Corn Production Fields Research Articles

4-Hydroxyphenylpyruvate dioxygenase (HPPD)-inhibiting herbicides: past, present, and future

AbstractThe herbicides that inhibit 4-hydroxyphenylpyruvate dioxygenase (HPPD) are primarily used for weed control in corn, barley, oat, rice, sorghum, sugarcane, and wheat production fields in the United States. The objectives of this review were to summarize 1) the history of HPPD-inhibitor herbicides and their use in the United States; 2) HPPD-inhibitor resistant weeds, their mechanism of resistance, and management; 3) interaction of HPPD-inhibitor herbicides with other herbicides; and 4) the future of HPPD-inhibitor-resistant crops. As of 2022, three broadleaf weeds (Palmer amaranth, waterhemp, and wild radish) have evolved resistance to the HPPD inhibitor. The predominance of metabolic resistance to HPPD inhibitor was found in aforementioned three weed species. Management of HPPD-inhibitor-resistant weeds can be accomplished using alternate herbicides such as glyphosate, glufosinate, 2,4-D, or dicamba; however, metabolic resistance poses a serious challenge, because the weeds may be cross-resistant to other herbicide sites of action, leading to limited herbicide options. An HPPD-inhibitor herbicide is commonly applied with a photosystem II (PS II) inhibitor to increase efficacy and weed control spectrum. The synergism with an HPPD inhibitor arises from depletion of plastoquinones, which allows increased binding of a PS II inhibitor to the D1 protein. New HPPD inhibitors from the azole carboxamides class are in development and expected to be available in the near future. HPPD-inhibitor-resistant crops have been developed through overexpression of a resistant bacterial HPPD enzyme in plants and the overexpression of transgenes for HPPD and a microbial gene that enhances the production of the HPPD substrate. Isoxaflutole-resistant soybean is commercially available, and it is expected that soybean resistant to other HPPD inhibitor herbicides such as mesotrione, stacked with resistance to other herbicides, will be available in the near future.

Migration of Oil Bodies in Embryo Cells during Acquisition of Desiccation Tolerance in Chemically Defoliated Corn (Zea mays L.) Seed Production Fields

Chemical defoliation of seed corn production fields accelerates seed maturation and desiccation and expedites seed harvest. Early seed harvest is important to minimize the risk of frost damage while in the field. This newly adopted seed production practice also allows seed companies to plan harvest and manage dryer space more efficiently. However, premature defoliation may interfere with the migration of oil bodies within embryo cells during desiccation and affect seed germination and vigor. The objective of this study was to investigate the effect of chemical defoliation on the migration patterns of oil bodies within embryo cells during desiccation. Chemically defoliated and non-defoliated plants from five commercial hybrid seed corn fields were sampled in 2014 and 2015. Whole ears with husks were harvested before and after defoliant application at 600 g H2O kg−1 fresh weight (fw), and weekly thereafter until seed reached approximately 300–350 g H2O kg−1 fw. Ten embryos extracted from center-row seeds were fixed to stop metabolic processes, then sliced, processed, and photographed using scanning transmission electron microscopy. The oil bodies within embryo cells followed normal migration patterns according to seed moisture content, regardless of defoliation treatment. Seed germination and vigor were verified and were not significantly affected by defoliation. Chemical defoliation is a viable production practice to accelerate seed corn desiccation and to manage harvest and seed dryer availability more efficiently without negatively affecting seed germination and vigor.

The Forecast of Corn Production Fields in Turkey with Arima Model

Corn has an important place in animal nutrition in addition to its importance in human nutrition in Turkey. Correct agricultural policies and strategies should be developed to increase corn production, which is a very important agricultural product in both human nutrition and animal husbandry. In this context, considering the corn cultivation areas of 1970-2019, predicting future corn cultivation areas is very important in terms of developing correct policies and planning production. This study aims to predict the cultivation areas of corn in the years 2020-2030 as a product that has not been analyzed using ARIMA models before. To accomplish this objective, data from a total of 50 years during the period 1970-2019 and the Autoregressive Integrated Moving Average (ARIMA) model were used to estimate the corn cultivation areas in Turkey.

