Greenhouse Disease Management
Fusarium Root and Stem Rot
Fusarium species are a cosmopolitan group of fungi that can cause a wide range of disease symptoms. They cause root and crown rots, and stem cankers in ornamentals. Fusarium diseases are caused by several Fusarium species, especially F. lateritium, F. solani, and F. oxysporum. As facultative parasites, they are very persistent. They can survive adverse conditions by entering dormancy as chlamydospores or in a saprophytic state on dead root fragments.
Disease Cycle
Round, thick-walled, single-celled chlamydospores are produced in abundance in killed tissues or pieces of colonized organic matter in the soil. Chlamydospores allow the pathogen to lie inactive in the soil when it lacks a suitable host and thus to survive periods of unfavorable conditions such as drought and low temperatures. The pathogen becomes active when a seedling root grows near chlamydospores.
Symptoms
Typically, when a plant is infected with Fusarium root rot, the taproot (usually the lower portion) and the lateral roots of the plant will rot, turning black or brown (See Figure 28.5). Usually the outer layers of the root beginning to decay and it may also show vascular discoloration. When lateral roots die off, new roots sometimes develop slightly above them on the part of the taproot which has not yet been infected. As infection increases, the oldest leaves begin to yellow and younger leaves are often stunted before becoming flaccid.
Cultural Management Strategies
Limiting host plant stress whenever possible from other pathogens can also reduce the incidence of Fusarium root and stem rot as the plant will have increased vigor and can withstand the fungi more easily. Wet or dry extremes enhance Fusarium development; drought stress can result in the rapid onset of symptoms. Surface clean and disinfect all bench surfaces, tools, trays, containers, and equipment that will contact the potting mix.
Chemical Management Strategies
A fungicide treatment plan is often necessary when dealing with fields that have a history of Fusarium root rot. While protectant fungicides can help manage Fusarium root rot, fungicides have little effect on Fusarium vascular wilts.
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