GLS and Bitter Rot Management at Harvest

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Bitter rot spots on GalaSymptoms of Glomerella leaf spot and bitter rot caused by Colletotrichum fructicola have been rapidly increasing throughout the region over the past few weeks. While we are still examining weather data to better understand later-than-normal symptom development in Western NC, our working theory right now is that the number of consecutive leaf wetting hours was simply too low to trigger an infection event and subsequent symptom development. Although we had a fairly wet July and early August, the majority of significant precipitation events were actually short in duration and occurred in the afternoon, giving the leaves ample time to dry prior to nighttime. In contrast, in 2019 the majority of leaf wetting hours occurred in the evening and leaves would remain wet for much of the morning. With conditions still favorable for GLS and bitter rot, I encourage you to continue on 7 to 10 day fungicide application intervals throughout harvest. While it might be extremely inconvenient to diversify fungicide programs based on cultivar harvest date, adapting cultivar-specific fungicide programs for cultivars highly susceptible to bitter rot may save a lot of heartache (and money) during storage. Here are some additional tips:

Bitter Rot Susceptible Cultivars 14 days prior to harvest:

Plan A:

  • ~14 days out: Captan 80WDG 3.75lb/A (or 4L 2.5 qt/A) + Prophyt 4 pts/A
  • ~7 days out: Merivon 5.5 floz/A + Captan 80WDG 2.5 lbs
  • ~Day of Harvest: Merivon 5.5 floz/A + Captan 80WDG 2.5 lbs

Plan B:

  • ~14 days out: Captan 80WDG 2.5 lb/A + Ziram 3 lb/A
  • ~7 days out: Merivon 5.5 floz/A + Captan 80WDG 2.5 lbs
  • ~Day of Harvest: Merivon 5.5 floz/A + Captan 80WDG 2.5 lbs

Plan C:

  • ~14 days out: Captan 80WDG 2.5 lbs + Prophyt 4pts/A
  • ~7 days out: Captan 80WDG 3.75lb/A (or 4L 2.5 qt/A) + Prophyt 4 pts/A
  • ~Day of Harvest: Merivon 5.5 floz/A + Captan 80WDG 2.5 lbs

Glomerella Susceptible Cultivars more than 14 days from harvest:

  • Application of Captan 80WDG 3.75 lb/A (or different formulation equivalent)+ Prophyt 4 pts/A OR Captan 80WDG 2.5 lb/A + Ziram 3 lb/A on a 7 to 10 day interval has worked well for us. If flyspeck/sooty blotch, or bot rots are a concern, you may want to include Inspire Super, Topsin (or different t-methyl product), or Aprovia tank mixed with Captan + Prophyt. Keep in mind, Inspire Super, Topsin, or Aprovia applied alone will NOT provide adequate control of Glomerella leaf spot or fruit rot.