Comparative performance and preservation of chemical management tools for powdery mildew on muskmelon

Over 6, 000 ha of muskmelons (Cucumis melo) are currently grown in the State of Arizona in the United States. Powdery mildew, caused by the fungus Podosphaera xanthii (formerly known as Sphaerotheca fuliginea) is an annual concern for growers in this arid region. The efficacy of several fungicides, applied alone, in mixtures or in a rotational program, was evaluated for control of powdery mildew on muskmelon. The role of selected adjuvants in management of the disease also was examined. All treatments in 2002 through 2004 field trials significantly reduced the severity of powdery mildew on muskmelon compared to nontreated plots. Of the chemistries evaluated, triflumizole and wettable sulfur were among the most effective fungicides in all three trials, reducing the severity of powdery mildew from 72 to 100% and 69 to 89%, respectively, compared to nontreated plants. Quinoxyfen was among the best performers in two trials, suppressing disease 86 and 100%. Reduction of powdery mildew severity by at least 70% in at least one trial also was achieved by azoxystrobin, chlorothalonil, myclobutanil, potassium bicarbonate, pyraclostrobin, thiophanatemethyl and trifloxystrobin. Disease control by mixtures of fungicides was equivalent to and sometimes significantly better than the performance of individual components of the mixture. Similarly, the rotational programs provided levels of disease control equivalent to and in one instance significantly better than the performance of each component of the rotational program. These rotational programs included pyraclostrobin alternated with triflumizole, quinoxyfen alternated with thiophanate-methyl, thiophanate- methyl alternated with pyraclostrobin, trifloxystrobin alternated with chlorothalonil, trifloxystrobin alternated with quinoxyfen, and triflumizole alternated with quinoxyfen. Adjuvants are often added to a fungicide spray mixture to improve the performance of the fungicide. Three adjuvants, Kinetic, No Foam A and Silwet L-77 significantly reduced the severity of powdery mildew on muskmelon when applied without a partner fungicide.