October 15, 2007

1. Grub damage – Green June Beetle
2. Rhizoctonia Large Patch (Zoysia Patch)
3. Dwarf Bermudagrass Greens Tolerate Preemergence Herbicides Differently

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1. Grub damage – Green June Beetle

Recently, we began to see some small burrows in finely cut turf including practice fields at men’s athletics. These are usually in the form of small mounds of soil with a burrow (hole) underneath (A and B). If the castings are brushed aside a small burrow appears (B and C) which can run several inches deep into the soil. This can resemble damage caused by mole crickets, but unlike burrows caused by mole crickets a soapy-water flush does not result in the insect pest in question coming to the surface. With a little work and the help of a shovel, trowel, or screw driver it is possible to find the culprit of these burrows (D) which is some type of white grub. Now, how do you figure out which one it is?

Green June Beetle burrowing

These particular larvae grow up to 1 to 2 inches in size which rules out many other scarab beetles (adults of white grubs) as being the possible culprit. The method to positively identify these larvae is to inspect the raster pattern. The raster pattern is a distinctive pattern of hairs, spines, and bare spaces on the underside of the last abdominal segment, in front of the anus (E,F and G). In the case of the green June beetle (Cotinis nitida) this is a pattern of two distinct parallel lines that are centered just under the anus (G) which is exactly what we see in our unidentified white grub (F). Another distinct identification characteristic of green June beetles is that they crawl on their back using the stiff bristles on the back of their abdomen. Watch a video of this behavior below. Therefore, different than other white grub species (masked chafer, Japanese beetle, May/June beetles) green June beetle larvae

  1. Burrow in the turf and cause surface mounding
  2. Crawl on their backs
  3. Can reach sizes of 1-2 inches
  4. Have two distinct parallel lines that are centered just under the anus as their raster pattern (NOTE: May/June beetles can also have large larvae with a similar parallel line raster pattern, but they do not crawl on their backs or surface burrow)

Adults of the green June beetle larvae are large (3/4 to 1-inch in length and 1/2-inch wide) with a dull brown top with lengthwise stripes of metallic green and a metallic green underside (H). Adults are active by day and can often be heard buzzing about before they are ever seen. There large bodies, loud buzzing sounds, and dive-bombing flight patterns can produce unfounded fear that they might attack or sting humans. Females are attracted to moist soils with high organic matter where they lay their eggs. As with other white grub species, the adult scarab beetles do not typically cause damage to turf. Like Japanese beetles and masked chafers, green June beetles have a one-year life cycle where the adults emerge from the soil in June-July, lay eggs in August, and overwinter as larvae. During fall and spring larvae burrow to the surface at night where they feed on organic matter in thatch or on decomposing clippings near the surface.

Damage from green June beetle larvae is seldom severe enough to warrant control. There are few cultural controls available. Avoid using manure-based organic fertilizers near the time of egg lay as this may attract female beetles. Increase turf vigor by fertilizing damaged areas or by overseeding damaged areas. Chemical control of the larvae can be achieved preventatively by applications of imidacloprid (Merit), halofenozide (Mach2), thiamethoxam (Meridian), or clothianidin (Arena) in July or August or by curative applications of carbaryl (Sevin) or chlorpyrifos (Dursban). Follow label instructions. One note of caution is that curative applications will result in dead green June beetle larvae on the surface since they feed at night and that is where they will come in contact with the insecticide. This can lead to an unsightly smelly mess on golf courses and athletic fields.

For a complete list of products see MP144 Insecticide Recommendations for Arkansas

Green June beetle identification
Click on the icon below to download a movie of a green June beetle crawling on its back.

Reference:
Potter, D.A. 1998. Destructive Turfgrass Insects: Biology, Diagnosis, and Control. John Wiley and Sons, Inc. Hoboken, NJ.


Aaron Patton and Jon Trappe
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2. Rhizoctonia Large Patch (Zoysia Patch)
Symptoms and Identification. As the growth of zoysiagrass is beginning to slow, we are starting to see the symptoms of Rhizoctonia Large Patch (zoysia patch). Rhizoctonia Large Patch (RLP) is the most significant disease of zoysiagrass in Arkansas. The pathogen is favored by moderate temperatures (between 50 and 86 degrees Fahrenheit), wet soils and long dew periods in the spring, fall and during cool summers. Symptoms are seen on both dormant and actively growing zoysiagrass. Symptoms first start as small areas (12 inches) where leaf blades assume a tan-orange color (A). These patches can then expand rapidly into well-defined large patches (B,C)(20 feet or more) and/or clusters of small patches (D). Patches will fade as temperatures increase in summer, but will often reappear in the same location when conditions become more favorable. There is no known resistance to Rhizoctonia Large Patch among zoysiagrass cultivars, but current research suggests there are differences in susceptibility among the cultivars. In order to have this disease properly identified you would need to collect an appropriate sample from this area and submit it to the plant diagnostic clinic via your county cooperative extension office. To collect the sample, use a small garden spade and collect an area right on the edge of the infected and uninfected turf. Cut a circle approximately four inches in diameter and about 2-3 deep. Leave the soil attached to the roots and put the sample into a plastic bag. Seal it up and take it to your county cooperative extension office.

Management. Cultural practices such as reduced nitrogen and irrigation may help reduce RLP, but an application of fungicide is often justified for best control. Research at Purdue and the University of Arkansas shows that best RLP control results from strobilurin fungicides (Heritage, Compass, Insignia) or flutolanil (Prostar). Application of DMI fungicides (Banner, Bayleton, Lynx, Rubigan, Eagle) are usually also effective, but control seems inconsistent from one season to another. Research has looked at whether either fall or spring fungicide applications may be more efficient, but there does not appear to be a strong trend. In general, fungicides can be applied anytime symptoms are evident and still provided good patch suppression. See the extension publication (FSA) linked below for more on biology and management of Rhizoctonia Large Patch. Also, contact your local extension office for additional information.

Large patch identification

More information about Rhizoctonia Large Patch is available at: http://turf.uark.edu/publications/factsheets/Rhizoctonia Large Patch Disease of Zoysiagrass FSA-7527.pdf

Click above for a video about Rhizoctonia Large Patch or go to the link below. http://www.aragriculture.org/diseases/audio/zoysia_patch_audio.htm

Aaron Patton and Steve Vann
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3. Dwarf Bermudagrass Greens Tolerate Preemergence Herbicides Differently
Dwarf bermudagrass (a.k.a. ultra-dwarf bermudagrasses) greens are gaining popularity in central and southern Arkansas. New cultivars are replacing Tifdwarf and Tifgreen putting surfaces because of their ability to produce better putting surfaces and tolerate lower mowing heights. New dwarf bermudagrasses include Miniverde, Champion, TifEagle, FloraDwarf and others. Bensulide (Bensumec 4FL or Pre-San 7G) and bensulide + oxadiazon (various trade names) are both commonly recommended for preemergent herbicide use on bermudagrass putting greens. Recent research in South Carolina found that these cultivars differ in their sensitivity to preemergence herbicides compared to Tifdwarf. In this study McCullough et al. (2007) reported that all bermudagrasses were damaged by mitotic inhibitors such as dithiopyr (Dimension), napropamide (Devrinol), and pendimethalin (Pre-M). They also evaluated the use of Oxadiazon (Ronstar), bensulide + oxadiazon, and bensulide on Miniverde, Champion, TifEagle, FloraDwarf and Tifdwarf. Their findings were:

  1. Across all cultivars oxadiazon did not reduce root mass as much as bensulide
  2. bensulide + oxadiazon, and bensulide reduced TifEagle root mass as rates were increased whereas oxadiazon did not
  3. TifEagle was damaged by bensulide + oxadiazon more than other cultivars

Practical implications:

  1. Do not use dithiopyr, napropamide, or pendimethalin on bermudagrass putting greens.
  2. At labeled rates oxadiazon, bensulide + oxadiazon, and bensulide can all be used safely on Miniverde, Champion, FloraDwarf, and Tifdwarf.
  3. Golf courses with TifEagle putting greens should only use oxadiazon as a preemergence herbicide on their putting greens.

Reference:
McCullough, P.E., T. Whitwell, L.B. McCarty, and H. Liu. 2007. Dwarf bermudagrass tolerance to preemergence herbicides. HortScience 42(3)673-677.

Aaron Patton and John Boyd


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