Greenhouse trials were conducted to determine the response of stevia to reduced-risk synthetic and nonsynthetic herbicides applied over-the-top post-transplant. In addition, field trials were conducted with stevia grown in a polyethylene mulch production system to determine crop response and weed control in planting holes to reduced-risk synthetic and nonsynthetic herbicides applied post-transplant directed. Treatments included caprylic acid plus capric acid, clove oil plus cinnamon oil, d-limonene, acetic acid (200 grain), citric acid, pelargonic acid, eugenol, ammonium nonanoate, and ammoniated soap of fatty acids. Stevia yield (dry aboveground biomass) in the greenhouse was reduced by all herbicide treatments. Citric acid and clove oil plus cinnamon oil were the least injurious, reducing yield by 16% to 20%, respectively. In field studies, d-limonene, pelargonic acid, ammonium nonanoate, and ammoniated soap of fatty acids controlled Palmer amaranth (>90% 1 wk after treatment (WAT). In field studies caprylic acid plus capric acid, pelargonic acid, and ammonium nonanoate caused >30% injury to stevia plants at 2 WAT, and d-limonene, citric acid, acetic acid, and ammoniated soap of fatty acids caused 18% to 25% injury 2 WAT. Clove oil plus cinnamon oil and eugenol caused <10% injury. Despite being injurious, herbicides applied in the field did not reduce yield compared to the nontreated check. Based upon yield data, these herbicides have potential for use in stevia; however, these products could delay harvest if applied to established stevia. In particular, clove oil plus cinnamon oil has potential for use for early-season weed management for organic production systems. The application of clove oil plus cinnamon oil over-the-top resulted in <10% injury 28 d after treatment (DAT) in the greenhouse and 3% injury 6 WAT postemergence-directed in the field. In addition, this treatment provided 95% control of Palmer amaranth 4 WAT.

Field studies were conducted to assess the efficacy of physical weed management of Palmer amaranth management in cucumber, peanut, and sweetpotato. Treatments were arranged in a 3 × 4 factorial in which the first factor included a treatment method of electrical, mechanical, or hand-roguing Palmer amaranth control and the second factor consisted of treatments applied when Palmer amaranth was approximately 0.3, 0.6, 0.9, or 1.2 m above the crop canopy. Four wk after treatment (WAT), the electrical applications controlled Palmer amaranth at least 27 percentage points more than the mechanical applications when applied at the 0.3- and 0.6-m timings. At the 0.9- and 1.2-m application timings 4 WAT, electrical and mechanical applications controlled Palmer amaranth by at most 87%. Though hand removal generally resulted in the greatest peanut pod count and total sweetpotato yield, mechanical and electrical control resulted in similar yield to the hand-rogued plots, depending on the treatment timing. With additional research to provide insight into the optimal applications, there is potential for electrical control and mechanical control to be used as alternatives to hand removal. Additional studies were conducted to determine the effects of electrical treatments on Palmer amaranth seed production and viability. Treatments consisted of electricity applied to Palmer amaranth at first visible inflorescence, 2 wk after first visible inflorescence (WAI) or 4 WAI. Treatments at varying reproductive maturities did not reduce the seed production immediately after treatment. However, after treatment, plants primarily died and ceased maturation, reducing seed production assessed at 4 WAI by 93% and 70% when treated at 0 and 2 WAI, respectively. Treatments did not have a negative effect on germination or seedling length.

Ammonium nonanoate is registered for weed control in certified organic cropping systems and may be useful to control cool-season weeds in organic Vidalia® sweet onion production. Ammonium nonanoate combined with tine-weeder cultivation was evaluated for weed control in organic onion in Georgia. There were no statistical interactions between main effects of herbicides and cultivation with a tine weeder for cool-season weed control and onion yield, indicating that ammonium nonanoate does not improve weed control compared with cultivation. Ammonium nonanoate at 4% and 6% did not adequately control weeds and onion yields were reduced. Ammonium nonanoate at 8% and 10% controlled cutleaf evening-primrose and lesser swinecress equal to the standard of d-limonene (14%), but the degree of control did not consistently protect onion yields from losses due to weeds. These results are in agreement with previous studies using clove oil and pelargonic acid. There is no advantage to using ammonium nonanoate for cool-season weed control in organic Vidalia® sweet onion production.

