Also known as Texas root rot, grape cotton root rot (grape phymatotrichum) is a nasty fungal disease affecting more than 2,300 plant species. These include:
- ornamental plants
- shade trees
Cotton root rot on grapevines is devastating for growers in Texas and much of the southwestern United States. The grape phymatotrichum fungus lives deep in the soil where it survives almost indefinitely. This type of root rot disease is extremely difficult to control, but the following information may help.
Grapes with Cotton Root Rot
Grape cotton root rot is active in the summer months when soil temperatures are at least 80 F. (27 C.) and air temperature exceeds 104 F. (40 C.), usually in the months of August and September. In these conditions, the fungus invades the vines through the roots and the plant dies because it is unable to take up water.
Early symptoms of cotton root rot on grapevines include slight yellowing and spotting of the leaves, which turn bronze and wilt very quickly. This usually happens within a couple of weeks from the first visible signs of disease. If you aren’t sure, pull a vine and look for fungal strands on the roots.
Additionally, you may see evidence of grape phymatotrichum fungus in the form of a tan or white colored spore mat on the soil around infected vines.
Controlling Grape Cotton Root Rot
Until recently, there were no effective treatments for control of the phymatotrichum fungus and planting disease-resistant vines was generally the first line of defense. However, various tactics such as the addition of organic matter to increase the soil’s ability to retain water and lowering the soil’s pH level to inhibit fungal growth have helped.
A New Treatment for Grapes with Cotton Root Rot
Fungicides haven’t been effective because the disease lives so deep within the soil. Researchers have developed a systemic fungicide, though, that shows promise for control of grapes with cotton root rot. A chemical product called flutriafol, may allow growers to successfully plant grapes in infected soil. It is applied between 30 and 60 days after bud break. Sometimes it is divided into two applications, with the second applied no closer than 45 days following the first.
Your local cooperative extension office can provide specifics regarding the availability of the product, brand names, and whether or not it is suitable in your area.