Diagnosis and Management of a New Disease of Cucurbits in Oregon

Diagnosis and Management of a New Disease of Cucurbits in Oregon

Summary

Winter squash is grown in the Willamette Valley of Oregon for fresh market sales and as a processing crop for pie filling and confectionary seed. However, a soilborne disease is reducing yield and quality of both fresh market and processing squash. The overarching goal of this project is to increase the economically viable production of winter squash and confectionary seed. This project will work towards that goal by diagnosing squash wilt and root and crown rot, identifying resistant/tolerant varieties, and evaluating the efficacy of crop rotation, fungicides, and other management strategies.

This project will engage farmer participants and other farmers throughout the course of the project. Field trials will be conducted on participating farm fields. Field tours will be conducted each fall. Project findings will be presented at the N. Willamette Hort Society Vegetable and Organic Days, the Oregon Processed Vegetable Annual Meeting, and the OSU Small Farms Conference. Farmers and buyers will interact with whole and cut squash at interactive conference booths each winter.

At least 200 farmers have learned about this disease complex through project outreach activities. These farmers have learned about the symptoms, pathogens and the effect on squash yield. They are also learning to diagnose and scout for the disease. Some farmers grew Tetsukabuto, a resistant variety, in 2016. They liked the field, storage, and culinary performance of this less susceptible variety. However, most cucurbit species and varieties have little resistance. Cucurbita maxima germplasm with resistance was identified for use in breeding resistant germplasm with market potential. Rotation (out of all cucurbits) will be an important strategy for the management of this disease, as is true for most soilborne disease caused by pathogens of limited host range. As farmers learn about the disease and its yield implications, and scout for it on their farms, they are considering how to implement longer cucurbit rotations. Some project farmers planted 2016 squash crops on ground with no history of cucurbit production. Fungicides will not be an effective management strategy for this soilborne disease complex.

Objectives/Performance Targets

Objective 1) Engage project farmers in project development, delivery, evaluation, and outreach

Objective 2) Identify causal agents of squash wilt and root and crown rot

Objective 3: Identify squash cultivars with resistance or tolerance to squash root and crown rot/wilt, as well as good yield and long shelf life

Objective 4: Evaluate the efficacy of crop rotation

Objective 5: Evaluate the efficacy of available fungicides

Accomplishments/Milestones

Objective 1) Engage farmers in project development, delivery, evaluation, and outreach

• Presentation on symptoms of soilborne disease complex and yield and quality of Tetsukabuto, a winter squash variety resistant to this disease. Sensory evaluation (tasting) of Tetsukabuto and other long storing winter squash varieties. North Willamette Hort Society Organic Day. Jan 12 2016 80 attendees
• Squash table (squash display, information on variety trials, soilborne and storage diseases), North Willamette Hort Society Vegetable Day. Jan 13 2016. 50 attendees.
• Squash presentations and field tour, Organic Seed Conference field day. February 4, 2016. Squash display, 4 poster presentations (squash sensory evaluation, soilborne disease complex diagnosis, variety trialing, squash storage). 150 attendees.
• Small farm training workshop. Squash production and storage presentation. Feb 10 2016. 15 attendees.
• Presentation on diagnosis, fungicide efficacy, and host range of soilborne disease complex of cucurbits. Processing Squash Management Field Day. July 13, 2016. 50 attendees.
• Overview of the winter squash project and 2016 field experiments. WSARE field tour. July 14 2016. 25 attendees.
• Dryland squash experiment field tour. Aug 9 2016. 25 attendees.
• Squash project field day (NOVIC field day). 4 poster presentations (squash sensory evaluation, soilborne disease complex diagnosis, variety trialing, squash storage). Sept 6 2016.
• Deficit irrigation in Golden Delicious presentation. Processed Vegetable Field Day. OSU Vegetable Farm. Sept 19 2016.
• Winter squash booth. Variety Showcase. Portland, OR. Oct 3 2016. 250 attendees.
• Organic processed vegetable rotation crop and rotation planning workshop. Brief presentation on soilborne disease problem in processing squash and possible rotation scenarios. Dec 1 2016. 25 attendees.

