Scientific Name

Phytophthora infestans

Overall Plant Symptoms

Gray to brown to black leaf scorch. Burnt appearance. Also can be seen on stems and fruit.

Leaf Symptoms

Tips to mid leaf with milky gray to brown collapse. Active infections have gray spores on underside.

Stem Symptoms

Stem sections milky brown to black, not in contact with soil. Confused with P. capsici which attacks stems near the soil.

Root and Fruit Symptoms

Fruit: brown, wrinkled leathery lesions.

Disease Source

In California, aerial spread of spores.

Source Peristence

Will flare up from old infections as conditions favor. Early season spread not understood in California.

Favoring Conditions

High free moisture or humidity and warm 70-85^o. Constant high humidity is the key to serious infections. Spreads very rapidly.

Critical Crop Time

Emergence to immediate pre- harvest. Devastating to yield prior to first color.

Controls/Management

Chlorothalonil, Quadris, Ridomil, Maneb or Mancozeb. (Tattoo Sect 18). Full plant coverage essential. No consistent curative treatments.

Additional Notes

Needs high humidity, VERY rapid disease spread.