Non-residual Herbicides Research Articles

Integrating fall and spring herbicides with a cereal rye cover crop for horseweed (Conyza canadensis) management prior to soybean

AbstractHorseweed is one of Kentucky’s most common and problematic weeds in no-till soybean production systems. Emergence in the fall and spring necessitates control at these times because horseweed is best managed when small. Control is typically achieved through herbicides or cover crops (CCs); integrating these practices can lead to more sustainable weed management. Two years of field experiments were conducted over 2016 to 2017 and 2017 to 2018 in Versailles, KY, to examine the use of fall herbicide (FH; namely, saflufenacil or none), spring herbicide (SH; namely, 2,4-D; dicamba; or none), and CC (namely, cereal rye or none) for horseweed management prior to soybean. Treatments were examined with a fully factorial design to assess potential interactions. The CC biomass in 2016 to 2017 was higher relative to 2017 to 2018 and both herbicide programs reduced winter weed biomass in that year. The CC reduced horseweed density while growing and after termination in 1 yr. The FH reduced horseweed density through mid-spring. The FH also killed winter weeds that may have suppressed horseweed emergence; higher horseweed density resulted by soybean planting unless the CC was present to suppress the additional spring emergence. If either FH or CC was used, SH typically did not result in additional horseweed control. The SH killed emerged plants but did not provide residual control of a late horseweed flush in 2017 to 2018. These results suggest CCs can help manage spring flushes of horseweed emergence when nonresidual herbicide products are used, though this effect was short-lived when less CC biomass was present.

Abundancia y cobertura de arvenses bajo manejo convencional y orgánico de café y banano

Certain weeds can be used as cover species in bananas and coffee plantations. The objective of this study was to compare ground cover and abundance of weed species, between the organic and conventional production systems of banana and coffee. Selected farms under organic or conventional management located at Limón and Alajuela were surveyed for weeds, during 2015 and 2016. The minimum area methodology was used to determine sampling site size. At each sampling site, all weed species were identified and grouped into their respective taxonomic families. Percent soil cover by each species was also estimated by means of a visual scale. In both crops, weed diversity was higher when the herbicide glyphosate was used for weed control, although the ground cover for these species was kept at a minimum. These results are thought to arise from the fact that under the organic production system, a hierarchy of dominant species is established, which in turn inhibit many of the somewhat less adapted species, whereas under the conventional production system, the use of a non-residual herbicide renders the ground with plenty of space for species regeneration from the soil propagule bank. Organic weed management in both crops showed higher soil cover by weeds, but from a lower number of species. In contrast, chemical weed management with glyphosate showed a higher number at species, but a significant reduction in ground cover by those weeds.

Herbicide options for managing competitive vegetation during the establishment of Pinus radiata and Pseudotsuga menziesii var. menziesii in Southland, New Zealand

BackgroundControl of weeds is important for survival, growth and uniformity of planted conifers, such as Pinus radiata D.Don and Pseudotsuga mensiesii var. menziesii (Mirb.) Franco. Despite pressure to find environmentally benign herbicides for these species, little research has identified non-residual herbicides that are cost-effective and result in minimal growth loss compared to those used operationally. The objective of this study was to compare efficacy and cost of current operational practice to a range of alternative herbicide treatments for the establishment of these two species using data from two trials located at the same site.MethodsTreatments for each species were applied in both the first and second year following planting and included weed-free controls, operational practice using terbuthylazine and hexazinone (applied as both spot treatment and broadcast application) and a range of treatments consisting of combinations of clopyralid, triclopyr and haloxyfop (CTH), applied with or without oversowing with less competitive grasses and annual herbaceous species. Application of glyphosate during winter was included within the Pseudotsuga mensiesii trial as a first year treatment only and as a second year treatment following spot application of CTH in the first year.ResultsFor the Pinus radiata trial, broadcast application of CTH in spring of years 1 and 2 was most effective, with mean stand volume (m3 ha−1), at 2.5 years, exceeding the weed-free control and operational treatment by 8 and 11%, respectively, although these differences were not statistically significant at the 5% level. Use of the operational treatment as a spot in the first year, followed by broadcast application of CTH in the second year, was moderately effective when used with or without oversowing. For the Pseudotsuga mensiesii trial, the four most effective treatments were the operational treatment, broadcast application of CTH during year 1 (CTH-Dec), broadcast application of CTH during spring of years 1 and 2, and broadcast application of glyphosate during winter (winter glyphosate). Although not significantly different, at 2.5 years mean stand volumes in these treatments were on average 24, 29, 33 and 35% lower than the weed-free control, respectively. Both CTH-Dec and winter glyphosate were less expensive than the operational treatment.ConclusionsThese results highlight potential treatments to either replace terbuthylazine and hexazinone, or reduce their use during establishment weed control for Pinus radiata and Pseudotsuga menziesii, notably for sites dominated by Cytisus scoparius L. (Scotch broom).