Objective 2) Identify causal agents of squash wilt and root and crown rot

• Five putative causal agents were identified:
  • Fusarium oxysporum f. sp. melonis
  • Fusarium oxysporum f. sp. cucumerinum
  • Plectosphaerella cucumerina
  • Fusarium solani 
  • Septophoma spp.

Objective 3: Identify squash cultivars with resistance or tolerance to squash root and crown rot/wilt, as well as good yield and long shelf life

Variety/host range trials in 2015 and 2016 showed that winter squash varieties of all three species of winter squash (Cucurbita. maxima, C. moschata, and C. pepo), as well as cucumbers (Cucumis sativus), melons (Cucumis melo) and watermelon (Citrullus lanatus), are susceptible to this disease complex. However, some are more susceptible than others. Summer squash and zucchini (both Cucurbita pepo) are not very susceptible.

Tetsukabuto, a commercial variety that is generated by a C. maxima x C. moschata cross, was much less susceptible than all other winter squash cultivars in field trials in 2015 and 2016; this variety is also very high yielding. Tetsukabuto was also resistant to storage rots and very long storing (even under barn-type storage conditions) in storage trials in 2015 and 2016, and was rated highly by chefs and consumers in sensory evaluations.

Thirty four accessions from the USDA GRIN C. maxima germplasm collection were assessed for disease resistance in a replicated trial conducted on farm field with high inoculum potential. Tetuskabuto was included as a resistant control. Golden Delicious and Uncle David were included as susceptible controls. The goal of the experiment was to identify germplasm with resistance for future breeding efforts. Tetsukabuto as well as 12 GRIN accessions were shown to have resistance to the soilborne disease complex and can be used in future breeding programs.

Objective 4: Evaluate the efficacy of crop rotation

A replicated 2016 irrigation trial planted to Golden Delicious compared disease severity on a split field; half had a history of intensive (3 out of 4 years) squash production and the other half had a history of extensive (1 out of 4 years) squash production. Severity was assessed on a 1-4 scale for root rot, crown rot, and vascular discoloration and a mean severity rating was calculated. Disease severity was lower (2.7 compared to 3.1, out of a maximum of 4) and yield was 22% higher on the field with a history of extensive winter squash production than on the field with a history of intensive (3 out of 4 years in winter squash) squash production.

Forty-nine farm Golden Delicious fields were evaluated for disease severity just before harvest in 2016. Twenty plants were collected per 25 acres in each field (fields ranged in size from 25 to 325 acres) and symptom severity was evaluated for root rot, crown rot, and vascular discoloration. Mean disease severity (across root, crown and vascular tissues) was mild in 49% of the fields, moderate in 33% of the fields, and severe in 18% of the fields. Rotation histories will be collected for these fields and rotation history will be related to disease severity. This data will reveal if there is a relationship between squash production intensity and yield and if specific rotation crops are related to disease severity.

Objective 5: Evaluate the efficacy of available fungicides

Two fungicide (prothioconazole) trials were conducted on farm fields planted to Golden Delicious or other processing squash with a known history of the soilborne disease complex. This fungicide was not effective in suppressing disease or increasing yield.

Impacts and Contributions/Outcomes

This disease complex has never been described previously. At least 200 farmers have learned about this disease complex through project outreach activities. These farmers have learned about the symptoms, pathogens and the effect on squash yield. They are also learning to diagnose and scout for the disease.

Some farmers grew Tetsukabuto in 2016. They liked the field, storage, and culinary performance of this less susceptible variety. However, few cucurbit species and varieties have resistance. Cucurbita maxima germplasm with resistance was identified for use in breeding resistant germplasm with market potential.

Rotation (out of all cucurbits) will be an important strategy for the management of this disease, as is true for most soilborne disease caused by pathogens of limited host range. As farmers learn about the disease and its yield implications, and scout for it on their farms, they are considering how to implement longer cucurbit rotations. Some project farmers planted 2016 squash crops on ground with no history of cucurbit production.

Fungicides will not be an effective management strategy for this soilborne disease complex.

Collaborators: