Final Report for FS13-273
Project Information
The heart of this project was replicated cucumber, melon and winter squash variety trials at Twin Oaks Seed Farm during the 2014 growing season. The goals were to evaluate resistance to Cucurbit Downy Mildew, to identify resistant seedstocks, and to look at eating quality and productivity in conditions of high downy mildew pressure. Downy mildew became severe in mid August and provided an excellent screen for our trials. We were successful at identifying several downy mildew resistant seedstocks of melon, cucumber and winter squash. Several of these will be very useful to growers as is, and some are useful for future breeding work.
We also conducted a screening for Striped Cucumber Beetle (SCB) preference. 2014 was a relatively low-pressure year for cucumber beetles, but we still managed to obtain useful results and to demonstrate a trial method that has further potential in higher SCB pressure situations.
This project is part of an effort to create and grow a vibrant seed system in our region. As such, we pursued networking and outreach not only about our trial results but about our broader seed movement goals. I presented at several agricultural conferences over the winter of 2014-2015, successfully connecting with growers throughout the mid-Atlantic and Southeast. We also conducted an online grower survey about cucurbit seed needs.
Introduction
Cucurbit Downy Mildew has been the number one limiting factor in cucurbit production at Twin Oaks Seed Farm, affecting seed crops as well as market crops of cucumber, squash, melon, gourd and watermelon every year. Since 2009 downy mildew (DM) has caused severe losses of these crops each year, including several complete crop failures. Downy mildew has a huge economic impact on growers throughout the Eastern U.S.
Cucurbit Downy Mildew is an oomycete pathogen that cannot survive in sub-freezing temperatures. However, it survives the winter in frost-free areas of Florida, Texas and Mexico, and the spores blow north on the wind each year. We have seen DM arrive in Virginia anywhere between June 15th and August 1st.
Mutations in the pathogen since 2004 have rendered most or all formerly-resistant slicing and pickling cucumber varieties non-resistant. (See NC State Study: http://cuke.hort.ncsu.edu/cucurbit/wehner/articles/mscall.pdf). Consequently, most sources of information about downy mildew resistance of melon and cucumber varieties are out-of-date and unreliable. We have found most standard melon, winter squash and cucumber varieties to be downy mildew-susceptible, and unsuited to late-season or mid-season plantings. Even early plantings succumb to the pathogen before the end of harvest some years, or are adversely affected. While organic producers are especially impacted by downy mildew because of a lack of effective fungicide control options, conventional growers are also impacted by the cost of fungicides and fungicide application. Even with fungicide, production can still be seriously affected.
689,100,000 pounds of fresh cucumbers were grown in the top 11 fresh-cucumber-producing states in 2014, worth $168,038,000. 10 of the top 11 states (all but California) are in the eastern US and affected by Downy Mildew. http://usda.mannlib.cornell.edu/usda/current/VegeSumm/VegeSumm-01-29-2015.pdf. 481,740 tons of pickling cucumbers were produced in the US in 2014, worth $175,634,000. All of the top 8 states are Eastern states affected by downy mildew. The majority of cantaloupe melons grown in the US come from the southwestern states. However, Eastern-grown melons, about 10% of the total, are at least a $30,000,000 industry.
In Michigan, which produces roughly 25% of the nation’s cucumbers, cucurbit fungicides cost $6.4 million/year, most of which is used to control downy mildew on cucumbers (Hausbeck et al. 2014: http://cuke.hort.ncsu.edu/cgc/conferences/cuc2014proceedings.pdf ). Extrapolating the cost of fungicides used each year in Michigan to the rest of the Eastern states, farmers spend in the range of $20 million each year on fungicides to manage cucurbit downy mildew. This figure does not include crop losses and reduced yields due to downy mildew.
In this project, we wanted to find varieties of melon, cucumber and winter squash that can withstand downy mildew, to share the results with other growers, and to gather the information necessary to move forward with seed production and breeding work of DMR varieties.
