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Managing Cucurbit Diseases | Farming News

by Atlanta Business Journal

One of the many things I enjoy about summer is fresh, local melons.

While crops shipped in from the South have improved in flavor over time, I still feel that local tastes best. I had my first local cantaloupe last week and look forward to more in the next few weeks.

But harvest season means disease season, and for growers it is important to manage diseases to achieve both maximum yield for you and maximum fruit quality for consumers like me.

Downy mildew has been reported in southern New Jersey and here in Lancaster County on cucumber. The strain of mildew that infects cucumber also will infect cantaloupe, so growers of these two crops should be applying downy mildew fungicides now.

In the past, I have observed that once downy mildew gets into a field, even with the best fungicides and a good spray schedule, you can never truly get ahead of the disease. Fortunately, we have several effective fungicides for downy mildew, so consult the Mid-Atlantic Commercial Vegetable Production Guide for a listing.

Be sure to rotate the chemistry of fungicides you apply to manage fungicide resistance, and follow disease reports to know when to start protecting other vine crops like squash and pumpkins.

Powdery mildew is the one disease that generally infects all vine crops that we grow locally every year. While this disease does not develop as quickly in the field as downy mildew, it will still spread throughout a crop and reduce fruit quality and yield.

Fungicide resistance has developed in recent years, so consult your supplier when purchasing fungicides to control powdery mildew. Reports that I have read indicate that resistance is not widespread (materials with widespread resistance are no longer recommended) but is more of a local or regional problem.

As a grower, you do not want to depend on a fungicide that might not be highly effective in controlling powdery mildew.

While almost all newer fungicides used for powdery mildew control are highly effective, a concern we have is that these chemicals are often what are known as single site of action materials, which means that it is easier for a disease to develop resistance against them than against other fungicides.

So, what is the best fungicide program for a grower to use to balance disease control and manage resistance?

Instead of using just two fungicides in rotation (A-B-A-B) use as many as your budget will allow. For example, in my research program I use four different modes of action (A-B-C-D), which gives me two advantages.

If one of my fungicides is less effective than the others, it is only used in my field about once per month, reducing the effect of reduced disease control.

The other advantage is, of course, resistance management since I am using four different modes of action. You should consider this type of rotation for downy mildew control as well.

You can also help with resistance management by including a protectant fungicide in the tank mix at each fungicide application.

In addition to helping with resistance management (protectants are generally multi-site mode of action), they also will help with controlling other disease that can occur in your vine crops. Be sure to the check labels to confirm that the material is labeled for use on your crop, and check the preharvest interval.

Finally, consider using one of the plant-resistance stimulating materials to potentially boost the plants’ own resistance to disease. Examples of this type of material are Regalia by Marrone and LifeGard by Certis (there are others).

While these materials are not standalone fungicides, they may help with disease management, particularly early in the season when disease pressure is relatively low.

In a recent Ohio State study looking at organic-certified materials for powdery mildew control in pumpkins, Regalia reduced the infection level of leaves treated and then exposed to mildew in an infected pumpkin field. While the study only followed mildew development for 10 days, the delay in leaf infection could be helpful in delaying the spread of mildew in your cucurbit field.

I always advise growers to use all tools available for disease management, starting with varietal resistance. The use of plant-resistance materials might be another useful early season tool for crop production.

Timothy Elkner is a Penn State Extension fruit and vegetable educator based in Lancaster County, Pennsylvania.

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