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Neem oil spray ruining my rose leaves?

Rose (MI Zone 6a)
3 months ago
last modified: 3 months ago

Every year I find myself having to deal with new problems affecting my roses. For the past 3 years I’ve been diluting organic neem oil with water and using that to spray on my rose bushes to prevent japanese beetles, aphids, and other pests. Hasn’t always been successful but for the most part good enough and I don’t want to constantly use carcinogenic pesticides. I would spray every week or every few days if it rained heavily in between.

Well, last year I began noticing what I thought was black spot affecting my rose bushes. I did some research and the pictures didn’t quite match what I saw on my rose leaves but I didn’t think much of it. I never made the connection that this “black spot” occurred after each time I sprayed neem oil until this year. It is also coupled with yellowing. I only sprayed them once a while ago and bam, all the leaves were affected.

New growth now doesn’t show any signs of this strange occurrence. I sprayed my roses with the blue BioAdvanced Insect, Disease, and Mite control the other day, obviously didn’t solve the problem but didn’t cause black spot either. It doesn’t look like it spreads anyway, in fact the shape of the spots looks exactly like droplets of the spray. Could it be too much water in the spray being burnt off the leaves or causing rot? Is using the same neem oil for consecutive years not safe (i.e. becoming moldy)? Is neem oil not the best option for roses?

I’m at a loss. I need something safe that I can at least use most times on my roses and keep the stronger stuff for occasional use. Or perhaps I can use the strong stuff that lasts long and just not use anything in between. I despise japanese beetles and can’t stand tiny pests as I frequently take cuttings indoors for arrangements. I need help please!

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