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 No chemicals are registered specifically to control this disease on hop. Ridomil as a crown drench for early-season downy mildew control has been reported also to control Phytophthora root rot. Other registered downy mildew fungicides will not be effective against this disease.