Greenhouse and Nursery - Web Blight

The following is an article on web blight, a Rhizoctonia disease of ornamental plants, from the Univeristy of Maryland.

Rhizoctonia Web Blight

This fungus has a very wide host range, causing disease on many crops, vegetables, ornamentals and even on turf-grasses. Moist conditions favor this disease- try to space susceptible crops so that the foliage dries after rains or irrigation. When the weather is hot and humid and night temperatures do not fall below 68° F, Rhizoctonia is happy and most vigorous. Rhizoctonia can cause root rot and stem cankers, but when it is growing on the aerial plant parts, and causing extensive aerial blight, it is called “web blight”. To diagnose, we examine the tissues and find the distinctive mycelium of Rhizoctonia. Look for fine, wispy, tan mycelium (especially in early morning before dew has dried) that is causing above ground plant parts to “melt down” and that sticks the dying plant parts together.

Management: Many fungicides are registered to control Rhizoctonia. These include (but are not limited to) Banrot, Chipco 26 GT, Cleary’s 3336, Compass, Heritage, Junction, Medallion, Protect T/O, Terraguard, and Terraclor.

Extracted from the March 21, 2008 edition of the "Greenhouse TPM/IPM Weekly Report" from the University of Maryland Cooperative Extension http://www.ipmnet.umd.edu/08Mar21G.pdf