Early-season Weed Research Articles

Alternative Weed Management Systems Control Weeds in Potato (Solanum tuberosum)1

Five weed management systems utilizing combinations of cover crops, herbicides, and cultivation were tested in potato in 1994 and 1995 in central Washington. A standard herbicide treatment of metribuzin applied preemergence (PRE) at 0.4 kg ai/ha (standard herbicide weed management system [STD]) was compared with (1) fall-planted winter rye followed by metribuzin at 0.4 kg/ha applied in a band in the potato hill, followed by reservoir tillage (rye cover crop with herbicide-banded and reservoir-tilled weed management system [RYESTD]); (2) cultivation with tine-tooth harrow followed by hilling with shovels and rolling cultivators (total-cultivation weed management system [CULT]); (3) fall-planted rapeseed followed by reservoir tillage (rapeseed cover crop and reservoir-tilled weed management system [RPSD]); and (4) reservoir tillage alone (reservoir-tilled weed management system [RESTIL]). In both years, early-season weed density and final weed biomass were lower in the STD, RYESTD, and CULT systems than in ...

Early Season Weed Competition Reduces Yield of Newly Planted Matted Row Strawberries

Competition from weeds and an interplanted sudangrass [Sorghum bicolor (L.) Moensch, formerly S. sudanense (Piper) Stapf.] cover crop was allowed to occur in newly-planted strawberries (Fragaria ×ananassa Duch.) for varying lengths of time, and at different times during the growing season. Newly planted strawberries were most susceptible to weed and cover crop competition during the first 2 months after planting, as both runnering (stolon formation) and subsequent yield were impacted. In 1994-95, 1 month of weed competition in June reduced yield by 20%, whereas 2 months of weed competition reduced yield by 65%. However, 1 month of uncontrolled weed growth later in the growing season had little to no impact on yield, although weed biomass was much less then. Herbicide (napropamide) use alone was insufficient to prevent weed competition and yield reduction. In our study, yield was reduced 0.67 t·ha-1 or 5.5% for each 100 g·m-2 of weed biomass. The data suggest that it is critical for growers to minimize weed competition early in the planting year when weed growth is greatest. Since an interplanted sudangrass cover crop displaced a portion of the weeds, it could be seeded later in the year to provide some weed suppression without a negative impact on yield. Chemical names used: N, N, Diethyl-2-(1-naphthalenyloxy)-propionamide (napropamide); N-(phosphonomethyl)glycine (glyphosate).

Broadleaf Weed Control in Ultra Narrow Row Bromoxynil-Resistant Cotton (Gossypium hirsutum)1

A field experiment was conducted over 2 yr to study efficacy of bromoxynil mixtures with pyrithiobac or MSMA applied postemergence (POST) with and without fluometuron or fluometuron plus pendimethalin preemergence (PRE) for control of broadleaf weeds in ultra narrow row bromoxynil-resistant cotton in the Mississippi Delta. Bromoxynil applied POST (single or sequential) provided variable control of common purslane (<9%), sicklepod (<35%), Palmer amaranth (<46%), prickly sida (>75%), hyssop spurge (>79%), hemp sesbania (>96%), and pitted morningglory (100%) at 4 wk after early POST (WAT). Broadleaf weed control increased when PRE herbicides were followed by bromoxynil or bromoxynil plus pyrithiobac or MSMA POST. Weed control generally decreased at harvest compared to 4 WAT, and the decrease was greater in bromoxynil POST-only programs compared to bromoxynil POST following PRE programs. Seed cotton yield with bromoxynil POST-only programs was lower (400 to 2,810 kg/ha) compared to bromoxynil POST programs following PRE herbicides (2,150 to 3,720 kg/ha). Early-season weed interference and variable control of weeds in bromoxynil POST-only programs resulted in greater cotton stand reduction and lower open bolls per plant compared to bromoxynil POST programs following PRE herbicides.Nomenclature: Bromoxynil; fluometuron; MSMA; pendimethalin; pyrithiobac; common purslane, Portulaca oleracea L. #3 POROL; cotton, Gossypium hirsutum L. ‘BXN 47’; hemp sesbania, Sesbania exaltata (Raf.) Rydb. ex A. W. Hill # SEBEX; hyssop spurge, Euphorbia hyssopifolia L. # EPHHS; Palmer amaranth, Amaranthus palmeri S. Wats. # AMAPA; pitted morningglory, Ipomoea lacunosa L. # IPOLA; prickly sida, Sida spinosa L. # SIDSP; sicklepod, Senna obtusifolia (L.) Irwin & Barneby # CASOB.Additional index word: Transgenic cotton.Abbreviations: EPOST, early postemergence; fb, followed by; LPOST, late postemergence; POST, postemergence; PRE, preemergence; UNR, ultra narrow row; WAT, weeks after EPOST application.

