The Influence of Iron-Containing Foliar Fertilizers on the Efficacy of Bispyribac and Their Impact on Bentgrass Discoloration, 2007 – Steve McDonald, M.S.

Introduction
Bispyribac-sodium (Velocity®) was released in 2004 and labeled for control of Poa annua (L.) and Poa trivialis (L.) in creeping bentgrass (Agrostis stolonifera L.) and perennial ryegrass (Lolium perenne L.) fairway turf. Research has shown that bispyribac-sodium has the potential for Poa annua and Poa trivialis management and that optimal time to apply this product may be when the average ambient air temperatures is 18°C (65°F). Research has also shown that under some environmental conditions, Velocity may elicit some objectionable yellowing to desirable turfgrass species. McDonald, et. al (2006), however, evaluated the impact of tank-mixing Velocity with one iron (Fe) containing product for its impact on amelioration of the discoloration. In those studies, it was determined that tank-mixing Velocity with a 12% Fe product may mask some of the objectionable discoloration, however more work is needed with other products and to also determine if the Fe may impact the herbicidal activity

Experimental Design and Structure
This study was conducted on a fairway maintained at 0.5 in height, located at Brookside Country Club in southeastern Pennsylvania, and comprised of approximately 80 to 85% creeping bentgrass and 15 to 20% Poa annua. Treatments and rates are outlined in tables below. Treatments were applied using a CO₂-powered backpack sprayer calibrated to deliver 408 gallons water per hectare (1 gallon of water per 1000ft²) at 250 kPa (36 psi). Individual plots were 2.5 x 5 ft and treatments were arranged in a randomized complete block design with four replications. 

Percent of plot area covered by healthy green Poa annua was rated visually on a 0 to 100 scale with 0 = no green, live P. annua and 100 = entire plot area covered by P. annua that was completely green and healthy. Creeping bentgrass and Poa annua injury was rated on a 0-5 scale with 0= no injury, 2.5= to thinning and yellowing and 5=brown dead turf. Percent bareground was rated on a 0 to 100 scale with 0 = no live turf, and 100 = entire plot area covered by green and healthy turf. Data were subjected to analysis of variance and significantly different means were separated using the least significance different test at P ≤0.05 using ARM. 

Results
Poa annua injury was rated on four occasions following the initial application of the treatments and data is shown in Table 1. On 8 June, four days after first application, all Velocity-treated plots had Poa annua injury higher than the untreated control. The agronomically highest level of injury was observed in the Velocity-alone treated plots. On 20 June, a similar trend was observed; however, the level of observed injury had substantially increased to greater than 1.7 on the 0 to 5 scale. By 26 and 30 June, the herbicide-induced injury was generally severe and few differences were observed. On most rating dates, plots treated with the Velocity + Fe products had slightly lower Poa annua injury ratings. This had been previously reported by research conducted in Maryland. The fertilizers may help the Poa annua withstand the activity of the herbicide or mask the injury. 

Bentgrass injury was rated five times and is shown in table 2. The visible injury appeared as yellowing and no thinning of bentgrass was observed on any rating date. Generally, on all rating dates, Velocity applied with Iron Combo and Irontech, had significantly less creeping bentgrass injury when compared to Velocity applied-alone. The treatment of Velocity + Gary’s Green® + Fe Chelate, did not provide for the same level of discoloration (visible injury) masking as the other two aforementioned Velocity + Fe treatments. The Velocity-alone treatment induced what should be considered typical injury to the bentgrass (below 1.28 on all rating dates. When the plots were again rated on 25 July no more visible bentgrass injury was observed. 

Poa annua control was rated by assessing the plots for percent of Poa annua coverage and also percent bareground, taking into assumption that the current bareground is probably dead or declined Poa annua. On 6 July, all plots treated with Velocity (either in combination or alone) had equal levels of Poa annua coverage, which was significantly less than the untreated control. Also, on that date, the percent of bareground was greater in all Velocity treated plots, when compared to the untreated control. This should be expected because of the thinned or dead Poa annua. The most bareground was observed in plots treated with Velocity-alone and could be do to the fact that the nutrients contained in the Fe products helped the bentgrass to ‘creep’ over some of the voids created by the thin or dead Poa annua. A similar trend was observed on the 25 July rating date, however the percent of bareground in the treated plots had decreased. Plots treated with Velocity-alone had the highest amount of bareground. 

Table 1. Poa annua injury as influenced by various Velocity applied alone or tank-mixed with a foliar iron fertilizer. 

^x Treatments were applied on 4 and 20 June 2007. 

^y Means in each column followed by different letters are significantly different (P ≤0.05) according to the least significant difference test. 

^z Poa annua injury was rated on a 0-5 scale with 0= no injury, 2.5= to thinning and yellowing and 5=brown dead turf. 

Table 2. Creeping bentgrass injury as influenced by various Velocity applied alone or tank-mixed with a foliar iron fertilizer. 

^x Treatments were applied on 4 and 20 June 2007. 

^y Means in each column followed by different letters are significantly different (P ≤0.05) according to the least significant difference test. 

^z Creeping bentgrass injury was rated on a 0-5 scale with 0= no injury, 2.5= to thinning and yellowing and 5=brown dead turf. 

Table 3. Percent of plot area covered by Poa annua and percent bareground as influenced by various Velocity applied alone or tank-mixed with a foliar iron fertilizer. 

^x Treatments were applied on 4 and 20 June 2007. 

^y Means in each column followed by different letters are significantly different (P ≤0.05) according to the least significant difference test. 

^z Percent of plot area covered by healthy green Poa annua was rated visually on a 0 to 100 scale with 0 = no green, live P. annua and 100 = entire plot area covered by P. annua that was completely green and healthy. 

McDonald, S. J., Dernoeden, P. H., and Kaminski, J. E. 2006. Creeping bentgrass tolerance and annual bluegrass control with bispyribac-sodium tank-mixed with iron and nitrogen. Online. Applied Turfgrass Science doi:10.1094/ATS-2006-0811-01-RS.