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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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BROWN PATCH AND PYTHIUM MAKING AN APPEARANCE THIS WEEK

August 5, 2010

The two pictures below are from Tim Christians at Makray golf course in Chicago. It has been very wet there and night temperatures have been high. He is seeing a lot of Brown Patch on greens and Pythium on bluegrass along the fairways. The fairways are bentgrass and they have been treated with phosphites to prevent Pythium. He is reporting a lot of success with phosphites the last two years for Pythium controls. I was a little nervous about relying on phosphites, but I cannot argue with success.

I had some other calls about brown patch earlier in the week. We had a lot of brown patch at the research station in June, but I usually don't expect it in early August. By Thursday, however, we were seeing a lot of brown patch on our bentgrass cultivar trial at the station as well. It must be the saturated conditions.

For some reason we are getting surprisingly little dollar spot at the station this summer. Last year we had plots loaded with dollar spot all summer. This year I had graduate student Derek York start a study on dollar spot. As would be expected, we have almost no dollar spot in the study area. Next year we'll do a study on saturated soil conditions and we'll get a drought.

I can report that our crabgrass work is doing extremely well at the research area this summer.

I have had a lot of questions on water grass lately from homeowners. As many of you know, there is no such thing as water grass. They are generally referring to crabgrass and other annuals that take over in wet weather. There are a lot of people out there who did not put on a preemerge this spring and are interested in the services of a good lawn care company next year.

PYTHIUM JUST STARTING ON BLUEGRASS ROUGH.

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