A unique mutation of I229V in SdhB, a target of succinate dehydrogenase inhibitor fungicides, was detected for the fluopyram-resistant isolate of S. Additionally, isolates sharing the same MLG varied by SdhB genotype. citrulli isolates, but the phenotypes were not associated with multilocus genotypes (MLG) determined by 16 microsatellite loci. Phenotypic differences in response to boscalid were detected among S. citrulli except two were resistant to azoxystrobin. citrulli isolates were sensitive to tebuconazole and sensitive to fluopyram, with one exception that was fluopyram-resistant. caricae isolates screened were resistant to tebuconazole and azoxystrobin, and sensitive to boscalid and fluopyram. caricae isolates to four different fungicides were determined based on in vitro mycelial growth assays and molecular markers based on genes encoding fungicide targets.Īll 19 S. To better understand the evolution and persistence of fungicide resistance in field populations, resistance profiles of unique and clonal genotypes of 113 Stagonosporopsis citrulli and 19 S. that cause GSB have rapidly evolved resistance to multiple classes of fungicides. In addition, formulations of fungicides may be improved and the rates and allowed application methods may change from year to year.Gummy stem blight (GSB) is a devastating disease of cucurbits that has been effectively managed with fungicide applications. Be aware of pre-harvest intervals, re-entry intervals, correct personal protective equipment. That brings me to one additional important point. These fungicides should not be used during the harvest period. Several very effective fungicides have long pre-harvest intervals (7 days). In the case of aerial applications, light rainfall may improve coverage by improving distribution of the fungicide within the plant canopy. Don’t worry about the fungicides being removed during a typical rain, because modern fungicides are formulated to persist on leaves and fruit following rain. This is true even for protectants, which have some “kick-back” activity. All fungicides are more effective if they are applied before disease development. Timing of the fungicide applications is very important. Group 4 fungicides such as Procure are still useful for a limited number of your powdery mildew applications, but should be used with excellent resistance management practices. Likewise the powdery mildew pathogen is resistant to strobilurins, and Topsin M. Choose other fungicides such as Fontelis, Luna Experience, Switch, or Inspire Super. Recently resistance to tebuconazole was reported in Georgia. For example, the gummy stem blight pathogen is resistant to strobilurins, Topsin M and Pristine. In selecting fungicides, be sure to stay informed about fungicide resistance (insensitivity) that has developed to watermelon disease pathogens. In addition to identifying what diseases are present in the field, assess what the most prevalent problems are in selecting what fungicide to use. There are many “look-alike” diseases and other diseases that mimic abiotic problems. Correct identification of the problem is critical. Protect additional fruit set from BFB with additional copper applications.Īpply the best fungicides for the diseases that are present in your field. Additional applications for BFB should be applied in two weeks as the female flowers open and again two weeks later. The first fungicide application should include a copper product to manage bacterial fruit blotch (BFB). Following the first spray, fungicides should be applied weekly. This early spray is very important to prevent disease in becoming established. Both Nathan and I have received numerous questions about best practices for fungicide application this year, so it is also a good time to review these best practices.įungicide applications should begin on watermelons when the vines are about 18 inches long or about when the first flowers open (these will be male flowers). Kate Everts, Vegetable Pathologist, University of Delaware and University of Maryland Nathan Kleczewski, Extension Specialist – Plant Pathology the season winds down, it is a good time to reflect on how well your fungicide program worked in 2014.
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