Getting rid of fungus gnats in the household

I have little black bugs flying around in my house. I am sure they are coming from my houseplants. Would you please tell me what would be a good product to spray on my plants to prevent this? Do you think they would be coming from my violets or my other plants?

— Barbara

Sounds like what you have is an annoying little insect called a fungus gnat. These little devils are small charcoal gray to black gnats. They are pretty much just a problem on houseplants, especially during the winter. The adult gnats do not feed on or damage plants, but they are extremely annoying I think they enjoy hovering two inches in front of your nose!

The larva of this insect lives in the soil, generally feeding on the harmless fungus that grows in dead organic matter. Very rarely they can build up in great enough numbers to cause some root damage.

One thing fungus gnats prefer is moist soil. A problem with fungus gnats usually indicates that the soil is being kept a bit too wet. Allowing the soil to dry a little more before watering again usually won’t eliminate the problem, but it often can cut it down to acceptable levels.

There are several ways to get rid of them. Probably the most popular is to treat the soil with a form of B.T. (the bacterium bacillus thuringiensis) that targets only fungus gnats. It gives pretty good control and is nontoxic. The product I have that contains it is called Mosquito Bits.

Applying a drench to the soil with a diluted solution of Permethrin or Malathion will give more immediate results. Water the plant well the day before drenching it. With Malathion, the drenching should be done outdoors because Malathion is pretty smelly (it’s not that hazardous, it just stinks). Let your plants sit outside for a day or two to air out, being careful to protect them from temperatures below 40 degrees. The drench should be repeated once or twice more at 10-day intervals.

When is the proper time to trim a fairly large limb from a globe willow?

— Dara

I think you can do this just about any time you want except for September and October (pruning then can stimulate succulent new growth at a time when you don’t want the tree to be growing. You want it to be going dormant).

I like to do most of my pruning on deciduous plants (those that lose their leaves over the winter) during the dormant season. The advantage is that I can more clearly see the branching structure of the plant without all those pesky leaves in the way and can make better decisions as to what to cut and how much to cut.

There’s really nothing wrong with doing it the middle of summer, and I’ve done that, it’s just that if I can plan ahead, I like to see exactly what I’m doing because it’s hard to put a branch back on the tree once you’ve cut it off.

Some people like to wait until early in the spring to do any pruning, and there is a little advantage to that. Pruning now will leave a big open wound that can dry out over the winter. This sometimes results in some minor dieback, especially in smaller twigs.

Pruning in mid- to late March leaves the wound open for a shorter period of time since the tree is about to break dormancy and will start healing the wound more quickly.

Frankly, I think that the advantage is slight enough not to worry about much.

Dennis Hill is the nursery manager at Bookcliff Gardens, Send questions to Bookcliff Gardens, 755 26 Road, Grand Junction 81506; or email .(JavaScript must be enabled to view this email address).


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