Effects of Peanut Stand Uniformity and Herbicide Regime on Weed Management and Yield

ABSTRACT Crop stand directly affects ability of any crop to compete with weeds. To capture this form of cultural weed control, final crop stands need to be uniform. Peanut stands are frequently non-uniform, despite the use of precision vacuum planters. Trials were conducted from 2009 through 2011 in Tifton, GA to determine the effect of non-uniform peanut stands on weed control, grade, and marketable peanut yield. Non-uniform peanut stands were established by modifying vacuum planter discs that created skips 18 cm wide and 36 cm wide at regular intervals and compared with peanut at a uniform stand. The weed control regimes chosen reflected differing degrees of residual weed control provided by flumioxazin or imazapic and addressed the need for residual weed control when peanut stands are non-uniform. Postemergence (POST) herbicides bentazon, paraquat, and 2,4-DB were chosen to test the theory that properly timed applications of non-residual herbicides will control weeds in skips without the need for preemergence (PRE) herbicides. There was no significant interaction between peanut stand uniformity and weed control regime for any parameter. Weed response to peanut stand was variable among species and inconsistent. Weed densities tended to be lower when the residual herbicides flumioxazin and/or imazapic were part of the herbicide regime. Peanut yields and percent total sound mature kernels were not affected by narrow (18 cm) skips, but were reduced two years out of three by wide (36 cm) skips. Peanut yields and grade were similar among weed control regimes that used PRE herbicides and POST herbicides with no residual weed control properties. These results indicate that weed control considerations are not a factor when peanut skips are <18 cm. The herbicide choices evaluated are capable of controlling weeds allowing peanut to compensate for non-uniform stands and not have yield reduction when skips are <18 cm.

Tolerance of Winter Wheat (<i>Triticum aestivum</i> L.) and Under Seeded Red Clover (<i>Trifolium pretense</i> L.) to Fall Applied Post-Emergent Broadleaf Herbicides

The fall application of post-emergent (POST) herbicides on winter wheat provided effective control of emerged winter annual, biennial, and perennial broadleaf weeds. In recent years, wheat producers have seen a shift to these weeds, due in part, to the adoption of reduced-and no-tillage practices and the use of non-residual herbicides such as glyphosate in the preceding soybean and corn crops. The tolerance of winter wheat to ten herbicides, applied POST in the fall, was evaluated between 2008 and 2011 at Exeter and Ridgetown, Ontario. Winter wheat yield was not reduced by applications of MCPA ester, dicamba/ MCPA/ mecoprop, clopyralid, bromoxynil/ MCPA, thifensulfuron /tribenuron +MCPA ester, fluroxypyr +MCPA ester, and pyrasulfotole/ bromoxynil. In contrast, 2,4-D ester and dichlorprop/2,4-D, caused visible injury in June and July of the following year and consistently decreased winter wheat yield by at least 10%. Applications of 100 g a.i. ha-1 saflufenacil also decreased winter wheat yield in two of the four harvest years examined. None of the herbicide options examined were safe on red clover when it was under seeded the spring following winter wheat planting. All herbicides significantly decreased red clover dry biomass one month after wheat harvest.

