Mustard Seed Fungus

About Mustard Seed Fungus

• Soil-borne Sclerotium rolfsii fungi causes the mustard seed fungus disease, and the environmental conditions have got to be just right for infections to occur. The fungi requires moist, acidic soils with an abundance of decomposing plant litter and air temperatures of 88 and 95 degrees Fahrenheit. This disease most commonly occurs in the warm, humid southern states, but can also appear in cooler areas during stretches of moist, warm weather. The sclerotia typically live in the top 2 to 3 inches of soil. Their thick, hard coverings allow them to survive for at least two years without a plant host. The fungal pathogens primarily spread through splashing water and contaminated gardening tools.

Disease Symptoms

• The mustard seed fungus attacks plants at or just beneath the soil line. The fungi girdle the stems and gradually cut off water flow, causing the infected plants to rot at their bases. This results in the lower leaves turning progressively yellow and dying from the end of the tips down. Affected plants might experience sudden wilting, stem collapse or even death. If you look closely at the stem near the soil line, you'll spot an abundance of white, cottony fungal growth. If left unchecked, this growth spreads up stems and across soil or mulch to infect nearby plants or organic debris.

Preventing Mustard Seed Fungus

• Because the mustard seed fungus is so difficult to control, prevention is your best strategy. Keeping the soil around plant bases free of weeds and leaf litter leaves the fungi little to feed upon. Using black plastic mulch helps prevent mustard seed fungus from taking hold by increasing soil temperatures, controlling weeds and preventing the pathogens from reaching and feeding on decomposing organic matter in the soil. Dense canopies promote moisture, which increases the incidence of this fungal disease. Increasing the space between plants and thinning out thick foliage helps keep mustard seed fungus infections at bay by allowing the foliage to dry more quickly.

Controlling Mustard Seed Fungus

• The only fungicides that can effectively treat mustard seed fungus are available only for commercial use, but home gardeners following a few cultural practices can help stop the spread of this disease once it occurs. Promptly remove and discard all problem plants along with fungal-infected soil and any plant litter within about a 6-inch diameter of the infected vegetation. Because the fungus needs oxygen to develop properly, burying affected plant tissue 6 to 12 inches deep can kill the pathogens. Plow under any remaining crop litter after your last harvest, but don't cultivate the soil located between plants or rows after planting.