Thursday, September 18, 2008
Sampling English boxwoods
John Arbogast
Landscape consultant John Arbogast answers your questions every Thursday. Send questions about your lawn, garden, plants, or insects to:
Dear John
5102 Greenfield St. SW
Roanoke, Va. 24018
Or send an e-mail. Answers will be given only in this column. Please don't send pictures or samples.
Recent columns
Q: I read a column of yours and wondered if my boxwoods might have English Boxwood Decline (EDB). I hope not. Should I first take two samples, as you suggest, and, if so, how should they be taken and collected? Plastic bags, or some other method? My yard has 60 boxwoods and they have done well for 10 years. All of a sudden, they are discoloring, straw-colored, and it is slowly affecting 30-50 percent of them, and I hope it is not going to spread to the entire landscape.
A: English Boxwood Decline is impossible to diagnose just by looking at the bushes. The symptoms that you described could be the result of a root problem, but the cause could be the pathogen that causes EBD, the microscopic ell worms called nematodes, and/or extended drought. English boxwoods have deep root systems, but the depth and the density of each boxwood root system are probably different. There also could be a sucking pest on some leaves causing browning, like mites, if the discoloration showed up after cool nights started, and there also could be some sort of environmental problem going on there.
So, with all these confusing possibilities, the only way to rule out EBD and/or nematodes in the soil or affected branches and roots -- both vectors that are impossible to kill in and on living plants -- is to take samples to your local Extension office to be sent immediately to your state’s Land Grant University plant disease laboratory. Correct diagnosis will tell you whether or not there is anything you can do, what is the likelihood of the problem spreading to your entire landscape, and whether you can replace brown English Boxwoods with new transplants next spring.
Take in your two fresh samples early in the work week so they don’t spend their weekend in a hot mail room. Place the samples in separate plastic bags, each twist-tied shut after completing. Collect sample No. 1 by using sharp hand pruners disinfected with a solution of alcohol and water. Cut a section of one of the recently browned branches so that you will have a 10-inch-long woody branch piece that includes some green leaves and brown leaves.
Sample No. 2 might require a slightly bigger plastic bag. Use a round-pointed shovel to dig a pencil-sized root section with a pint size or slightly larger chunk of soil still clinging to the roots from under one of the English Boxwood recently discolored leafy branches. Put this into the plastic bag but do not add any water to it, which could make the sample turn to mush by the time the laboratory opens it. The soil clinging to the boxwood roots can be used by the nematode laboratory that works with your state’s Land Grant University plant disease laboratory. Provide as much information about the problem and the boxwoods on the plant clinic form from your local Extension office. Complete forms required to go with the bags.
Unless your boxwoods live in one of the states that has received ample water this year or your landscape has a built-in irrigation system, the severe drought is the likely guess from me. A helpful solution to assist the boxwoods and slow down the spread of browning is to soak the plants, but only once per dry week.
Two very useful jobs at this time are to prune out only dead parts now plus remove fallen leaves and any debris from inside boxwoods.
Q: I am a home-school mom and I would like to know of the largest tree in Roanoke. I would like to take my kids on an outing to see it. Would you happen to know where it is?
A: Sorry, but I have not heard anything about an active Big Tree Search program in Roanoke, which was part of an organized program in the state since I took early retirement in 2002. I nominated many years ago a winning huge oak that is still living on the grounds of the Fishburn home, now the Roanoke Parks and Recreation center on 13th Street in Southwest Roanoke. I’ve also heard about some big trees on Mill Mountain near the parks and rec's Discovery Center. Call the Roanoke Valley Extension Office at 540-772-7524 for information about big trees in Roanoke.
