Check rosemary for spider mites

Q: My rosemary has many yellow leaves.Steve Preston, email

A: The first thing I would check for is spider mites. My neighbor's rosemary plant is "eat up with 'em"! Clip off an 8-inch-long branch and slap it onto a piece of white paper. If you see little yellow dots crawling across the white surface, my suspicions are confirmed. Spider mites can partially be controlled by spraying the plant each day with a strong stream of water. You could also use insecticidal soap or horticultural oil on the plant, but this won't be very successful because there are so many leaves to cover. To be honest, I'd fertilize the plant lightly and hope that it can fight off the spider mites with the help of naturally occurring beneficial insects. If your plant is too far gone to save, remove it from your property and plant another rosemary in a different spot.

Q: Our small pond in front of our house has been very low. It developed red algae a month ago. My husband dipped his finger in the water, and there was green algae underneath the red algae. Can we kill the algae? Is it harmful to the fish?Barbara Chapo, Woolsey

A: Algae in a pond is most often caused by high nutrient concentrations. Algae is a plant, so it responds to fertilizer just like your flowers do. First, make sure absolutely no fertilizer from the lawn runs into the pond. Second, use a lawn rake to remove as much algae from the water surface as you possibly can. While algae does not hurt fish per se, if lots of it dies at the same time, it will remove oxygen from the water and the fish will suffocate. There are herbicides registered to use for algae control, but you must be very careful to kill only small areas of algae (or weeds) at a time. I have a guide to managing ponds and controlling weeds at bit.ly/GApondalg.

Q: My 20-year old magnolia suddenly died over the winter; it was totally brown. Just recently, it has sprouted new growth from the trunk. What should I do to encourage it?Susan Powell, Buford

A: Nature sometimes finds a way back from the edge of death! It's possible that last year's drought plus the March freeze killed many leaves on your tree. Magnolias have dormant buds underneath the bark so, with the limbs gone, the tree activated the buds to grow new leaves. There is no way to predict whether the tree will be able to produce enough leaves in time to re-establish its health. If there is no reason to cut the tree down, I would simply leave it alone and see what happens. Do not fertilize; this would stress the weakened tree.

Q: I've had a hard time controlling weeds in my Bermuda lawn this year. Is it possible the above-normal rain has had an effect?Tony DeMaria, Forsyth County

A: It’s very possible that the extra rain has benefited weeds. The definition of a weed is “a plant that out-competes the plant you want.” If you have not fertilized regularly, the Bermuda grass may be unable to dominate the crabgrass as it should. It’s also possible that rainfall has diminished the action of the pre-emergent you applied months ago. It might be a good idea to apply crabgrass preventer once again and make sure your lawn is well-fed.