By M. Putnam
Cause Ilyonectria destructans (formerly Cylindrocarpon destructans) can cause a root rot of ginseng as well as a decay of woody seedlings such as confers. This fungus has also been associated with replant failure when ginseng is planted back into ground that had already been used for ginseng production (however, many other problems, biotic and abiotic, are likely involved). A different fungus causes the disorder known as rusty root.
Roots of all ages appear susceptible. The fungus penetrates the epidermis directly followed by intracellular hyphal growth in the cortex. Wounding and acidic (pH 5) growing conditions contribute to disease severity. Increased iron availability either in the soil or as foliar amendments was found to encourage disease severity by encouraging fungal growth and sporulation. Wet soils were not found to be a major factor.
Symptoms Plants may fail to come up in the spring; during the growing season, plants may rapidly wilt and not recover or show other symptoms of stress such as premature leaf coloration. Lesions progress over the surface of the root and move deep into the cortex. In advanced cases, lesions extend throughout the cross-section of the root, effectively severing it in two. The disease also can start at the root tip, causing a firm decay that progresses toward the crown. Under cool, moist conditions, the rot may progress to within 0.5 inch of the crown before the foliage wilts. In its most severe form, the disease leaves behind nothing but a fragile shell of the root; with the interior completely rotted away.
Cultural control The following have been suggested.
- Maintain a neutral soil pH through the use of lime for acidic soils.
- Avoid foliar applications of iron for plants grown on neutral or alkaline soils.
- Minimize damage or wounding of roots during planting and harvest.
- Affirm WDG at 6.2 oz/A. Can be used in structures but not open fields. Group 19 fungicide. 4-hr reentry.
- Cannonball WP at 4 to 8 oz/A applied through drip irrigation or drenching to the root zone of the treated acre on a 14- to 21-day interval. Do not use within 1 year (PHI of 365 days) of harvest. 12-hr reentry.
- Ph-D WDG at 6.2 oz/A as a drench. May be applied on the day of harvest. Group 19 fungicide. 4-hr reentry.
References Rahman, M. and Punja, Z.K. 2006. Influence of iron on cylindrocarpon root rot development on ginseng. Phytopathology 96:1179-1197
Rahman, M. and Punja, Z.K. 2005. Factors influencing development of root rot on ginseng caused by Cylindrocarpon destructans. Phytopathology 95:1381-1390.