July 3, 2003

Hortiscope

Ronald C. Smith, Horticulturist
NDSU Extension Service

Q: What will happen if you fertilize your lawn with crabgrass preventer or Scott's turf builder and don't water it? Will it burn your lawn? When can you transplant an iris? My hosta leaves turned brown from frost in May. Can I cut them back? (E-mail reference)

A: Nothing will happen to your lawn because the material is "prilled" which means it will not activate until it rains or you provide irrigation. Most quality fertilizers have this or similar a treatment for just that reason. You are too late for the crabgrass preventer to be effective this year. Fall is the best time to transplant an iris. Yes, you can cut the hosta leaves back.

Q: Can I grow flowers in soil where rhubarb has been removed or should I have the soil replaced? (E-mail reference)

A: I've had no problems planting flowers where rhubarb once stood.

Q: I planted several tulips around our wishing well. As they finished blooming, I planted mums among them for fall blooming. May I spread a thin layer of shredded cedar bark or eucalyptus bark around the mums after the tulip leaves have dried up and I've pulled them? Or would water leach anything bad from the bark and hurt my tulips or mums? ( Watertown, S.D.)

A: It should not be a problem as long as the bark is not fresh. It should be weathered in a pile for about a year.

Q: I have a 10-gallon sprayer that I pull behind my lawn tractor and would like to spray for mosquitoes on a half acre of seeded grass. What would be the best type of insecticide to use and how much per 10 gallons of water? I have used Malathion in a 1 gallon sprayer. (Valley City, N.D.)

A: Malathion is certainly an acceptable mosquito control. I would suggest contacting vector control in Valley City to find out what they recommend using. The rate depends on the concentration of the product. That's why label instructions have to always be followed because there is no one formula.

Q: Looking at the list of lawn diseases on NDSU's Web site, it looks like the lawn probably has mildew. We have a large farmyard and the largest diseased area is behind our house to the west under some trees. The area seems to be getting larger and looking worse as time goes. The area does receive some sun in the morning and again in the afternoon. We have received a great deal of rain the past few weeks. Should we treat in some way? (Fairdale, N.D.)

A: I wouldn't worry too much about powdery mildew on your turfgrass. I have some showing up on my bluegrass as well. It should disappear as soon as the weather clears and we get some real summer weather for a change. Usually this means that the wrong species is growing in that location. You might want to correct the problem by selective pruning if that is possible or by planting creeping red fescue instead.

Q: I bought a Haralson apple tree last spring (2002) but now I’ve heard that I need at least two apple trees in order to get apples. Is this true? I have a flowering crab apple tree that is about 300 to 400 feet away. Will this help with pollination or should I buy another Haralson and plant it closer to the other one? Also, I recently planted some trees I bought from my local Soil Conservation District. They are bur oak, Siouxland cottonwood, amur maple, Colorado spruce, and nanking cherry. Do all the trees need lots of water? Fertilizer? (Battle View, N.D.)

A: The crabapple will pollinate your Haralson but don't be too anxious to harvest apples. It will probably take five years before you see anything of consequence. The trees you purchased from the Soil Conservation district should be watered but don’t overwater. You don’t need to fertilize unless you have very sandy soil.

Q: I have a lot of crab grass in my lawn along with other weeds. Will "Trimex Classic" take care of the crab grass and should it be applied? (E-mail reference)

A: It is unusual to see crabgrass in a lawn this early. Usually it doesn’t make its presence known visually until late July or August since it’s a warm season grass. It has simply been too cold and rainy for a lot of growth to take place. Could you be seeing quackgrass instead? Quackgrass enjoys this type of weather. You need to read the label to see what the herbicide takes care of since I’m not familiar with it and don't have a copy of the label in my office.

Q: Please help! My yard is being held hostage by an awful case of creeping Charlie. My dad insisted upon taking care of it himself instead of hiring a professional. He succeeded in killing the entire lawn but not the creeping Charlie. It survived and is now flourishing. I can’t get rid of it! I think it's quite possible that I have the most unattractive yard on the face of the earth. I would love if you could offer some words of advice that wouldn't be too costly since there is a lot of ground to cover. (E-mail reference)

A: Anything difficult to control is not usually done cheaply. What you should hope for is competency. I suggest that you turn to a certified lawn care operator who would have material of high enough octane to take care of good old creeping Charlie.

