Are you dirt tired of tending to your rose bushes, only to see them wither and die? Problems like black spot and cane borers are definitely a thorny situation, but they’re not impossible to solve. Read on for pro tips from our gardening experts on how to treat common rose problems.
Rose problems and solutions
Rose black spot is a common fungal disease among roses. It won’t immediately kill your plant, but it can pose a serious problem if left untreated. Black spots, as the name suggests, present as splotches on the leaves and canes of your plant. These spots weaken your roses and cause them to be more vulnerable to harsh weather conditions and other diseases.
A rose with a severe black spot problem will have paler flowers and fewer leaves. You will also see the infected rose leaves turning yellow and brown – a direct effect of their decreased capacity to photosynthesise. Your once-healthy rose plant will have difficulty taking in nutrients and developing properly. Over time, your roses will become sickly and wither.
What causes black spot
Black spot on roses is a disease caused by the fungus Diplocarpon rosae. Fungal spores can spread to the stems and leaves of your rose plants through splashing water and soil cultivation. The spores can also be transferred between rose plants by grubs and insects.
Prevention of black spot
If you want to avoid black spot, the best choice for you as a rose grower is to pick disease-resistant roses. Should you still opt for a rose variety that’s not immune to fungal diseases, there’s no need to worry.
These are the ways to protect your rose bushes from black spot:
- Keep your roses well-ventilated, as plants are most at risk of black spot when the weather is warm and moist. Plant roses at least 1m apart to allow air to circulate well around your plants.
- Prune rose bushes to remove dead leaves, flowers and stems. This will let sunlight in and encourage good airflow. Professional pruning experts advise having the cuttings disposed of properly to prevent the spread of infection to healthy plants.
- Keep your roses dry at all times. When watering, avoid spraying water on the leaves and stems.
How to treat rose black spot
You can start treating black spot even before you see dark splotches and yellowing leaves on your roses.
Follow these tips below to stop the spread of black spot:
- A fungicidal spray on new leaves can prevent black spot from growing on your plants. You can treat roses during spring, when new buds start to form. Spray all parts of the rose bush, from the leaves and flowers down to the stems.
- A weekly spray is recommended during the rainy season for extra protection. For best results, use a fungicide with penconazole, myclobutanil, mancozeb, sulfur, or copper – these chemicals are effective in preventing fungal growth.
- Use a dormant spray or horticultural oil during winter to smother remaining fungal spores.
Powdery mildew presents as a grayish white powder on the leaves and flower buds of roses. A rose infected with powdery mildew will have distorted leaves and unhealthy-looking flowers. In more severe cases, the infected leaves fall from the plant and the flowers fail to open.
What causes powdery mildew
Similar to black spot, powdery mildew is a fungal disease that attacks roses. It usually appears during the growing season when the evening air is particularly humid. The fungus Sphaerotheca pannosa, which causes powdery mildew, thrives in dark, shaded areas and colder conditions.
Prevention of powdery mildew
Disease-resistant roses are always a convenient choice for rose growers, but you can still plant any rose variety that suits your liking.
Follow the tips below to prevent powdery mildew from growing on your roses:
- Avoid planting roses in shaded areas to deter fungi from growing on your plants.
- Position your roses under full sun to keep the leaves, stems, and flowers dry at all times.
- When pruning, dispose of infected cuttings properly to prevent powdery mildew from spreading to healthy plants.
How to treat powdery mildew
Compared to other fungal diseases, powdery mildew is relatively easy to treat.
These are tried-and-tested methods on how to stop powdery mildew on roses:
- Spray fungicide with mancozeb, lime sulphur, tebuconazole, myclobutanil or triforine on your roses to treat powdery mildew. You can also do this treatment during the growing season as a preventive measure.
- If you prefer a green alternative, an organic spray made of water, non-detergent soap, and bicarb soda works just as well.
- For an easy DIY solution, mix 1 part full cream milk with 10 parts water. Spray the mixture on your roses.
