Newfoundland Horticultural Society

 A ROSE GROWER'S PRIMER – V

byHarry McGee ©National-Roses-Canada 2009

In the first four segments of this primer, we examined (I) how to match your time you have available with the kinds of roses you choose to adopt, (2) where to position them and how to give them a deluxe planting, (3) how to winterize the tender ones, and (4) how to feed, water and prune them.

Now we enter the most controversial aspect of caring for roses: protection against disease and pests. Like most others I have subscribed in the past to the necessity of spraying roses against fungus and insects. Because of unwise breeding in the past, roses have genetic material making them susceptible to fungal infection. Instead of starting over again to exclude this inheritance, breeders have tried to get rid of the susceptibility by selection of cultivars that appear not to exhibit it. This means selecting one seedling out of tens of thousands of random crosses. The genes are still there but for one reason or another, are just suppressed. This propagation strategy became necessary as roses became repugnant to green-minded people who clamoured for laws against spraying. Gradually, roses are coming to market that are quite resistant to disease. They will at some point replace all the disease-prone roses we have known. Why?

Well, several cities in Canada and at least one province have already banned garden pesticides used indiscriminately. Already the weed industry is moving to such agents as Sarritor to eliminate broad-leafed weeds. (The agent is a fungus that consumes the weed and then disappears.) In December 2008, the Canadian Association of Physicians for the Environment (CAPE) launched a campaign to get public support for spreading that pesticide ban across Canada. They point out that there has been demonstrated a strong link between pesticides and certain cancers (leukemia, brain, prostate, kidney, and pancreas), between pesticides and fetal death and birth defects, and between pesticide exposure and Parkinson's disease. You likely share with me the loss of a close relative or friend from one of these pathologies. I can no longer tell you to spray or dust roses! I have not done so myself for two years, even though I sprayed for many years using face mask, latex gloves and protective clothing. The toxic molecules are insidious, progressing to the soil or your washing machine. I peel all large fruit and vegetables before eating or cooking. There are no acceptable levels of carcinogens.

The principal fungal diseases of roses are black spot, mildew (both powdery and downy) and rust. Spores of black spot (aptly named) are all over, either carried over on the rose plant from last year or on some other host. They get under the skin of rose leaves and erupt later unless you take action to stop the infestation. Covering the first green growth in the spring with a fine misting of a fungicide is no longer acceptable. Actually a fungicide does not kill the disease (as the name suggests) once it gets under the skin of the leaf. It only arrests the disease at best. Instead of spraying or dusting, take the following preventative measures.

First, clean up every trace of last year's rose leaves and either garbage or incinerate them. Do not compost them, as that will not eliminate the spores. As well, examine all last year's wood for signs of disease and prune it out. (hybrid tea, floribunda, grandiflora roses must be pruned down from knee-high to four or five inches anyway to encourage proper growth.) Eliminate all pruned wood.

Secondly, begin to talk to your roses every day starting with the first growth in spring. In reality, examine them daily for the earliest sign of black spot. When found, finger pick the leaf before it has a chance to bounce raindrops to the next leaf. Garbage it. Some people are so good at this detection that they can get through a season only using this sanitation alternative to spraying, especially if they live in a low humidity region. Much has been written about spraying with sodium bicarbonate [baking soda] to coat the leaves and it has been shown to be effective in delaying the onset of black spot for as much as three weeks. Actually anything to coat the leaves will hold off the infection. Even milk. Milk is getting good reviews as a preventative for powdery mildew (white). This form of mildew only comes to the garden when daytime and nighttime temperatures diverge significantly in the late summer or fall. As for downy mildew (purple), only copper-based preparations will treat it. Do so in a very clinical way on an isolated basis, or better yet, eliminate the plant. For rust, strip the affected leaves at first sight and garbage. It will not go far afield.

Third. As the bush begins to grow, prune out all the little aimless blind twigs and all leaves at the base of every rose plant and remove all cobwebs and things such as weeds that will reduce air circulation. Black spot spores get established in the first foot of plant growth. If it is bare, they have no springboard for infesting the whole bush. As well, keep the rosebushes well spaced and well pruned to allow for good air circulation and quick drying conditions. Good pruning practice includes getting rid of unproductive canes if they are thickening the bush to the point of stopping air circulation. If they are not impeding circulation, leave alone to permit food production.

