Downy Mildew Variety Trials at Twin Oaks Seed Farm

Reader Contribution by Edmund Frost

Seed harvest season is starting. Today was our first 2014 harvest of tomatoes and watermelon for seed. Things will start slowly, and by about the second week of August we will be swamped with tomatoes, muskmelons, watermelons and cucumbers.

I’ve been growing seeds at Twin Oaks for six years now, and have a pretty good idea of what to expect out of the harvest season, which for us runs from early August to late October.

This year though we have added a major new focus to our operation: variety trials, and lots of them. Last November I applied for a SARE grant to trial cucumber, muskmelon and winter squash, with a focus on Cucurbit Downy Mildew resistance, and we got the grant. We grow a lot of cucurbit family crops, and Downy Mildew has been the #1 problem we’ve encountered. This was especially true in 2013, when DM showed up on our farm in June. Downy Mildew overwinters in Florida, and blows north on the wind each year, thriving when the weather is wet. It starts with yellow spots on the leaves. The spots grow and turn brown and the leaf dies. DM can easily defoliate an entire field of a susceptible variety of cucumber, muskmelon, squash or gourds. Most commonly grown varieties are susceptible to current strains of DM. Our smaller observation trials in 2013 found that only a few varieties out of 35 muskmelons and 35 cucumbers were able to produce a crop under heavy DM pressure. Read more about Downy Mildew and about our 2013 trials here.

Our Winter Squash Trial (on July 22nd 2014):

If you live on the eastern US (especially the Southeast and Mid Atlantic) or in the eastern part of the Midwest, Downy Mildew is likely a significant problem for your cucumber, muskmelon and squash crops, at least in a high pressure year. If you live elsewhere in the US, Downy Mildew may be of academic interest but is probably not directly relevant to your garden.

So heres what we’re doing. This winter I did a lot of research on potentially Downy Mildew resistant varieties. I chose 45 winter squash, 35 muskmelon and 55 cucumber varieties to include in our trials. We planted late, because some years Downy Mildew doesn’t arrive here until August.

Most of the entries in these trials are replicated, which means we plant each variety in several places throughout the field. If the trial is successful this will provide results that can be statistically verified and can’t be attributed to natural variation of the field. We will be observing Downy Mildew on the leaves, and evaluating fruit quality and productivity (which DM can strongly impact if pressure is high). We hope to find varieties that have high DM resistance and high quality fruits. We also hope to find varieties that can be used in breeding projects.

Variety trials are an essential part of quality seed systems. We need to know how different varieties and seedstocks perform in relation to each other in order to do further work with them. Variety trials are the basis by which we can recommend or choose to work with one variety over another. It is important that this kind of evaluation be done on a regional and local basis. Organic Seed Alliance has an excellent publication about how to set up on-farm variety trials.

We planted the cucumbers on July 12th, the muskmelons on June 28th, the winter squash on June 10th and the tropical pumpkins (long season winter squash) on May 20th. We’ve been busy cultivating and hoeing, setting up irrigation, training the winter squash vines (different entries shouldn’t grow into each other),and checking on what the first winter squash fruits look like.

The winter squash trial especially, which has the biggest plants, looks really good. Its going to be a job to keep the varieties separated, even at 12 foot row spacing. I’m hoping that many of the entries will soon start looking a lot less good soon! and that the Downy Mildew will finally get here (I’ve been regularly checking the Downy Mildew forecast website). Variety trials can make you think opposite from most growers.

Stay tuned for the results! There will be preliminary results by September, and final or near-final results in November. Reports and updates will be available on our website, and I will post updates on this blog as well.

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