Stem canker is a fungal disease that presents as dark or discoloured splotches on your roses’ canes. It can spread to other parts of your plant, including the base, and infect other branches as well.
What causes stem canker
Stem canker is caused by different species of fungi. These include Botryosphaeria, Leptosphaeria, Coniothyrium, and Cryptosporella. A sick or malnourished plant is susceptible to a stem canker infection.
Your rose plants can get stem canker after pruning if a wound is left exposed. Stem canker fungi can also enter roses after a flower has been cut off, or if there are damaged areas in your plant brought by hail or winter.
Prevention of stem canker
Along with keeping your roses healthy and well-nourished, these are the ways to prevent stem canker from growing on your plants:
- Give your roses enough sunlight and air circulation to deter fungal and bacterial growth.
- Fertilise your roses in early spring through late summer to keep them robust and encourage new growth.
How to treat stem canker
There is no fungicide that can treat stem canker on roses, but this disease can be managed by the following methods:
- Prune infected leaves, stems, and flowers immediately at the first sign of disease to prevent spreading the infection.
- Trim off dead plant parts where bacteria and fungi thrive.
- Apply a fungicide on open plant wounds to stop fungi, bacteria, and viruses from entering.
- Disinfect shears or secateurs with bleach after pruning an infected plant.
Rust is a rose leaf disease that can cause defoliation. You’ll be able to identify rose rust by the reddish-orange flecks on your roses’ leaves. These flecks appear during spring and early summer. During late summer, the flecks are accompanied by brown spore masses.
When your plant has rose rust, it won’t be long before leaves start dropping from your plant. A rose plant infected with rose rust will have a hard time undergoing photosynthesis, and may eventually become sickly and vulnerable to other diseases.
What causes rose rust
The fungus Phragmidium mucronatum causes rust in roses. One particular trait of this fungus is its choice of host. Unlike other fungal diseases that easily spread from plant to plant, rose rust specifically infects roses only. That doesn’t mean that you can let your guard down when it comes to rose rust. It can still be transferred to healthy roses via fungal spores carried by wind.
Prevention of rose rust
Prevent rose rust from spreading to healthy roses by following these tips:
- Remove infected leaves from your rose plants.
- Make sure that there is enough air circulation to keep your plants dry, as fungi thrive in humid conditions.
- Prune your roses regularly to ensure that your plants have proper ventilation.
- Trim off old, withered, or infected leaves and flowers and dispose of them properly. Not only do these dead plant parts consume nutrients intended for healthier areas of your plant, but they are also a breeding ground for fungal and bacterial growth.
- It’s best to water your plants before noon to allow them to dry. When watering, avoid splashing water on the buds and leaves.
How to treat rose rust
Treat rose rust through these methods:
- Spray infected leaves with fungicide that contains mancozeb, myclobutanil, or triforien. You can also use an organic treatment of lime sulphur or bicarb soda.
- Remove infected leaves immediately and dispose of the cuttings to prevent the infection from spreading.
Botrytis is a fungal disease that causes spotted flowers and blotchy canes in roses. Among the variety of rose diseases, botrytis is one of the most identifiable. Once-vital flowers lose their colour and firm structure to give way to brownish, withered-looking petals. Flower buds infected with botrytis also fail to open and eventually droop. This disease can considerably diminish the beauty of any rose bush.
What causes botrytis
Botrytis is caused by the fungus Botrytis cinerea. An infection can be spread through wind-blown botrytis spores, or transferred through unsanitised gardening tools like shears and secateurs.
Prevention of botrytis
No home owner likes seeing forlorn-looking roses in their garden. To combat the growth of botrytis on your roses, it’s important to observe the following:
- Keep your garden clean at all times.
- Rake away all dead leaves that fungi and bacteria can use as a breeding ground.
- Prune off excess foliage growth and remove old flowers, leaves, and stems from your plant for better air circulation.
- Apply fungicide on the cut as a protective layer against fungal disease. Make sure that your shears are cleaned with bleach after each use to prevent spreading spores from plant to plant.
- When watering, avoid getting water on the leaves – moisture is a trigger for fungal growth on roses.
How to treat botrytis
These are the ways with which you can treat botrytis in roses:
- Spray roses with a fungicide containing mancozeb, thiophanate methyl, or chlorothalonil. These ingredients are proven to be effective against botrytis.
- Spray copper fungicide in winter when your rose plants are dormant.
- Neem oil, a weak fungicide, can be used in less severe cases. Take care not to use too much neem oil during hot weather, however, as this can cause your rose plants to get sunburned.
Rose rosette disease
Rose rosette disease is a viral disease that distorts the appearance of your roses. Rose bushes will start to develop reddish growths on their stems one to three months after getting infected. Rose branches also become swollen and have an unusually high number of thorns.
The leaves of an infected rose bush will look smaller than their healthier counterparts, and flowers look unhealthy, thin, and distorted. Rose rosette disease symptoms typically appear during late spring to early summer. Once a rose plant gets sick, the virus quickly travels to other parts of the plant. In a few years’ time, the infection will take over and your roses will eventually die.
What causes rose rosette disease
Rose diseases and pests usually go together, as in the case of rose rosette disease. The rose leaf curl mite is the carrier of the rose rosette virus (RRV), which is transmitted to the rose plant during the mite’s feeding. Not all rose leaf curl mites carry RRV, but those that do pose a serious threat to your roses.
Prevention of rose rosette disease
Among the different rose varieties, the wild multiflora rose is particularly vulnerable to rose rosette disease.
These are the ways you can prevent the spread of rose rosette disease:
- Remove infected rose plants from your garden. Check that all of the roots of the infected rose plant have been taken out as well. This will ensure that the mites won’t linger in the soil and transfer to other plants.
- Space your roses at least 1m apart to protect them from contracting rose rosette disease from an infected plant.
- Never graft sick rose cuttings onto healthy canes. Even if the stem of an infected rose plant is asymptomatic, it can transmit the virus to a healthy plant through contact.
- Always disinfect cutting tools with bleach after pruning diseased plants.
- Spray bifenthrin pesticide fortnightly from April through September to deter rose leaf curl mites from transferring to nearby plants.
How to treat rose rosette
Unfortunately, there is no known cure for rose rosette disease. The best course of action for your roses is careful prevention. Removing roses infected with rose rosette from your garden will stop the disease from spreading to healthy rose bushes.
Rose mosaic is a viral disease that causes yellow leaves on roses. When your rose plant has rose mosaic disease, the leaves will have yellow patches or wavy lines on them. This disease affects the overall aesthetic of your plants and weakens their constitution. If left untreated, they become more susceptible to drought, cold weather, and other diseases.
What causes rose mosaic
Rose mosaic is caused by the rose mosaic virus (RMV). RMV spreads to healthy roses primarily when infected cuttings are grafted onto healthy roses.
Prevention of rose mosaic
When it comes to viral diseases such as rose mosaic, an ounce of prevention is worth a pound of cure.
These are the ways you can protect your roses from getting infected with rose mosaic:
- Make sure to check for healthy plants when purchasing from a nursery or plant store — roses with rose mosaic on their leaves should be avoided.
- Prune off infected leaves from your plant and dispose of the cuttings properly.
- Disinfect your gardening tools with bleach after pruning off diseased plant parts.
How to treat rose mosaic
There is no known treatment for rose mosaic disease, but it can be prevented. Remove yellowing leaves as soon as you see symptoms of rose mosaic on your roses, then dispose of them properly.
Crown gall is a bacterial disease that causes tumor-like growths, or galls, on the stems or roots of rose bushes. Galls can be light green during their early stages and change into a dark brown colour as they mature. The size of the swellings can be anywhere from small lumps, to growths that are several centimetres across. Galls are a danger to your roses’ health because they inhibit water and nutrients from reaching other parts of the plant.
A rose bush that is infected with crown gall will have discoloured and lackluster leaves, stunted growth, and a higher susceptibility to other infections.