Bees Occurring in Corn Production Fields Treated with Atoxigenic Aspergillus flavus (Texas, USA)

A saprophytic soil fungus, Aspergillus flavus, produces aflatoxin (toxigenic strains) in the kernels of corn (Zea mays L.) and seeds of many other crops. Many strains of A. flavus do not produce toxigenic aflatoxin, and soil application of these atoxigenic strains is a suppressive control tactic to assist in controlling toxigenic conspecifics. Effects of atoxigenic A. flavus applications on honey bees (Apis mellifera L.) and other bees are unknown, and basic information on bee occurrences in cornfields treated with and without this biological agent is needed to inform integrated pest management in corn. Fields receiving atoxigenic A. flavus applications of FourSureTM were compared to nearby control fields in three counties in corn production regions in eastern Texas. In each cornfield, 20 bee bowl traps were deployed along four equal transects located between corn rows, with contents of the bowls (i.e., bees) retrieved after 24 h. Eleven bee genera from four families were collected from cornfields, with only two honey bees collected and zero honey bees observed in transects. The sweat bee genus Agapostemon (primarily composed of the Texas striped sweat bee A. texanus) was most abundant in cornfields (44% of the total number of bees collected), followed by long-horned bees (Melissodes spp., 24%). The southernmost county (i.e., San Patricio) produced over 80% of the total number of bees collected. Bee numbers occurring in cornfields with applications of atoxigenic A. flavus applications were not significantly different from those of nearby control fields. Although not statistically significant, total numbers of bees tended to be lower in FourSure-treated fields than in control fields. More extensive research on bee abundances in relation to the effect of atoxigenic A. flavus is warranted.

Mechanism of atrazine resistance in atrazine- and HPPD inhibitor-resistant Palmer amaranth (Amaranthus palmeri S. Wats.) from Nebraska

Palmer amaranth (Amaranthus palmeri S. Wats.) is one of the most problematic weed species in agronomic crops in the United States. A Palmer amaranth biotype multiple-resistant to atrazine and 4-hydroxyphenylpyruvate dioxygenase (HPPD) inhibitors was reported in a seed corn production field in Nebraska. Rapid detoxification mediated by cytochrome P450 monooxygenases and increased HPPD gene expression were reported as the mechanisms of mesotrione resistance in atrazine- and HPPD inhibitor-resistant Palmer amaranth biotype from Nebraska; however, the mechanism of atrazine resistance is unknown. The objectives of this study were to investigate target site or non-target site based mechanisms conferring atrazine resistance in Palmer amaranth from Nebraska. 14C-atrazine absorption and translocation studies revealed that reduced atrazine absorption or translocation were not involved as one of the mechanisms of atrazine resistance. Instead, greater 14C-atrazine absorption and recovery in treated leaves were observed in resistant compared with susceptible Palmer amaranth. No known mutations including Ser264Gly substitution in the psbA gene causing target site based atrazine resistance were observed. However, the parent 14C-atrazine was metabolized rapidly <4 h after treatment in resistant plants, conferring enhanced atrazine metabolism as the mechanism of resistance.

Basis of Atrazine and Mesotrione Synergism for Controlling Atrazine‐ and HPPD Inhibitor‐Resistant Palmer Amaranth

