Methyl bromide has been widely used for weed control in polyethylene-mulched tomato production. With the phaseout of methyl bromide in the United States, an effective alternative is needed. Field experiments were conducted in 2007 and 2009 to determine if allyl isothiocyanate (ITC) would provide substantive weed control in tomato along with crop tolerance under low-density polyethylene (LDPE) and virtually impermeable film (VIF) mulch. Treatment factors included two mulch types (LDPE and VIF) and six rates of allyl ITC (0, 15, 75, 150, 750, 1,500 kg ha−1). A standard treatment of methyl bromide : chloropicrin (67 : 33%) at 390 kg ha−1 under LDPE mulch was also established. Allyl ITC was broadcast applied and incorporated in soil before forming raised beds and laying plastic mulch. Tomatoes were transplanted 3 wk after applying allyl ITC or methyl bromide treatments. Tomato injury was ≤ 8% in all treatments at 2 wk after transplanting (WATP). Allyl ITC at 913 (± 191) kg ha−1 was required to control yellow nutsedge, Palmer amaranth, and large crabgrass equivalent to methyl bromide at 6 WATP and maintain marketable tomato yield equivalent to methyl bromide treatment. VIF mulch was not effective in increasing weed control or improving the marketable yield of tomato over LDPE mulch. This research demonstrates that allyl ITC under an LDPE mulch can have a practical application for weed control in polyethylene-mulched tomato in the absence of methyl bromide.

Isothiocyanates (ITCs) were evaluated as an alternative to methyl bromide (MeBr) for control of Palmer amaranth, large crabgrass, and yellow nutsedge; reduction of tuber density; and increase in marketable tomato yield in low density polyethylene (LDPE)-mulched tomato production. Allyl ITC was applied at 450, 600, and 750 kg ai ha−1; metham sodium (methyl ITC generator) was applied at 180, 270, and 360 kg ai ha−1; and MeBr plus chloropicrin (mixture of MeBr and chloropicrin at 67 : 33%, respectively) was applied at 390 kg ai ha−1. A nontreated weedy check was included for comparison. There was no injury to tomato plants following allyl ITC, metham sodium, or MeBr application. Allyl ITC at 750 kg ha−1 or metham sodium at 360 kg ha−1 controlled Palmer amaranth ≥ 79%, large crabgrass ≥ 76%, and yellow nutsedge ≥ 80% and was comparable to the weed control with MeBr. Highest rates of allyl ITC and metham sodium reduced yellow nutsedge tuber density (≤ 76 tubers m−2) comparable to the MeBr application. Total marketable tomato yield was ≥ 31.6 t ha−1 in plots treated with allyl ITC at 750 kg ha−1 or metham sodium at 360 kg ha−1. Marketable tomato yield from the highest rate of allyl ITC or metham sodium were similar to the yield (38.2 t ha−1) with MeBr treatment. Therefore, allyl ITC at 750 kg ha−1 and metham sodium at 360 kg ha−1 are effective alternatives to MeBr for Palmer amaranth, large crabgrass, and yellow nutsedge control in LDPE-mulched tomato.

Methyl bromide (MeBr), classified as a Class I ozone-depleting substance, has been banned for ordinary agricultural uses. Weed control in commercial bell pepper production is complicated by the ban on MeBr and the lack of other available and effective soil fumigants. A field study was conducted to evaluate the effectiveness of allyl isothiocyanate (ITC) and metam sodium (methyl ITC generator) as MeBr alternatives for control of Palmer amaranth, large crabgrass, and yellow nutsedge; and for increasing marketable yields in low-density polyethylene (LDPE) –mulched bell pepper. Allyl ITC was applied at 450, 600, and 750 kg ha−1; metam sodium was applied at 180, 270, and 360 kg ha−1; and MeBr plus chloropicrin (67% and 33%, respectively) was applied at 390 kg ha−1. Allyl ITC and metam sodium did not injure bell pepper. Allyl ITC at 750 kg ha−1 or metam sodium at 360 kg ha−1 controlled Palmer amaranth (≥ 83%), large crabgrass (≥ 78%), and yellow nutsedge (≥ 80%) comparably to MeBr. Yellow nutsedge tuber density was ≤ 84 tubers m−2 in plots treated with the highest rate of allyl ITC and metam sodium and was comparable to the tuber density in MeBr-treated plots. Although allyl ITC at 750 kg ha−1 controlled weeds comparable to MeBr, total marketable bell pepper yield with allyl ITC was lower than the yield with MeBr. Conversely, total marketable bell pepper yield with the highest rate of metam sodium (53.5 ton ha−1) was equivalent to the yield (62.5 ton ha−1) in plots treated with MeBr. In conclusion, metam sodium at 360 kg ha−1 is an effective MeBr alternative for weed control in LDPE–mulched bell pepper.

