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whats wrong with my knockout roses ??

11 years ago

I planted some knockouts about three weeks ago. They were fine until recently. What kind of fungus is this and what should my course of action be? I thought this type of rose was more resistant to this. I water only at the base of plant. Also how much water do they need? Could this be from too much or not enough water. I water every couple of days because its been very dry here. Its also very hot and humid. But last week it was dry and cooler at night. Hopefully someone can help me.

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Comments (6)

karl_bapst_rosenut
11 years ago
How about a closer or larger picture
carolsewzit
Original Author
11 years ago
"How about a closer or larger picture"

If you double click on the picture it should enlarge it. At least it does for me. Let me know if this works for you please.
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What is wrong with this Knockout Rose
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SW -- a photo would be very helpful, but considering it's Knockout, and considering that you're in Houston, I'll almost bet money that the problem is chili thrips. Do they have black veins and blackish stripes or spots on the stems? (see http://www.houstonrose.org/ctko1.jpg) While the Knockout series tends to be highly resistant to fungus diseases, they are extraordinarily susceptible to chili thrips. If that's the problem, you really have only three choices: 1. Replace them with a different variety. 2. Live with it and realize you're going to have a lot of dieback, regularly. Or 3. Spray for them.
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And water deep, not just a surface wetting. Roses like at least and inch of water per week. So water it slowly for a long period of time about twice a week. In very hot, dry weather you will need to water even more often. If you water early in the morning you can hose them off too, leaves will have plenty of time to dry off during the day, but if you're watering in the evening then try not to get the leaves wet.
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Looks healthy! The white marks on your leaves are probably from rose slugs which are greenish worm like creatures that vary in size from small to 3/4" +... They can mostly be found under the underside of leaves... Pick them off or try hosing them off... Birds and wasps like to eat them... Least toxic spray to use would be something like Safers Insecticide Soap follow directions to be effective.. Or just let it alone and hopefully wasps and birds eat them for you...
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Roses planted under the eaves are prone to spider mite infestations (bad), so the center of the bush should be at least three feet from the foundation for that reason. Knock Out is a vigorous plant. It can handle a lot of pruning. I've seen them routinely pruned to 12" each spring and they are six feet tall by Labor Day. After each bloom cycle, take hedge shears and remove six inches of growth from all sides of the plant to keep them small enough for your planting site. What to plant to complement your roses is a matter of personal taste. You could weed and mulch heavily then set in a flat of annuals each year and the bed would stay neat and tidy. You could choose perennials and do a bit more maintenance. If you prefer to go with perennials, we need to know your location (nearest big city & state) to make useful recommendations.
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buford
11 years ago
I know it's a knockout, but that looks like blackspot to me.
catsrose
11 years ago
On the average, 1" of water penetrates 4" of soil. Thus, if your roots are 12" down, you want to give them 3" of water. If your soil is very clay and/or drains slowly, give less. Roses do not like wet roots. Water deep and less often; roots on the surface need more water and dry out more quickly. Deep roots make the plant more secure and keep the roots at a more even temp. Deep, less frequent watering forces the roots down. The best test is to stick your finger in the soil. If it is still moist at the tip of your finger, wait another day.

You can spray a fungicide or you can live with it. Blackspot doesn't kill and it thrives only in a arrow rage (app 70-80 + humidity). Once it gets hot and dry, the blackspot will back off. I live with because I prefer a no-spray garden.
seil zone 6b MI
11 years ago
Yes, that's black spot and YES, KOs can and do black spot.
michaelg
11 years ago
Respectfully, I have to disagree with the above prescription for water. How much water the soil can hold depends on the soil type, and how much to add depends also on how moist it is. But typically, in your midwestern location, one inch per week is adequate with high temperatures running in the 80s or low 90s. Plants could use maybe 1.3 inches with higher temps, or low humidity and wind. One inch is 4-5 gallons per square yard. With sandy soil, water less than an inch at a time, but more often (at least twice a week), as it can't retain much water.

3" at a single application is way excessive. With temps in the 80s, I water less than one inch per week and my roses never stop growing vigorously. In Florida with sandy soil and temps in the mid-90s, we watered 3/4 of an inch every three days if it didn't rain.

Every gardener should have a rain gauge.

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