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Hortiscope

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

By Ron Smith, Horticulturist

NDSU Extension Service

Q: What chemical can I use to prevent squash vine borer? At what stage of development is the chemical applied? Thanks! (email reference)

A: I have some information for you from my colleagues at the University of Minnesota Extension Service. Most management options are limited to control of the hatching larvae before they enter the plant. Once the larvae invade the stem, it is difficult to treat squash vine borers. Home gardeners can take a proactive stance against squash vine borers by monitoring for the presence of adult borers starting the last week of June. Monitoring tells you if and when squash vine borers are present. This information helps you determine what further management measures may be necessary. There are two methods for detecting squash vine borer adults. The first is the actual observation of adult activity in the garden. These moths are conspicuous insects when flying and easy to detect. In addition, the adults make a very noticeable buzzing sound when flying that is easy to detect. You also can use yellow trap pans to detect squash vine borer adults. This can be any container, such as a pan, pail or bowl, that is yellow and filled with water. Because squash vine borer adults are attracted to yellow, they will fly to the container and be trapped when they fall into the water. Place the traps by late June and check the traps at least once a day. When you notice squash vine borer adults in your traps, you know they are active and it is time to take further action. The action that entomologists Hahn and Burkness from the University of Minnesota recommend is physical exclusion with a floating row cover or the use of insecticides. They suggest using carbaryl or permethrin and following label directions. To view their publication, go to http://www.extension.umn.edu/distribution/horticulture/M1209.html.

Q: Can I plant hollyhocks in a tall, narrow clay planter? (email reference)

A: I’ve seen them growing under worse situations and looking stubbornly good. Try it because you have nothing to lose.

Q: I have weigela bushes that came with the house I bought. A few are in a planting area that I did not trim this spring because most of what I read said not to prune. They had beautiful pink flowers in the spring, but they didn’t last long. Some of the leaves and branches are shriveling. This is the first season that I have had the plants. When I looked at the house last summer, I believe they had flowers on them. I really don't know what to do because I have no experience with this plant. Can you suggest something? We live in southern New Jersey. The plants get full sun all day and into the evening. I water the plants once a week. Thank you for your time. (email reference)

A: My best suggestion is to get in touch with the Extension Service in New Jersey. To do this, go to http://njaes.rutgers.edu/county/ and click on your county to find your contact. He or she will be able to direct you to a horticulturist at Rutgers University if the agent doesn’t have any answers.

Q: I have a lilac outside my porch that I transplanted from the main plant about nine years ago. The main plant belonged to my grandmother. I would like to get it to bloom. Last year, it had one beautiful bloom on it. The bush is somewhat shaded, but we are planning on cutting out all the trees around the area to give the plant more sun. I hate to move it because the location is where I wanted it to be. I did get a sucker that I planted outside my kitchen window. This area gets a lot of sun. Should I prune it, and when is the best time to prune it if it hasn't flowered? If I put coffee or tea grounds at the base of the plant, will that make it bloom? Is my nine-year-old lilac bush mature enough to bloom? One website I read said that the maturity of the plant before it blooms has to be seven to 14 years old. (email reference)

A: Age only counts from seed, not with a division from a mature, flowering plant. Cut the dead bloom back before July 1. Opening up the tree canopies around the lilac will help tremendously in getting it to bloom. There is a direct correlation among sunlight duration and intensity and the ability of lilacs to bloom. Don’t fertilize or do any unneeded pruning. Pruning encourages vegetative growth. Finally, be patient. Coffee grounds will not keep it from flowering or make it flower any sooner. However, don’t stop adding it whenever you can. It makes a good source of slow-release nutrients in small amounts.

Q: We have this lovely giant spruce tree on the east side of our house. It is close to being 40 years old and is at least 25 feet tall. Lately, most of the lower branches and needles are turning sort of a pinkish brown and appear dead. However, there are small areas of new growth appearing on the very ends of the needles. The needles appear to be healthier at the top of the tree. Can you offer any explanation with this poor description of what is taking place with our beautiful tree? We live just northwest of Aberdeen, S.D. We love your column. Keep up the great work. (email reference)

A: This sounds like it could be a needle cast disease getting started on your tree. This disease generally infects the older growth, while leaving the current growth alone, at least for the time being. The best thing you can do is to contact the South Dakota State University Plant Diagnostic Lab so you can send in a couple of representative samples to confirm what the problem is. Go to http://www.sdstate.edu/ps/plant-clinic/upload/SDSU-PDC-Specimen-ID-form.pdf for a form to download and fill out. It also has the lab’s phone number listed. Thank you for the very kind comments about the column. It is appreciated!

