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Aphids most often attack the buds of roses. Small infestations can be controlled with a blast of water or hand-picking.
Roses sometimes get a bad rap for being prone to pests and disease. But with just a little extra care, they'll reward you with beauty and fragrance. Just make sure you know how to control the four most common problems:
Found throughout the United States, these small, soft-bodied insects may be pale green, pink, black, or yellow, depending on the species. Some stages of the life cycle are winged, others wingless. Aphids feed on a wide variety of plants, including roses. Clustering on tips of new growth and leaf undersides, they feed by sucking out plant juices, causing leaves to become distorted and yellow. Aphids secrete a sugary fluid called honeydew that attracts ants and may cause the growth of a sooty black fungus on leaves. In small numbers aphids do little damage, but they reproduce rapidly. Control while the population is still small.
Controls: Aphids are easy to control. Simply washing plants with a strong spray of water will reduce their numbers dramatically. Insecticidal soap is more effective. Horticultural oil will eliminate them. When spraying, be sure to cover leaf undersides. A variety of natural insect parasites and predators also reduce their numbers, the main reason you don't want to be overly aggressive with sprays.
Japanese beetles can be devastating. Once you see the first beetle, look for signs of more, which are sure to follow. Be sure to check in the buds of opening roses, a favorite food of the beetles. Because the beetles are relatively large and slow to react, they are easy to pick off roses by hand.
Still primarily a pest of the eastern U.S., they turn up west of the Rockies from time to time. They're a problem for gardeners because they have an appetite for a wide variety of plants. Adults feed on just about every kind of flower or vegetable, sometimes in disturbingly large crowds. They chew out the leaf tissue between the veins, leaving a lacy skeleton. When they attack roses, you'll often find them in the center of the bud, eating the tender petals. Prior to pupating, the white, 1-inch long, C-shaped grubs live in the soil and feed on the roots of most all plants. Grubs are often a problem in lawns.
Controls: There's a cockroach-like relentlessness about Japanese beetles that can get under a gardener's skin. But we're not helpless. The beetles are relatively big and easy to see, and they're not real quick. They are pretty easy to just pick up or knock into a can of soapy water.
Yellow target traps baited with a pheromone attractant work, but sometimes too well. Don't place one near your garden or you'll be pulling beetles in from all over town.
Deter adult beetles from feeding by spraying neem oil. Use parasitic nematodes in lawns and garden beds for control of grubs.
This fungus disease occurs all over the North America and infects a wide variety of plants. A powdery white growth covers the upper surface of leaves, which eventually turn yellow and dry. Older leaves are usually infected first. The fungus competes with the plant for nutrients, reducing flowering and weakening or even possibly killing the plant if infection is severe. This disease usually develops late in the season on mature plants and thrives in both dry and humid weather. It can spread rapidly.
Prevention and control: Choose disease-resistant roses. Potassium bicarbonate fungicides are effective when applied according to label directions.
The foliage of this rose shows signs of blackspot.
This fungal disease is named for the black spots that form on the leaves. Eventually, the blackened areas are surrounded by yellow, and the damage covers the whole leaf. In severe cases, the plant can lose all of its leaves. High humidity and heat create ideal conditions for the spread of the disease because the spores only travel in water droplets.
Prevention and control: Prevent problems by spraying every 10 to 14 days with neem oil or a baking soda-based fungicide. Of the two products, neem is better at controlling an outbreak in progress. Both are good for prevention. Avoid watering the leaves, or water early in the day. Be sure to remove and destroy diseased foliage. Ensure good circulation around your roses by pruning to open the center of the plant. Roses should not be packed in among other plants.