There is little doubt that the rose is the king of the garden. For centuries, roses have been beloved for their beauty, and they have long been a symbol of love, fidelity, and commitment. Roses are among the most popular of all plants for the home garden, grown by amateur gardeners and professional growers alike.
Of course roses are also prone to a number of problems, including some not encountered by other types of flowers and plants. It is important for any gardener considering adding roses to his or her garden to learn about the special needs of these most majestic of plants.
Rose Problem 1 - Black Spots on the Foliage
This is perhaps the most common of all rose problems. The disease in question is known as "black spot." These black spots (Diplocarpon Rosae) generally appear as a circular shape with fringed edges on the foliage, and the disease may cause the leaves to appear yellow as well. Leaves less than two years old are most susceptible to this disease. Black spot can winter over, so autumn pruning is necessary or the entire cycle will repeat itself come spring.
TIP: Our expert gardening advisor, Rachel Klein suggests, "To prevent black spot, make sure to space your roses correctly. Small tea bushes should be placed 3 feet apart and larger rose bushes four feet apart. This will allow for good air circulation. Also, when watering your roses, water from the bottom without getting the leaves wet, early in the morning."
The key to combating this disease is to remove the infected foliage as quickly as possible, including removing any leaves which may have fallen around the rose. In addition, there are a number of commercial preparations designed to fight the disease that causes black spot. Since this problem is so common, it is a good idea for rose gardeners to have a supply of these preparations on hand. This will allow the problem to be addressed quickly, mitigating the damage to the plants.
TIP: Rachel adds, "A great non-chemical measure against black spot is sulphur. The fungus that causes black spot cannot germinate in a sulphur film. However, the sulphur must be in place before the spores land on the plant. While plants are dormant in the spring, spray thoroughly with a wettable sulphur (sold at nurseries). The sulphur will wash off during rains, so reapply frequently. This is a great preventative measure for chemical-free gardens and also works well against mildew and rust."
Rose Problem 2 - Distorted and Stunted Plants
This is another common rose disease, this one known as powdery mildew. This is a fungal disease, and it coats the stems, foliage, and buds with what appears to be a white powder. This coverage in turn causes the leaves to turn purple and appear unsightly.
TIP: Rachel adds, "The fungus will then begin drawing on the moisture and nutrients in the leaves. The first sign of powdery mildew is a crinkling of young leaves. Be on the watch—powdery mildew can spread rapidly and needs to be caught early. Plants that have been weakened by over-watering, drought, crowding, or nutrient deficiencies are most susceptible to this fungus. The best preventative measure is to ensure your roses are growing in the best possible conditions."
In order to combat the problem of powdery mildew, spray the affected areas with an antifungal spray. As with black spot treatment, it is a good idea for the rose gardener to keep a bottle or two of this antifungal spray on hand in your garden shed. As with all rose diseases, early treatment is the key to success.
Rose Problem 3 - Damaged Leaves
The leaves of roses can be especially susceptible to damage, with the undersides of leaves often being the first to show such damage. One of the most common leaf conditions is a disease known as rust, named for the reddish orange blisters that appear. These reddish orange discolorations will turn black in the fall and sprout anew in the spring if not completely obliterated. Ultimately, this disease leads to complete defoliation of the plant.
If your roses are troubled by rust, be sure to remove all affected leaves. In addition, spraying the remaining foliage with an organic anti-fungal spray once a week can be a big help.
TIP: Rachel suggests, "Any appearance of rust must be dealt with immediately. Rake up and dispose of all of the foliage under the bush, as rust can winter over and lay dormant on fallen leaves. Again, make sure you are watering in the morning, only at the base of the shrub, and providing adequate spacing and air circulation. Dusting or spraying your bushes with sulphur will not kill the rust, but will prevent the next generation from germinating."
Rose Problem 4 - Stunted and Malformed Flowers and Foliage
Many rose gardeners complain that their roses suffer from stunted and malformed flowers and foliage. While there are many conditions that can cause this problem, one of the most common causes is spider mites. These spider mites are tiny and may be either yellow, red, or green, and they cling to the underside of the leaves, where they suck the juices and nutrients from the plant.
While spider mites are certainly troublesome, in many cases the problem can be cured simply by applying a strong stream of water to the foliage to dislodge the mites.
TIP: Rachel advises, "When wetting, be sure to spray the undersides of the leaves as well. Be careful about using broad-spectrum insecticides for spider mites. While mites may be listed on the label, insecticides are generally not effective against them. Also, the insecticides will kill off the mites' natural predators, which may actually cause a spike in the infestation. Instead, apply neem oil to your roses. Neem oil is an all-natural organic oil that is non-toxic and will not affect the other insects in your bed. Neem oil can cause discoloration of the blooms in some cases, so apply to a small test area first. Then, spray the oil on the tops and bottoms of the leaves and around the base of the bush once a week until the mites are gone."
Rose Problem 5 - White Webbing on the Leaves
If you notice weak foliage, leaves that appear to be blotched, or leaves that have white webbing on them, you could have an aphid problem. Aphids are common visitors to the rose garden, and like spider mites they damage the plants by sucking their natural juices out through the leaves. Aphids may be brown, green, or red, and they can sometimes be seen clumped together in groups under the flowers and leaves.
As with spider mites, aphids can often be controlled with a strong stream of water, or through the introduction of beneficial insects that naturally feast on aphids.
TIP: Rachel adds, "Lady bugs might be considered lucky because of their natural inclination to wipe out aphid populations. They can be bought in some nurseries (or simply found in nature) and if released on the bushes properly, can help to reduce your aphid problem. Neem oil applications are also an effective aphid repellent."
Rose Problem 6 - Unopened or Distorted Blooms
There are a number conditions that can cause blooms to not open completely, or to appear distorted, but one of the most common is known as thrips. Thrips often appear as slender brownish or yellowish winged insects, and they often live near flower buds. These insects also suck the vital juices from the flowers, resulting in distorted or poorly formed blooms. If you peel back the petals on an suspect bloom, you will probably be able to see either the thrips themselves or their feces.
If thrips are suspected, remove any flowers that show signs of infestation. Frequent clipping and disposal of spent blooms can reduce your risk of thrip infestation. In addition there are a number of commercial preparations that can help gardeners deal with this common problem.
TIP: Rachel says, "Insecticides are only somewhat effective since these topical treatments may not reach the insides of the buds, where the thrips reside. Neem oil and insecticidal soaps have some effectiveness against thrips. Applications should be often, as much as every other day, to keep up with the fast life cycle of these critters."
Although roses may be at risk for some common garden problems, with a little know-how you can nip diseases such as these in the bud. You'll be able to enjoy years of gorgeous blooms.