Q: I’m trying to identify the insects on my schefflera houseplant. I caught the little flies on sticky yellow traps and I’m trying to figure out what they are, and how to treat my plant to get rid of them. The plant itself appears healthy. – Alice C.
A: For the best approach to controlling these nuisances that flit around houseplants, I asked coworker Janet Knodel, North Dakota State University’s Extension entomologist, to share advice.
Knodel said, “Most of the flies looks like a dark fungus gnat and one looks like a Drosophila fly of unknown species. For integrated pest management, control should focus on the larvae in soil, not the flies. I would try Gnatrol, a natural occurring bacterium in the soil, to kill the larvae with a soil drench. One source of the product is Arbico Organics. The product contains the bacterium Bacillus thuringiensis israeliensis, which preys upon the fungus gnat larvae in the soil.”
Another product that contains this same bacterium is Mosquito Bits, which is available at many local retailers, and is labeled for fungus gnat control. The bacterium kills larvae which turn into adult flies, breaking the fungus gnat lifecycle and eventually neither larvae nor adult flies will be present.
Knodel continues with other control measures, “Other biological insecticides to use for adult flies are insecticidal soap and neem oil. Also, water only when necessary to avoid constantly wet soil, and remove any water that drains into bottom saucers. Fungus gnats are mainly just a nuisance unless populations are high.”
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Q: I have a question about Green Giant Thuja Arborvitae, which is listed in some places as growing 3. feet per year. Would these do well in the sandy soils by Audubon, Minn? I see different answers online. – Luke O.
A: Green Giant Arborvitae belongs to the evergreen species, Thuja plicata, that is not winter-hardy enough for our region. It's a Zone 5 shrub, and North Dakota and Minnesota are in Zones 3 and 4, meaning we're too far north for it to survive. The too-good-to-be-true growth rate of Green Giant might be a bit of marketing hyperbole.
Several types of well-adapted arborvitae that grow well in our region and will provide the screening you seek include Techny Arborvitae and Brandon Pyramidal Arborvitae. Both are commonly found in area garden centers. Arborvitae in our area grow about 12 inches per year.
Q: What is your opinion on thatching versus aeration of lawns, and timing of these? – Pete M.
A: De-thatching, also known as power-raking, is beneficial if the thatch layer is over one-half inch thick. Thatch is the un-decomposed tan-colored layer between grass blades and soil, which can interfere with water and air movement into the soil, if a thick layer builds faster than it decomposes. A certain amount of thatch is healthy, because it conserves moisture, shades grass roots and keeps lawns cool in summer’s heat.
Core aeration, which lifts out little plugs of soil and thatch, is especially helpful in alleviating hard-packed soil. Dethatching and core aeration both open the turf profile for better penetration of air and water.
Both operations are best delayed until the grass is green and actively growing during the last half of May, based on recommendations from North Dakota State University and University of Minnesota. Turf researchers also suggest August as a good month for aeration and power raking.
If you have a gardening or lawn care question, email Don Kinzler, NDSU Extension-Cass County, at firstname.lastname@example.org. Questions with broad appeal may be published, so please include your name, city and state for appropriate advice.