Black Spot--The Plague of Roses

Rose Bud--2009--Cindy Boney

Beautiful green, healthy leaves are what any gardner would love to have on rose bushes.  Unfortunately, Pat and I are struggling with one particular disease:  Fungal Leaf Spot or black spot. Black spot thrives in humid areas.  Although this blog is a Southwest Gardner's Journal, Pat and I do live in an area that can experience high humidity for a good portion of the year.  Not realizing that humidity is the main factor in feeding this fungus has kept us in the dark as to what to do to help keep our rose bushes healthy.

Black Spot on Leaves--Google Image

Black spot can spread quickly.  As the spots appear, the fungus begins to attack the leaves turning them yellow and then brown.  Leaves eventually fall off and if left unchecked, the entire plant can begin losing leaves at a rapid pace.  Proactive inspection of rose bushes is the best cure.  In researching this problem, I have come up with some action steps I plan to use to help Pat keep this nasty fungus away from our roses this year.

1. Apparently, it is necessary to "look closely" at your rose bushes on a regular basis.  So, I shall inspect rose bushes weekly for the nasty spots.
2. Avoid watering rose bushes from the top.  If watering from the top is unavoidable, water in the morning.  One of our problems is Pat usually waters the lawn and flower beds at 5 in the evening in the summer.  When it's hot, one would think the leaves would have time to dry, but perhaps not.  It may be that I will have to water the yard and beds in the mornings in the summertime to help prevent black spot. 
3. When spots first appear, apply a sulfur fungicide immediately.  Pat and I attended a gardening seminar in Austin, Texas, today, and the handout recommended a sulfur fungicide because it is the least toxic for the environment.  Other articles I have consulted suggest using the same thing. (Fertilome Broad Spectrum Liquid Fungicide appears to be the most toxic according to Grow Green.) 
4. Prune rose bushes when they are dry.  If the purpose of pruning is to help remove the fungus, remove plant material from the area immediately and disenfect shears with 10% bleach solution.  Don't forget to oil shears when finished to prevent rust.
5. Prune rose bushes so that air is able to circulate around the bushes freely to help keep them dry.

Pat and I have lost one Antique Rose bush to this nasty disease, and although our Knockout Roses are disease resistant, I am fearful that they still may get the nasty plague. Keeping my fingers crossed for 2011!