BELMONT, N.Y. — You bought your roses and planted them and so far they have been doing well, so what now? Roses are affected by a few diseases and three specific pests. I am sure you bought your roses from a reputable nursery which was the first step in having healthy roses as discussed last time.
The ones I am most affected by are green worms, Japanese Beetles and aphids.
The worms are harder to spot as they are the same color as the leaves while the beetles are a beautiful metallic color and easily seen. Green worms can be found either curled up on a leaf, under a leaf or stretched out along a stem holding the leaflets. They are voracious eaters and can reduce a leaflet with its stem to a skeleton in record time. Visible evidence of their activity includes large roundish areas missing in leaves and if you look you may see the worm that has done the damage. These are usually about ¼ to ½ inch long stretched out but manage to curl themselves into a coil about 1/8th inch long. They are easier to spot when they are feeding on the flower or buds due to the color contrast.
Japanese Beetles are easier to spot with their coppery green metallic coloring and large size (a little less than 1/2”) making it harder for them to hide. My grandchildren think they are beautiful! They release a congregation pheromone and can occur in clusters where they will eat the leaves in a lace like pattern. They will also crawl inside the flowers and eat from the inside or the back of the flowers.
Aphids are very tiny, a little smaller than a sesame seed, which would make them hard to see if they occurred singularly, however, hundreds of them cluster on the stem and bud of a flower. They have sucking mouth parts which draw the juices out of the stem and bud causing it to droop over.
Prevention and Treatment
I try to avoid pesticides if possible and am not shy about grabbing worms and beetles and stepping on them. More organized gardeners would go into the garden with a dish of soapy or salty water and drop the offending pests into that. I am not that organized. For aphids, you can direct a spray of water from a garden hose at them to wash them off or use an insecticidal soap.
What about Japanese Beetle Traps? My husband bought two of them one year, probably after listening to me fuss about the beetles, and I had more beetles that year than I had before or since. Now I know, that the traps are baited with a pheromone and were actually attracting MORE beetles to my garden, YIKES!
Usually I have a great deal of trouble with Black Spot, a fungal disease. This disease is most common in humid weather or years that have rainy days with little opportunity for plants to dry out. It can also occur in dry times if you always water your plants from the top getting the leaves wet. You will notice black spots on the leaves that have yellow around them and then the leaves fall off. This is most noticeable in July and August. Plants may become almost completely defoliated. Some plants will continue to bear flowers on bare stems. Management: Rake and remove infected leaves from around the plant to reduce spore load and do a complete leaf cleanup in the fall. Water from below – you don’t want the spores to be wet as they need moisture to germinate. Do not plant your roses densely, more air circulation rids you of those wet, humid conditions the fungus need to survive. Choose varieties that are resistant to black spot. Some varieties are more susceptible to this disease: Hybrid tea, tea roses, polyanthas and hybrid perpetuals.
Dr. Horst, from Cornell University came up with a natural remedy for black spot on roses, give it a try: mix 4 teaspoons of baking soda and 2 tablespoons of horticulture oil in a gallon of water, mix well, then put in a sprayer and soak the entire plant being sure to get both sides of the leaves. This can be done every 7 days. In really bad years you may have to use chemical controls if everything else fails.
Another one that invades my garden is Powdery Mildew. This is a fungus causing a white/grey powder to appear on leaves and stems and can increase in humid weather. One of my favorite roses, a rambler from the early 1900’s, Dorothy Perkins, is affected by powdery mildew every year. She is one of the Seven Sisters group and bears quarter sized fuchsia pink roses in great clusters each spring. You might be asking why I keep her if she is so prone to powdery mildew every year! My Grandfather rescued her for me at a house demolition and I love the show she puts on every spring. Management: Again, choose disease resistant varieties, avoid overcrowding and water from the bottom. Some susceptible plants include hybrid teas, small flowered ramblers and climbers. Dr. Horst’s recipe works on powdery mildew too! For both powdery mildew and black spot, do not let the fallen leaves lie on the ground. Rake up and burn or dispose of elsewhere possibly in a black plastic bag. Do not compost them – most home compost piles do not get hot enough to kill the spores and you will be re-infecting your plants next year!
Yellowing between the veins of upper leaves can be indicative of Chlorosis, a lack of iron in the plant. Treatment is some form of soluble iron administered in watering, at the base of the plant. It may take several applications to see improvement in the plant, follow the label directions. If only a small amount of leaf turns yellow, it may also be Water Logging. This means the plant is in too wet a location, is over watered &/or does not get enough sun. In this case, your rose should be moved to a dryer location or follow directions in first article for planting roses.
A granular fertilizer applied in the spring will help prevent some of these problems. A healthy plant is able to resist disease better. These fertilizers are often 3 month fertilizers but can be repeated mid-summer; follow directions on container for application. Be careful not to apply fertilizer too late in the summer or you will have a flush of new growth in the fall that will be killed by an early frost.
Roses should be pruned regularly to keep them in good health and looking good. In spring, you are pruning to remove dead canes that have not overwintered and canes that cross over in the middle of the plant that could impede air circulation and make the plant more susceptible to disease. It will also maintain the appearance of the plant and prevent cane damage from rubbing against each other in wind events. Further pruning can be done to shape the plant if you want to keep it looking a certain way or within a certain area. Start at the bottom of the plant and work up. This enables you to see what goes where, especially with older roses where canes may be intertwined. Thorns on older roses are vicious so be sure to wear heavy gloves. Always clean up the cuttings and leaves when you are finished. Leaving them lay at the base of the bush can provide a breeding ground for disease. Diseased canes should never be composted.
Every time you cut a flower for arrangements make sure you are using pruners. Always be sure your pruners are clean and sharp for all pruning work. Dirty pruners will spread disease and dull ones can cause damage to the canes. Cut the cane at a 45 degree angle sloping away from the center of the plant and just above a 5 leaflet stem. This will encourage re-blooming.
Winter Protection: Do I need it?
In Western NY, Yes! Roses are more susceptible to wind than cold. The wind will dry out the plants and cause them to die. After pruning, place a mound of mulch or pine boughs at the base of the plant. Try not to use leaves. It is tempting to use leaves as there are so many available in the fall, but they may carry disease or become saturated and cause your plants to rot. The gentleman who gave me this information had done this and lost several prize plants. If you must use leaves, at least run them through a mower first so they don’t mat and allow them to dry out in the sun before applying to your roses.
I use round stock or rebar to support my plants (the tutors available were too expensive and some are made of hollow metal which rusts and collapses. The rebar will rust but not collapse). Rebar is easy to wrap with burlap and can be held in place with spring type clothes clips and twine. I have used the Styrofoam cones, but they break, are difficult to store and I had problems with them flying down the road on a windy day.
Alternatively, you can dig a trench next to your plant and lay the plant in the trench and cover it for winter with several inches of soil. This is a painful process – with the plant getting its pound of flesh before being buried (gloves or not). Also, it takes longer for the plant to begin spring growth as you have to wait for the soil to unfreeze before you can dig it out in the spring. Whichever method you use, be sure to uncover when temperatures begin to warm in the spring or you plants will suffer heat damage.
Jackson and Perkins
Dr. D.G. Hessayon The New Rose Expert.
Time Life Encyclopedia of Gardening: Roses
Cornell Cooperative Extension
–Pam Jones, Master Gardener Volunteer
CCE Allegany County
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