Management of Fusarium Wilt of Cucurbits with Vetch Cover Cropping and Grafted Transplants

Final Report for OW12-034

Project Type: Professional + Producer
Funds awarded in 2012: $49,158.00
Projected End Date: 12/31/2014
Region: Western
State: Oregon
Principal Investigator:
Dr. ALEXANDRA STONE
Oregon State University
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Project Information

Abstract:

Cucurbit production for confectionary seed, processing, and fresh market in western Oregon has become less profitable due to a soilborne disease. Fresh market farm fields of cucumbers, melons, and winter squash, as well as fields of Golden Delicious squash grown for confectionary seed, were scouted by project staff for diseases and disorders. 

Opportunities to sell vegetables throughout the winter have expanded because of the growth of winter sales opportunities through wholesale and retail markets and CSAs. However, many farmers have not been able to meet this increasing market demand due to losses from storage rots.

The objectives of this project were to:

1) Scout for, diagnose, and identify the host range of soilborne cucurbit diseases occurring on farms in the Willamette Valley.

2) Scout for and diagnose storage diseases of cucurbit crops and determine the impact of harvest date and gypsum applications on crop quality and storage rot incidence.

3) Engage farmers in learning how to reduce cucurbit losses to soilborne diseases and storage rots.

4) Disseminate project results to a wider audience of farmers and agricultural professionals.

5) Evaluate impact of project activities on farmer knowledge and intentions.

Several seasons of field scouting revealed that cucumbers, as well as varieties of all three winter squash species (Cucurbita pepo, C. moschata, and C. maxima), are affected by this soilborne disease. In addition, the potential yield loss in a crop with high disease incidence and severity has been shown to be 75% or greater across all of those cucurbit types.

Fusarium spp. and Plectosphaerella cucumerinum were cultured from diseased crowns, roots, and vascular tissues of diseased plants in 2013, but not all could be identified to species using cultural methods. A new graduate student isolated 1,400 fungal isolates from winter squash and cucumber plants collected from a wide variety of field locations in 2014; she will complete identification and then evaluate them for their pathogenicity on cucurbits in 2015. 

Storage squash of diverse winter squash cultivars were diagnosed with Fusarium fruit rots (Fusarium spp), black rot (Phoma cucurbitacearum), gray mold (Botrytis cinerea), and white mold (Sclerotinia sclerotiorum). An early harvest date either improved or had no effect on fruit quality through December 2014. In addition, there was no apparent impact of gypsum applications on fruit rot incidence as of that date.

Farmers have received diagnoses of critical diseases impacting profitability of fresh market and processing cucurbit crops. In the last year of the project, farmers will participate in workshops in which they will learn about the host range and potential yield losses associated with the soilborne disease and about strategies to avoid storage rots. Information on the diagnosis and management of all diseases will be disseminated through articles published to oregonvegetables.com (such as Winter Squash Storage Rots and their Management (see outeach section). In winter 2014-15, an online survey will be sent to all farmers who sent in samples, allowed field scouting or participated in winter meetings to determine how their knowledge of cucurbit field and storage diseases/problems and their future management intentions had changed as the result of their participation in the project. Management of these diseases will increase crop quality and farm profitability, and extend the winter squash marketing season into mid-winter.

Introduction

Cucurbit production for confectionary seed, processing, and fresh market in western Oregon has become less profitable due to a soilborne disease that is now being diagnosed. A farm growing wholesale fresh market slicing cucumbers came to OSU for help with this crop, as their cucumber plants wilted and died before the end of the production season and yields were declining dramatically. The problem in cucumbers was originally diagnosed (by a diagnostic lab) as Fusarium wilt. During the first year of this project it became clear that the cause of the problem was not Fusarium wilt of cucumbers. Instead, it is a disease of the root and crown (and possibly vascular system), and it affects not just cucumbers but other cucurbits, including winter squash varieties of Cucurbita pepo, C. moschata, and C. maxima. The Willamette Valley produces confectionary pumpkin seed from approximately 5,000 acres of the winter squash cultivar ‘Golden Delicious’ which is susceptible to this disease.

