The rain over the past few weeks has accelerated symptoms of Glomerella leaf spot and bitter rot throughout western NC. At the Research Station in Mills River, we had about 4 inches of rain that fell this past weekend. From a very wet run I had in Fletcher Park on Sunday, I know very heavy rain was localized in some areas so make sure to check weather stations/rain gauges nearby your orchards. If it rained 1.5 inches or more since the last time you applied a fungicide or it's been longer than 10 days, I would try to get orchards covered before the rain arrives tomorrow afternoon. At the very least, consider a hitting all 'Honeycrisp' planting and cultivars that are susceptible to bitter rot. Depending on the amount of rain that falls over the next few days, you may need to head out a reapply as soon as Friday-Monday.

In regards to what to apply this week consider the following options for GLS and bitter rot concerns:

1. Captan 80WDG (5 lb) OR
2. Captan 80WDG (2.5 lb) + Merivon (5.5 fl oz) or Cabrio (12 oz) if no resistance to these materials or any FRAC 11 fungicides OR
3. Captan 80WDG (2.5 lb) + Aprovia (7 fl oz) Aprovia has a 30 day PHI in apple

If you are more concerned about Marssonina leaf blotch consider these options:

1. Captan 80WDG (2.5 lb) + Merivon (5.5 fl oz) OR
2. Captan 80WDG (2.5 lb) + Cevya (5 fl oz)

In addition, conversations with Greg Nix, Jon Klimstra, and Gene Klimstra prompted us to do a full scale calcium trial for GLS and bitter rot management this season. For this trial, we applied Captan 80WDG (2.5 lb/A) every other week (i.e. every 14 days) beginning at first cover (April 21) to our Glomerella Gala Research block. Dowflake (Calcium Chloride, 85%) was applied at 4 different rates: 2.5 lb, 5 lb, 7.5 lb, and 10 lb (per 100 gal) weekly through 8th cover (June 8) and then applied every other week (i.e. every 14 days) on the weeks Captan was not. In other words, from 8th cover until today Captan was rotated with Dowflake. As of today, we have only rated GLS incidence on leaves. Next week we will make our final fungicide application in the block and conduct a harvest fruit and final leaf rating. However, I wanted to share some exciting preliminary results!

To summarize the graph above, the untreated treatment received no fungicides or calcium the entire season. The "no calcium" treatment received only Captan 80WDG (2.5 lb/A) every other week. The next four bars are the different rates of calcium with Captan 80WDG applied biweekly as described just above the graph.

As you can see, the "no calcium" treatment in which Captan was applied every other week resulted in the highest incidence of GLS numerically compared all other treatments except for the untreated check. However, this was no different than the treatments that received 2.5 or 5 lb Dowflake. GLS incidence was slightly higher but not statistically different in the 10 lb/100 gal rate of Dowflake (last bar) compared to the 7.5 lb/100 gal rate - the best treatment for GLS. We did observe significant injury to leaves in treatment receiving the highest Dowflake rate, which is not surprising given the rate and the frequency to which it was applied.

While I stress this is just one year of incomplete data these results do have me excited - at least for the foliar stage of the disease! The treatment of Dowflake 7.5 lb/100 gal + Captan 80WDG (applied every other week) had a GLS incidence of 18.1%. In the no Dowflake/Captan every other week treatment the GLS incidence was 55.9%. For this trial, this equates to more than 3x less incidence of GLS just by adding 7.5 lb/100 gal Dowflake for treatments in which Captan was applied every other week! If you're curious, as of July 21st GLS incidence was 11.6% in a treatment in which Captan was applied weekly starting at 1st cover. Stay tuned for our fruit rating in a few weeks!