Palmer amaranth (Amaranthus palmeri S. Watson) resistant to atrazine [6‐chloro‐N‐ethyl‐N’‐(1‐methylethyl)‐1,3,5‐triazine2,4‐diamine] and 4‐hydroxyphenylpyruvate dioxygenase (HPPD)‐inhibiting herbicides was confirmed in a seed corn (Zea mays L.) production field in Nebraska, in 2014. Neither atrazine nor HPPD inhibitors (mesotrione [2‐(4‐mesyl2‐nitrobenzoyl)‐3‐hydroxycylohex‐2‐enone], tembotrione {2‐[2‐chloro‐4‐(methylsulfonyl)‐3‐[(2,2,2‐trifluoroethoxy) methyl]benzoyl]‐1,3‐cyclohexanedione}, or topramezone {[3‐(4,5‐dihydro‐3‐isoxazolyl)‐2‐methyl‐4‐(methylsulfonyl)phenyl](5‐hydroxy‐1‐methyl‐1H‐pyrazol‐4‐yl)methanone}) applied post‐emergence were able to control resistant Palmer amaranth even at greater than label rates. However, their tank mixtures even at lower than the label rate provided more than 90% control under greenhouse and field conditions. The objectives of this study were to investigate the effect of atrazine on mesotrione absorption and translocation when tank mixed or vice versa in atrazine‐ and HPPD inhibitor‐resistant Palmer amaranth from Nebraska. Tank mixing commercial formulation of atrazine at 560 g ha−1 increased 14C‐mesotrione absorption to 51% compared to 39% with 14C‐mesotrione alone. However, 14C‐atrazine absorption or translocation was not affected by mesotrione at 26 g ha−1 in the tank mixture. Similarly, mesotrione did not affect the metabolism of 14C‐atrazine in resistant or susceptible plants when tank mixed compared to 14C‐atrazine applied alone. Increased absorption of mesotrione when tank mixed with atrazine could be one of the reasons of atrazine and mesotrione synergism besides their biochemical interaction in the atrazine‐ and HPPD inhibitor‐resistant Palmer amaranth biotype from Nebraska.Core Ideas Atrazine applied in tank‐mixture increased mesotrione absorption. Mesotrione applied in tank mixture did not affect atrazine absorption and translocation. Atrazine metabolism was not affected by mesotrione applied in tank mixture.

Economics of Management of Photosystem II‐ and HPPD‐inhibitor‐Resistant Palmer amaranth in Corn

Core Ideas Glufosinate + dicamba had similar Palmer amaranth control as glufosinate. Glyphosate + dicamba had similar control as glyphosate. Pre‐emergence followed by post‐emergence and post‐emergence‐only programs had similar control. A Palmer amaranth biotype resistant to photosystem (PS) II‐ and 4‐hydroxyphenylpyruvate dioxygenase (HPPD)‐inhibitor in continuous seed corn production fields in southcentral Nebraska is a management challenge for corn growers. Field studies were conducted on a grower’s field in 2014 through 2016 near Shickley in Fillmore County, Nebraska to determine the efficacy of herbicide programs for control of resistant Palmer amaranth, net economic return, and yield of glyphosate‐ and glufosinate‐resistant corn. Based on contrast analysis, pyroxasulfone + fluthiacet‐ethyl + atrazine applied pre‐emergence (PRE) had the highest (95%) Palmer amaranth control compared with saflufenacil + dimethenamid‐P, mesotrione + S‐metolachlor + atrazine (91 to 92%), and acetochlor + clopyralid + flumetsulam (87%) at 21 d after PRE in 2014 to 2015. Glufosinate or glyphosate alone, or tank‐mixed with dicamba applied post‐emergence (POST)‐only or aforementioned PRE herbicides followed by POST programs had 89 to 99% control at 28 and 72 d after POST in 2014 to 2015. Corn yields and net returns were higher where PRE followed by POST and POST‐only herbicide programs were used compared with PRE‐only programs in glufosinate‐ and glyphosate‐resistant corn in 2014 and 2016. In 2015, corn yields and net returns were similar where PRE‐only, POST‐only, and PRE followed by POST herbicide programs were used in glufosinate‐ and glyphosate‐resistant corn. Results of this study suggest that effective PRE followed by POST herbicide programs are available for controlling PS II‐ and HPPD‐inhibitor‐resistant Palmer amaranth in corn and growers need to adopt an integrated weed management approach to reduce the chances of evolution of herbicide‐resistant weeds.