Fresh market winter squash sales currently end for many farmers in December. However, as the opportunities to sell vegetables throughout the winter has expanded (because of the growth of winter sales opportunities through wholesale and retail markets and CSAs), farmers have been trying to sell squash later into the winter. For many farmers, this has not been successful due to losses from storage rots. Most farmers do not have adequate storage facilities for winter squash, nor are they aware of the available research-based information on how to grow, harvest, and store squash to maintain its quality later into the winter. As the result of this need, the project expanded its scope to address the diagnosis and management of storage rots. The project identified currently available information on the production, harvest, and storage of more typical winter squash varieties (acorn, delicata, kabocha, and butternut) to improve storage duration and quality and began the process of ground-truthing that information under Willamette Valley conditions.

Project Objectives:

Objective 1) Scout for, diagnose, and identify the host range of soilborne cucurbit diseases occurring on farms in the Willamette Valley.

Objective 2) Scout for and diagnose storage diseases of cucurbit crops occurring on farms in the Willamette Valley and determine the impact of harvest date and gypsum applications on crop quality and storage rot incidence.

Objective 3) Engage farmers in learning how to reduce cucurbit losses to soilborne diseases and storage rots.

Objective 4) Disseminate project results to a wider audience of farmers and agricultural professionals.

Objective 5) Evaluate impact of project activities on farmer knowledge and intentions.

Cooperators

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Research

Materials and methods:

Cucurbit wilt/crown and root rot:

In summers of 2012-2013, fresh market farm fields of cucumbers, melons, and winter squash, including fields of Golden Delicious squash grown for confectionary seed, were scouted by Stone for symptoms of root and crown rot, vascular discoloration, wilting, or early die-back. More than 80 samples were taken to the OSU Plant Clinic if a diagnosis could not be made by consulting disease diagnostic guides.

In summer 2014, samples were collected from Golden Delicious, cucumber, and fresh market winter squash fields exhibiting symptoms of root and crown rot, vascular discoloration, wilting, or early die-back. Samples were brought to the Johnson lab for evaluation. Hannah Rivedal cultured fungi from diseased tissues and is now identifying those cultures. In 2015 she will evaluate isolates for their ability to cause the symptoms observed in the field.

Winter squash storage and losses:

In winters 2012-13 and 2013-2014, farmers storing winter squash into the fall and winter were asked to submit samples of diseased squash for diagnosis. Fruit rots were diagnosed by the OSU Plant Clinic.

In summer 2014, kabocha ‘Cha-Cha’, delicata Zeppelin, acorn ‘Jet’, and butternuts ‘JWS 6823’ and ‘Nutter Butter’ were grown in a replicated complete block trial with four replications at the OSU Lewis Brown Horticultural Farm. Each variety was grown with and without 5T/A gypsum soil application. Half of each plot was harvested both early (September 9 for all except butternuts which were harvested September 16) and late (September 29 for all except butternuts which were harvested October 6). In two plots per variety, all female flowers were tagged with flowering date. At harvest, all fruits were stored in a walk-in cooler at 55°F and 55 percent relative humidity (all but butternuts) or a greenhouse maintained at 55°F (butternuts) with no humidity control. Fruit bins were rotated and fruits were evaluated monthly for rot incidence (percent of fruit rotten) and quality (dry matter and Brix).

Research results and discussion:

Cucurbit wilt/crown and root rot:

Yields of cucumbers, pumpkins, and winter squash have been declining over a 25-year period on a diversified vegetable farm with on a strict four year rotation, most likely due to this disease problem (Fig. 1). Yield losses range from about 400 to 1,000 lbs per year over the 25 years of cucurbit production.

In summers of 2012 and 2013, a field of Golden Delicious was diagnosed with Phytophthora fruit and crown rot (Phytophthora capsici). A wilt of cantaloupe was diagnosed as Fusarium wilt of cantaloupe. For the other samples, Fusarium spp. (most often F. oxysporum) and Plectosphaerella cucumerinum were cultured from diseased crowns, roots, and vascular tissues, but not all could not be identified to species using cultural methods.

In 2014, many varieties of squash were sampled from all three Cucurbita species: C. pepo, C. moschata, and C. maxima. In addition, two fields of cucumbers (Cucumis sativus) were sampled. Fungi were isolated from root, crown, and stem segments of these plants. DNA was extracted from 1,400 of the fungal isolates. The isolates selected had morphological similarities to F. oxysporum and P. cucumerinum or appeared in one or more fields at a high frequency. The isolates are now being identified using PCR for specific species of interest and DNA sequencing. Isolate identification will be completed in early 2015. Pathogenicity tests will be conducted in the greenhouse in 2015 to determine which of the isolates (singly or in combination) generate the symptoms observed in the field.

