NEWS for North Dakotans
Agriculture Communication, North Dakota State University
7 Morrill Hall, Fargo, ND 58105-5665

June 10, 1999

Ron Smith, Extension Horticulturist
North Dakota State University

Q: Last fall we noticed numerous bugs invading our linden tree. At first glance, the bugs resembled box elder bugs, but we don't think they were. The tree has many holes bored into the bark but looks healthy this spring. Will this kill the tree? Will the bugs spread to other trees? What can we do to get rid of the bugs? (Enderlin, N.D., e-mail)

A: The insects you saw could be any number of characters, as the lindens are not subject to severe attack from any particular species in our region. With the numerous ashes that we have planted, it could have been the redheaded ash borer, the apple tree borer, or it could have been a social species of insect that caused no direct damage to your tree. The holes could have been a coincidence of activity from the redheaded sapsucker. If the holes appear as a ring around the tree, that is the likely culprit.

You say the tree appears healthy now, and if that is the case, I would leave well enough alone, and not spray anything unless positive identification can be made of the problem. The best protection against borers is to maintain a healthy tree—most especially keeping it from becoming drought stressed. The stressed tree appears to be a "flag" to attract the borers in the area, making a bad situation worse.

Q: I would like to know about a tree, which has no name as far as I'm concerned. The leaves get very large, about the size of your hand. Then later on in the season it gets little white cluster of flowers which smell very sweet. Also, they drip sticky juice, almost like honey. I would like to know the name of the tree because it has beautiful foliage. (Litchville, N.D.)

A: Piece of cake! American linden. One of my favorites. Which cultivar, I can't tell, but at least you know the species!

Q: I would like your opinion of good varieties of American linden trees and which ones would not be desirable for the Grand Forks area. (Grand Forks, N.D., e-mail)

A: A good cultivar of American linden? They are all good, with differing characteristics. First of all, the "pure" cultivars of American Linden: Dakotah American linden, a South Dakota introduction (but rarely available); Front Yard linden, an introduction from Bailey Nursery of Minnesota; Boulevard American linden, dependably hardy for all of North Dakota and developing a narrow, pyramidal form that gets approximately 50 feet high and 25 feet wide; and Redmond linden, a nice pyramidal form and one that I have on my property, which is doing quite well after getting off to a slow start.

Then there are the American linden hybrids: Dropmore linden, Glenleven linden, Norlin linden, Shamrock linden and Wascana linden.

These are all northern introductions that should do well in your area. I have no data on their rates or forms of growth. I would suggest sticking to one of the cultivars rather than the hybrids and visiting a couple of the local nurseries or garden centers in your area to see what else they can tell you besides what I have listed here. I would definitely recommend purchasing locally, rather than through a mail order catalog in this instance.

Q: I have several rain barrels connected together with a drain at the bottom. They are open at the top, and I can draw water off from the bottom. What is the best way to control mosquitoes from breeding in the rain barrels? I have heard that putting oil on water keeps the larvae from being able to breath. What kind of oil can/should I use? Can I just put a couple of tablespoons of vegetable cooking oil in each barrel? Will this effectively control the mosquitoes from breeding in my barrels?

I want to be able to use the water for watering plants. I have heard of using oil like diesel fuel on ponds, but I don't want something toxic on my house, deck and garden plants. Will the cooking oil bother the plants? Especially if the water is just drawn off the bottom? What else is recommended? (Lisbon, N.D., e-mail)

A: There are several approaches I can suggest in your particular case. One, get a couple of goldfish for each barrel. The fish do an excellent job of keeping down mosquito larvae, plus they would provide trace amounts of fertilizer for your plants when you water. Be sure to rescue the fish before winter cold moves in.

Two, I would suggest using the "summer grade" of dormant oil (an oxymoron, actually). This is a light-weight oil that should disperse itself over the water surface and cause the larvae to suffocate. Or, as you suggested, a light-weight vegetable oil would do the same thing. The dilution rate would be so small that you need not worry about any possible toxic effects on plants, especially since you are taking the water from the bottom of the tank.

Q: Please advise me as to what I can do to level my lawn that has become very bumpy and uneven, possibly due to nightcrawlers. (Jamestown, N.D.)

A: Several things: roll with a ballast roller, topdress with topsoil, power rake—you may try any or all.

Q: What can I do about red spots on our young maple tree? (Dent, Minn.)

A: Nothing! Enjoy the mosaic that the eriophyid mites have created on your silver maple. They cause no harm, and there is no effective spray for them.

Q: Every time my tomato plants get ripe they get black scab on them. I have to pick them green, then let them ripen. I planted them other places, but they still get that scab on them. One person said I water them too much or dig around them too much. Last year I didn't water them much, and they still got black scab. Is there something I can spray on the tomato plants? (Georgetown, Minn.)

A: It could be the variety of tomato you are planting. Do you save the seed each year? If so, that's your No. 1 mistake. Plant them deep, in full sun, and water only around the base of the plant, without splashing on the leaves. If you are a vigorous cultivator in your garden, try to stay away from the plants themselves with the hoe—hand weed around them. Also, try mulching your plants with organic matter this year to see if that helps.

Q: I would like to know why my pumpkins had lots of vines but no fruit for three years in a row? Also, how do you keep rabbits away from trees in winter? They killed trees this winter. (Glenfield, N.D.).

A: There are several reasons why you get all vine and no fruit on your pumpkin: too much fertilizer, not enough sunlight, cool, rainy weather at bloom time, or no pollinating insect activity.

Keep rabbits away from trees with a tree wrap of hardware cloth or plastic. Be sure it is above the expected snow line by at least 2 feet.

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Do you have a gardening or houseplant question? Write to Hortiscope, Box 5051, NDSU Extension Service, Fargo, ND 58105 or e-mail to Ron Smith at ronsmith@ndsuext.nodak.edu.

Source: Ron Smith (701) 231-8161 ronsmith@ndsuext.nodak.edu

Editor: Dean Hulse (701) 231-6136