by Dr. R. M. Riedel

Anthracnose and Powdery Mildew commonly occur on pumpkins in Ohio. Gummy Stem Blight (Black Rot on fruit), Target Spot, Downy Mildew and Phytophthora Blight are less frequently found.

Basic Fungicide Program

Chemical control of pumpkin diseases is based on regular applications of broad spectrum fungicides such as:

1. chlorothalonil (for example, Bravo, Terranil),

or

2. maneb (for example, Maneb 80).

Chlorothalonil is generally considered to be more effective at controlling fungal diseases, although it is more expensive to use. Some markets may not accept produce treated with EBDC fungicides such as Maneb. Anthracnose is generally the first serious fungal disease to appear in Ohio. It may require applications of fungicides starting in Mid-July. Fungicide applications may be necessary on a 7 to 10 day schedule from mid-July until fruit is harvested.

Modifications of Basic Program for Specific Diseases

1. Powdery Mildew

To control Powdery Mildew, one of the following fungicides should be ADDED to chlorothalonil or Maneb:

1. Benlate,

or

2. Bayleton

Neither should be used alone since they do not give adequate control of other fungal diseases. Moreover, Powdery Mildew fungi occurring on pumpkin in Ohio rapidly become resistant to Bayleton when it is used alone. Powdery Mildew generally does not appear in Ohio before the last week of July or the first week of August. If Powdery Mildew development is severe, sprays may be required until harvest to protect handle quality.

More on Powdery Mildew

2. Downy Mildew

To control Downy Mildew, either:

1. SUBSTITUTE Ridomil/Bravo 81W for a scheduled chlorothalonil spray,

or

2. ADD Ridomil 2E to scheduled chlorothalonil spray.

Do not use Ridomil alone on aerial parts of the plant since it does not control other fungal diseases, and its use alone may give rise to Downy Mildew fungi resistant to the chemical. Downy Mildew affects only the foliage of the pumpkins. The disease occurs late, usually, and if pumpkins have already turned orange it may not be necessary to control the disease. Generally, only one or two sprays are required late in the growing season to prevent damage from Downy Mildew.

3. Phytophthora Blight

This disease occurs rapidly after flooding rains in hot weather if the soil is infested with the fungus. To adequately control this disease, pumpkins should never be planted immediately following other vine crops or peppers. Poorly drained soils should be avoided for pumpkin production.

If pumpkins must be produced in infested soil, Ridomil must be applied early in the season. Ridomil used after symptoms begin to develop will not adequately control the disease. If Ridomil/Bravo 81W is used routinely in the spray program, Phytophthora Blight should be less of a problem. However, this is an expensive control program and seasonal limits on Ridomil application may prevent use of the material during periods of maximum disease development.

Crop Rotation and Chemical Control

Crop rotation is vital to good pumpkin production with or without fungicide applications. If possible, fields should be rotated out of pumpkin or vine crops for at least two years. Pumpkins have fewer diseases when they follow grass crops such as field or sweet corn, or small grains. To be most effective, chemical control of fungal diseases must be used in conjunction with cultural controls. Moreover, many important soil borne diseases such as Fusarium Fruit Rot can only be controlled by crop rotation.