Rose Insects and Diseases
Learn about Rose Maladies and How to Prevent and Identify Them
Aug 11, 2009
Roses can be affected by a host of different insects and can contract some deadly diseases. In order to protect your roses from these nasty things it is a good idea to take a good look at them once they start to green up and branch out in the spring all the way until they die back for the winter. Check the flowers – are the petals being eaten, are they browning and curling up before their time? Do the leaves have holes in them; do they have unusual colorings or spots on them? Does the whole rose bush look like its wilting? Check for insects inside the petals and under the leaves.
Insects
Some of the insects that will make dinner of your roses are aphids, spider mites, and thrips. It is probably a good idea, if you’ve had the problem with these insects in the future, to obtain horticultural oil made specifically to control them. Your local nursery should have this oil in stock and will know what you need. It is very important that you follow the directions exactly or you can kill your roses. This type of oil should NOT be applied when the outside temperature exceeds 90 degrees. In fact, it is a good idea to ONLY apply the oil when the outside temperature is in the low to middle 70’s. Therefore, it has to be applied in the spring.
Insecticidal soaps are a good thing to use during the summer and fall to deter bugs. It is harmless to roses yet most of the time it will harm the bugs infesting your roses. This method works sometimes, but if you have a highly virulent bug population, it might decrease the number but it won’t get rid of them totally.
Sometimes the bugs can be knocked off your rose bushes by a spray of water, just spraying them down might keep them away for a little while. However, most roses don’t like being hit with water and their leaves and flowers will spot and you could knock the petals off.
Diseases
Blackspot is a disease that will stump most rose gardeners and make them pull out their hair. This disease usually shows up in the spring but can last all summer. It is identified by black spots and yellow discoloration on the leaves. The leaves will drop leaving you a plant with only canes. The disease develops in water so be sure the leaves of your roses don’t have water laying in them very long. You can rarely get rid of this disease once you get it, but there are ways of preventing it. Spray fungicides on your roses on a regular basis to prevent this. If you do get it cut off diseased leaves and remove everything you cut plus all the leaves of the ground and discard them. Spray in the spring and middle of summer.
Powdery Mildew is another disease that shows up in the summer especially when it is very humid outside. It is identified by new leaves becoming curled and twisted with a powdery white substance on the undersides. Remove all leaves and stems that are affected and dispose of them and the ones that have fallen to the ground. Apply fungicide during the summer to prevent this from happening to your roses.
Spot Anthracnose is somewhat like blackspot and does appear about the same time. It is identified by small red, brown, or purple spots on the leaves. The center of the spot dries out and turns white and may fall out of the leaf. The whole leaf will then turn yellow and drop. This fungus also comes from water on the leaves. A fungicide in the spring will usually prevent this disease from appearing.
Canker is an especially nasty disease as there is no cure for it. When you see canker you must cut the canes to where the disease seems to be. It is identified by red or brown sunken spots with dark margins around them that are seen on the canes of the roses. This is a fungal disease that comes from water sitting on leaves.
Rust is a fungus that spreads when the air is moist and the temperature is moderate. It starts as an orangish powerdery substance on the undersides of leaves and then yellow and brown spots appear on the leaf which will wilt or curl. You will need to remove and destroy infected leaves, even those that fall to the ground.
Your local nursery will be able to give you good advice on how to get rid of these diseases, as it depends on the weather and conditions in your area.
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