You are here: Home Columns Hortiscope Hortiscope
Document Actions


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

By Ron Smith, Horticulturist

NDSU Extension Service

Q: I have black ants eating the beets in my garden. Last year, they ate the tassels off my sweet corn. What chemical or natural control could I use to get rid of the ants? (email reference)

A: Several ways will work. Spraying the individual or columns of ants with a toxic insecticide does little good because more ants will come to replace those that were killed. Baking soda sprinkled around the plants will repel and kill the ants, depending on what species of ants are in your garden. You also can use a mixture of Borax (1 c.), sugar (2/3 c.) and water (1 c.). Soak some cotton balls in the solution and place them where the ants are active. The ants will treat it like a food and die after eating it. If you can find the nest where they are originating from, get some diatomaceous earth and pour it in and around the hole. The ants will get small cuts that will cause dehydration and death.

Q: I have a Dutch elm-resistant tree in my yard. The tree has little, white fuzzy things on it. They have been on there the last few years, but it has been getting worse. There has been some leaf drop as well. The fuzzy things are sticky. Please let me know if you have any ideas what the problem is and how to get rid of it. (email reference)

A: The problem appears to be cottony cushion scale. The tree can be treated with a systemic insecticide by a professional arborist who will kill these sap-sucking pests and give the tree some protection into next year. The tree has a very heavy population of these pests, so something should be done about it between now and next spring before the tree starts to leaf out. If you cannot get anyone to do the task this summer or fall, another alternative is to have the tree sprayed with dormant oil next spring before new growth takes place. Along with the dormant oil, do a systemic insecticide injection or crown soak at the same time.

Q: I have a tree that produces berries. I don’t think it’s a honeysuckle tree, but I could be wrong. Do you have a website that you would recommend that I can use to compare the pictures with the berry and leaf structure of my tree? (email reference)

A: There is a good website that has plenty of photos for making comparisons to what you have. To access the photos, go to or

Q: I’ve read all your information about dieffenbachia but didn't find anything to exactly answer my question. My plant is about 35 to 36 inches tall and in a pot that is 11 inches in diameter. I feel like the plant is getting top heavy, but I don't know what the ratio of height to width and depth of the pot should be. I would greatly appreciate your answer. (email reference)

A: I don’t know that I’ve ever heard of the proper ratio between the size of the plant and container. Logic would dictate that the two should be somewhat in balance. Remember that it is the plant that is the focal point, not the pot. The pot should complement the overall aesthetics of the setting. To me, your pot is too small because it is gaining your attention in relation to the size of the plant. From a purely practical standpoint, you don’t want the plant to be tippy from being in too small a pot.

Q: I have a black walnut tree that needs two limbs removed because they are too low to the ground for mowing purposes. Is it too late in the season to cut off the limbs? (email reference)

A: No, it is not. However, get it done as soon as possible to allow plenty of time for the pruning wound to heal. No need to apply any wound dressing.

Q: The bark is pealing on my honey locust. Also, the bark is splitting on a Canada red cherry tree in my yard. The bark on the honey locust started pealing in 2009. I cut several dead branches out of the tree in 2010. There still is one large dead branch in the tree that needs to be removed. In addition to the split bark, the Canada red cherry tree doesn't have as many leaves as the other Canada red cherry trees in the yard. Can you identify what is wrong with these trees? Thank you for your help. (email reference)

A: The problem with the honey locust is a disease called nectria canker. Unfortunately, there are no chemicals to control this problem. Increasing the vigor of the tree through watering (also to avoid water stress) and planting an appropriate tree on the proper site will help prevent a nectria infection. In addition, avoiding untimely pruning or other wounding will help. As for the cherry tree, the problem is sun scald. It hits most trees in late winter when the temperatures are fluctuating widely from the sun shining on the west or south side of the trees while still dormant. This raises the internal temperature to the point of physiological activity, which is followed by a sudden drop in temperature when the sun goes down or is covered by clouds. Ice crystals suddenly form in active cells, causing rupturing, which manifests itself in split bark. The tree usually handles this stress satisfactorily, but it can be prevented by wrapping the tree in Kraft paper or plastic sleeves in the fall before the freezing weather sets in.

Q: I have green worms in some cotoneasters. They are about an inch long. Will they kill the trees? What do you suggest for controlling the worms? (email reference)

A: The worms very likely are pear slugs feeding on the cotoneasters. They are not slugs as one would think, but they look like slugs and also are somewhat pear-shaped. They are the larval stage of the sawfly adult, and feeding on cotoneaster is at the top of their menu. Insecticides such as Sevin, Malathion and Spinosad will control them. Left unchecked, they can greatly weaken the plant and make it vulnerable to other problems lurking in the environment. Also, their feeding makes for one ugly-looking shrub.

Q: We have a 9-year-old silver leaf maple tree. For the past few years, the tree's leaves have turned black or brown around the tips and then wilted. Eventually, the leaves fall off. It gets plenty of water because we have a watering system. Does it have a disease? Can we fix it? I was thinking about digging it up and replanting it in the backyard. Any advice would be helpful. (Spring, Texas)

A: The tree is marginally heat-hardy for your part of the country. The fact that you keep it watered is why it is still surviving the continuously torrid temps of Texas. It has survived for nine years and probably will survive another nine. If you would like another opinion, contact the Extension Service agent in your area to get someone to look at your tree. Go to and click on your county to contact an agent.

Q: I have a row of 25 to 30 arborvitaes. In early spring, one started turning brown and then turned completely brown. I trimmed the dead branches that I could reach. In the last few weeks, the arborvitae on each side of the first one also started to turn brown in various spots. I've looked for worms and insects, but I haven't found any. Is there anything I can do to stop whatever it is from working its way up and down the line of arborvitae? (email reference)

A: This is a problem that can only be addressed by an onsite diagnosis. I suspect a canker development on the dying branches or some borer activity. Contact the Penn State University Extension agent where you live. To find someone, go to In all likelihood, the agent will look at the planting in your yard or request that a sample be sent to the diagnostic lab for analysis to give you accurate recommendations.

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 For answers to general horticultural questions, go to

NDSU Agriculture Communication – Aug. 8, 2012

Source:Ron Smith, (701) 231-7971,
Editor:Rich Mattern, (701) 231-6136,
Prairie Fare: Prairie Fare: Kitchen Hacks to Prevent Culinary Disasters  (2019-08-15)  An ingredient substitution may save your meal.  FULL STORY
Use of Releases
The news media and others may use these news releases in their entirety. If the articles are edited, the sources and NDSU must be given credit.

Powered by Plone, the Open Source Content Management System