Field Identification
Actinobacteria that roughen tuber skin with corky pits and cracks—cosmetic havoc for market growers, soup-pot annoyance for everyone else. Infection spikes in dry soils with high pH, fresh manure, and lots of new root growth.
Superficial russeting to deep pitted lesions; pathogen survives in soil on crop debris. Related Streptomyces species cause similar symptoms; diagnosis in the field is pattern plus soil history, not a petri dish hobby.
How to Deal With It
Organic Control Methods
No reliable foliar cure; soil applications of competitive microbials (certain Bacillus and Streptomyces antagonist products) show variable trial results—read OMRI listings.
Green manures of mustard or sudangrass biofumigation can suppress inoculum when incorporated properly; maintain diverse rotations to build suppressive soil communities.
Keep soil pH near 5.2–5.5 for scab-sensitive varieties if crops allow; avoid fresh manure before potatoes; use scab-resistant cultivars; ensure consistent soil moisture during tuber initiation.
Increase organic matter to buffer moisture swings; avoid excessive tillage that leaves cloddy dry pockets around young tubers.
Use certified seed; lengthen rotation away from potatoes and beets; irrigate during knobby tuber formation in dry springs.
Let Nature Handle It
Natural Enemies
- Antagonistic Streptomyces spp.
- Competitive Bacillus spp.
Threat Map