Golf Course Management

JUL 2013

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research % bermudagrass recovery from spring dead spot disease Treatment Rate (pounds/acre) Bermudagrass recovery (%)† June 21, 2011 June 28, 2012 − 46 a‡ 59 a Barricade 0.651 23 cd 24 cd Pendulum 2.23 33 b 38 b Surflan 1.49 21 cd 26 bc Dimension 0.499 22 cd 33 bc Ronstar 3.03 55 a 57 a Specticle 0.031 14 d 13 d Tower 1.49 25 bc 34 bc Untreated check † Percent spring dead spot cover was converted to percent bermudagrass recovery by comparison to initial percent spring dead spot cover recorded on April 25, 2011, or April 27, 2012. ‡ Means within a column followed by the same letter are not signifcantly different from one another. Table 1. Percent bermudagrass recovery from spring dead spot disease in June in response to pre-emergence herbicide applications made in March to a Tifway bermudagrass fairway at Hillcrest Country Club in Lubbock, Texas. (Table 1). No bermudagrass phytotoxicity was observed in response to pre-emergence herbicide applications throughout the length of either trial (data not shown). Ronstar. Bermudagrass recovery from spring dead spot was unaffected by applications of Ronstar at 3.03 pounds/acre (3.4 kilograms/hectare). Bermudagrass recovery from spring dead spot in non-treated check plots measured 46% in 2011 and 59% in 2012, which was similar to results for Ronstar treatments (~56%) at 14 weeks after treatment (Table 1). Ronstar is absorbed primarily by shoots of susceptible weeds as they germinate and emerge through the herbicide-treated zone of the soil profle (22). Recovery from spring dead spot requires the encroachment of bermudagrass stolons from surrounding, healthy plants. Bermudagrass stolons that come into contact with Ronstar-treated soil only absorb minimal amounts of the herbicide; therefore, turfgrass rooting is not adversely affected (22). Other researchers have observed similar results in bermudagrass treated with Ronstar (10). DNA and other herbicide families. Dinitroaniline, pyridine and chloroacetamide herbicides are absorbed by roots and shoots of susceptible weeds as they germinate and emerge through the herbicide-treated zone of the soil profle (15). Stolons that come into contact with these herbicides in the soil may have diffculty rooting because of abnormal swelling of turfgrass root tips and formation of "clubbed roots" (9,13), which potentially reduce bermudagrass recovery from spring dead spot. In our research, Pendulum at 2.23 pounds/ acre (2.5 kilograms/hectare) resulted in only 33% to 38% bermudagrass recovery from spring dead spot at 14 weeks after treatment, regardless of year. Surfan, Barricade, Dimension and Tower applications resulted in 21% to 25% bermudagrass recovery from spring dead spot by 14 weeks after treatment in 2011. In 2012, bermudagrass exhibited similar recovery in response to Barricade (24%) and Surfan (26%), and 33% recovery measured in response to Dimension and 34% in response to Tower at 14 weeks after treatment. These fndings support those of other researchers (8,10). However, our results differ from those of other researchers (2) who did not observe differences in the recovery of traffcked Tifway bermudagrass in response to pre-emergence herbicide applications. They found that bermudagrass recovery was similar in response to Ronstar or Pendulum applied at 3.03 pounds/acre (3.4 kilograms/hectare), Barricade at 0.499 pound/acre (0.56 kilogram/hectare), Echelon (prodiamine + sulfentrazone, FMC Corp.) (0.713 + 0.356 pound/acre [0.8 + 0.4 kilogram/hectare]), and Dimension (0.356 pound/ acre) at one to seven weeks after traffc simulations ceased. The researchers surmised this was due predominantly to bermudagrass growth from underground rhizomes, whereas recovery in our research relied on bermudagrass stolon encroachment. In other research that, like ours, measured bermudagrass recovery from surrounding stolon encroachment of healthy tissue (5), poor regrowth July 2013 GCM 83

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