How to Manage Pests

UC Pest Management Guidelines

SYMPTOMS

Purple spot is of major concern when new spears are emerging and being harvested. The pathogen produces elliptical, slightly sunken lesions 0.03 to 0.06 inch across and up to 0.125 inch long. Initially lesions are reddish-purple and later develop a tan-brown center, especially if the lesion is large. Lesions usually appear on the lower half of new spears and are very superficial. The internal tissue of the spear is not affected.

COMMENTS ON THE DISEASE

Purple spot is worse following cool, wet weather during spear emergence. The disease is usually most intense where debris from the previous year's fern growth is lying on the soil surface. The sexual stage, Pleospora allii, develops on this debris. Wounding of the spear is not necessary for infection; however, wounds created by blowing sand can increase the incidence of disease.

Once dry weather conditions develop, the disease subsides.

MANAGEMENT

Good field sanitation is important in managing purple spot and other diseases. Last season's fern growth, which is the primary inoculum source, should be burned, chopped and incorporated, or removed from the field before new spears emerge. Chemical treatments are not recommended in California for this disease.

Organically Acceptable Methods
Good field sanitation is acceptable for use in an organically certified crop.

PUBLICATION

UC IPM Pest Management Guidelines: Asparagus
UC ANR Publication 3435
Diseases
R. M. Davis, Plant Pathology, UC Davis
B. J. Aegerter, UC Cooperative Extension, San Joaquin County
Acknowledgment for contributions to Diseases:
R. J. Mullen, UC Cooperative Extension, San Joaquin County
F. F. Laemmlen, UC Cooperative Extension, Santa Barbara County

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