Symptoms and Signs
Fusarium causes a dry rot of infected tubers, although a moist rot may occur if secondary infection by soft rot bacteria is also involved. Initially, lesions appear as brown to black flecks on the tuber surface. Lesions later form large, hollow cavities. Frequently, the lesions appear wrinkled on the tuber surface with numerous white tufts of mycelium. Infected seed pieces may completely decay.
Comments on the Disease
Fusarium spp. are present in all soils and are found on the surface of all tubers. Wounds are required for infection. Fusarium cannot penetrate intact tuber skin, lenticels, or suberized (healed) seed pieces.
Management
Proper handling and curing is usually sufficient to give economic control of dry rot in storage. Allow tubers to mature before harvest and prevent damage to tubers during harvest and storage operations. Wound healing reduces infection by Fusarium; to speed the healing process, hold tubers at 50° to 55°F with good ventilation and a relative humidity of at least 95% for the first 2 to 3 weeks of storage.
Seed piece decay is reduced when seed pieces are planted under conditions that favor rapid suberization; Fusarium cannot infect cut surfaces after they are suberized. Warm the seed tubers to 50°F before cutting, and keep cutting and handling equipment disinfected. Plant when the soil temperature is at least 45°F and when soil moisture is 60 to 80% of field capacity. Plant seed with a pulp temperature warmer than the soil temperature. If possible, avoid irrigation before emergence. When planting conditions are likely to favor seed piece decay, treat cut seed pieces with a fungicide.
| Common name | Amount to Use | REI‡ | PHI‡ | |
|---|---|---|---|---|
| (Example trade name) | (hours) | (days) | ||
| Not all registered pesticides are listed. The following are ranked with the pesticides having the greatest IPM value listed first—the most effective and least likely to cause resistance are at the top of the table. When choosing a pesticide, consider information relating to the pesticide's properties and application timing, honey bees, and environmental impact. Always read the label of the product being used. | ||||
| SEED TREATMENT | ||||
| A. | FLUDIOXONIL | |||
| (Maxim PSP) | 0.5 lb/100 lb seed pieces | 12 | NA | |
| MODE OF ACTION GROUP NAME (NUMBER1): Phenylpyrrole (12) | ||||
| B. | FLUTOLANIL/MANCOZEB | |||
| (MonCoat MZ) | 0.75–1 lb/100 lb seed pieces | 24 | NA | |
| MODE OF ACTION GROUP NAME (NUMBER1): Succinate dehydrogenase inhibitors (7)/ dithiocarbamates and relatives (M3) | ||||
| POSTHARVEST - STORED POTATO TUBERS | ||||
| A. | AZOXYSTROBIN/FLUDIOXONIL/DIFENOCONAZOLE | |||
| (Stadium) | 1.0 fl oz/2,000 lb of tubers | NA | NA | |
| MODE OF ACTION GROUP NAME (NUMBER1): Quinone outside inhibitors (11)/ PhenylPyrroles (12)/ DeMethylation inhibitors (3) | ||||
| B. | PHOSPHITES | |||
| (Phostrol) | 0.1 gallon / ton of tubers/0.5 gal | 4 | NA | |
| MODE OF ACTION GROUP NAME (NUMBER1): Phosphonates (33) | ||||
| ‡ | Restricted entry interval (REI) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing. Preharvest interval (PHI) is the number of days from treatment to harvest. In some cases the REI exceeds the PHI. The longer of two intervals is the minimum time that must elapse before harvest. |
| 1 | Group numbers are assigned by the Fungicide Resistance Action Committee (FRAC) according to different modes of actions. Fungicides with a different group number are suitable to alternate in a resistance management program. In California, make no more than one application of fungicides with mode of action group numbers 1, 4, 9, 11, or 17 before rotating to a fungicide with a different mode of action group number; for fungicides with other group numbers, make no more than two consecutive applications before rotating to fungicide with a different mode of action group number. |
| NA | Not applicable |