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Ask the Experts – April 2017

By Kelly Young

Queen’s wreath

We live in a townhome with a south-facing patio. Can you recommend a vine that will provide shade in summer and allow the sun to warm us in winter—and won’t damage the stucco on our home?

Queen’s wreath (Antigonon leptopus) is a fast-growing vine with heart-shaped leaves that blooms in late summer and early fall in shades of pink, red or white. Plant it in full sun and give it a trellis for support, since it can’t grip walls—and won’t ruin your stucco—like some other vines will. Native to Mexico, queen’s wreath is semitropical, meaning it loves the heat of summer but is also frost-sensitive. Its foliage will generally die during the winter, even in the low desert. Cut this vigorous vine back in December, and the new growth will start when temperatures warm up in the early spring. This beauty will give you the shady coverage you want during hot weather and, with a little work, will allow you to bask in the welcome winter sun.

I just noticed that my snapdragons are covered in brownish-red spots. When I touch the leaves, my fingers become stained with the same color. What could be causing this?

It sounds like your snapdragons are infected with a rust disease, which are fungal diseases that cause blisterlike spots on leaves and stems of a wide variety of plants. Although not very common in Arizona, snapdragons are susceptible to a rust disease caused by the fungus Puccinia antirrhini. Unfortunately, once your plants are infected, the only treatment is to pull them out and dispose of them. You may want to avoid using snapdragons in that bed for a year or two, to starve the fungus out. Or, chat with your nursery professionals to find a snapdragon variety that is resistant to rust disease.

I have a small greenhouse in Tucson in which I grow tomatoes. Lately, whiteflies have been a problem. I’ve seen recipes online for homemade organic insect sprays. Can I really use regular dish soap to kill these troublesome pests?

According to Peter Warren, entomologist and extension agent at the University of Arizona Cooperative Extension in Pima County, “Soaps are made of fatty acids. Some types of fatty acids are toxic to insects, while others are toxic to plants. It’s important to make sure that you don’t use something that is harmful to your plants.” I recommend that you purchase an insecticidal soap that is specifically formulated to kill insects and is also safe to use on plants.


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