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Homepage / Special Features  / Gardening 101  / Ask the Experts – June 2017

Ask the Experts – June 2017

By Kelly Young

Yerba Mansa

Can you recommend a native plant to put near my pond? I want something low-growing that can handle moist soil.

Yerba mansa (Anemopsis californica), also called lizard tail, is native to wetlands in the southwestern U.S. and used by native people to treat a variety of maladies. This low-growing, creeping perennial produces a lovely flowering stalk with white bracts. You can find yerba mansa in garden centers that sell pond plants, or you might meet a gardener who is willing to share some of theirs. The plant readily self-propagates by runners and will need occasional thinning. To learn more about the medicinal uses of yerba mansa and other native plants of the Southwest, pick up a copy of “Healing With Plants in the American and Mexican West,” by Margarita Artschwager Kay.

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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