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I was wondering if I should or can I spray for black spot during the dormant months to kill spores for the Spring? Or am I just wasting my time? Also why is black spot so bad in the earlier months of spring and summer? Thanks! Renee
From: Virginia | Registered: Oct 2002
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I think the increase in black spot in spring and early summer is due to the increased rainfall and humidity providing the perfect conditions for it to thrive.
I continue treating my roses up until the first hard freeze.
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They have not developed any good preventative, type fungicide yet. There are many out there that claim to be, but I have not yet seen one that works. At least that is cost effective. A fungicide works a little bit differently then other pesticides, such as herbicides or insecticides, where they kill the target pest. Most fungicides act as a shield or barrier so the fungi or disease can not harm the plant. The barrier usually lasts for a few weeks, and most of the time the weather conditions that were favorable for the diseases development have changed by the time that the fungicide has been applied. Some fungicides will attack the fungi directly, but none of them will kill the spores. Even if they did, the spores are so abundant in our world it would be virtually impossible to eradicate them. Fungi spores are finer molecules of water, and flow freely with the wind, landing where ever chance brings them. It take the right conditions (usually heat and humidity depending on the variety of fungi) however to make the fungi strong enough to hurt plants.
"The barrier usually lasts for a few weeks, and most of the time the weather conditions that were favorable for the diseases development have changed by the time that the fungicide has been applied."
The barrier usually lasts for a few weeks, and most of the time the weather conditions that were favorable for the diseases development have changed by the time that the fungicide has wore off.
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