Fall and Spring Preplant Herbicide Applications Influence Spring Emergence of Glyphosate-Resistant Horseweed (Conyza canadensis)

Horseweed (Conyza canadensis) is a common weed in no-till crop production systems. It is problematic because of the frequent occurrence of biotypes resistant to glyphosate and acetolactate synthase (ALS)-inhibiting herbicides and its ability to complete its life cycle as a winter or summer annual weed. Tactics to control horseweed while controlling other winter annual weeds routinely fail; herbicide application timing and spring emergence patterns of horseweed may be responsible. The objectives of this experiment were to (1) determine the influence of fall and spring herbicides with and without soil residual horseweed activity on spring-emerging glyphosate-resistant (GR) horseweed density and (2) evaluate the efficacy and persistence of saflufenacil on GR horseweed. Field studies were conducted in southern Indiana and Illinois from fall 2006 to summer 2007 and repeated in 2007 to 2008. Six preplant herbicide treatments were applied at four application timings: early fall, late fall, early spring, and late spring. Horseweed plants were counted every 2 wk following the first spring application until the first week of July. Horseweed almost exclusively emerged in the spring at both locations. Spring horseweed emergence was higher when 2,4-D + glyphosate was fall-applied and controlled other winter annual weeds. With fall-applied 2,4-D + glyphosate, over 90% of the peak horseweed density was observed before April 25. In contrast, only 25% of the peak horseweed density was observed in the untreated check by April 25. Starting from the initiation of horseweed emergence in late March, chlorimuron + tribenuron applied early fall or early spring, and spring-applied saflufenacil at 100 g ai/ha provided greater than 90% horseweed control for 12 wk. Early spring–applied saflufenacil at 50 g ai/ha provided 8 wk of greater than 90% residual control, and early spring–applied simazine provided 6 wk of greater than 90% control. When applied in late spring, saflufenacil was the only herbicide treatment that reduced horseweed densities by greater than 90% compared to 2,4-D + glyphosate. We concluded from this research that fall applications of nonresidual herbicides can increase the rate and density of spring emerging horseweed. In addition, spring-applied saflufenacil provides no-till producers with a new preplant herbicide for foliar and residual control of glyphosate- and ALS-resistant horseweed.

EVALUACIÓN DE HERBICIDAS RESIDUALESPARA EL CONTROL DE MALEZASEN GUANÁBANA (Annona muricata L.)

The objective of this study was to determine the effect of residual and non residual herbicides on weed control in a soursop (Annona muricata L.) plantation established in a square system at Los Idolos, Actopan, Ver. The randomized complete block design with four replications was used. The experimental plots had a 5 x 5 m area, each with one soursop tree in the center. Twelve treatments were evaluated (diuron + hexazinone at 1.09 + 0.14, 1.63 + 0.20, 0.87 + 0.33 and 1.31 + 0.49 kg a.i.·ha-1, diuron + paraquat at 0.20 + 0.40 and 0.30 + 0.60 kg a.i.·ha-1, oxyfluorfen + glyphosate at 0.48 + 0.71 kg a.i.·ha-1, oxyfluorfen + paraquat at 0.48 + 0.40 kg a.i.·ha-1, paraquat at 0.40 kg a.i.·ha-1, glyphosate at 0.71 kg a.i.·ha-1, glufosinate at 0.30 kg a.i.·ha-1 and a weedy check). The dominant weed species was crowfoot grass [Dactyloctenium aegyptium (L.) P. Beauv.], 10 broadleaf weed species were also present. Weed control was evaluated at 15, 30, 60 and 90 days after application (DAA), and dry weed weight was quantified at 90 DAA. It was found that diuron + paraquat at 0.30 + 0.60 kg a.i.·ha-1 was the treatment with the highest control of D. aegyptium. Broadleaf weeds were efficiently controlled with diuron + hexazinone at 1.63 + 0.20, 0.87 + 0.33 and 1.31 + 0.49 kg a.i.·ha-1. Weed biomass production was lower with residual herbicides than with non-residual herbicides.

Efficacy of Residual And Non-Residual Herbicides Used in Cotton Production Systems When Applied with Glyphosate, Glufosinate, or MSMA

