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

By Ron Smith, Horticulturist

NDSU Extension Service

Q: I have a violet that friends gave me three or four years ago. It stops blooming in September. In the past, I've snipped off the leaves that are bad until there are just a few left. Then I cut off the rest of the stem. I keep watering it once in a while, so it has come back every spring. Do you think that it would be OK to cut off the whole thing now, rather than a little at a time? (e-mail reference)

A: Not really. Allowing the foliage to remain on the plant as long as it is green will keep it producing photosynthates that are stored in the crown. This provides the energy for the plant to recover in the spring. I would try to address the reason why the violet goes through this decline. My best guess is that it does not get sufficient light. Consider getting a plant light that is meant for flowering houseplants. I think you'll see a big difference. Also, when you water, do so at the base of the container and use tepid water. Before watering, allow the water to sit out overnight so it comes to room temperature and diffuses the chlorine and other gases that might be detrimental to the plant. Above all, keep water off the foliage.

Q: We have a row of trees with older caragana bushes in it. I have noticed that the branches have become weak and break easily, even the larger ones. I was told I could cut the bushes down to the base and they would grow back. What might cause the weak branches and will the trimming help for next year? If so, can I cut them down now? (Wahpeton, N.D.)

A: It is up to you if you want to cut them back to the ground in this freezing weather. You can do it in the early spring after the weather warms a little, but trim the bushes before they break buds. The weak stems probably are caused by a combination of stem cankers and borer activity, which is not uncommon in a planting that old. Take a sharp chain saw and carefully buzz them off at ground level. Haul all the cut branches away for use as kindling.

Q: My mother has a huge Christmas cactus that is about 200 years old. We have a picture of my great-great-grandmother with it. Last summer, she took in a couple of other cacti plants to mother them back to health. She now has very small bugs (thrips) that are no larger than a pencil tip all over the cactus plants. She was told by her Extension agent to put bags over the plants and spray with a broad-spectrum insecticide spray. She has done this twice, but the bugs are still there. Do you know of anything else she can do? She is almost 82 years old and is now talking of throwing the cactus out! I have a fogger that might help if I can find out what spray to use. (e-mail reference)

A: A Christmas cactus that old is a national treasure! Don't throw it out because we'll save it somehow. To control most houseplant pests, look for Bonide Systemic Houseplant Insect Control or Bayer Rose and Flower Insect Killer with the active ingredient imidacloprid. It provides effective, lasting protection against aphids, soft scale, mealybugs, thrips and whiteflies. It is registered for indoor and outdoor use. Thrips are a particular headache because of their small size and ability to hide in and among the small folds of the flower buds when sprays are being used. These systemics will make their next meal their last one. Also, I would appreciate a photo of this amazing plant!

Q: As emerald ash borer seems to begin its march north, many people want to know why the bug hasn't threatened other species, such as maples. Why, for that matter, does the Dutch elm beetle only prey on elm trees? I tried to find a reason but didn't find one. If you could answer this in an upcoming column, you would be doing a great service to your readers. (Park Rapids, Minn.)

A: Good questions about insects and diseases of woody plants. Some insects, such as the emerald ash borer (EAB), evolve as a species-specific pest. That means they genetically are wired to be attracted to that one species of woody plants for feeding and reproductive purposes. No other tree species will do. If all the ash trees were wiped out, this pest would disappear as well unless it mutated to be able to feed on something else in the plant kingdom. While the adult feeds on the foliage, the damage is negligible. However, the larvae feed on the inner bark of ash trees. This disrupts the tree's ability to transport water and nutrients. Emerald ash borer probably arrived in the United States on solid wood packing material carried in cargo ships or airplanes originating in Asia. Emerald ash borer also is established in Windsor, Ontario. It was found in Ohio in 2003, northern Indiana in 2004, northern Illinois and Maryland in 2006, western Pennsylvania and West Virginia in 2007 and Wisconsin and Missouri in 2008. It was just found in Minnesota. Since its discovery, EAB has killed more than 40 million ash trees in southeastern Michigan, with millions more lost in Ohio, Illinois, Indiana, Pennsylvania, West Virginia, Missouri, Wisconsin and Virginia. The borer has caused regulatory agencies and the U.S. Department of Agriculture to enforce quarantines in Indiana, Illinois, Maryland, Michigan, Ohio, Pennsylvania, West Virginia, Wisconsin and Missouri to prevent potentially infested ash trees, logs or firewood from moving out of those areas. The borer has cost municipalities, property owners, nursery operators and forest product industries millions of dollars. This is not a pest to be taken lightly as it moves east, south and west into our territory. There is good news and bad news associated with this pest. It is impossible to try to get a program going that is economically and physically feasible to save the ashes that are in the forests. That's the bad news. The good news is that specimen trees can be saved in municipalities by injections similar to what were used for Dutch elm disease. The cost of the injections is a limiting factor when many trees are ash in any one community. Dutch elm disease is carried by two species of elm beetles: the native and European. Both have the capability of infecting susceptible elms with this destructive fungus if they are carrying the spores on their bodies. The beetle feeding activity is not lethal to the tree because the elm beetles and elm trees have evolved through the eons without disastrous effects. It is when the fungus arrived in America on some infected elm logs that the disease took off. The operational word here is “susceptible." Research has found that some trees were immune to the pathogen and could be propagated asexually. Other research crossed different elm species to find a genetic combination that would be resistant. In addition, the elm beetles seem to be a little more finicky in their selection of feeding sites. The beetles often prefer smaller trees to those that have a larger canopy. Such is not the case with the EAB. It will attack large and small ash trees.

Q: I live in Canada and have several cyclamen plants. Several have developed leaves and flowers that are sticky, so now the window sill also is sticky. They appear healthy and some have bloomed for the second year. (Prince Edward Island, Canada)

A: Your plant is being plagued by cyclamen mites. These are sap-sucking pests that resemble spiders when observed under a microscope or strong magnifying glass. In greenhouse operations, they are a threat to the financial viability of the operation. African violets, cyclamen, dahlia, gloxinia, snapdragon, geraniums, chrysanthemums, larkspurs, begonias, fuchsias, petunias and New Guinea impatiens are highly susceptible to cyclamen mites. However, cyclamen is injured more than any other plant. This mite also is a pest on outdoor strawberries. This is an introduced species that was recorded first in New York in 1898. It now generally is distributed in greenhouses and retail outlets throughout the country. That is why it is important to check a plant carefully for any pest infestation before bringing it home. Bargain-priced plants with infestations are not bargains, so just leave them alone! Often it is better to simply dump the plant when the infestation gets as bad as you seem to be describing. However, if you want to attempt to save these plants and are good at controlling the temperature of water, they can be dipped (pot and all) in water at 110 degrees for 15 to 20 minutes. Insecticides are not practical and do not provide good control.

Q: How do you root a goldfish plant? (e-mail reference)

A: Your goldfish plant should root if the stem has finished flowering. To help the process, add bottom heat and use a rooting powder. Stick them either in pasteurized soil or vermiculite.

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.


NDSU Agriculture Communication

Source:Ron Smith, (701) 231-8161, ronald.smith@ndsu.edu
Editor:Rich Mattern, (701) 231-6136, richard.mattern@ndsu.edu
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