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Powdery Mildew

Posted by Nathaniel Bouman 
Powdery Mildew
November 13, 2017 07:30PM
I've got a bad powdery mildew problem in my apple orchard. The stokes red are particularly bad off (the whole orchard is 3 years old) and it's affecting the growth of the trees. Most of the smaller branches are sheathed in white on the stokes red. It's a problem that really took off during the drought of 2016 (no rain but it stayed humid enough here). I was too inexperienced to catch it then and then this past season my attempts at control were kind of haphazard. I tried:
potassium bicarbonate
sodium bicarbonate
stylet oil
Trees seemed to perk up after the stylet and bicarbonate (potassium or sodium didn't seem to make much difference) but nothing got rid of the ghost twigs on the most badly affected varieties.
I hate trying to treat this because it's taking time away from working on whole tree health.
Has anyone encountered this kind of problem? Can you recommend a protocol for cutting down this pathogen? Do I have to engage in radical pruning?

Nat Bouman
Growing cider varieties in Zone 5b
On B.118 at 18X24
Susquehanna County, Pennsylvania
Re: Powdery Mildew
June 12, 2018 09:33PM
There is research on the use of Hops resin acid extracts as an effective counter to powdery mildew (Pseudoperonospora Humuli) . There is a conversation where this comes up in a thread titled Holistic Approach to Fire Blight in this forum if further rabbit holing is desired.

Karn Piana
Zone 7 Semi-Arid Steppe
Northern New Mexico
Re: Powdery Mildew
October 08, 2019 02:51AM
Had a tough season with Powdery Mildew here in Nassau Count, Long Island NY.. Not surprising, as the humidity was heavy as usual. I'm wondering if anyone has any experience with spraying milk or whey for powdery mildew. I'm told the grape growers are having success with it.

Also, can report that I used pheromones for Oriental Fruit Moth with great success.... It is expensive, but it works.

Tks in advance
Re: Powdery Mildew
October 08, 2019 03:18AM
I’ve tried milk. Started with powdered milk and rehydrated to make “milk” and then added to tank to make a 10% solution. I sprayed early in the PM season and mid growing season. I noticed no appreciable difference, sadly.

Nat Bouman
Growing cider varieties in Zone 5b
On B.118 at 18X24
Susquehanna County, Pennsylvania
Re: Powdery Mildew
October 08, 2019 10:43PM
Do you include SeaCrop in your spraying? I had powdery mildew in my fledgling orchard for several years. Each spring pruning more and more out. Started SeaCrop three years ago. Not a pruning since has been due to white blight.

Lakes Region NH @ 1200' or so

393 planted towards a 440 goal mixed apple, pear, plum and apricot...
Re: Powdery Mildew
October 09, 2019 05:33AM
Just remember that there are different species of "mildews" out there. Not all react the same to "milky" sprays. That said, I know that veg growers have had success spraying a yogurt or whey spray rather than just milk. Its the probiotics that works. In some cases mildews can be superficial, while others can be more invasive meaning that they infiltrate the cuticle of the fruit or veg. For apple, I would begin to work with a stronger probiotic yogurt spray, potassium bicarb or stylet oil (or combo) for better control. Bear in mind that the inoculum overwinters in the bud scales and is first active right after bud break. Start early, don't wait for normal PM weather.

Mike Biltonen, Know Your Roots
Zone 5b in New York
Re: Powdery Mildew
October 09, 2019 06:06PM
My hats off once again to those who create an ecosystem that can do without spraying. Perhaps if I had spent more years in developing the meadow in the woods before planting I would have succeeded. I only gave it one and with little diversity in seeding. Then came the planting of trees, with no spray. Bad move. Fast forward to the third year of planting. I purchase a 100 gallon Pak-Tank with hand application.

Started with a basic soup of EM-1, Fish/Seaweed, Neem/Karanja and Kelp. Fish and Seaweed disappears mid-summer. I also hit the trunk all the way to the ground each foliar application; I find it keeps the borers at bay. First spray at green tip or so, then three more every 7-10 days. From then to Halloween, I apply every two weeks. Two years of spraying later the trees overall were faring better, but the PM was not going away, it was spreading.

It appeared end of the first year of planting. At first, I tried to just wash it away with a dousing of alcohol, then wipe, then hydrogen peroxide and wipe. Next summer, when it came back I took a propane plumbers torch to a couple branches; hoping to burn the white fluff but somehow not damage bark and the vascular underneath. Yes, shake your head, while I hang mine in shame.

Second Spring has me pruning without repentance. Whole limbs go. I am also, at this point, dealing with another biologic pressure blown in by a Hurricane; but that is another post another time. Spraying begins. Following spring I am pruning out more PM. That growing season I keep spraying basic soup. Spring of 2017 I prune even more, and start casting about for a fix.

I settle on SeaCrop for evidence it will address my other infection, and hope that it will also help against the fluffy stuff. March of 2017 I go through the orchard and prune out all limbs, and one whole tree because of whatever strain of PM was spreading here on the hill. April sees the 4 holistic sprays getting 2 gallons of SeaCrop added to a 100 gallon recipe. Following the 4 spring applications, I used 1 gallon in a 100; every spray. That was the only change/addition to my augmenting the orchard. At the end of the summer I saw zero re-emergence of the PM that propagated here. March of 2018 required no pruning for PM. Followed same application protocols for last year. Zero evidence of PM last fall or this March.

Hard decision to make with two equally compelling testimonies. Certainly it would be much cheaper to continue with milk products. You could fall on the grenade of science and source both SeaCrop and yogurt/whey, then spray half and half. Maybe you find each work equally, or even that SeaCrop does nothing on your biologic. Perhaps before you do anything, take samples of your infection and identify categorically the strain that you are attempting to control. Your little bugger might not be hardy this far north or at my altitude. In the end when you do find a way to control it you have documented both the approach and the biologic that will be effected.

In the pursuit of more data points, could all users of SeaCrop document and post their history and ongoing situation with respect to Powdery Mildew...
Re: Powdery Mildew
October 17, 2019 02:09AM
My sincere thanks to you all for your advice! I think I will try the SeaCrop in part of the orchard, and whey in another to begin with.... Luckily, I can get whey from our Amish friends, so the probiotics should be intact (no pasteurization).

I will report back next year on my findings

Glenn Aldridge
Restoration Farm
Nassau County, Long Island, NY
Re: Powdery Mildew
June 20, 2020 04:49AM
There is some good research on the efficacy of whey with powdery mildew on wine grapes in Australia. I’ll see if I can find the paper. We do not have issue with mildew but I used whey in a spray last late summer/fall. Go with a very dilute concentration and make sure you get good mixing. It will severely burn pears.

Jim Gerlach
Nashi Orchards
Vashon Island, WA
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