Rose Pests and Diseases
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.
We look at the most common rose pests and diseases that can afflict your beautiful roses, along with symptoms and control options.
One particularly common rose pest is aphids. Aphids are tiny, pear-shaped, sucking insects that love to feed on new growth. There are several species and they may be yellow, green, or blackish. They can be referred to as greenfly or blackfly, but they are not actually flies.
Although a single aphid is not a big threat, aphid colonies can grow shockingly quickly and you will easily be able to see them on your roses. As they feed, the plant will become 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 mould growing on the honeydew
- Clusters of aphids
- Ants crawling on the plants and feeding on the honeydew
Since aphids 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.
Another great option is the Yates Rose Gun, it works well on aphids, thrips, caterpillars, whitefly and mites, simply spray liberally, including the underside of leaves. A second application may be required.
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 resistance 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. 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
Black spot starts as small black spots on the leaves that enlarge and become ringed with yellow, eventually turning the whole leaf yellow. Once yellow, the leaves begin falling from the plant and a severely infected plant will totally defoliate.
Start with a thorough Autumn 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, spray with neem oil.
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
Young leaves will begin to pucker or crinkle. Then you will see mould forming on the leaves and stems followed by a thin white coating that will begin to spread.
If you live in an area where powdery mildew often occurs, you can use a homemade baking soda spray as a preventative measure. It does not work well after powdery mildew is present.
Once your plants are showing symptoms, the easiest control is this homemade milk spray (1 part milk to 2-3 parts water). It is surprisingly effective and can even be used on edible plants, like cucumbers and squash.
Symptoms of Thrip Damage
Thrips will cause buds to distort. If the buds do open, you may also see brown streaks on the individual petals. They also feed on the leaves, causing them to curl upwards or distort.
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 Autumn clean-up is essential.
If you start to see buds distorting, remove any buds showing symptoms.
There are natural predators 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 such as Yates Rose Spray.
A Rust infection is easy to spot.
Symptoms of Rust Damage
Small orange pustules spots form on the undersides of the leaves. This fungus can also cause defoliation. Rust is most prevalent when nights are cool.
Treatment of Rust is similar to treatment of Black Spot. Good sanitation and a preventative dormant spray after pruning. Once infected, remove all infected leaves and try Neem oil for control.
This term applies to a small insect that currently has over 8000 known species. The adults are generally immobile and permanently attached to the plant that they are sucking the sap from.
Symptoms of Scale Damage
You will notice white crusted stems. Scale found on roses includes cottony cushion scale, red scale and rose scale. Scale feeding on a plant can affect the vigour and also produce honeydew. Honeydew is a sweet waste product which can attract insects like ants and wasps.
Oil sprays kill all stages of scale insects and have a low impact on other beneficial insects that may be present. Lime Sulphur is a useful tool in reducing the scale population. Spray on to bare stems after winter pruning. It is also advised that you spray the rose bushes with a fine pressure hose after treatment to remove the scale that may still be attached to the plant. The best treatment is prevention, scale is found on weak roses.
Related to spiders, mites are pinkish-red in colour and cluster on the underside of leaves.
Symptoms of Mite Damage
Preferring the underside of leaves, spider mites can often be difficult to see. Evidence of their presence is silvering of leaves where the spider mites have destroyed individual leaf cells. Also look out for fine webs or eggs on the underside of leaves.
Luckily these little mites dislike water. A strong spray of water on the top and undersides of leaves is usually all it takes to move these critters along. Neem oil is another option that will help to eradicate larger infestations, make sure you spray multiple times to ensure that you have treated the eggs too.