Evaluation of Potential Cover Crops for Inland Pacific Northwest Vineyards

Numerous cover crops for orchards and vineyards have been evaluated, but many selections do not necessarily perform well in the cold, arid environment of the inland Northwest. A cover crop between vine rows can mitigate wind erosion and subsequent damage to young vines. However, low rainfall, gusty winds, and sandy soils that cause significant wind erosion problems can exacerbate cover crop establishment, and cold winters can limit cover crop survival. During 1998, 175 plant accessions were screened for performance as vineyard cover crops at Prosser, Washington. Assessed attributes included percent emergence, percent vegetative cover, stand duration, and plant height. Based on that assessment, seven domestic selections and four foreign Medicago species (medics) were identified for additional evaluation in a research trial in 1999. Additionally, seven accessions and two mixes of species that met the growth criteria and had commercial availability were evaluated in a commercial, drip-irrigated vineyard near Prosser in 1999. Vine water potential and soil moisture were determined in addition to the identical growth criteria from the 1998 study. Cover crop treatments did not lead to detectable water stress in the vines (midday y = -0.84 to -1.30 MPa). However, dry soil between vine rows due to precision drip irrigation inhibited germination and establishment of legumes; therefore, grasses had better emergence rates. Of the mixed species, a grass mix (Canada) composed of crested wheatgrass (Agropyron cristatum L.), pubescent wheatgrass (Elytrigia intermedia L.), and perennial rye (Lolium perenne L.; 40:40:20), depleted soil water the least and showed the least effect on vine water potential. Early season weeds were suppressed by most cover crop species; however, season-long suppression of weed growth was observed only for the Canada mix and crested wheatgrass cv. Fairway.

Competitive Potential and Economic Analysis of a Glyphosate-Tolerant/Conventional Soybean (Glycine max) Mix1

Field studies were conducted in 1997 and 1999 to determine the effect of a broadcast-seeded glyphosate-tolerant/conventional soybean seed mix on soybean seed yield, gross profit margin from weed management, and early-season weed suppression prior to a single glyphosate application. Tests were established by broadcasting and incorporating 494,000 seeds/ha glyphosate-tolerant soybean in combination with 0 to 1,976,000 seeds/ha conventional soybean. Glyphosate at 1.12 kg ai/ha was applied at the V5 to V6 soybean growth stage to kill all conventional soybean plants and emerged weeds. The broadcast planting technique was effective in establishing a soybean stand on a silt loam but was ineffective on a silty clay soil. Hemp sesbania and pitted morningglory control, resulting from interference with soybean, were correlated with percent soybean groundcover (R2 = 0.961 to 0.971) and population (R2 = 0.821 to 0.860) at the V5 to V6 soybean growth stage. Although not significant, increased yield and gross profit margin of dryland soybean occurred as the total seeding rate of the seed mix increased from 494,000 to 741,000 seeds/ha. A dryland seeding rate of 741,000 compared to 494,000 seeds/ha resulted in 438 kg/ha and $93.78/ha increase in seed yield and gross profit margin, respectively. Interference between the two soybean cultivars at 1,976,000 seeds/ha reduced yield. Irrigated soybean at 988,000 seeds/ha produced the greatest seed yield and gross profit margin at 2,987 kg/ha and $555.86/ha, respectively. Maximum yields were attributed to early-season weed suppression.Nomenclature: Glyphosate; hemp sesbania, Sesbania exaltata (Raf.) Rybd. ex A. W. Hill #3 SEBEX; pitted morningglory, Ipomoea lacunosa L. # IPOLA; soybean, Glycine max (L.) Merr. ‘Delta King 5961 RR’.Additional index words: Broadcast-seeded soybean, low-input agriculture, Roundup Ready soybean, safe site, soybean groundcover, Amaranthus hybridus, Amaranthus palmeri, AMACH, AMAPA.Abbreviations: DAP, days after planting; WAT, weeks after treatment.

