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.

Use of PRE herbicides for control of annual grassy weeds during commercial sod production has been limited. Research was conducted from 2010 to 2013 evaluating the effects of pendimethalin (3.36 kg ai ha−1), dithiopyr (0.56 kg ai ha−1), prodiamine (0.6 kg ai ha−1), oxadiazon (3.36 kg ai ha−1), prodiamine + sulfentrazone (0.84 + 0.41 kg ai ha−1), dimethenamid-P (1.68 kg ai ha−1), and indaziflam (0.03 and 0.05 kg ai ha−1) applications at sprigging on the establishment rate and tensile strength of ‘Tifway' hybrid bermudagrass sod at harvest (377 d after sprigging). All herbicides increased the days required to reach 50% hybrid bermudagrass cover compared with the nontreated control. Days required to reach 50% hybrid bermudagrass cover were lowest for oxadiazon and prodiamine (39 to 44 d), greatest for both rates of indaziflam (65 to 141 d), with dimethenamid-P, prodiamine plus sulfentrazone, pendimethalin, and dithiopyr ranking intermediate (45 to 63 d). Both rates of indaziflam reduced sod tensile strength at harvest compared with the nontreated control during a single year of the study; no other differences in sod strength due to herbicide treatment were detected at any time.

‘Replay' and ‘JS501’ perennial ryegrass cultivars have been conventionally bred for reduced sensitivity to glyphosate, potentially allowing the herbicide to be used for selective weed control in overseeded bermudagrass. Field experiments were conducted to evaluate optimal glyphosate application rate, regime (single and sequential applications), and timing for annual bluegrass control in bermudagrass overseeded with these cultivars. Additionally, greenhouse experiments were conducted to compare the sensitivity to glyphosate of Replay and JS501 to susceptible cultivars ‘Caddy Shack' and ‘Top Gun II' through log-logistic rate-response analysis. In field experiments, only two treatments resulted in > 90% annual bluegrass control and < 25% perennial ryegrass injury. These two treatments were a single application of 280 g ae ha−1 glyphosate in January and 140 g ha−1 followed by an additional 140 g ha−1 applied in January. Perennial ryegrass cultivars were compared using 50% inhibition (I50) values, i.e. 50% visible estimates of injury or 50% reduction in clipping weight. I50 values obtained 6 wk after treatment from injury data were 2.56, 2.64, 0.81, and 0.84 g ha−1 glyphosate for Replay, JS501, Caddy Shack, and Top Gun II, respectively. Replay and JS501 were similar in sensitivity to glyphosate and were up to four times more tolerant than Caddy Shack and Top Gun II across rating dates and data types.

Tall fescue is a commonly used turfgrass in the temperate and transition zone areas of the United States. During hot, humid summers, tall fescue is under stress and is susceptible to Rhizoctonia solani (brown patch) infection, causing turf thinning, leading to encroachment from weeds, such as bermudagrass. Field trials were established to evaluate the effect of mowing height and fertility programs on disease severity and bermudagrass encroachment in tall fescue. Mowing at 10 cm resulted in less bermudagrass encroachment than did a 6-cm mowing height. Increasing the nitrogen fertilization level from 49 to 171 and 220 kg N ha−1 generally led to more bermudagrass encroachment at the 6-cm, but not the 10-cm, mowing height. Plots receiving 220 kg N ha−1 annually at the 6-cm mowing height had the most brown patch. Turfgrass cover was greatest in plots mowed at 10 cm and receiving 220 kg N ha−1 annually.

Propane flaming could be an alternative tool for PRE control or suppression of early-emerging weeds in organic and conventional crops. The objective of this study was to test the tolerance of selected early-season weeds to broadcast flaming in no-till systems. Four winter annuals (tansy mustard, henbit, cutleaf evening primrose, and field pennycress), one summer annual (common lambsquarters), and one perennial (dandelion) species were included in the study. Except for dandelion, the response to propane flaming was evaluated at two growth stages. Flaming treatments were applied using an all-terrain-vehicle-mounted flamer moving 4.8 km h−1, and propane pressure was adjusted to deliver doses of 0 (nonflamed control), 22, 34, 48, 67, and 90 kg ha−1. The response of each species to propane doses was described by log-logistic models based on visual ratings of weed control and dry matter reduction. Response to broadcast flaming varied among species and growth stages. Common lambsquarters, tansy mustard, and henbit were more susceptible to flaming than cutleaf evening primrose, field pennycress, and dandelion. On the basis of visual ratings, propane doses between 54 and 62 kg ha−1 effectively controlled (90% control) common lambsquarters at the early growth stage (five-leaf), tansy mustard at both growth stages (nine-leaf and flowering), and henbit (flowering). However, a higher propane dose (> 80 kg ha−1) was necessary to obtain 90% control of common lambsquarters in later growth stage (11-leaf) and early growth stage of henbit (nine-leaf). Cutleaf evening primrose, field pennycress, and dandelion exhibited higher levels of tolerance to broadcast flaming. A 90% control of these species was not achieved even with the highest propane dose (90 kg ha−1) utilized in the study. Results of this study indicate that a single application of broadcast flaming can be an effective tool for controlling tansy mustard, henbit, and common lambsquarters and temporary suppression of cutleaf evening primrose, field pennycress, and dandelion.

