build a better melon, cuke, squash? cucurbit downy mildew research at twin oaks seed farm

Training Vines in Winter Squash TrialEVER WONDER what goes into building a better strain of seed, one that can resist pests and diseases? Edmund Frost of Twin Oaks Seed Farm in Virginia has spent the last two growing seasons looking for insights on how eventually to build a better Cucurbit– pumpkins and squash, melons, or cucumbers–in the face of downy mildew and striped cucumber beetles.

All growing season, I get questions asking how to prevent, or cure, one vegetable garden disease or pest or another–especially on Cucurbits.  My answers are mostly not perfect ones, because almost faster than we figure out some effective tactic, plant diseases can outsmart us by mutating, or getting an edge from dramatically changing weather patterns–or by moving into regions where they were not previously known.

So what can be done, longterm, beyond trying to “fix” the one outbreak in just your, or my, backyard, and especially: What’s the bigger answer without turning to chemicals?

The answer hopefully lies in research: research that identifies the best current varieties, and often leads to breeding of more disease-resistant and regionally adapted varieties, using the best genetic traits from the research to strengthen future generations.

I thought it would interesting as an example to go behind the scenes of one such research project, and see what goes into the beginnings of building better organically produced seed for our farms and gardens–in this case the Cucurbit project at Twin Oaks.

Twin Oaks Community is a nearly 50-year-old intentional community and home to 100 people—the nation’s oldest secular income-sharing community. A number of businesses, from tofu-making to hammock-building to Twin Oaks Seed Farm, which grows for a half-dozen familiar retail seed companies, including Southern Exposure, Fedco, Seed Savers, Sow True, and Baker Creek, are its shared economic pulse.

With help from Cornell University, the Organic Seed Alliance, plus Southern Exposure Seed Exchange and Sow True Seed, along with a recent grant from the sustainable agriculture arm of the USDA, Edmund and crew have been pushing Cucurbits to the limits, and beyond–looking at downy-mildew resistance and striped cucumber beetle resistance, as well as taste, sweetness and productivity.

Melon Trial Evaluation Edmund FrostEdmund (above left, in the field) joined me on the radio  to talk about how the research works, what varieties have promise so far, and where he imagines some of the building blocks of that better Cucurbit may come from long term. The transcript of our Oct. 6. 2014 conversation:

a cucurbit downy mildew q&a with edmund frost

Q. Now, I know growing seeds is not a “get rich quick” scheme, or some overnight thing—it requires years of commitment, and passion. Tell us what drew you to seed farming.

A.  I had been involved in organic farming, and I was also involved in activism, and especially anti-GMO activism–looking at the corporations that are really trying to control the whole of our seed supply. After organizing conferences and marches, I was wanting to do something more hand-on. To basically start doing the work of creating and sustaining alternatives. That’s how I got started in seed farming.

Q.  At Twin Oaks you work with open-pollinated crops, meaning non-hybrid varieties, and especially pumpkins, melons and cucumbers—and you produce them organically, yes? 

A. Yes, on about 4 acres of seed crops and 2 acres of cover crops in the rotation.

cucurbit downy mildewQ. The phrase “downy mildew” has been in the news for gardeners, with specific strains in basil, for instance, and impatiens–and yes, especially Cucurbits.  Those are not one disease, but different species of organisms, all fungus-like if not technically fungi. In squash and its relatives, what does Cucurbit downy mildew do?

A. Cucurbit downy mildew can basically defoliate a plant. It starts with light brown spots on the leaves—or even spots on the leaves that are just a lighter color than the rest of the leaf. And then they turn into brown spots, and once you have a number of them, after a few days, it can kill the whole leaf. I have seen crops where downy mildew showed up, and the crop was mostly dead within a week.

Q. Where is downy mildew experienced? Up North, I was always more familiar with powdery mildew, but not downy until more recent years–or at least not till very late in the season, when it really didn’t matter, because the harvest was nearly mature. But now, I do get it, and earlier.  How does the disease get around to different areas?

A. Downy mildew can’t survive the winter, or freezing temperatures. It overwinters in warm areas—for us that’s the South of Florida—and every year when it gets warm, the spores blow up North on the wind. They’ll make it all the way up to New England and the Upper Midwest. But this disease is basically unheard of in the Western two-thirds of the country; it’s mostly an Eastern phenomenon. It’s widespread in other areas of the world as well.

downy mildew map ipm pipeQ. I was interested to see that downy mildew has become such an issue that there is even an interactive realtime map called Cucurbit Downy Mildew IPM PIPE, administered by North Carolina State University, where people report their outbreaks.

I was not surprised to see big clusters in the mid-Atlantic, but there were reports in Texas, way up in Wisconsin, and reports that came in as early as June in places like Ohio. As our weather patterns change, the spores can move around to new places—like on hurricane aftermath.

