Last updated on July 8th, 2019
(Updated for 2019.) DRAT. While inspecting my roses the other day, I discovered that some of the shrubs (like ‘Mary Rose,’ above) are showing signs of “blackspot.” Details about this insidious fungal disease, and why — according to extensive research — a weekly spray of milk and water is the smartest way to control it:
The infected leaves will eventually turn a sickening shade of yellow and then drop to the ground. And, if left untreated, the fungus will continue to attack other leaves on the shrub (young leaves are the most vulnerable). These, of course, will turn yellow and fall to the ground, too, until the shrub looks shockingly nude.
Now, I’m not opposed to scantily-clad statues in my garden. But I like my roses fully clothed.
According to author and horticultural professor Jeff Gillman, who has conducted extensive research on blackspot remedies, a spray composed of one part milk and two parts water is the best answer to the disease. When applied weekly, the solution controls blackspot as well as any synthetic fungicide, including Chlorotalonil.
Why does milk work against blackspot? Well, nobody knows for sure. Gillman thinks it is the lactoferrin that milk contains. Lactoferrin helps to fight diseases in people.
Of course, Mr. Gillman is talking about cow’s milk here, any fat content you prefer. Rice, soy, and almond milk will have no affect on roses.
Spraying is work, but it isn’t hard work. Just be sure to wet both the top and bottom of leaves. Pick up any fallen leaves, too. Otherwise, the spores of the fungus can splash back onto the rose during a rain storm.
UPDATE: After spraying my roses weekly during the summers of 2012 through 2019, I discovered the method really works. Hallelujah!
ANOTHER UPDATE: Reader Jeff Powell (comment #130 below) shared this happy news: Good to hear that the 2/3 water and 1/3 milk solution works on blackspot. The solution also acts as a deer repellent according to the West Virginia Botanical Garden. I have used this combo for 2 years and can also testify to this working!!! Many of my friends, who live in more heavily deer infested areas, have also tried this….and all but 1 tell me that it works.
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