Bacterial soft rot

Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.

Many of Michigan’s growers are now busy propagating material for the upcoming season. As a result I am seeing an increase in greenhouse samples in the MSU Diagnostic Lab. One of the more common problems I’ve received is bacterial soft rot of various plants in propagation. Growers should be aware of bacterial soft rot symptoms and keep them in mind when scouting.

Several bacterial pathogens cause soft rot symptoms. The bacteria that cause soft rot problems are able to “digest” cell walls within the host. The cell wall is a critical component of each plant cell; this process kills the plant cells and symptoms quickly become visible. Symptoms of bacterial soft rot include water-soaking, collapsing of tissue and in general a slimy rot. In some cases, the main stem is primarily affected, in other cases the disease can quickly progress on the foliage. Either way, the end result is complete collapse of unrooted cuttings and young plugs. Young, tender tissue is particularly susceptible.

Warm temperatures, high relative humidity and leaf wetness—conditions that are typically present in propagation—create an ideal environment for bacterial soft rot pathogens. Regular, careful scouting of plant material in propagation is critical. Plants with soft rot symptoms should be quickly removed and destroyed. Chemical treatments may help limit spread but will not “cure” plants that are already showing symptoms. As always sanitation is very important in disease control. Equipment used to handle propagation material should be regularly disinfested.

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