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.

Field studies were conducted from 2009 to 2011 in Oregon and from 2006 to 2008 in California to evaluate the response of various crops to imazosulfuron soil residues 91 to 731 d after application (DAA). Imazosulfuron rates applied in Oregon were 224 or 450 g ai ha−1 PRE, sequential 224 g ha−1 PRE and POST, or 450 g ha−1 as a tank mixture with PRE applied S-metolachlor at 1,060 g ai ha−1 followed by 224 g ha−1 POST to potato. Imazosulfuron was applied on bare ground PRE at 224, 336, and 450 g ha−1 and applied sequentially at 450 g ha−1 in California. Sugar beet planted 91 to 364 and 458 to 731 DAA were injured 83 to 94% and 54 to 78% among imazosulfuron rates and application timing in 2007 and 2008, respectively. Alfalfa planted 701 DAA at rates greater than 224 g ha−1 was injured, and the forage yield was reduced. Onion, spinach, carrot, and broccoli were also injured by imazosulfuron residues when planted 91 to 731 DAA, regardless of the rate or interval before planting. Imazosulfuron applied at 224 to 450 g ha−1 458 to 731 d before planting head lettuce resulted in moderate injury that did not reduce fresh-weight yield. The results indicated that imazosulfuron residues in the soil have the potential to injure many rotational specialty crops for 2 yr or more in soils with pH > 6.9.

In 2010, a grower survey was administered to 1,299 growers in 22 states to determine changes in weed management in the United States from 2006 to 2009. The majority of growers had not changed weed management practices in the previous 3 yr; however, 75% reported using weed management practices targeted at glyphosate-resistant (GR) weeds. Growers were asked to rate their efforts at controlling GR weeds and rate the effectiveness of various practices for controlling/preventing GR weeds regardless of whether they were personally using them. Using the herbicide labeled rate, scouting fields, and rotating crops were among the practices considered by growers as most effective in managing GR weeds. Sixty-seven percent of growers reported effective management of GR weeds. Between the 2005 and 2010 Benchmark surveys, the frequency of growers using specific actions to manage GR weeds increased markedly. Although the relative effectiveness of practices, as perceived by growers, remained the same, the effectiveness rating of tillage and the use of residual and POST herbicides increased.

Ground ivy and khakiweed are troublesome broadleaf weeds of warm-season turfgrass. Field studies were conducted in Tennessee (TN) and Texas (TX) from 2008 to 2010 to evaluate the efficacy of sulfentrazone plus metsulfuron and carfentrazone plus metsulfuron tank mixtures compared with metsulfuron alone for control of ground ivy and khakiweed. In TN, sulfentrazone plus metsulfuron and carfentrazone plus metsulfuron provided accelerated control of ground ivy compared with metsulfuron alone. Over a 2-yr period, ground ivy control with metsulfuron at 10, 21, and 42 g ai ha−1 ranged from 0 to 5% 7 d after treatment (DAT) and 12 to 60% 14 DAT. Ground ivy control with mixtures of sulfentrazone plus metsulfuron ranged from 40 to 72% 7 DAT and 87 to 100% 14 DAT. Similarly, carfentrazone plus metsulfuron controlled ground ivy 5 to 32% 7 DAT and 23 to 93% 14 DAT. In TX, carfentrazone plus metsulfuron and sulfentrazone plus metsulfuron controlled khakiweed greater than metsulfuron alone 7 and 14 DAT as well. Few differences in ground ivy and khakiweed control were detected 56 DAT because metsulfuron applied alone at 21 g ai ha−1 controlled both weeds > 77%, similar to each mixture. These data indicate that when applied in mixtures, sulfentrazone and carfentrazone accelerate ground ivy and khakiweed control with metsulfuron but do not affect long-term efficacy.

