Field experiments were conducted in Louisiana to evaluate the effectiveness of tillage, tillage plus herbicide, and herbicide-only fallow programs in controlling bermudagrass. Tillage of fallow fields three times at 3- to 4-wk intervals between row formation in late May and planting in late September or early October reduced bermudagrass infestations in the newly planted crop in December 44 to 51%. When the final tillage operation was replaced by glyphosate postemergence at either 2.24 or 3.36 kg ai/ha in late August, bermudagrass infestation level in December on the surface of the newly planted rows was reduced to below 20%. Two applications of glyphosate at 3.36 kg/ha were more effective than tillage only and as effective as tillage twice followed by glyphosate in reducing bermudagrass infestation levels in the newly planted crop. Application of atrazine at 3.36 kg ai/ha, imazapyr at 0.68 kg ai/ha, metribuzin at 1.68 kg ai/ha, or sulfometuron at 0.14 and 0.28 kg ai/ha to newly formed rows in late May of the fallow period did not reduce the need for tillage or an application of glyphosate during the fallow period to control bermudagrass, but imazapyr at 1.12 kg/ha did. Sugarcane shoot populations in December of the fallow year were similar for the treatment programs despite differences in bermudagrass infestation levels, which ranged from 11 to 94%. However, sugarcane stalk number and height and cane and sugar yield in the plant-cane crop the following year were highest when glyphosate was applied to bermudagrass as two applications either alone or following the application of atrazine or metribuzin, when tillage was followed with one application of glyphosate, and in 1 yr when imazapyr alone was applied to newly formed rows.

Sulfometuron at 17 g ai/ha in the planting furrow (13% of the anticipated fallow-field application rate) inhibited sugarcane emergence and development and ultimately reduced sugar yields in the initial production year by 13% when compared to a weed-free control that contained no herbicide in the planting furrow. Residual levels of metribuzin in the planting furrow representing 100% of the standard fallow-field application rate of 1,680 g ai/ha had no adverse effect on sugarcane development or sugar yield. When applied only to the soil surface immediately after planting, sulfometuron did not injure sugarcane, and sugar yields were equivalent to standard, at-planting, preemergence (PRE) applications of either metribuzin at 2,020 g/ha or a mixture of pendimethalin plus atrazine each at 2,240 g ai/ha. To minimize sugarcane injury, sulfometuron should be kept out of the germinating zone of lateral buds along planted sugarcane stalks.

The response of the sugarcane cultivars HoCP 91-555, HoCP 85-845, and LCP 85-384 to flumioxazin during the first (plant cane) and second (first ratoon) production years was evaluated within two identical experiments, the first starting in 2000 and the second in 2001. In the plant-cane crop, flumioxazin application timings were PRE immediately following planting, fall postemergence (FPOST) 6 wk after planting, early spring postemergence (ESPOST), postemergence-directed spray (PDS) following layby cultivation, and sequential applications of FPOST followed by ESPOST. During the first-ratoon crop, flumioxazin was applied ESPOST, late-spring (LSPOST), PDS following layby cultivation, and sequentially LSPOST followed by PDS. Flumioxazin injury to sugarcane consisted mainly of stunted growth and reddening and necrosis of treated leaves. In plant cane, injury was 28% 2 wk after treatment (WAT) when applied ESPOST in one experiment but less than 10% in the other, and was no more than 13% in either experiment at 6 WAT. In the first-ratoon crop, injury was around 15% when applied ESPOST in the first experiment, but no injury was observed 6 WAT. However, in the first ratoon, injury to all cultivars was 25 to 30% when following a LSPOST application. When applied as a PDS, injury was no more than 15% 4 WAT in either plant-cane or first-ratoon sugarcane. Stalk height was reduced 15 cm compared to the nontreated control when flumioxazin was applied as a sequential application (FPOST followed by ESPOST) in plant cane and by 23 cm (LSPOST followed by PDS) in first-ratoon sugarcane. In plant cane ESPOST applications of flumioxazin reduced sugar yield (9 to 28%) within all three cultivars used in this study in both experiments with only one exception. Sequential (FPOST followed by ESPOST) applications reduced sugar yield within all cultivars (6 to 37%). PDS applications at layby reduced yields (7 to 12%) in the first experiment, but not in the second experiment. In the first-ratoon crop, LSPOST applications of flumioxazin reduced sugar yield (7 to 11%), sequential flumioxazin applications (LSPOST followed by PDS) reduced sugar yields (8 to 19%), and PDS applications at layby did not reduce yield. It appears that there is little if any difference in tolerance to flumioxazin for the cultivars used in this experiment. To avoid risk of yield loss, flumioxazin should not be applied as an over-top POST treatment to weeds in actively growing sugarcane, and care should be taken to minimize spray contact with sugarcane leaves when applying flumioxazin as a PDS at layby.

Paraquat applied from mid-February through early April over 2 yr was evaluated for sugarcane tolerance and Italian ryegrass control. Sugarcane 31 cm tall at application was injured 16 to 25% and 8 to 14% 28 and 56 d, respectively, after mid-March application of paraquat at 0.35 or 0.70 kg ai/ha. Early-April application to 61-cm-tall sugarcane caused 13 to 25% injury. The observed injury was not reflected in reduced sugarcane shoot population or height or sugarcane or sugar yield when compared with diuron, the standard herbicide treatment. Italian ryegrass control 28 d after the mid-February application of paraquat alone at 0.53 or 0.70 kg/ha was variable, ranging from 80% in 1994 to no more than 66% in 1995. For each year, diuron at 3.2 kg/ha in combination with both rates of paraquat increased Italian ryegrass control 28 d after the mid-February application 11 to 17 percentage points. At 56 d after the mid-February application, addition of diuron proved beneficial only in 1994 when the paraquat and diuron combinations controlled ryegrass 93% compared with no more than 62% for paraquat applied alone. In contrast, Italian ryegrass was controlled the second year no more than 80% 56 d after the mid-February application of paraquat alone or with diuron. Paraquat applied at 0.70 kg/ha with diuron in mid-March controlled Italian ryegrass 80 and 86% 28 d after treatment in 1994 and 1995, respectively. For the standard herbicides metribuzin, terbacil, and diuron applied in mid-March, weed control was no greater than 38%. Although differences in Italian ryegrass control among herbicide treatments were observed, efficacy was sufficient to reduce weed competition such that sugarcane growth and yield were not negatively affected.