Cause A fungus-like microorganism, Phytophthora citricola, that survives in soil by long-lived oospores. It also may survive in infected plant parts but not in dead tissue except as oospores. The disease requires abnormally wet soils and is most often observed in areas of fields with soil or irrigation conditions that cause water to pool. The disease, normally restricted to certain areas of a field due to past rill irrigation and soil conditions, may become more generally distributed within a given field with more extensive use of drip irrigation.
Symptoms Aboveground symptoms include bine decline and wilt. Bine and root system tissue is blackened and soft-rotted.
Cultural control Avoiding practices or conditions that lead to pooling water normally is a good control practice.
Chemical control Few chemicals are registered specifically to control this disease on hop.
- Orondis Gold (Group 49 + 4) at 20 to 36 fl oz/A as a soil application at planting or as soon as plants begin to grow in established fields. Preharvest interval is 45 days. 48-hr reentry.
- Ridomil Gold SL as a crown drench for early-season downy mildew control has been reported also to control this root rot. Although this disease is not on the label, the material can be applied to hop in Oregon for black root rot. 48-hr reentry.
Biological control
- Bexfond at 7 to 14 fl oz/A for soil applications via drenches, in-furrow applications, drip irrigation, or sprays, followed by irrigation, reapply on 4-week intervals. 4-hr reentry. O