Evaluation of Halloween Pumpkin Varieties Resistant to Powdery Mildew, 2016

This replicated experiment was conducted at LIHREC in 2016.

Topics on this page:

• Procedures
• Results
• Tables
• Images

Pumpkins are a very important crop on Long Island.  Powdery mildew is the most common disease affecting this crop, occurring every year throughout Long Island.  Management is needed to avoid loss in yield and/or quality.  When not adequately managed, leaves die prematurely leading to death of vines and pumpkin handles, fruit color can be less intense, and loss of leaves exposes fruit to sunscald.  Maintaining solid handles into October is very important for u-pik pumpkins. Resistant varieties and fungicides are the only management tools.  Resistant varieties have been increasing in importance as their number increases.  There are few hybrids on the market today that do not have resistance to powdery mildew (PMR).  Thus it is now possible to have a planting of all PMR varieties yielding the diversity of fruit types that customers are looking for.  When developing an integrated management program, it is valuable to know how effectively powdery mildew can be managed with resistant varieties and whether there are inherent differences in resistance among them to guide selection.

Procedures

Two experiments with field-grown pumpkins were conducted at the Long Island Horticultural Research and Extension Center (LIHREC) in Riverhead, NY. The goal was to evaluate pumpkin varieties for their ability to suppress powdery mildew when used as the sole management program and also combined with a fungicide program for powdery mildew.  Focus was on recently released varieties.  Controlled release fertilizer (N-P-K, 19-10-9) at 525 lb/A (101 lb/A of N) was broadcast over the bed area and incorporated. Beds were formed, drip tape was laid, and beds were covered with black plastic mulch.  Plots were three adjacent rows each with four plants spaced 48 in. apart.  Seed were hand planted.  To separate plots and provide a source of inoculum, two plants of a powdery mildew-susceptible zucchini squash variety (Spineless Beauty) were planted between each plot in each row.  The experiment that received a fungicide program for additional control of powdery mildew was sprayed with a tractor-drawn sprayer at weekly intervals starting at first observation of symptoms. The program was: Vivando 15 oz/A on 8 and 31 Aug and 14 Sep, Torino 3.4 oz/A on 18 Aug and 7 Sep, and Procure 8 oz/A on 24 Aug.   Plots were assessed for severity of powdery mildew symptoms on upper and lower leaf surfaces on 8, 17 and 25 Aug, and 2 Sept.  Area Under Disease Progress Curve (AUDPC) values were calculated from 8 Aug through 2 Sept.  AUDPC is a summation measure of disease severity over time.  Fruit quality was evaluated in terms of handle condition for mature fruit.  Handles were considered good if they were green, solid, and not rotting.

Results

Through the pair of experiments, it was documented that the resistant pumpkin varieties tested vary in ability to suppress powdery mildew and none provide enough suppression to be used as the only practice to successfully control this disease.  In the tables, varieties are organized based on sum of the four AUDPC values with the variety least affected by powdery mildew listed first.  Only two varieties (Progress and Rhea) provided significant level of control of powdery mildew (were significantly less severely affected) compared to a susceptible variety in absence of fungicides for powdery mildew.  Achieving a commercially-acceptable degree of control necessitated applying fungicides.  A 7-day fungicide program was used with an alternation of Vivando, Torino, and Procure for a total of six applications in the second experiment.  Ares, Rhea, Superior, and Progress were significantly less severely affected by powdery mildew than the susceptible variety Gold Challenger.  All varieties had numerically fewer symptoms.  Progress performed especially well with 73% control relative to Gold Challenger.  Superior performed second best overall.  These varieties have homozygous resistance (resistant gene from both parents).  Conditions were highly conducive for powdery mildew in 2016.  Progress produced smaller pumpkins then the other varieties (average 8.4 lb/fruit).  Kratos produced the largest fruit (16 lb).  In these experiments fruit handle quality was not closely related to powdery mildew severity as is typical in fungicide efficacy experiments.  Only one significant difference was detected, perhaps reflecting additional factors impacting handle quality, including genetic differences among the varieties in handle traits and days to maturity, which affects leaf senescence.

Conclusion

The results provide growers information they need to effectively manage powdery mildew, namely that resistant pumpkin varieties are an effective component of the control program, those with homozygous resistance are the best choice, and targeted fungicides also need to be applied to achieve a commercially-acceptable level of control.

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 funding from the Friends of Long Island Horticulture Grant Program.  Any reference to commercial products is for information only; no endorsement is intended

Tables

Table 1. Pumpkin variety assessment without fungicide program for powdery mildew.

Table 2. Pumpkin variety assessment with fungicide program for powdery mildew.

Images