Soybean SOIL BORNE DISEASES
TABLE of CONTENTS
- Charcoal Rot
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- thrives under cool / rainy conditions. The seed rots in the soil and the plant usually dies all at once. If infection occurs after emergence, the plants wilt and the leaves turn grayish-green before turning brown in a day or two. Pythium causes a soft watery rot. The fungi survive in soil and crop debris as oospores and mycelium. There are no rescue treatments and little, if any differences in variety resistance.
- thrives at higher temperatures than Pythium. The rot usually starts at the roots and moves upward, resulting in a slower death than that caused by Pythium. Symptoms include a brown discoloration that moves upward starting at the soil surface. This disease is most likely to occur on very poorly drained soils. The fungi survive in soil and crop debris as oospores and mycelium. There are no rescue treatments once the disease occurs. Resistance is available if needed by variety selection.
- root and stem rot is easier to pinpoint than the previous two diseases. Infected plants exhibit a shrunken reddish brown lesion on the lower stem. In severe cases, the lesion may encircle the entire stem, girdling and killing the plant. More often, the lesion will retard the growth of the plant without killing it. Rhizoctonia causes a firm, dry, brown to reddish-brown decay of the roots and stem below or near the soil line. It often appears during warm, dry weather following an extended cool, wet period. It is most likely to attack and infect soybean plants that were slow to emerge because of adverse weather conditions. There are no rescue treatments and no specific variety resistance to this disease.
- Charcoal Rot
- is caused by the fungus Macrophomina phaseolina. The disease appears in dry, hot weather or when plant growth is limited by some factor. Affected plants lack vigor and die early. Numerous black specks (sclerotia) appear when the "bark" is peeled from the stem base and roots giving diseased tissues a grayish-black color. Black streaks appear inside the roots and lower stem when the plant is split open. sclerotia are frequently formed in the pithy area of the stem.