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

By Ron Smith, Horticulturist

NDSU Extension Service

Q: When is the best time to prune a caragana hedge? (email reference)

A: The best time is in the early spring before new growth emerges. Generally, when this question is posed about caragana, it really needs pruning. If you want to slow it down, prune it now to remove the leaf cover, which is pumping photosynthates into the system of the plant for storage to use next growing season. The early spring pruning should be done if you want to cut a woody, funky hedge back and to get it to thicken again that year. It will come back vigorously and bring you lush, leafy growth that you can shape. This pruning can be done right down to the crown of the plant using a sharp chain saw.

Q: My raspberries are on the east side of the garage, so they get plenty of sun. Later in the day or evening, some may get shade from the garage. I alternate rows, so one spring we mow a row down and pick from the other row. This year, something is eating the leaves, as you can see from the photos. Because something is eating the leaves, I’m getting a much smaller crop of berries. I always enjoy reading your column. Keep up the great work. (email reference)

A: Thanks for the nice comments about the column. Also, thanks for the outstanding photos. The damage looks like something Japanese beetles would do to the rose family, which includes raspberries. The problem is that Japanese beetles have not been documented in North Dakota as of yet. For this time of year, I can't tell you what insect would be doing that much leaf feeding but leaving the veins alone. Can you scout a little and see if you can find the culprits? If they are Japanese beetles, they usually feed at night and then crawl off somewhere cool to sleep. If it is a caterpillar of some kind, such as a fall cankerworm, there should be some evidence of them. You could spray Sevin on the plants. However, if the damage has been done and the insect pest exited, it would be akin to locking the barn door after the animals departed. I really hope this isn’t Japanese beetle damage. If they are established in the state, we will have a major headache on our hands. Almost any other insect is easier to control than this voracious beast! I look forward to more photos or information from you. In the meantime, I'll show your photos to our entomologist to see if she has any ideas.

Q: We have several arborvitae trees. This summer has been abnormally hot. The trees were doing great but now are showing brown spots. We have been watering them frequently, but nothing has improved. Do you have any suggestions on how to get rid of the brown spots? (Wisconsin)

A: Brown spots don't translate into anything definitive that I can assist you with. It could be from insect or disease activity or something in the environment, such as a dog, causing the discoloration. At the very least, I would need a couple of sharp photos and a little more written description for me to come close to giving you good advice.

Q: Let me thank you for posting so many answers to questions because I’ve learned so much by reading your responses. We just bought our first house and were thrilled to find that there are all kinds of edible plants on the property, as well as six apple and six pear trees. I’ve never dealt with fruit trees before, so it’s been quite an experience. There’s a lot to know and do, but we’re having lots of fun. After reading your article, I believe a couple of the apple trees have brown rot, so I’ve been pulling and destroying the fruit. Next year, I plan to spray with lime-sulpher in early spring. I also think that the apple and pear trees have bitter pit because of the descriptions I found. We had a drought this year beginning around the time the fruit began growing and lasting until just a couple of weeks ago. However, when I looked up images of fruit with bitter pit, I’m now not so sure it is my problem. It has similar looking spots on the outside and browning on the inside. While the images I found showed the fruit maintaining a relative apple or pear shape, the fruit on our trees (especially the apples) are completely misshaped. Other than the spots, the skin appears normal and there’s no leaf damage. Could this still be bitter pit? Would the fruit still be edible for pies or applesauce? (Rochester, N.Y.)

A: Thank you for telling me where you live. That allows me to guide you very accurately in your quest for relevant, research-based information. There is no better place to turn to in your state than to Cornell University Extension resources. For more information from Cornell, go to and There are agents in every county of the state who stand ready to assist you with your problems. If the agent doesn’t know the answer, the university will have someone on the faculty who can dig it out for you. Congratulations on your new home and the fun challenges and rewards that will be coming your way.

Q: I am hoping you can help me save my begonias. I have 13 baskets of tuberous begonias hanging under my scrub oak trees that surround my home. Last year, thinking I was being good to them, when it came time to repot and start warming them up, I used new basket liners and Miracle-Gro potting soil in the baskets. I don't think that could have caused my problem, but I don't know. They started out looking very healthy and growing well but then started developing white patches on the stems. These became larger, turned brown, shriveled and caused the whole stem to break off. The bulbs continue to put out new stems and some of the old stems continue to grow and flower. Is this problem some strain of wilt disease? What do I do about it? After the plants die in the fall, I store them in my garage until spring. (email reference)

A: Something has changed in the ecosystem of the begonias. It could be the basket liners, potting soil, drainage or the water. The change is causing a pythium-type of rot to take place on the stems of the begonias. It could be the media stayed too wet too long. Perhaps your hanging basket liners are not voiding the water quickly enough.

Q: I have a huge grapevine growing on a chain link fence. Last year was wonderful because I got so many grapes. This year, the vine grew what would have been another beautiful crop but the grapes are drying up as they are ripening. What is causing this? (email reference)

A: Look at the year we’ve had. We have had excess rain and high temperatures and humidity. Because of this weather, grapes, especially vigorously growing varieties, become vulnerable to lurking pathogens waiting for the opportunity to infect. For infection or disease to occur, a vulnerable host (grape vine), virulent pathogen (many out there) and the right environment (which we’ve had) are needed. If you want an exact determination of what it is that is destroying your crop, you would need to send a sample showing the symptoms to our plant diagnostic lab at NDSU. For information on how to contact the lab, go to If it is any comfort, there are many old standby crops, such as rhubarb, sweet corn, carrots and even zucchini squash, that have been wiped out this year because of the weather conditions.

