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Black Spot

(October 2010)

QuestionI have had a recurring problem with my hydrangeas.  They get a black spot which causes the leaves to shrivel.  I have used a triple action-fungicide, miticide, insecticide, but with no results.  What should I use to clear up this problem?


AnswerI don't think there is a hydrangea without a leaf spot this fall.  The growing season was not kind. Spray schedules now are not effective.  The leaves will be dropping as soon as we have a killing frost.  Practice good sanitation, and rake up the old leaves this fall or winter.  Watch the new growth in the spring. If you have the leaf spot early in the season every year, then a preventative fungicide only spray would be in order (you don't need the miticide, insecticide part). If it only happens late in the season, I wouldn't worry.

(October 2007)

QuestionMy rose bush has black spots on the leaves and they turn yellow and fall  off. I have sprayed it with disease spray from the gardening center but it hasn’t helped.  Now it has almost no leaves and looks like it could die.  It usually blooms a lot in the spring and summer, but this year it only bloomed  in the spring and has been pitiful ever since.  I have had it for about 10 years and don’t want to lose it. What can I do?  Also there was an ant bed underneath it (small black ants and we sprayed them, could they have damaged the plant?


AnswerYour rose bush has the classic rose fungus disease called black spot.  This was a great season for diseases of all types, but if you have a susceptible variety, you typically have the disease every year in Arkansas.  Spraying after you see the disease is usually a futile attempt at control.  The key is to start your spray schedule in advance of the disease—soon after the plant kicks into growth in the spring.  Sprays every week to three weeks—depending on what product you use, will be necessary throughout the season. Black spot can weaken a rose bush, and if it occurs year after year, it can weaken it enough for it to die, but it should come back strong next spring with proper pruning, spraying and fertilization. I  don’t think the ant spray had any effect.

(May 2010)

QuestionI moved from an apartment to a house about 2 years ago and decided to plant some rose bushes. They bloomed twice that season but the leaves had black spots on them, so I treated them with sulfur. It helps with the spots for about two weeks and the leaves look very healthy, however the bush has not bloomed yet. All my neighbors roses around us have bloomed. And we only have one shoot growing out of three. It'll start out with new shoots growing at the bottom but they die off after about a month. We fertilize with miracle grow. Is there anything we can do to encourage it to grow? Is there something different we can do to cure the black spots?


AnswerFirst, how much sunlight do you get? Most roses need a minimum of 6 hours per day.  It sounds like you have a hybrid tea rose which is highly susceptible to blackspot of roses, and does need full sun.  It also should bloom all summer long and be quite vigorous.   Hybrid tea rose bushes should be pruned back hard in late February—normally to a height of anywhere between 8 and 18 inches.  The new shoots should not be dying back.  Check the sunlight and the drainage.  You may want to invest in some new roses.  If you don’t have full sun, the Knock out roses will bloom in as little as 4 hours of sunlight per day.  They bloom almost non-stop until frost and do not get blackspot. If you want to keep what you have, weekly sprays of fungicides will be needed.  Although sulfur can be effective early in the season, when temperatures heat up, it can cause some burn to the foliage. One or two sprays are not going to cut it with highly disease prone plants—you have to be diligent all season.  That is why I opt for disease free plants that don’t require sprays.  There are many good options.  Fertilize with a slow release fertilizer every month.  The water soluble fertilizers are fine, but they don’t last as long.  If you do decide to replant, add some organic matter into the soil prior to planting.

(March 2010)

QuestionI have a question about spots on the stems of knock out roses. Is this a disease? I thought knockouts were supposed to be disease resistant. Do they need to be sprayed like other roses? The plants in question are in our church courtyard and only get drip irrigation.


AnswerKnock out roses are very disease resistant and I would not spray them.  We did see a few signs of blackspot last season, due to all that rain.   That was pretty atypical as far as our growing seasons go, so I am not judging the disease resistance on this past year.  Prune your knock outs as you would any shrub rose now, removing up to 1/3 of the old growth.  Watch the plants this spring and if you see any problems, let me know.  I think the Knock-out series are outstanding shrubs with almost constant bloom from late spring through frost and they are low maintenance to boot!

(July 2007)

QuestionMy running rose is losing all of its leaves. It bloomed very well earlier this year, but looks awful now.  Can you tell me what the problem is? The plant is only about two years old.


AnswerThe common fungal disease black spot, has defoliated many roses this growing season.  This disease attacks a variety of roses, from bush types to climbers.  The disease starts off with small black spots on the leaves, which over time yellow and fall off.  If you grow a variety that is susceptible to the disease, the key is to spray in the spring after they begin growing with a fungicide such as Daconil, Funginex, Immunox or Bayer All in one Rose spray.  Regular spray schedules are needed all season long following the label directions.  At this point, starting a spray program would be futile. Trying to control a disease that has become firmly entrenched is fighting a losing battle. Prevention is key.  For now,  I would water when dry, lightly fertilize and hope for a better year next year.


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