December 12th

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Fungicide control of powdery mildew of jack-o-lantern pumpkin in Illinois, 2003.

Powdery mildew, caused by the fungus Sphaerotheca fuliginea, is an important disease of pumpkin in Illinois and worldwide. This disease can result in serious yield losses. Powdery mildew is diagnosed by white, powdery mold on plant tissues. The disease first appears on lower stems and petioles (Figure 1). As the disease continues to develop, the white, moldy spots occur on the underside of leaves (Figure 2). Symptoms on the upper leaf surfaces (Figure 3) usually signal an outbreak.

Powdery mildew can be managed effectively by planting resistant cultivars and application of fungicides. Resistance in the plants is usually partial and may require additional complementary control practices. Fungicide application is a common control practice of powdery mildew of cucurbit crops.

A field experiment was conducted at the University of Illinois Vegetable Research Farm near Champaign, IL. Fertilizers, 115 lb nitrogen, 101 lb phosphorus, and 120 lb potassium, per acre, were broadcast and incorporated on 27 Mar. Seeds were sown 18-inch apart in single-row plots, 25 ft long. The plots were spaced 40 ft apart in a randomized complete block design with three replications. Twelve fungicides, including Acrobat 50WP, AgriFos 400FL, Bravo Ultrex 82.5WG, Cabrio 20EG, Cuprofix Disperss 36.9, Cuprofix Disperss 80, Flint 50WG, Nova 40W, Phostrol 53.6SC, Pristine 38 WG, Procure 50WS, and Quadris 2.08SC, in 16 different combinations (treatments), were spray applied onto plants. Application of fungicides began on 21 July and continued (at 7-day intervals) until 22 September. Fungicides were applied with a backpack sprayer, using 50 gal of water per acre. Severity of powdery mildew (percentage of total area of vines and leaves infected) was visually evaluated weekly from 8 August to 26 September. Disease severity was assessed at four locations (43 sq ft each) in each plot, and at the same locations, throughout the season (a total of seven evaluations). Area under disease progress curve (AUDPC) for each treatment was calculated.

Powdery mildew was first observed on 12 July and its severity increased as the season progressed. Overall, severity of the disease was significantly higher in unsprayed plots than the sprayed plots. Cabrio, Flint, Nova, Pristine, Procure, and Quadris, applied in combination with other fungicides, provided excellent protection of plants against powdery mildew. However, Procure applied alone on biweekly intervals, did not provide adequate protection against powdery mildew. Best control of powdery mildew was achieved with treatments that included Pristine.