Evaluation of PRE and POST Applied Herbicides Along With Cover Crop Residue for Control of Escape Weed Species in Tomato Production Systems
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Field studies were conducted to evaluate the efficacy of selected preemergence (PRE-) and postemergence (POST-) applied herbicides in combination with a fall planted rye cover crop and spring planted sunn hemp cover crop for controlling troublesome escape weed species in tomato production. The studies consisted of eight herbicide treatments in conjunction with cover crop, rye (no herbicides), and a nontreated control (no herbicides or cover crop) arranged in a randomized complete block design. Herbicide treatments were S-metolachlor PRE- + trifloxysulfuron POST-, S-metolachlor PRE- + halosulfuron POST-, fomesafen PRE- + trifloxysulfuron POST-, fomesafen PRE- + halosulfuron POST-, S-metolachlor PRE- only, fomesafen PRE -only, trifloxysulfuron POST- only, and halosulfuron POST- only. Weed densities of yellow nutsedge and pigweed were taken two and four weeks after application of PRE herbicides as well as two and four weeks after POST- herbicides from a 1.0 m2 section within each plot. This was done by randomly placing a1.0 m2 PVC square frame up against each row. The entire area (encompassed by the PVC square) in which weed density was measured had been treated with both PRE- and POST- herbicides. Tomatoes were harvested twice during the growing season and separated between marketable and unmarketable according to USDA growing standards. Plant height was measured 30 days after planting to evaluate potential crop injury by PRE- herbicide treatments. Data were collected via counting the number of weeds within each sample to determine which herbicide combination exhibited the greatest weed control when combined with a cover crop. The addition of PRE- and POST-applied herbicides to the rye cover crop significantly reduced both pigweed spp. (i.e. Amaranthus hybridus and Amaranthus spinosus) and yellow nutsedge (Cyperus esculentus L.) density compared to the rye cover crop only. Pigweed density was lowest in treatments of fomesafen PRE- + trifloxysulfuron POST- and fomesafen PRE- (0.11 no•m-2 for both) Additionally, all herbicide and rye treatments reduced yellow nutsedge density when compared to the rye only (19.1 no•m-2) and bareground (2.96 no•m-2) treatments. Marketable yield was highest in the fomesafen PRE- treatment (2,853 kg•ha-1), but similar to treatments of trifloxysulfuron POST- (2,321 kg•ha-1), fomesafen PRE- + halosulfuron POST- (2,153 kg•ha-1), as well as, the rye only treatment (2,731 kg•ha-1). In the sunn hemp study conducted at Auburn University, treatments influenced both pigweed spp. (i.e Amaranthus hybridus and Amaranthus spinosus) and yellow nutsedge (Cyperus esculentus L.) density,(P <0.0001; Table 3). Pigweed density was lowest in the halosulfuron PRE-applied only treatment, but was similar to treatments of S-metolachlor PRE- + halosulfuron POST- , S-metolachlor PRE- (4.7 no•m-2, trifloxysulfuron PRE- (5.3 no•m-2) ,and sunn hemp only (4.8 no•m-2), which all reduced pigweed density in comparison to the bareground treatment (7.0 no•m-2). The addition of PRE- and POST-applied herbicides made to the sunn hemp cover crop did not reduce pigweed density compared to when herbicides were excluded (sunn hemp only). Yellow nutsedge density was lowest in the treatment receiving S-metolachor PRE- + trifloxysulfuron POST- (2.3 no•m-2), but was similar to treatments of fomesafen PRE- + trifloxysulfuron POST- (3.4 no•m-2), fomesafen PRE + halosulfuron POST -(3.4 no•m-2), S-metolachlor PRE- (4.1 no•m-2), trifloxysulfuron POST- (4.2 no•m-2), halosulfuron POST- (3.2 no•m-2), and the bareground control (3.9 no•m-2). All treatments except S-metolachlor PRE- + halosulfuron POST- and fomesafen reduced yellow nutsedge density compared to the sunn hemp only treatment (7.2 no•m-2). Plant height was influenced by treatments 30 days after planting (DAP) (P = 0.010; Table 4). The bareground treatment reduced plant height (58.1 cm) compared to all other treatments. Plant height across all remaining treatments was similar. Marketable fruit yield was influenced by treatments (P <0.0001; Table 2); however, there were no differences in unmarketable fruit yield (P=0.18; Table 2). Marketable yield was highest for the treatment of fomesafen PRE- (2,853 kg•ha-1) and similar to the trifloxysulfuron POST -(2,321 kg•ha-1), fomesafen PRE- + halosulfuron POST- (2,153 kg•ha-1) treatments, as well as, the sunn hemp only treatment (2,731 kg•ha-1). Fomesafen PRE- + Trifloxysulfuron POST- was the best overall treatment, although pigweed species densities were similar to bareground treatments. This combination did not reduce plant height, subsequently the yields were very high compared to other treatments.