Weed management in the organic Vidalia® sweet onion production system is largely dependent on multiple cultivations with a tine weeder. Earlier research suggested cultivation with a tine weeder did not predispose onion bulbs to infection during storage. Trials were conducted from 2012 through 2014 near Lyons, GA, to determine the interactive effects of cultivation, weed removal, and a biofungicide on weed densities, onion yield, grade, and diseases of stored onion. Cultivation twice or four times at biweekly intervals with a tine weeder reduced densities of cutleaf evening-primrose, lesser swinecress, and henbit compared with the noncultivated control, although weeds surviving cultivation were very large and mature at harvest. Cultivation generally improved onion yields over the noncultivated control, except in 2014, when baseline weed densities were high and weeds surviving cultivation were numerous. Weeds removed by hand weeding improved onion yields, but that effect was independent of cultivation. Four applications of a biofungicide derived from giant knotweed had no effect on onion yield. Cultivation had no effect on incidence of the fungal disease botrytis neck rot, with inconsistent effects on the bacterial diseases center rot and sour skin. Weed removal with hand weeding did not affect diseases of stored onion. The biofungicide had no effect on diseases of stored onion. These results demonstrate the limitations of cultivation when cool-season weed infestations are dense. With no interactions among main effects, weed control and onion yield response to cultivation and hand weeding are independent. Cultivation for weed control is much less costly than hand weeding. With no interaction between the cultivation and weed removal main effects, it is not necessary to supplement tine weeder cultivation with costly hand weeding.

Woolly distaff thistle is a long-lived winter annual that threatens the ranching and dairy industries within the North Coast counties of California, particularly the organic producers. No peer-reviewed publications have documented effective control options or integrated management approaches for this species. We conducted two experiments, each replicated, in Marin County, California. The first compared several conventional herbicides at two timings and rates, while the second compared a conventional herbicide treatment with organic and integrated organic control methods, including an organic herbicide (mixture of capric and caprylic acids). Results of the conventional herbicide treatments showed most spring applications (March or April) of aminopyralid, aminocyclopyrachlor, clopyralid, and combinations of aminopyralid + triclopyr, or aminocyclopyrachlor + chlorsulfuron had greater than 99% control of woolly distaff thistle with fewer than 1.5 seedlings per 27-m2 plot by the end of the growing season. Higher rates were generally necessary to achieve the same level of control with winter (January) applications. In the organic herbicide treatments, the most consistent treatment was a combination of mowing followed by 9% (v/v) or the organic herbicide. This treatment was slightly less effective compared with aminopyralid but did have better than 95% control of woolly distaff thistle. The results of this study provide control options for both conventional and organic ranching practices where woolly distaff thistle is a problem.

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.

Sustainable weed management strategies are needed for organic orchard systems. A study was conducted in an almond orchard in Fresno, CA from 2009 to 2011. Treatment comparisons included steam, flame, and broad applications of either lemongrass oil or D-limonene. An untreated control was also included. The experimental design was a randomized complete block with four replications. Weekly evaluations on percent weed control were taken and weed biomass was sampled 4 to 8 wk after treatment (WAT). Weed control and biomass differed between seasons but, in general, steam and flame provided as much as 95% control 1 WAT. However, the effects lasted only 3 to 4 wk as new weeds emerged or the treated weeds overcame the suppressive effects of the thermal treatments. Weed biomass was 95% lower in the steam- and flame-treated plots compared with the untreated plots in summer. Both steam and flame were more effective on certain erect-growing broad-leaved weed species than on prostrate-growing weeds and grasses. Lemongrass oil provided very little weed control. However, D-limonene provided up to 95% weed control 1 WAT and in one experiment 53% control was observed up to 5 WAT. This herbicide also resulted in lower weed biomass than the untreated and the thermal-treated plots. Monthly applications of steam or flame or applications of D-limonene every 5 to 6 wk may have to be made to adequately suppress weeds in organic almond orchards. Cost estimates of propane use were $41 to 56 ha−1 and $26 ha−1 for the steam and flame treatments, respectively. The cost of D-limonene was estimated as $275 ha−1. To optimize weed control and costs, these tools may need to be used in combination rather than by themselves.