Spreading dogbane is a troublesome weed of wild blueberry fields. Field studies were conducted in 2008 and 2009 to evaluate efficacy of different herbicides and application techniques on spreading dogbane as well as blueberry tolerance. Results indicated that summer-broadcast nicosulfuron at 25 g ai ha−1 with 0.5% v/v blend of surfactant with petroleum hydrocarbons suppressed (> 60%) spreading dogbane at three of four sites. Spot sprays with dicamba at 1 kg ae ha−1 effectively controlled (> 80%) spreading dogbane with minimal (19 to 23%) blueberry damage at three of four sites. Glyphosate spot sprays at 5 g ae L−1 water provided more effective and longer control than hand pulling. Wiping with glyphosate at 154 g ae L−1 water or wiping triclopyr at 29 g ae L−1 water onto the shoots is also an effective control method for localized patches of spreading dogbane. Although low to moderate crop damage may accompany these techniques, it may still be tolerable for growers to apply these options to limit long-term yield loss caused by spreading dogbane.

The synergistic interaction between mesotrione, a hydroxyphenylpyruvate dioxygenase (HPPD)-inhibiting herbicide, and atrazine, a photosystem II (PS II)-inhibiting herbicide, has been identified in the control of several weed species. A series of dose–response studies examined the synergistic effect of these herbicides on a susceptible (S) wild radish population. The potential for this interaction to overcome target-site psbA gene-based atrazine resistance in a resistant (R) wild radish population was also investigated. Control of S wild radish with atrazine was enhanced by up to 40% when low rates (1.0 to 1.5 g ha−1) of mesotrione were applied in combination. This synergistic response was demonstrated across a range of atrazine–mesotrione rate combinations on this S wild radish population. Further, the efficacy of 1.5 g ha−1 mesotrione increased control of the R population by a further 60% when applied in combination with 400 g ha−1 of atrazine. This result clearly demonstrated the synergistic interaction of these herbicides in overcoming the target-site resistance mechanism. The mechanism responsible for the observed synergistic interaction between mesotrione and atrazine remains unknown. However, it is speculated that an alternate atrazine binding site may be responsible. Regardless of the biochemical nature of this interaction, evidence from whole-plant bioassays clearly demonstrated that synergistic herbicide combinations improve herbicide efficiency, with lower application rates required to control weed populations. This, combined with the potential to overcome psbA gene-based triazine resistance, and, thereby, regain the use of these herbicides, will result in more sustainable herbicide use.

Citron melon is a monoecious and hairy annual vine commonly found in citrus orchards and cotton and peanut fields. There is limited information available on citron melon control with PRE- and POST-applied herbicides in Florida citrus. Experiments were conducted to evaluate the response of citron melon to 11 PRE and 18 POST herbicides under greenhouse conditions. Indaziflam applied PRE at 0.095 kg ai ha−1 resulted in 13% citron melon emergence at 14 d after treatment (DAT). The majority of PRE herbicides did not affect emergence at 14 DAT. Efficacy of PRE herbicides at 21 DAT resulted in > 90% control of citron melon with bromacil, premix formulation of bromacil + diuron, flumioxazin, indaziflam at 0.073 and 0.095, norflurazon, and simazine. Citron melon control was < 30% 21 DAT following PRE-applied diuron, oryzalin, and flazasulfuron. Control of citron melon varied by POST herbicides and growth stage. Regardless of citron melon growth stage, glyphosate, glufosinate, saflufenacil, paraquat, and flumioxazin provided > 90% at 7 and 14 DAT. Carfentrazone, flazasulfuron, imazapic, pyrithiobac-Na, rimsulfuron, trifloxysulfuron, and premix of 2,4-D + glyphosate controlled citron melon at least 90% when applied to two- to four-leaf plants. Control was reduced when application was delayed to the six- to eight-leaf stage. Bentazon and halosulfuron controlled citron melon 11 to 31% regardless of growth stage. Biomass of citron melon at 14 DAT was reduced > 50% in all herbicide treatments except with bentazon and halosulfuron applied at both stages, and dicamba, mesotrione, imazapic, and rimsulfuron applied to six- to eight-leaf citron melon. The results of this study indicate that citron melon can be adequately controlled with several PRE- or POST-applied herbicides; however, research is required to evaluate PRE followed by POST programs or their tank mixtures for season-long control of citron melon under field conditions.

Glyphosate-resistant (GR) sugarbeet is commonly grown in rotation with GR corn, but there is limited information relating to volunteer GR corn interference or control in GR sugarbeet. Field studies were conducted near Lingle, WY and Scottsbluff, NE in 2009 and 2010 to quantify sugarbeet yield loss in response to volunteer corn density and duration of interference, and determine appropriate control practices for use in GR sugarbeet. Hybrid corn resulted in a similar competitive effect on sugarbeet sucrose yield as clumps of F2 volunteer corn. Clumps of volunteer corn were controlled 81% compared with 73% for individual plants. Linear regression indicated sucrose yield loss of 19% for each corn plant m−2 up to 1.7 plants m−2 at three of four experimental sites. Pearson correlation coefficients between percentage sucrose yield loss and proportion of sunlight reaching the top of the sugarbeet canopy ranged from −0.42 to −0.92. The duration of corn interference required to cause a 5% sucrose yield loss (YL5) ranged from 3.5 to 5.9 wk after sugarbeet emergence (WAE) for hand-weeding or herbicide removal, respectively, due to the length of time herbicide-treated volunteer corn continued to shade sugarbeet plants. Differences between herbicide and hand-removal methods were attributed to the time lag between when the treatments were applied and when the corn ceased to block light from the sugarbeet canopy. Sethoxydim generally provided less volunteer corn control compared with either quizalofop or clethodim, and control increased with the addition of an oil adjuvant. If a grower were to implement a volunteer corn control practice 3.5 WAE, economic sugarbeet yield loss would be avoided. In eastern Wyoming and western Nebraska, the sugarbeet crop will typically have between four to eight true leaves at 3.5 WAE, and therefore this would be an optimal time to control volunteer corn. If volunteer corn is being hand weeded, the YL5 estimate will also increase, and thus the window of time to control volunteer corn would be wider.

Largeleaf lantana is a perennial shrub that commonly infests pastures, roadsides, and natural areas. Many experiments have been conducted to manage this weed, but few successful herbicides have been found. Little information is available for the effectiveness of fluroxypyr, aminopyralid, or aminocyclopyrachlor on largeleaf lantana. Experiments were conducted in central Florida on dense, natural infestations of largeleaf lantana. Aminopyralid (0.12 kg ha−1), fluroxypyr (0.56 kg ha−1), and aminocyclopyrachlor (0.2 kg ha−1) were either applied in the fall (approximately 2 mo before frost) or in the fall followed by a spring application. Aminopyralid was ineffective on largeleaf lantana, and neither one nor two applications resulted in > 20% control 1 yr after treatment (YAT). Fluroxypyr applied once in the fall resulted in 12% control at 1 YAT, but two applications resulted in 80% control after 1 yr. The combination of fluroxypyr + aminopyralid, applied twice, resulted in approximately 90% control 1 YAT. A single application of fluroxypyr + aminopyralid failed to provide greater than 20% control. Conversely, aminocyclopyrachlor applied once in the fall provided 98% control of largeleaf at 1 YAT. Where aminocyclopyrachlor was applied twice, largeleaf lantana control was 100%. From these data, largeleaf lantana can be effectively controlled by two applications of fluroxypyr, two applications of fluroxypyr + aminopyralid, or a single application of aminocyclopyrachlor. Individual plant treatments were also investigated using herbicides applied as basal or cut surface applications. At 1 YAT, only triclopyr + aminopyralid provided > 90% control as a basal application. The other herbicide combinations appeared to be effective earlier, but significant regrowth had occurred by 1 YAT. Cut surface applications were similar with triclopyr + aminopyralid and triclopyr + fluroxypyr providing effective control. Neither triclopyr alone nor imazapyr provided effective control for 1 YAT with basal or cut surface applications.

Field research was conducted near Saint Joseph, LA, in 2008 and 2009 to evaluate Texasweed interference in drill-seeded rice. Season-long Texasweed interference at 1 plant m−2 was estimated to cause 5% yield loss. Yield loss from 10 and 50 plants m−2 was 31 and 61%, respectively. Yield loss was primarily due to a reduction in effective tillers per square meter. Thousand-grain weight of rice was not affected by season-long Texasweed interference. Path analysis indicated yield component compensation, i.e., a reduction in effective tillers per square meter probably caused an increase in grains per panicle. However, that effect was not strong enough to reverse the detrimental effect of reduced effective tillers per square meter on rice yield. The critical period of Texasweed interference to cause more than 5% yield loss was estimated to be between 0 and 6 wk after rice emergence.

Methiozolin selectively controls annual bluegrass in cool-season turfgrasses, and practitioners may wish to reseed desirable species in treated areas. Field experiments were conducted to evaluate reseeding intervals for creeping bentgrass, perennial ryegrass, and tall fescue following methiozolin applications. Turfgrass establishment varied for species, application timing (0, 2, 4, or 6 wk before seeding, WBS), and rates tested (0.56, 1.12, or 2.24 kg ai ha−1). Reductions in turf cover suggest that seeding of creeping bentgrass, perennial ryegrass, and tall fescue should be delayed 2 wk after methiozolin treatments at 0.56 kg ha−1. However, reseeding should be delayed after methiozolin treatments at 1.12 kg ha−1 for approximately 4, 4, and 2 wk for creeping bentgrass, perennial ryegrass, and tall fescue, respectively. Similarly, establishment was reduced on all dates from the nontreated after 2.24 kg ha−1 was applied at 4 WBS, suggesting that reseeding should be delayed for at least 6 wk on all three species at the high rate.

Fruit trees in orchards of the mid-Atlantic region of the United States are often planted in vegetation-free rows alternating with grass alleys. Grass managed to suppress weeds but to compete minimally with fruit trees may be an alternative to herbicide and tillage. This research was conducted in the greenhouse and field to assess five different grasses that may suppress weeds without reducing yield of fruit trees. In the greenhouse with high seeding rates, red fescue competed more effectively than did chewings fescue, tall fescue, and perennial ryegrass with three weeds (damesrocket, cornflower, and chicory). However, with reduced seeding rates, similar to rates used in the field, grass competitiveness with weeds was similar between red fescue, tall fescue, and perennial ryegrass. Similar results were obtained during a 4-yr field experiment; roughstalk bluegrass competed least effectively with weeds but the other four grasses provided similar weed suppression—generally providing as much weed suppression as traditional herbicides. None of the candidate grasses significantly reduced yields of 10-yr-old apple and peach trees, although fruit size was affected by some grasses. The grass that was least suppressive of yield, roughstalk bluegrass, was the least effective in controlling weeds. Annual mowing in combination with four of the grasses tested is one option to manage the orchard floor with reduced herbicides, but fruit size may decrease.

The weed management needs of organic producers are unique because they rely primarily on cultural and physical management strategies. Recommendations regarding commonly used tools for weed management could benefit this sector of agriculture. The objectives of this research were to (1) determine the optimum time of day for propane flaming to achieve maximum weed reductions while minimizing corn damage; (2) assess whether flaming, rotary hoeing, or a combination of the two tools best manages early-season weeds without injuring dry beans; and (3) evaluate the use of growing degree days (GDD) to optimize rotary hoe timing. Experiments were carried out between 2006 and 2009 in Hickory Corners and East Lansing, MI. Flaming reduced broadleaf weed densities by at least 82% when done in the morning to midafternoon but only reduced densities by 58% when weeds were flamed in the evening. Common lambsquarters, redroot pigweed, and velvetleaf were easier to control by flaming than common ragweed and common purslane. Flaming did not reduce grass weed densities. When comparing flaming and rotary hoeing, the two treatments that achieved the highest level of weed control and highest dry bean yields were flaming prior to bean emergence followed by two rotary hoeings and rotary hoeing three times (no flaming). However, the added cost of the flamer may only be justified when wet conditions make rotary hoeing ineffective. Flaming dry beans POST resulted in significant injury and yield reductions of 60%; therefore this practice is not recommended. Timing rotary hoe passes every 300 GDD (base 3.3 C) from the time of soybean or dry bean planting resulted in fewer passes compared with the 7-d or 150 GDD treatments, while maintaining similar levels of weed control and yields similar to the weed-free treatment in 1 of 2 yr for each crop.

Calendula is an alternative oilseed crop whose seed oil is valued as a substitute for tung oil and a replacement for petroleum-based volatile organic compounds in paints and other coatings. Calendula tolerances to most POST-applied herbicides are unknown. Two POST-applied herbicides were tested for tolerance by calendula. Imazamethabenz at 0.44 kg ai ha−1 plus surfactant and desmedipham plus phenmedipham at 0.36 + 0.36 kg ai ha−1 were tolerated by calendula, but the latter herbicide must be applied after the four–leaf-pair stage of growth to avoid severe injury. Neither herbicide adversely affected calendula seed yield if applied at the four–leaf-pair stage. Because these herbicides can control several weed species, calendula tolerance to them may encourage more growers and crop advisors to test this new oilseed crop on commercial farms.

Yellow nutsedge is a problematic weed in polyethylene-mulched tomato production. Soil fumigation with methyl bromide is the most effective method of controlling nutsedges, but because of ozone depletion, the phase-out of methyl bromide has complicated nutsedge control in polyethylene-mulched tomato and other vegetable crops. Plants belonging to the Brassicaceae family produce glucosinolates, which upon tissue decomposition generate biocidal isothiocyanates and therefore can be used as a biological alternative for yellow nutsedge control. Field experiments were conducted in 2007 and 2009 to study the influence of soil amendment with ‘Seventop’ turnip cover crop on the interference of yellow nutsedge planted at 0, 50, and 100 tubers m−2 in raised-bed polyethylene-mulched tomato production. There was no advantage of soil amendment with Seventop on reducing yellow nutsedge interference in polyethylene-mulched tomato. Regardless of soil amendment, increasing initial tuber density from 50 to 100 tubers m−2 increased yellow nutsedge shoot density, shoot dry weight, and tuber production at least 1.7, 1.6, and 1.6 times, respectively. As a result, tomato canopy width, shoot dry weight, and marketable yield decreased with increasing initial tuber densities. However, increased tuber density had minimal impact on tomato height. Relative to weed-free plots, interference of yellow nutsedge at 50 and 100 tubers m−2 reduced marketable yield of tomato up to 32 and 49%, respectively. Shading of the middle and lower portion of tomato plants by yellow nutsedge shoots could be the major factor for reducing tomato growth and yield in weedy plots. It is concluded that soil amendment with Seventop turnip is not a viable option for reducing yellow nutsedge interference at 50 and 100 tuber m−2 in polyethylene-mulched tomato.

Thermal heat has been utilized for nonselective weed control methods. These methods are highly variable in application and efficacy. One effective weed–seed-control determining factor is achieving the thermal death point of targeted weed seeds. The thermal death point varies by weed species, temperature, and exposure time. Our objective was to determine the thermal death point of large crabgrass, cock's-comb kyllinga, and Virginia buttonweed at short thermal exposure periods. Studies conducted utilized 5 and 20 s exposure periods for incremental range, 60 to 250 C temperatures. Sigmoid regression curves were used to predict weed seed mortality by temperature and exposure time. A significant interaction between exposure period and temperature occurred for each weed species. Weed species increased in susceptibility to 20 s thermal heat as follows: Virginia buttonweed < cock's-comb kyllinga < large crabgrass. Increasing thermal exposure time from 5 to 20 s reduced thermal temperature by 21 C to achieve 50% mortality for large crabgrass and by 10 C for cock's-comb kyllinga. Virginia buttonweed achieved 50% mortality at 99 C for 5 and 20 s exposure periods. These data indicate that at least 50% weed seed mortality can be achieved at 99 and 103 C for 20 and 5 s exposure periods, respectively, for these weed species.

