It was another bad year for Marsonnina leaf blotch and someone just asked me how I deal with it. Legitimate research is woefully inadequate in this country because conventional apple production in the humid region already stops MLB because active fungicide is on the leaves throughout the growing season. My schedule is based on 5 years of controlling it successfully in many different orchards.
For a home grower I recommend two summer sprays, but my experience on this also includes at least two fungicide sprays in the spring, not because it is necessary to control MLB but because I’m also controlling for scab and cedar-apple-rust. I am not sure if only the summer sprays will be effective by themselves, but my hunch is that they would be.
Basic spray schedule.
1st spray 6-7 weeks after petal fall (early July here) Myclobutanil and Captan at highest legal rate.
2nd spray 30 days later. Same materials at same rate.
I actually use Indar and Pristine mixed with Captan instead of myclobutanil, but they are not available in packaging for small home orchards. I also sometimes use Flint or Topsin M. I spray stone fruit in orchards at the same time so I usually need fungicides that are labeled for stone fruit as well. .I have read of Chinese growers successfully using myclo.
I like having one fungicide with kickback in the mix because it may be necessary to kill existing spores on the leaves. Myclo and Indar have kickback and are also locally systemic so don’t wash off in rain. Topsin M is much more affordable than Indar or Pristine and is labeled for stonefruit against brown rot and is locally systemic.
This has worked in the NY and CT locations I’ve employed it but I don’t know if it is enough in areas south of me with longer seasons. Perhaps further north only one summer spray would be adequate.
Goldrush, my favorite apple, suffered nearly complete defoliation. Based on this comparison from North Carolina State I believe the trees had severe Marsonnina Leaf Blotch and Glomerella Leaf Spot, and perhaps Frogeye leafspot too. A heavy crop also all rotted, probably due to bitter rot, which is the same bacteria as GLS. My other apples and pears were relatively unbothered by diseases using myclobutinal plus Regalia plus Southern Ag Garden Friendly Fungicide (Bacillus amyloliquefaciens), I’m not looking for perfect results, just enough to get a reasonable crop.
For dealing with MLB the author of the NC State article recommends “Cevya (only fungicide in USA labeled for this disease), Merivon, Sercadis, Inspire Super, captan”, and for dealing with GLS “Mancozeb, captan, and fungicides containing a strobiluring/FRAC 11 fungicide. (e.g. Luna Sensation, Flint Extra, Merivon, Pristine) Aprovia (FRAC 7) and Omega provide moderate activity. MUST APPLY ON A 7 to 10 DAY INTERVAL.”
Do you think Captan in rotation with Bonide Fruit Tree and Plant Guard is a reasonable option for dealing with these diseases on Goldrush.? I believe it has the same active ingredients as Pristine, plus an unwanted (by me) insecticide. As you pointed out, Indar and Pristine are not available in packaging for small home orchards.
Thank you for bringing this up. It is significant enough that I am considering top-working all of my trees with GD in their genes. Goldrush and Suncrisp were very bad, but I did get some edible fruit from Suncrisp. Hooples seemed to get it a bit later than the others, but it is a young tree that is coming into bearing. Unfortunately, I put a bunch of Rubinette grafts on my Chestnut crab, which I may regret. After a couple of years of this, I am almost ready to erase Golden Delicious from my backyard.
First, I wouldn’t rotate Captan, it is a lock fungus has extreme trouble breaking so use it in every fungicide app where it offers some control, especially in home orchards where resistance should take many times longer to develop than in a 100-1,000 acre monoculture. Actually that’s a good reason to use in in every app in commercial production. As far as I know, no fungus pest has developed resistance to Captan.
Also, given the above and other factors take university guidelines with a grain of salt. They always suggest much more intervention than I have found to be needed in a small orchard. The research they are using often is not in real life circumstances, it is in a laboratory which only shows the immediate and not the long term efficacy of any given fungicide and underestimates the importance of using a systemic in the presence of rainfall. These professors generally don’t focus on real life scenarios, especially pathologists, because they usually don’t have orchards. The research universities do is for commercial production and most commercial production already has MLB under control in the course of controlling other pests. . .
However, info about what works in a lab is useful and is another source of info to work from when developing you own methods.
As far as your actual question- I have no idea, but I would try to find the ingredient in a formula without insecticide.
For Marsonnina Leaf Blotch fungicide spray once in July and once in August worked well enough for me - only about 10% damage. In 2022 also added two additional sulfur sprays in Sept in addition to the July and August sprays and that worked 100%. Sulfur alone may be adequate for organic growers if sprayed often enough.
Thanks for supporting my point. University guidelines really do tend to be excessively conservative.
for smaller orchards. I also get pristine fruit without doing a single summer spray in June which their research deems impossible because the inoculum is supposed to start establishing then if apples are unprotected- they say once it is established control is impossible. Often my last Spring spray in during the end of May and when I wait until about July 7th to control summer diseases and do biweekly sprays into Sept if get pristine fruit with most varieties most years including seasons with lots of summer precip. On my own property, Goldrush is an exception, it gets messy in Sept if I don’t spray though that month, which I never do. On other orchards is usually a different story- my site is too darn sheltered from wind.
I’m not disagreeing with you @alan about what works for you. Your success and my failures are what led me to ask my initial question. As has been discussed in many threads on our forum, climate plays a big factor in disease pressure, and being so much further south than you I’ve got a longer growing season, higher temps, and possibly more spring and summer humidity. I wonder how much those conditions affect MLB, and the need for sprays?
It does appear that the NC State folks are basing their recommendations on what works for them in the field, not the lab. For instance, here’s a quote from them last year, which I think accurately represents the rationale behind their advice:
“On a stroll through our Glomerella research orchard today, no trees in which captan was applied on a 7 to 10 day interval had any symptoms of GLS or bitter rot. However, treatments in which captan was applied on a 14 day interval beginning at 1st cover were another story.”
Read more at: Apple Disease Update: Week of July 3 2023 | NC State Extension
I apologize for taking this thread in the GLS direction instead of focusing on MLB, but my point is that their advice seems based on practical results. Of course, the results they are looking for by providing guidance to commercial growers are different than the results I’m hoping to achieve.
NC State’s MLB fungicide recommendations are from groups M4(captan), 3, 7, 9, and 11. The Bonide product has been the only homeowner product I’ve located so far with the same active ingredients as Pristine, which has fungicides from groups 7 and 11, and is recommended for GLS. As I noted above, the Bonide product contains an unwanted pesticide. I’ve used Captan in the past, using PH appropriate water, spraying once a month, and was very unhappy with the results. Perhaps I’ll try radically shortening the Captan spray interval and see what happens.
They manage one orchard, I manage 100 and their comment about Captan requiring tight intervals is known to anyone who does this stuff for a living. That is the point of using a systemic with kickback. How do you suppose I can control scab and CAR with only two spring apps? My Cornell gurus don’t tend to believe me when I claim I can do this.
However, I wasn’t disagreeing with you either, and I always make a point of the difference in pest pressure from one region to another and even from one orchard to another, sometimes when they are only walking distance apart.
However, if you go conservative and spray as much as guidelines suggest, you may never find out what you really need. I will take risks to learn, even if it sometimes bites me.