Last month, as I was thinking about what topic I planned to write about this month, I decided on downy mildew since it often shows up in the area sometime in July.
However, downy mildew was confirmed on cucumber in Lancaster County at the end of June and has already been reported on cucumber and cantaloupe in New Jersey as well as on cucumber in Maryland and Delaware.
So instead of writing about watching for this disease, I will jump right into management.
There are several pathotypes, or groups, of downy mildew that affect cucurbits, or vine crops.
The first pathotype affects cucumbers and cantaloupe. The second affects cucumbers and cantaloupe as well as the other vine crops, including watermelon, pumpkin and squash.
Knowing which pathotype is present in your area is important because it determines the need for preventive fungicide applications on your crops.
Now that we have a confirmed case of downy mildew on cucumber in Lancaster County, cucumber and cantaloupe growers in Lancaster and surrounding counties should start making fungicide applications.
If you are growing one of the other vine crops such as pumpkin or watermelon, you do not need to include any downy mildew specific fungicides in your protective program since those crops are not at risk yet.
Continue to watch for notifications that downy mildew has been found on one of these crops in our area before you spend money on downy mildew fungicides.
A listing of fungicides that control downy mildew can be found in the 2020-2021 Mid-Atlantic Commercial Vegetable Production Recommendations.
The most effective materials are listed first; be sure to use products with at least two different modes of action to help manage disease resistance.
Downy Mildew 101
A few more notes on downy mildew.
First, it is easier to prevent an infection of this disease than to clean up an infected field, so be sure to start protective fungicide applications when needed.
Second, be sure that you have properly identified the disease present on your vine crop so that you are using the correct fungicide to control it. Protectant fungicides will give limited control of a variety of diseases, but the better materials are often specific for a certain disease.
Review the appearance of the diseases you are most likely to find on your crops so that you can tell what you have in your field, and select the most appropriate fungicides to use.
Downy mildew is characterized by an angular appearance on a leaf, and you can find purplish spores on the undersides of the leaves when the humidity is high, such as early in the morning.
Angular leaf spot also causes wedgelike lesions on the leaves, but there will not be any spore production on the underside of the leaves because this disease is caused by bacteria.
Different sprays are needed to control these diseases, so it is important to be able to distinguish between them.