Use of Cover Crop Mulches in a No-till Furrow-irrigated Processing Tomato Production System

No-till processing tomato (Lycopersicum esculentum Mill.) production in four winter cover crop-derived mulches was evaluated in 1997 and 1998 in Five Points, Calif. The effectiveness of two medics, `Sava' snail medic (Medicago scutellata Mill.) (sava), and `Sephi' barrel medic (Medicago truncatula Gaertn.) (sephi), and two cereal/legume cover crop mixtures, triticale/`Lana' woolypod vetch (X Triticosecale Wittm./Vicia dasycarpa Ten.) (triticale/vetch) and rye/`Lana' woolypod vetch (Secale cereale L./V. dasycarpa) (rye/vetch), was compared with two conventionally tilled fallow controls (with and without herbicide) (fallow+h and fallow-h) in suppressing weeds and maintaining yields with reduced fertilizer inputs. The comparison was conducted as a split plot, with three N fertilization rates (0, 100, and 200 lb/acre; 0, 112, and 224 kg·ha-1) as main plots and cover crops and fallow controls as subplots. Tomato seedlings were transplanted 3 weeks after the cover crops had been mowed and sprayed with herbicide. There were no significant differences in weed cover in the no-till cover crop treatments relative to the fallow controls in 1997. Early season weed suppression in rye/vetch and triticale/vetch plots was similar to herbicide-treated fallow (fallow+h) in 1998, however, later in the 1998 season weed suppression was best in the fallow+h. Tissue N was highest in the fallow treatments in both 1997 and 1998. Yields were highest in the triticale/vetch and fallow and lowest in sephi treatments in 1997, but there were no differences among treatments in 1998. These results demonstrate the feasibility of no-till mulch production of furrow irrigated processing tomatoes and identify opportunities for further optimization of the system.

Economics of Weed Management in Glufosinate-Resistant Corn (Zea maysL.)1

Abstract: Field experiments were conducted in 1997 and 1998 near Columbia and Novelty, MO, and at Urbana, IL, to evaluate corn injury, weed control, corn yield, and estimated economic returns with weed management programs in glufosinate-resistant corn. Herbicide programs included acetochlor preemergence (PRE) followed by glufosinate alone or with atrazine postemergence (POST) and total POST programs consisting of single and sequential applications of glufosinate alone or tank mixed with acetochlor, atrazine, or acetochlor plus atrazine. Metolachlor PRE followed by dicamba plus atrazine early POST (EPOST) and metolachlor plus atrazine PRE were included for comparison. In the total POST treatments, mid-POST applications controlled shattercane and common cocklebur better than EPOST applications. However, yield reductions as high as 23% occurred because of early-season weed interference, although weeds were controlled later in the season. Applying atrazine with glufosinate generally increased control of giant...

Influence of annual forages on weed dynamics in a cropping system

Alternatives to herbicides are needed for weed control. Field studies were conducted in 1994/1995 and 1995/1996 to investigate the nature of forage crop-weed dynamics and to test the effect of single year forage crops on the density and community composition of annual weeds in a following field pea (Pisium sativum L.) test crop. Five spring-seeded forage treatments were compared with wheat (Triticum aestivum L.) grain crops (with or without herbicides for grassy and broadleaved weeds): winter triticale (Triticosecale) (simulation grazed); spring triticale (silage); spring/winter triticale intercrop (silage, then simulation grazed); alfalfa (Medicago sativa L.) (hay); sorghum-sudangrass (Sorghum bicolor [L.] Moench × Sorghum sudanese [Piper]) (hay); and a weedy fallow (silage). A fall rye (Secale cereale L.) grain crop and a sweet clover (Melilotis officinalis L.)/winter triticale double crop (hay, then simulation grazing) were included in the 1995/1996 trial. All forage systems were at least as effective as the sprayed wheat control in suppressing wild oat (Avena fatua L.); however, effects on other weeds, especially broadleaved species, were variable. Biennial crops provided the best early season weed control, while long-season systems such winter triticale and the triticale intercrop provided the best late season weed control. Forages shifted the weed community composition away from wild oat and green foxtail (Setaria viridis L. Beauv.) to a similar or greater extent than herbicide-treated wheat. Forage systems that did not provide season-long crop competition tended to have more broadleaved weeds. Some forage systems increased pea grain yield the following year (relative to the sprayed wheat control); however, forages alone did not eliminate the need for herbicides in the pea crop. Annual forages may play an important role in integrated weed management, especially for wild oat, however further research to refine forage-based weed management systems is needed. Key words: Integrated weed management, alfalfa, intercropping, double cropping, organic farming