Abrasive weed control is a novel weed management tactic that has great potential to increase the profitability and sustainability of organic vegetable cropping systems. The objective of this study was to determine the effect of air-propelled organic abrasive grits (e.g., organic fertilizers) on weed seedling emergence and growth and vegetable crop growth. A series of thirteen greenhouse trials were conducted to determine the susceptibility of weeds to abrasive weed control with one of six organic materials including: corn cob grits, corn gluten meal, greensand fertilizer, walnut shell grits, soybean meal, and bone meal fertilizer. In addition, crop injury was quantified to determine the potential utility of each organic material as abrasive grits in tomato and pepper cropping systems. Of the six organic materials, corn gluten meal, greensand fertilizer, walnut shell grits, and soybean meal provided the broadest range of POST weed control. For example, one blast of corn gluten meal and greensand fertilizer reduced Palmer amaranth (one-leaf stage) seedling biomass by 95 and 100% and green foxtail (one-leaf stage) biomass by 94 and 87%, respectively. None of the organic materials suppressed weed seedling emergence when applied to the soil surface, suggesting that residual weed control with abrasive grits is unlikely. Tomato and pepper stems were relatively tolerant of abrasive grit applications, though blasting with select materials did increase stem curvature in tomato and reduced biomass (corn cob grit) and relative growth rate (corn gluten meal and greensand) in pepper. Results suggest that organic fertilizers can be effectively used as abrasive grits in vegetable crops, simultaneously providing weed suppression and supplemental crop nutrition. Field studies are needed to identify cultural practices that will increase the profitability of multifunctional abrasive weed control in organic specialty crops.

Field trials were conducted to evaluate the effect of simulated glyphosate drift rates applied to two non-irrigated potato cultivars in the late tuber bulking stage grown for potato seed production. Mother plants receiving a sublethal glyphosate application had similar yields regardless of the year or cultivar. ‘Red LaSoda' seed pieces visually evaluated the following spring had more sprout inhibition from glyphosate-treated plots. With ‘Russet Burbank', only seed pieces from mother plants that received more than 18 g ha−1 glyphosate showed sprout inhibition. Total yield reductions the year following glyphosate treatments were attributed to fewer and smaller tubers from plants that did not emerge or were delayed in emergence. Red LaSoda seed pieces from mother plants receiving ≥ 71 g ha−1 glyphosate yielded less than the nontreated. In 2005, Russet Burbank seed pieces from mother plants receiving ≥35 g ha−1 glyphosate had reduced yields, whereas in 2006, all glyphosate treatments reduced total yield compared with the nontreated.

Corn gluten meal (CGM) and white mustard seed meal (MSM) can release biologically active allelochemicals and have been demonstrated to be useful as PRE alternative weed control products. The objective of this study was to compare the effects of CGM and MSM on the emergence and aboveground dry weight of five broadleaf and two grass weed species. Greenhouse experiments were conducted using 26 by 53 cm plastic trays filled with a mix of field soil and potting soil (4 : 1 by wt). CGM and MSM were mixed with 1.5 kg of soil mix and applied at rates equivalent to 2,240, 4,480, and 6,720 kg ha−1. Overall, MSM was more effective than CGM for controlling weeds. Averaged over application rates and compared to the nontreated control, emergence rates were 17, 27, and 34% for kochia, common lambsquarters, and barnyardgrass, respectively, in CGM-amended soil, and 14, 13, and 6% for kochia, common lambsquarters, and barnyardgrass, respectively, in MSM-amended soil. Averaged over application rates, green foxtail and common lambsquarters aboveground dry biomass were 40 and 25% of the nontreated control, respectively, in CGM-amended soil. Green foxtail and common lambsquarters shoot biomass in MSM-amended soil was 13 and 5% of the nontreated control, respectively. Significant interactions were observed for meal by rate on redroot pigweed seedling emergence and redroot pigweed, barnyardgrass (Moscow), and annual sowthistle (Moscow) aboveground dry biomass. These interactions can be attributed to the fact that herbicidal effects were less evident in response to higher application rates using MSM compared to higher CGM application rates. Overall, this greenhouse study indicates MSM is more effective than or at least equal to CGM for broadleaf and grass weed control at the same application rate.

