Pumpkin Fruit Blights & Rots and Their Management

Key Points

  • Rotate fields away from cucurbits for 2 or more years
  • Reduce pumpkin fruit contact with bare soil
  • Use a general fungicide program early in season
  • Use more specific fungicides based on field history and first signs of disease

As pumpkins size up and we approach harvest, pumpkin growers may notice a number of different diseases on fruit in fields. These diseases can be caused by true fungi or by fungus-like organisms. A good general practice to reduce all rots, blights, and spots shown here, is to rotate the field to grain crops for at least two seasons before going back in with any cucurbit. This will help reduce pathogen inoculum in the field, since grain crops are nonhosts for many of these pathogens.

Figure 1. Cottony leak. (Photo: Gerald. Holmes, California Polytechnic State University at San Luis Obispo, Bugwood.org)

Figure 1. Cottony leak. (Photo: Gerald. Holmes, California Polytechnic State University at San Luis Obispo, Bugwood.org)

Figure 2. Phytophthora fruit rot. (Photo: M. McGrath, Cornell University).

Figure 2. Phytophthora fruit rot. (Photo: M. McGrath, Cornell University).

In the current season, another general cultural practice that can reduce blights and rots is to reduce fruit contact with bare soil. Soil can harbor a number of pumpkin pathogens, and moisture held by the soil can increase disease. If crops are produced on black plastic, fruit may be moved up to the plastic to reduce soil contact. In no-till systems, ensuring an adequate crop residue layer can help distance pumpkins from soil.

As with powdery and downy mildews, being able to tell the difference between different kinds of fruit rots allows growers to make more effective fungicide choices. A general early-season fungicide program, which relies on weekly sprays with chlorothalonil or mancozeb with intermittent sprays of systemic products, may be found in ID-36, page 110. At first signs of the fruit rots in Figures 1, and 3 to 6, apply more specific fungicides in the FRAC groups indicated in Table 1. If entering a field known to have Phytophthora blight (Figure 2), specific fungicides should be applied preventatively.

Figure 3. Anthracnose. (Photo: Gerald. Holmes, California Polytechnic State University at San Luis Obispo, Bugwood.org)

Figure 3. Anthracnose. (Photo: Gerald. Holmes, California Polytechnic State University at San Luis Obispo, Bugwood.org)

Figure 4. Plectosporium blight. (Photo: M.A. Hansen, Virginia Tech)

Figure 4. Plectosporium blight. (Photo: M.A. Hansen, Virginia Tech, Bugwood.org)

Table 1. Pumpkin fruit diseases by pathogen type, with effective fungicides by FRAC group
True fungi Oomycetes Mucor
Anthracnose (M, M+11, M+22, 1, 3+9, 3+11, 7, 7+11, 9+12, 11, 11+27) Cottony leak (M, 4, 28) Choanephora fruit rot (M)
Plectosporium blight (M, 3+9, 3+11, 7+11, 11) Phytophthora fruit rot (M, 11+27, 21, 40, 43, 40+45)
Fusarium fruit rot (M)
Figure 5. Fusarium fruit rot. (Photo : Paul Bachi, UK)

Figure 5. Fusarium fruit rot. (Photo: Paul Bachi, UK, Bugwood.org)

Figure 6. Choanephora fruit rot. (Photo: Gerald. Holmes, California Polytechnic State University at San Luis Obispo, Bugwood.org)

Figure 6. Choanephora fruit rot. (Photo: Gerald Holmes, California Polytechnic State University at San Luis Obispo, Bugwood.org)

For Additional Information

  • Vegetable Production Guide for Commercial Growers (Vining Crops section, ID-36)
  • IPM Scouting Guide for Cucurbit Crops (ID-91)

 

By Emily Pfeufer, Extension Plant Pathologist

 

Posted in Vegetables
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