Genetic Diversity and Population Structure of Pythium irregulare from Soybean and Corn Production Fields in Ohio.

High levels of genetic diversity have been described within the Pythium irregulare complex from several host plants; however, little is known about the population structure in fields used for grain production. Therefore, the objective of this study was to evaluate the genetic diversity and population structure of 53 isolates baited from 28 soybean and corn production fields from 25 counties in Ohio. Genetic diversity was characterized based on sequence analysis of the internal transcribed spacer (ITS1-5.8S-ITS2) region and with 21 simple sequence repeat (SSR) markers. In addition, aggressiveness on soybean, optimum growth temperature, and sensitivity to metalaxyl fungicide were determined. ITS sequence analysis indicated that four isolates clustered with P. cryptoirregulare, whereas the remaining isolates clustered with P. irregulare that was subdivided into two groups (1 and 2). Cluster analysis of SSR data revealed a similar subdivision, which was also supported by structure analysis. The isolates from group 2 grew at a slower rate, but both groups of P. irregulare and P. cryptoirregulare recovered in this study had the same optimum growth at 27°C. Variability of aggressiveness and sensitivity toward metalaxyl fungicide was also observed among isolates within each group. The results from this study will help in the selection of isolates to be used in screening for resistance, assessment of fungicide efficacy, and disease management recommendations.

Soil‐Test Biological Activity with the Flush of CO2: I. C and N Characteristics of Soils in Corn Production

Core Ideas Soil nitrogen mineralization can be predicted with the flush of CO2. Soil texture does not alter the relationship between the flush of CO2 and N mineralization. Large quantity of mineralizable N in surface soils is possible with conservation management. The flush of CO2 is an appropriate indicator for soil‐test biological activity. The flush of CO2 is a rapid and reliable indicator of soil N availability. Nitrogen limits crop production when insufficient and harms the environment when excessive. Tailoring N inputs to cropping systems remains a high priority to achieve production and environmental goals. We collected soils from 47 corn (Zea mays L.) production fields in North Carolina and Virginia at depths of 0 to 10, 10 to 20, and 20 to 30 cm and evaluated soil C and N characteristics in association with soil N mineralization. Soil organic C at a depth of 0 to 10 cm varied among sites from ∼10 to 80 g kg–1, and generally declined with depth because of many sites with no‐tillage management. Net N mineralization during 24 d of aerobic incubation (25°C, 50% water‐filled pore space) was 54 to 114 mg N kg–1 (24 d)–1 at 0 to 10 cm, 22 to 41 mg N kg–1 (24 d)–1 at 10 to 20 cm, and 12 to 22 mg N kg–1 (24 d)–1 at 20 to 30 cm (middle 50% of observations at each depth). Total soil N was positively associated with net N mineralization (r2 = 0.58), but the flush of CO2 during 3 d was even more closely associated with net N mineralization (r2 = 0.77). Association between the flush of CO2 and net N mineralization did not change significantly when data were sorted by different regions or soil textural classes. The flush of CO2 is a rapid, reliable, and robust indicator of soil‐test biological activity. The strong association of the flush of CO2 with net N mineralization also corroborated use of the flush of CO2 as a rapid and reliable indicator of soil N availability.

Soil‐Test Biological Activity with the Flush of CO2: II. Greenhouse Growth Bioassay from Soils in Corn Production

