Evaluation of New Butternut Squash Variety Resistant to Powdery Mildew, 2019

This replicated experiment was conducted at LIHREC in 2019.

Topics on this page:

• Procedures
• Results
• Tables
• Images

Powdery mildew (PM) is the most important disease affecting cucurbit crops, occurring every year throughout Long Island as well as the rest of the US.  Management is needed to avoid loss in yield and especially fruit quality.  Flavor of melons and squashes is poor and they lack sweetness when leaves senesce prematurely due to a disease like PM not being successfully managed.  Fungicides and PM resistant (PMR) varieties are the only management tools for PM.  Using an integrated program with fungicides applied to PMR varieties is recommended to minimize selection pressure on the pathogen to develop resistance.  This pathogen has proven adept at developing resistance, especially to targeted fungicides.  PMR cucurbit varieties are an important tool for managing this important disease for both organic and conventional growers on Long Island.  In past evaluations at LIHREC, PMR varieties have exhibited a range in level of suppression from poor to excellent.  It is helpful for growers to know how well new varieties perform in terms of ability to suppress a disease, in order to select a fungicide program to achieve desired level of control, and also to know yield and fruit quality compared to standard varieties to determine whether a new variety is suitable for their operation.  The goal of this project was to evaluate a new butternut squash variety: Gabrielle.  Two adjacent experiments were conducted. One was treated weekly with PM fungicides starting at first detection of symptoms to evaluate the PMR varieties as part of an integrated management program.

Procedures:

Experiments were conducted at the Long Island Horticultural Research and Extension Center (LIHREC) in Riverhead, NY, in a field with Haven loam soil.  Controlled-release fertilizer (N-P-K, 15-5-15) at 675 lb/A (100 lb/A N) was broadcast over the bed area and incorporated on 24 Jun.  Beds were formed with drip tape and covered with black plastic mulch also on 24 Jun. A waterwheel transplanter was used to make planting holes in the beds and apply starter fertilizer.  Two seeds were placed by hand in each opening on 28 Jun, plots were thinned to one plant per hole or missing plants replaced with transplants on 5 Jul so that each plot consisted of 12 plants. To separate plots and provide a source of inoculum, there was a single powdery mildew-susceptible zucchini squash plant (cv. Spineless Beauty) between each plot in each row.

Plots were three 15-ft rows spaced 68 in. apart with 12 plants per plot. There were two adjacent experiments. In one experiment, PM was not managed while in the second experiment, it was treated with fungicides to evaluate the PMR varieties as part of an integrated management program: Procure, Quintec, and Vivando applied in rotation weekly. A randomized complete block design with four replications was used.

PM severity on upper and lower leaf surfaces was rated in each plot on 15, 22 and 29 Aug; 4, 9, and 17 Sep.  Area Under Disease Progress Curve (AUDPC) values were calculated from 15 Aug through 17 Sep to obtain a summation measurement of PM severity. Fruit were harvested when mature.  Fruit quality evaluations were conducted with CCE and LIHREC staff plus Cornell Gardeners.  Squash were baked and tasted plain without any seasonings or butter.

Results:

Powdery mildew was first observed in these experiments on 15 Aug at low levels and not in all plots. The fungicide program was very effective. Due to low disease severity, there were no expected differences between varieties, so further assessments focused on the untreated experiment. Severity data presented in the tables is only from the untreated experiments. All PMR varieties were significantly less severely affected by PM on both upper and lower leaf surfaces than the susceptible variety included for comparison. but the benefit of genetic resistance became less apparent as disease pressure increased later in the season, especially on lower leaf surface (Table 1). These results indicate that fungicides are an important component of a management program for PM. Percent control achieved with the PMR varieties on upper/lower leaf surfaces based on AUDPC values was 49%/38% for Gabrielle and 67%/53% for Quantum.

Margaret Tuttle McGrath
Plant Pathology and Plant-Microbe Biology Section, SIPS, Cornell University
Long Island Horticultural Research and Extension Center
3059 Sound Avenue, Riverhead, NY 11901
mtm3@cornell.edu

Acknowledgments: This project was supported by the National Institute of Food and Agriculture, U.S. Department of Agriculture, Hatch under NYC-153409 and the Friends of Long Island Horticulture Grant Program. 

Tables

Table 1. Severity of powdery mildew on susceptible and resistant varieties of butternut squash that were not treated with fungicides for this disease.

Table 2. Fruit of susceptible and resistant varieties of butternut squash were evaluated on a 1 (poor) to 5 (excellent) scale for several parameters by CCE and LIHREC staff plus Cornell Gardeners.  Values are average rating, overall average, and percentage of raters who indicated they would buy the variety.

Images

Figure 1. Fruit of Gabrielle, Quantum, and Waltham butternut squash (2 fruit halves each).