Robert N. Klein

Winter Wheat Cultivar Characteristics Affect Annual Weed Suppression1

Thirteen hard red winter wheat cultivars were evaluated for their ability to suppress summer annual weeds in grain production systems near North Platte, NE, from 1993 through 1997. ‘Turkey’, a 125-yr-old landrace selection, suppressed both broadleaf and grass weeds more than other cultivars. Some relatively new cultivars, such as ‘Arapahoe’, ‘Jules’, ‘Pronghorn’, and ‘Vista’ suppressed summer annual grasses almost as well as Turkey. Total weed density was negatively correlated with number of winter wheat stems/m2, mature winter wheat height, and lodging. Weed density after wheat harvest was positively correlated with delay in winter wheat seeding date and was negatively correlated with precipitation 0 to 30 d after winter wheat seeding, during tillering, tillering to boot stage, and heading to maturity stage. Mean air temperature 0 to 30 d after wheat seeding was positively correlated with weed density. In the spring, weed density was positively correlated with temperatures during the tillering stage, tillering to boot stage, and heading to maturity stage. Stinkgrass and witchgrass densities were positively correlated with severity of wheat leaf rust. The highest grain-producing cultivars included three medium height cultivars ‘Alliance’, Arapahoe, and ‘Niobrara’. Alliance wheat produced 53% more grain than Turkey, and the other two produced 43% more grain. Nomenclature: Stinkgrass, Eragrostis cilianensis (All.) E. Mosher #3 ERACN; witchgrass, Panicum capillare L. # PANCA; winter wheat, Triticum aestivum L.; leaf rust, Puccinia recondita f. sp. tritici. Additional index words: AMAAL, AMARE, CHELR, competition, ECHCG, integrated weed management, KCHSC, lodging, POROL, precipitation, seeding date, SETVI, temperature, wheat stem density. Abbreviation: HRW, hard red winter.

Problem weed control in glyphosate-resistant soybean with glyphosate tank mixes and soil-applied herbicides.

Abstract Although glyphosate controls many plant species, certain broadleaf weeds in Nebraskas cropping systems exhibit various levels of tolerance to the labeled rates of this herbicide, including ivyleaf morningglory, Venice mallow, yellow sweetclover, common lambsquarters, velvetleaf, kochia, Russian thistle, and field bindweed. Therefore, two field studies were conducted in 2004 and 2005 at Concord and North Platte, NE, to evaluate performance of (1) seven preemergence (PRE) herbicides and (2) glyphosate tank mixes applied postemergence (POST) at three application times for control of eight weed species that are perceived as problem weeds in glyphosate-resistant soybean in Nebraska. The PRE herbicides, including sulfentrazone plus chlorimuron, pendimethalin plus imazethapyr, imazaquin, and pendimethalin plus imazethapyr plus imazaquin provided more than 85% control of most weed species tested in this study 28 d after treatment (DAT). However, sulfentrazone plus chlorimuron and pendimethalin plus imazethapyr plus imazaquin were the only PRE treatments that provided more than 80% control of most weed species 60 DAT. In the POST glyphosate tank-mix study, the level of weed control was significantly affected by the timing of herbicide application; control generally decreased as weed height increased. In general, glyphosate tank mixes applied at the first two application times (early or mid-POST) with half label rates of lactofen, imazamox, imazethapyr, fomesafen, imazaquin, or acifluorfen, provided more than 80% control of all species that were 20 to 30 cm tall except ivyleaf morningglory, Venice mallow, yellow sweetclover, and field bindweed. Glyphosate tank mixes applied late POST with lactofen, imazethapyr, or imazaquin provided more than 70% control of common lambsquarters, velvetleaf, kochia, and Russian thistle that were 30 to 50 cm tall. Overall, glyphosate tank mixes with half label rates of chlorimuron or acifluorfen were the best treatments; they provided more than 80% control of all the studied weed species when applied at early growth stages. Results of this study suggested that mixing glyphosate with other POST broadleaf herbicides, or utilizing soil-applied herbicides after crop planting helped effectively control most problematic weeds in glyphosate-resistant soybean in Nebraska. Nomenclature: Acifluorfen; chlorimuron; fomesafen; glyphosate; imazamox; imazaquin; imazethapyr; lactofen; pendimethalin; sulfentrazone; common lambsquarters, Chenopodium album L. CHEAL; field bindweed, Convolvulus arvensis L. CONAR; ivyleaf morningglory, Ipomoea hederacea Jacq. IPOHE; kochia, Kochia scoparia (L.) Schrad. KCHSC; Russian thistle, Salsola tragus L. SASKR; velvetleaf, Abutilon theophrasti Medik. ABUTH; Venice mallow, Hibiscus trionum L. HIBTR; yellow sweetclover, Melilotus officinalis (L.) Lam. MEUOF; soybean, Glycine max L.

