How to Manage Pests

UC Pest Management Guidelines

SYMPTOMS

Initially infected plants may be stunted. Outer leaves exhibit marginal and interveinal browning, followed by eventual collapse. Inner leaves remain green but are stunted and exhibit brownish black streaks or blotches. This last symptom sometimes helps to distinguish this disease from Phytophthora crown rot.

COMMENTS ON THE DISEASE

The fungus is not host-specific and infects many weed species and crops worldwide. It is especially destructive in semi-arid areas where soils are irrigated. Inoculum densities may be high following planting of susceptible crops. Disease severity is greater when high levels of nitrogen are used.

MANAGEMENT

Preplant fumigation is an important component of managing Verticillium wilt in strawberry fields. If fumigation is not desirable, select fields isolated from established growing areas, avoiding any fields with detectable levels of the pathogen or with a history of susceptible crops. Crop rotation with broccoli has been shown as an effective way to reduce Verticillium in the soil. Solarization of formed beds may be used to reduce pathogen levels in areas that get adequate amounts of sunshine and warm weather during summer months, although the usefulness of this technique for reducing Verticillium wilt in strawberries is unknown.

Cultural Control

If infested fields cannot be avoided and fumigation is not feasible, either solarize the soil or implement a crop rotation program. Cover crops of cereal rye or ryegrass can help to reduce soil levels of Verticillium. Use relatively tolerant strawberry cultivars when practical. Also, use drip irrigation and avoid excess amounts of nitrogen fertilizer.

Soil Solarization. In warmer areas of the state, solarization has been shown to be effective for the control of soilborne pathogens and weeds. Solarization is carried out after the beds are formed and can be effective if weather conditions are ideal (30-45 days of hot weather that promotes soil temperatures of at least 122°F). The effectiveness of solarization can be increased by solarizing after incorporating the residue of a cruciferous crop, in particular broccoli or mustards, into the soil or following an application of metam sodium (40 gal/acre). For more details on how to effectively solarize soil, see Soil Solarization: A Nonpesticidal Method for Controlling Diseases, Nematodes, and Weeds, UC ANR Publication 21377.

Crop Rotation. Rotating strawberries with broccoli can significantly reduce levels of the Verticillium pathogen in the soil and has been shown to be an economically viable option under moderate levels of Verticillium wilt disease pressure.

Organically Acceptable Methods

Select fields isolated from established growing areas. If fields have detectable levels of the pathogen or a history of susceptible crops, plan to solarize the soil, preferably after incorporating the crop residue from broccoli or mustards. Use drip irrigation and practice crop rotation with a nonsusceptible crop such as broccoli. Avoid high nitrogen fertilizers.

Monitoring and Treatment Decisions

If drip fumigation is planned, good results have been obtained with a sequential application of chloropicrin (200 lb/acre) or 1,3-dichloropropene/chloropicrin (300 lb/acre) followed 7 days later with metam sodium (45 gal/acre) or metam potassium (37 gal/acre).

More information on strawberry fungicides

• Treatment timing

PUBLICATION

UC IPM Pest Management Guidelines: Strawberry
UC ANR Publication 3468
Diseases
S. T. Koike, UC Cooperative Extension, Monterey Co.
W. D. Gubler, Plant Pathology, UC Davis
G. T. Browne, USDA Crops Pathology and Genetics, UC Davis

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