If you keep your rose bushes healthy with plenty of sunlight, food, and water, you should encounter few problems, no matter what type of rose you’re growing. However, even though roses are sometimes considered to be the queen of flowers, even the queen can experience problems and need some outside help. A single aphid is not a big threat, but aphid colonies can grow shockingly quickly, and you will easily be able to see them on the plants. As they feed, the plant will become puckered, brittle, and yellow and the plants will slip into decline. Symptoms of aphid infestation and damage include:
Distorted flower buds and leavesSticky honeydew substance that is secreted by the aphidsBlack sooty mold growing on the honeydewClusters of aphidsAnts crawling on the plants and feeding on the honeydew
Because they are such tiny, tender insects, you can often control aphids by hosing off the rose bush with a strong blast of water. You will need to hit all areas of the plant, including the undersides of the leaves, and you will need to do this more than once. You might always want to try a homemade spray remedy to control aphids. If water does not seem to be controlling them, try insecticidal soap. Make sure the plant is completely coated. The soap needs to make contact with the aphid. An organic, natural way to control aphids is by attracting lady beetles to your garden. Lady beetle larvae are voracious predators of aphids. Black spot (Diplocarpon rosae) is a fungal disease, and warm, wet, or humid weather plays a big part in its development. If black spot has infected plants in the area before, the spores are probably still around, waiting for the ideal conditions. It only takes about seven hours of warm moisture for black spot spores to germinate, but you might not see symptoms for several days. Once you do, act quickly, because new spores are produced every three weeks. Black spot starts as small black spots on the leaves that enlarge and become ringed with yellow, eventually become turning the whole leaf yellow. Once yellow, the leaves begin falling from the plant the infection is severe, and the plant will totally defoliate. To control black spot, start with a thorough fall clean-up of fallen leaves and debris because the fungal spores can over-winter. Because black spot is exacerbated by poor growing conditions and stressed plants, make sure your rose bushes receive full sun, plenty of water, and good air circulation. If you see evidence of black spot, spraying with Bordeaux Mix, neem oil, or sulfur is effective. Young leaves will begin to pucker or crinkle, then you will see mold forming on the leaves and stems followed by a thin white coating that will begin to spread throughout the rose bush. If you live in an area where powdery mildew often occurs, you can use a homemade baking soda spray as a preventative. This treatment does not work well after powdery mildew is already present. Once your plants are showing symptoms, the easiest control is a homemade milk spray. It is surprisingly affective and can even be used on mildew-prone edible plants, such as cucumbers and squash. Symptoms start as small circular spots of varying sizes. Eventually, a purple halo develops. As things get worse, the spots expand and the centers turn to a grayish-tan as the tissue dies out. The spots form mainly on the leaves, but can occur on other parts of the plant. To control the fungus, first remove and dispose of affected leaves as soon as you see them. Also remember to remove all fallen leaves and debris at the end of the season to limit spores that can over-winter. As with black spot and powdery mildew, a fungicide will offer some degree of control. Instead of a commercial product, you can try a baking soda or milk remedy. Finally, mulch under your rose bushes to prevent spores from splashing up onto the plants. The bacterium enters the plants through wounds, from pruning, transplanting, or breakage. It starts as a small growth near the soil line on the stem, crown, or roots. Crown gall can easily be confused with the graft union, but the graft union will not continue to grow larger. New crown galls are usually pale colored and somewhat round. As they enlarge, they become rough, irregularly shaped, and hard. They can eventually start to rot, but they will return. There is no cure for crown gall. If you have an infected rose, dig it up and dispose of it somewhere other than the compost bin. Crown gall bacterium can over-winter in the plant and soil. It is spread to other plants by splashing water. Do not replant roses in that spot for at least five years. To avoid crown gall:
Only purchase certified, disease-free roses. Even then, inspect the base for unusual growths.Clean your pruners between cuts with a dilute bleach solution (1 part bleach to nine parts water) or rubbing alcohol.Minimize wounds by using sharp pruners, control insect pests, and watching the mower and string trimmer.
It’s hard to miss these bronze and green metallic beetles. They feed on the leaves and skeletonize them, eventually defoliating the entire plant. They can also devour and distort flowers and buds. The adults are hard to get rid of. Hand-picking them and dropping them into a bucket of soapy water is the best method, although a tedious one. If you can eliminate them while they are still in the grub stage in your lawn, the fewer adults will emerge to become a problem. It’s possible that the plant will not exhibit any symptoms; it will just decline. However, most infected roses will have one or more of the following symptoms:
Yellowing in a mosaic pattern Chlorotic (yellow) rings or wavy lines (which can look similar to leaf miner damage.) Yellowing of the veins Mottled flower color
Unfortunately there is no control. Cutting out the cane with symptoms is only cosmetic, because the virus is systemic. Avoid the problem by buying certified virus-free plants. Adult rose curculios feed on the flower buds, poking their long snots inside. That would be bad enough, but they also deposit their eggs inside the closed buds. If the flowers open, they will be full of ragged holes. Rose curculios have a preference for yellow and white roses. Not planting those colors will cut down on populations. Hand-picking is the preferred method of control. You can also gain some measure of control by removing existing buds, when you see rose curculios on your plants. The buds might have eggs inside them. Always dispose of garden debris throughout and at the end of the season. If you do have a severe problem with them, any broad spectrum or organic insecticide should work. Be aware of three species of rose slugs. The European rose slug (Endelomyia aethiops) only produces one generation per year. The curled rose slug sawfly (Allantus cinctus), which curls up when not eating, usually produces two generations per year and the bristly rose slug sawfly (Cladius difformis) is covered in hair-like bristles and has the ability to up to six generations per year. Rose slugs feed on the leaves of rose bushes. They remove just the soft tissue, leaving the leaves looking translucent between the veins. A small infestation isn’t worth worrying about, as the damage is mainly cosmetic. However a large population can severely weaken the plant. Start scouting for the larvae in mid-spring. At this stage, they can be hosed off with a good blast of water. Neem oil and insecticidal soap are also effective, but avoid using any insecticides, though, because sawfly slugs have many natural predators, including birds, parasitic wasps, and predatory beetles. Flower thrips will cause buds to distort. If the buds do open, you might also see brown streaks on the individual petals. Chilli thrips cause damage to the rose buds, leaving them dried out and brittle. They also feed on the leaves, causing them to curl upwards or become distorted. Thrips are difficult to get under control because they live inside the rose buds and their populations can grow quickly. They can also over-winter in debris, so fall clean-up is essential. If you start to see buds distorting, remove any buds showing symptoms. Natural predators, such as pirate bugs and other beneficial insects, can help in the battle. If you see thrips are being preyed upon, do not use an insecticide or you will kill the predators, too. Thrips are difficult to control with pesticides, and results are often best achieved using a variety of methods: horticultural oils, insecticidal soaps, and proper horticultural practices for growing and maintaining rose bushes.
