Halosulfuron Has a Variable Effect on Cucurbit Growth and Yield

Halosulfuron is a proposed alternative to methyl bromide for managing nutsedges (Cyperus spp.) in several vegetable crops, including cucurbits. Field studies were conducted to evaluate the crop sensitivity to halosulfuron in a spring squash (Cucurbita pepo L.)—fall cucumber (Cucumis sativus L.) rotation from 2000 to 2002. Treatments included application of halosulfuron to the soil surface after forming the bed, but before laying mulch (halosulfuron-PRE), halosulfuron applied through drip irrigation (halosulfuron-DRIP) after forming bed and laying mulch, metham applied through drip irrigation after forming bed and laying mulch, a nontreated control with mulch, and nontreated control without mulch. Each treatment was applied to both direct seeded and transplanted zucchini squash. Halosulfuron treatments reduced squash plant diameter relative to metham, however plant diameters in halosulfuron-PRE (transplant and direct seed) and halosulfuron-DRIP (transplant) treatments were not different from the nontreated control. Halosulfuron-PRE delayed squash fruit production relative to the mulched nontreated control. However, application of halosulfuron-PRE and halosulfuron-DRIP did not reduce squash yield at the conclusion of the season, relative to the nontreated control. Cucumbers were transplanted and direct seeded into previous squash plots and received either an application of halosulfuron-DRIP, or were not treated. Differences in cucumber yields were not detected with second crop treatments. Cucumbers appear to have adequate tolerance to halosulfuron, making it a potential replacement for methyl bromide for nutsedge control. Suppression of early season squash growth by halosulfuron may hinder the adoption of halosulfuron as a methyl bromide alternative for squash. Yellow and purple nutsedge are among the most troublesome vegetable weeds in Georgia and the southern U.S. (Webster, 2002; Webster and MacDonald, 2001). The impending elimination of methyl bromide will soon leave vegetable growers without a valuable tool for pest management, with limited options for suppression of nutsedge growth (Harrison and Fery, 1998). Halosulfuron (Sandea; Gowan Company, Yuma, Ariz.) has been identified as a potential herbicide for use in several cucurbit crops (Batts et al., 2001; Brown and Masiunas, 2002; Haar et al., 2002; Johnson and Mullinix, 2002). Halosulfuron, applied in a number of crops controlled yellow and purple nutsedge (Blum et al., 2000; Derr et al., 1996; Vencill et al., 1995), impeded tuber production (Lowe et al., 2000; Nelson and Renner, 2002; Warren and Coble, 1999), and reduced tuber viability (Molin et al., 1999). Previous studies with cucurbits indicated that certain species and cultivars within a species had greater sensitivities than others (Buker and Stall, 2001; Stall and Majek, 1995; Webster et al., 2003), and application method affected crop injury (Garvey et al., 1997; Mitchem and Monks, 1997). To minimize inputs, growers have opted to leave mulched beds in place for multiple crops. This can increase the difficulty in managing pests, as many of the fumigant treatments (including methyl bromide) require application before installation of polyethylene mulch. Previous studies have indicated that metham and 1,3-dichloropropene can be successfully applied through drip irrigation, providing management options for specific pests in existing beds that will be re-cropped (Ajwa et al., 2002; Csinos et al., 2002; Webster et al., 2001). However, application of herbicides (nonfumigants) through drip irrigation has not been previously reported. The option of halosulfuron application through the drip irrigation could be a beneficial means of controlling nutsedge at establishment of the mulched bed, as well as in second and third crop use of the mulched bed. The objective of this field study was to evaluate the effect of halosulfuron, applied to the soil surface and through the drip irrigation, on zucchini squash and cucumber growth and yield in a plasticulture system. Materials and Methods Field studies were conducted in Tifton, Ga., at the Blackshank Farm in 2000 and at the Jones Farm in 2001 and 2002. The soil type in 2000 was a Dothan loamy sand (Fine-loamy, kaolinitic, thermic Plinthic Kandiudults) consisting of 86.8% sand, 9.6% silt, 3.6% clay (Perkins et al., 1986; Soil Survey Division, 2001) with 0.8% organic matter and pH 6.0. In 2001 and 2002 the soil type was a Tifton loamy sand (Fine-loamy, kaolinitic, thermic Plinthic Kandiudults) consisting of 86.5% sand, 7.0% silt, 6.5% clay (Soil Survey Division, 2001) with 0.8 to 1.0% OM and pH of 6.3 to 6.5. Raised beds (15 cm tall) were formed in one operation (Blue Line Superbedder 4000; Kennco Mfg., Inc.) and polyethylene mulch and drip tape applied in a separate operation (Blue Line Plastic Mulch Layer 3000; Kennco Mfg., Inc.). Black low-density polyethylene mulch (thickness of 32 μm) and drip tape (T-Tape: output of 250 L·h per 100 m at 0.55 Bar, tubing wall 0.2 mm thick, emitters spaced 20 cm apart) were laid in plots (1.8 × 6.1 m), with a bed top of 0.76 m. Treatments were arranged as a randomized complete block design with four replications. Each bed was treated with Inline, a mixture of 133 kg·ha a.i. 1,3-dichloropropene and 73 kg·ha a.i. chloropicrin, injected through the drip irrigation system (1500 ppm injected over 6 h, followed by flushing of the lines for 1 h) 17 to 20 d before planting. The test was managed uniformly for fertility and pests following University of Georgia Extension recommendations (Boyhan et al. 1999). At planting, all plots received an application of 168 kg·ha of 10N–16P–0K through drip irrigation. Throughout the growing season, plots were watered 3 to 5 times a week (based on need) and each week received 22 kg·ha of 7N–0P–5.8K liquid fertilizer injected through the drip irrigation system. The study was a split-split plot design with main plots as nutsedge management treatment applied to squash (first crop), subplots as squash and cucumber planting method (direct seeded or transplanted), and sub-subplots as treatment before cucumber (second crop). Main plot treatments included 1) metham (sodium salt formulation) applied through the drip irrigation at 145 kg·ha a.i. (maximum registered use rate) following mulch laying; 2) halosulfuron at 39 g·ha a.i. applied preemerence to the soil surface after forming the bed, but immediately before mulch laying (halosulfuron-PRE); 3) halosulfuron at 39 g·ha a.i. applied through the drip irrigation following mulch laying (halosulfuron-DRIP); 4) nontreated control with mulch, and 5) nontreated control without mulch (bare ground). Metham was mixed with 3.8 L of water and injected into the drip PEST MANAGEMENT HORTSCIENCE 40(3):707–710. 2005. Received for publication 8 Sept. 2004. Accepted for publication 2 Nov. 2004. We acknowledge the technical support of James E. Davis in coordinating this study, with assistance from Thomas E. Sklany. We also acknowledge the assistance of Duncan McClusky and Emily Cheek of the University of Georgia Library, Tifton Campus. This research was partially funded by the Interregional Research Project-4 (IR-4). Mention of a trademark, proprietary product, or vendor does not constitute a guarantee or warranty of the product by the USDA and does not imply its approval to the exclusion of other products or vendors that may also be suitable. To whom reprint requests should be addressed; e-mail [email protected].