What"s Wrong with My Roses? The Top 10 Usual Suspects
What's Wrong with My Roses?
Roses have a reputation for being problem prone. Sometimes this reputation is well deserved. Anyone who has grown an older variety of rose has most likely had to deal with black spot on an annual basis. That's starting to change, as many modern roses are bred to be extremely disease resistant and very low maintenance.
If you keep your roses healthy, with plenty of sunlight, nutrients and water, you should have fewer problems no matter what type of rose you are growing.
However even though roses may be considered the Queen of Flowers, even the queen can experience problems and need some outside help.
The following pages profile 10 common pests and diseases that can afflict your beautiful rose bushes, along with symptoms and control options.
Aphids on Roses
One particularly common rose pest is aphids. Aphids are tiny, pear-shaped, sucking insects that love to feed on succulent new growth. There are several species and they may be yellow, green, or blackish. You may see them referred to as greenfly or blackfly, but they are not actually flies.
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
Controls
Since they are such tiny, tender insects, you can often control them by hosing the rose off with a strong blast of water. You will need to get all areas of the plant, including the undersides of the leaves, and you will need to do this more than once.
If water does not seem to be controlling them, you can try insecticidal soap. Make sure the plant is completely coated. The soap needs to make contact with the aphid.
Black Spot on Roses
The words "black spot" often come to mind when a gardener hears "roses". It is the disease most often considered when growers are breeding for resistant and many modern roses are indeed problem free. However there are still plenty of roses that are susceptible and you should always keep an eye out for signs it is developing.
Black spot is a fungal disease (Diplocarpon rosae). Weather plays a big part in the development of black spot.
Warm, wet or humid weather is the perfect environment. If black spot has been in the area before, the spores are probably still around, waiting for the ideal conditions. It only takes about 7 hours of warm moisture for black spot spores to germinate, but you may not see symptoms for several days. Once you do, act quickly, because new spores are produced every 3 weeks.
Symptoms of Black Spot on Roses
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 and a severely infected plant will totally defoliate.
Controls
Start with a thorough fall clean-up. Spores can over-winter so do not leave any leaves or other debris on the ground.
Since black spot is exacerbated by poor growing conditions, make sure your plants get plenty of water and good air circulation.
If you do see evidence of black spot, spraying with Bordeaux Mix, neem or sulfur is effective.
For more control measures, read Black Spot on Roses - What to Do and How to Prevent It.
Cercospora Leaf Spot of Roses
Black spot is not the only fungal disease to commonly attack roses. Cercospora leaf spot, sometimes referred to as rose leaf spot, is caused by the fungus Cercospora rosicola. It's not the same fungus as black spot, but they share many of the same characteristics.
Symptoms of Cercospora Leaf Spot on Roses
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.
Controls
First, remove affected leaves as soon as you see them. Also remember to remove all 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. Again, instead of a commercial product, you can try both the baking soda remedy or the milk remedy.
And finally, mulch under the roses to prevent spores from splashing up onto the plants.
Crown Gall on Roses
Crown gall affects a wide array of plants and roses are definitely one of them. It is a plant disorder caused by the bacterium Agrobacterium tumefaciens, that interferes with the plants ability to take up water and nutrients. This results in poor growth and weak plants that are easily stressed and injured.
Symptoms of Crown Gallon Roses
The bacterium enters the plants through wounds, from pruning, transplanting or breakage.
It starts as a small growth near the soil line, on either the stem, crown, or roots. Crown gall can easily be confused with the graft union, but the graft union will not keep getting larger. New crown galls are usually pale colored and somewhat round. As they enlarge they become rough, irregularly shaped, and hard. They may eventually start to rot, but they will return.
Controls
There is no cure. 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 in the soil. It is spread to other plants by splashing water. Do not replant roses in that spot for at least 5 years.
Tips for avoiding crown gall:
Japanese Beetles on Roses
Although Japanese beetles feed on many different plants, if they are in the neighborhood you can be certain they will be on your rose plants. They tend to congregate in large numbers and can cause a great deal of damage quickly.
Symptoms of Japanese Beetle Damage to Roses
It's hard to miss these bronze and green metallic beetles. They feed on the leaves and leave them skeletonized, eventually defoliating the entire plant.