Efficacy and Economics of Weed Management in Glyphosate-Resistant Corn (Zea mays)1

Field experiments were conducted in 1997 and 1998 near Columbia and Novelty, MO, and Urbana, IL, to evaluate crop injury, weed control, corn yield, and net economic returns provided by weed control programs in glyphosate-resistant corn. The herbicide programs evaluated included acetochlor preemergence (PRE) followed by (fb) glyphosate with or without atrazine postemergence (POST) and total POST programs consisting of single and sequential applications of glyphosate alone and tank-mixed with actochlor, atrazine, or both. Metolachlor PRE fb dicamba plus atrazine POST and metolachlor plus atrazine PRE were included for comparison. In the total POST treatments, mid-post (MPOST) applications provided better control than early-post (EPOST) applications on weeds that germinated throughout the growing season such as shattercane and common cocklebur, but also resulted in yield reductions of up to 23% caused by early-season weed competition. The addition of atrazine to glyphosate POST generally increased control of common cocklebur, morningglory species, and common waterhemp. EPOST or PRE fb EPOST applications generally provided higher yields than MPOST treatments, although MPOST treatments often provided equal or greater weed control at midseason. Treatments including two herbicide applications tended to provide greater weed control, yield, and profit than those with a single application. Input costs for glyphosate-resistant corn are slightly higher than nontransgenic hybrids. However, net economic returns are similar and the use of glyphosate POST allows greater flexibility in POST weed management decisions.Nomenclature: Acetochlor, 2-chloro-N-(ethoxymethyl)-N-(2-ethyl-6-methylphenyl)acetamide; atrazine, 6-chloro-N-ethyl-N′-(1-methylethyl)-1,3,5-triazine-2,4-diamine; dicamba, 3,6-dichloro-2-methoxybenzoic acid; glyphosate, N-(phosphonomethyl)glycine; metolachlor, 2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide; common cocklebur, Xanthium strumarium L.#3 XANST; common waterhemp, Amaranthus rudis Sauer # AMATA; ivyleaf morningglory, Ipomoea hederaceae (L.) Jacq. # IPOHE; pitted morningglory, Ipomoea lacunosa L. # IPOLA; shattercane, Sorghum bicolor (L.) Moench. # SORVU; corn Zea mays L. # ZEAMX ‘MON802’.Additional index words: Corn yield, acetochlor, atrazine, dicamba, economic returns, metolachlor, AMATA, ABUTH, CHEAL, IPOHE, IPOLA, POLPY, SETFA, SORVU, XANST, ZEAMX.Abbreviations: ALS, autolactate synthase; EPOST, early postemergence; fb, followed by; MPOST, mid-postemergence; OM, organic matter; POST, postemergence; PRE, preemergence; WAT, weeks after treatment.

014 Weed Control and Productivity of Field-grown Cut Flowers

A set of studies was established in Summer 1998 to determine the tolerance of field-grown cut flower species to specific preemergence herbicides, the effectiveness of weed control by those materials, and to determine if productivity of cut flowers is affected either by the herbicides or by colored mulches. Pendimethalin provided excellent early season weed control, but poor late-season control. It consistently caused injury at 4 lb a.i./A and sometimes at the 2 lb a.i./A rate. Oryzalin provided good to excellent weed control, but slightly injured celosia and zinnia when applied at 4 lb a.i./A. Napropamide provided excellent early season weed control, but marginally acceptable weed control later in the season. Though napropamide caused some injury to celosia early in the season when applied at the high rate, no injury to any of the plants was observed later in the season. Prodiamine and trifluralin were the overall safest of the herbicides, but they provided the weakest weed control. OH-2 was very effective when placed on the soil surface, but was less effective when placed on an organic mulch. The organic mulch was designed to keep the OH-2 particles from splashing on to the crop plant and injuring the plants. OH-2 tended to be safer placed on a mulch than on the soil surface, but statice was slightly injured even when a mulch was used.

