Questions on: Disease Control
Ron Smith, Horticulturist, NDSU Extension Service
Q: I have a fungus on the lawn. I believe we got the fungus from a lawn mower that is used at many homes. Do you think that if I let the same person mow the lawn, I will never get it under control? It already seems better with one spreading of Milorganite and a fungicide. (e-mail reference)
A: Diseases can be spread by lawnmowers. It would be unrealistic to think it wouldnít. Dollar spot is an environmentally triggered disease. Milorganite is a good choice because it serves as an antagonist to the turf pathogen. If you are convinced that the fungus got on your lawn that way,
you might encourage the mowing crew or individual to hose down the underside of the mowers before using them on your lawn (good luck!).
Q: Iíve got a nasty case of rust. It seems to have originated on the west side of our property where some mature wild plum trees are growing. They were infested with a mix of fungus last spring. Iíve written them off. The rhubarb in the vicinity of the plum trees is now plum dead.
The rust appears to have migrated to the east. I have second-year sown grass adjacent to (east of) the plum trees that is so rusty, it turns my shoes orange when I walk in the grass. Adjacent to the grass is second-year sod, which does not show signs of the rust. Our house is next to the sod, but is surrounded by river rock. Will the foundation plantings in the river rock perish? The foundation plantings are within 20 feet of the sown grass with rust. Iím concerned the rust is migrating across my yard with the prevailing winds. It appears to have killed two crimson king maple trees I planted this spring. (Fergus Falls, Minn.)
A: Rust is usually associated with an alternate host and appears on newly seeded grass. At this time next year the rust should be a thing of the past. To help your lawn out now, apply a small amount of fertilizer and water it in. This will stimulate new growth, which will allow you to mow, bag, and dispose of the clippings. The rust that is on your grass will not hurt your other ornamental plantings. Your crimson king maples did not die from rust fungus. Something else did them in.
Q: Last fall you recommended that I use a pre-emergence chemical to control forsythia that has infested my lawn. What is a good chemical and can it be purchased as a dry application? When would be the proper time to apply it? (Portland, N.D.)
A: You have a better memory than I have! A post-emergent would be better. I was wrong if I said to use a pre-emergent herbicide. Being a woody plant, the forsythia sprouts would be vulnerable to a treatment or two of Trimec. The Trimec goes to the roots and kills them. Apply the chemical when they are actively growing. Be sure to follow label directions.
Q: Is there such a thing as a fairy ring? My sister has this ring on her lawn that seems to be getting bigger every year. It is a green spot with some lighter green coloring and brown in the middle. Someone told her it is called a fairy ring. We have never heard of such a thing. Is there a spray to take care of the problem or will she have to dig it out and put new dirt in and replant? (Oakes, N.D.)
A: There isnít a spray available to control the problem. Regular fertilization will mask the effects as it spreads and eventually runs its course. It is the result of decaying organic matter in the soil from old tree stumps, wooden foundations, or excessive thatch. It will outgrow itself in due time unless you are willing to dig up the lawn and replace it with fresh topsoil and then replant.
Q: There is a white powder on my grass that seems to be spreading. It started on the boulevard but has now spread to the back yard. It has to be some sort of mold. Can it do any damage to the quality of my yard? Is there a treatment for it? It seems to sit on the blades of the grass and is not causing any real harm but I don't want it to turn into something major. (Fargo, N.D.)
A: This is powdery mildew that usually shows up on Kentucky bluegrass that has been seeded within the last year. It usually shows up on grass that is in shade part of the day and is getting normal fertilization and watering. It is non-lethal to grass. Powdery mildew can be controlled by using good management practices such as mowing at the optimal height of two and a half to three inches, mowing frequently (using not more than a third of the blade at each mowing), and mowing when the grass is not wet. Unless this is a particularly susceptible cultivar to this fungus, as the grass matures, it will develop resistance to this benign fungus. If this turns out to be a recurring problem, then the problem is, most likely, too much shade for the cultivar being grown. You then have the option of either re-establishing a turfgrass system with resistant species or cultivars that can thrive under those particular conditions or opening the tree canopies to allow for greater sunlight penetration.
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: We're seeing a number of lawns locally with some obvious yellow patches but there doesn't seem to be any pattern. Would you surmise that we're likely dealing with one of the snow molds such as pink snow mold? It just showed up in the last week or so. We had a couple of late snows. (Cando, N.D.)
A: It could very well be. If it doesnít disappear in 30 days, then it could be an iron deficiency or yellow tuft (downy mildew).
Q: We are looking for information on rust in lawns. Our lawn specialists are seeing some of it and customers are concerned about it. We know a little bit about it but would like to know more so we can give our customers good information on what to do. (Fargo, N.D.)
A: Rust on some cultivars of Kentucky bluegrass is common at this time of year, as well as on some recently, within the last year, seed lawns. The rust fungus on just about any other ornamental crop is cause for concern, but not on the bluegrass lawns we have in our area. It is simply an aesthetic unsightliness that is temporary. Spraying isnít economical or practical. The best way to control rust is to fertilize and water to encourage new growth, mow a little shorter than normal and collect the clippings. Shade grass should be mowed at normal heights and frequencies with the clippings collected. If people want to overseed with a resistant cultivar of bluegrass, tell them that park Kentucky blue is a very good one to use where the lawn is not irrigated with an automatic system.
