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You CAN Protect Your Roses From Dread Diseases Like BlackSpot--Without NastyChemicals, of Course!
Question. Mike: My climbing rose looks great fromafar—15 feet high and wideand full of foliage and blooms. But alas, it would be hard to find aleaf that doesn't show the telltale signs of black spot. In a few weeksthe blooms will be finished and the foliage will begin to fall off.Bummer! I spray it thoroughly with the Cornell formula and am in theprocess of concocting some FCT (Fermented Compost Tea). Maybethat will do the trick.
But this has happened for the last 3years, and I have yet to have anysuccess in battling the Black Spot. I'm concerned that my compost pile(which is inescapably 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 otherplants get Black Spot? How exactly does BS spread? Thanks,
----Tim Kent;Ardmore, PA
Answer. Hmmmm. This is highly unusual,Tim. Despite manypeople's fear that ALL roses are one disease spore away from arespirator, many types—especially climbers—tend to be as tough as theirthorns. It's generally the 'long-stemmed' varieties—hybrid teas,floribundas and grandifloras—that resist illness like a day care workerwhose health insurance just ran out.
I can only guess you have that rareexception—a black spot-proneclimber. OR that the poor thing is so crowded any disease will have afield day.
Anywho, black spot is a fungus. It first appears as roundblack spotswith distinctive frilly edges on rose leaves. Then the leaf turnsyellow, the spots get bigger and the leaf falls off. And yes, if itsbad enough, the whole plant will be bare by the middle of summer. ItONLY affects roses—no other plants, but it is hands-down the worst ofthe many, many diseases that affect roses.
And it's not the compost that'skeeping it going—it's the rose itselfand/or the mulch underneath it. Like most rose illnesses, the diseaseoverwinters in infected canes and in old mulch on the ground. Thespores wake up when Spring warms up, multiply like a runny nose in akindergarten class, and then the first rain splashes what are nowbillions of nasties back up onto the leaves—often completely infectingan entire plant in one single, warm, wet day. Then a new generation isborn from those spores every two weeks.
That's why I always tell folks withdisease-prone roses—again, all ofthis advice applies to battling ANY disease, not just black spot—toremove all the old mulch from around their plants VERY early in theSpring, 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 physicallysmother some of the little diseaseyguys. And organisms in the compost will create an environment that'shostile to disease reproduction, compete with disease organisms forfood, and—my favorite—eat any new spores that drop down. You GO,compost!
You also need to prune off any badlooking stuff as soon as the plantsstart to leaf out in the Spring. (Always cut well PAST obvious signs ofinfection, into nice healthy tissue to keep disease off your pruners,and don't let your prunings hit the ground.) And, of course, remove anyinfected leaves as soon as they reveal their nasty selves.
Rose Health Insurance Plan: Sprayweekly with The Cornell Formula,regular compost tea, Fermented Compost Tea, aerated compost tea, acommercial sulfurspray or—even better—a rotation of several ofthese. Always spray in the morning, always remove any discoloredleaves before spraying, always make sure to soak the undersides of theleaves, and never use a sprayer that has held herbicides, pesticides orother chemicals.
• In one gallon ofwater, mix and repeatedly shake:
• 1 tablespoonbaking soda
• 2 dropsdishwashing liquid or insecticidalsoap
• 1 tablespoon oil.You can use vegetable oil, but'horticulturaloil' will work better, especially one of the newlighter-weight "summer oils". (Cowboy Gardeners: Do NOT use motor oilor WD-40 or any other such foolish thing.)
Regular compost tea
Early in the morning, place some ofyour finest quality compost in aporous cloth container and put it in a container full of cool water (anold sock for a gallon of water; a pillowcase or burlap sack in a cleantrash can full; if its city water, let it sit for a day first and stirit a few times). Let it steep for 24 hours, then strain the liquid thatnext morning and spray immediately; you want to use it right away toget the maximum number of little compost guys fighting for you. (Returnthe contents of your 'tea bag' to your compost pile.)
Fermentedcompost tea ("FCT")
Take some brewed compost tea, placeit in a bucket with a mosquitoscreen over the top and let it sit out in a shady spot for two weeks.Scrape off the scum, avoid the sediment on the bottom, strain andspray; fermentation makes for a very potent disease-fighting spray.(Return both scum and sediment to your compost pile!)
Aerated compost tea
Again, make a batch of compost tea inthe morning, but drop someaquarium bubblers in there to add air as it brews—or use one of thecommercial devices that do this, like The Soil Soup machine or GardensAlive's "Compost Tea kit". That extra air will greatly multiplythenumber of helpful little compost guys in your tea.
If THAT doesn't keep black spot andother dread diseases at bay, you'veprobably got crowded, wet roses that are gasping for air. NEVER wateroverhead, and NEVER water in the evening. If a rose needs water, let ahose drip at its base for an hour in the morning.
Increase the airflow around yourroses by pruning away or removing anybig plants that have grown too close, and by pruning the roseitself—especially branches that are crossing and any branches in thecenter. Climbing roses especially like to have a lot of airspace downbelow, so take out some canes the first couple of feet down there. Andif you could ask Superman to turn the plant so that it gets morningsun, so much the better.
You Bet Your Garden ©2004 Mike McGrath