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.

Weed Control in Soybean (Glycine max) with Green Manure Crops

Greenhouse and field experiments were initiated to evaluate rapeseed and mustard species as green manure crops for weed suppression. Under greenhouse conditions incorporating 20 g fresh wt leaf and stem tissue of rapeseed, two white mustards, and brown mustard into 450 g Sharpsburg, silty clay loam soil resulted in significant reductions in weed emergence, biomass, and height. Kochia, shepherd's-purse, and green foxtail emergences were reduced by all green manure crops. Redroot pigweed emergence was reduced by all green manure crops except brown mustard, and velvetleaf emergence was reduced by white mustards only. Kochia and shepherd's-purse fresh weights were reduced by all green manure crops, while redroot pigweed and velvetleaf fresh weights were reduced by brown mustard and white mustard var. Salvo. Green foxtail fresh weight was reduced by all green manure crops except rapeseed. With the exception of shepherd's-purse, no relationship between glucosinolate content of the incorporated green manure and suppression of weed growth was found. Under field conditions, early spring-planted green manure crops reduced early season weed biomass in soybean at one of the two locations. Mustard species as green manure crops reduced total weed biomass in soybean by 40% 4 weeks after emergence (WAE) and 49% 6 WAE. Soybean biomass and yield were sometimes reduced by the incorporation of green manure crops in treatments containing weeds; however, hand-weeded plots with green manure treatments yielded similar to hand-weeded plots without green manure.

Evaluating Thrips Control in Peanuts using Percent Damage Leaflet Ratings, 1997

Abstract At-plant, in-furrow applied insecticides were evaluated for tobacco thrips control at the Peanut Belt Research Station in Lewiston-Woodville. Variety NC-7 peanuts were planted on 36-inch rows on 7 May at approximately 100 lb seed/acre. Soil temperature was 70°F and the soil was moist. The humic matter was 0.6% and soil pH was 5.9. Soil series consisted of Rains + Goldsboro sandy loam. Prowl and Vernam were used for early-season weed control. Plots were 2 rows wide by 50 ft long and each plot was separated by two buffer rows. Plots were arranged in a RCB design with four replicates. Plot ends were separated by 5-ft barren strip. Peanuts were planted using a Cole planter and in-furrow treatments were placed in the furrow with seed using electric Gandy boxes. The in-furrow application of Orthene 97% was applied by mounting spray nozzles directly behind the seed tube and connecting these to a CO2 sprayer on the planter. The sprayer was operated at 40 psi delivering approx. 30 gpa using 8003 flat-fan nozzles. Treatment rates and application techniques are listed in table. Peanuts were managed under standard agronomic practices. Thrips control was evaluated by determining the abundance of damaged leaflets per plot on 3, 12, and 16 Jun. Twenty-five, newly opened leaflets per plot were randomly selected and examined for thrips damage. The number of damaged leaflets was recorded. Stand counts were taken on 16 Jun. Yield was determined by digging, drying, and weighing peanuts from both rows of each plot on 7 Nov. All data were transformed (square root ofx + 0.50) prior to ANOVA and DNMRT. Actual means are presented in table.

Thrips Control in Peanuts, 1996

Abstract At-plant, in-furrow applied insecticides were evaluated for TT control at the Peanut Belt Research Station in Lewiston-Woodville, NC. NC-7 variety peanuts were planted on 36 inch rows on 9 May at approximately 100 lb of seed/acre. Soil temperature was 70°F and the soil was moist. The humic matter was 1.5% and soil pH was 5.9. Soil series consisted of Rains + Goldsboro sandy loam. Prowl and Vernam were used for early season weed control. Plots were 2 rows wide by 50 ft long and were separated by 2 buffer rows. Plots were arranged in a RCB design with four replicates. Plot ends were separated by 5 ft barren strip. Peanuts were planted using Cole® planter and in-furrow treatments were placed in the furrow with seed using an electric Gandy® boxes. The in-furrow treatment of Orthene 75S was applied by mounting spray nozzels directly behind the seed tube and connecting these to a CO, sprayer on the planter. The sprayer was operated at 40 psi delivering approx. 30 gpa. Foliar treatments of Orthene 75S were applied on 13 Jun by using a CO2 backpack sprayer operating at 40 psi delivering approximately 30 gpa. Treatments, rates and application techniques are listed in the table. Peanuts were managed under standard agronomic practices. Thrips control was evaluated by determining the abundance of damaged leaflets per plot on 5,13, and 20 Jun. Twenty-five, newly-opened leaflets per plot were randomly selected and examined for thrips damage. Inaddition, thrips control was evaluated by collecting 10 unopened leaflets per plot on 5 Jun. Samples were placed in vials of alcohol and returned to the laboratory where the number of adults and larvae were counted. Larval counts were used as the basis for control since they provide a better indicator of efficacy than do the more mobile adults. All data were transformed (square root ofX + 0.50) prior to ANOVA and DNMRT. Actual means are presented in the table.