Winter squash storage and losses:

Fruits of diverse winter squash cultivars sent in for diagnosis from more than 10 farms were diagnosed with Fusarium fruit rots (Fusarium spp), black rot (Phoma cucurbitacearum), gray mold (Botrytis cinerea), and white mold (Sclerotinia sclerotiorum). See http://horticulture.oregonstate.edu/content/winter-squash-storage-rots-and-their-management.

Evaluation of the 2014 storage trial is ongoing. Preliminary data analysis (see attachment) indicates that in 2014, the early harvest had either no or very little impact (kabocha and acorn, Figs. 1 and 2) or a positive impact (delicata and butternut, Figs. 3 and 4) on Brix, with a more lasting effect in delicata. Change in quality of the crop as it is stored varied by variety. Acorn did not change very much in quality over time and never achieved the Brix levels of the other squash types. Delicata was at its sweetest in October and November. Delicata harvested early in September and stored for three weeks was sweeter than delicata harvested in late September. In contrast, the eating quality (as determined largely by Brix, but also by dry matter, which contributes to textural quality) of kabocha and butternut appears to be continuously improving over time; they should not have been sold or consumed immediately after harvest, but stored to increase Brix before sale.

Gypsum applications increased fruit calcium contents in acorn and delicata; interestingly, gypsum application reduced calcium contents in kabocha (Fig. 5). Gypsum applications had no impact on fruit calcium content of two varieties of butternut (data not shown). Gypsum application had no effect on fruit rot incidence in November or December evaluations (data not shown).

Participation Summary

Educational & Outreach Activities

Participation Summary

Education/outreach description:

Cucurbit wilt/crown and root rot:

Diagnosing cucurbit wilt. Alex Stone. Presentation, PNW Vegetable Association meeting, November 2013. 60 attendees.

Diagnosing cucurbit root and crown rot. Hannah Rivedal and Alex Stone. Presentation, Cucurbit weed control field day, July 2014. 20 attendees.

Diagnosing cucurbit root and crown rot. Hannah Rivedal and Alex Stone. Presentation, Processed Vegetable Grower Field Day, July 2014. 50 attendees.

Designing for Disease Management workshop. Alex Stone. Washington Tilth Producers, November 2014. 85 participants.

Rotation for management of soilborne diseases. Alex Stone. North Willamette Horticultural Society, Organic Day. January 2015. 80 attendees.

An extension article will be published when diagnosis of this disease is complete.

Winter squash storage and losses:

Winter squash storage rots and their management. Alex Stone and Lane Selman, 2014. Oregonvegetables.com article. Available at http://horticulture.oregonstate.edu/content/winter-squash-storage-rots-and-their-management

Winter squash production and storage workshop. Alex Stone and Lane Selman. Gathering Together Farm. February 2014. 20 farmer attendees.

Winter squash culinary event. November 2014. Firehouse Restaurant, Portland, Oregon. 35 farmer, chef, wholesaler, retailer participants. Video available at https://vimeo.com/116907585

Facebook Group: Squash Party. 95+ farmer, chef, wholesaler, retailer, consumer members.

In 2015:

Squash production and storage workshop, February 20 2015. Gathering Together Farm, Philomath, Oregon. 30 farmers and ag professionals will gather to 1) share farmer production strategies, 2) try their hand at brix testing of stored squash, and 3) learn about project-generated information on the impact of variety selection, harvest timing, and storage on fruit storability and quality.

Squash culinary event, February 20 2015. Gathering Together Farm, Philomath, Oregon. 50 farmers, chefs, retailers and wholesalers will gather to look at stored squash, learn about quality testing including Brix, taste roasted and raw squash, taste squash recipes (soup, salad and pasta) using stored squash, and discuss how to increase squash production and consumption throughout the fall and winter in western Oregon.

Project Outcomes

Project outcomes:

Farmers have received diagnoses of critical diseases of fresch market and processing cucurbit crops. In early 2015 farmers will participate in workshops in which they will learn more about the host range and potential yield losses associated with the soilborne disease and about strategies to manage the soilborne disease and avoid storage rots. Information on the diagnosis and management of all diseases will be disseminated through articles published to oregonvegetables.com (see Outreach). In winter 2014-15, an online survey will be sent to all farmers who sent in samples, allowed field scouting, or participated in winter meetings to determine how their knowledge of cucurbit field and storage diseases/problems and their future management intentions had changed as the result of their participation in the project. Management of these diseases will increase crop quality and farm profitability and extend the winter squash marketing season into mid-winter.

