Roses/Problem with knockout roses
I planted 30 double knockout roses 5 years ago, and the first 3 years they did fine with no pruning and they had lots of blooms. These were supposed to be very hardy with few problems, but last year I saw the leaves on a few of the bushes were dry and transparent with only the veins visible, although they bloomed as usual. I cut these back, but also noticed that these and many others had grayish patches and many dead branches. This year I cut off anything that looked dead before any growth appeared, so the whole rose garden now looked very sparse compared with the full bushes I had a few years ago. When the leaves came in this spring, eventually all of them became affected with this same condition as mentioned above, but not the buds and blooms. Is this caused by a disease or insect infestation? I would hate to destroy the whole rose garden if this will happen in future years. What can be done about it?
Sorry to hear you are having these problems.
This is basically a trace mineral deficiency.
It is related to the soils health.
You did not mention
1. what you were feeding the plants
2. what if any compost you use
3. what if any rock dust you use
4. conditions are the plants (near a lawn?)
5. your soil ph? ( should be around 6.5 to 6.8 for best results)
Here are some basic things you need to do
1. get yourself some good home made compost.
add 1 coffee cans worth every year (about 1 lb) mixed into base.
2. get yourself a good organic rose fertilizer (not much nitrogen is bad)
3. get some rock dust (google rock dust and your city. you should get someone nearby or a store that sells). Rock dust provides a good mineral source. Try Arbico.com or try http://store.invisiblegardener.com/rock-dust/
4. buy a good organic foliar spray that provides all the needed trace minerals as well as microbs for plant health. I make my own so you can try Superseaweed. http://www.invisiblegardener.com/online_store/superseaweed_microactivator.html
Spray several times per week at start then once per week for blooming.
5. Find a good acid mulch. Try azalea/gardenia mix. Add a small layer several times per year.
6. do not over water as it is bad. No over head.
the disease sounds like brown spot disease along with trace mineral deficiency (viens).
that can be solved by going thru above steps.
let me know if this helps you.