Q: We planted a new lawn one year ago. It suffered through the drought this summer but recovered nicely. Now it is full of rust. Is there something we can do? We did not water the grass during the very dry season. (Madison, S.D.)
A: The rust is nothing to worry about. It usually shows up on newly planted turfgrasses at this time of year. I suggest using a winterizing fertilizer to promote a little growth. You can mow and collect the clippings, if you wish, to help reduce the pathogen population. Next year rust should not be a problem. It isn't worth the expense and impact to apply any fungicides at this time.
Q: I had a homeowner bring in lawn moss on soil. She says it is growing in open area. I usually associate moss in shady damp areas. I found some information from Minnesota to control it with copper sulfate. What else would you suggest? (Ellendale, N.D.)
A: Improve the soil surface drainage, along with core aeration, power raking, and the judicious use of lime. Copper sulfate works but can be toxic to other plant material, grass, as well as woody plants. I suggest the mechanical means first, then the chemicals if that fails.
A: Shade grown grass is more vulnerable to pathogens and other stresses than grass grown in full sun. Based on what you have told me about the pattern of infection, I believe it is one of the snow mold fungi that is causing the problem. This fungus typically develops on well-tended grass that goes into the winter in a tender condition, as is the case with shaded grass, where snow piles up, or the grass and soil is saturated with water going into the winter, or coming out of it. I suggest core-aeration of the lawn area. It would also benefit the oaks as well. This improves the surface drainage, helping to dry the soil, and altering the environment for the pathogen. Make the last mowing in the fall shorter by about an inch to cut down on material for the pathogen to establish upon. There are fungicides that can be applied in the fall before winter arrives, if you want to go that route, but I would suggest it only if the cultural practices don't work first.
Q: I have noticed orange looking spots in my lawn this fall. Please let me know what is wrong and what I should do to treat it. I have tried to trim most of it off. I hope that helped. (Oakes, N.D.)
A: You've got a perfect example of the rust fungus! It shows up on some species of grass and not others. It is almost always nonlethal to home lawns. You did the right thing--cutting off the diseased grass and disposing of it. While there are chemicals you can apply that would help control this disease, I don't encourage it. The grass usually outgrows it, or the environmental conditions change over a short time period and the visible symptoms disappear. Just continue to follow good maintenance: mow regularly, fertilize a couple of times each year and water when needed.
Q: There are many spots throughout the south side of the house that have dead grass (large and small patches). A friend of mine said that we have grub worms under the grass and that is what is killing it. Is that right? What do you think it is and what can I use to restore the grass? (Fort Ransom, N.D.)
A: The only way to be certain of a diagnosis like that is to peel the grass back around the leading edge of dead patches of grass. I have not seen grubs as the cause of dead grass for the past several years. In most instances it has been a disease like pythium, Necrotic ring spot or one of the snow molds.
Q: For the last two or three years, appearing in the spring, we have had large circles in the lawn (and the circles are almost perfectly round) where the grass is thick and green. Sometimes the circles are intertwined but more likely are single. This year we have nine circles and I'm really curious to know if we have an underground rodent that I should be concerned about or if it's an animal marking its territory or what. I should tell you that the only part of the circle that is nice and green is the circumference. The center is just plain grass and the diameter of the circles is usually about five feet at the minimum.
A: Your lawn problem sounds like classic Fairy Ring disease. This is caused by decaying organic matter such as dead tree stumps and roots. It is progressive, with the circles enlarging each year. The only thing you can do is mask it with fertilization and core aeration. Eventually, the fungus will outgrow itself.
Q. Our lawn was sodded last summer and this spring we noticed some round circles on it. Is this a fungus or mold and how do we treat it?
Thank you. Enjoy reading your column. (Walhalla, N.D.)
A. It is likely that you have one of the two snow mold fungi--gray or pink. For the homeowner it makes little difference which one it is. Right now, light raking with a broom rake should suffice, with a light overseeding with Kentucky bluegrass/perennial ryegrass mix.
As the soil temperature warms, and the grass begins growing to where you have mowed it at least once, consider aerating the lawn. This will improve surface drainage and help overcome soil/sod interface incompatibility, and cut down on the incidence of this disease.
In late fall--October--I suggest fertilizing with Milorganite, Restore or some other organic.
Q. I am sending a sample of grass from a diseased area on my lawn. It was from an area that looks somewhat like a circle or ring and is light-colored. It is on the north side of the house where a lot of snow sat all winter on ground that was not frozen. Can you tell me what it might be and how I can treat the area? There are several areas like this in my back yard.
Thank you for any assistance you might give me. (Oakes, N.D.)
A. Your sample was loaded with a fungus known as gray snow mold, Typhula ishikariensis. This fungus has had a "field day" this year with snow lasting so long over unfrozen turf.
It has been found that most snow mold problems can be significantly reduced via the following management approaches:
1. Dormant fall fertilization with a slow-release nitrogen carrier like Milorganite or Sustane.
2. Mowing until leaf growth has stopped, and making the last mowing a notch lower where the snow mold is a chronic problem.
3. Using snow fences to spread drifts better.
4. Limiting winter traffic over the area.
5. Aerating to improve drainage.
For this year, lightly rake the affected areas, picking up the debris. Fertilize lightly once grass growth begins, and reseed any bare spots.
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