Field experiments were conducted to evaluate weed control provided by glyphosate, glufosinate, and MSMA applied alone or in mixture with residual and nonresidual last application (LAYBY) herbicides. Herbicide treatments included glyphosate early postemergence (EPOST) alone or followed by glyphosate, glufosinate, or MSMA late-postemergence (LPOST) alone or tank-mixed with one of the following LAYBY herbicides: carfentrazone-ethyl at 0.3 kg ai/ha, diuron at 1.12 kg ai/ha, flumioxazin at 0.07 kg ai/ha, fluometuron at 1.12 kg ai/ha, lactofen at 0.84 kg ai/ha, linuron at 0.56 kg ai/ha, oxyfluorfen at 1.12 kg ai/ha, prometryn at 1.12 kg ai/ha, or prometryn + trifloxysulfuron at 1.12 kg ai/ha + 10 g ai/ha. Residual herbicides were also applied alone LPOST. Weeds evaluated included barnyardgrass, broadleaf signalgrass, coffee senna, entireleaf morningglory, hemp sesbania, ivyleaf morningglory, johnsongrass, large crabgrass, Palmer amaranth, pitted morningglory, prickly sida, redroot pigweed, sicklepod, smooth pigweed, spiny amaranth, and velvetleaf. Treatments containing MSMA provided lower average weed control compared to those containing glyphosate or glufosinate, and residual herbicides applied alone provided inadequate weed control compared to mixtures containing a nonresidual herbicide. Across 315 of 567 comparisons (55%), when a LAYBY herbicide was added, weed control increased. The most difficult to control weed species at all locations was pitted morningglory. Barnyardgrass and hemp sesbania at the Mississippi location and hemp sesbania at the Louisiana location were collectively difficult to control across all treatments as well.

Temporal Weed Interference with Young Pecan Trees

Vegetation surrounding pecan (Carya illinoinensis Wangenh. C. Koch) trees in a 4.3 × 6 m area was either controlled with a nonresidual herbicide for the entire growing season, not controlled, or controlled at certain times during the growing season. After three growing seasons, trunk diameters were suppressed 54% when vegetation was not controlled, 47% when not controlled until 1 Aug., and 37% if not controlled after 1 June compared to entire growing season vegetation control. Trunk diameters were not significantly different from entire season vegetation control when vegetation was controlled from 1 June through fall frost or vegetation controlled from April until 1 Aug. Vegetation in the plots was typically dominated by cool season herbaceous dicots in May and June, and warm-season grasses during August and September.

Responses of winter wheat ( Triticum aestivum L.) to autumn applied post-emergence herbicides

The adoption of new production practices such as no-till and the use of non-residual herbicides such as glyphosate in the preceding crop has resulted in an increase of winter annual, biennial, and perennial weeds in winter wheat in Ontario. Few post-emergence (POST) autumn applied herbicide options are available to control these weeds. Five field trials were conducted in Ontario to evaluate the POST application of dicamba at 140 and 280 g ai/ha, 2,4-D amine, MCPA amine, dichlorprop plus 2,4-D ester, bromoxynil plus MCPA ester, and thifensulfuron-methyl plus tribenuron-methyl. The autumn POST application of dicamba, MCPA amine, bromoxynil plus MCPA ester, and thifensulfuron-methyl plus tribenuron-methyl did not cause any visual injury and there was no decrease in winter wheat height or yield. The POST application of 2,4-D amine and dichlorprop plus 2,4-D ester caused minor visual injury at 24–31 weeks after treatment (WAT). Winter wheat height was reduced as much as 8% with the POST application of dichlorprop plus 2,4-D ester. Yield was reduced up to 9% and 14% with the POST application of 2,4-D amine and dichlorprop plus 2,4-D ester, respectively. Based on these results, the POST application of 2,4-D amine and dichlorprop plus 2,4-D ester premix in the autumn results in unacceptable injury in winter wheat. However, dicamba, MCPA amine, bromoxynil, MCPA ester, and thifensulfuron-methyl plus tribenuron-methyl have an adequate margin of crop safety for use in weed management in winter wheat in Ontario.

Herbicides Reduce Seed Production in Reproductive-Stage Yellow Starthistle (Centaurea solstitialis)

Herbicides with residual activity more effectively control infestations of yellow starthistle, a facultative winter annual, because seed banks quickly furnish replacement plants after nonresidual herbicide treatments. Picloram has been applied to rosettes in fall or spring, but new infestations of yellow starthistle are often discovered when plants are more noticeable in bud or flower stages. Eradication, containment, and revegetation are facilitated if weed seed rain can be stopped. This study evaluated whether registered rates (0.14, 0.28, and 0.42 kg ae/ha) of picloram, alone and with 2,4-D at 1.12 kg ae/ha, can prevent seed production when applied to yellow starthistle at bud or flower stage. Picloram applied at bud stage curtailed both seed production and germination, reducing seed production by 42 to 86% and viability by 80 to 99%. Neither the picloram rate nor the addition of 2,4-D to the spray solution affected the percentage of nonviable seeds. The addition of 2,4-D further decreased germination of developed seeds only at the lowest picloram rate. At flower stage, picloram and 2,4-D neither killed mature plants nor consistently reduced the quantity and quality (viability) of seeds. Bud stage was the phenological limit for effective reduction of viable seed by picloram, which caused both bud abortion and lower seed germination.

