Field Identification
The oomycete that helped rewrite Irish history—still demolishes tomatoes and potatoes when cool nights, warm days, and leaf wetness align. Water-soaked spots turn brown from the edges inward; white sporulation shows on leaf undersides in humid mornings.
Fuzzy pathogen growth on abaxial surfaces; stems show dark lesions; fruit and tubers rot firm then fuzzy secondary chaos. Spores blow miles on storms, so your neighbor’s neglect becomes your emergency.
How to Deal With It
Organic Control Methods
Copper fungicides on a tight protectant schedule; some regions allow additional biologicals—reapply after rain. No organic silver bullet once epidemics explode; removal beats denial.
Compost teas and microbial antagonists are backup singers only; hyperparasites exist in soil but do not rescue foliage under invasion pressure.
Choose resistant cultivars where available; widen row spacing; trellis tomatoes for airflow; avoid overhead water; destroy infected plants in sealed bags—not the compost pile.
Upland tomatoes under high tunnels with leaf dryness protocols; rogue hot spots immediately.
Use certified seed potatoes; eliminate cull piles and volunteer solanums; track regional disease maps and start copper before wet spells if history is bad.
Let Nature Handle It
Natural Enemies
- Hyperparasitic Fungi (soil-borne, limited foliar effect)
- Competitive Microbes in Mulch Systems
Threat Map