Pied Beauty

Gerard Manley Hopkins (1844-1889)

Glory be to God for dappled things—
For skies of couple-colour as a brinded cow;
For rose-moles all in stipple upon trout that swim;
Fresh-firecoal chestnut-falls; finches' wings;
Landscape plotted and pieced—fold, fallow, and plough;
And all trades, their gear and tackle and trim.

All things counter, original, spare, strange;
Whatever is fickle, freckled (who knows how?)
With swift, slow; sweet, sour; adazzle, dim;
He fathers-forth whose beauty is past change:

Praise him.

Saturday, June 26, 2010

Black Spot: Live With It

This is black spot, a fungal disease particularly common to roses, caused by the organism Diplocarpon rosae.  It's a summer problem:  the fungus needs at least 7 hours of temperatures above 74° and moisture.  Does that sound like Houston or what?  I think we are in for another 3 months of temperatures above 74° and the humidity here is enough to cause fungal problems on inanimate objects.

Black spot is a problem for roses because eventually these leaves all turn yellow and drop.  A bad infection can cause defoliation of the entire plant.  The disease is most pronounced on new leaves, and young plants can be killed outright. 

Fighting black spot requires good cultural habits.  Try not to get water on the leaves of the roses, and space them far enough apart to ensure good air circulation. Remove diseased leaves from the plants and keep the fallen ones raked up and out of the compost pile.  The organism that causes black spot can overwinter in garden debris and jump right back up when temperatures warm up.  Select resistant varieties if you can -- more and more rose breeding is focused on disease resistance.

There are conventional fungicides that can be applied to control black spot:  Synthetic protectant-type fungicides can be used in small quantities and don't appear to contribute to the problem of resistant disease organisms.  Systemic fungicides tend to promote resistant diseases and often negatively affect soil micro-organisms.  The most frequently recommended organic solution is sulfur, which has problems of its own.  Yes, it's organic and yes, it's been used for thousands of years.  But it only works while a film of sulfur remains on the leaf and thus must be frequently reapplied.  Sulfur also tends to build up in the soil, and can burn plants if applied when the weather is hot (like it is when black spot is a problem).  It can also cause problems with non-pest and beneficial insects.  And sulfur mining's not the most environmentally friendly thing you can do either!

So we're left with disease-resistant roses.  Bear in mind that disease resistance doesn't necessarily mean disease-proof.  I've seen black spot on Knockout roses and every other kind of resistant rose.  The strong ones fight it off, but if you're looking for picture-perfect foliage, skip the roses.  In our climate, you'll be resorting to some pretty heavy chemical weaponry to maintain perfection.

Here are some great pictures of sulfur mining and here are the rose cultivars that have been awarded Earth-Kind status, in part because they are resistant (not immune) to black spot.


  1. Those pictures of sulphur mining are well worth clicking thru to. Glorious pictures of a hard life, far away from neatly packed garden chemicals (which I don't and have never used). Ours roses must survive, and flourish or die, with peanut shell mulch, regular organic feeding, and water when necessary.

  2. This is a great post on black spot! I too have decided to plant resistant varieties and hope for the best. I just stumbled across your blog. I love the poem. I will be back, to explore your blog further!

  3. And you, might enjoy going from sulphur mining to this 'gold chain'? http://rosemarywashington.wordpress.com/2010/06/26/love-what-is-plentiful/

  4. PS Will be linking back to you tomorrow. Diana

  5. I once started my garden with all roses, and got black spot by the early Summer, kept trying for about 3-4 years and gave up . Knock out roses , all roses I bought developed it . Wasted money on about 15 rose bushes and trees , with South Carolina's humidity which is typically around 75-85 % most days...I was a bozo to have tried. But, I have a cottage garden of sorts in my backyard now, only two stray roses left. Hate black spot, and did not want to spray chemicals like a madwoman at my roses all the time. Ok, good post ! Gina

  6. Thanks for the comments, Deb and Gina, and thanks for the great link, Diana.
    Look forward to hearing from you all soon!

  7. I also love the Hopkins poem.
    I have only three rose bushes in my garden - New Dawn, a knock-off Knockout, and an old-fashioned tea rose (don't know anything else about it except that it's dark pink). I spray with Neem Oil and try to follow your suggestions for good cultural habits. But in hot and humid Eastern NC three rose bushes, even disease resistant ones, are all I want!

  8. wonderful information - thank you! I have used tea tree oil for mold in household items - what do you think of a teat tree oil spray?

  9. Anne Marie, I think tea tree oil perhaps would kill the mold on that particular leaf but if you live in a climate where mold flourishes, and you plant susceptible roses, it will come back again and again. I don't recommend applying "household" products in the garden unless they are specifically listed for it. I am a strict label-follower, to avoid unintended consequences and for safety reasons. So mostly I just do without and don't apply anything at all...