need more than one year of a non-host including weed hosts to reduce inoculum level.	YES, May need more than one year of non-host when populations are high. A single year of SCN resistant soybeans may not reduce populations for susceptible varieties to yield well.	NO
Does row spacing make a difference?	YES, Drill beans tend to have higher incidence of white mold.	NO	NO, Drilled beans, however, eliminate the cultivation option.
Does seeding rate help?	YES, Avoid excessive seeding rates.	NO	NO, Stand loss may lower population below intended if susceptible variety.
Does soil fertility make a difference?	YES, Disease can be worse if canopy lodges.	YES, Adequate fertility can counter root inefficiency caused by soybean cyst nematode	NO
Do seed treatments help?	TBZ fungicides on seed lots known to have white mold	NO	Metalaxyl (Ridomil and Apron) seed treatments can help reduce damping off in some conditions. Not season long control. Susceptible varieties only.
Are there post planting chemical treatments that work?	MAYBE, Fungicides and some herbicides (e.g. Cobra) may reduce white mold losses. Economics, timings and rates not well worked out.	NO, Nematicides may provide temporary supression of populations but not season long control.	NO

Management reference for white mold, soybean cyst nematode, and Phytophthora in Soybeans 1998

Management reference for white mold, soybean cyst nematode, and Phytophthora in Soybeans
1998