Q: I have found evidence of Asian ambrosia beetles on my crape myrtle. I have read that I should destroy the tree. — Shawn O’Banion, email
A: The damage done by this insect depends on how many of the beetles bored holes into your crape myrtle and how much fungus they deposited. You won’t know with any certainty until you notice wilting leaves. If you saw only a few “toothpicks,” the tree might survive the invasion. Wait until mid-June to decide what to do. Even if you have to cut off the top of the tree, it will likely resprout at the bottom. One of the strong shoots can be trained to become a new central trunk.
Q: French marigolds have been shown to control root-knot nematodes in small areas. Marigold root extract is available from China. Have any studies been done using it for nematode control? — Charles Bowen, Sharpsburg
A: In my view, the research is inconclusive. Yes, marigold roots produce a chemical that can aid in the reduction of root-knot nematodes and other organisms, such as fungi, bacteria, insects and some viruses. African and French marigolds are the most commonly used species. But I could not find any research that proves that root extracts are definitively effective. A better method of controlling nematodes is to plant a block of marigolds two months before planting nematode-susceptible vegetables like beans, okra and tomatoes. Till the marigolds into the soil before planting. Research is clearer that living marigolds planted en masse can suppress nematodes.
Q: Our deck is in the shade of a big tulip tree. This past week this tree as been raining down large splats of something all over the deck. We think it might be scale insects that suck the juice from tree with the resulting nasty shower. — Linda Bishop, email
A: Your diagnosis could be correct! Scale insects do suck sap from plants and they do exude copious amounts of honeydew. It also could be caused by a big population of aphids. Systemic insecticides will control either insect. Look for products that contain either imidacloprid or acetamiprid.
Q: According to the Atlanta Rose Society, I should fertilize regularly with a “balanced” fertilizer like 10-10-10 or 16-4-8. Intuitively, the former is “balanced” with equal percentages (10-10-10), whereas the latter is not. Am I misunderstanding something? — Dan Cowles, Cumming
A: Although semantically it seems that 10-10-10 is a “balanced” fertilizer, in truth it is unbalanced, because it contains much more phosphorus than plants need. Imagine if you were fed a pound of protein, a pound of carbohydrates and a pound of vitamins and minerals each day. You’d get a “balanced” diet but it would be wildly misproportioned for human health. In truth, most plants thrive with fertilizers that contain a 4-1-2 ratio of nitrogen, phosphorus and potassium. 16-4-8 is an example. This is a fertilizer ratio that’s balanced to most plants’ needs. Lawn fertilizers that contain a high percentage of nitrogen, such as 26-0-4, are balanced to the needs of grass, which demands more nitrogen than flowers or shrubs. I admit that I’m guilty of recommending 10-10-10. My excuse is that it is readily available at garden centers and 16-4-8 is not. If you’re looking for a general purpose fertilizer, try to find a product that semi/sorta has a 4-1-2 ratio.
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