Fourth. As Robert Osborne so eloquently argues, build up your garden soil organically so that it is a living organism "whose intricate interactions produce the nutrient and biological support for healthful growth" of all vegetative things. If a plant is busting with health, it will discourage fungal infection. Sun, rain, air and a life-giving growing medium will keep your roses pleasingly healthy. (Weeds too.)

Fifth. Relax a bit. Accept less than perfection. You are picking off diseased leaves. After the first flush of bloom, the plant will produce a second round of growth and bloom. It will look restored. If it is beyond any level of acceptance, shovel prune. My first 'William Shakespeare' developed over a period of three years into a black-spot distribution centre and had to be removed from the garden. I know it is hard to do when the rose is a dear favourite or has a sentimental attachment. If you cannot bear to let it go, remove it to a remote isolated comer where it can pollute in peace.

It is much easier to scout for disease-resistant roses than to battle well known rose diseases. It is better to battle well known rose diseases with non-spray techniques (above) than to endure chemotherapy and radiation.

Critters! Aphids? Buy ladybugs. Do not open them until after nightfall; otherwise they will fly away home. If you open their package when it is dark, they will settle on the roses where you place them and wait for visual flying conditions. However after a few hours, they forget the homing instinct and settle down to their proper business of chomping aphid adults and nymphs. I don't have to buy any, as I have no difficulty squishing aphids between thumb and index. (If you don't have a green thumb before, you will afterward.) Time is essential. Catch them before they begin to multiply. No problem, as you talk to your roses every day. Safer's soap is also an acceptable defence. Just spritz the little blighters before they take over.

Spider mites are generally too small to see. If you tap a dying twig over a piece of white paper and see a lot of specks fall, it is probably spider mites. They can be dispatched with a strong jet of water. When they fall from their feeding stations on the twig, they cannot return. They die.

Nothing can stop female critters from flying into your garden and depositing eggs. Nothing can stop you from spotting an egg cluster or the emerging green worms during your daily talks. Thumb and index. Japanese beetles are the ugliest visitors especially when they pile up in copulating hordes. Daily talks will dispatch them before they gather in sufficient numbers to orgy. Gall flies elude me. They must fly in when I am napping or at night when my radar does not work. Watch for signs of slight swelling of canes and prune out below the swelling. It is essential to spot the swelling before the larvae growing inside it emerge to pupate in the soil. Garbage the swelling. Consider the suitability of the end of the cane for softwood cutting and cloning.

Bacteria! All soils have the bacteria that will invade a cut in a rose root and cause root gall or crown gall. Being below ground, it is difficult to detect. When a rosebush does poorly for no apparent reason, dig around it using a blunt instrument with no sharp edges. If you find a fat growth on the root a few inches below the surface, say goodbye to the poor plant. Remove it and garbage. No amount of tears or treatment will save it. At some time in the past you have got too close to the root with a hoe and the nasty bacteria invaded the cut and caused the cancer-like growth. Some people insist on removing the soil around the plant as well.

Virus! Another fatal disease. Mosaic causes leaves of an infected plant to appear chlorotic, and the whole bush to decline. Whereas chlorosis is caused from an iron deficiency, this yellowing of leaves in the familiar skeletal pattern is caused by a viral infection and nothing can eliminate it. Unfortunately the virus can be spread on your secateurs. If you inadvertently cut into a virused plant, treat the blades of your secateurs with alcohol or bleach to prevent the virus being transmitted to the next plant. Sorry to tell you that the whole plant must be disposed of in the garbage. Viruses don't just drop in for a visit; they usually come in the plant from the supplier. Use only the most reputable suppliers.

Another virus is rose rosette. This is carried on little mites that are blown in from the south where the virus is used deliberately to infect multiflora hedges to keep them in check. The mites can be borne aloft on strong winds. The virus may become obvious if it causes ‘witches broom’ growth on the plant, but it may only cause the plant to do poorly. It may be mistaken for the mild effects of herbicide drift. Nothing can cure the plant and it must be disposed of.

Remember to consult with your local rose society members or district rose specialist about questions you have either on things I have covered or things I have not included.  I regret ending an article with such a withering deluge of bad things affecting roses. In the next issue, I will tell you how to enjoy your rose blossoms.                

By permission of the author  .   .   .  HM