Q: The college here in Devils Lake is spraying their spruce for Rhizosphaera. They are wondering if the white pines need to also be sprayed. The white pines are not close to the spruce. (Devils Lake, N.D.)

A: It wouldn’t hurt to spray the pine trees as well.

Q: What can we do with an oak tree that was hit by lightning last night? The tree lost a major branch and will have a large wound when we are done trimming it. I am concerned about oak wilt because there are three or four other oaks around it. Is the tree going to die either way? (Oxbow, N.D.)

A: A tree that has been directly hit by lightening is history. It will become apparent immediately or in a very short time. All the leaves will turn brown. You might check the other oaks in anticipation of them dying as well. That will depend on whether or not root grafting has taken place between the plants. You basically have two choices. You can prune only what is needed for safety purposes and hope that your tree(s) is an exception to a lightening hit and will survive and come back next year. The other choice is to simply write the tree off and get it out of there while the getting is good.

Q: Over the years we have planted several spruce varieties and have become educated on needle cast. Normally we treat with a spray composed of copper sulfate. Now we cannot seem to find a source. Do you have any suggestions? (Sioux Falls, S.D.)

A: Use Bravo (chlorothalonil) instead copper sulfate. Bravo it is the better treatment for such maladies on conifers.

Q: After I fertilize my hanging petunias they stop producing flowers and get green bulbs that have little black seed-like things in them. How do I prevent this from happening? (E-mail reference)

A: I have never heard of this happening before. Usually just the opposite occurs. The petunias hanging in baskets on the NDSU campus bloom profusely after they are fertilized.

I can only suggest that you remove the "black seed like things" when they appear. New growth should produce new flowers. I would also take note of the variety of petunia and not use it again in the future.

Q: When should I trim my magnolia tree, Hydrangea tree, lilac tree and azalea bush. Also, both the Magnolia and lilac are sporadic bloomers. What should be added to the soil? (New London, Minn.)

A: As a general recommendation, prune flowering shrubs and trees right after they have flowered. Usually the magnolia and lilac have no particular soil recommendations. The azalea requires an acid soil that is high in organic matter like sphagnum peat moss. Sporadic blooming may be due to shade encroachment from surrounding trees.

Q: I have four maple trees in my yard that are very large and doing well. The exception is a tree on the east side. Some leaves have a very yellow color while others are tinted brown. I have done some looking through the materials I have but am not sure what it could be although it does look a little like vertcilium wilt. Could it possibly be lacking nutrients? (Lisbon, N.D.)

A: Sounds like the terminal phases of iron chlorosis. Once the trees start down that slope of iron deficiency, which some are genetically disposed to, there is no return. The tree should be removed immediately or in the near future.

Q: Last year I started a strawberry bed that grew beautifully. I pinched off the blossoms to encourage bigger fruit for this year and even snipped off the runners in the fall to encourage the parent plant to grow larger. This year the plants came back but they just aren't growing. They did start to blossom but the plants just don’t seem to be doing anything. Some have died and turned black. I gave them a shot of Miracle-Gro and a fungicide to discourage root rot. I don't know what else to do. (Tioga, N.D.)

A: Flower removal last year was a good idea but I have never heard of removing the runner plants. I suspect that you got some cultivar that is not well-adapted to your area. You have done all you can so just be patient and see what happens this year and next. Allow the plants to runner normally this summer.

Do you have a gardening or houseplant question? Write to Hortiscope, Box 5051, NDSU Extension Service, Fargo, ND 58105 or e-mail to Ron Smith at ronsmith@ndsuext.nodak.edu. Note to e-mail correspondents: please identify your location (city and state) for most accurate recommendations.

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Source: Ron Smith, (701) 231-8161, ronsmith@ndsuext.nodak.edu
Editor: Rich Mattern, (701) 231-6136, richard.mattern@ndsu.nodak.edu