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Yes, you CAN Protect Your Roses From Dread Diseases

You CAN Protect Your Roses From Dread Diseases Like BlackSpot--Without Nasty Chemicals, of Course!

Question. Mike: My climbing rose looks great from a far—15 feet high and wide and full of foliage and blooms. But alas, it would be hard to find a leaf that doesn't show the tell tale signs of black spot. In a few weeks, the blooms will be finished and the foliage will begin to fall off. Bummer! I spray it thoroughly with the Cornell formula and am in the process of concocting some FCT (Fermented Compost Tea).  May be that will do the trick.

But this has happened for the last 3 years, and I have yet to have any success in battling the Black Spot. I'm concerned that my compost pile(which is in escapably in the same vicinity as the affected rose) may betainted. Is there any chance that this compost is (inadvertently) spreading the black spot—maybe even to other plants?  Do other plants get Black Spot?  How exactly does BS spread?  Thanks, 
                   ----Tim Kent;Ardmore, PA

Answer.  Hmmmm. This is highly unusual,Tim. Despite many people's fear that ALL roses are one disease spore away from are spirator, many types—especially climbers—tend to be as tough as their thorns. It's generally the 'long-stemmed' varieties—hybrid teas, flori-bundas and grandi-floras—that resist illness like a day care worker whose health insurance just ran out.

I can only guess you have that rare exception—a black spot-prone climber. OR that the poor thing is so crowded any disease will have a field day.  

Any who, black spot is a fungus. It first appears as round black spots with distinctive frilly edges on rose leaves. Then the leaf turns yellow, the spots get bigger and the leaf falls off. And yes, if its bad enough, the whole plant will be bare by the middle of summer. It ONLY affects roses—no other plants, but it is hands-down the worst of the many, many diseases that affect roses.

And it's not the compost that's keeping it going—it's the rose itself and/or the mulch underneath it. Like most rose illnesses, the disease over winters in infected canes and in old mulch on the ground. The spores wake up when Spring warms up, multiply like a runny nose in a kindergarten class, and then the first rain splashes what are now billions of nasties back up onto the leaves—often completely infecting an entire plant in one single, warm, wet day. Then a new generation is born from those spores every two weeks.

That's why I always tell folks with disease-prone roses—again, all of this advice applies to battling ANY disease, not just black spot— to remove all the old mulch from around their plants VERY early in the Spring, replace it with an inch of fresh compost on top of the soil, and replace THAT with a fresh inch once a month throughout the season.

The compost itself will physically smother some of the little diseasey guys. And organisms in the compost will create an environment that's hostile to disease reproduction, compete with disease organisms for food, and—my favorite—eat any new spores that drop down. You GO, compost!

You also need to prune off any bad looking stuff as soon as the plants start to leaf out in the Spring. (Always cut well PAST obvious signs of infection, into nice healthy tissue to keep disease off your pruners, and don't let your prunings hit the ground.) And, of course, remove any infected leaves as soon as they reveal their nasty selves.

Rose Health Insurance Plan: Spray weekly with The Cornell Formula, regular compost tea, Fermented Compost Tea, aerated compost tea, a commercial sulfur spray or—even better—a rotation of several of these.  Always spray in the morning, always remove any discolored leaves before spraying, always make sure to soak the undersides of the leaves, and never use a sprayer that has held herbicides, pesticides or other chemicals.

The Cornell Formula.  
•    In one gallon of water, mix and repeatedly shake:
•    1 tablespoon baking soda
•    2 drops dishwashing liquid or insecticidal soap
•    1 tablespoon oil.You can use vegetable oil, but' horticultural oil will work better, especially one of the new lighter-weight "summer oils". (Cowboy Gardeners: Do NOT use motor oil or WD-40 or any other such foolish thing.)


If THAT doesn't keep black spot and other dread diseases at bay, you've probably got crowded, wet roses that are gasping for air. NEVER water overhead, and NEVER water in the evening. If a rose needs water, let a hose drip at its base for an hour in the morning.

Increase, the airflow around your roses by pruning away or removing any big plants that have grown too close, and by pruning the rose itself— especially branches that are crossing and any branches in the center. Climbing roses especially like to have a lot of air space down below, so take out some canes the first couple of feet down there. And if you could ask Superman to turn the plant so that it gets morning sun, so much the better.

You Bet Your Garden  ©2004 Mike McGrath


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