P-092 - A reevaluation of chemical control options for the management of clubroot in broccoli

A recent clubroot outbreak in Virginia caused nearly 50% yield loss in broccoli, underscoring a need to reassess management strategies. Host resistance is often absent in locally adapted cultivars, so IPM approaches typically combine soil pH adjustments with fumigation or soil-applied fungicides. Chloropicrin fumigation at recommended rates can be costly, but the effectiveness of reduced rates is not well studied. While fungicide transplant drenches are standard for spring broccoli, fall crops are direct seeded, requiring different fungicide rates for banded applications. In 2024, two small plot field trials were established with a grower cooperator on 11 Apr (transplant drench fungicides) and 31 Jul (banded fungicides). A replicated strip trial with chloropicrin applied at 140, 112, and 84 kg/ha was established on 20 Mar and transplanted on 11 Apr. In spring, disease pressure was high in nontreated plots (100% incidence, 73.7 Disease Severity Index (DSI)). DSI values for plots treated with Omega, Elumin, and Ranman transplant drenches did not differ from the nontreated control. Blocker reduced the DSI by 27.8% compared to the nontreated control but did not improve marketable yield. In the strip trial, all chloropicrin treatments failed to reduce disease incidence and DSI compared the nontreated control. In the fall trial, disease pressure was lower (41.4% incidence, 14.5 DSI), but the banded fungicide treatments failed to control the disease. Preliminary results suggest limited effectiveness of current chemical control options for clubroot in broccoli.