It was also our goal to situate these trials in the context of a broader movement to create a vibrant seed system in our region. Such a movement must include regional trialing, breeding and seed production work, as well as networking and information sharing. We want the results from our trials not only to benefit produce growers, but to provide a model for farmers who participate or who might participate in seed growing, research and breeding in the Southeast and mid-Atlantic. With these goals in mind, I presented results from our trials at several agricultural conferences in the winter of 2014-2015, and conducted a growers survey about cucurbit seed and variety needs.
1)To perform a replicated trial of 35 cucumber seedstocks, along with an unreplicated screening of 23 additional cucumber seedstocks, in conditions of high downy mildew pressure, in order to identify resistant seedstocks that are able to produce a worthwhile crop in these conditions.
2)To perform a replicated trial of 32 melon seedstocks, along with an unreplicated screening of 4 additional melon seedstocks, in conditions of high downy mildew pressure, in order to identify resistant seedstocks that are able to produce acceptably sweet melons in these conditions (downy mildew impacts melon sweetness).
3)To perform a replicated trial of 20 winter squash / tropical pumpkin seedstocks, along with an unreplicated screening of 23 additional seedstocks, in conditions of high downy mildew pressure, in order to identify resistant seedstocks that are able to grow and yield well in these conditions; also to evaluate eating quality for these seedstocks.
4)To also evaluate the above melon, winter squash and cucumber seedstocks (the replicated entries in the DM trial) for Striped Cucumber Beetle preference.
5)To conduct a grower survey about cucurbit seed and variety needs that can help inform future trialing and breeding work.
6)To reach other growers with our results and ideas on these topics.
Cooperators
Research
Cucumber Trial:
- 35 replicated entries and 23 single entries planted in a randomized complete block design layout.
- 6 foot row spacing; 1 foot between plants and five feet between entries in-row.
- Provided Nitrogen with early cowpea cover crop, supplemented by tofu okara side dressing at a rate of 1.75 tons per acre. 2013 crop was sorghum-sudan cover crop.
- Planting date was June 27; transplant dates were July 12 and 13. We planted late for increased downy mildew exposure.
- We obtained many of the seedstocks from the USDA’s North Central Plant Introduction Station in Ames, Iowa. This is a great resource. Most of the entries were chosen because they showed resistance in a previous test or because we otherwise suspected DM resistance. We based many of our choices on the results of North Carolina State’s 2008-2009 DM cucumber screening: http://cuke.hort.ncsu.edu/cucurbit/wehner/articles/mscall.pdf
- The susceptible control was Straight Eights and the moderately resistant control was Marketmore 76.
- From mid-August through mid-September we recorded foliage ratings for downy mildew using a 1-9 scale; 1 being unaffected and 9 being dead. We also took foliage ratings for Bacterial Wilt, on a scale of 1-6. We recorded yields and marketable yields and also did a variety tasting. Fruit rot and misshapen fruit were the main reasons for fruit being categorized as unmarketable. We harvested every 2-3 days.
- We surrounded the melon and cucumber trial with ‘Homemade Pickles’ cucumber plants, to prevent ‘edge effect,’ whereby plants on the edges are exposed to fewer DM spores from their neighbors.
Melon Trial:
- 32 replicated entries and 4 single entries planted in a randomized complete block design layout.
- 7 foot row spacing; 1.5 feet between plants; 6 feet between entries in-row.
- Provided Nitrogen with early cowpea cover crop, supplemented by tofu okara side dressing at a rate of 1.75 tons per acre. 2013 crop was sorghum-sudan cover crop.
- Planting date was June 13; transplant dates were June 28 and 29. We planted late for increased downy mildew exposure.
- Controls were Delicious 51, Hale’s Best and Athena.
- Many of the seedstocks for the trial came from the USDA Plant Introduction Station in Ames, Iowa.
- From mid-August through mid-September we recorded foliage ratings for downy mildew using a 1-9 scale; 1 being unaffected and 9 being dead. We also took foliage ratings for Bacterial Wilt, on a scale of 1-7. We recorded yields, brix readings and taste ratings of all the cantaloupe type melons between mid August and mid September. We were not able to brix test or taste test every single fruit, but gathered a representative sample from each entry on each harvest date, and tested more than half of the melons in each entry. I decided to stop recording harvests and brix for non-cantaloupe types due to time constraints, and because most of these did not show promise in terms of downy mildew resistance, or died from Bacterial Wilt.
