Indaziflam is an alkylazine herbicide used for preemergence control of annual weeds in warm‐season turfgrass. Growth chamber studies were conducted to determine the effect of indaziflam rate on bermudagrass (Cynodon dactylon L. Pers.) shoot and root initiation as influenced by soil texture and organic matter (OM). Bermudagrass plants propagated from stolons were planted in five different growing media, including pure sand (100% sand), sand (92% sand, 6% clay) with or without OM (2%), and loamy sand (82% sand, 12% clay) with or without OM (2%). Indaziflam at rates of 48 or 16 g ha−1 followed by drenches of 2.5 cm of water were applied to the bermudagrass plants after maximal root length reached 30 cm. Bermudagrass growing in pure sand, regardless of indaziflam rate, showed the most injury, with root and shoot biomass reduced to <10 and <32%, respectively, compared with the nonherbicide‐treated control 38 d after treatment (DAT). Increase in clay content and addition of OM at 16 g ha−1 indaziflam significantly improved root biomass to ≥40% at 38 DAT. Despite inhibitions to root growth, aboveground tissues of plants growing in sand and loamy sand with OM showed minimal or no changes in turf color and coverage at 16 g ha−1 indaziflam. Results of this study indicate that small amounts of clay and OM in sandy soil aid in reducing bermudagrass phytotoxicity risk of 16 g ha−1 indaziflam.

Wetting agents are the primary tool used to control soil water repellency (SWR) and localized dry spot (LDS), especially on sand-based soils. However, the effect of repeated applications of wetting agents on soil microbial populations is unknown. This two-year field experiment investigated six wetting agents representing different chemistry effects on a creeping bentgrass (Agrostis stolonifera L.) putting green with existing SWR. Four out of the six wetting agents improved soil volumetric water content in the second growing season, while others showed no effect. This result was negatively correlated to the development of LDS, and positively correlated to occurrence of an air-borne turf disease. Soil microbial populations, determined by soil phospholipid fatty acid (PLFA) analysis, found that none of the treatments applied caused a shift in microbial populations between fungi and bacteria, or gram-positive and gram-negative bacteria. The stress indicators such as saturated to mono-unsaturated fatty acids were not affected by the wetting agents applied as well. However, the wetting agent that contains alkyl block polymers (ABP; Matador) with proven capability for removal of soil organic coatings showed inhibition of microbial populations at one evaluation timing. This result suggested a temporary restriction in soil carbon availability for soil microorganisms following repeated ABP application, which likely contributed to the elevated LDS development observed. Another wetting agent, a combined product of a nonionic surfactant plus acidifiers (NIS; pHAcid), which is designed to reduce inorganic carbonates while enhancing wetting, elevated all soil microbial populations tested at the end of the experiment, indicating a desirable improvement in soil health. However, repeated application of NIS did not reduce SWR at the conclusion of this experiment, which, in combination with a previous report, suggested a minimal disturbance of soil organic coatings of the hydrophobic sand. Overall, this experiment suggested that soil microbial populations can be affected by wetting agents which may further influence SWR, yet the actual effect on soil microorganisms varies depending on the chemistry of the wetting agents.

2263 RESEARCHZoysiagrass (Zoysia japonica Steud.) has relatively good tolerance to most turfgrass diseases compared with other turf species, with the exception of large patch, which is caused by Rhizoctonia solani Kühn AG 2-2 LP (Green et al., 1993). The infected yellow to brown patches could vary from <0.3 to >6 m in diameter. Without control, affected zoysiagrass starts to thin out and eventually dies, leaving voids that are often infested by weeds and typically taking most of the growing season for the turf to recover. Environmental conditions that favor large patch occurrence are relatively wet

This research evaluated oriental mustard [Brassica juncea (L.) Czern.] seed meal (MSM) for safety and efficacy in control of dollar spot (Sclerotinia homoeocarpa F.T. Benn.) in vitro and on creeping bentgrass (Agrostis stolonifera L.) turf. As a plant residual, MSM is the seed fraction that remains after seeds are crushed and oil is removed. The meal contains both nitrogen and secondary compounds termed glucosinolates. When moist, glucosinolates convert to fungicidal isothiocyanates. The in vitro study determined that MSM at higher rates completely suppressed S. homoeocarpa mycelial growth. A field study was conducted for 2 yr with three sequential applications of MSM at seven rates ranging from 0 to 1680 kg ha−1, in addition to the fungicide iprodione at 3.1 kg a.i. ha−1. In 2007, the severity of dollar spot infections varied among MSM treatments, with greater rates reducing dollar spot up to 82% compared with untreated control. In 2008, MSM at 1680 kg ha−1 reduced dollar spot by 60% or greater 8 to 14 wk after initial application (WAIA). After application of MSM at 1120 kg ha−1 or greater, the color of creeping bentgrass color was reduced 1 point on a 1 to 9 scale, but this reduction in color only lasted for 2 wk, and turf color in treated plots increased significantly by 6 WAIA compared with the untreated plots. Collectively, our results suggest that MSM is an organic material that could be integrated into a dollar spot management program on turf for minimizing selection of pathogen resistance to fungicides.