Effect of Planting Patterns and Inter-row Cultivation on Competition Between Corn (Zea mays) and Late Emerging Weeds

Narrower corn row widths, higher crop densities, and interrow cultivation may be used as part of integrated weed management (IWM). During a three-year study, we tested whether these factors affected corn growth, development and grain yield at final harvest, and weed biomass when weeds were late-emerging (after the three-leaf stage of corn). Increasing corn density from 7 to 10 plants m−2or decreasing row width from 75 to 50 cm significantly increased corn leaf area index (LAI), and reduced photosynthetic photon flux density (PPFD) available for a mixture of weed species located below the corn canopy. Narrower rows and higher corn density significantly reduced biomass of late-emerging weeds. Corn yields increased significantly (10 to 15%) only when narrower rows were used. Intraspecific competition between corn plants in the higher density significantly reduced early corn growth and offset any gain in yield from reduced weed competition. In comparison to plots where late-emerging weeds grew uncontrolled, interrow cultivation did not decrease biomass of late-emerging weeds, hence did not increase corn yield. We recommend using narrower row widths to reduce weed competition and increase corn yield. Increased corn densities had no net yield benefit. Early-season weed management is crucial as the later-emerging weeds were less important in terms of their effect on yield.

Weed Control and Sweet Corn (Zea maysvar.rugosa) Response in a No-till System with Cover Crops

Studies were conducted at the Main Agricultural Experiment Station in Fayetteville and the Vegetable Substation in Kibler, Arkansas, in 1992 and 1993 on the same plots to evaluate weed suppression by winter cover crops alone or in combination with reduced herbicide rates in no-till sweet corn and to evaluate cover crop effects on growth and yield of sweet corn. Plots seeded to rye plus hairy vetch, rye, or wheat had at least 50% fewer early season weeds than hairy vetch alone or no cover crop. None of the cover crops reduced population of yellow nutsedge. Without herbicides, hairy vetch did not suppress weeds 8 wk after cover crop desiccation. Half rates of atrazine and metolachlor (1.1 + 1.1 kg ai ha−1) reduced total weed density more effectively in no cover crop than in hairy vetch. Half rates of atrazine and metolachlor controlled redroot pigweed, Palmer amaranth, and goosegrass regardless of cover crop. Full rates of atrazine and metolachlor (2.2 + 2.2 kg ai ha−1) were needed to control large crabgrass in hairy vetch. Control of yellow nutsedge in hairy vetch was marginal even with full herbicide rates. Yellow nutsedge population increased and control with herbicides declined the second year, particularly with half rates of atrazine and metolachlor. All cover crops except hairy vetch alone reduced emergence, height, and yield of sweet corn. Sweet corn yields from half rates of atrazine and metolachlor equalled the full rates regardless of cover crops.