A. Yes.

Q. As if 36 cucumber varieties and 38 muskmelons from your first year of trials, in 2013, wasn’t enough–you sought out more genetics in 2014, yes? You really expanded—so tell us about the 2014 trials.

A. Last fall I applied for funding from the UDSA, a grant program called SARE, and my goal was to do something like I had done last year, but to replicate it. What that means is to have three different entries of each variety in the trial. That gives you results that you can do statistical analysis on, and make them more verifiable and therefore more people are interested in looking at them.

Q. Does that mean three different plants of each variety, or three different blocks of plants of each variety, spread around the acreage?

A. Three different blocks of plants, and it is randomized where those blocks will be. In our trial, each block has five plants.

Q. How else did the 2014 research expand and evolve?

A. I also wanted to build on what we did last year. We had very dramatic results, and there was a small handful of varieties that were able to grow and produce well in high-pressure downy mildew conditions. Most of them weren’t, in both melons and cucumbers.

This year I wanted to verify that, and also look for new varieties that would be standouts.

cucumbers at field dayQ. You really looked afar afield in finding new varieties.

A. I found out about the USDA’s Plant Introductions Program, and basically for many years now, people have been going out and collecting seeds from different parts of the world and sending them back to USDA seed banks to maintain that genetic material. The people at the seed banks grow them out periodically to maintain them.

If you’re doing research work, the seed is available for free. I was able to look on their website and find varieties from Thailand, and China, and all over. They have some data on their site, including some tests about downy mildew resistance that had been done in the 1990s, and I also looked at other research that had been done at North Carolina State, and I thought about what I had found in 2013, too: that some of the Chinese cucumbers we’d grown did really well, so I was especially looking for more Chinese types. [Some are the longer, thinner kinds in the photo above, from a recent field day at Twin Oaks.]

edmund frost and squash harvestQ. And you found some at the USDA seed bank. Other resources for 2014 crops?

A. With the winter squash, I didn’t use the USDA, because I had so many good options I’d already found to order. I had contacted Linda Wessel-Beaver at the University of Puerto Rico about tropical pumpkins; and got some through Baker Creek Seeds from Thailand and Panama; I got a few on eBay from Jamaica and Cuba that have done well.

I’m trying out the tropical pumpkins with the idea that there’s more downy mildew there—it’s endemic, all year round—so I thought those things had a good chance of doing well. The question is whether they’re too long-season or not.

Q. Yes, perhaps too long for our frost-free season in many parts of the U.S.  But the idea was to get as much genetics that might have resistance into the second year of trials. That said: Everyone should understand the idea of a trial like this is to subject the plants to as much pressure from the disease or insect pest you’re interested in as possible, correct?

A. Downy mildew is usually not present early in the season. What I have done in my trial is delay planting—the cucumbers I planted in early July, the squash in mid-June. I wait a good bit after you’d normally plant to get your earliest yields.

I do want to make it tough for the plants in terms of downy mildew, but I don’t want to make it tough in terms of anything else.  I give them good fertility, good water, good weed control.

Seminole Pumpkin with Waltham Butternut in ForegroundQ. How do you evaluate the plants at payoff time–what are the criteria in Year 2 for each crop? What makes a winner?

A. It’s a little different for cucumbers, melons, and squash. One thing that’s the same for all, though: You look at the leaves, and downy-mildew pressure on the leaves. I’ve been doing that every week to 10 days. You can get a good read that way. [Above photo: ‘Seminole’ pumpkins, background, and defoliated ‘Waltham Butternut,’ foreground.]

The other way is to look at the yield—or with melons, at the sweetness. With winter squash, you can look at both of those, and also the dry-matter content and keeping quality.

With cucumbers there is a really strong correlation with downy mildew and yield. For instance, the susceptible varieties, the ‘Straight Eight,’ averaged about 2 pounds of yield from five plants.

Q. Two pounds? That’s not many cucumbers.

A. Not really worthwhile, no. Some of the most resistant varieties gave me 45 pounds per five plants. Basically if the plant is dead or dying, it’s not going to give you many cucumbers—but there are also other factors. Some plant are just naturally more productive than others.

Q. You said before that some of the Chinese cucumbers tend to do well—was that true on this year’s trials?

A. A handful did well, yes, and some did very well. One from Shandong Province in China was in the mid-40s yield. Another bred by Turtle Tree Seeds in New York called ‘Shintokiwa’ did very well. And then there was maybe six or seven others that averaged in the 30ish-pound range.

Q. With the melons, you evaluated the sweetness because downy mildew can deprive the melons of their sweetness by taking the foliage away too soon?

A. You look at the foliage ratings, and look at the sweetness, and there is a pretty clear correlation. We had some of our better melons testing 9 or 10 or 11 Brix, and the ones that had a lot of downy mildew testing 5 or 6 Brix, which you really wouldn’t want to eat that.

