Louisiana Plant Health Management: Slime Molds

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Slime mold at base of a tomato plant grown in a raised bed. LSU AgCenter archive photo.

Slime molds are very common during extended periods of overcast skies and warm and wet weather. They appear as a crusty or powdery coating on any surface, including wooden planks used for making raised beds, garden mulch, lawns, or even on the leaves and stems or trunks of different kinds of plants and trees grown in gardens. The encrusted cover is usually a powder buildup that wipes off easily. This dusty coating may appear in all ranges of different colors, including ashy-gray, brown, charcoal-gray, dark red, purple or bright yellow. One particular slime mold is named as “dog’s vomit” due to its appearance. During favorable weather slime molds may remain in your garden or turf for few days to more than a week.

Slime molds are nonparasitic organisms that are classified as myxomycetes, a group of free-living amoeboid protists. Slime molds feed primarily on bacteria and other microorganisms. Their life cycle is a bit complicated and has two different stages, which consist of an amoeboflagellate stage and a plasmodium stage. After feeding on soil microbes, fungi and organic matter, the amoeboid cells during the amoeboflagellate stage grow and multiply to form a plasmodium stage with a greasy, viscous slimy appearance.

The greasy-looking slimy plasmodium may take on one of many colors or remains clear. It creeps upward on grass leaves, low-growing plant materials, lower trunks of trees and ground covers to support itself up off the ground for better spore dispersal. The plasmodium further bunches up and develops into a fruiting or sporangium stage. This stage is the most visible and is commonly noticed in gardens and lawns. In this elevated stage, the mature spores are released for dispersal by wind, rain or other vectors. As weather dries, the sporangia dry to a crusty or dusty “crud.” Slime molds tend to reappear in the same general areas when conditions become favorable again.

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Slime mold growing on leaf surfaces of Greek oregano. Photo by Leigh Ann Cabaniss.

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Slime mold growing on the surface of wet mulch. Photo by Andre Brock, LSU AgCenter.

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Slime mold growing on the leaf blades of turfgrass. Photo by Raj Singh, LSU AgCenter.

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Slime mold growing on the trunk of a tree. Photo by Will Afton, LSU AgCenter.

9/8/2021 8:47:46 PM
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