Diagnosis and control of winter squash storage rots in western Oregon

Project Overview

GW18-157
Project Type: Graduate Student
Funds awarded in 2018: $25,000.00
Projected End Date: 03/31/2019
Grant Recipient: Oregon State University
Region: Western
State: Oregon
Graduate Student:
Major Professor:
Dr. Kenneth Johnson
Oregon State University

Information Products

Commodities

  • Vegetables: cucurbits

Practices

  • Crop Production: irrigation, winter storage
  • Pest Management: chemical control, cultural control, integrated pest management, mulches - general
  • Production Systems: dryland farming
  • Sustainable Communities: local and regional food systems

    Abstract:

    Winter squash could be an important locally-grown winter food and provide critical winter
    income to farmers in western Oregon if it could be successfully stored. In the Willamette Valley,
    severe storage losses currently prevent sales through winter markets. For example, in reputedly
    long-storing cultivars, losses from 50-100% have been observed by December. Little is known
    about the causal agents of these uncommonly severe rots and their prevention. Consequently,
    this project will characterize causes of squash fruit rots and evaluate practical methods to reduce
    their incidence. A preliminary investigation of squash rots has shown that Fusarium culmorum is
    frequently associated with diseased fruits. Interestingly, this fungus is known as a floral pathogen
    of grasses and other monocots. Oregon’s Willamette Valley is a major grass seed production
    area, and grasses are common cover crops for diversified farmers. Consequently, the hypotheses
    are that F. culmorum is abundant due to regional cropping patterns, it is successfully rotting
    squash because this fungus infects flowers, and the common floral-end rots of squash are caused
    by pathogens that colonize flowers. In field inoculation trials, I will confirm the pathogenicity of
    F. culmorum and other fungi associated with squash rots. I will conduct field experiments at
    research and grower farms to evaluate if fruit rots are reduced by a) dryland production, b) nongrass
    mulches (via mechanisms of reduced pathogen inoculum and unfavorable environmental
    conditions for fungal dispersal and colonization), and c) chemical control. I will evaluate squash
    storability over time in a closed farm bay, which is the most profitable storage method for the
    region. This project will provide a profile of an important disease and methods to reduce its
    incidence, which will increase profitability of winter squash through a direct reduction of
    postharvest fruit losses.

    Project objectives:

    Objective 1. Identify the most significant pathogens reducing winter squash storability in
    the Willamette Valley
    To develop management plans for a disease problem, a clear diagnosis of the pathogens
    involved is necessary. To do this, we will employ molecular and morphological identification
    techniques as well as in-field pathogenicity trials.
    Hypothesis: We hypothesize that F. culmorum as well as other organisms previously identified,
    (other Fusarium spp., Botrytis spp., Phoma spp. and Sclerotinia sclerotiorum) are rotting squash
    fruit, but that F. culmorum causes the early-in-storage and most devastating losses.
    Protocol: Identification of potential winter squash rot pathogens Winter squash from the 2017
    growing season with representative rots have been cultured for fungi from diseased areas.
    Systematic symptom descriptions characterizing the date at which the rot started, as well as the
    color, location (floral-end, stem-end, side of fruit) and severity (percent squash area rotted) of the
    rot have been recorded. Morphology and DNA sequencing of the Internal Transcribed Spacer
    and Elongation Factor 1 alpha gene regions are being used to identify the fungi. Following rot
    characterization, we will better understand which of the pathogens rot fruit early/middle/late in
    the storage season, and where the pathogen infects the fruit. Floral-end rots are likely initiated
    from flower infection (in the field during the growing season), while rots beginning at the stemend
    and the side of the fruit are more likely due to pathogens present on the surface of the fruit
    with the rot initiated via wounds created during handling (harvest).
    Determine if F. culmorum and/or other important squash rotting fungi colonize flowers.
    In summer 2018, we will plant 3 plots of susceptible winter squash varieties ‘Sunshine’ and
    ‘Bonbon’ in an irrigated field with a vetch mulch to control for rain splash of naturally occurring
    soilborne pathogens onto flowers. Female, fruit-bearing, squash flowers will be sprayed with
    liquid suspensions of potential pathogens identified from 2017. Potential pathogen inoculation
    treatments will include a broth-only control, F. culmorum, and other consistently-associated fruit
    rot pathogens from characterizations described above. Flowers will be sprayed after opening and
    monitored throughout the season for deterioration, fruit abortion and rot symptoms after fruit set.
    Fruit from inoculated flowers will be taken to the lab and cultured to confirm infection occurred
    from the inoculated fungi. This will complete the diagnosis of the fruit rot pathogens and articles
    will be prepared for dissemination to growers and scientific journals, following conclusion of the
    experiment.
    Objective 2. Evaluate the efficacy of dryland production, organic mulches and chemical
    control for the suppression of fruit storage rots.
    In-season management strategies that are easily implemented and cost effective are
    important to winter squash profitability. To evaluate different management strategies, we will
    plant on-farm trials in the growing season of 2018.
    Hypothesis: We hypothesize that squash grown in dryland plots will have less disease and store
    longer than squash grown in irrigated plots. We also hypothesize that a vetch mulch will reduce
    disease incidence in irrigated plots because the mulch acts as a physical barrier, suppressing
    splash of soilborne squash rotting fungi onto the flowers. We hypothesize that a cereal mulch
    will increase rot disease incidence in irrigated plots because F. culmorum residing in the cereal
    mulch will splash onto flowers. We hypothesize that a chemical spray at bloom will reduce the
    ability of the pathogen to infect flowers and reduce disease incidence.
    Protocol: Dryland versus Irrigated Production effects on storage rot incidence To compare
    storability of squash grown under dryland and irrigated production, we will plant field trials at
    the Oregon State University Vegetable Research Farm, Gathering Together Farm, and 47th St.
    Farm. At all locations, there will be dryland and irrigated plots of our two representative,
    susceptible squash cultivars ‘Sunshine’ and ‘Bonbon.’ At all locations and in both irrigated and
    dryland experiments, there will be three replicates of 5 plants of each variety planted in 10-footlong
    plots in rows 60 inches apart. Winter squash
    will be direct seeded into dryland plots and
    transplanted into irrigated plots. Plants will be
    grown through the season and fruits harvested for
    storage at 45 days after pollination. Individual fruit
    weights and fruit number will be recorded.
    Mulching effects on storage rot incidence
    To compare methods for disease reduction,
    additional plots in the irrigated and dryland fields
    of ‘Sunshine’ and ‘Bonbon’ will be mulched using
    cereal mulch and vetch mulch. Plots will be
    mulched at planting. As above, there will be three
    replicates of 5 plants of each variety planted in 10-
    foot-long plots in rows 60 inches apart.
    Transplants or seed will be sown into the mulches depending on irrigation production of the plot.
    Plants will be grown through the season and fruits will be harvested for disease evaluation and
    storage at approximately 45 days after pollination. Individual fruit weights and counts of
    harvestable fruit will be recorded. Figure 4 shows an example of a field plot.
    Chemical control effects on storage rot incidence To determine the efficacy of fungicide
    sprays as a control of storage rots, a set of plots at the Vegetable Research Farm will be planted.
    Figure 4. Field experiment map. Gray is
    control, yellow is cereal mulch, green is vetch
    mulch. Plots such as this will be repeated at all
    three farms in irrigated and dryland fields.
    As above, there will be plots in both the dryland and irrigated fields. And as above, there will be
    three replicates of 5 plants of each variety planted in 10-foot-long plots in rows 60 inches apart.
    These plots will be sprayed with prothioconazole (Proline 480 SC) at the rate of 5.7 fl. oz./acre
    using backpack sprayers. Plots will be sprayed twice, once at first bloom and again 14 days later.
    Plants will be grown through the season and fruits will be harvested for disease evaluation and
    storage at approximately 45 days after pollination. Individual fruit weights and counts of
    harvestable fruit will be recorded.
    Storage Trials Fruit grown at the Vegetable Research Farm will be placed in bins and
    stored in a closed barn bay maintained at >32F and ambient humidity [5,10]. In OSU storage
    trials this has been shown to be the most profitable storage environment [9,10]. Fruit grown at
    Gathering Together Farm and 47th Ave. Farm will be placed in bins and stored in a shaded
    greenhouse or barn maintained at >32F and ambient humidity. In November, January and March,
    evaluations of the number of rotted fruits and the color and location of rot will be recorded.
    Disease symptoms will be photo-documented (see Scholarly Publications section). Diseased
    fruits will be removed from storage as they are detected.
    Statistical analysis Storage data will be analyzed using the statistical program R.
    Regression models comparing yield to irrigation practice, mulch type, squash variety and rot
    incidence and severity will be analyzed.
    Profit analysis Following storage trial results, final yields and total potential profits,
    using average market prices from GTF and 47th Ave. Farm will be determined. Cost of labor and
    management techniques will be compared and an extrapolated cost of management and
    profitability bulletin will be developed for dissemination at outreach events.
    Educational Outreach Plan
    Objective 3. Engage growers in project planning, activities and outcomes
    Many farmers have inspired and informed this project. Both project farmers (GTF and
    47th Ave Farm) have partnered with OSU personnel in the past on squash and other projects. We
    will present results of our trials at field days and grower meetings.

    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.