Noisy Boxwood? Little Flying Hotdogs are Probably to Blame
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Q. While working outside this past weekend, I noticed a crackling or popping noise coming from my boxwoods. I inspected the plants closely, but didn't find any insect infestations or bee nests. I don't have any prior experience caring for boxwoods, but assume this "crackling" is out of the ordinary.
- ---Will in Califon, NJ
- ---Kevin in Marshall VA
- ---Jamee in Parkesburg, PA
Seriously, when the first 'noisy boxwood' email came in, I did wonder a bit about the mental state of the sender, as I had never heard of this phenomena. But then MANY other emails rapidly followed, several of which even identified the potential cause for me (which was a huge help—thank you!). I thought that after 25 years in the business I had heard it all, but 'noisy boxwood' proved me wrong.
Anyway, although the common name of this loud pest is the Boxwood Leaf Miner, Lynn R. Batdorf, Curator of the National Boxwood Collection at the U.S. National Arboretum in Washington, DC, explains that the insect in question is actually a type of gall midge that stays in one spot once it settles inside a boxwood leaf. Most true leaf miners—like the ones that attack spinach and columbine—make visible roadmap-like trails as they travel around inside the leaf. (Mr. Batdorf also stresses that the word 'boxwoods' does not exist; its 'boxwood' in both the singular and plural form.)
Although these pests actively (and noisily) feed for only a brief period of time, our expert explains that they can be a serious problem, sometimes doing enough damage to cause the eventual death of the plant. He adds that they only infest American boxwood and ignore the English boxwood, which contain alkaloids deadly to the insects. This is zero help to our noise-afflicted listeners, but excellent information for folks thinking about installing these highly popular evergreen shrubs in the future; if you choose a (more expensive) English boxwood, your shrubs will remain silent.
The noisy little fiends that are currently inside infested boxwood will soon emerge as adult flies. Many sources describe them as looking like orange mosquitoes, but Mr. Batdorf adds that they are also very distinctively shaped: "like little orange hot dogs", and tend to be pretty obvious as they hover around the boxwood, mating and getting ready to begin raising a new generation of noisy brats. In the mid-Atlantic area, this emergence typically occurs towards the end of April, beginning of May (often coinciding with the blooming of local weigela).
Destroying as many of these adults as possible can dramatically reduce the size of the next generation. I suggested doing so with an organic insecticide like neem or spinosad—both of which are very safe for people and the environment. But Mr. Batdorf trumped me by explaining that sharp sprays of plain water can prove just as deadly to the apparently fragile little flying hot dogs.
Mr. Batdorf agrees that the excessive growth caused by chemical fertilizers can attract pests like this to plants, and adds that boxwood is also often inadvertently weakened by homeowners who mistakenly acidify its soil. "Boxwood thrives in a soil pH of 6.8 to 7.5", he explains; that neutral-to-slightly-alkaline range is the exact opposite of the kind of soil pH that shrubs like azaleas and rhododendrons prefer. So some fertilizing/acidifying products that say they're 'for all evergreens' actually may help kill this one.
Mr. Batdorf suggests a dusting of dolomitic lime to raise the pH when soils are acidic. (I mentioned my preference for wood ash as a pH raiser, but he abstained an opinion as he was unfamiliar with its use.) He does like my idea of a compost mulch for gentle nutrition, but adds to use "only an inch; the shallow roots should not be mulched any deeper than that."
He adds that hungry, carnivorous birds like chickadees, wrens and the nuthatch are often attracted to the noise that emanates from heavily infested plants when the weather warms in the Spring, but that the birds can do a lot of damage to the plant as they tear apart the leaves to feast on the larvae. I was previously going to suggest attracting winged warriors to the area for such a feast, but now I'm thinking that maybe it's better to just care for the plants properly and knock the adults down as they emerge in the Spring.
Just don't give up on boxwood to avoid the problem; you would then be plagued by evil spirits! Mr. Batdorf explains that the tradition of ringing a home with boxwood goes back to Russian cultures of the 13th Century, when boxwood's poisonous alkaloids and the extreme density of its branches (it's one of the few woods that sinks when placed in water) identified it as an excellent choice for keeping evil spirits away from a home.