Thrips Control in Peanuts, North Carolina, 1995

Abstract At-plant, in-furrow applied insecticides were evaluated for tobacco thrips (Frankliniella fusca) control at the Peanut Belt Research Station in Lewiston-Woodville, NC. NC-7 variety peanuts were planted on 36 inch rows on 8 May at approximately 100 lb of seed/acre. Soil temperature was 74°F and the soil was moist. The humic matter was 1.1% and soil pH was 5.4. Soil series consisted of Rains + Goldsboro sandy loam. Prowl and Vernam were used for early season weed control. Plots were 2 rows wide by 50 ft long and each plot was separated by 2 buffer rows. Plots were arranged in a RCB design with four replicates. Plot ends were separated by 5 ft barren strip. Peanuts were planted using Cole® planter and in-furrow treatments were placed in the furrow with seed using electric Gandy® boxes. The in-furrow application of Orthene 75S was applied by mounting spray nozzles directly behind the seed tube and connecting these to a CO2 sprayer on the planter. The sprayer was operated at 40 psi delivering approx. 30 gpa. Foliar treatments of Orthene were applied on 30 May by using a CO2 backpack sprayer operating at 40 psi delivering approx. 30 gpa and using 8003 flat fan nozzles. Peanuts were managed under standard agronomic practices. Thrips control was evaluated by determining the abundance of damaged leaflets per plot on 30 May and 20 Jun. Twenty-five, newly opened leaflets per plot were randomly selected and examined for thrips damage. In addition, thrips control was evaluated by collecting ten unopened leaflets per plot on 9 Jun. Samples were placed in vials of alcohol and returned to the laboratory where the number of adults and larvae were counted. Larvae counts were used as the basis for control since they provide a better indicator of efficacy than do the more mobile adults. All data were transformed (square root of X + 0.50) prior to ANOVA and DNMRT. Actual means are presented in tables.

Compatibility and Efficiency of In-Row Cultivation for Weed Management in Corn (Zea mays)

Information on the effects of multiple weed management tactics in corn is needed to develop integrated weed management systems. The effectiveness and compatibility of an in-row cultivator as compared to a standard interrow cultivator used with reduced rates of a soil-applied herbicide, rotary hoeing, and/or a bioeconomic model for POST herbicide selection was examined. Weed control with a single rotary hoeing at corn emergence controlled annual weeds similarly to two rotary hoeings. One-third recommended use rate of alachlor controlled weeds similarly to a two-thirds rate. Reduced rates of alachlor controlled more weeds than rotary hoeing over 2 yr. The in-row cultivator required early-season weed control (rotary hoeing or reduced alachlor rate) for optimum efficacy. The in-row cultivator provided better weed control than the standard cultivator while the cost of operating the two cultivators was similar. Thus, the in-row cultivator was more efficient than the standard cultivator. Furthermore, less intensive early-season weed control was required with the in-row cultivator for maximum weed control as compared to the standard cultivator. Rotary hoeing plus the in-row cultivator provided similar weed control to other weed management tactics that required both soil-applied and POST herbicides. Gross margin was influenced more by corn yield than cost of weed management tactics.

Developing Cover Crops for Weed Control in Establishment Year for Strawberries

The goal of our program is to learn how to effectively establish first-year strawberry plantings without using herbicides. Before strawberry transplanting, four treatments were established: winter wheat, a dwarf Brassica sp., napropamide (2.24 kg·h–1) plus hand hoeing and rototilling, and no weed management. `Honeyoye' transplants were set into plots measuring 6.1 × 7.32 m on 21 May 1993 and 10 May 1994. Weekly data was taken on the percentage of soil area covered with plant material, height, and stage of development of plants, and weeds present. Weed transects and plant dry weights were done periodically during the growing seasons. The most promising cover crop treatment was the dwarf Brassica sp. for early season weed suppression because of rapid germination and short stature. Winter wheat was very competitive with the strawberry plants. The herbicide treatment had the largest inputs; however, it did produce the largest strawberry plants at the end of the season.

Effect of Soybean (Glycine max)Cultivar, Tillage, and Rye (Secale cereale)Mulch on Sicklepod (Senna obtusifolia)

Field studies were conducted to determine the effect of soybean cultivar, tillage, and rye mulch on sicklepod growth. Early-season sicklepod height was not affected by tillage or mulch. Sicklepod was tallest when grown with ‘Centennial’ or ‘Biloxi,’ the tallest cultivars, and shortest when grown with a dwarf isoline of ‘Tracy M,’ the shortest cultivar. Soybean competition reduced early-season weed density by 30 to 50%, depending on the cultivar. Centennial and dwarf Tracy M caused a 30% reduction in early-season sicklepod biomass while ‘Sharkey’ and Biloxi reduced sicklepod growth by 40%. By late-season, sicklepod biomass reduction ranged from 18% (Tracy M) to 55% (Biloxi) and was directly related to soybean cultivar height. Mulch or no-tillage independently reduced sicklepod biomass.