Weed Management in Glyphosate Resistant Soybean: Weed Emergence Patterns in Relation to Glyphosate Treatment Timing

Knowing when weed species are likely to emerge can aid in developing effective integrated weed management programs. When using nonresidual herbicides such as glyphosate for weed control, treatment timing is critical. This study characterized the emergence patterns of common lambsquarters, common sunflower, common waterhemp, eastern black nightshade, ivyleaf morningglory, shattercane, and woolly cupgrass in soybean, in relation to common glyphosate application timings. Approximately 90% or more of common lambsquarters, common sunflower, and common waterhemp seedlings emerged before the end of May, both in 2000 and 2001. Both ivyleaf morningglory and shattercane emerged from late April to mid-August, allowing these species to avoid glyphosate applications timed to prevent early-season weed competition. Avoidance through periodicity in emergence underscores the importance of integrating multiple tactics to ensure that difficult to manage weeds are not selected for in this management system.

Response of wild oat (Avena fatua) to residual and non-residual herbicides in canola (Brassica napus) in western Canada

It has been stated that soil residual herbicides, by controlling successive flushes of weeds, increase effective kill (efficacy) over the growing season, and thus impose a higher selection pressure for resistance in weeds than non-residual herbicides. To investigate this issue, the responses of wild oat to increasing rates of residual and non-residual herbicides in canola and wild oat recruitment in the following year were examined in a field study conducted in Saskatchewan, Canada, from 1997 to 2000. The rate-response curves of the wild oat variables indicated that efficacy of the soil residual herbicides, ethalfluralin and triallate, and of the non-residual herbicide, glufosinate, was generally lower than that of imazamox/imazethapyr (residual), sethoxydim, and glyphosate (non-residual). Emergence of wild oat in spring wheat (Triticum aestivum L.) grown in the following year did not differ among herbicides applied in the preceding crop year, nor was there a significant herbicide by rate interaction. The results suggest that the soil residual activity o f these herbicides does not strongly influence selection pressure, estimated by reduction in wild oat seed return in canola. Key words: Brassica napus, Avena fatua, selection pressure, herbicide resistance

Changes in weed community composition as influenced by cover crop and management system in continuous corn

Abstract Weed suppression by cover crops grown during the winter fallow period in continuous corn may lead to a reduction in herbicide use. Rye, crimson clover, and subterranean clover cover crops were compared with corn stubble under a conventional management system (CS) that included plowing and use of preemergence residual herbicides and a low-input management system (LIS) that included no-tillage and use of a presowing nonresidual herbicide for three consecutive years (1994–1996). Cover crop and above-ground weed biomass prior to desiccation were not influenced by management system. Cover crop biomass ranged from 1,420 to 5,657 kg ha−1 for rye, from 563 to 4,217 kg ha−1 for crimson clover, and from 563 to 4,248 kg ha−1 for subterranean clover. At crop planting, rye reduced weed biomass from 54 to 99%, crimson clover from 22 to 46% (with a negative value in 1995), and subterranean clover from 21 to 67%. Weed growth suppression was usually higher in years when cover crop biomass was higher. There were n...

Temporal Effects of Chemical Weed Control on Tart Cherry Tree Growth, Yield, and Leaf Nitrogen Concentration

This experiment was conducted to determine temporal weed management parameters for tart cherry (Prunus cerasus L.) orchards. Annual ryegrass (Lolium multiflorum L.) and lambsquarter (Chenopodium album L.) were planted in tree rows of a 4-year-old tart cherry orchard. Weeds either were not controlled or controlled with nonresidual herbicides during the following intervals: all-summer; May, June, July, or August; preharvest (April-July); or postharvest (late July to frost). Trees in all-summer, June, and preharvest weed-free plots had more shoot growth, more nodes, longer internodes, greater leaf area, and higher concentrations of leaf nitrogen than did those in the weedy control and postharvest, July, or August treatments. A larger increase in trunk circumference was observed in all-summer and preharvest weed-free plots than in postharvest and weedy plots. Early-summer weed control was important for tree vegetative growth. Tree yield (fruit weight and number) was greater on trees without weed competition postharvest than in those treated in May, June, July, or in weedy controls. Late-season (after late July) weed control is therefore important for fruit yield.

