my rosebush has black spots. what can i do?

Question

what is causing this and what can ido toprevent this/

Answer 1

Black spot is caused by a fungus called Diplocarpon rosae. Some roses are more susceptible than others. The spores that spread the fungus are carried by water as it is splashed onto other areas or other plants.
It's important to clean up fallen leaves & allow good air circulation around plants.

Jerry Baker (Master Gardener) advises using a fungicide to knock out the fungus, & then using a homemade control for Black spot: Spray them with a mixture of 1 tbsp. of baking soda, 1 tbsp. of light vegetable oil, and 1 tbsp. of soap in 1 gallon of water. http://www.jerrybaker.com/index.asp?PageAction=Custom&ID=2

Other Methods of control:
Sulfur powder is a preventative. Dust roses infected with black spot with sulfur powder. Sulfur will not kill the fungus spores, but it will prevent a new generation from germinating.

Dormant oil or Bordeaux mixture when plants are dormant (usually in winter).

Mix a handful of cornmeal in the soil around your rose bushes to control black spot. Cornmeal controls diseases by providing and stimulating existing beneficial microorganisms that feed on pathogens.

Water early in the day so the leaves dry quickly, or water just the base of the rose bush so the leaves won't get wet & the fungus will not get the opportunity to spread & thrive. The fungus is most serious in regions of high rainfall and high humidity because "the infection takes place only when water remains on the leaves for seven or more hours". http://www.ext.vt.edu/pubs/plantdiseasefs/450-617/450-617.html

Good luck with your rose bush! Hope this helps.

Answer 2

With black spot you first need to clean up the area by removing all the nasty leave and leaf litter around the bush. You should also remove the mulch if there is any and replace with new. Next you can either purchase a fungicide from you local garden center. Ortho rose defense is pretty good, but you can also go home made and alternate vinegar and baking soda sprays.
If you do this you will need two 32oz spray bottles.

Vinegar spray: 1tablespoon Apple cider vinegar, 1teaspoon dish soap, 1teaspoon canola oil. Spray tops and bottoms of leaves, stems, and ground once a week. The vinegar raises the pH and the black spot fungus hates it.

Baking Soda spray: Same as above except substitute baking soda for the vinegar. All other ingredients are the same.
Also spray once a week, however, use vinegar on say Sundays and then the baking soda spray on Wednesdays.

We experience a summer monsoon here in OK and half my roses got black spot. I've been treating them with these home made solutions and there is no sign of the fungus at all now. Even my hybrid tea is fungus free.

Good luck on the black spot. Hope this helped.

Answer 3

It sounds like black spot disease. It's caused by a fungus. Here's a link to the info about it, how to prevent it and how to cure it:
http://www.ext.vt.edu/pubs/plantdiseasefs/450-617/450-617.html

Answer 4

get some whole ground corn meal and spread around the ground under the plants then get a product called rose defense and spray the leaves water only from the \bottom not the foliage