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Trinexapac-ethyl (TE) [4-(cyclopropyl-a-hydroxy-methylene)-3,5-dioxocyclohexanecarboxylic acid ethyl ester] effects on turfgrass root architecture are not known. It has been postulated that PGR application could cause photoassimilate that is normally used for shoot growth to be funneled to root growth. This study evaluated the effects of a single TE application on kentucky bluegrass (KBG) root and shoot growth for seven weeks. Individual KBG plants were grown in a hydroponic system and harvested weekly. At each harvest, tiller height, tiller number, and color ratings were recorded. Estimates of total root length (TRL), root surface area (SA), and average root diameter were measured using the WinRhizo system. Trinexapac-ethyl reduced plant height for 4 weeks followed by a period of postinhibition growth enhancement. Trinexapac-ethyl increased tiller number over the course of the study and slightly enhanced plant color. Trinexapac-ethyl reduced TRL and SA 48% and 46% at 1 week after treatment (WAT) followed by an accelerated growth rate 1 to 4 WAT. Trinexapac-ethyl had no effect on root diameter. On a tiller basis, TE initially reduced TRL and SA 30% and 31%, respectively. Total root length per tiller and root surface area per tiller were reduced by TE treatment, but by 7 WAT, those differences were no longer significant. Initial reductions in TRL and SA per tiller may reduce tiller competitiveness for water and nutrients. Based on data for TRL and SA per tiller, shoot and root growth must be considered in total to fully understand TE effects on plant growth. Field research is needed to corroborate results from hydroponic-studies and examine the effect of various TE rates and multiple applications on turfgrass root and shoot growth.
Six field trials were conducted in 2009 and 2010 to study postemergence control of annual bluegrass (Poa annua L. var. Hausskn Timm) in kentucky bluegrass (Poa pratensis L.) with mesotrione. Mesotrione was applied at 11 different rate and application intervals to an area of kentucky bluegrass that was naturally infested with annual bluegrass. Mesotrione rates of 56 g·ha−1 applied two or three times per week for a total of 10 applications or 84 g·ha−1 applied two times per week for a total of seven applications provided consistent control of annual bluegrass but required significant application labor and resulted in minor kentucky bluegrass injury. Other treatments that required fewer applications, 110 g·ha−1 applied twice per week for five applications or 186 g·ha−1 per week for three applications, also achieved high levels of control under high air temperatures, but control levels can vary significantly as temperatures fluctuate and seasons change. Mesotrione can successfully control annual bluegrass in kentucky bluegrass when frequent applications at low rates are applied or when environmental conditions are conducive to control.
The shade tolerance of black currants (Ribes nigrum cv. Consort) was studied by measuring the growth and productivity of mature plants in the field for three seasons under full sun or artificial shade netting in Urbana, IL. Shade treatments reduced photosynthetically active radiation (PAR) from 37% to 83%. Yield was not reduced in shade levels up to 65% but decreased by as much as 66% under 83% shade. Shade had minimal effect on stem rejuvenation in the first 2 years, but reduced rejuvenation in the third year from 14 new stems in full sun to eight new stems in 83% shade. Stem diameter decreased 8% to 19% with 83% shade, whereas no changes were observed in up to 65% shade. Plant height increased 5% to 8% from open sun to 83% shade. Specific leaf weight decreased and leaf area increased with shade. Powdery mildew severity increased with shade, and disease-resistant cultivars should be considered for understory crops. Our results indicate that growth and productivity of black currants can be maintained in moderate shade but shade levels beyond 65% will significantly reduce agronomic performance.
Annual bluegrass (Poa annua L.) is an invasive weed producing copious amounts of viable seed that compete with seedling turfgrasses during renovation. These field studies were conducted to determine the effectiveness of dazomet (tetrahydro-3,5-dimethyl-2H-1,3,5-thiadiazine-2-thione), a granular soil sterilant that breaks down in soil to release methyl isothiocyanate (MITC), for controlling the soil seed bank of annual bluegrass during turfgrass renovation. Field trials in Urbana, Ill., and West Lafayette, Ind., in Spring and Fall 2000 and 2001 evaluated dazomet rate from 0 to 504 kg·ha-1 and soil preparation techniques to determine the most effective practices to reduce annual bluegrass reestablishment into a creeping bentgrass (Agrostis stolonifera L.) seeding. The interval, in days, between dazomet application and creeping bentgrass planting was also examined to determine the optimal seeding time as measured by the level of annual bluegrass reestablishment. Spring trials generally gave poor results that were attributed to windy conditions resulting in rapid loss of MITC. The annual bluegrass soil seed bank was reduced 46% in spring trials compared to 78% in fall trials. Increasing dazomet rates reduced the absolute number of viable annual bluegrass seeds remaining in the soil. However, significant quantities of viable seed remained, regardless of dazomet rate. Annual bluegrass infested the renovated turf in all trials to varying degrees. Dazomet rates of 420 or 504 kg·ha-1 yielded the lowest rates of annual bluegrass reestablishment. Trials conducted in the fall at these rates resulted in annual bluegrass cover of 1% to 20% in the resulting turf. Creeping bentgrass planted at 1 day after dazomet application had significantly less annual bluegrass than when seeded at 7 or 9 days after dazomet application. Dazomet is a tool that can help reestablish a new turf with lower levels of annual bluegrass. However, eradication of annual bluegrass with dazomet is not likely and environmental conditions will dramatically affect the success of the sterilization.
Roughstalk bluegrass (Poa trivialis L.) is a troublesome weed on golf courses, home lawns, and athletic fields from the Midwest to the mid-Atlantic states. Bispyribac-sodium and sulfosulfuron have recently been labeled for roughstalk bluegrass control, but their use needs to be refined. Our objective was to determine the most effective herbicide strategies for control of roughstalk bluegrass. Initial studies were conducted during 2005 in Illinois and Indiana and follow-up studies in 2006 in Indiana, Illinois, South Dakota (partial shade and full sun), and Wisconsin. Applications starting in the warmer temperatures of late May and June 2005 were more effective than those starting in mid-May. Bispyribac-sodium (a.i.) was applied at 74 or 114 g·ha−1 four times at 2-week intervals decreased roughstalk bluegrass cover to 1% and 0% 12 weeks after initial treatment (WAIT) in Illinois and Indiana in 2005, respectively, whereas sulfosulfuron (a.i.) at 13 or 27 g·ha−1 applied twice at 2-week intervals decreased cover to no less than 18%. In 2006, bispyribac-sodium was most effective in Indiana and Illinois decreasing cover to as low as 4%, whereas sulfosulfuron was most effective in South Dakota resulting in a decrease in cover to as low as 7%, and both herbicides performed similarly in Wisconsin. Three applications of sulfosulfuron (a.i.) at 27 g·ha−1 at 2-week intervals or four applications of bispyribac-sodium (a.i.) at 56 or 74 g·ha−1 at 2-week intervals were most effective for roughstalk bluegrass control.