Q: We have a willow tree that has leaves covered with many small bumps. After searching the Web, I don’t think it is leaf gall but can’t find anything remotely similar to my problem. This tree sprouted up on the edge of our pond in a cluster with two other willow trees that are not affected. My 10-year-old son has taken to nursing these trees and is somewhat desperate to save the one with the problem. I am sending you photos with the hope you can let us know what we are dealing with. Your website seemed the most knowledgeable we found. Thanks for taking the time to help us with this problem. (email reference)

A: Willows are notorious for their disease proclivity. While this infection looks disastrous for the tree, it seldom results in the tree dying. It likely will cause a complete defoliation of the tree. However, with good cleanup this fall and not stimulating succulent, soft growth next spring, your son’s patient should pull out of this infection. To be on the safe side, I’d suggest a general fungicide, such as Captan or Chlorothalonil, be applied next spring just as new growth is emerging. Repeat as needed when the first evidence of anything like this manifests itself again.

Q: I assume that the best time to prune is after the leaves have fallen. Also, I don't understand the theory of sprinkling water the evening before a frost. Could you elaborate on why this is done? Should I spray the whole tree with water or just the ground around it? One year, we tried covering the tree with a large sheet of plastic and had a light bulb under the plastic to generate a little heat, but it didn't help. (email reference)

A: By watering plants several days or more before cold weather threatens, you can relieve some stress if they are suffering from drought. Water also creates heat, so watering your plants right before a freeze creates a source of warmth that slowly will fade during a long, cold evening. This alone is not going to provide protection from a hard freeze but can be used with covers to make a small difference on a marginal night. The second way water is used is by sprinkling plants on a cold night. The basic concept involves the physics of water. If you were to chart the drop in temperature of water, you would see that it drops steadily to about 32 degrees and then levels off before dropping again after the water freezes. It takes a lot of energy to push water to change from liquid to solid. That is the key to using water to protect plants. Water is sprinkled on the plants and then freezes, causing a small amount of heat to be released as it changes from a liquid to a solid form. Then another drop lands and freezes, releasing more heat. As long as there is a thin layer of liquid water on the surface, the interior of the ice will not drop below about 32 degrees. Most importantly, you must not stop sprinkling after the temperature rises above 32 degrees. You have to continue to sprinkle until almost all the ice is melted because the process also works in reverse. As the ice goes from solid to liquid, it absorbs heat that causes super cooling. So you theoretically could have made it through the freeze but then lost the plants in the morning after the temperatures started rising. Keep in mind that this works only when the freeze is temporary and not too severe. Dipping down to 28 degrees for a few hours before dawn is OK, but dipping down to 18 degrees will eliminate the protective effect. As to your question on pruning, wait until spring starts approaching.

Q: Our lawn was flooded in June and July. Since the water receded, no new growth, including weeds, has appeared. I tilled the lawn last weekend and plan on seeding this fall. How much fertilizer should I apply before seeding? What analysis would you recommend? At what rate should I apply the seed? I have a large lawn, so watering it daily is not possible. Should I dormant seed the lawn in mid to late October and have it germinate in the spring or should I plant in mid-September? Someone told me to apply lime to kill bacteria in the soil that the river water may have left. Do you agree? Thanks for your assistance. (Minot, N.D.)

A: There is a product on the market that is referred to as winterizer turf fertilizer. It has a modest amount of nitrogen in it and ample phosphorus and potassium to help the emerging seedlings tough it through the winter months. I would suggest seeding now and then overseeding in October to act as a dormant covering. This will condition or prime the seed to sprout and grow next spring. It also will fill in the areas that might have suffered winterkill or washout during autumn rains. Seed a mixture of Kentucky bluegrass, creeping red fescue and perennial rye at the rate of 3 to 4 pounds per 1,000 square feet. Be sure the bluegrass is of the common type, such as Park or Kenblue. If the label states common Kentucky bluegrass ecotypes, then you have grass that doesn’t need to be treated like royalty for it to grow and look decent. In other words, it doesn’t need frequent fertilizing and watering. The key to good grass is high purity and germination percentages and no weed seed. Typical purity percentages are 98 percent or more, with a germination rate of 85 percent or more. The higher the percentages, the better. As for the lime treatment, this is a typical snake oil recommendation that is not supported by science or research. The UV rays from the sun do a better job than anything else. Lime is the last thing most soils in North Dakota need. Good luck and let me know if you have any other questions.

Q: We have a problem with our carrots. They are just growing tops but there are no carrots below. We had nice carrots last year. Can you tell me what's wrong? (email reference)

A: This is largely a heat issue more than anything. If the temperature stays in the upper 80s to 90s, this would interfere with the roots developing properly or at all. Too much nitrogen usually results in hairy carrot roots. The problem could be a combination of the soil being too rich in nitrogen and the temperatures being too high for proper roots to develop.

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 – Aug. 24, 2011

Source:Ron Smith, (701) 231-7971,
Editor:Rich Mattern, (701) 231-6136,
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