- We surrounded the melon and cucumber trial with ‘Homemade Pickles’ cucumber plants, to prevent ‘edge effect,’ whereby plants on the edges are exposed to fewer DM spores from their neighbors.
Winter Squash Trial:
- 20 replicated entries, plus 23 single entries, planted in a randomized complete block design layout.
- 12 foot row spacing, 2 feet between plants and 12 feet in-row between entries.
- Fertilized with tofu okara at 4 tons per acre; compost at 2 tons per acre (side dressed); potassium sulfate and magnesium sulfate at 200 pounds per acre each (side dressed); previous crop was grass hay.
- Planting date (direct seeding) was June 10th for most entries, with a May 20th planting date for the Caribbean tropical pumpkins. We planted late for increased downy mildew exposure.
- We had to train the vines every few days all summer.
- Most of the entries are Cucurbita moschata species. Many are tropical pumpkins, including from Puerto Rico, Cuba, Jamaica, Panama, China, India, Costa Rica and Thailand. Several varieties are from the Southeast US. In general we looked to the south for the seedstocks to trial.
- Control is Waltham butternut.
- Using a 1-9 scale we recorded foliage ratings starting on August 22, through mid October, and measured yields at harvest.
- We tested three squash from most entries for dry matter content and brix; and described flavor, color, sweetness and texture in a taste test. We did not test some of the entries that performed poorly in the field.
- We surrounded the trial with Waltham butternut plants, to prevent ‘edge effect,’ whereby plants on the edges are exposed to fewer DM spores from their neighbors.
Cucurbit Variety and Seed Needs Survey: Survey is attached. I promoted the survey at all of my presentations on the trial results, in the Common Wealth Seed Growers seed catalog, through Virginia Association for Biological Farmers newsletters and through Eastern Carolina Organics.
Striped Cucumber Beetle Preference Trial: We planted transplants of six one-plant replications of each variety of squash, melon and cucumber, in a randomized complete block design layout. We rated beetle damage to plants on a scale of 1-9 (1 being unaffected and 9 being dead from SCBs), and counted beetles on plants on two dates for each trial (May 23rd, May 24th and May 26th). We had intended to evaluate this trial longer, but cucumber beetle pressure was low, and decreased to near zero by the second evaluation.
Advisors: I designed the Striped Cucumber Beetle trial based on discussions with Jeffrey Gardner of Cornell University. Dr. Michael Mazourek of Cornell and Micaela Colley of Organic Seed Alliance provided advice about overall project design and framework, and about how to set up and conduct the main downy mildew trials. Dr. Mazourek provided advice and help throughout the course of the trials.
Thank you Sapphyre Miria, Shua Younkin, Nina Lankin, River Oneida and others on the Twin Oaks seeds crew for your work in support of this project.
Cucumbers: The results from the cucumber trial were striking. Some varieties, such as Straight Eights, our susceptible control, died back quickly in mid-August from DM and produced very little: 2.1 pounds on average from five plants. Several of the resistant varieties yielded over 35 pounds per 5 plants and stayed green into mid-September. Yields and downy mildew ratings were well correlated overall. Marketmore 76, a standard with intermediate resistance, yielded an average of 11.7 pounds from each 5 plant entry. SV4719CS, another variety listed as resistant, yielded an average of 13.3 pounds. We found 15 varieties that yielded more than twice as much as these standards. Several of the standouts, including PI 432885 and 618894, were Chinese trellising cucumbers from the USDA’s North Central Regional Plant Introduction Station. Other standouts included Cornell’s DMR-264 (a green slicer) and DMR-261 (a white slicer); Ivory Queen, a white slicer from Cook’s Garden; Shintokiwa Long from Turtle Tree Seeds; White Emerald from Baker Creek; PI 605996, a russet-when-ripe cucumber from India; and PI 426170, a pickling cucumber from the Phillipines.
