What Kind of Mold Have I Grown When it Looks Fuzzy Like a Spider Web?

You may see white mold with long strands in your compost heap.


Leonid Karchevsky/iStock/Getty Images

In the garden, you usually notice molds when they're growing on a plant or in the soil. Most molds, or fungi, break down organic material, and they're necessary in recycling nutrients. Others can cause plant diseases, or can benefit plants by mutually beneficial relationships. Molds grow by means of hollow, threadlike structures called hyphae. The hyphae interweave and tangle into an often cobwebby mass, called a mycelium. Often these cobwebby growths are hidden, growing beneath the soil or in wood. Sometimes they're out where you can see them.

Cobweb Disease

A mold that can infect cultivated mushrooms, cobweb disease, forms spider web-type growth that covers mushroom fruiting bodies. Several types of fungus can cause this disease, including Dactylium dendroides. The first sign of infection is usually small, circular patches of mold on the mushroom-raising soil, which spread to the mushrooms. The gray cobwebby mycelia can change as they grow into a floury or powdery form. Low relative humidity and good air circulation discourage the growth of cobweb disease fungi.

Brown Patch Disease

Also called rhizoctonia blight, brown patch disease attacks cool-season lawn grasses. Small, brown patches form in lawns, and can enlarge to extensive brown areas. The fungi causing the disease live in the soil and invade the grass leaves and shoots in mild infections. If the disease progresses, the fungus also affects the roots. Look for the cobwebby mycelia at the edges of the brown lawn patches early in the morning; they disappear as the dew dries. Dethatching the lawn and making sure it's not overwatered can help get rid of the problem.

Dematophora Root Rot

If you've found white, cobwebby fungal growth in soil around pear (Pyrus communis) or apple (Malus domestica) tree roots, it's a possible sign of white root rot or dematophora root rot. The trees show symptoms of yellowing leaves, fewer and smaller leaves, and poor growth. There's no effective control for this disease, and you shouldn't replant apples or pears in infected soil. Pear grows in U.S. Department of Agriculture plant hardiness zones 4 through 9 and apple grows in USDA zones 3 through 8.

Other Cobwebby Fungi

A familiar type of cobwebby fungal growth is bread mold (Rhizopus stolonifer). If you store bread in a warm, dark, moist environment, it often develops bread mold after a few days. The fuzzy, webby-looking hyphae quickly cover the bread surface, with black, round fruiting bodies above the hyphae. Bread mold also infects a number of fruits and vegetables. Another example of a mold attacking ripe fruit, coprinus rot affects apple and pear fruit in the last month before they're picked. Coprinus rot forms white, cobwebby growth on the fruit surface.

About the Author

Carolyn Csanyi


Photo Credits

  • Leonid Karchevsky/iStock/Getty Images
bibliography-icon icon for annotation tool Cite this Article