Thursday, March 10, 2005

How to kill moles

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.

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Q: How can I rid my front yard of a colony of moles that have taken up residency there? They started modestly in the fall and have now made hills and tunnels everywhere.

A: Try any of the following, equally good methods:

Hire a wildlife management company. Let them worry about the required state permits when wildlife is caught alive and moved and about the liability if accidents occur with traps. If mole control in Virginia involves strong fumigants or toxicants, the user/purchaser must be a certified pesticide applicator. These chemicals for mole control are legally classified as "Restricted Use Only."

Try the new soil drench mole repellent available to homeowners on lawn areas that moles are tunneling under. This repellent contains castor oil or ricinus oils.

If moles are to be kept out of a limited area, such as a flowerbed or small garden, install an "L" barrier on the edge of the area to physically keep moles from tunneling through. This should extend about 10 inches deep into the soil and then have a horizontal part, which is the bottom of the "L," extending OUT several inches. The vertical part of the "L" should protrude about five inches above the surface.

Try trapping moles yourself. In order for trapping to be effective, you must work for several days to identify mole tunnels that are repeatedly used and will thus be good tunnels for trapping. Mole feeding tunnels are used one-time only and thus not considered "active paths" that are used over and over. You're on your own with trapping. I have heard of people stabbing themselves when trying to set the snap mechanism of a mole "kill trap." It is much safer to dig "pit traps" in an active path for moles to drop into. Keep in mind that live-trapped moles might scratch or bite. Also, if you plan to move live captured animals off your property, the necessary permit must first be obtained from the Virginia Department of Game and Inland Fisheries.

Q: The property that we purchased about six years ago has crowded walnut trees adjacent to the road. We have taken down a few of these trees and have been unsuccessful in planting other types of trees there. We have learned that walnut trees produce some kind of toxin in the soil. How can we neutralize this and what types of trees might have a better chance of growing among walnut trees?

A: Black walnut trees produce the persistent toxin called juglones, chiefly from their roots. Plants known to be affected are certain vegetables including tomatoes and potatoes plus landscape ornamentals usually in the acid-loving category, and some annual and perennial flowers.

I don’t know of any shade trees that are susceptible to this toxin. There is nothing that can be used to neutralize juglones remaining in black walnut soil. This toxin stays in that soil for at least two years following tree removal.

I don’t have a reliable walnut-resistant tree list, but I would suggest waiting those two years after black walnut removal before planting in that soil.

Look at other possible causes of failure of trees that you planted because tree roots should grow fairly deep below the soil with juglones. Post-planting stressful weather as well as too frequent or too little watering can cause new tree failure. Remove the walnut stump and the larger roots left in the location following tree cutting.

Q: How do I get my 8-year-old, sparsely flowering nandina to bloom and produce berries?

A: Large nandinas produce flowers that become berries from young growth, so stimulate this by pruning in early spring. Divide your nandina stalks into thirds scattered throughout what’s already there. Cut one-third only lightly. The second group should be pruned to remove about one-third of their present height. Cut the last third group heavier to remove two-thirds of their height. This process prevents mature nandinas from becoming leggy as well as stimulating flowers.

Q: What is the best time to put down crabgrass preventer? Please give other hints for reducing this lawn weed in my fescue lawn.

A: Apply the first crabgrass preventer of the lawn season when the soil and air are warming up enough to make crabgrass seeds germinate. A good signal of this time is heavy blooming of forsythias. Look on the product label to see if additional future applications are suggested. Some crabgrass preventers loose their strength several weeks after application and require another application in 6 weeks. Short mowing encourages crabgrass, so be sure that your mower is set at 2-1/2 inches or slightly higher for your fescue. Excessive watering either by sprinklers we control or rains that we don’t control can leach preventer down lower than the ½ inch depth where it is needed.

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