I'm relatively new to roses. 4 bushes I put in a 6 weeks ago are now covered in black spot. Any suggestions other than a nasty spray Garden Works suggested?
The easiest thing is to avoid susceptible sorts, as I have done for years. However, many built-up modern hybrids, as well as some not-so-modern ones are prone--there may not be one that has particular attributes desired readily presenting itself. I have been to two unsprayed PNW collections and seen most kinds there infested, the small number of resistant ones noticeable for this attribute. Said to be a relationship between this and potassium deficiency, possibly maintaining optimal levels of this nutrient would have some effect. (Sample soil and have it tested to keep track of soil nutrient levels).
Sprinkle cinnamon, especially on lower leafs, if rain is forecast. It would work better as a deterrent (next year), but it could help keep the infection from spreading and defoliating your plants.
I don't know if "you" would consider copper as "nasty", but it can be fairly effective in controlling Black Spot on roses. You use water out of copper pipes in your home and I don't think that is considered nasty. West Vancouver has a pesticide bylaw that would prevent the use of "nasty's" anyway. One of my great customers uses left over teabags on his roses, and now has some new "Shell Busy" mixture with epsom salts and whatever else. His roses are absolutely incredibly beautiful. Maybe Shell Busy has a web site with this info on it, did I spell his name right? Jim.
You might also like to look for new disease-resistant hybrids being selected, introduced and promoted in recent years by major producers.