Small broomrape is a holoparasitic plant that attaches to the roots of red clover as well as several other host plants. Hosts and false hosts produce stimulants that induce small broomrape germination but small broomrape does not attach to a false host. Wheat has been identified as a false host for small broomrape; therefore, studies were conducted to investigate the effect of red clover and wheat root exudates on small broomrape germination. In one study, the effect of exudates from red clover and wheat at multiple growth stages on small broomrape germination was evaluated. Red clover induced small broomrape germination at all growth stages tested but was greatest (78%) in the presence of exudates from red clover at the three-trifoliolate stage. Maximum small broomrape germination was 25% when exposed to exudates produced by one-leaf-stage wheat. In a second study, the relationship between small broomrape germination and host growth condition was evaluated using root exudates from red clover or wheat grown under several temperature conditions for either 4 or 8 wk. For the different temperatures, there were no differences in small broomrape germination when exudates of red clover grown for 4 wk were used. Small broomrape germination was reduced when exposed to exudates from red clover plants grown for 8 wk at 10 C compared with plants grown at 15, 20, and 25 C. Differences in small broomrape seed germination were observed with temperature under which wheat was grown for 4 wk, but not for 8 wk. Although wheat exudates resulted in less small broomrape seed germination than red clover exudates, growing wheat as a false host in a small broomrape-infested field could be an important component of an integrated management plan.

Cantaloupe and watermelon growers in the southeastern United States use a system of hybrid transplants grown on narrow low-density polyethylene (LDPE) mulch-covered seedbeds with overhead irrigation and use the mulch cover for only one crop. LDPE mulches are costly to remove from the field and dispose. Biodegradable mulches that eliminate removal and disposal costs would be of significant benefit, provided that weeds are adequately suppressed. Cotton gin trash is a biodegradable waste product, composed of fiber fragments and seed pieces. Using a proprietary process, cotton gin trash can be chopped, pressed, and heated into a loose mat and stored on a continuous roll. Preliminary studies were conducted in 2010 and 2011 to determine if rolled cotton fiber mulch made from gin trash could be applied as a seedbed cover using conventional application equipment and adequately suppress weeds. Mulching materials (rolls 91 cm wide) were applied with a mulch layer that produced a finished seedbed 40 cm wide. ‘Athena' cantaloupe and ‘Crimson Sweet' watermelon were transplanted using a waterwheel transplanter. Mulching materials included rolled cotton fiber mulch sprayed with boiled linseed oil after mulch application, rolled cotton fiber mulch sprayed with black latex paint, black LDPE, and bare ground. Herbicide treatments included ethalfluralin, halosulfuron, and glyphosate applied as directed spray and nontreated with herbicides. Rolled cotton fiber mulch was easily applied with a conventional mulch layer with no modification and minimal adjustment, producing no tears or holes. Biodegradable cotton fiber mulch treated with boiled linseed oil or black latex paint suppressed weeds equally well as LDPE and all were better than bare-ground plots. Herbicides improved control of all weeds over the nontreated control and this effect was independent of weed suppression provided by seedbed mulches. Cantaloupe and watermelon yields were not affected by seedbed mulches, but were increased by weed control provided by herbicides.

There are limited PRE herbicide options available to provide residual weed control in sweet corn grown on organic soils in the Everglades Agricultural Area (EAA). Field studies were established to determine the efficacy of PRE applied saflufenacil + dimethenamid-P at six rates ranging from 10 + 88 to 319 + 2802 g ai ha−1 on weed control and sweet corn tolerance on organic soils in the EAA in 2011 and 2012. Saflufenacil + dimethenamid-P is a premix recently labeled for PRE weed control in field corn at 50 + 438 to 90 + 788 g ha−1 depending on soil texture. There was no phytotoxic effect of PRE applied saflufenacil + dimethenamid-P on sweet corn. At 42 d after treatment, common lambsquarters, common purslane, and spiny amaranth were controlled 90% with saflufenacil + dimethenamid-P at 58 + 508, 71 + 622, and 58 + 512 g ha−1, respectively. Sweet corn yield at 95% of the weed-free yield was estimated to be obtained at 69 + 606 g ha−1 of saflufenacil + dimethenamid-P. Our results show that saflufenacil + dimethenamid-P at 69 + 606 to 71 + 622 g ha−1 controlled three common weeds and maintained acceptable sweet corn yield. Labeled rates of saflufenacil + dimethenamid-P for field corn on mineral soils were adequate for weed control in sweet corn on organic soils.

Cholla infestations can be problematic on rangelands in North America, Australia, Africa, and Europe, and treatment options for this plant are limited because of its ability to resprout from broken stem fragments. We investigated dragged-rail treatments, where iron rails are dragged across the rangeland by tractor and knock plants over while uprooting them, as a treatment option for tree cholla in southeast New Mexico. Railing effectively controlled tree cholla plants over 0.5 m tall, but did not effectively control plants smaller than 0.5 m. Nevertheless, treatment did effectively reduce overall cholla density: Treated areas averaged 40 to 50 plants ha−1, whereas nontreated areas averaged over 350 plants ha−1. Railing can be an effective means of cholla control, especially if followed by another treatment, such as prescribed fire, that is known to be effective against the smaller sizes of cholla.