Effect of tillage on timing ofSetariaspp. emergence and growth

Weed management can be a significant challenge in cropping systems, partly because the effects of tillage systems on weed seedbank and seedling population dynamics are not well understood. Field research was conducted from 1994 to 1996 in established tillage plots consisting of moldboard plow (MP), chisel plow (CP), and no-tillage (NT). The objectives were to determine the effects of long-term tillage systems on the timing and duration ofSetariaspp. emergence and percentage cumulative emergence from the soil seedbank and to investigate the effect of tillage onSetariaspp. density and seed production following glyphosate application atSetariaspp. heights of 5, 10, and 15 cm. NT contained a greater number ofSetariaspp. seed in the 0- to 1-, 1- to 3-, and 3- to 6-cm depths than MP or CP systems. There was little difference between the three tillage systems at depths greater than 6 cm.Setariaspp. emergence was greater in NT than in MP or CP in 1994 and 1996 and greater than in MP in 1995. There was a substantial increase inSetariaspp. emergence in NT between 3 and 4 weeks after planting (WAP) in 1994 and between 5 and 6 WAP in 1995 and 1996. Significant emergence did not occur past 5 to 6 WAP in 1994 and 1995 but continued over a longer period of time in 1996.Setariaspp. plants consistently reached targeted herbicide application heights 4 to 9 d earlier in NT than in CP and MP. In 1994, finalSetariaspp. density was greater in NT compared to CP and MP at the 5- and 10-cm herbicide application timings. When glyphosate was applied to 15-cm-tallSetaria, very few weeds were present following application across all tillage systems. In 1995, NT resulted in greaterSetariaspp. density than MP or CP across all application timings. There was no difference in finalSetariaspp. density between MP and CP across all glyphosate timings in 1994 and 1995. Seed production was negligible in MP and CP, regardless of glyphosate timing. In NT, however, significant seed production occurred, especially with early application. Results indicate that the effectiveness of nonresidual herbicides forSetaria faberiHerrm. control is influenced by tillage system and the timing of application.

Economic Analysis of Alternative Herbicide Regimes on Roundup Ready Soybeans

Roundup (glyphosate) is a nonresidual herbicide that controls grasses and dicot weeds but is injurious to soybeans. The development of Roundup-resistant soybeans [Glycine max (L.) Merr.] (Roundup Ready soybeans) by Monsanto could allow farmers to substitute Roundup for all other herbicides to reduce production costs and weed control risk. Field trials at the University of Tennessee Milan Experiment Station from 1995 through 1997 were used to compare 1997 returns above variable costs for Roundup and 11 other herbicide systems on conventionally tilled, Roundup Ready soybeans. Although yields of only four herbicide systems on Roundup Ready soybeans were significantly lower than the yield of Roundup on Roundup Ready soybeans, net returns of nine systems were significantly lower. The significantly lower net returns resulted mostly from higher herbicide costs. Chemical companies would have to reduce the costs of most non-Roundup herbicide systems to unreasonably low levels (close to or less than zero) before farmers would have an economic incentive to use them instead of Roundup on Roundup Ready soybeans. Budgeted production costs for Roundup on Roundup Ready soybeans (Roundup Ready seed at $26/50 lb bag) were also compared with budgeted production costs for the non-Roundup herbicide systems on conventional soybean varieties (public-domain seed at $10.50/50 lb bag). Seven of the 11 non-Roundup herbicide systems on conventional varieties had costs that were greater than Roundup on Roundup Ready soybeans, suggesting that lower seed costs for the non-Roundup systems were more than offset by higher herbicide costs. Yields required to cover the cost differences between the non-Roundup herbicide systems and Roundup on Roundup Ready soybeans were calculated. These yield differences were added to the experimental yield obtained with Roundup on Roundup Ready soybeans to arrive at a break-even yield. A decision criterion for profit-maximizing farmers was developed from these break-even yields; if a profit-maximizing farmer expects to receive a yield from his/her highest-yielding conventional variety that is less than the break-even yield, the farmer should consider planting Roundup Ready soybeans to obtain a higher expected profit. If the decision criterion suggests staying with the conventional variety, the farmer should consider the nonbudgeted benefits of Roundup Ready soybeans, such as improved timeliness of planting and reduced weed control risk, before making the decision. To obtain more conclusive evidence about the relative profitability of Roundup Ready soybeans, future research should include side-by-side variety trials, more years of data, and no-tillage production methods.

619 Temporal and Spatial Weed Control Effects on Tart Cherry Orchards

This experiment was conducted to determine temporal and spatial weed management characteristics for tart cherry orchards. Annual ryegrass and lambsquarter were planted in tree rows of a 14-year-old tart cherry orchard. Vegetation was controlled with nonresidual herbicides (Gramoxone + B-1956) either all season, May, June, July, August, before harvest, after harvest, or not controlled. Shoot growth measurements showed significantly more growth by trees without weed competition during the entire season, May, June, and before harvest compared to the weedy control and postharvest, July, or August treatments. Weedy early season plots reduced the shoot growth by half. All season, before harvest, May, and June weed-free plots showed higher amounts of leaf N compared with weedy controls or late-season treatments. Early season weed control is more important than late season. Vegetation-free areas of 0, 2, 3, and 4 m2 were maintained during 1998 by postemergence herbicides. Tissue analysis showed higher N concentration in leaves with vegetation controlled to 2 m2 or more compared to the weedy control. The critical vegetation free area for young cherry trees is between 0 and 2 m2.

Effects of tillage and crop rotation on physical properties of a loam soil

Advances in the development of non-residual herbicides have increased the interest in minimum tillage systems as an alternative to conventional cultivation. This study compared the effects of conventional tillage (CT), minimum tillage (MT) and zero-till (ZT) with continuous winter wheat, winter wheat-summerfallow, and winter wheat-barley-summerfallow on various properties of a Brown Chernozemic loam. Saturated hydraulic conductivity (HC), soil moisture retention, bulk density (BD) and infiltration rate of the soil were measured. The effects of crop rotation by tillage or crop rotation on these soil physical properties were not significant after 8 years of tillage. In general, the BD of the soil under ZT was greater than that under CT in the tillage zone and was lower below the tillage zone. The HC of ZT soil was less than that of CT soil in the tillage zone and greater below the tillage zone. Infiltration rates were not different among the tillage treatments. Although significant differences in some soil properties occurred among tillage treatments, these differences were likely to be too small to affect crop production.

Effect of fallowing practices on the growth and yield of wheat in south-eastern Australia

The effects on crop establishment, crop development and the yield of wheat of two methods of fallow preparation, at each of three lengths of fallow were investigated over 5 years on red duplex and associated soils in north-central Victoria. The two methods of preparation were: scarifying, which involved the repeated use of a tined tillage implement; and herbicide application, which involved the repeated use of non-residual herbicides to control weeds during the fallow phase. The three lengths of fallow were winter, spring and autumn, which were approximately 10, 8 and 2 months respectively. Grain yield on the scarifier treatments was 0.26 t/ha greater (P<0.10) than on the herbicide treatments. Grain yield on winter fallow was 0.46 and 0.56 t/ha greater (Pt0.01) than on spring and autumn fallows, respectively. Crop yield was positively correlated (R2= 0.49) with soil nitrate determined at the time the crop was sown, but was independent of available soil water content determined at that time. Winter fallowing conserved 15 and 29 mm more water than did spring and autumn fallowing respectively, and mineralized 26 and 28 kg/ha more nitrogen than did spring and autumn fallows respectively. Crop establishment (No. of plants/m of row) on the herbicide treatment was 89% (P< 0.05) of that on the scarifier treatment, but this was not the reason for the reduced grain yield on the herbicide treatment. The lower yields were caused by depressed crop vigour (number of spikes/m of row) which in turn was largely a consequence of the inefficient uptake of nitrogen. The yield benefits of scarifying appear to reflect the importance of the initial two or three cultivations.