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Published August 26, 2011, 12:00 AM

Hortiscope: Now is the time to attack persistent weeds

Q: Do lawns generally show any response to micronutrients, such as iron, sulphur, zinc or boron, so that a soil test would be worth the effort?

By: Don Kinzler, INFORUM

Q: Do lawns generally show any response to micronutrients, such as iron, sulphur, zinc or boron, so that a soil test would be worth the effort? I have been fighting with creeping charlie for many years. I have been using products that contain triclopyr, such as Ortho Weed-B-Gon Chickweed, Clover and Oxalis Killer, which seems to kill the weeds, but they return in subsequent years. It is tough on grass because the grass turns brown. It also is tough on bushes if you spray near their roots.

I have tried some Ortho Weed-B-Gon MAX Plus Crabgrass Control. It contains quniclorac, along with 2,4-D, MCPP and dicamba, but I have not had as much success with it. It could be because I didn’t use as high amounts as called for on the label. Do you have any suggestions? (email reference)

A: Your lack of sustained success probably is tied to timing. Starting around Aug. 25 and running through the end of September is the best time to attack persistent weeds. The products you listed are fine, and I encourage you to use the maximum recommended dose. However, avoid attacking the weeds in the spring and concentrate on getting them in the fall. With shortening days in late August and into September, plants are assimilating more photosynthates into their crowns, rhizomes and root systems.

Making applications of the appropriate herbicide at the right concentration at this time of year tends to translocate the herbicide throughout the plant’s system to give you a more complete kill.

Established weeds have extensive root systems that can regenerate new foliage after it appears that you have succeeded in killing them, so vigilance and persistence are required to knock them out.


Q: I really enjoy your horticulture information website. I watched this video (www.youtube.com/watch?v7ORa54wnK8g) about pruning apricot trees. Can you tell me if it is necessary to prune a tree that never has been pruned? I have attached a photo of my tree. It flowers every spring, but here in Santa Fe, N.M. (7,200 feet), we usually get a frost that kills the flowers. Should I prune my tree? If so, when should I do it? Is there anything I can do to prevent the frost from freezing the flowers? (email reference)

A: Good grief! Never been pruned hits the nail on the head. The call is yours to make. However, if you watched the video, you know that pruning opens the canopy for better air movement and sunlight penetration.

At your elevation, about the only thing you can do is to turn a sprinkler on in the evening before a frost is predicted or cover part of the tree with a large sheet and apply the water. It may or may not work, but it is worth a try because you probably are going to keep the overgrown tree on your property, so you might as well try to get some delicious fruit off it.


Q: I planted two apple, one cherry and one peach tree last year. I water them diligently. They seemed healthy this spring and had many blossoms. We had an extremely wet spring, so I didn’t water them. I did have some trouble with Asian beetles. They bored holes in some of the leaves before I got rid of them.

The trees started dropping leaves and fruit in July, so now one apple tree is almost bare and the others look rough. Before the apple leaves fell, they had some brown and gray spots. Will the trees survive and come back healthy next year? Is there anything I should be doing for them at this point? (email reference)

A: It sounds as if your trees were hammered pretty hard with beetles and a disease. Chances are the trees will recover and come back next spring. Be sure to pick up all the fallen leaves and twigs this fall. Remove any leaves that might remain on the tree going into the winter to prevent reinfection. Spray the tree with a Bordeaux mixture next spring before new foliage emerges. Use a fungicide containing Captan, Chlorothalonil or Propiconazole and follow the directions carefully.

Monitor the tree for any return insect activity and take action to control with an insecticide, such as Sevin, and follow label directions. With all the rain and humid weather, don’t water or fertilize from this point on because the new growth would be too vulnerable to lingering pathogenic spores.


Q: I am trying to get hydrangea bushes to flower. I planted four Annabelle hydrangeas on the north side of my house a few years ago. Only one survived, so I planted three replacement bushes this spring. The original bush is growing nicely but only put out one blossom clump. The others are growing slowly. I also planted an Annabelle on the southwest corner of our house about five years ago. It is in poorer soil (more clay) than those on the north side (black soil).

