Reduced Fungicide Applications and Host Resistance for Managing Three Diseases in Pumpkin Grown on a No-Till Cover Crop.

Two recent changes in Maryland pumpkin production are (i) planting no-till into a cover crop with soil surface residue (70% of acreage) and (ii) adoption of cultivars with moderate resistance to powdery mildew. Pumpkin cultivar resistance to powdery mildew, planting method (no-till cover crop or conventional tillage bare ground), and fungicide schedules were examined for development of powdery mildew (caused primarily by Podosphaera xanthii), Plectosporium blight (Plectosporium tabacinum), and black rot (Didymella bryoniae), and pumpkin yield and quality. Fungicide application intervals were (i) nontreated, (ii) 7 days, (iii) 14 days, or (iv) 7 days early and 14 days late season. Pumpkin grown no-till on hairy vetch and hairy vetch plus rye cover crops had an average 36% less Plectosporium blight and 50% less black rot than those grown conventional tillage on bare ground. Powdery mildew was less severe on cv. Magic Lantern, which is moderately resistant to this disease, than on susceptible cv. Wizard. Regression equations to describe the impact of disease and treatment on pumpkin fruit number, weight, and peduncle quality (healthy, intact peduncles) were developed using three-stage least squares procedure. Powdery mildew caused the greatest reduction on fruit number, weight, and peduncle quality compared with other diseases. Plectosporium blight reduced fruit number in 1999 and 2000, and fruit weight and peduncle quality in 2000. Hairy vetch and hairy vetch plus rye cover crops resulted in greater fruit number (1,033 and 858 more marketable fruit/ha, respectively) than bare ground in 2000. Powdery mildew resistance (Magic Lantern) combined with pumpkin production on a cover crop resulted in lower levels of powdery mildew (average areas under the disease progress curve 1,474 versus 2,379), Plectosporium blight (average 5 versus 16% severity), and black rot (average 153 versus 217 symptomatic fruit/ha) compared with conventional production (Wizard on bare ground). A reduced fungicide schedule resulted in acceptable disease management, yield, and peduncle quality of Magic Lantern grown on a cover crop; Magic Lantern grown on a cover crop and sprayed every 14 days yielded the same as or more than Wizard grown on bare ground and sprayed weekly.