Application Placement and Relative Humidity Affects Smooth Crabgrass and Tall Fescue Response to Mesotrione

Abstract

Much research has been conducted on mesotrione activity on crops and weeds, but information is lacking in regards to the relative contribution of soil and foliar absorption of mesotrione. Three experiments conducted at Virginia Tech's Glade Road Research Facility in Blacksburg, VA, evaluated the effects of 50 and 90% relative humidity (RH) on the activity of mesotrione applied to foliage, soil, and soil plus foliage. Tall fescue injury ranged from 0 to 21% and was significant in 6 of 20 comparisons. Three of these injury events were caused by soil plus foliar applications, which were always more injurious than foliar only applications, which were more injurious than soil-only applications. Both application placement and RH significantly influenced smooth crabgrass responses to mesotrione. Smooth crabgrass phytotoxicity was lowest when mesotrione was applied only to foliage and highest when mesotrione was applied to soil and foliage. Increasing RH from 50 to 90% caused a 4- to 18-fold increase in plant phytotoxicity when mesotrione was applied only to foliage. By dissecting the plant canopy, it was noted at 14 d after treatment, when averaged over RH, that white leaves comprise 16% of leaves when only foliage was treated and 55 and 62% when applied to soil plus foliage and soil only, respectively. Furthermore, white tissue was found predominately in the two youngest leaves when mesotrione was applied to soil or both soil and foliage, but in older leaves when applied only to foliage. Data indicate mesotrione entering plants through soil travels quickly to growing points and has an equal or greater effect on plant phytotoxicity than foliar-absorbed mesotrione. In addition, foliar-absorbed mesotrione appears to increase in plants significantly with increasing RH, but does not move rapidly to growing points.

Urea Ammonium Nitrate Additive and Raking Improved Mesotrione Efficacy on Creeping Bentgrass

“…Johnson and Young (2002) reported that mesotrione was more effective at low temperature and high relative humidity, with foliar application on large crabgrass. Increased relative humidity also was reported to increase smooth crabgrass (Digitaria ischaemum) and tall fescue (Schedonorus phoenix) control by mesotrione application (Goddard et al, 2010). Therefore, more research is needed to explain the different raking effects from 2 years.…”

Goosegrass and Bermudagrass Response to Rates and Tank Mixtures of Topramezone and Triclopyr

“…Several triketone herbicides have been shown to control annual grasses (Johnson and Young, 2002; Bollman et al, 2008; Goddard et al, 2010) but are highly injurious to bermudagrass (Brosnan and Breeden, 2013). The amount of bermudagrass injury caused by triketone herbicides depends on the specific herbicide, application rate, and application frequency (Kopsell et al, 2010; Brosnan et al, 2011; Elmore et al, 2011a, 2011b).…”

Methods of Assessing Bermudagrass [Cynodon dactylon] Responses to HPPD‐Inhibiting Herbicides

“…Reductions in F v /F m occur as soon as 6 h after herbicide treatment, long before the appearance of visual symptoms (Barbagallo et al, 2003). As a result, multiple researchers have used F v /F m assessments to supplement visual ratings of mesotrione activity in field and greenhouse studies (Goddard et al, 2010; McCurdy et al, 2008, 2009; McElroy and Walker, 2009). However, direct relationships between F v /F m and carotenoid pigment concentrations following HPPD‐inhibiting herbicide treatment to turfgrass have not been reported.…”