Methyl bromide has been a key fumigant for broad-spectrum weed control in polyethylene-mulched bell pepper. However, the ozone-depleting nature of methyl bromide has led to its scheduled phaseout from U.S. agriculture. Thus, an effective alternative to methyl bromide is needed. Field trials were conducted in 2007 and 2009 to evaluate the crop response and weed control efficacy of allyl isothiocyanate (ITC) in polyethylene-mulched bell pepper. The experiment included various combinations of two mulch types (low density polyethylene [LDPE] and virtually impermeable film [VIF] mulch) and six rates of allyl isothiocyanate (0, 15, 75, 150, 750, 1,500 kg ha−1). Additionally, a standard treatment of methyl bromide/chloropicrin (67 : 33%) at 390 kg ha−1 under LDPE mulch was included for comparison. Bell pepper injury was < 3% in all treatments, except 11% injury at 1,500 kg ha−1 allyl isothiocyanate under VIF mulch at 2 wk after transplanting (WATP). VIF mulch did not provide additional weed control and marketable pepper yield over LDPE mulch. Allyl isothiocyanate at 932 (± 127) kg ha−1 controlled yellow nutsedge (90%), Palmer amaranth (97%), and large crabgrass (92%) through 6 WATP and maintained the marketable yield equivalent to methyl bromide treatment. This research demonstrates that allyl ITC under an LDPE mulch can serve as a potential alternative to methyl bromide for weed control in polyethylene-mulched bell pepper.

Nutsedge control is challenging in commercial vegetable production in the absence of methyl bromide, and therefore, an effective alternative is needed. This study investigated allyl isothiocyanate (ITC) as a methyl bromide alternative for purple nutsedge control under polyethylene-mulch. Greenhouse experiments were conducted to compare the retention of allyl ITC in treated soil (3,000 nmol g−1) under low-density polyethylene (LDPE) and virtually impermeable film (VIF) mulches. Field experiments were conducted to evaluate the effectiveness of allyl ITC (6 rates: 0, 15, 75, 150, 750, 1500 kg ai ha−1) under VIF mulch against purple nutsedge. Additionally, a standard treatment of methyl bromide+chloropicrin (67 : 33%) at 390 kg ai ha−1 under LDPE mulch was included for comparison. In the greenhouse experiment, the predicted half-life of allyl ITC under LDPE and VIF mulch was 0.15 and 0.59 d, respectively. In the field experiment, it was predicted that allyl ITC at 1,240 and 1,097 kg ha−1 under VIF mulch is required to control purple nutsedge shoot and tubers equivalent to methyl bromide + chloropicrin at 4 wk after treatment (WAT). It is concluded that allyl ITC under VIF mulch would need to be applied at 2.8 to 3.2 times the standard treatment of methyl bromide + chloropicrin under LDPE mulch for commercially acceptable purple nutsedge control.

Isothiocyanates have been implicated in the cancer-protective effects of brassica vegetables. When cabbage is consumed, sinigrin is hydrolysed by plant or microbial myrosinase partly to allyl isothiocyanate (AITC), which is mainly excreted as N-acetylcysteine conjugates (NAC) of AITC in urine. The effect of cooking cabbage on the excretion of NAC of AITC, and glutathione-S-transferase (GST) and uridine 5′-diphospho-glucuronosyl transferase (UGT) activity in rat liver and colon was investigated. Germ-free (GF) and human faecal microbiota-associated (HFM) rats were fed a control diet containing 20 % raw, lightly cooked, or fully cooked cabbage for 14 d. When plant myrosinase was present, excretion of NAC of AITC/24 h was increased by 1·4 and 2·5 times by the additional presence of microbial myrosinase after consumption of raw and lightly cooked cabbage respectively. When plant myrosinase was absent, as after consumption of fully cooked cabbage, excretion of the AITC conjugate was almost zero in GF and HFM rats. None of the cabbage diets modified hepatic GST activity. When microbiota was absent, colonic GST was 1·3-fold higher after fully cooked cabbage, and hepatic UGT was increased by 1·4–1·8-fold after all cabbage diets, compared with the control feed. There were no differences in GST or UGT following cabbage consumption when microbiota was present. It is possible that other constituents of cabbage, rather than metabolites of glucosinolates per se, may be responsible for changes in phase 2 enzyme activity. The main effect of cooking cabbage and altering colonic microbiota was on excretion of NAC of AITC.

The isothiocyanate, sulforaphane, has been implicated in the cancer-protective effects of brassica vegetables. When broccoli is consumed, sulforaphane is released from hydrolysis of glucoraphanin by plant myrosinase and/or colonic microbiota. The influence of meal composition and broccoli-cooking duration on isothiocyanate uptake was investigated in a designed experiment. Volunteers (n 12) were each offered a meal, with or without beef, together with 150 g lightly cooked broccoli (microwaved 2·0 min) or fully cooked broccoli (microwaved 5·5 min), or a broccoli seed extract. They received 3 g mustard containing pre-formed allyl isothiocyanate (AITC) with each meal. Urinary output of allyl (AMA) and sulforaphane (SFMA) mercapturic acids, the biomarkers of production of AITC and sulforaphane respectively, were measured for 24 h after meal consumption. The estimated yield of sulforaphane in vivo was about 3-fold higher after consumption of lightly cooked broccoli than fully cooked broccoli. Absorption of AITC from mustard was about 1·3-fold higher following consumption of the meat-containing meal compared with the non meat-containing alternative. The meal matrix did not significantly influence the hydrolysis of glucoraphanin and its excretion as SFMA from broccoli. Isothiocyanates may interact with the meal matrix to a greater extent if they are ingested pre-formed rather than after their production from hydrolysis of glucosinolates in vivo. The main influence on the production of isothiocyanates in vivo is the way in which brassica vegetables are cooked, rather than the effect of the meal matrix.