Bacterial Wilt (BW) was an additional complicating factor which in some cases caused different entries of the same seedstock to yield and perform differently. The purpose of the BW evaluation was not so much to produce definitive findings on BW tolerance but to be able to point to BW as well as DM as a factor affecting yield. However, we observed that two varieties, PI 432885, DMR-261 appeared more tolerant of BW. Our ability to assess BW tolerance on varieties that died back early from DM was limited.
DM may not have been distributed evenly throughout the field due to edge effect on the western edge, which had better foliage ratings and yields than the rest of the trial. The predominant wind comes from the west, so plants on the western edge experience less DM spores blowing on them from their neighbors, and thus are subjected to less DM pressure. To address this we planted a moderately susceptible cucumber around the whole of the cucumber and melon trials; the melons were to the west, so the immediate neighbors to the westernmost row of cucumbers were melons. Melons are immune to some strains of DM; I believe these strains were active in our cucumbers but could not proliferate in the melons. This led to an edge effect in our western row of cucumbers. Replication 1 of entries 1-14 were in the western row.
See attached file for data from the cucumber trial. This document includes in-depth treatment that shows data from the different replications, and a printable summary.
Melons: Downy Mildew in the melon trial was also severe. There was a correlation between Downy Mildew foliage ratings and sugar content of the fruit (brix readings). The three sweetest varieties were Seminole, Tai Nang, and Trifecta, with brix averages of 9.8, 11.8 and 10.4 respectively. Keep in mind that this is in a late-planted trial under very heavy Downy Mildew pressure. As a reference point, Hales Best averaged 5.6 brix; Delicious 51 averaged 6.8 brix. Several varieties had moderate sweetness and foliage resistance, including Hannah’s Choice, Edisto 47 and Sivan.
Bacterial Wilt was severe for many of the non-cantaloupe varieties, causing plants to die to an extent that in some cases made it difficult to tell if it was DM or BW that killed them. It impacted the cantaloupe types less, but did have an affect on sweetness of some of the melons in many of the blocks. Tai Nang No 2, a DMR standout, was more affected by BW than most orange cantaloupes. BW evaluation was not so much to produce definitive findings on BW tolerance but to be able to point to BW as well as DM as factors affecting yield and sweetness for the entries.
See three attached documents for melon trial data:
1)In-depth cantaloupe data; includes data from different replications.
2)Data summary for cantaloupes.
3)Foliage ratings for all melon types.
Winter Squash: In the winter squash trial, we saw almost complete dieback of the Waltham butternut plants in late August. Quite a few varieties showed good Downy Mildew resistance, especially the tropical pumpkins. We included tropical pumpkins from Puerto Rico, Cuba, Jamaica, Thailand, China and Panama, and many of these proved to be very DM resistant. There was decent fruit set on the Waltham, and many of the fruits were marketable; however DM significantly lowered quality and yield. An F3 cross between Seminole pumpkin and Waltham did well in the trial, with DM foliage ratings similar to Seminole and yields 60% higher than Waltham. Some of the Caribbean tropical pumpkins showed huge yields. Fruit quality was quite variable in several of these seedstocks, or poor in some cases, but the presence of high quality fruits point to potential for breeding and selection projects. Most but not all of the tropical pumpkins made it to maturity. Caribbean tropical pumpkin fruits tend to be very large, which is often not desirable with market growers. Two Thai varieties, Thai Kang Kob and Thai Rai Kaw Tok showed good DM resistance and exceptional eating quality, though were not high yielding (Thai Rai Kaw Tok was slightly higher yielding but slightly lower quality than Thai Kang Kob). A Chinese tropical pumpkin (it came to us without a name) showed very good eating quality, good productivity, good foliage resistance, good keeping quality and attractive medium-sized fruits. It has potential to become a popular market variety in our region. Most of the entries were moschata species; the few that were maxima and pepo species were significantly impacted by vine borer as well as Downy Mildew. Many of the maximas were also impacted by Bacterial Wilt.
Powdery Mildew was not a big factor in the trial, except that it severely impacted Table Queen Vining Acorn squash plants.
