Symptoms and Signs
Verticillium wilt becomes evident when lower leaves on the vine turn yellow and wither. Symptoms progress upward until the entire plant yellows and wilts. Vascular tissue of stems becomes a light brown, which is best observed near ground level. Some tubers from infected plants may develop a light brown discoloration in the vascular ring near the stem end. Wilt causes early senescence of plants in yield loss in heavily infested fields when susceptible varieties are grown.
Comments on the Disease
The fungus persists in soil for long periods. Infection is favored by cool weather and moist soil, but symptom development is favored by high temperatures since the disease interferes with water transport in the stems.
Careful variety selection is the key management tool for this disease. When resistant cultivars are chosen yield loss rarely occurs. Russet Norkotah is a very susceptible cultivar. Yield loss up to 25% can occur when choosing a susceptible variety.
Rotating out of potatoes and other susceptible crops can reduce inoculum and subsequent plant infection (the longer the rotation, the better, no less than 3 years). Crop rotation is not a curative disease management option because the host range of Verticillium is very wide and microsclerotium persist in the soil for a long time. Cereals, corn, and sorghum are good rotation crops. Avoid pepper, tomato, eggplant, and strawberry.
Treatment is rarely required for Verticillium wilt in California areas outside the Klamath Basin. In the Klamath Basin, where susceptible varieties are grown, fumigation with metam sodium can be cost effective, especially when inoculum levels are high. High levels of lesion nematode are known to exacerbate the disease and fumigation with 1,3-dichloropropene* has been shown to decrease disease severity when lesion nematode is present.
|Common name||Amount per acre||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.|
|(Vapam, Sectagon)||37.5–75 gal||See label||NA|
|(Telone II)||Label rates||See label||NA|
|COMMENTS: Does not target Verticillium wilt, but indirectly lessens its severity by reducing lesion nematodes, which can exacerbate the disease. Only use if lesion nematodes present along with Verticillium wilt.|
|‡||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.|
|*||Permit required from county agricultural commissioner for purchase or use.|
|§||Do not exceed the maximum rates allowed under the California Code of Regulations Restricted Materials Use Requirements, which may be lower than maximum label rates.|