Intensive cultivation in organic peanut is partially effective, but in-row weed control remains problematic. In an attempt to improve in-row weed control, irrigated trials were conducted from 2011 to 2013 near Ty Ty, GA to determine the feasibility of early-season cultivation perpendicular to row direction using a tine weeder when integrated with other weed-control practices. Combinations of perpendicular cultivation (cultivation perpendicular to row direction), parallel cultivation (cultivation in the same direction of the rows), and banded applications of herbicides derived from natural sources were compared. Perpendicular cultivation improved overall weed control and peanut yield (two years of three), but this benefit was independent of weed control from any form of parallel cultivation. Additionally, tractor tire tracks from perpendicular cultivation across the rows repeatedly crushed peanut seedlings. Parallel cultivation with the tine weeder was generally more effective than parallel cultivation with sweeps, particularly for southern crabgrass and Texas millet. Herbicides derived from natural products were inconsistent in controlling dicot weeds, ineffective in controlling annual grasses, and did not protect peanut yield from weed interference.

Growing crops that exhibit a high level of competition with weeds increases opportunities to practice integrated weed management and reduce herbicide inputs. The recent development and market dominance of hybrid canola cultivars provides an opportunity to reassess the relative competitive ability of canola cultivars with small-grain cereals. Direct-seeded (no-till) experiments were conducted at five western Canada locations from 2006 to 2008 to compare the competitive ability of canola cultivars vs. small-grain cereals. The relative competitive ability of the species and cultivars was determined by assessing monocot and dicot weed biomass at different times throughout the growing season as well as oat (simulated weed) seed production. Under most conditions, but especially under warm and relatively dry environments, barley cultivars had the greatest relative competitive ability. Rye and triticale were also highly competitive species under most environmental conditions. Canada Prairie Spring Red wheat and Canada Western Red Spring wheat cultivars usually were the least competitive cereal crops, but there were exceptions in some environments. Canola hybrids were more competitive than open-pollinated canola cultivars. More importantly, under cool, low growing degree day conditions, canola hybrids were as competitive as barley, especially with dicot weeds. Under most conditions, hybrid canola growers on the Canadian Prairies are well advised to avoid the additional selection pressure inherent with a second in-crop herbicide application. Combining competitive cultivars of any species with optimal agronomic practices that facilitate crop health will enhance cropping system sustainability and allow growers to extend the life of their valuable herbicide tools.

Flaming can be an effective nonselective, nonchemical method of weed control. It has been more effective against broadleaf weeds than grasses. Experiments were conducted with a conveyor bench burner apparatus to evaluate flaming to kill broadleaf and grass seedlings at the 0- to 2- and 2- to 4-leaf stages. Most 0- to 2-leaf green foxtail seedlings were killed when flamed at 2, 4, and 6 km/h conveyor speed. A few plants survived when flamed at 8 km/h. Green foxtail seedlings at the 2- to 4-leaf stage were more tolerant to flaming than 0- to 2-leaf green foxtail, and substantial numbers of plants survived at all flaming speeds except 2 km/h. Barnyardgrass was more tolerant to flaming than green foxtail, and many 0- to 2- and 2- to 4-leaf seedlings survived after flaming. However, fresh weight of the live plants at 14 d after treatment was reduced. Some large crabgrass plants survived flaming at both growth stages. Flaming at 2 km/h reduced seedling number and fresh weight, but there was significant regrowth. Common ragweed was more susceptible to flaming at the 2- to 4-leaf stage than at the 0- to 2-leaf stage. Redroot pigweed and common lambsquarters were susceptible to flaming at both 0- to 2- and 2- to 4-leaf stages.

Cultivation is a proven means of weed control in organic peanut. However, weeds present in-row often escape control. Research trials were conducted in Ty Ty, GA to modify cultural practices to help suppress weed emergence in-row. Modified cultural practices were three row pattern/seeding rate combinations; twin rows (four rows on a seedbed) seeded at the recommended (1X) seeding rate that produced 13 seed m−1 in each row, twin rows seeded at the 2X seeding rate that produced 23 seed m−1 in each row, and wide rows (two rows on seedbed) seeded at the recommended seeding rate that produced 23 seed m−1. Four cultivation regimes were evaluated; cultivation with a tine weeder at weekly intervals for 6 wk, cultivation with a tine weeder at weekly intervals for 8 wk, scouring with a brush hoe at vegetative emergence followed by the tine weeder for 6 wk, and a noncultivated control. There were no interactions between row pattern/seeding rates and cultivation regimes for any parameter measured. There was inconsistent response of weed control and peanut yield to row pattern/seeding rates. Weed control and peanut yields were similar with tine weeding for 6 wk, 8 wk, or with the brush hoe followed by the tine weeder. Weed management in organic peanut was not improved by altering peanut cultural practices that facilitate quicker canopy closure, and the use of narrow row patterns should not be based on attempts to improve weed control in organic peanut. Narrow row patterns provide other benefits to organic peanut production and those attributes should influence decisions on the choice of row pattern, not weed control.