Q: I planted a hydrangea (not sure what kind) a few years ago. My hubby kept running over it with the lawn mower. He finally realized its location, so now it is tall and has very pretty green leaves. How long does it usually take hydrangeas to mature? I seem to remember as a kid my grandfather cutting ours back so they would be full-grown by the next year. (email reference)

A: It probably will flower this year. Many, if not most, hydrangeas will flower on the current season’s growth, which is what your grandfather’s plant did. Allow it to grow unimpeded this year by keeping your hubby away from it. You should see some blooms in the near future.

Q: I have some perennials in my flowerbed that where damaged in a severe thunderstorm. My bleeding heart and delphinium plants had the leaves totally shredded. The bleeding heart just has branches. I am wondering if I should cut it back or leave it alone. It is the end of June. These plants were doing so well before the storm. They were big and bushy, and the delphinium was starting to bloom. What should I do to save my plants? (email reference)

A: Welcome to the club! If there is any green leaf or stem tissue remaining, then leave it alone. There may be some revival on the part of the delphinium. I doubt that the bleeding heart will do anything at this point in the season.

Q: I bought a weeping birch about six years ago. Until this year, it has done well. Sometime during the winter, it bent to where the top is touching the ground. It is about 30 feet tall. Why did this happen? Is there anything I can do about it? (Carnation, Wash.)

A: That is a little too much “weeping” to be good for the tree. Why this happened, I have no idea. I would suggest that you contact a local certified arborist to make a determination if a well-placed pruning is in order. To find an arborist near you, go to http://www.treesaregood.com/findtreeservices/FindTreeCareService.aspx. Be sure to check credentials and insurance before allowing any major work on your property.

Q: I was delighted to find your website. I have a croton that was doing great. However, it requires a lot of water. I live at 7,000 feet elevation, so watering requirements are a bit different. After six months of great growth, I noticed weblike structures on the new growth. It seems to be killing off the new tendrils of the croton. What is it and can I spray it? (email reference)

A: Those are spider mites getting established on your plant. Spray the croton with water several times a day to get them dislodged and killed. It will take a couple of days at least. If they return, then get a miticide from a local garden center to control the mites. I cannot make recommendations for every possible situation houseplants are grown in. That is why growing a plant of any kind is both an art and science. Continue with the regime you have found successful. When I’m at a mile high or more, I consume much more water than when I'm closer to sea level, as I am here in Fargo.

Q: My wife and I have a nice backyard garden that is all organic. We don’t use any chemicals on the lawn or garden. Our biggest mistake may have been getting city compost when we planted the garden after buying the house. I’m guessing there were many unwanted things that came along with the compost. We have several weeds in our garden and yard. One in particular drives me crazy. I spent two hours on my hands and knees trying to pick it out of our onions. It resembles the shape of lettuce or dandelion leaves. It has a tinge of purple on it and has very tiny saw teeth along the edges. It grows so thick in our onions and cucumbers that you can’t see the ground. If that description helps at all, let me know. What is a good book that you would recommend for identifying weeds in Minnesota or North Dakota? What methods would you recommend for getting rid of weeds without using chemicals? Would a thick bed of lawn clippings between the rows help with weed control? (email reference)

A: If the leaves have a milky sap to them when broken, the problem very likely is prickly lettuce. About the only nonchemical way that I know of to control this obnoxious weed is to cover it with blacktop or concrete. Mulch only will delay it coming back with a vengeance. There are organic ways some people use to control weeds, but they are marginally effective at best. The use of vinegar sprayed on the foliage will slow them down somewhat, but I guarantee repeat applications will be needed. As for a good book, you would be better off scouting weed identification websites. One of many sources to consider is at http://weeds.cropsci.illinois.edu/weedid.htm. You will find prickly lettuce listed on the website. Click on the link to see if it is prickly lettuce giving you a backache. If not, then check for annual sow thistle, which also is a strong candidate. Finally, a site that promotes the vinegar approach is at http://www.northcoastgardening.com/2009/03/organic-weed-control-how-to-kill-weeds/. Good luck!

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 – July 6, 2011

Source:Ron Smith, (701) 231-7971, ronald.smith@ndsu.edu
Editor:Rich Mattern, (701) 231-6136, richard.mattern@ndsu.edu
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