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Don Kinzler, Published April 23 2010

Linden’s leaves stayed because of fall moisture

Q: My Redmond linden still has leaves on it from last year. I planted the tree three to four years ago, but this is the first time it has done this. Will I have problems with the tree going into the spring or is this normal? (West Fargo)

A: This is not normal for this species. It very likely is the result of the fall being too wet for too long. If you recall, we had a very wet fall going into winter. This keeps trees from hardening off properly, which is evidenced in many cases with the foliage remaining through the winter. You likely have nothing to worry about this year, but we hope that the last two wet and snowy winters will become a thing of the past. Our soil is heavy clay, which doesn’t help matters, either, because this type of soil tends to hold moisture much too long. This problem may be mildly harmful in a case like yours or could kill trees outright because the roots are saturated for too long.

Q: We moved to this property about a year ago. In our front yard, we have a Norway spruce tree that is at least 40 years old. We had the tree pruned and treated for mites by a tree service. We also fed it fertilizer and minerals and cabled the tree about half way up where it had split. Our tree sits atop a small incline, so it catches a lot of wind, snow and ice. Two sections near the split had a good deal of solidified sap that was removed. The tree is beautiful and looks much better after having it worked on. We never have had a Norwegian spruce, so we are not well-versed on its care. Will these treatments help sustain our tree or are we throwing good money after bad? Thank you so very much for any advice. (Wilmington, Ohio)

A: The Norway spruce is a majestic tree. From your comments, I would imagine your tree fits that billing nicely. It also sounds like the treatment the tree service company provided for this specimen is just what the doctor ordered. Trees, like us, lose their vigor as they age and need assistance and encouragement to continue to weather life’s storms. You did the right thing and the tree should serve your interests for a decade or more depending on the capricious moods of Mother Nature. I would encourage you to work into your budget an annual checkup of the spruce by the tree service company. It will be worth the investment. Think of the gap in the landscape setting that would be created if the tree was removed. I have a tree in my yard that another expert told me wouldn’t last more than six or seven years. That was 25 years ago. The tree looks beautiful in my yard, much to the credit of my International Society of Arboriculture certified arborist who makes annual visits to trim out the normally dead wood that occurs and checks for disease or insect problems. It is a tree that draws favorable comments from all who see it and is worth the money I spend on it each year. In essence, you are doing the right thing and I encourage you to keep it up.

Q: I need to create a privacy and sound screen from a busy highway near Boston. I am getting thuja occidentalis nigra trees. I want to create a very thick screen. How close together should or can I plant them? Some part of the screen can handle two rows. If I am planting multiple rows, what arrangement should I use? I also am getting some thuja occidentalis techny. Should I mix these two? (Boston, Mass.)

A: I wouldn’t recommend mixing the two because their rate of growth is different and so is their eventual height. The nigra will get to about 25 feet tall with a spread of up to 10 feet. The techny will be slower in growth and get to 15 feet in height. If you want a really thick planting, set the nigra as your background plants. About 8 feet in front of the nigra, but between the spaces, plant the techny. Make them your facing plants because they usually are the more attractive of the two species.

Q: What type of insect spray can be used on a plum tree to prevent worms from entering the fruit? When, how often and what time of year should I spray? (e-mail reference)

A: This most likely is the plum curculio you are referring to. Plum curculio overwinters as an adult in ground litter or other protected places in and around orchards, particularly in nearby woods or fence rows. Overwintered adults become active when the mean temperature reaches 50 to 60 degrees for three to four days. They begin moving toward trees when the maximum temperature reaches 70 degrees for two or more days. This series of temperature events often takes place shortly before or as plums bloom, especially in the middle and upper South. Plum curculios are reluctant fliers when it is cool. Most adults probably walk to the trees when temperatures are less than 70 degrees. Initially, overwintered adults feed on succulent buds, foliage and blooms. A pre-oviposition period following emergence from hibernation may vary from six to 17 days, depending on the temperature. Egg-laying begins as soon as the young fruit forms. The eggs are deposited in shallow cavities chewed into the fruit surface by the female curculio. A single female lays from 60 to 150 eggs. Sometimes during the egg-laying process, the weevil may introduce spores of brown rot fungus to the fruit, which usually leads to the entire fruit rotting from the inside out.

Controlling this pest requires the application of both cultural methods and the timely application of insecticides. The cleaning of all debris under and near the trees is essential to help break the cycle. Next, the timely application of insecticides, such as Sevin or Malathion, is important. The first application should be made when the tree is at about 75 percent petal drop. This is to try to protect the pollinating insects that are active when the tree is in full bloom. Spray kills the feeding adult female curculio, which is your objective. Spray again in about seven to 10 days. Spraying after that point is of no value because once the eggs are inserted and the grub begins feeding, there is no effective control method.

A tactic claimed to be effective by old-time peach growers in Georgia who were bedeviled by this insect is to use a padded, heavy mallet to strike the trunk of the tree (mature trees only). Doing this in the early morning coolness will dislodge the resting weevils from the developing fruit. If you have a sheet placed under the canopy of the tree at that time, you then can vacuum or sweep up the fallen adults and dispose of them. While this will not eliminate this pest by 100 percent, it keeps insecticides from being used.

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 ronald.smith@ndsu.edu.