Unit 10: Soybean Diseases

 Bacterial Blight Occurs on leaves of the SB  Small angular spots  Appear yellow at first  Later turn brown to black  Diseased leaves eventually die and fall Spots can spread from leaves to stem and pods Can spread rapidly in a field Bacteria are seed-borne

Unit 10: Soybean Diseases Bacteria can overwinter on dead leaves Crop rotation and tillage can reduce possible infestation Some varieties may have partial resistance  Bacterial Pustule Foliar disease Light-green spots in early stages that develop into red-brown spots on the leaves  Portions of the infected spots on leaves often drop out

Unit 10: Soybean Diseases Overwintering  Stays on diseased seed  Stays on diseased plant materials Treatment  Bury diseased plant material w/ tillage  Crop rotation Resistant varieties are available Warm-weather disease developing after bacterial blight

Unit 10: Soybean Diseases  Sclerotinia Stem Rot Mostly confined to the Corn Belt states Mold disease that has migrated from infection of edible beans Requires cool, wet summer  May not be a problem every year Spores infect the blossoms, most visible during pod development Leaves wilt and turn gray before dying No effective control

Unit 10: Soybean Diseases  Phytophthora Root & Stem Rot One of the most serious SB diseases in the U.S. Occurs when exposed to cool, wet conditions, on poorly drained soils Can kill seed and seedlings during germination and emergence Seedlings wilt and appear water-soaked Disease attaching older plants  Dark brown discoloration from soil line upward

Unit 10: Soybean Diseases Secondary infections may occur  White fungal growth on top of rotting areas Below ground  Tap root dark brown  Root system rots Control methods  Resistant varieties are best  Fungicide seed treatment can help control

Unit 10: Soybean Diseases  Brown Stem Rot Caused by soil-inhabiting fungus Decays the interior of the stem Attacks the plant early in the season  Symptoms are slow developing  Often not observed until infection is in advanced stages Center of diseased plants are reddish brown Crop rotation is the best control  Rotate out for 2 years

Unit 10: Soybean Diseases  Pod & Stem Blight Can occur wherever SB are grown Stem & pod can be heavily dotted black, spore filled sacs Effects  May girdle stem  Kill plant  Prevent seed development  Fungus can penetrate seed and destroy subsequent germination

Unit 10: Soybean Diseases Overwintering  Survives in infected seeds  Stays on diseased plant material Control methods  Crop rotation  Plant disease-free seed  Downy Mildew Fungal disease Seed-borne First leaves of infected seeds unfold w/ mildew on them

Unit 10: Soybean Diseases Control  No resistant varieties  Must use crop rotation, tillage, and disease-free seed  Purple Stain Symptoms  Pink to dark purple stain on seed Reduces seed value in the market Seedlings from diseased seed may die Control  Use treated seed  High quality seed

Unit 10: Soybean Diseases  Asian Soybean Rust Severe foliar damage  Destroys photosynthetic tissue  Early defoliation  Early maturation Yield losses can be 10-80% 6 hours of wet conditions and temps 59-82º ideal for germination  Dry conditions will restrict it

Unit 10: Soybean Diseases Spores penetrate cells directly instead of wait for another opening in the leaf  9-10d from initial infection to next stage of spore production Common hosts include kudzu, vetch, yellow sweet clover Spreads w/ wind patterns