They can also devour and distort the flowers and buds.
Controls
The adults are hard to get rid of. Hand picking is the best method, although a tedious one. If you can catch them as grubs, you have more options. Full Japanese beetle control options are outlined in Controlling Adult Japanese Beetles in the Garden.
Rose Mosaic Virus
Rose Mosaic virus refers to 2 viruses, Prunus Necrotic Ringspot Virus (PNRSV) and Apple Mosaic Virus (ApMV). It is spread by vegetative propagation of roses (buds, scion or root stock), but does not spread from plant to plant. It may only manifest on 1 cane, but the whole plant is infected and will exhibit poor vigor, with few flowers and stunted growth.
Symptoms of Rose Mosaic Virus
This is a tricky one, because it's possilb ethe plant will not exhibit any symptoms, it will just decline.
But most infected roses will have one or more of the following:
Controls
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.
Powdery Mildew on Roses
As with black spot, powdery mildew is a fungal disease that lies dormant until the right conditions appear. For powdery mildew, those conditions would be hot, dry days with cool, moist nights.
Symptoms of Powdery Mildew on Roses
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.
Control
If you live in an area where powdery mildew often occurs, you can use a homemade baking soda spray as a preventative.
It does not work well after powdery mildew is present.
Once your plants are showing symptoms, the easiest control is this homemade milk spray. It is surprisingly affective and can even be used on edible plants, like cucumbers and squash.
Rose Curculios
Rose curculios are reddish-brown weevils with dark snots. They are only about 1/4 in. long, but they can cause a lot of damage. Even the small, white larvae feed on damage
Symptoms of Rose Curculio Damage on Roses
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.
.
Controls
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 may have eggs inside them. And always dispose of any debris throughout and at the end of the season.
If you do have a severe problem with them, any broad spectrum insecticide should work.
Thrips on Roses
Rose and pear slugs are two different insects and neither is a true slug. They are the lavae of sawflies, small flying insects. They look like slugs because they secrete a slimy substance that covers their bodies. Rose sawflies are yellowish-green and can get as large as 3/4 in. Pear slugs are a reflective greenish-black and a little smaller, at about ½ in. Although roses are not the preferred food of pear slugs, they will feed on a variety of plants.
There are 3 species of rose slugs to be aware of. The European rose slug (Endelomyia aethiops) only produces 1 generation per year. The curled rose slug sawfly (Allantus cinctus), which curls up when not eating, usually produces 2 generations per year and the bristly rose slug sawfly (Cladius difformis) is covered in hair-like bristles and has the ability to up to 6 generations per year.
Symptoms of Rose Slug Damage
Rose slugs feed on the leaves of rose bushes. They remove just the soft tissue, leaving the leaves looking translucent between the veins.
Controls
A small infestation isn't worth worrying about. The damage is mainly cosmetic. However a large population can severely weaken the plant.
Start scouting for the lavae in mid-spring. At this stage they can be hosed off with a good blast of water. Neem and insecticidal soap are also effective, but try and hold off on any insecticides, though, because sawfly slugs have lots of natural predators including: birds, parasitic wasps, and predatory beetles.
Thrips are a common insect pest. Flower thrips are slender and brown, with yellow wings that feed on flower buds. Chilli thrips, which are becoming an increasing problem in home gardens, are pale with dark wings. They feed on all parts of the plant.
Symptoms of Thrip Damage to Roses
Flower thrips will cause buds to distort. If the buds do open, you may also see brown streaks on the individual petals.
Chilli thrips cause damage to the buds, leaving them dried out and brittle. They also feed on the leaves, causing them to curl upwards or distort.
Controls
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.
There are natural predators such as pirate bugs and other beneficial insects, that can help in the battle. If you see your thrips are being preyed upon, do not use an insecticide or you will kill the predators, too.
A systemic insecticide is the best control, if used as a foliar spray. There are several available and you should look for one that is specifically labeled for use on thrips. According to Texas A&M recommendations, those containing spinosad (pronounced spin-OH-sid) have shown the least environmental impact.
Roses have a reputation for being problem prone. Sometimes this reputation is well deserved. Anyone who has grown an older variety of rose has most likely had to deal with black spot on an annual basis. That's starting to change, as many modern roses are bred to be extremely disease resistant and very low maintenance.
If you keep your roses healthy, with plenty of sunlight, nutrients and water, you should have fewer problems no matter what type of rose you are growing.
However even though roses may be considered the Queen of Flowers, even the queen can experience problems and need some outside help.
The following pages profile 10 common pests and diseases that can afflict your beautiful rose bushes, along with symptoms and control options.
Aphids on Roses
One particularly common rose pest is aphids. Aphids are tiny, pear-shaped, sucking insects that love to feed on succulent new growth. There are several species and they may be yellow, green, or blackish. You may see them referred to as greenfly or blackfly, but they are not actually flies.
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
- Distorted flower buds and leaves
- Sticky "honeydew"
- Black sooty mold growing on the honeydew
- Clusters of aphids
- Ants crawling on the plants and feeding on the honeydew
Controls
Since they are such tiny, tender insects, you can often control them by hosing the rose off with a strong blast of water. You will need to get all areas of the plant, including the undersides of the leaves, and you will need to do this more than once.
If water does not seem to be controlling them, you can try insecticidal soap. Make sure the plant is completely coated. The soap needs to make contact with the aphid.
Black Spot on Roses
The words "black spot" often come to mind when a gardener hears "roses". It is the disease most often considered when growers are breeding for resistant and many modern roses are indeed problem free. However there are still plenty of roses that are susceptible and you should always keep an eye out for signs it is developing.
Black spot is a fungal disease (Diplocarpon rosae). Weather plays a big part in the development of black spot.
Warm, wet or humid weather is the perfect environment. If black spot has been in the area before, the spores are probably still around, waiting for the ideal conditions. It only takes about 7 hours of warm moisture for black spot spores to germinate, but you may not see symptoms for several days. Once you do, act quickly, because new spores are produced every 3 weeks.
Symptoms of Black Spot on Roses
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 and a severely infected plant will totally defoliate.
Controls
Start with a thorough fall clean-up. Spores can over-winter so do not leave any leaves or other debris on the ground.
Since black spot is exacerbated by poor growing conditions, make sure your plants get plenty of water and good air circulation.
If you do see evidence of black spot, spraying with Bordeaux Mix, neem or sulfur is effective.
For more control measures, read Black Spot on Roses - What to Do and How to Prevent It.
Cercospora Leaf Spot of Roses
Black spot is not the only fungal disease to commonly attack roses. Cercospora leaf spot, sometimes referred to as rose leaf spot, is caused by the fungus Cercospora rosicola. It's not the same fungus as black spot, but they share many of the same characteristics.
Symptoms of Cercospora Leaf Spot on Roses
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.
Controls
First, remove affected leaves as soon as you see them. Also remember to remove all 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. Again, instead of a commercial product, you can try both the baking soda remedy or the milk remedy.
And finally, mulch under the roses to prevent spores from splashing up onto the plants.
Crown Gall on Roses
Crown gall affects a wide array of plants and roses are definitely one of them. It is a plant disorder caused by the bacterium Agrobacterium tumefaciens, that interferes with the plants ability to take up water and nutrients. This results in poor growth and weak plants that are easily stressed and injured.
Symptoms of Crown Gallon Roses
The bacterium enters the plants through wounds, from pruning, transplanting or breakage.
It starts as a small growth near the soil line, on either the stem, crown, or roots. Crown gall can easily be confused with the graft union, but the graft union will not keep getting larger. New crown galls are usually pale colored and somewhat round. As they enlarge they become rough, irregularly shaped, and hard. They may eventually start to rot, but they will return.
Controls
There is no cure. 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 in the soil. It is spread to other plants by splashing water. Do not replant roses in that spot for at least 5 years.
Tips for avoiding 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 4 parts water) or rubbing alcohol.
- Minimize wounds by using sharp pruners, control insect pests, and watching the mower and string trimmer.
Japanese Beetles on Roses
Although Japanese beetles feed on many different plants, if they are in the neighborhood you can be certain they will be on your rose plants. They tend to congregate in large numbers and can cause a great deal of damage quickly.
Symptoms of Japanese Beetle Damage to Roses
It's hard to miss these bronze and green metallic beetles. They feed on the leaves and leave them skeletonized, eventually defoliating the entire plant.
