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

By Ron Smith, Horticulturist

NDSU Extension Service

Q: I came across your website while I was doing some research on growing sweet corn. I have had success in the past, but the last two years, the tassels have sprouted and pollinated long before any of the ears even have started to grow. As a result, I get no corn. Do you know what causes this to happen and how I can prevent it or possibly get corn from my crop this year? (email reference)

A: Your question is a stumper! I never have had that problem in almost 50 years of growing sweet corn. I forwarded a copy of your question to Marcelo Carena, our NDSU corn breeder. Here is his response to your problem: The main problem you have is the hybrid you purchased. If you had this problem last year, then change the hybrid and request one that better supports drought and heat. Even though you water the corn, the stress from drought and heat this year is so intense that it caused a delay between pollen and silk emergence. This is the first symptom we use to discard drought-susceptible corn. My advice for this year is to continue watering until maturity. There is nothing else you can do with this hybrid except to keep watering the plants during the grain-filling period (the grains that were able to be pollinated). This period is the second (after flowering) most sensitive to drought. My advice for next year is to avoid planting this particular hybrid and request that the company provide you with hybrids that are drought- and heat-tolerant.

Q: I have beautiful gladioluses in my garden that are in full bloom. They have been there for the last three years. The problem with the gladioluses is that they grow too tall. After the buds start opening, the stems are not strong enough, so they bend over. By the time the buds open, most of the stems are broken or bent forward. Why is this happening? Thank you for your time and attention. (email reference)

A: Just about anyone I’ve known who grows gladioluses stakes them with bamboo to keep them upright. I’d suggest you do that as well. You also might try planting them a little deeper to see if that helps give them some stability. However, I think staking still would be needed to protect them during stormy weather.

Q: I have five cactus plants. Three are by themselves and two are together. One of the cactus plants keeps growing to one side, so I have to keep rotating it every week or two. Why is that? Also, I have another one that has a moldlike substance on the top and a little on the sides. Can you please help me? I also have two that the thorns are falling off. (Michigan)

A: You need to contact the Michigan State University county Extension office where you live to get your concerns answered. The horticulturist will want, as a minimum, to know what variety of cactus you are referring to and if the plants are all one variety or five different ones. The horticulturist also will need to know if you are fertilizing the plants and your watering regime. To find a horticulturist in your area, go to and then click on your county. Also, a couple of high-quality photos would help in resolving the problems.

Q: I am landscaping around my new house. I was planning on putting up a fence in my backyard for my dog, but my association nixed a fence. I am thinking that I can do the same thing if I plant a hedge. I will need something that grows fairly fast and is dense enough to keep a dog in. I am willing to trim the hedge but don’t want a hedge with berries because it is messy and attracts too many birds. Do you have a suggestion? My landscaper was thinking cotoneaster, but they have berries. I don’t want something that gets woody and has to be cut to the ground all the time. A type of evergreen would be nice because I wouldn’t have to worry about leaves. However, evergreens might get a little spendy. (Bismarck, N.D.)

A: How about planting forsythia, lilac, spirea or hydrangeas? I would suggest a mix-and-match hedge to provide some variety. However, local associations usually do not allow that because it wants uniformity in appearance. Be sure to check with the association before committing the time and money.

Q: I heard you yesterday on the radio answering a question about a silver maple that you thought had severe chlorosis and was a goner. We have a maple that we have been treating for chlorosis since last fall. The leaves are yellow and have crinkly brown leaves at the end of the branches. We have been working with the nursery that planted the tree. The recommendation was to apply iron. We put liquid iron into the ground last fall and twice since then. About five weeks ago, we also added aluminum sulfate. We did that because the people at the nursery told us that our soil is so alkaline that we need to try to acidify it. The tree hasn't seemed to respond at all. Do you have any other suggestions? We would rather not lose the tree. (email reference)

A: The problem with pH-generated iron chlorosis is in the method and timeliness of the response. A temporary fix can be achieved by using a liquid formulation sprayed over the foliage of the tree. At this stage in the season, it probably is too late to have any impact. I would encourage you to continue with the applications of chelated iron and acidifying fertilizers. If the tree ends up dying and you want to replace it, do so with a hybrid or cultivar that is noted for being resistant to pH-induced iron chlorosis. Seedling selections are a shot in the dark because they may or may not be resistant.

Q: I had some people ask me about their squash. They said they have white, very hairy worms on their squash. The worms are about an inch long. They said there are a lot of them on the bottom side of the leaves on the lower parts of the plant and on the veins. They said that they don’t appear to be eating the leaves. Would you have an idea what they are? If they don’t appear to be eating the plant, will the worms have any effect on the squash? Is there something they should do to get rid of the worms? (email reference)

A: The fact that the worms are not eating is an indication that they are ready to molt or go into the pupa stage of development, which then leads to the adult emerging as a butterfly, moth or some other adult form. If their presence bothers them, recommend Spinosad insecticide because it is approved for organic use and is effective as a contact material.

Q: I sprayed Florel last and this year to inhibit seed production on my cottonwood tree. It worked last year but it failed completely this year because I evidently picked the wrong time to spray. The company that manufactures Florel recommends spraying "from midbloom to full bloom." What does that mean? Does it mean midway as the leaves are forming or midway as the pods are forming? The arborist in this area is not familiar with Florel. (email reference)

A: Cottonwood trees have to be the most challenging of trees for controlling flowering and fruit. You must really like challenges. Determining midbloom on a mature cottonwood is a real challenge. Basically, it refers to when approximately 50 percent of the flowers are open and the balance are about to open. That is why two applications usually are recommended to get maximum control of any fruit development.

Q: I am wondering how to get rid of a broadleaf grass growing in my lawn. I have no idea what it is. The leaves are up to 1/2 inch wide. It looks like grass but is much coarser. There is too much of it to dig out, and I'd have holes all over my lawn. I've sprayed with weed killer and used other lawn-care products, but nothing seems to kill it. It grows taller, wider and coarser than regular grass. Is there a way to get rid of it? I'm afraid it will take over the whole lawn. (email reference)

A: This probably is meadow fescue or a pasture grass that you are battling. Selective herbicides are not available, so the only alternative you have is to spot kill it with glyphosate (Roundup or equal) and wait for the surrounding desirable grasses to move in and occupy the space. In some situations, the best choice is to nuke out the entire lawn with glyphosate. This would need to be done by a lawn care company that performs this service on a regular basis. Mow the dead grass short, collect the clippings and seed into the dead material. The seed will germinate and a new lawn will be established.

Q: Can you tell me if tomato hornworms are a pest or only an occasional problem? They have stripped the tops of my tomatoes. However, I don't want to kill them as I think the hawk moth they become is rather rare. Please let me know as soon as possible because I am stripping other stems and leaves to feed my charges while I wait for your answer. The hornworms are on six plants and I hope that is where they remain. It feels great to have them, though. We rarely use any pesticides, so the weeds and bugs are pretty healthy. Do you know if tomato hornworms are endangered? It seems they were treated as a bad bug when I was a kid. Of course, the garden could be the difference between food in the cellar or less food. (email reference)

A: Tomato hornworms are just occasional pests and shouldn’t be killed. Allow them to feed and go into their far more attractive and entertaining adult stage. If they are an endangered species, it certainly isn’t evident here in Fargo or anywhere else that I’ve heard. Yes, the caterpillars are gross to look at, but they grow up to be beautiful adult moths. You could always plant an alternate crop, such as tobacco, for them to munch on and still have your tomatoes. I have only seen about three or four at a time in a typical garden setting.

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. 1, 2012

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