A Greener View by Jeff Rugg

Q: Something is eating half of my rose leaves. It leaves a paper-thin layer on the leaf, but it eats the rest. I saw a slug on the leaf, but this doesn't look like slug damage to me.

A: It sounds like your roses have rose slug sawfly larvae. They eat the layers of a leaf and leave the top. You can see through the remaining layer since it's so thin, but many times they eat the leaf and just leave the veins. The adult is a small wasp that hatches from the pupa in the spring to lay eggs on the rose leaves. The female has a saw-like ovipositor that inserts the eggs into the leaf.

The small larvae are covered in a wet slime and look like slugs. They look clear and you can see inside to the rose leaf they are digesting — they are the same color as the leaf and are often hard to see. As they become larger, they look like a caterpillar, but they don't turn into moths or butterflies.

Usually, there are not too many larvae and no control is necessary. If there are many visible on the roses, just take a gloved hand and squish them or hose them off the plants. Slug baits won't work as they are not slugs. Bacillus products won't work either, since they only kill caterpillars of moths and butterflies. Typical insecticides labeled for roses will work, if required.

Q: My day lilies are usually beautiful, but they already have long stripes of yellow and dead areas on the leaves. I looked for insects, but I didn't see any. I don't think I over-fertilized, but I don't know what else to look for.

A: The most likely problem is a simple fungus disease called day lily leaf streak. First, you might see small oval dead or dying spots. Next, the central veins of the leaf turn yellow and eventually the whole leaf dies. The disease shows up in areas that stay wet during the cool seasons. Sometimes, the weather keeps the plant wet or the plant could be near an irrigation system.

There are some varieties of day lily that are resistant. Fungicides need to be used before the problem develops to prevent it. Remove all the infected leaves and destroy them. Tools, gloves and other things that come in contact with the infected leaf can spread the disease.

Another day lily problem is called day lily rust. It also forms dead and dying streaks on the leaves, but they are longer streaks and not oval spots. This disease releases orange, dusty fungal spores on the bottom of the leaf. Anything brushing up against them will turn orange. First found in the United States in 2000, this disease can't survive Northern winters, so it's only found in the Southern states.

Q: My white variegated hostas suddenly have holes all over them. The other hostas next to them don't have holes, so this thing prefers the white ones. I haven't seen anything on the leaves and there were no yellow or dead spots first, just holes.

A: This answer gets the real slugs. They usually feed at night, unless the weather is rainy in the daytime. They need soil moisture to move around. Use a flashlight and look for them at night. They leave a wet slimy trail — it reflects the light so you can track them down. Try placing some wet newspapers or small boards on the ground in the hosta bed. In the morning, lift them up and look for the slugs. If you find them, just stomp on them or drop them into a jar of soapy water.

Insecticides won't work on slugs as they are a mollusk like a clam or snail. Baits work, as does cheap beer. Don't use the beer if you have pets that can get to it. Even wild animals like raccoons will drink the beer, so if you don't enjoy destroying them by hand, the bait traps will work.

Slugs like a lot of different kinds of plants, so you may need to place traps or baits in other locations in your flowerbeds.

E-mail questions to Jeff Rugg, University of Illinois Extension at jrugg@illinois.edu. To find out more about Jeff Rugg and read features by other Creators Syndicate writers and cartoonists, visit the Creators Syndicate website at www.creators.com.

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