Skip-Row Planting Patterns Stabilize Corn Grain Yields in the Central Great Plains

The highly variable climate of the central Great Plains makes dryland corn (Zea mays) production a risky enterprise. Twenty-three field trials were conducted across the central Great Plains from 2004 through 2006 to quantify the effect of various skip-row planting patterns and plant populations on grain yield in dryland corn production. A significant planting pattern by plant population interaction was observed at only one of 23 trials, suggesting that planting pattern recommendations can be made largely irrespective of plant population. In trials where skip-row planting patterns resulted in increased grain yields compared to the standard planting pattern treatment (every row planted using a 30-inch row spacing), the mean grain yield for the standard planting treatment was 44 bu/acre. In those trials where skip-row planting resulted in decreased grain yield compared to the standard planting pattern, the mean yield was 135 bu/acre. The plant two rows, skip two rows planting pattern is recommended for riskaverse growers in the central Great Plains where field history or predictions suggest likely grain yields of 75 bu/acre or less. Planting one row and skipping one row is recommended for growers with moderate risk-aversion and likely yield levels of 100 bu/acre or less.

Glyphosate Spray Drift Management with Drift-Reducing Nozzles and Adjuvants1

Field experiments were conducted to evaluate the effect of five spray-nozzle types and three drift-control adjuvants (DCA) on glyphosate spray drift. The extended-range (XR) flat-fan nozzle at 280 kPa was used as the standard comparison. DCAs were evaluated for drift reduction with the use of the XR and air-induction (AI) nozzles. Wind speed ranged from 1.3 to 9.4 m/s (3 to 21 mph). Lethal drift (DL) and injury drift (DI) were determined by downwind visual observation of grain sorghum response. Drift distances were measured from the spray swath edge. The Turbo FloodJet and AI nozzles reduced DL distance by 34%. All four drift-reducing (DR) nozzles reduced DI distance by 22 to 32%. Reducing the pressure of the XR flat-fan nozzle from 280 to 140 kPa did not reduce DL or DI distance. When applied through AI nozzles, each DCA increased droplet volume diameter, one DCA reduced DI distance and none reduced DL distance when applied through XR tips. The DCAs did not affect DL or DI distance. Nomenclature: Glyphosate; grain sorghum, Sorghum bicolor (L.) ‘Topaz’. Additional index words: Drift-control adjuvant, flat-fan nozzle, flood nozzle. Abbreviations: AI, air induction; AMS, ammonium sulfate; DAP, days after planting; DAT, days after treatment; DCA, drift-control adjuvant; DG, preorifice flat fan; DI, injury drift; DL, lethal drift; DR, Combo-Jet; GR, glyphosate resistant; HRC, herbicide-resistant crops; TD, TurboDrop; TF, Turbo FloodJet; TT, Turbo TeeJet; VMD, volume median diameter; XR, extended range.

