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Unusual September Weeds and Diseases in Iowa

September 24, 2013

With last week’s abnormally warm September weather, several diseases and weeds were discovered around the state of Iowa. Brown patch thrived with night temperatures above 70F⁰ coupled with high humidity. Brown patch is caused by the fungal organism Rhizoctonia solani. Damage affects the leaf blade from the tip down and is usually noticed in grasses which receive high amounts of nitrogen fertilization. Symptoms are straw colored irregularly shaped foliar lesions with a brown boarder. R. Solani can attack most cool-season grasses, but is most commonly noticed on creeping bentgrass greens, tall fescue lawns and Kentucky bluegrass.

Symptoms on bentgrass putting greens appear as a copper/gray-colored “smoke rings” ranging from a few inches to several feet where mycelium can be seen. Figure 1 below was taken last week by Dan Strey at the ISU research station. Figure 2 is from University of Missouri Extension IPM: Identification and management of turfgrass disease - looking at leaf and sheath lesions of brown patch.  

 

Figure 1: Brown Patch at ISU research station
Figure 2: University of Missouri publication looking at tall fescue foliar syptoms of brown patch

 

There are many fungicides that provide brown patch control such as Daconil, Banner Maxx, Heritage, and several others. Cultural practices such as reducing nitrogen levels and preventing long periods of wet conditions can reduce disease pressure. With temperatures tapering off over the weekend, hopefully it will be the end to the high temperature summer diseases in Iowa.

Oddly enough, in the middle of September we have also seen crabgrass and goosegrass seedlings germinating at the ISU research farm. Normal crabgrass germination occurs in mid-April to mid-May depending on your location in the state. Crabgrass is easily identified with fine hairs on the leaves and sheaths as well as its distinctive “protruding fingers” seedheads. Crabgrass also has a rolled vernation, while goosegrass has a folder vernation. 

Goosegrass is often mistaken for crabgrass and some people incorrectly refer to it as “silver crabgrass” because if it’s silvery appearance of the lower sheaths.  Goosegrass generally germinates 2-3 weeks later than crabgrass in the spring. The seed stalks of goosegrass also appear somewhat like a zipper with two individual seeds protruding in two directions. In figure 3 and 4 below you will see the side by side comparison from the Scotts grass manual.

Figure 3 and 4: Goosegrass and Crabgrass comparison from Scotts grass manual

Goosegrass is very difficult to control, even with the use of preemergence herbicides. The best postemergence option is a nonselective herbicide such as glyphosate. Optimal crabgrass postemergence control is obtained when applied while the crabgrass is small and actively growing. The use of fenoxyprop, quinclorac, and dithiopyr are the best options.

 

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Name That Patch – Early Spring Brown Spots

March 28, 2011

Parts of the Midwest are getting hit with another round of snow but there is no denying that spring continues to inch closer by the day. In fact, before this last blast of winter weather, spring activities were slowly getting underway. Trees were beginning to break dormancy, bulbs were peaking through the soil, and lawns were starting to green up.

This process has already started across parts of the Midwest and some of you may have noticed patches, or areas of brown in your lawn. It’s typical to receive a number of questions from your clients about the cause of these brown spots during spring green-up. There are a number of reasons why these patches can appear and this article will address some of the most common reasons and discuss what action, if any, is needed to remedy the situation.

Dormant warm-season grasses
Most lawns in the upper Midwest contain cool-season grasses like Kentucky bluegrass, perennial ryegrass, and tall and fine fescues. Occasionally lawns, or parts of the lawn, will contain warm-season grass species. Examples of these could include zoysiagrass, buffalograss, or nimblewill. Whereas cool-season grasses grow best in the spring and fall, warm-season grasses prefer the mid-summer months and will remain dormant (brown) longer into the spring until warmer temperatures arrive.

If zoysiagrass or buffalograss are the cause of your brown spot there isn’t much you can do other than exercise patience until warmer weather arrives. Nimblewill can be selectively controlled with Tenacity herbicide. Tenacity herbicide will be made available to homeowners later this spring. Consult a lawn care professional for more information about Tenacity herbicide.
 

Dormant patches of nimblewill are very noticeable early in the spring.  Nimblewill can be selectively controlled with Tenacity herbicide.  Consult with a lawn care professional about the availability and use of Tenacity herbicide.

 

Warm-season grasses such as buffalograss are still brown while cool-season grasses such a fine fescues begin to green-up.

Leftover annual grassy weeds
Annual weeds such as crabgrass are always a concern and last year they seemed to be particularly troublesome. In lawns that had severe outbreaks, some of these annual grassy weeds may still be present. The good news is that you don’t have to worry about controlling leftover annual weeds. They have completed their lifecycle and are no longer alive. They did however drop seed and you may consider using a pre-emergence herbicide for the upcoming season.

 

Goosegrass, an annual grassy weed, is still present from the previous growing season. 

Snow molds
Damage from pink and gray snow mold is most evident shortly after the snow melts. The grass will usually appear off-color and be matted down. Chemical applications to control snow molds in the spring are seldom recommended as most of the damage has already taken place. You can help your lawn by raking up the matted areas of grass with a leaf rake. Chances are there is some live turf hiding underneath. The picture below shows an area of gray snow mold on the Iowa State University central campus.

 

Gray snow mold on the Iowa State University campus. 

Dog spots
Damage from animal urine will definitely create brown spots in the lawn. Where you can usually count on some recovery from snow mold damage, dog spots are very effective at killing grass. The best course of action is to remove the dead grass, break up the soil with a hand trowel or rake and re-seed the area. Note: Seed will not germinate and grow if a pre-emergence herbicide is to be used. The exception to this rule is when Tenacity or Siduron herbicides are used. Consult with a lawn care professional for more information about these products.

 

Man's best friend.  Undoubtedly charming, but damaging to grasses.

Salt damage
De-icing materials that contain sodium can be quite harmful to turf. Brown patches or areas of turf along driveways, sidewalks, or streets could be caused from salt damage. Depending on the severity of damage, reseeding may be necessary. Aerification and watering (or rainfall) can help flush salts through the soil profile and improve the conditions of the site.

Marcus Jones
Graduate Research Assistant

Nick Dunlap
Undergraduate Research Assistant

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QUACKGRASS WAS THE BIG WINNER IN DROUGHT

November 13, 2012

Quackgrass (Elymus repens) is known for its long clasping auricles and its extensive rhizome system.  It is one of the most persistent and difficult to control weeds in cool-season lawns.  Rhizomes give this species an ecological advantage over other grasses during extended dry periods.  While Kentucky bluegrass also has a rhizome system, quackgrass has a more extensive system and will out compete Kentucky bluegrass in dry years.

This was the case in this year's drought in the Midwest.  Lawns went through an extended period of dormancy that in many areas lasted for months.  This fall, we are seeing Kentucky bluegrass lawns recover. But wherever there was quackgrass in the lawn, it has gained an even bigger foothold.

Last week, I was asked to look at a lawn that one of my students cares for through his lawn care service.  It had been a mostly Kentucky bluegrass lawn up to this year, but following the drought, nearly everything that is recovering is quackgrass from the rhizome system.

Roundup will kill it, but the problem is that Roundup generally does not translocate through the entire rhizome system.  When you reseed, there is always some living rhizome tissue and quackgrass returns.  I generally recommend repeated applications of Roundup, followed by sodding.  Even that extreme treatment generally fails, however, and the quackgrass returns.

Figure 1.  Long clasping auricles of quackgrass.

 Figure 2.   Quackgrass rhizomes.

Figure 3.  Lawn in central Iowa that is nearly all quackgrass following the drought of 2012.

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