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Ron Smith answers questions about flowers, trees, gardens and shrubs.

By Ron Smith, Horticulturist

NDSU Extension Service

Q: I have several problems with some tiger lilies. There are brownish pods on the plants and they do not flower. Might these pods be an insect or disease problem? (Crosby, N.D.)

A: You are correct in your analysis of the situation. Tiger lilies flourish under benign or intended neglect. Typically, tiger lilies are a shoe-in for flowering dependability, so you may have insect or disease problems. Also, the flowering may have been delayed because of environmental conditions this year.

Q: I cut some rhubarb root from a friend’s garden to transplant into my garden. The root started off growing really well, but then got invaded by ants. Some of the ants seemed to be eating parts of the leaves. I wasn't sure what to use to fix the problem. Someone mentioned using diotomaceous earth because it is organic. I used some but now regret it. It seemed to kill a lot of the leaves and the ants stayed. I'm wondering if the rhubarb is even useable anymore. What can I use to get rid of the ants and can I save the plant? I am thinking of transplanting it to a different spot. (e-mail reference)

A: I never have heard of rhubarb-eating ants! Their presence on plants usually means plant sucking insects, such as aphids, also are on the plant. The ants are acting as farmers by milking the aphids of the nectar they extract from the plant. The dirt you used would not have caused any harm to the plants. It also would not have controlled the ants or whatever is feeding on the plants.

Q: When is the proper time to trim young river birch trees? We would like to trim some of the lower limbs. (e-mail reference)

A: If they need pruning, you can do it now. Be sure you don't trim any more than necessary. River birches usually are a landscape tree that don't need much pruning work.

Q: I have some gold raspberry bushes that have been giving wonderful berries for about eight years. This spring, I cut them to about the 3- to 4-foot level before full leaf growth. I usually cut them to the ground after a couple of hard frosts. Now the bushes are giving purple berries. Will they go back to being gold or have they been cross-pollinated to purple? Can I get my gold berries back or should I buy new plants next spring? I live in upstate New York near Rochester. (e-mail reference)

A: I'm afraid your raspberry bushes have reverted back to giving purple berries. A return to the fall gold berries won’t happen. You are left with the choice of accepting these purple berries or digging them out and replanting some new raspberry bushes.

Q: I planted two crab apple trees in my yard here in central Georgia. Two days after planting them, all the leaves turned brown but did not fall off. I have continued to water the trees, especially during the heat wave. (e-mail reference)

A: The trees likely are suffering from transplant shock. My guess is that they were held in a nursery or garden center that had at least 50 percent shade. When you moved them to a sunny area, they went into shock, which resulted in the dead foliage you are seeing. Keeping the soil moist is a good idea, but it is too easy to overdo it. Saturated soil is as bad, if not worse, than soil that is too dry. Space your watering to every three days or so. It also depends on the amount of rain you get and the temperature. Check the soil to be sure it is dry to the touch on the surface before watering again. You could compound things with excess watering by causing root rot to develop. The tree probably will not releaf until next spring. That is assuming it stays alive in its semidormant state until then. You might contact the nursery where you made the purchase to see if they can offer some suggestions or replacements.

Q: I was looking for information on the NDSU website for the rate of Sevin to use to control apple maggot flies. I’m also looking at different formulations. You mentioned spraying at petal drop and 10 days later. It is my understanding the apple maggot flies don't emerge from the soil until after a rainfall in July. What is the purpose of spraying at petal fall? (e-mail reference)

A: Apple maggots and coddling moths are two very destructive apple tree pests. In dealing with coddling moth problems, the apple tree should be sprayed at petal fall and again in 10 to 14 days. The apple maggot begins laying eggs from late June to the end of August, depending on where you live. In most instances, the homeowner does not distinguish between these two pests, so I assume the worst and advise spraying at petal drop followed by 10- to 14-day intervals. Carbaryl is formulated as Sevin 50 WP and Sevin XLR (4 pounds of active ingredient per gallon). For insect control, the Sevin 50WP should be used at a rate of 0.5 to 1 pound per 100 gallons. The Sevin XLR formulation is 0.25 to 1 quart per 100 gallons. Carbaryl gives excellent control of leafhoppers, codling moths, Oriental fruit moths and Japanese beetles. It provides good control of cicadas and redbanded leafrollers. Carbaryl also is used as a fruit thinner on several apple varieties. Carbaryl may be applied within a day of harvest. However, Carbaryl may roughen the fruit lenticles.

Q: I was wondering if you could recommend the best tool for giving my weeping willow a haircut. Is there something out there that can take a little bit of the labor out of this job? (e-mail reference)

A: A haircut? I assume you mean cutting the drooping branches back somewhat without going after each little branch. I'd suggest an electric hedge trimmer. You need to be careful to not cut the electrical cord. If you can find one that can be used without a cord, that would be the way to go. Almost everyone who has an electric trimmer has cut the cord at least once. If they haven't yet, it is just a question of time before they do.

Q: We had a replacement steeplechase arborvitae planted during our very hot Washington, D.C., summer. We watered it twice a day for the first two weeks so it would establish itself. The temperatures are in the mid-90s and we have had very little rain. I am concerned about the recent browning at the tip of the branches. I would like to know if you have any thoughts or guidance on how to better monitor the plant and what to look for. (e-mail reference)

A: Twice-a-day watering is too much and does no good during high temperatures. You are taking a chance on creating anaerobic conditions in the root zone that could result in root rot. I would suggest backing off on the watering to a good soaking every two or three days or when the soil feels a little dry. If you feel compelled to water more during hot spells, a daily light watering of the foliage with your garden hose will help somewhat. However, back off on the present watering cycle you are using or you for sure will kill the arborvitae.

To contact Ron Smith for answers to your questions, write to Ron Smith, NDSU Department of Plant Sciences, Dept. 7670, Box 6050, Fargo, ND 58108-6050 or e-mail

NDSU Agriculture Communication

Source:Ron Smith, (701) 231-8161,
Editor:Rich Mattern, (701) 231-6136,
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