For several years now, growers of cantaloupes, cucumbers and watermelons in Georgia have been without an effective late-season fungicide for suppression of their most destructive disease — gummy stem blight.
Although many materials are labeled, problems exist with each of them. Chlorothalonil (Bravo, Echo) is very effective against the disease but has been implicated in causing a rind burn on watermelons if applied under certain conditions and within three weeks of harvest.
The benzimidazole chemistry (Benlate and Topsin M) worked well until they began having problems with resistance in the early to mid-1990s. Strobilurin fungicides such as Quadris (azoxystrobin) and Cabrio (pyraclostrobin) did demonstrate excellent efficacy, but resistance to these materials has developed in the gummy stem blight pathogen over the past few years.
Studies in Georgia have shown that 91 percent and 82 percent of the gummy stem blight isolates tested across the state were resistant to strobilurin fungicides in 2001 and 2002, respectively. That leaves only mancozeb products, which always have been only marginally effective against gummy stem blight when conditions were very favorable for disease development.
However, it seems that help has arrived with the new cucurbit label for Pristine by BASF. Pristine is a pre-mix of pyraclostrobin (active ingredient in Cabrio) and boscalid (active ingredient in Endura). This new product covers a wide range of crops and diseases. Probably the most significant thing gained with these new labels is the excellent gummy stem blight suppression demonstrated by Pristine.
In the summer of 2003, trials at Attapulgus and Tifton, Ga., demonstrated that three sprays of Pristine rotated with Bravo or three sprays of Pristine made after three initial sprays of Bravo significantly suppressed gummy stem blight compared to a full-season Bravo program.
Also, Pristine applied on a full-season schedule significantly suppressed gummy blight compared to full-season Bravo at both locations. This new combination product also brings to the table both powdery and downy mildew suppression. These two diseases have plagued Georgia watermelon growers for the past two years.
It is important to note that Pristine should be applied as a preventative and rotated with other chemistries like Topsin M, chlorothalonil or mancozeb for resistance management purposes. It also should be stressed that Pristine should NEVER be used in the green house for any reason because of the high risk of resistance developing rapidly to that class of chemistry.