Cause Albugo occidentalis, a fungus that is not uncommon on spinach but usually of minor importance. It also infects weedy species of Chenopodium. Warm days followed by cool, dew-forming nights favor disease.
Symptoms White pustules will develop on the lower, sometimes upper surface of infected leaves as well as on petioles, and the upper leaf surface will be yellowish.
Cultural control
- Bury infected host residue by deep-plowing.
- Do not plant spinach in consecutive years. Three-year rotations may be necessary.
- Control susceptible weeds.
Chemical control
- Actigard (Group P01) at 0.5 to 0.75 oz/A every 7- to 10-days controls disease by inducing host-resistance pathways. Do not apply within 7 days of harvest. 12-hr reentry.
- Badge SC (Group M1) at 1 to 2.25 pints/A on 7- to 10-day intervals. Preharvest interval is 0 days. 24-hr reentry for greenhouse use; 48-hr reentry for all other applications.
- Cueva (Group M1) at 0.5 to 2 gal/100 gal water on 7- to 10-day intervals. May be applied on the day of harvest. Poor control as a stand-alone product. 4-hr reentry. O
- Presidio (Group 43) at 3 to 4 fl oz/A on 10-day intervals in combination with another fungicide that has a different mode of action. Preharvest interval is 2 days. 12-hr reentry.
- Previsto (Group M1) at 0.75 to 2 quarts/A on 7- to 10-day intervals. 48-hr reentry. O
- Ridomil Gold Copper (Group 4 + M1) at 2 lb/A as 1 or 2 applications on a 14-day interval. Preharvest interval is 3 days. 48-hr reentry.