Controlling Disease While Pruning Roses by Mike Kelly
Some things to look for when pruning roses are dead or diseased wood, and galls. Our common rose disease, downy mildew, besides affecting the leaves, does the worst damage by getting into the canes, eventually killing the cane. If it progresses to the crown, it will end up destroying the entire plant. So when pruning, be aware of any dead wood at the point you make your pruning cut. This is evidenced by the wood of the cane being brownish on one side, or even all the way across. You must cut back until all the wood showing after the cut is healthy, a white or light greenish white color. Freeze damage will appear similarly.
Gall is one of the very few bacterial diseases affecting plants, as is fire blight on apples and pears. Gall on roses can appear on the cane, the crown, or on the roots. It is a rather smooth round growth, dime to quarter sized or larger. If on the cane, the cane will be weakened, smaller, blooms will be few and poor, and death will eventually occur within a year or so. If the gall is high enough up on the cane, the cane can be cut off as far below the gall as possible, again being sure the wood where the cut is made is healthy. Gall may or may not reappear on the same cane or bush, and you should remember to keep an eye out so if it does recur it can be removed as soon as possible. Root gall is rather insidious, as not being visible, all you may notice is a general lack of vigor of the infected bush. If and when the plant succumbs, and is dug out, the gall will be seen. Crown gall is usually a fatal condition; though I have one rose I was able to saw the infected portion of the crown completely off, and that rose is still doing well several years later.
I confess to not being as sanitary as some when pruning, in that I don’t sterilize my pruning tools between plants. If you have gall it is a good idea to do so, a 50-50 solution of bleach and water will work. Be certain to rinse the pruners well after pruning, and oil lightly, as bleach is very corrosive. In the case where a rose as been killed by gall, plant something besides a rose back in that location, as the bacteria that causes gall lives for ages in the soil.
This year while pruning, several times I cut off what I thought was an area of the cane killed by downy mildew. However the wood was completely healthy, just the cane had this dead looking area. I attribute this to the new spray Agri- Fos actually killing the downy mildew, and the plant healing. I never use a dormant spray on roses, as no product available to use as a dormant spray can kill fungus spores. Agri- Fos is not to be used on a dormant plant. When the rose is well leafed out this coming spring, and the temperatures are in the low to mid fifty degree range, then spraying or drenching with Agri-Fos should begin, and continue at three week intervals. If you do this, you will experience amazingly healthy and luxurious rose bushes, as I did last summer after I started using this product.
Now is the time to add lime to the soil. A cupful sprinkled around each rose bush is needed to maintain the desirable nearly neutral pH. Wood ash also works well as a soil sweetener, at the same amount as lime. I have had good luck in controlling moss with wood ash, sprinkled heavily enough to lightly cover the moss. I don’t fertilize until March, but if adding manures that can be done now. The soil is still too cold for the soil creatures to be active so I would also wait before applying any organic fertilizer that needs to be changed by the microbes in order to become available to the plant.