Pumpkin Spray Program 2012

Kate Everts, Vegetable Pathologist, University of Delaware and University of Maryland; keverts@umd.edu

I frequently am asked for a “good” spray program for pumpkins. This is always difficult because a spray program depends on field history (i.e. has Phytophthora crown rot occurred in the field), production practices (no-till vs. bare ground), and the grower’s philosophy about control (Cadillac treatment program vs. minimal inputs).

Preventative practices are more effective than trying to minimize the damage from a disease after it occurs. Practices such as growing pumpkin on a no-till cover crop and using a powdery mildew tolerant cultivar will allow growers to stretch their spray interval.

Powdery mildew is the most common disease – it will damage leaves and the pumpkin “handles”. Downy mildew is an extremely damaging disease, however it does not overwinter here and sprays for downy mildew should only be applied when it is present in the Mid-Atlantic. Other diseases that occur, such as Bacterial wilt or virus diseases need to be treated by managing the vectors.

Keep the following in mind:
● Know what diseases are the most common on your farm. Previous problems with black rot, Phytophthora blight, anthracnose, scab or other diseases may indicate that these diseases are likely to be problems again.

● Begin spraying when vines begin to run.

● Use a protectant such as chlorothalonil every time (don’t worry about resistance developing).

● Spray every 7 to 14 days.

● The most common disease in our area is powdery mildew. However it is not always present early in the season. Scout 50 old leaves in your field for powdery mildew lesions. If powdery mildew is present in the field, apply materials that are targeted for it. If it is not present, spray with a protectant, then scout again before your next spray and adjust the spray accordingly.

● Familiarize yourself with the extension publication “Commercial Vegetable Production Recommendations” section on pumpkins. Fungicides included in the “Recommendations” have been tested and performed well in the Mid-Atlantic region.

● A good fungicide spray program will increase yields and improve quality. The single best way to improve handle quality is to control foliar and fruit diseases with fungicides.

The program:
The best way to save money on your spray program is to start with a protectant program such as either chlorothalonil plus copper or mancozeb plus copper. Add targeted products to your protectant program based on what diseases are in the area or known to be on the farm (downy mildew, powdery mildew, Phytophthora crown and fruit rot, etc.)

Powdery Mildew: The following are targeted for powdery mildew and have been tested in our region. Apply them with a protectant. Select two that are in a different FRAC code groups, and alternate them.

Downy Mildew: Management of downy mildew should use the following products tested in our area. Select two that are in different FRAC code groups, and alternate them.

Plectosporium can be managed with applications of Quadris Top, Cabrio or Flint.

Phytophthora crown and fruit rot needs to be managed intensively. In fields with potential problems, apply Mefenoxam (Ridomil Gold or Ultra Flourish) pre-plant for early season control. Once the canopy closes, subsoil between the rows to allow for faster drainage following rainfall. Fungicide applications will only suppress Phytophthora, and reduce spread.

When conditions favor Phytophthora crown and fruit rot development, tank mix one of the following fungicides with fixed copper:
Revus (FRAC code 40), Ranman (FRAC code 21), Presidio (FRAC code 43), Forum (FRAC code 40), or Tanos (FRAC code 11 + 27).