A Smorgasbord of Soybean Diseases

	Dean Malvick Assistant Professor of Plant Pathology Department of Crop Sciences (217) 265-5166; dmalvick@illinois.edu		Wayne Pedersen Associate Professor of Plant Pathology Department of Crop Sciences (217) 333-3847; wpederse@illinois.edu
		Darin Eastburn Associate Professor of Plant Pathology Department of Crop Sciences (217) 244-9632; eastburn@illinois.edu

Many different diseases reduce soybean yields in Illinois every year. Soybean diseases periodically cause significant yield losses in patterns and locations that are difficult to predict. No single soybean disease typically causes significant damage over the entire state, but many acres of soybeans suffer from significant disease damage each year. The occurrence of each disease depends, in part, on environmental conditions and the cultivar grown. The basis of a good disease management program is the appropriate selection of cultivars and the proper identification of diseases.

This tour stop will provide the opportunity to examine and discuss a number of soybean diseases and to practice disease identification skills.

A	B
C	D
Figure 1. Can you identify which plant has BSR, which has SDS, which has BPMV, and which has Phytophthora rot symptoms? (See answers on this page.)

Brown Stem Rot (BSR): Yellow and dark brown areas between leaf veins and pith is dark brown; leaves and petioles drop; no bluish mycelium on roots (Fig. 1A).

Sudden Death Syndrome (SDS): Yellow and dead areas between the leaf veins; premature leaf drop, but petioles remain attached to stem; pith remains white, but vascular tissue may be brown; bluish mycelium and spores on roots (Fig. 1B).

Bean Pod Mottle Virus (BPMV): Leaves may appear mottled shades of green and yellow with rough surface; stems may remain green after maturity; seeds are often discolored light to dark brown (Fig. 1C).

Soybean Mosaic Virus (SMV): Leaves may appear shades of green and yellow with definite puckering; may resemble herbicide drift; seeds are often discolored with black or brown color bleeding from the hilum.

Stem canker: Characterized by a dark brown color at site of infection; may have small black spots on the stem in random arrangement.

White mold: Also known as Sclerotinia stem rot; identified by the presence of white fluffy mycelium, especially in dense canopy; dark sclerotia, which appear the size of rodent droppings, may be found in or on infected stems or mixed in harvested seed.

Pod and stem blight: Found on soybean stems and pods, small black spots (pycnidia) may be arranged in rows, generally worse in wet fall weather.

Soybean cyst nematode (SCN): Characterized by the presence of white-brown cysts on the soybean roots; may cause stunting and yellowing of plants, but not always.

Phytophthora rot: May kill soybean seedlings before emergence, at seedling stage, or throughout season; infection is through root and causes a dark purple-brown color on stem from soil-line up; usually found in wet soils (Fig. 1D).

Pythium seed and seedling rot: Also found in wet soils, but usually kills soybean seedlings at emergence; hard to distinguish from Phytophthora.

Rhizoctonia root rot: Characterized by dark red dry lesions with distinct margins at or just below the soil line; may cause wilting.

Charcoal rot: Common in hot, dry years and has small black structures, micro-sclerotia, found in the pith if the stems are split.

Back to Agronomy Day 2003 Index