See attached documents for winter squash trial data:
1)Data summary
2)In-depth data; includes data from different replications
3)Additional data for maxima and pepo species seedstocks
Striped Cucumber Beetle (SCB) Trial
Low beetle pressure during the trial was an obstacle for this part of our project. However, the trial showed potential as a method for evaluating striped cucumber beetle preference, and did yield some interesting and useful results.
The results of the cucumber portion of the SCB trial were inconclusive. However, in the melon and winter squash portions of the trial, we identified several varieties with significantly better and worse beetle susceptibility than average. Less-preferred melons (by cucumber beetles) were Hannah’s Choice, Delicious 51, Seminole, Aurora, Schoon’s Hardshell, Pride of Wisconsin, Earlichamp, Trifecta and Golden Gopher. More preferred were PI 126006, PI 217974, PI 304743, PI 378059, PI 368062, PI 441988, and Sivan. It is notable and interesting that all of the less-preferred melons were U.S.-developed varieties of orange cantaloupe, while all of the more preferred varieties were from outside of the U.S. Seminole melon and Trifecta were also standouts in the downy mildew evaluation; their good performance in the SCB trial serves as an additional recommendation for these varieties. Less-preferred (by SCBs) winter squash were Waltham, 6823 PMR, and Seminole x Waltham F3, all butternut types. More preferred winter squash were Cherokee Candy Roaster and Jamaican Longneck. SCB counts on cucumbers and melons did not correlate to damage ratings, but there was some correlation with squash.
Striped Cucumber Beetle Trial results are attached.
Cucurbit Survey
An insufficient number of people responded to the survey to be able to use it to draw conclusions about growers’ cucurbit variety and seed needs in the region. However, some interesting and useful information was gathered.
Eight commercial growers (four certified organic and two non-certified organic) and nine gardeners completed the survey. Among the commercial growers, 5/7 respondents (note that not everyone answered every question) said that there are not able to find cucumber varieties with adequate disease resistance. 5/5 respondents said they are not able to find melon varieties with adequate disease resistance. 6/8 respondents said they are not able to find winter squash varieties with adequate disease resistance. 7/8 commercial growers said they would be very interested in using regionally trialed and regionally produced open-pollinated cucurbit seeds.
5/6 commercial growers have problems with downy mildew in cucumbers; 2/3 have DM problems in melons and 6/8 have DM problems in winter squash. Other common problems included cucumber beetles, squash bugs and powdery mildew.
The survey responses are attached.
Note: a slideshow with pictures of numerous entries from the trial, and information about downy mildew is attached. I used this in presentations about the project at sustainable agriculture conferences in the winter of 2014-2015.
Educational & Outreach Activities
Participation Summary:
Interview with Margaret Roach: http://awaytogarden.com/cucurbit-downy-mildew-research-twin-oaks-farm/
Virginia Association for Biological Farming Newsletter: https://vabf.files.wordpress.com/2012/03/v37n4_vabfnewsletter_final.pdf
Common Wealth Seed Growers Catalog and Website: www.commonwealthseeds.com
I presented results from our project at several conferences over the winter of 2014-2015, including those organized by Carolina Farm Stewards Association, Virginia Association for Biological Agriculture, Southern Sustainable Agriculture Working Group, and Pennsylvania Association for Sustainable Agriculture. The slide show I gave at these conferences can be seen at www.commonwealthseeds.com/research.
Project Outcomes
- Gathering and publication of data that will be useful to growers in choosing what varieties of melon, cucumber and winter squash to plant in high DM pressure conditions.
- Identification of several melon varieties with ability to produce good quality melons in high DM pressure conditions. This includes Seminole, Trifecta and Tai Nang No 2 (which was not previously listed or known as a DMR variety).
- Identification of 15 cucumber varieties with the ability to produce twice as well as standard varieties that are currently labeled as resistant, such as Marketmore 76 and SV4719CS. Some, like the Chinese trellising types, will be useful to growers in the eastern U.S. as direct market varieties. DMR-264 and DMR-261 have potential for wholesale production. Many of these seedstocks have potential to provide sources of DM resistance in breeding projects. It is notable that we found good DM resistance in cucumbers originating from several different areas, including China, India and the Phillipines. To effectively combat future mutations of downy mildew, we need breeding strategies that incorporate multiple sources of resistance.