Effect of Planting Depth and Isoxaflutole Rate on Corn Injury in Nebraska

Field experiments were conducted at five sites in Nebraska in 2000 and 2001 to determine the effect of planting depth and isoxaflutole rate on the response of an isoxaflutole-sensitive corn hybrid, ‘Pioneer 33-G’ across variable environments. Corn was planted at depths of 2.5 and 5.0 cm, and isoxaflutole was applied PRE at the recommended (1×) and twice the recommended (2×) rate. The effects of planting depth and herbicide rate on injury varied considerably across site–years. When injury was evident, it was generally greater at the high rate of isoxaflutole (2×) and at the shallow planting depth (2.5 cm). In most site–years, corn recovered from early season injury, and yields were not reduced, except at Scottsbluff, NE, and North Platte, NE, where soils were lower in organic matter and higher in pH. Isoxaflutole rates should be carefully selected for soils with low organic matter and high pH. Nomenclature: Isoxaflutole, corn, Zea mays L

Enhanced atrazine degradation is widespread across the United States

BACKGROUND Atrazine (ATZ) has been a key herbicide for annual weed control in corn, with both a soil and post-emergence vegetation application period. Although enhanced ATZ degradation in soil with a history of ATZ use has been reported, the extent and rate of degradation in the US Corn Belt is uncertain. We show that enhanced ATZ degradation exists across much of the country. RESULTS Soils from 15 of 16 surveyed states had enhanced ATZ degradation. The average ATZ half-life was only 2.3 days in ATZ history soils, compared with an average 14.5 days in soils with no previous ATZ use, meaning that ATZ degrades an average 6 times faster in soils with previous ATZ use. CONCLUSION When ATZ is used for several years, enhanced degradation will undoubtedly change the way ATZ is used in agronomic crops and also its ultimate environmental fate.

The effect of adjuvants, pesticide formulation, and spray nozzle tips on spray droplet size.

Many factors, including adjuvants, pesticide formulations, and nozzle tips, affect spray droplet size. It is important to understand these factors as spray droplet size affects both drift and efficacy of pesticides, which is a main concern with pesticide application. A laser particle analyzer was used to determine the spray droplet size and distributions of a range of formulations sprayed through several types of nozzle tips. Nozzles included were extended range flat fan sizes 11003 and 11005 (Spraying Systems XR), air induction flat fan sizes 11005 and 11004 (AI), air induction extended range flat fan size 11005 (AIXR), preorifice flat fan size 11005 (TT), and a second preorifice flat fan size 2.5 (TF). Several deposition/retention adjuvants were studied, including Array, Interlock, In-Place, and Thrust. Another study looked at diflufenzopyr + dicamba (Status, BASF) in combination with several adjuvants. Also, three fungicides were evaluated at differing spray volumes. Results indicated that the droplet size of some nozzle tips is more affected than others by changes in the contents of the spray solution.

Evaluation of Soybean (Glycine max) Canopy Penetration with Several Nozzle Types and Pressures

Fungicides, when applied in the most effective way, can greatly improve the efficacy of the fungicide, reduce the risk of resistance, and potentially increase yields or preserve crops. When making fungicide applications, there are several things that must be considered. Most sprayers use hydraulic nozzles with pressure against an orifice. The applicator must consider which type of nozzle to use (both orifice size and nozzle type) as well as operating pressure.

A Research Plot Herbicide Application System1

A tractor-mounted, air-pressurized, herbicide application system was designed and constructed for use in weed management research on cropland, pastures, and rangeland. The spray system was designed to minimize wind-induced spray pattern distortion, to enable accurate application of multiple treatments, to withstand the stresses of use on uneven and rough terrain, to apply herbicide treatments reliably, to be easy to transport, to be constructed with readily available spray system components, and to enable quick diagnosis and resolution of operational problems. The spray system has a total shield frame length of 5.2 m. The shielded frame comprises three sections. The two outside sections are connected to the center section by hinges so that they can be folded up and over the center section for transport or storage. Four spray booms are mounted inside the shield with a 50-cm distance between nozzles. Herbicides are usually applied with the bottom of the shield placed 20 cm above the soil or plant surface. This height provides 100% overlap of the spray pattern between adjacent nozzle tips. The spray system has been a durable and reliable tool that accurately and quickly applies herbicide treatments. Additional index words: Application technology, cropland, pasture, rangeland, weed control. Abbreviations: ID, inside diameter; PVC, polyvinylchloride.