own). These results were contrary to those reported in turf. Previous studies have shown that flazasulfuron effectively controlled grass weeds such as tall fescue (Lolium arundinaceum (Schreb.) S.J. Darbyshire) [11], southern crabgrass (Digitaria ciliaris (Retz.) Koel [10], smooth crabgrass (Digitaria ischaemum (Schreb. ex Schweig) Schreb. ex Muhl.) [27], annual bluegrass (Poa annua L.), and perennial ryegrass [11,15]. Furthermore, Brecke et al. [25] reported that flazasulfuron 0.05 kg a.i. ha–1 provided similar or greater control of southern crabgrass 60 DAT than MSMA.

Control of broadleaf weeds with flazasulfuron varied by rates and rating times. (Figure 1). In general, initial weed control at 15 DAT was low, then increased until 45 DAT, then declined thereafter. Florida/Brazil pusley was moderately controlled with the application of high rates of flazasulfuron (0.10 and 0.20 kg∙ha–1) compared to the low rate; however, control at any flazasulfuron rate did not exceed 75% at 45 DAT. By 60 DAT, control was similar across flazasulfuron rates (Figure 1(A)). Initial control of Spanishneedles at 15 DAT varied by rate such that control with flazasulfuron at 0.20 kg a.i. ha–1 was higher than the lower rates (0.05 and 0.10 kg a.i. ha–1). From 30 to 60 DAT, control of Spanishneedles (78% - 85%) was similar across flazasulfuron rates at 30 DAT, but later in the season control was reduced (60%) (Figure 1(B)). Horseweed control with flazasulfuron varied by rates at 15 DAT such that there was greater control (73%) with flazasulfuron at 0.20 kg a.i. ha–1 compared to the lower rates (Figure 1(C)). At 30 to 60 DAT, control of horseweed was similar at all flazasulfuron rates. Common ragweed was not controlled by flazasulfuron at any rate. Highest control (<70%) was at 30 DAT and declined thereafter, and by 60 DAT control did not exceed 25% (Figure 1(D)).

Results of these studies indicated broadleaf weed control with flazasulfuron alone varied among species. Other studies indicated that season-long control of wild violets (Viola spp.) and field pansy (Viola rafinesquei Greene) was achieved with a single application of flazasulfuron at rates much lower (0.008 to 0.039 kg a.i. ha–1) than those used in this study [12]. Flazasulfuron at rates greater than 0.035 kg a.i. ha–1 controlled yellow rocket (Barbarea vulgaris R. Br.) and prostrate knotweed (Polygonum aviculare L.) 90% at 8 WAT [11]. Similarly, Virginia buttonweed was controlled with flazasulfuron at 0.05 and 0.08 kg a.i. ha–1 [14], as was other broadleaf weeds such as lawn burweed (Soliva sessilis Ruiz & Pavon), henbit (Lamium amplexicaule L.), and Viola species [12,13]. However, some weed species, such as common lespedeza (Lespedeza striata (Thunb.) H.&A.) and buckhorn plantain (Plantago lanceolata L.), were not effectively controlled with flazasulfuron [11,28,29]. In this study, common ragweed was not controlled by any of the flazasulfuron rates

Figure 1. Control of Florida/Brazil pusley (A), Spanishneedles (B), horseweed (C), and common ragweed (D) with different rates of flazasulfuron. Means within a rating period for each weed species followed by the same letter are not significantly different at α = 0.05.

evaluated.

Overall grass control was better with tank mixes than flazasulfuron alone at all rating periods (Figure 2). Grass control at 15, 30, and 60 DAT was greater when flazasulfuron was tank mixed with glyphosate compared to other tank mix partners. However, overall grass control with flazasulfuron at 0.05 kg∙ha–1 plus glyphosate 0.84 kg∙ha–1, and flazasulfuron at 0.05 kg a.i. ha–1 plus diuron at 2.70 kg a.i. ha–1 was similar to norflurazon at 2.70 kg a.i. ha–1 plus diuron at 2.70 kg a.i. ha–1. The greatest control (90%) of grasses was achieved at 45 DAT with the application of flazasulfuron at 0.07 kg a.i. ha–1 plus glyphosate at 1.70 kg a.i. ha–1 while the other tank mix treatments gave similar control. Similar results were reported by Brecke et al. [25] but using different herbicides as tank mix partners of flazasulfuron in turf. They reported that greater control of southern crabgrass was achieved when flazasulfuron was tank mixed with other herbicides such as prodiamine, pendimethalin, or quinchlorac in turf. Askew et al. [30] reported that flazasulfuron at 0.002 and 0.004 g a.i. ha–1 tank mixed with quinchlorac at 0.307 kg a.i. ha–1 gave 80% and 73% control of smooth crabgrass, respectively.

Tank mixing flazasulfuron with other herbicides improved broadleaf weed control (Figures 3 and 4). Except for eastern black nightshade and horseweed, broadleaf weed control at 15 DAT was significantly better with all tank mix treatments compared to flazasulfuron applied alone (Figures 3 and 4). By 60 DAT, control of all broadleaf weeds declined but was still acceptable (> 60%). Good control (65% - 74% and 71% - 78%) of pusley species was achieved with flazasulfuron at 0.70 kg a.i. ha–1 plus glyphosate at 1.70 kg a.i. ha–1, and flazasulfuron plus diuron at 15 and 30 DAT. Control with flazasulfuron plus glyphosate (at lower rates for both herbicides) was comparable with flazasulfuron plus diuron and norflurazon plus diuron at all rating periods. By 60 DAT, control with all herbicide treatments decreased with flazasulfuron tank mixed with either glyphosate or diuron, giving similar level of control. Overall, there was good control (>60%) of Florida/Brazil pusley with all tank mix treatments.

