I purchased three apple scions/grafts at the HOS event earlier this spring. The grafts took beautifully and the trees are growing! However, I noticed that two of them have powdery mildew on the newest leaves at the top. How should I treat this on such a new specimen? I have them growing in 1-gallon containers on my back porch that faces north. Perhaps I should put them in a full sun location? Thanks so much for any advice! -Meredith
This year was the first time I ever helped collect scionwood with the Home Orchard Society for pear-wood and what I know now is many apples are donated elsewhere. Then there at the government agency (pears), many us volunteers were given a "collections list" for only the most adapted cultivars of pear trees to our area. So I am not sure I have very much faith in what apples cultivars are donated. I am sure we live in a moist area and that powdery mildew must love a shady place and a more vulnerable apple cultivar. Which I suggest yours might be, if we know the name? -or anybody else chiming in that knows more about apples and the disease to back me up??
Liberty and Empire are the two varietals.
They are generally pretty good with disease. I've never gotten powdery mildew or any other big disease problem on Liberty and I've grown it for decades. You could use fungal compost tea, which is complicated to make if you don't know how. There was a protocol that I found fascinating for spraying milk, I think on powdery mildew. It has to be in sunlight.
I'll see if I can find it.
Yeah, I 'd put it in the ground on the SOuth side, but that's me.
The article lists the mode of action starting from ultraviolet light upon a protien, in turn producing a fungus poison and safe mode of action towards the plant's waxy protective layers. (ie. science news) The very reason I bring this up is the lack of ultraviolet exposure these 2 varietal apples have growing on the north side. In which case moving to the south the day of application makes more sense, then the rest of the week back again.
It also makes good sense to monitor the conditions of potted apples with a soils insertion thermometer, as poor a root health system caused by too high a reading can make a normally resistive variety suseptible to anything.
To make sense of what I just said regarding ill apple roots and health issues -it has been reported a problem (in 1972) when above 77F for apple roots.
Another worded example in my same WSU link: "in one study roots from an M.9 rootstock died at 77oF. At high temperatures oots matured fast, browned, sloughed, and were infected by pathogens (Nelson and Tukey, 1955"
I always knew there were these potted issues. I once was relocated into an apartment due to my employer. The more cold water on my temporary placed pots of trees on the side steps the better they were.
Yeah, those newly grafted sions, aren't in robust health yet.
Warm water containing a dash of dishwashing detergent ( enough to break the surface tension), add a cap-full or two of chlorox per quart? Spray it on with handheld bottle type sprayer. I have found this effective in the past.
Just few treatments, should do the trick.
Chlorine is very very effective against mildews. The Neem solutions used to spray roses, should also be effective.
Vitus Vinifera grapes (wine grapes) are easily overwhelmed by PM. And once you got it, it is very difficult to stop it. So you need to have a regiment if there is the tendency. I have used Lime Sulfur as a preemergent spray but a guess they baned it. Guess someone was pointing it at their eyes. Bordeaux mix (sulfur), spray oil, special soaps and/or base products such as clorine or baking soda work. Even milk is used. PM will adjust so you have to rotate it.
Interestingly, PM loves 60-80 temps, shade and low airflow.
The American labrusca foxy grapes are tougher against disease and tastier in my opinion.