2020 Apple Disease Update: 2nd Cover

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leaf with scab lesions

With the warm and humid/wet weather conditions in Western NC this week, hopefully your trees were well protected against Glomerella leaf spot, bitter rot, and fire blight. Fungicide applications this week should continue to be made with GLS and bitter rot on the brain. That’s not to say that other diseases such as apple scab, flyspeck/sooty blotch, and powdery mildew should be ignored. Rather, fungicides used for GLS/bitter rot should provide control against several other diseases. Since everyone’s spray schedule and resistance concerns are highly individualized, I find it difficult to provide a “one size fits all” recommendation for fungicide sprays. However, here are some scenarios and ideas that could help:

  • Scenario 1: “I have not applied a strobilurin (FRAC 11; e.g. Sovran, Flint WG/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, my suggestion would be to spray a strobilurin fungicide + mancozeb (e.g. Manzate). We have not tested Sovran efficacy against GLS or bitter rot, but the other products mentioned above provide excellent control against the disease. Apply mancozeb at 1/2 rate and strobilurin fungicide at the maximum labeled rate.
  • Scenario 2: “I applied a strobilurin (FRAC 11; e.g. Sovran, Flint WG/Extra, Pristine, Merivon, Luna Sensation) fungicide for my last fungicide spray”. If this is your situation, then well timed! My suggestion would be to consider an application of Aprovia + mancozeb OR Fontelis + mancozeb. Again, Fontelis or Aprovia should be applied at the maximum labeled rate for apples and mancozeb at 1/2 rate. In last week’s post I presented some promising data on Aprovia and Fontelis efficacy against GLS and bitter rot. An added bonus is that Aprovia is one of the more potent scab fungicides on the market right now. If powdery mildew control is more of a concern, I’d lean more towards Fontelis.
  • Scenario 3: “I did not apply a strobilurin (FRAC 11; e.g. Sovran, Flint WG/Extra, Pristine, Merivon, Luna Sensation) fungicide for my last spray, but I’ve already applied it twice this season. If this is your situation, then follow my suggestion for Scenario 2.” Looking at the weather forecast through the weekend, the conditions do not look ideal for a GLS/bitter rot infection event. Sure, when it rains, ascospores from overwintering inoculum can and likely will be dispersed. The mancozeb + SDHI fungicide combo should be enough to combat this though.
  • Scenario 4: “I do not feeling like paying for those expensive single-site fungicides and I only want to use multi-site protectants.” Considering annual application limits with multi-site protectant fungicides like captan and mancozeb, this approach may be difficult to sustain. Especially since 14 day fungicide application intervals are too long in the southeast. However, if you decide to go this route, consider a half and half application: 1/2 rate Captan + 1/2 rate Mancozeb. Legally, this is the highest rate of mancozeb you should be applying at this point in the season and applying 1/2 rate of captan will give you more mileage to get through the season. After 3rd cover, I’d suggest substituting mancozeb for something more legal (depending on cultivar and how many mancozeb applications you’ve already made) like Ziram.

fire blight on leaf

I must also provide you my weekly PSA about fire blight in the region. When I went to MHCREC today, I continued to see open blossoms still hanging on for dear life in my Rome Beauty block. This may also be the case for some other cultivars. If you did not protect any lingering blossoms this weekend, you may want to consider jumping on the sprayer tomorrow morning and applying the max rate of strep allowed for fire blight in any blocks that still have open flowers. There was an infection event today and the risk is high tomorrow (5/6); you should be able to get 24 hours of kickback activity. I’d also suggest applying Regulaid with the strep to help it’s movement into the tissue. Also make sure to scout any nursery trees or young plantings for scattered blossoms. I’ll also put out my weekly reminder that if Prohexadione calcium has not been applied twice (or once) in your block then strongly consider getting that out this week as well. Last week’s post covered application rates for different production scenarios but certainly contact me with any questions.