Knock Out Roses: Diseases and Prevention
Knock Out roses are known for being disease resistant, but they can still develop some of the same diseases that affect other roses. Here’s what you need to know about the most common Knock Out rose diseases and how to prevent and treat them.
Common Knock Out Rose Diseases
The five most common diseases of Knock Out roses are:
- Black Spot Fungus: Causes black spots on leaves, which can eventually turn yellow and drop off.
- Botrytis Blight (Gray Mold): Causes gray or brown mold on flowers, buds, and stems.
- Powdery Mildew: Causes a white powdery growth on leaves and stems.
- Rust: Causes orange or yellow spots on leaves, which can eventually turn brown and drop off.
- Stem Canker: Causes cankers (dead areas) on stems, which can weaken the plant and lead to dieback.
Rose Rosette Disease (RRD)
RRD is a serious virus that can affect Knock Out roses. Symptoms include:
- Reddish new growth that remains red instead of turning green
- Abundance of short shoots near the tops of canes (“witches’ broom”)
- Distorted, underdeveloped leaves
- Thicker or spiraling canes
- Unusual number of thorns
- Deformed or mottled blooms
Preventing Knock Out Rose Diseases
The best way to prevent diseases in Knock Out roses is to keep them healthy and vigorous. This means:
- Watering them regularly, especially during hot, dry weather.
- Fertilizing them regularly with a balanced fertilizer.
- Pruning them to remove dead or diseased canes and improve air circulation.
- Mulching around them to retain moisture and suppress weeds.
- Inspecting them regularly for signs of disease or pests.
Treating Knock Out Rose Diseases
If you do find signs of disease on your Knock Out roses, there are a few things you can do to treat them:
- Black Spot Fungus: Apply a fungicide containing chlorothalonil or mancozeb.
- Botrytis Blight (Gray Mold): Remove infected plant parts and apply a fungicide containing thiophanate-methyl or iprodione.
- Powdery Mildew: Apply a fungicide containing sulfur or neem oil.
- Rust: Apply a fungicide containing propiconazole or triadimefon.
- Stem Canker: Prune out infected canes and apply a fungicide containing thiophanate-methyl or iprodione.
RRD: There is no cure for RRD. Once a rose bush is infected, it should be dug up and disposed of.
Using Pesticides and Herbicides Safely
If you need to use pesticides or herbicides on your Knock Out roses, be sure to follow the directions on the label carefully. Wear protective clothing and avoid spraying on windy days.
Organic Methods for Controlling Diseases
There are a number of organic methods you can use to control diseases in Knock Out roses, including:
- Companion planting: Planting certain plants near your roses can help to deter pests and diseases. For example, planting garlic or onions near roses can help to repel aphids and spider mites.
- Integrated pest management (IPM): IPM is a holistic approach to pest and disease control that emphasizes using a variety of methods, including cultural practices, biological controls, and pesticides, in a way that minimizes environmental impact.
By following these tips, you can help to keep your Knock Out roses healthy and disease-free.
