Our knockout rose bushes have greyish spots on the leaves, which seem to eat a hole in the leaf right where the spot is. Our bushes are covered with them. We have looked carefully and it is not an aphid or any kind plant pest. Can you tell me what this is and how to get rid of it?
At first, I thought you might have powdery mildew. However, the powdery mildew typically does not make holes in the foliage. Some worms and caterpillars, on the other hand, come out at night to do feast on plants, so it still could be a pest of some sort that you just are not able to see due to the timing of the attacks. I would recommend spraying the bushes down with some Ortho Bug B Gon or similar insecticide.
Sometimes water droplets get on the leaves from sprinkling systems or even a mild rain. Then the sun comes out hot and intense and the droplets act like little magnifying glasses on the foliage, causing burn spots that then turn into holes where the leaf has been burned. This can happen with the application of some water soluble fertilizers and other sprays that are applied at the wrong time of day.
How frequently should Knockout Roses be watered?
Watering the Knock Out roses is not really any different than the other rose bushes. These articles should help: https://www.gardeningknowhow.com/ornamental/flowers/roses/watering-roses.htm https://www.gardeningknowhow.com/ornamental/flowers/roses/water-roses-droughts.htm
Planted 5 knockouts last spring and they did great. This spring they bloomed and were beautiful. Then, about a month ago, I noticed one plant beginning to have wilted leaves. The leaves began to turn yellow, fall off, and the rose bush died. Now, 2 more are doing the same thing. That's 3 out of 5. One bush looks healthy, has started re-blooming. And last but not least, the 5th bush, although re-blooming, now has very few leaves. Can you give me any ideas as to what may be happening. I have seen signs of voles in my yard for the first time and my neighbor says they are the culprit, but I cannot find any signs in or around the rose bed.
It very well could be the voles. Typically, you will not see anything on the surface of the ground. They burrow around underground and feed on the roots. Without their root system, the roses cannot support the top growth, thus it wilts and dies. This can be a slow death too as the voles destroy/eat more and more of the root system of each rose bush. This article should help: https://www.gardeningknowhow.com/plant-problems/pests/animals/vole-control.htm
What do you do to get your Yellow Knock Out roses to maintain their yellow color? When they are in the bud stage, they are yellow; but when they are in full bloom, they turn white.
Unfortunately this happens with most yellow roses when the weather gets hotter. In the cooler spring temps and early fall temps the yellow color is typically richer and lasts longer. You can also add some extra potassium to the soils as it will help build the root system and enhance the color in roses and other flowers. If you have never given your roses Kelp Meal, that is another thing you can give them that helps them fight stresses and disease, along with providing some great nutrients. The stronger the rosebush is, the brighter the bloom color and overal vigor of the rosebush.
Why are some of the roses on the bushes a dull color? And some are really bright and pretty.
Usually the blooms that are more dull in color are the older blooms that are just about done. The more vividly colored blooms are usually the newer blooms that have just opened up or have only be open a day or two. When they are just about done with their bloom life cycle the color gets more dull, then the petals fall off. More buds are usually already forming by this time to bring on new blooms. If some new blooms are bright and some not, then it could be a problem with a fungus or virus affecting the rosebush.
What is the best treatment for Knock out roses that have a fungus or virus?
If you have a virus in the roses, there really is not much you can do. The viruses that I am aware of will typically stunt the growth and make markings on the foliage. Some will eventually kill the rosebush. If it is just funguses you are dealing with, then an earth friendly fungicide named Green Cure works very well to cure and keep funguses away. There are also some others on the market such as Banner Maxx or its generic form named Honor Guard. For black spot that is out of control, Mancozeb works the best.
What is a good product to put on these roses to make them more acidic? They are double knock outs.
Adding some good old sphagnum peatmoss will help get the soils more acidic. However you want to do a pH test to be sure where the soils pH level is first. Also adding some rabbit manure to the soils will bring the acid level up as well as provide some soil building nutrients to the soils. For a quick hit of acid if you are sure it is low, water the roses with some Miracid by Miracle Gro.