NOTES: For the disease control products listed below, one product trade name and formulation is provided for each active ingredient (common name) as an example of rates, preharvest interval (PHI), restricted entry interval (REI), and special instructions. In many cases, there are other products available with the same active ingredient. Please see Table 26 and Fungicides and Bactericides Alphabetically Listed by Trade Name for more information on products with the same active ingredients.
The symbol OG indicates a product is listed by the Organic Materials Review Institute (OMRI) as approved for use in organic production. See Organic Certification section for more details.
Prevention is essential for disease control in sweet potato. The most important diseases are root diseases which become systemic; once infected it is not possible to cure the plant. Vegetative propagation is an ideal vehicle for disease perpetuation. Start with healthy propagating stock and inspect frequently in the production cycle. Planting stock should be produced and stored separately from commercial sweet potatoes. Careful handling and proper curing at harvest are primary disease prevention measures. Application of fungicides and bactericides are not as effective as proper curing in controlling post-harvest diseases. Practice good sanitation of farm equipment, storage bins, and storage rooms.
Rhizoctonia Root Rot and Stem Canker
- azoxystrobin (Abound aka Quadris F): 0.4 to 0.8 fl oz/1000 row feet; PHI 14d, REI 4h, Group 11. Apply in-furrow or as banded applications over row. Rotate with a fungicide from a different FRAC Group. See label for rates and directions for postharvest rots.
- Bacillus subtilis strain QST 713 (MinuetOG):12.0 to 24.0 oz/A; PHI 0d, REI 4h, Group BM02. Soil application.
- laminarin (Vacciplant): 14.0 to 22.0 fl oz/A; PHI 0d, REI 4h, Group P04.
- Reynoutria sachalinensis extract (Regalia CGOG): See label for rates; PHI 0d, REI 4h, Group P05.
- Trichoderma harzianum strain T-22 [KRL-AG2] (Rootshield WP): See label for rates; REI 4h, Group BM02. For seed treatment and transplant and field production.
Black Rot (Ceratocystis fimbriata)
One of the most significant diseases of sweet potato, black rot is the common name for the decay of fleshy roots and symptoms on sprouts and vines. Successful control of black rot depends on selection of healthy seed roots, fungicide treatment, crop rotation, proper curing, and effective sanitation.
- thiabendazole (Mertect 340F): 107.0 fl oz/100 gal water or 8.0 fl oz/7.5 gal water; REI 12h, Group 1. Dip the seed roots in the suspension for 1-2 minutes and plant immediately. Do not use treated roots as food or feed. See label for additional information on postharvest treatment for black rot.
Soft Rot (Rhizopus spp.)
Careful handling and proper curing at harvest are primary disease prevention measures. Application of fungicides and bactericides are not as effective as proper curing in controlling postharvest diseases. Practice good sanitation of farm equipment, storage bins, and storage rooms.
- fludioxonil (Scholar SC): 16.0 to 32.0 fl oz/100 gal; Group 12. Postharvest dip/drench. See label for application methods. (Not for use in Maine).