Possible Resistance Issues In Curcubit Downy Mildew

Pumpkins are really difficult to grow here because our disease and insect pressure is so strong at normal planting time. Here are some that have been flowering for a few weeks and first we saw flowers dropping. It turns out that these are male flowers with the long stems. It blooms for a day. The female flowers have shorter stems and come out usually a week after. With the heat this weekend, likely caused us to lose some flowers. For now, we need to watch for the female flowers and make sure those are not dropping. They have a 1-2 inch stem with a swollen base were pumpkin is forming.

We also have to be aggressive with disease prevention. Here is some early signs of downy mildew. There are some resistance concerns we need to be aware of with downy mildew in curcubits. Here is an update from Hunt Sanders, Disease Management Specialist in UGA Department of Plant Pathology:

“Based on what we are seeing in our cucumber trials this year, we may be experiencing some fungicide resistance problems in downy mildew of cucumber this fall.  Some plots that have been sprayed with a Ranman/ Zampro rotation have a great deal more downy mildew in them than we are used to.  We are using an older cucumber variety in these trials with no downy mildew resistance, but we still should not be seeing the level of disease severity in these plots that we are seeing.  The trial in question is an industry trial with different fungicide rotations which makes it hard to determine which product (Ranman or Zampro) might be experiencing a problem. We have initiated a follow up fungicide screening trial that will help clear up what we are currently seeing. Results from the screening trial should be available in 3-4 weeks.  Until that time all we know is that we are seeing increased levels of downy mildew in plots that were sprayed with a Ranman/Zampro rotation.  I have been in contact with Dr. Langston about current downy mildew recommendations and

Downy Mildew – Pumpkin

we both want to stress how important it is to tank-mix products that contain mancozeb or chlorothalonil with the products Ranman or Zampro.  In the current environment it is critical that your growers tank-mix these products.  If you have a grower that experiences an outbreak of downy mildew that he cannot control with the current fungicide recommendations please contact me and I will investigate the situation.”