Fungicide applications this week should continue target GLS and bitter rot. However, don't lose site of Marssonina leaf blotch, particularly in blocks which had a bad outbreak last year. For Marssonina, I'd suggest relying on mancozeb or captan PLUS Cevya, Inspire Super, or Indar. Of these fungicides, only Cevya has Marssonina actually included on its label. While the strobilurins such as Flint, Cabrio, or Sovran have not shown strong efficacy in our field trials against MLB, the SDHI (FRAC 7) component of Merivon has. Therefore, you may want to include Merivon if you are concerned about GLS/bitter rot AND MLB in some blocks.
At this year's SE Winter Apple Conference, Ella Hinchliffe (a research associate in my program) and I introduced a new heat map for apple fungicide efficacy. It's pretty simple to follow: The darker the blue, the more effective a fungicide is for a particular disease. Hopefully this format helps with looking across the fungicide efficacy tables full of letters or numbers that you find in the spray guides. Please let us know what you think. If you'd like a laminated copy, reach out to me or your county agent and we will be sure to get some your way!
Here's a PDF version if you'd like to print yourself a copy:
For fungicide options this week let's look at a few scenarios:
Scenario 1: “I have not applied a strobilurin (FRAC 11; e.g. Cabrio, Flint Extra, Pristine, Merivon, Luna Sensation) fungicide yet this season”. If this is your situation and you are fairly certain your Colletotrichum population causing GLS and bitter rot does not have resistance to strobilurins (FRAC 11), my suggestion would be to spray a strobilurin fungicide + mancozeb this week. While Flint Extra and Luna Sensation provide great control against bitter rot, in our trials at the MHCREC, Merivon and Cabrio have provided superior control of Glomerella. Apply mancozeb at 1/2 rate (3 lb/A) and strobilurin fungicide at the maximum labeled rate.
Scenario 2: “I applied a strobilurin (FRAC 11) fungicide for my last fungicide spray”. Great! This week consider an application of mancozeb and either Inspire Super, Cevya, or Indar for Marssonina control if this is a concern. This will also help with powdery mildew control. If you feel like going the cheaper route, a half rate of mancozeb should be sufficient for GLS/bitter rot control given the temperatures at the end of this week, but it won't manage powdery mildew.
Scenario 3: “I do not feeling like paying for those expensive single-site fungicides." If you decide to go this route, 3 lb/A mancozeb will likely be alright for most diseases (except powdery mildew) if it doesn't rain too much. While DMI fungicides are not effective for controlling GLS or bitter rot in NC, including a more inexpensive and older FRAC 3 like Rally 40WSP or Procure would be helpful in controlling mildew and apple rust.
In recent years, we started spraying 'Red Delicious' specific programs at the MHCREC. Why? Because captan is more effective for controlling Alternaria leaf spot than mancozeb. While in most cultivars, I urge you to hold off on captan until after third cover, Alternaria needs to be targeted now. My suggestion for spraying 'Red Delicious' over the next three weeks is the following:
