By C. M. Ocamb
Cause Several different fungi can cause root rot, including Fusarium, Rhizoctonia, and Macrophomina spp. Lupine plants in seed production with symptoms of root rot caused by Fusarium have been found in western Oregon while Macrophomina has been reported in Washington. Macrophomina and Rhizoctonia are soilborne fungi that is favored by dry and warm soil conditions and have an extensive host range including beans, brassicas, clover, corn, cucurbits, grape, lettuce, peppers, onion, strawberry, tomato, tree fruits, and conifers. Root rot development caused by Macrophomina and Rhizoctonia is enhanced by high temperatures. Fusarium tolerates a wider set of environmental conditions under which root rot can develop. All of these fungi produce long-term survival structures that can persist for several years and can be dispersed by movement of infested soil. Microsclerotia produced by Macrophomina and some Fusarium spp., sclerotia produced by Rhizoctonia, and chlamydospores produced by some Fusarium spp. are located in host tissues and released into the soil as infected roots decay.
Symptoms Severely infected plants will show wilting, stunting, and eventually die. Roots will have areas of dry brown rot when infected by Macrophomina while roots infected by Rhizoctonia will develop a dry rot, dark brown to black in color. Fusarium infections can result in a reddish to brownish to grayish rot on the roots.
- Do not plant lupine in the same soil more than once every 5 years.
- Control soil compaction.
Avoid planting after any crop that had Rhizoctonia or other root rot problems.