Calgary Rose Society - Rose Diseases and Pests

You've got some beautiful roses. They're blooming, they're gorgeous. Problem is, when you get close to them, they don't look quite as wonderful. They've got bugs or some weird colour on the leaves or holes in the leaves. What's going on?

Growing roses is not without its disease and pest problems. We've tried to cover all possibilities here, complete with photos, but if you've got something we haven't listed, please email us with a good description and/or a photo and we can try to help.

Please remember that we grow roses in Calgary, in the chinook belt and in Zone 3. If you grow roses outside of these conditions, we recommend that you contact an organization that grows roses where you do. They may be better able to recognize problems we don't encounter here.

Click on the statement that matches your rose problem for a description, photo and recommended cures.

• My rose has a white powdery coating on the leaves.
• There are black spots on the leaves of my rose.
• There are small red fuzzy spots on my rose leaves.
• There are small white patches and/or irregularly shaped holes in the leaves of the rose.
• There are large round, regular holes in the rose leaves.
• Some of the rose buds/blooms look like they have been partially eaten.
• There are small, fluorescent green bugs on my rose buds.

One last thing. Deer (and rabbits) love roses, especially the new green shoots. And there's nothing you can do other than to build a tall fence. And if your problem isn't addressed here, please email us your question.

My rose has a white powdery coating on the leaves.

Your rose has powdery mildew. It can also cause affected leaves to appear crinkly and wilted. It most commonly results from water being left on the leaves.

How to avoid it? Water in the mornings so that the leaves have time to dry before nightfall. Try not to get water on the leaves. To prevent spread, you can use a chemical spray, or try 1 part skim milk in 3 parts water.

There are black spots on the leaves of my rose.

Your rose has a fungus called black spot. The spores can be airborne or can be passed from rose to rose on garden tools or gardener's hands.

To prevent its spread, remove the infected leaves and throw them away. Fallen leaves should also be removed and tossed out. If you have a severe case of blackspot, it may be advisable to prune away the infected canes. Wash your tools/hands before moving on to another rose.

Chemical sprays are available, or you could try a spraying mixture of 1 part skim milk and 3 parts water as in the case of powdery

There are small red fuzzy spots on my rose leaves.

Your rose has a rose disease called rust. This is one we don't have a good photo of, but it looks exactly like fuzzy patches of bright orange rust on the underside of leaves. As the orange spots grow, they change colour to brown then black.

If detected early (in the orange-black leaf infestation stage), rust can be eradicated. Remove the infected leaves and destroy them. Keep an eye out for another breakout. If the disease has progressed to the stage of cane infestation, there is really nothing you can do, remove the infected plant and destroy it.

There are small white patches and/or irregularly shaped holes in the rose leaves.

Your rose has a pest called a rose slug. The rose slug is a sawfly that belongs to the hymenoptera family. The larvae feed on the underside of the rose leaves. When the larvae are small they usually "windowpane" the leaves by eating only the bottom layers of leaf tissue. As they get bigger they eat right through the leaf.

Chemical treatments sprayed on the underside of the leaves, where the rose slugs dine, can help. Or try the pick-and-squish method or you could use a high pressure water spray on the underside of the leaves. Repeat as necessary (and more than once will be).

There are large round, regular holes in the rose leaves.

Leaf cutter bees are dining on your roses. The holes they produce look like bite marks and are more regular, rounded and larger than the holes caused by rose slugs.

Unfortunately, there is nothing you can do to get rid of these bees. They don't live on the roses, they merely visit for the fly-through wallpaper store. You'll have to grin and bear it (and have some pretty ugly looking foliage). On the bright side, the bees will not kill the rose.

Some of the rose buds/blooms look like they have been partially eaten.

Your roses most likely have a bug called thrips or rose curculios. Thrips are a small fly that love to nibble around the edges of petals and into rose buds. The petal edges will look irregular and brown and it will look like something has taken a bite out of your buds. Curculios have a long proboscis that they use to bore into buds. They are reddish and about 6 mm (1/4 in.) long.

Usually with both of these, you will notice the damage before you notice the bugs. Control is difficult - you can try sprays but you need to get it into the buds where the damage occurs. Your best bet is to remove and destroy infected buds and blooms, and if you want, use a chemical spray. Keep in mind that a chemical spray that attacks the thrips or curculios will also attack their predators. Curculios are fairly slow moving and can sometimes be caught and squished. Their defense is to roll into a ball and drop to the ground. If you are attempting to catch them, hold your hand or a container underneath to catch them if they drop.

There are small, fluorescent green bugs on my rose buds. Lots of them!

These are aphids. They feed on the sap of roses (buds and stems) and particularly like the new growth. To get rid of an aphid infestation, you could purchase insecticide from any garden centre. Spray according to directions. You will need to re-spray every time you see more aphids. It is much more environmentally friendly to try the mush-and-squish method or a strong spray of water to wash them off your roses. Watch for re-infestation.

You can also try encouraging the predators of aphids to live in your garden. The best known of these is the common lady beetle (lady bug). Several species of these live in Alberta, and they can also be purchased at some garden centres. Bot the lady bugs and their black and orange larva are voracious predators of aphids, as are the larva of green lacewings and hover flies.