Weed control in organic peanut production is difficult and costly. Sweep cultivation in the row middles is effective, but weeds remain in the crop row, causing yield loss. Research trials were conducted in Ty Ty, GA to evaluate implements and frequencies of cultivation to improve in-row weed control in organic peanut. Implements were a tine weeder and power takeoff-powered brush hoe that targeted weeds present in the row. Frequencies of cultivation were at vegetative emergence of peanut (VE), 1 wk after VE (1wk), 2 wk after VE (2wk), sequential combinations of VE/1wk, VE/2wk, and VE/1wk/2wk. All plots were cultivated with a sweep cultivator to control weeds in row middles. The tine weeder tended to be easier to operate and performed more consistently than the brush hoe. Both implements performed best when initial cultivation was at VE. Delaying the initial cultivation reduced overall effectiveness. Plots with the best in-row weed control were hand-weeded once to control escapes and harvested for peanut yield. The best overall combination of weed control, minimal use of salvage hand-weeding, and maximum peanut yield resulted from sequential cultivation at VE/1wk using either the tine weeder or brush hoe, row middle sweep cultivation, and preharvest mowing.

Propane flaming could be an effective alternative tool for weed control in organic cropping systems. However, response of major weeds to broadcast flaming must be determined to optimize its proper use. Therefore, field experiments were conducted at the Haskell Agricultural Laboratory, Concord, NE in 2007 and 2008 using six propane doses and four weed species, including green foxtail, yellow foxtail, redroot pigweed, and common waterhemp. Our objective was to describe dose–response curves for weed control with propane. Propane flaming response was evaluated at three different growth stages for each weed species. The propane doses were 0, 12, 31, 50, 68, and 87 kg ha−1. Flaming treatments were applied utilizing a custom-built flamer mounted on a four-wheeler (all-terrain vehicle) moving at a constant speed of 6.4 km h−1. The response of the weed species to propane flaming was evaluated in terms of visual ratings of weed control and dry matter recorded at 14 d after treatment. Weed species response to propane doses were described by log-logistic models relating propane dose to visual ratings or plant dry matter. Overall, response of the weed species to propane flaming varied among species, growth stages, and propane dose. In general, foxtail species were more tolerant than pigweed species. For example, about 85 and 86 kg ha−1 were the calculated doses needed for 90% dry matter reduction in five-leaf green foxtail and four-leaf yellow foxtail compared with significantly lower doses of 68 and 46 kg ha−1 of propane for five-leaf redroot pigweed and common waterhemp, respectively. About 90% dry matter reduction in pigweed species was achieved with propane dose ranging from 40 to 80 kg ha−1, depending on the growth stage when flaming was conducted. A similar dose of 40 to 60 kg ha−1 provided 80% reduction in dry matter for both foxtail species when flaming was done at their vegetative growth stage. However, none of the doses we tested could provide 90% dry matter reduction in foxtail species at flowering stage. It is important to note that foxtail species started regrowing 2 to 3 wk after flaming. Broadcast flaming has potential for control or suppression of weeds in organic farming.

Weed control in organic peanut is difficult and lack of residual weed control complicates weed management efforts. Weed management systems using corn gluten meal in combination with clove oil and sweep cultivation were evaluated in a series of irrigated field trials. Corn gluten meal applied in a 30 cm band over the row at PRE, sequentially at PRE+2 wk after emergence, and PRE+2wk+4wk did not adequately control annual grasses and smallflower morningglory. Similarly, a banded application of clove oil applied POST did not adequately control weeds. The only treatment that improved overall weed control was sweep cultivation. Peanut yields were not measured in 2006 due to heavy baseline weed densities and overall poor weed control. Peanut yields were measured in 2007 and were not affected by any weed control treatment due to poor efficacy. While sweep cultivation improved weed control, weeds were controlled only in the row middles and surviving weeds in-row reduced peanut yield. Even when used in combination with sweep cultivation, corn gluten meal and clove oil were ineffective and offer little potential in a weed management system for organic peanut production.