There was excellent control of Spanishneedles (>85%) with all tank mix treatments at 15 DAT (Figure 3(B)). At 30 and 45 DAT, all treatments containing flazasulfuron gave 91% to 94% and 88% to 93% control, respectively; however, control with flazasulfuron tank mixed with diuron was similar to flazasulfuron alone and norflurazon plus diuron at 30 DAT. Control for Spanishneedles declined with time, and it was 70% - 81% by 60 DAT.

Figure 2. Overall grass control with the different herbicide treatments. FLA is flazasulfuron at 0.05 kg a.i. ha–1, FLA1 + GLY1 is flazasulfuron at 0.05 kg a.i. ha–1 plus glyphosate at 0.84 kg a.i. ha–1, FLA2 + GLY2 is flazasulfuron at 0.07 kg a.i. ha–1 plus glyphosate at 1.70 kg a.i. ha–1, FLA + DIU is flazasulfuron at 0.05 kg a.i. ha–1 and diuron at 2.70 kg a.i. ha–1, and NOR + DIU is norflurazon at 2.70 kg a.i. ha–1 plus diuron at 2.70 kg a.i. ha–1. Means within a rating period are not significantly different at α = 0.05.

Control of common ragweed was higher with all tank mix treatments compared to flazasulfuron alone at all rating periods except at 45 DAT (Figure 3(C)).

Eastern black nightshade control did not vary among herbicide treatments at 15 DAT (Figure 4(A)). At 30 DAT, control with flazasulfuron tank mixed with either glyphosate or diuron was higher compared to flazasulfuron alone and the growers standard. The highest control of eastern black nightshade (93%) was achieved at 45 DAT with flazasulfuron at 0.07 kg a.i. ha–1 plus glyphosate at 1.70 kg a.i. ha–1. Additionally, control of eastern black nightshade with flazasulfuron tank mixed with glyphosate at 0.84 kg a.i. ha–1 or diuron and norflurazon plus diuron were similar and significantly higher than flazasulfuron alone. By 60 DAT, control of eastern black nightshade with all herbicide tank mixtures declined but was still acceptable with control ranging from 65% to 83%. Early horseweed control at 15 DAT was similar across herbicide treatments (Figure 4(B)). By 30 DAT, all tank mix treatments provided better control of horseweed compared to flazasulfuron alone. From 30 to 60 DAT, all herbicide treatments containing flazasulfuron provided similar control of horseweed. However, control of horseweed with flazasulfuron at 0.05 kg a.i. ha–1 tank mixed with glyphosate at 0.84 kg a.i. ha–1 or diuron was comparable to flazasulfuron alone and norflurazon plus diuron at 45 and 60 DAT. Overall, there was good control of horseweed with all herbicide treatments which averaged 70% across rating periods.

4. Conclusions

The results of this study indicated a differential response

Figure 3. Control of FL/BR pusley (A), Spanishneedles (B) and common ragweed (C) using different herbicide treatments. FLA is flazasulfuron at 0.05 kg a.i. ha–1, FLA1 + GLY1 is flazasulfuron at 0.05 kg a.i. ha–1 plus glyphosate at 1.70 kg a.i. ha–1, FLA2 + GLY2 is flazasulfuron at 0.07 kg a.i. ha–1 plus glyphosate at 1.70 kg a.i. ha–1, FLA + DIU is flazasulfuron at 0.05 kg a.i. ha–1 plus diuron at 2.70 kga.i. ha–1, and NOR + DIU is norflurazon at 2.70 kg a.i. ha–1 plus diuron at 2.70 kg a.i. ha–1. Means within a rating period followed by the same letters are not significantly different at α = 0.05.

among citrus species to flazasulfuron, with grapefruit being the most sensitive and tangerine the least sensitive. Phytotoxicity was observed when flazasulfuron was applied alone or when tank mixed with glyphosate or diuron; however, injury to citrus was reduced when flazasulfuron was tank mixed with either glyphosate or diuron. Further studies are needed to understand the factors

Figure 4. Control of eastern black nightshade (A) and horseweed (B) using different herbicide treatments. FLA is flazasulfuron at 0.05 kg a.i. ha, FLA1 + GLY1 is flazasulfuron at 0.05 kg a.i. ha–1 plus glyphosate at 0.84 kg a.i. ha–1, FLA2 + GLY2 is flazasulfuron at 0.07 kg a.i. ha–1 plus glyphosate at 1.70 kg a.i. ha–1, FLA + DIU is flazasulfuron at 0.05 kg a.i. ha–1 plus diuron at 2.70 kg a.i. ha–1, and NOR + DIU is norflurazon at 2.70 kg a.i. ha–1 plus diuron at 2.70 kg a.i. ha–1. Means within a rating period followed by the same letters are not significantly different at α = 0.05.

that may impact phytotoxicity of flazasulfuron on grapefruit trees.

Flazasulfuron alone at the rates tested did not provide adequate control of grasses and some broadleaves weeds. Tank mixing flazasulfuron with glyphosate or diuron improved efficacy on weeds. However, the rate which adequately controlled weeds proved to be detrimental to young grapefruit trees. The rate at which sufficient control of weeds is attained and the rate at which there is minimal phytotoxicity should be determined before flazasulfuron can be commercially used in citrus. Furthermore, studies on the efficacy of flazasulfuron and other tank mixture combinations with other postemergence herbicides should also be explored.

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NOTES

*Corresponding author.

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