Control of Cantaloupe Powdery Mildew, 2007
University of Arizona
Michael Matheron & Martin Porchas
Objective: Conducted to test the efficacy of various Conventional and Bio Fungicides on 'Topmark' Cantaloupes infected with Powdery Mildew (Podospaera xanthii), this study demonstrated the degree of control achieved by various applications.
Method: Plots used in study were located at the University of Arizona, Yuma Agriculture Center. Conditions were in a silty clay loam soil (7-56-37 - sand-silt-clay), the pH was 7.2, organic matter content (O.M.) was 0.7%, no significant rainfall occurred during the experiment, and temperatures and relative humidity were favorable for powdery mildew development throughout duration of trial. The Cantaloupe was seeded March 6, 2007, sprinkler irrigation was used to germinate the seeds on beds with 80 inches between bed centers, and subsequent irrigations were made by furrow irrigation. Replicated five times in a randomized complete block design (each plot consisting of 25 ft. of row), the treatments were applied via foliar application with a tractor-mounted boom sprayer which delivered 50 gal/acre at 100 psi. Applications were made on May 17 when fruit was up to 3.5 inches in diameter and plants were covering the bed, May 24 when fruit was about 4 – 4.5 inches in diameter and the plants wer e covering the bed and some of the furrow, May 31 when the fruit was about 4.5 – 5 inches in diameter and initial netting was developing, June 8 when fruit was 5 – 5.5 inches in diameter and netting was more developed, and June 15 when the melons were at the front end of maturity. "Juane canary", a variety very susceptible to powdery mildew, was planted in single beds at the north and south boundaries of the trial to serve as a nursery for production of the powdery mildew fungal spores.
On June 20 - 23 the disease severity was determined for each plot by collecting 10 leaves at random from each plant and yield was determined by counting the number of marketable cantaloupes in each plot.
Results: A moderate – high level of disease developed on the untreated cantaloupe. Observations in the study suggest that disease control on the upper leaf surface of the treated plants has the potential to significantly reduce powdered mildew compared to no treatment (when applied directly to the leaf surface with relatively good coverage). There was no evidence of Phytotoxicity observed with any of the treatments in the study. Additionally, most treatments administered were of combinations of 2 or more fungicide products, or a fungicide product with the addition of an adjuvant. Companion Biological Fungicide performed well in the study as a "single" product. Bio Fungicides reduce and prevent fungal diseases using different modes of action like antagonism, competition, antibiosis, enhance nutrient uptake and inducing host resistance (not to mention having much softer chemistries) comparative to conventional or traditional fungicides which consist mostly of systemic chemical fungicides with a single point mode of action that acts on a specific protein or structure (initially this can be very effective, however at the same time vulnerable to the onset of resistance).
Figure 1 - Incidence
Disease Ratings
0 1 2 3 4 5
No powdery mildew colonies present on plant 1 to 5 powdery mildew colonies on leaf surface 6 to 10 powdery mildew colonies on leaf surface More than 10 colonies to 25% of leaf surface covered with powdery mildew 26 to 50% of leaf surface covered with powdery mildew 51 to 100% of leaf surface covered with powdery mildew

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