Yard and Garden: Fungi and Molds

AMES, Iowa — Fungi and molds are popping up and out in Iowa lawns and gardens thanks to cool, wet conditions the past few weeks. Horticulturists with Iowa State University Extension and Outreach tell gardeners how to identify and manage some of the more common ones. To have additional garden questions answered, contact the ISU Hortline at hortline@iastate.edu or call 515-294-3108.

There are horn-shaped, foul-smelling objects growing in my mulched flower beds. What are they? 

The foul-smelling objects are likely stinkhorns. Stinkhorns are a type of fungus or mushroom. The common name is derived from their appearance and smell. Stinkhorns usually appear in cool, wet periods in late summer and early fall.

Several species of stinkhorn are found in Iowa. The fungi live off dead organic matter and are commonly found in mulched areas in the landscape. Stinkhorns start off as an egg-like, golf ball-sized structure in the soil. As the fungus develops, a stalk grows upward and is topped with a slimy cap coated with a mass of olive green to brown spores. The putrid smell of the stinkhorn cap attracts flies and other insects. The flies and other insects crawl on the stinkhorn, get covered with slime and spores, then fly away to other areas, disseminating the spores. Stinkhorns range from four to eight inches in height.

Stinkhorns are not poisonous or harmful to plants or people. Eventually, the stinkhorns wither away and disappear. Individuals can rake up and discard the fungi if their appearance or smell is bothersome.

(ISU Plant Diagnostic Clinic photo - Mutinus caninus, a common stinkhorn)

A yellow, foam-like growth has suddenly appeared in my mulched perennial bed. What is it and will it harm my plants? 

The growth in your perennial bed is probably a slime mold (It is sometimes referred to as dog vomit slime mold because of its yellow, bile-looking appearance). Slime molds are primitive fungal-like organisms. Slime molds feed on bacteria and other organisms in the mulch. They do not harm plants.

Slime molds are usually a temporary nuisance. Within a few days, slime molds typically dry up and turn into white, powdery masses. Most individuals simply let the slime molds dry up and fade away. However, the slime molds can be scooped up and discarded if you find them objectionable.

(ISU Plant Diagnostic Clinic photo - Slime mold on turf grass)

There are tiny, cup-like structures growing in a mulched area in my yard. What are they? Will they harm my plants?

The objects that resemble small cups or miniature bird’s nests are bird’s nest fungi. Bird’s nest fungi grow on decaying organic matter. The tiny fungi are only one-fourth inch in diameter. The nests (fungi) are commonly brown, gray or white and contain brown or white “eggs.” The “eggs” are spore-containing structures called periodioles. The eggs are splashed out of the nest by falling raindrops and adhere to nearby objects. The periodioles eventually dry, split open and release their spores.

Bird’s nest fungi are not harmful to plants. However, bird’s nest fungi can become a nuisance when the eggs stick to homes, cars and other objects as they are difficult to remove. Loosening the mulch with a rake (permitting the mulch to dry out) creates a less favorable environment for bird’s nest fungi and should reduce their numbers. Fungicides do not control bird’s nest fungi.