Air layering is an easy way to propagate an azalea branch

A: I would wager that you had gardenia whiteflies in abundance on your shrub last year. The black leaves are covered with a film of sooty mold, which grows on the undigested sap excreted by the sucking insects last summer. The dark film hinders sunshine from penetrating to the gardenia’s leaf surface. Your situation is not an emergency, but if you let it continue, it will weaken your gardenia. The easiest way to control whiteflies is by applying a systemic insecticide, like imidacloprid, after the blooms fall. If you want to kill the insects immediately, use any garden insecticide, including insecticidal soap and neem. Aim the spray at the underside of leaves since that’s where the insects live. The black film on the leaves will gradually disappear in a month or so.

Q: I have a foxtail palm on which the fronds are not opening. I had a local service tell me it was a boron deficiency and they fertilized it but it hasn’t helped at all. Jeff Feig, Sarasota, Florida

A: A typical symptom of boron deficiency in palms is the foliage on new fronds sticks together so the frond does not open. It looks like a stick is emerging from the trunk. Assuming a boron deficiency is what you have, it is extremely important to know what your landscaper applied. There is a fine line between too little and too much. Excess boron will kill the palm if you follow one application with another. Find out exactly what the story is, and if you need more boron, apply a product named Solubor carefully according to label directions.

Email Walter at . Listen to his occasional garden comments on “Green and Growing with Ashley Frasca” Saturday mornings on 95.5 WSB. Visit his website, , or join his Facebook Page at , for his latest tips.