They can also devour and distort the flowers and buds.
Controls
The adults are hard to get rid of. Hand picking is the best method, although a tedious one. If you can catch them as grubs, you have more options. Full Japanese beetle control options are outlined in Controlling Adult Japanese Beetles in the Garden.
Rose Mosaic Virus
Rose Mosaic virus refers to 2 viruses, Prunus Necrotic Ringspot Virus (PNRSV) and Apple Mosaic Virus (ApMV). It is spread by vegetative propagation of roses (buds, scion or root stock), but does not spread from plant to plant. It may only manifest on 1 cane, but the whole plant is infected and will exhibit poor vigor, with few flowers and stunted growth.
Symptoms of Rose Mosaic Virus
This is a tricky one, because it's possilb ethe plant will not exhibit any symptoms, it will just decline.
But most infected roses will have one or more of the following:
- Yellowing in a mosaic pattern
- Chlorotic (yellow) rings or wavy lines (Can look similar to leaf miner damage.)
- Yellowing of the veins
- Mottled flower color
Controls
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.
Powdery Mildew on Roses
As with black spot, powdery mildew is a fungal disease that lies dormant until the right conditions appear. For powdery mildew, those conditions would be hot, dry days with cool, moist nights.
Symptoms of Powdery Mildew on Roses
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.
Control
If you live in an area where powdery mildew often occurs, you can use a homemade baking soda spray as a preventative.
It does not work well after powdery mildew is present.
Once your plants are showing symptoms, the easiest control is this homemade milk spray. It is surprisingly affective and can even be used on edible plants, like cucumbers and squash.
Rose Curculios
Rose curculios are reddish-brown weevils with dark snots. They are only about 1/4 in. long, but they can cause a lot of damage. Even the small, white larvae feed on damage
Symptoms of Rose Curculio Damage on Roses
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.
.
Controls
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 may have eggs inside them. And always dispose of any debris throughout and at the end of the season.
If you do have a severe problem with them, any broad spectrum insecticide should work.
Thrips on Roses
Rose and pear slugs are two different insects and neither is a true slug. They are the lavae of sawflies, small flying insects. They look like slugs because they secrete a slimy substance that covers their bodies. Rose sawflies are yellowish-green and can get as large as 3/4 in. Pear slugs are a reflective greenish-black and a little smaller, at about ½ in. Although roses are not the preferred food of pear slugs, they will feed on a variety of plants.
There are 3 species of rose slugs to be aware of. The European rose slug (Endelomyia aethiops) only produces 1 generation per year. The curled rose slug sawfly (Allantus cinctus), which curls up when not eating, usually produces 2 generations per year and the bristly rose slug sawfly (Cladius difformis) is covered in hair-like bristles and has the ability to up to 6 generations per year.
Symptoms of Rose Slug Damage
Rose slugs feed on the leaves of rose bushes. They remove just the soft tissue, leaving the leaves looking translucent between the veins.
Controls
A small infestation isn't worth worrying about. The damage is mainly cosmetic. However a large population can severely weaken the plant.
Start scouting for the lavae in mid-spring. At this stage they can be hosed off with a good blast of water. Neem and insecticidal soap are also effective, but try and hold off on any insecticides, though, because sawfly slugs have lots of natural predators including: birds, parasitic wasps, and predatory beetles.
Thrips are a common insect pest. Flower thrips are slender and brown, with yellow wings that feed on flower buds. Chilli thrips, which are becoming an increasing problem in home gardens, are pale with dark wings. They feed on all parts of the plant.
Symptoms of Thrip Damage to Roses
Flower thrips will cause buds to distort. If the buds do open, you may also see brown streaks on the individual petals.
Chilli thrips cause damage to the buds, leaving them dried out and brittle. They also feed on the leaves, causing them to curl upwards or distort.
Controls
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.
There are natural predators such as pirate bugs and other beneficial insects, that can help in the battle. If you see your thrips are being preyed upon, do not use an insecticide or you will kill the predators, too.
A systemic insecticide is the best control, if used as a foliar spray. There are several available and you should look for one that is specifically labeled for use on thrips. According to Texas A&M recommendations, those containing spinosad (pronounced spin-OH-sid) have shown the least environmental impact.
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