- Identification of 20 winter squash and tropical pumpkin seedstocks with much better downy mildew resistance, yield and plant performance in Virginia conditions than Waltham Butternut, Buttercup and Table Queen Vining Acorn. Several of these, including Chinese Tropical Pumpkin, Thai Kang Kob, Thai Rai Kaw Tok and Seminole have good potential as market varieties. Chinese Tropical Pumpkin may be the best find, as it has small fruit size, excellent eating quality, a small seed cavity, good productivity and good downy mildew resistance. Seminole x Waltham F3, part of a breeding project in progress, showed very good potential for creating a high yielding DMR butternut variety with very good eating quality. Finally, many of the tropical pumpkin seedstocks showed good potential for breeding and selection projects, as downy mildew resistance and yields were very good, and eating quality, while highly variable, was excellent for some plants of Cuban Neck Pumpkin, Jamaican Shortneck and Jamaican Longneck.
- Demonstration of a method for testing cucumber beetle preference that shows potential for future projects, especially in settings of higher cucumber beetle pressure. The trial also indicated that U.S.-developed orange cantaloupe type melons tend to be less preferred by cucumber beetles than many melons developed elsewhere. This merits further investigation.
- Demonstration of successful on-farm variety trialing, which is an important part of the healthy seed system we want to create in our region.
- Successful outreach and dissemination of results at conferences organized by Carolina Farm Stewards Association, Virginia Association for Biological Agriculture, Southern Sustainable Agriculture Working Group, and Pennsylvania Association for Sustainable Agriculture.
Potential Contributions
Also see Accomplishments section.
North Central Regional Plant Introduction Station plans use our downy mildew data in the ‘Observations’ section of cucumber variety profiles, and to use our melon and cucumber variety pictures in profiles.
This project has helped launch Common Wealth Seed Growers, a growers cooperative and seed company that currently has eight members, and of which I am Director. We published our first retail catalog for the winter of 2015, which included DMR-264, Trifecta, Thai Kang Kob and Seminole-Waltham F3. We plan to continue to specialize in downy mildew resistant varieties, which will be possible in large part due to our 2014 trials. Next year we will be releasing several more DMR varieties identified in the trial, including Seminole melon, Tai Nang No 2 melon, DMR-261 cucumber, Shandong Si Gua 1210 cucumber (PI 432885), Chinese Tropical Pumpkin, Thai Rai Kaw Tok pumpkin and Cuban Necked pumpkin.
This project will serve as the starting point for several breeding projects of melon, cucumber, winter squash and moschata summer squash. I have applied for or been included in several grant proposals to fund these projects. More specifically, I have plans to breed several lines to DMR butternut squash; DMR slicing and pickling cucumbers with diverse sources of DM resistance; DMR and Vine Borer resistant moschata summer squash; and wholesale-suitable DMR orange cantaloupe melons.
Future Recommendations
Also see Accomplishments and Potential Contributions sections.
The results of our downy mildew trial yielded good results in one year. However follow-up trials that include the standouts we identified are needed to confirm the results in other locations affected by DM. We will be continuing our evaluation of many of these seedstocks in the process of ongoing breeding and selection work.
More resources are needed for breeding work of DMR melon, winter squash and cucumber, including for on-farm organic breeding of open-pollinated varieties. I believe that there is potential to develop several much-needed new DMR varieties using the DMR sources we identified or confirmed in our trials. More resistance sources and DMR varieties could surely be identified by pursuing additional screenings.
A similar set of trials focused on downy mildew in watermelon and gourds would also be useful to Southeast growers, as well as a trial focused on downy mildew and vine borer preference in summer squash.
I would like to see more research on cucumber beetle preference for all cucurbit types, and on Bacterial Wilt tolerance for melon, cucumber, pepo squash and maxima squash.