If you’ve tried to prevent rose problems with the tips in this article, but still ended up with some pests (it happens!), here are the methods I recommend to get rid of pests on roses the organic way.
(Obviously, before spraying anything, read the instructions on the bottle and be sure to suit up appropriately – organic choices are usually safer, but that doesn’t mean you want to get it on your skin or eyes.)
For fungus problems like black spot, rust and powdery mildew:
Sulfur (not lime-sulfur) is an effective way of getting rid of fungus organically during the growing season, and is usually my first choice for a fungicide. I use a sulfur spray every 1-2 weeks at the first sign of a problem. Coat the under and the upper sides of the foliage well.
Sulfur is harmful to beneficial mites, so if you’ve put out beneficial mites nearby, don’t use sulfur. It is safe for honeybees, though!
Jeff Gillman, author of The Truth About Organic Gardening, suggests spraying weekly with a mixture of 1 part milk to 2 parts water to treat fungus problems. Check out this quirky video here in which he mocks some organic fungicides and synthetic fertilizers.
I haven’t tried the milk treatment yet, but he’s a scientific-minded fellow, so I trust that it works. I’m guessing that spraying weekly and covering every surface of the leaves, upper and undersides, are the keys to success with this method.
Serenade, a bio-fungicide, is a new-ish spray that I’m testing in the gardens I maintain this year. Basically it is a type of bacteria (Bacillus subtilis) that attacks the fungi causing problems on your roses. Word around the nursery is that it’s effective if sprayed regularly, once a week.
I like using biologically-based controls like Serenade (where one beastie eats another) because the action is usually so specific that it doesn’t harm good bugs, birds, or us.
Pick the infected leaves off. This is a free and simple way to reduce pest populations, and you can do this in conjunction with any of your sprays.
To get rid of aphids:
Prevention is the best cure, as aphids just love that soft new growth that occurs from over-fertilizing, using synthetic fertilizers, or a plant not getting enough light. If you do end up with a problem, try these fixes:
Insecticidal soap is fairly effective at killing aphids, while being pretty harmless to beneficial bugs. It works by sticking to a bug and smothering it, so once it’s dry it doesn’t really hurt anything. You have to keep up with it to be effective, but it’s a simple cure for a small infestation.
You can also attract beneficial insects that eat aphids, like lacewings and ladybugs, by planting nectar plants like daisies, yarrow, lavender, catmint/ Nepeta, and flowering sages/ Salvias. What rose wouldn’t look great with some lavender or Shasta Daisies planted nearby?
If you’re trying to attract beneficials, be careful not to use broad-spectrum insecticides in your garden, like most synthetics, or the organic Pyrethrum. You’ll kill the good bugs along with the bad.
If you’re going to buy beneficial insects, I’d choose lacewings over ladybugs, since lacewings often arrive in an egg form, meaning you have them for their voracious larval stage AND the adult stage. Ladybugs arrive as flighty grownups and most of them take off as soon as you let them go.
Stop caterpillars from decimating leaves:
Now, before telling you how I kill caterpillars in the garden, I want you to think first about what caterpillars become. If you’re planting things in the garden to attract butterflies, then killing caterpillars may be counter-productive to your goals.
You’ll usually find caterpillars on the undersides of leaves that have been munched, so if you see damage, turn the leaves over and look to see if caterpillars have caused it.
For me, the first step is trying to pick them off. A couple caterpillars won’t kill your plant and aren’t that big of a deal. If you don’t want them on your roses, set them on your neighbor’s patch of weeds or some sturdy perennial that you don’t care too much about.
If you end up with lots of caterpillars all at once, too many to reasonably pick off, there’s a biological spray that works great called BT, Bacillus thuringiensis kurstaki. It’s brewed from a soil-dwelling bacteria and it’s only effective on caterpillars, so it won’t harm beneficial bugs or birds.
BT (sold as Caterpillar Killer by Safer) makes caterpillars stop eating almost immediately, though the caterpillars stay on the plant for about a week, until they die.
Even though caterpillar damage can be dramatic, plants usually recover quickly and I’ve never seen anything actually die from them, so don’t worry too much if they’ve scalped your rosebush – it’ll be back!
Snails and Slugs:
Snails and slugs aren’t usually a pest for roses, but many flowers have problems with them, so go here to learn how to kill snails and slugs organically.