Economic Analysis

Cucurbit wilt/crown and root rot:

As the soilborne disease affecting cucurbits has never previously been researched or diagnosed, there has never before been any data on the economic impact of this disease. The figure showing the decline in yield in cucumber, pie pumpkin, and winter squash on a farm with a four year rotation reveals that economic losses to this soilborne disease are considerable and affect many crops. Slicing cucumber yields fell approximately 900 lbs per year over a 25 year period; a total loss of 23,000 pounds (or 65-70% of yield) for a crop that had yielded between 30,000 and 35,000 pounds. Other winter squash types appear to be similarly susceptible, although more field scouting and yield accounting must be done to better estimate yield losses.

Winter squash storage and losses:

One participating farmer who wholesales butternut squash reports that as the result of his learning from this project about best harvest and storage practices, his storage losses as of January 2015 have been only 2% of his butternut crop, while in past years losses have been 25-50%.

Farmer Adoption

Cucurbit wilt/crown and root rot:

Cucurbit wilt and root/crown rot: The farm that had the severe soilborne disease problem in slicing cucumbers is no longer growing slicing cucumbers as their yields were so low. Other farmers just learning about this problem are considering how to lengthen their cucurbit rotation to reduce disease risk.

Winter squash storage and losses:

Squash storage: As the result of the February 2014 winter meeting, one farmer grew long-storing squash (Marina di Chioggia and Musque de Provence) for distribution in winter CSA boxes. Several farmers harvested their retail and wholesale kabocha, kuri, and small hubbard squashes early to reduce sun scalding after the vines went down, thereby increasing quality and marketable yield. One farmer harvested his wholesale butternut squash in early September and stored it in a high tunnel for several weeks; thereby getting the squash out of the field clean and dry and increasing Brix early in the fall. He then stored it in a clean dry storage unit with a dehumidifier. As the result of these changes in his harvest and storage practices, he has (as of December) reduced storage losses from 25-50% to less than 5%, and he predicts he will sell butternuts into February.

Recommendations:

Areas needing additional study

Cucurbit wilt/crown and root rot:

A graduate student, Hannah Rivedal, is working on the diagnosis of this disease as described above. Hannah extracted DNA from 1,400 fungi of interest across all the fields scouted in 2014. Using PCR for specific species of interest and DNA sequencing, Hannah has begun to identify these cultured fungi. In the coming months, she will complete the identification of the fungi and begin pathogenicity tests in the greenhouse. This should allow her to confirm which fungi are causing the disease and whether or not more than one fungus is responsible for the issues growers have seen in the past. The next step will be to develop management strategies; for example, rotation length, early season deficit irrigation (to slow early disease development), and resistant and/or tolerant or less susceptible varieties. As an example, through scouting (and the slope of the yield regression in Figure 1) it appears that pumpkins exhibit much less root and crown necrosis than other winter squash.

Winter squash storage and losses:

There is a great deal of additional research needed on how best to grow, harvest, and store winter squash to make squash available to consumers and profitable to farmers throughout the winter months. Production and storage management research topics include: harvest timing, degree day modeling to predict harvest timing, best storage environment for each squash type, and how to assess quality to determine when the squash should be sold and consumed. There is a need to trial diverse varieties of common types, such as delicata, acorn, kabocha, and butternut for their quality, profitability, and storability, as well as less common long storing types such as Winter Sweet, Lower Salmon River, Confection, Sibley, and Sweet Meat. One of the problems with both the common and unusual squash is that farmers, buyers, and consumers do not know how to determine if they are ripe and when their prime ‘eating season’ is. This can only be determined by growing and storing the squash, destructively harvesting it monthly throughout the winter, and assessing it for quality in the lab and for flavor and culinary use in partnership with consumers and chefs. Identifying winter squash varieties that are profitable for the farmer when sold out of storage throughout the winter must be done in partnership with buyers (institutional, restaurant, wholesale, retail), chefs, and consumers to ensure that squash varieties have good market and culinary potential when stored over time. An effective marketing campaign will be necessary to get the word out to farmers, buyers, and consumers about the new varieties, how to grow and store them, when their prime ‘eating season’ is, and the best ways to prepare and eat them.

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.