Tuesday morning, a little after 7 in the morning, my little text notification sound went off. Was it one of my crew, telling me that the box truck was stuck in the mud again? No, it was the Cucurbit Downy Mildew alarm system, telling me that Downy Mildew had been found in Hunterdon County, NJ on butternut squash. 1% of the field was infected, and 0.1% of the leaf was infected. Every summer, Downy Mildew blows it’s way up from the south, riding on summer thunderstorms and coming to take down our squash and cucumber fields. It seems like every year there’s a new plant disease that comes out, and these diseases are one of our big challenges, particularly for organic growers who can’t resort to fungicides to “clean up” a problem once it starts. So what does the savvy organic farmer do? There are a number of tools in our toolbox. and we typically try to put them all to use. The first tool is resistant varieties. Our latest planting of summer squash is all varieties that are resistant to Powdery Mildew (one of the other diseases that has the potential to cut our squash season short). We also have some new varieties of cucumber that are resistant to Downy Mildew. They have extremely exciting names like “DMR 401” and “DMR 264,” and come from a farmer-led breeding program from Virginia called Commonwealth Seeds. Incidentally, the Organic Farming Research Foundation, on whose board I serve, just awarded Commonwealth Seeds a grant to extend that resistance to pickling cucumber varieties as well. That would be great, because I certainly don’t get around to making pickles until fall myself. Another tool is working on giving the plant everything it needs to grow healthy and strong and ward off disease. We are currently spraying on a cocktail of foliar nutrients and two different beneficial organisms (like probiotics for the leaf surface). Then we are alternating that with a spray of potassium bicarbonate (closely related to the sodium bicarbonate that most of us know as baking soda). I have never sprayed for powdery mildew before, but we had it show up early in our greenhouse cukes so I tried it this year, and it worked! It’s supposed to help with Downy Mildew, too. We will find out soon to what extent our strategies have worked. Yesterday at 10 AM, my text sound went off again: Downy Mildew was found in Franklin County, MA. 5% of the field was infected, and 5% of the leaf.
The dreaded Powdery Mildew on our squash
non-fat milk (1part milk to 10 parts water) sprayed onto the top & underside of leaves also works.