Q. And that’s the Brix scale for testing sweetness. Which melons were standouts?

A. One called ‘Trifecta,’ bred by Cornell, did really well. One called ‘Tai Nang’ [below] that I got from the USDA was the sweetest in the trial, and a surprise find. We have really enjoyed working with Cornell, and a couple of cucumbers that they provided did really well.

Tai Nang MelonWith winter squash, the tropical pumpkins, and especially the Thai pumpkin—which is one I have actually gotten the chance to taste already—did well, and had good eating quality and matured in time.

Q. So now on you go on toward next year—and I know you already have ideas for breeding directions, and plans to share the insights from the trials, and so on. What’s next?

A. I will be talking at farming conferences this winter, and we’ll be posting the results on our website. I’m also thinking about how we could go forward in breeding. For instance, we could cross a resistant cucumber from India with one from China, and get two different kinds of resistances in the same cucumber—these are the kinds of things to I’m already thinking about.

Edmund Frost leads field dayQ. So Edmund, you’ll be there in Virginia dreaming of the possibilities all winter, until the work starts again. I’ll share the results with readers meantime—and thank you.   [Edmund leading a recent field day at the farm, above.]

(Photos courtesy of Edmund Frost and Twin Oaks Seed Farm.)

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  1. Stella says:

    This summer my vegetable garden was decimated by downy mildew. As much as I tried, we lost most of our cucumber crop, all of our melons and most of the winter squash and pumpkins. When can we expect to be able to purchase disease-resistant seed ? I don’t want to go thru another season like this one but don’t want to resort to chemicals to save next year’s crop.

    1. Edmund Frost says:

      Some of the standout varieties from our trials will be for sale this year (starting late November) through commonwealthseeds.com. Some that we liked are new finds though and won’t be available till a year from now because we have to do the seed growouts.

  2. DragonHawk7 says:

    I lost my cucumbers to downy mildew this year too and I am located in Kansas City Missouri! My pumpkins are stunted but I am getting several. I also had one honeydew melon plant that produced lots of flowers but only one fruit. The honeydew and pumpkins were planted in the same bed but the cucumbers were about 20 feet away in another bed.

    I’m hoping we get a good long cold spell this year to help kill off some of these diseases and pests!

    1. margaret says:

      Sorry about your disease issues, DragonHawk7. I managed to get a good winter squash harvest, at least, but it was general cold here all summer.

    1. margaret says:

      Me, too, Kate. :) We are all lucky that such committed individuals devote themselves to this kind of work. Gotta love our farmers!

  3. Lori says:

    I love this site. In depth, awesome articles remind me of the way Rodale’s “Organic Gardening” magazine USED to be (past tense). Great job on an interesting and torturous subject that is the bane of many gardeners.

    1. Lori says:

      P.S. I forgot to say that I had a surprisingly productive year with my cucumbers, squash and melons. They did succumb to downy mildew but I was amazed by their productivity. I attribute it to loads of fall compost the season before and using wood chips as mulch to keep the soil evenly moist. Made a huge difference. I am still going to pursue the varieties mentioned for next year so that, hopefully, downy mildew will be held further at bay.

    2. margaret says:

      What a nice compliment, Lori. Having been gardening a long time, and seeing new issues each year, I’m fascinated by these somewhat-esoteric topics and always happy when readers send feedback like yours. :)

  4. Laura says:

    We do container and straw bales in our small yard in SW Ohio. I had leaves that looked like the picture on the cucumbers. My tomato and potato containers that were in close proximity also got a disease. Perhaps it was a little more rust in color. My seeds were supposedly organic. They were bought at a local garden center and not a big box store. Lots of info! Skipping cucumbers next year sounds like a plan.

  5. Margaret Z says:

    In the south I always get some sort of mildew or fungus close to the end of the season but this year is struck early, even after a cold winter. So, I am solarizing the bed and making sure to rotate crops next year.

    I am going to look for these varieties of melons for next year.

    Thanks for the great articles!


    1. Edmund Frost says:

      Note that Downy Mildew doesn’t overwinter in the soil. It only survives on living cucurbit plant tissue in areas that are frost free. Then it blows north on the wind each year.


    It would be so helpful if all comments could include geographical location. Perhaps, even just an Area number (Area 8).

  7. I had good success with sour milk spray on my pumpkins. The lactic acid seems to stop it in its tracks and with regular spraying new leaves do not get infected. A pumpkin vine penetrated my greenhouse behind a heat storage barrel and thrips spread it to my cantaloupes. I was not able to spray them consistently enough so I only got one not so sweet fruit.

  8. Mike says:

    I love the work you are doing. I have had very little trouble with downy mildew in recent years, but once upon a time it used to get so bad that I would simply not grow certain crops. I have had some good crops of Butternut, but pumpkins perform terribly. I really want that Seminole variety, is that for sale anywhere?

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