Rhizoctonia
Gary W. Moorman, Professor of Plant Pathology
The pathogenic fungus, Rhizoctonia, is known to cause root rots, stem rots, damping-off and, in some cases, a blight of leaves. It is a soil-borne fungus favored by warm, moderately moist soil conditions. The fungus is able to persist in the soil as hyphae, sclerotia, and basidiospores. Once the fungus begins to grow in the plant the infected areas decay quickly, causing brown to reddish brown lesions to form at or just below the soil-line. If conditions remain favorable for disease development, the lesions will enlarge, forming dry sunken cankers which may eventually girdle the plant. The young hyphae are colorless but turn brown with age. Soil particles often cling to the cankered areas of the plant when removed from the soil because of the coarse, brown mycelium. Leaves touching the soil can be infected. The fungus will web to neighboring leaves quickly under high humidity conditions and will rot leaves quickly. Under magnification, hyphal branches are at 90 degree angles to the parent hypha and there is a cross-wall and a constriction of the cell at the base of each branch.
Symptoms
- Plants wilt during midday
- Stems rot at soil line with brown to reddish brown lesions
Conditions Favoring Rhizoctonia Growth
- Warm soil temperatures, 12 to 32C (70 to 90F)
- Even, moderate soil moisture (65% soil saturation) unless plant is injured, then higher soil moisture favors growth
Control
- Proper soil pasteurization eliminated Rhizoctonia from the potting mix.
- Encourage prompt growth (older plants are more resistant)
- Fungicides: Be certain the crop to be treated is listed on the fungicide label.
- captan* can be incorporated in the soil before planting to prevent damping-off.
- iprodione (Chipco 26019*), thiophanate methyl (Clearys 3336* or Domain FL*) or copper (Phyton 27*) can used as a heavy spray at the base of the plants or as a drench.
- PCNB (Terraclor*) can be incorporated in the soil before planting or used as a drench.
- chlorothalonil (Daconil 2787*) treatments should begin at transplant.
- thiophanate methyl + etridiazole (Banrot*), triflumizole (Terraguard*) or fludioxonil (Medallion*) can be applied as soil drenches.
*Trade name
Active Ingredients and Trade Names of the Chemicals
| FRAC Group No. | Risk Level | Class | Acive ingredient | REI Restricted Entry Interval | Trade names (EPA Reg. no.) |
|---|---|---|---|---|---|
| 1 | 3 | Benzimidazole | thiophanate methyl | 12 | 3336 (1001-69), OHP 6672 (51036-329-59807), Fungo Flo (51036-329-59807) Systec 1998 (48234-12) |
| 2 | 3 | Dicarboximide | iprodione | 12 | Chipco 26GT (100-1138), Chipco 26019 (264-481), Iprodione (51036-361), Sextant (51036-361-59807) |
| 12 | 2 | Phenylpyrol | fludioxonil | 12 | Medallion (100-769) |
| 14 | 1 | Aromatic hydrocarbon | PCNB | 12 | Revere (400-407-10404), Blocker (5481-211), Terraclor (400-399), Defend (5481-444-1001) |
| M | 1 | Copper, complex | copper sulfate | 12 | Phyton 27 (49538-3) |
| Combined 1 products | |||||
| 1 + M | Thiophanate methyl + etridiazole | Banrot (58185-10) | |||
Rhizoctonia hypha with right-angle branching Rhizoctonia webbing on infected poinsettia stem and roots.
cross-wall near base of branch.
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Issued in furtherance of Cooperative Extension work, Acts of Congress, May 8 and June 30, 1914, in cooperation with the U. S. Department of Penn State College of Agricultural Sciences research and extension programs are funded in part by Pennsylvania counties, the Commonwealth of Pennsylvania, and the U.S. Department of Agriculture.
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