Dewberry is a weed found on cranberry bogs that spreads quickly, causes high yield loss, and has no effective management strategy. Finding options to manage damaging perennial weeds in a perennial crop system, such as cranberry, is key to long-term industry sustainability. This study presents preliminary data on the use of flame cultivation (FC) in cranberry weed management. Utilizing weeds transplanted from commercial cranberry farms to a prepared area at the UMass Cranberry Station, we evaluated three handheld propane-fueled FC instruments: infrared torch, open flame torch, and an infrared torch with a spike. A single, midsummer exposure (zero, low, medium, or high duration) with each FC was tested. The industry standard of using a single wipe application of an herbicide solution (111 g L−1 ae glyphosate, isopropylamine salt) was also included in the evaluation. Dewberry shoot, root, and total biomass decreased linearly as exposure increased; the effect of FC tool type was not significant. Data indicated that, regardless of the specific torch utilized, spot treatment with FC reduced dewberry biomass. The results of this exploratory study suggest that FC may offer an alternative technique for managing woody weeds and that further research is warranted.

This greenhouse experiment examined the response of homozygous susceptible and acetolactate synthase (ALS) inhibitor–resistant plants from six Canadian kochia accessions with the Pro197 or Trp574 mutation to six alternative herbicides of different sites of action. The null hypothesis was ALS-inhibitor–resistant and –susceptible plants from within and across accessions would respond similarly to herbicides of different sites of action. This hypothesis was accepted for all accessions except that of MBK2 with the Trp574 mutation. Resistant plants of that accession were 80, 60, and 50% more sensitive than susceptible plants to pyrasulfotole, mesotrione (hydroxyphenylpyruvate dioxygenase [HPPD] inhibitors), and carfentrazone (protoporphyrinogen oxidase [PPO] inhibitor), respectively. However, no differential dose response between resistant and susceptible plants of this kochia accession to bromoxynil, fluroxypyr, or glyphosate was observed. A previous study had found marked differences in growth and development between resistant and susceptible plants of this accession, but not of the other accessions examined in this experiment. Negative cross-resistance exhibited by resistant plants of accession MBK2 to PPO and HPPD inhibitors in this experiment may be a pleiotropic effect related to the Trp574 mutation.

Late summer goosegrass control is difficult in turfgrass as POST herbicide efficacy is reduced on mature plants. Field experiments were conducted to evaluate single and sequential nicosulfuron applications tank-mixed with foramsulfuron or sulfentrazone for late summer goosegrass control and safety to bermudagrass and seashore paspalum. All single-treatment applications controlled goosegrass < 62%, whereas sequential sulfentrazone, nicosulfuron, and nicosulfuron + sulfentrazone applications controlled goosegrass 52, 73, and 84%, respectively. Sequential foramsulfuron applications controlled goosegrass < 55% but nicosulfuron tank-mixtures did not improve control. Bermudagrass was injured < 20% by 1 and 3 wk after all single and sequential treatments. Sequential treatments of nicosulfuron alone or tank-mixed with sulfentrazone caused unacceptable seashore paspalum injury (> 20%) 1 and 3 wk after the second application, whereas foramsulfuron or sulfentrazone alone applied sequentially caused < 17% injury. Seashore paspalum seedhead control at 9 wk after intial treatment was poor (< 70%) from all single-application treatments and sequential sulfentrazone applications, but control was good (80 to 89%) to excellent (> 90%) from all other treatments. Overall, sequential treatments of nicosulfuron alone or tank-mixed with sulfentrazone appear to have potential for POST control of mature goosegrass in bermudagrass, but seashore paspalum injury was unacceptable.