Field experiments were carried out during two growing seasons at Adnan Menderes University, Faculty of Agriculture, in Aydın-Turkey to evaluate the weed control efficacy of olive processing waste (OPW) in okra, faba bean, and onion. OPW was incorporated into the soil prior to seeding at 10, 20, 30, and 40 tons (t)/ha. Non-treated plots and plots treated with trifluralin in okra and pendimethalin in faba bean and onion were used for comparison. OPW suppressed common purslane, redroot pigweed, and junglerice in okra; littleseed canarygrass, annual bluegrass, wild chamomile, and shepherd's-purse in faba bean and onion. OPW was in most cases equally as effective as soil herbicides; however, 10 t/ha provided sometimes lower efficacy than herbicides. OPW had no negative effects on okra and faba bean, while onion was negatively affected by doses over 30 t/ha. Overall, OPW can be applied at 10 to 20 t/ha doses for weed control with adequate crop safety.

Laboratory and greenhouse experiments were conducted to determine the herbicidal effect of plant-derived oils and to identify the active ingredient in an oil with herbicide activity. Twenty-five different oils were applied to detached leaves of dandelion in the laboratory. Essential oils (1%, v/v) from red thyme, summer savory, cinnamon, and clove were the most phytotoxic and caused electrolyte leakage resulting in cell death. Each of these essential oils in aqueous concentrations from 5 to 10% (v/v) plus two adjuvants (nonionic surfactant and paraffinic oil blend at 0.2% [v/v]) were applied to shoots of common lambsquarters, common ragweed, and johnsongrass in the greenhouse; shoot death occurred within 1 h to 1 d after application. Essential oil of cinnamon had high herbicidal activity, and eugenol (2-methoxy-4-[2-propenyl]phenol) was determined to be this oil's major component (84%, v/v). Dandelion leaf disk and whole-plant assays verified that eugenol was the active ingredient in the essential oil of cinnamon. Essential oils are extracted from plants and thus may be useful as “natural product herbicides” for organic farming systems.

Organic wheat and small grains are produced on relatively few acres in the inland Pacific Northwest. The objective of this study was to examine how the nitrogen (N) dynamics of cropping systems (CSs) produced during the transition phase impacted organic wheat yield and protein levels in the first 2 years of certified organic production. Certified organic spring wheat (SW) was produced in 2006 and winter wheat (WW) in 2007 following nine, 3-year transitional cereal, small grain and legume-intensive CSs. SW and WW following perennial alfalfa + oat/pea forage or 3 years of legume green manure tended to be more productive than wheat that followed systems that contained a small grain crop for at least 1 year during the transition. In addition to increasing soil N, well-established stands of forage and green manure provided adequate cover to reduce weed establishment prior to organic production. Effective weed control strategies were as important as increasing soil inorganic N levels for improving organic wheat production. Choice of crop type, cultivar and rotation is important in organic wheat systems and in this study, WW had better stand establishment, competition with weeds and higher overall yield than SW and would be a better-suited class of wheat for organic production in situations where spring weeds are the dominant problem. Regardless of CS or crop type, supplemental soil fertility (primarily N) during the organic production phase will be necessary to maintain high soil N levels and wheat yields in these dryland systems.

Organic farmers in western Canada rely on tillage to control weeds and incorporate crop residues that could plug mechanical weed-control implements. However, tillage significantly increases the risk of soil erosion. For farmers seeking to reduce or eliminate tillage, potential alternatives include mowing or using a roller crimper for terminating green manure crops (cover crops) or using a minimum tillage (min-till) rotary hoe for mechanically controlling weeds. Although many researchers have studied organic crop production in western Canada, few have studied no-till organic production practices. Two studies were recently conducted in Saskatchewan to determine the efficacy of the following alternatives to tillage: mowing and roller crimping for weed control, and min-till rotary hoeing weed control in field pea (Pisum sativum L.). The first study compared mowing and roller crimping with tillage when terminating faba bean (Vicia faba L.) and field pea green manure crops. Early termination of annual green manure crops with roller crimping or mowing resulted in less weed regrowth compared with tillage. When compared with faba bean, field pea produced greater crop biomass, suppressed weeds better and had less regrowth. Wheat yields following pea were not affected by the method of termination. Thus, this first study indicated that roller crimping and mowing are viable alternatives to tillage to terminate field pea green manure crops. The second study evaluated the tolerance and efficacy of a min-till rotary harrow in no-till field pea production. The min-till rotary hoe was able to operate in no-till cereal residues and multiple passes did not affect the level of residue cover. Field pea exhibited excellent tolerance to the min-till rotary hoe. Good weed control occurred with multiple rotary hoe passes, and pea seed yield was 87% of the yield obtained in the herbicide-treated check. Therefore, this second study demonstrated that min-till rotary hoeing effectively controls many small seeded annual weeds in the presence of crop residue and thus can reduce the need for tillage in organic-cropping systems.