Core Ideas Grass growth in the greenhouse was dependent on soil nitrogen mineralization. Soil‐test biological activity was a valuable indicator of nitrogen mineralization. Biological activity, residual inorganic nitrogen, and total nitrogen were most important. Soil nitrogen (N) mineralization is variably affected by management and edaphic conditions. A routine soil test that reflects both soil biological activity and N mineralization could improve predictions for N fertilizer recommendations to cereal grains on different soil types and landscape settings. We collected soils from 47 corn production fields in North Carolina and Virginia at depths of 0 to 10, 10 to 20, and 20 to 30 cm and evaluated soil C and N characteristics in association with sorghum‐sudangrass [Sorghum bicolor (L.) Moench ssp. Drummondii] dry matter production and N uptake during 6 to 8 wk of growth in the greenhouse. Plant dry matter and N uptake were strongly associated, as expected. Plant available N (sum of net N mineralization during 24 d of aerobic incubation + residual inorganic N) had the strongest association with plant dry matter production (r2 = 0.76) and N uptake (r2 = 0.85). However, the flush of CO2 during a 0‐ to 3‐d period following rewetting of dried soil was nearly equally effective at r2 = 0.74 and r2 = 0.76, respectively. Multiple regression models with 4 ± 2 additional variables led to r2 = 0.88 ± 0.10 among different separations of data based on depth, region, and soil textural class. We suggest the optimum combination of variables to predict soil N availability would be the flush of CO2, residual inorganic N, and total soil N concentration, as they balance relevant scientific information with limited soil‐testing resources (time and labor). We demonstrated that the flush of CO2 was a rapid and reliable indicator of soil N availability.

Morphological and molecular characterization of Brazilian populations of Diatraea saccharalis (Fabricius, 1794) (Lepidoptera: Crambidae) and the evolutionary relationship among species of Diatraea Guilding.

The sugarcane borer or corn stalk borer, Diatraea Guilding is polyphagous insect pest of many important crops such as corn, sorghum and sugarcane. Losses arising from the attack of Diatraea species have been a serious problem, which may cause loss in sugarcane production around 0.25% in sugar, 0.20% in alcohol and 0.77% of body weight for every 1% infestation and up to 21% in corn production fields. In Brazil, the most commonly reported species are Diatraea saccharalis (Fabricius, 1794) and Diatraea impersonatella (Walker, 1863) (= D. flavipennella). However, multiple other species of Diatraea have been identified in Brazil according to the literature. Currently, little information exists on the presence of the other species causing injury to sugarcane and corn. The objectives of this study were to improve the accuracy of species assignment, evaluate the population genetic structure, and address many of the outstanding questions of systematics and evolution of Brazilian populations of D. saccharalis. To address these main questions, classical taxonomic methods were used, focused on morphological characterization of the reproductive organs, especially the male genitalia. In addition, genetic studies were performed using simple sequence repeats (SSR) and a fragment of cytochrome C oxidase subunit I (COI) gene. The data and findings from this research will contribute to the understanding of evolutionary aspects of insect pests in order to develop more effective and sustainable population management practices.

First Report of Sugarcane mosaic virus group IV Isolates from the Corn Production Fields in China

First Report of <i>Sugarcane mosaic virus</i> group IV Isolates from the Corn Production Fields in China

Confirmation and Control of Triazine and 4-Hydroxyphenylpyruvate Dioxygenase-Inhibiting Herbicide-Resistant Palmer Amaranth (Amaranthus palmeri) in Nebraska

Palmer amaranth is a difficult-to-control broadleaf weed that infests corn and soybean fields in south-central and southwestern Nebraska and several other states in the United States. The objectives of this research were to confirm triazine and 4-hydroxyphenylpyruvate dioxygenase (HPPD)-inhibiting herbicide-resistant Palmer amaranth in Nebraska and to determine sensitivity and efficacy of POST-applied corn herbicides for control of resistant and susceptible Palmer amaranth biotypes. Seeds from a putative HPPD-resistant Palmer amaranth biotype from Fillmore County, NE were collected from a seed corn production field in fall 2010. The response of Palmer amaranth biotypes to 12 rates (0 to 12×) of mesotrione, tembotrione, topramezone, and atrazine was evaluated in a dose–response bioassay in a greenhouse. On the basis of the values at the 90% effective dose (ED90) level, the analysis showed a 4- to 23-fold resistance depending upon the type of HPPD-inhibiting herbicide being investigated and susceptible biotype used for comparison. This biotype also had a 9- to 14-fold level of resistance to atrazine applied POST. Results of a POST-applied herbicide efficacy study suggested a synergistic interaction between atrazine and HPPD-inhibiting herbicides that resulted in &gt; 90% control of all Palmer amaranth biotypes. The resistant biotype had a reduced sensitivity to acetolactate synthase inhibiting herbicides (halosulfuron and primisulfuron), a photosystem-II inhibitor (bromoxynil), and a protoporphyrinogen oxidase inhibitor (fluthiacet-methyl). Palmer amaranth biotypes were effectively controlled (≥ 90%) with glyphosate, glufosinate, and dicamba, whereas 2,4-D ester provided 81 to 83% control of the resistant biotype and &gt; 90% control of both susceptible biotypes.

