Anthracnose is another one of those annoying fungal diseases that can turn up on roses, especially when the weather is cool, damp, or humid. It is not always as commonly talked about as blackspot or rust, but it can still cause plenty of damage if it gets established.
The first signs are usually dark marks or spots on the leaves. These may be brown, black, purple, or grayish, and some can develop pale or papery centers as the damaged tissue dries out. In some cases, the spots may join together, leaving larger blotches or ragged-looking patches on the foliage.
How Anthracnose Spreads
Like many rose diseases, anthracnose is helped along by moisture. Spores can spread when water splashes from infected leaves onto healthy ones, especially if the foliage stays wet for a long time.
This is why I try not to water over the top of roses if I can avoid it. If the leaves do get wet, it is much better for that to happen early in the day, so they have time to dry before nightfall.
Cooler, damp weather can make the problem worse, and roses with poor air movement around them are usually more likely to suffer.
Worse Than Blackspot?
Anthracnose can look a bit like blackspot at first glance, but I tend to think of it as the nastier relative. Blackspot is ugly and can certainly weaken a rose, but anthracnose may also affect the quality of the growth and flowers.
A light infection may only mark a few leaves, but a worse case can cause foliage to yellow, dry, or fall early. If the plant keeps losing leaves, it has less energy to put into healthy growth and blooming.
Prevention
Prevention is much easier than trying to fix a bad infection later.
Remove infected leaves as soon as you notice them, and pick up fallen leaves from around the base of the rose. I would not compost diseased foliage, because it is better not to risk spreading the problem back through the garden.
Good air movement also helps. Try to avoid overcrowding roses, prune out congested growth where needed, and water at the base of the plant rather than spraying the leaves.
Treatment
If anthracnose is only mild, removing affected leaves and improving the growing conditions may be enough to keep it under control.
For a more persistent problem, you can treat it in much the same way as blackspot. A suitable rose fungicide may help protect new growth, but it is important to remember that fungicides are usually a control measure, not a magic cure for leaves that are already badly infected.
I have also used a milk spray as a gentler home treatment for fungal problems on roses. A common mix is one part milk to two parts water, sprayed over the foliage in the morning so the leaves have time to dry. It is not a guaranteed cure, but it may help reduce fungal activity when used regularly, especially before the problem becomes severe.
The main thing is to keep checking the plant. Remove diseased leaves, keep the area clean, and try to stop the disease building up from season to season.
Related Pages