What causes crown gall
Agrobacterium tumefaciens is the bacteria responsible for causing crown gall in roses. Damaged or stressed rose plants secrete a substance that attracts this bacterium into your plant. When the bacterium enters your plant, it starts a mutation within normal plant cells that causes them to form gall-like swellings.
Prevention of crown gall
These are the ways you can prevent your roses from forming crown gall:
- Plant rose bushes in healthy, disease-free soil. Make sure that the planting site for your rose plant has no previous history of the disease.
- Take care not to cause any damage or injury to your roses that can trigger the bacteria to transfer to them.
How to treat crown gall
With crown gall, early treatment is key. You can nip the spread of crown gall among healthy roses with these methods:
- When you suspect that your rose bush has crown gall, remove the entire plant and dispose of it.
- Spray an insecticide to deter insects from damaging your plant.
- You can protect your plant by soaking seeds or bare root cuttings in a solution that contains Agrobacterium radiobacter. This bacterial strain is effective in preventing crown gall growth.
You’ve probably seen tiny green, brown, or pink insects clustered on your rose’s leaves, stems, and flowers. These insects are called aphids, and they are some of the most common rose pests you can find in your garden.
An untreated aphid infestation is one possible explanation why your rose plants are losing their beautiful flowers and developing discoloured leaves. These parasites drink the sap from your plants and cause them to become malnourished and lackluster. The presence of aphids also triggers sooty mould growth on the leaves of your rose plants. When you see a dark powdery residue on your leaves (rather unsightly, that’s for sure), you’ll likely find aphids on your rose bushes as well.
How to treat aphids in roses
Treating your rose’s aphid problem will nip sooty mould growth right in the bud.
Fortunately, the solution to treating an aphid infestation is simple:
- Using a spray, apply a layer of horticultural oil or neem oil on your rose plants. Do this in the evening when there’s no more sunlight, as oil amplifies the sun’s rays and causes leaves to get sunburned.
- For more severe aphid infestations, repeat the treatment fortnightly until all the aphids are eradicated.
- Remember to always follow the instructions on the labels when using any type of pesticide.
Rose midges are tiny white fly larvae that feed on your roses. Adult midges have a mosquito-like appearance, and can present as white or reddish in colour. These pests lay their eggs on the flowers and tips of new leaves. When the eggs hatch, the larvae feed on rose tissue and take in nutrients intended for your plants.
A plant with a rose midge infestation will have deformed or shriveled leaves, and buds that won’t open properly. The unhealthy plant eventually weakens and loses its flowers in the process. A rose bush not producing flowers can be a sign that it is under a rose midge attack.
How to treat rose midge in roses
This is an effective method to treat a rose midge infestation:
- Apply an insecticide on the soil surrounding your rose plants. Rose growers use a systemic insecticide specially formulated for rose midge control.
- You may have to repeat the treatment 10 days after your first application if the infestation is severe.
Cane borers are moth larvae that burrow into rose canes. A rose infested with cane borers will have wilted leaves and swollen canes. If left untreated, it won’t be long before your plant will weaken and wither.
How to treat cane borers in roses
Follow these tips to get rid of cane borers in your rose bushes:
- Prune off infested canes and dispose of them properly.
- Make sure to remove the borers in the canes, then apply white glue on the cuts to seal them.
Thrips are tiny insects that suck sap from your roses. These rose pests burrow on the undersides of leaves, causing silvery streaks to appear on the leaves’ surface. They also bore holes into the petals of flower buds and deform them.
Thrips in small numbers will do little to damage your roses, but sizable infestations can weaken your plant and make them susceptible to disease.
How to treat thrips in roses
To rid your rose bushes of thrips, simply follow the methods below:
- Prune off infested flowers and dispose of them properly.
- Spray the plants with insecticides containing imidacloprid, acetamiprid, or pyrethrins.
Rose care and maintenance
Growing roses does not come without challenges, and it can sometimes feel overwhelming. With the treatment methods above, you’ll feel more confident about addressing rose diseases and pest infestations. Before you know it, you will have healthy, picture-perfect roses in your garden to enjoy.