The southwestern bush gets huge but has not flowered. I fertilize those on the north side of the house with 10-30-10 fertilizer. I haven’t fertilized the one on the southwestern side yet. I also planted a couple of endless summer hydrangeas. The one on the east side of the house that is shaded by an evergreen tree has had several pink blossoms each summer.

I’m waiting to see how the one I planted this summer on the west side of the house does. So far, it has its original pot blossoms but seems to droop during the hot afternoons, so I give it more water than the other plants. Someone at the greenhouse told me to cut them back almost to the ground in the fall, which I did. Was this information correct? I really want to have the huge, prolific blooming hydrangeas that others in my community seem to have. I want to pick the blossoms for indoor vases. What can I do to encourage these bushes to survive and blossom? My other perennials seem to do fine. (Mayville, N.D.)

A: Nonblooming Annabelle hydrangeas? That has to be one of the rarest events in horticultural history! I think you are being too nice to them from what you said in your note. Cut them back to stubs this fall after a killing frost and don’t fertilize any more. With minimal care, they should bloom profusely on the current season’s growth. They need almost no care after the initial year of establishment. As for the one wilting during hot days, that is perfectly normal.

As the plant matures, that will cease to happen. Anyone who can get a lavender plant to come back after one of our winters definitely has a green thumb and doesn’t need much help from me.


Q: We live in northwestern North Dakota. What would be a good choice for a grass variety for reseeding our yard? We live on a farm, so the yard is big and we can’t water. I’m not sure what kind of grass we have right now. My wife doesn’t like it because it does not stay green all year and it has very coarse blades.

She wants something that looks nice and will stay green all summer. She also wants a grass with fine blades so that it feels soft and we can go barefoot on it.

Can we overseed into our existing lawn or should we kill it off and start from scratch? Any tips to keep what lawn we do have green all summer? I think it is a crested wheatgrass blend. When is a good time to overseed or reseed a yard?

Can I plant shrubs and trees in the fall or is spring better? (email reference)

A: You probably will not get a barefoot-type lawn if you can’t water. Fescues are a good bet, but without water and fertilizer, that is an impossible dream.

If you are going to attempt this, now is the time to begin. Seeding into crested wheatgrass is a good start. There are no guarantees of success but, with luck, it might mix into something you and your wife might halfway be able to enjoy.

Try to locate navigator creeping red fescue for the overseeding. I have had extremely good luck in recommending this variety. It is a competitive, fine-bladed, low-nutrient-requiring type of grass. Once established, navigator is good at resisting drought and disease. Fall is a good time to do landscaping, so get to it while the weather is in the mood to cooperate.


Q: My mother-in-law told me that you know a lot about Japanese beetles. They are devouring my prized birch tree. I have done some research on the Internet and tried all of the suggestions on how to get rid of them, but nothing is working.

I also tried sprays on my flowers, but to no avail, so I pick them off. I even tried hanging dead beetle sachets. I hung up a bird feeder and have attracted many birds, but none of them seem to eat beetles.

What is the lifecycle of these beetles? They seem to be laying eggs and having beetle orgies. Will they die soon or will they stick around until they freeze? Since they fly, will attempting to kill the grubs in the early spring make a dent in the population? Do they have any predators? (email reference)

A: Your mother-in-law is one fantastic woman, so please give her my regards. You hit the nail on the head when you said Japanese beetles like sex orgies. Yes, controlling the grub stage will help thin the population somewhat. Getting back to the sex, there are pheromone traps that will attract them. The traps lead the beetles into thinking they will have the time of their lives only to be disappointed because there are no mates inside and they cannot get out. Of course, the traps are not 100 percent effective.

Japanese beetles usually come in cycles. They come in heavy numbers one year but light the next. As bad as this year is, it shouldn’t be as bad next year. See if you can locate a product called Bacillus thuringiensis (Bt). It is a soil-borne bacterium that will cause the grubs to get sick and die. It is effective for many years after the application and not harmful to warm-blooded animals. A combination of Bt and pheromone traps will do a good job of keeping them in check without putting toxins into the environment.


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 email ronald.smith@ndsu.edu.

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