Responses of an HPPD Inhibitor-Resistant Waterhemp (Amaranthus tuberculatus) Population to Soil-Residual Herbicides

Field experiments were conducted in 2010 and 2011 at a Mclean County, IL seed corn production field where resistance to foliar-applied 4-hydroxyphenylpyruvate dioxygenase (HPPD) inhibitors was confirmed in waterhemp. Corn herbicides were applied to the soil at 1 and 2 times (1× and 2×, respectively) the recommended field use rate, while soybean herbicides were applied only at 1× the recommended rate. Waterhemp control and density were determined 30 and 60 d after treatment (DAT). In corn, 1× rates of mesotrione, safened and unsafened isoxaflutole formulations, atrazine, andS-metolachlor provided less than 70% control 30 DAT, while control with acetochlor was greater than 80%. One and 2× rates of acetochlor and 2× rates of mesotrione and unsafened isoxaflutole provided the greatest reduction of waterhemp density across years. At 30 DAT in soybean, sulfentrazone, flumioxazin, metribuzin, and pyroxasulfone provided the highest levels of waterhemp control (84 to 92%), as well as the greatest reduction in waterhemp density both years. A dose–response experiment with soil-applied mesotrione was performed under controlled greenhouse conditions using three waterhemp populations: MCR15 (seed collected from the McLean Co. site), NH41 (progeny obtained from the McLean Co. population by an additional generation of mesotrione selection in the greenhouse), and a sensitive (S). Emergence counts 21 DAT revealed higher seedling survival of MCR15 and NH41 at mesotrione rates of 105 g ha−1or less compared with the sensitive control. Resistant-to-sensitive (R/S) ratios for NH41 and MCR15 were 12.7 and 8.8, respectively. Field results indicate the McLean Co. waterhemp population demonstrates reduced sensitivity to soil-applied HPPD-inhibiting herbicides. This is supported by greenhouse results that demonstrate reduced sensitivity to mesotrione in MCR15 and NH41.

Amaranthus develops resistance to HPPD inhibitors in seed corn production fields - another example of lack of diversity in the weed control program

In 2010, a hybrid seed corn production field was confirmed to be infested with a population of Amaranthus tuberculatus that was not controlled by postemergence applications of all tested commercially available HPPD-inhibitor herbicides. In glasshouse and field studies, resistance to post-emergence applications of mesotrione, tembotrione and topramezone was confirmed. In addition, this population was identified to be resistant to ALS-inhibitors and to triazines. A. tuberculatus is a very competitive weed, which can appear in high population density and can emerge even very late during the season. A. tuberculatus is dioecious and therefore an obligate outcrosser, which is leading to high genetic variability within a population. All these biological features increase the risk of developing resistance to herbicides. Therefore, the field history explains clearly that this resistance developed under specific conditions. In this field, inbred corn was grown for at least seven consecutive years. Inbred corn is much less competitive with weeds compared to hybrid field corn and herbicide options are reduced vs. hybrid field corn production. In addition due to the resistance to triazines, only one effective mode of action (HPPD) has been used post-emergence to control A. tuberculatus for over seven consecutive years. The resistance development in this A. tuberculatus population is clearly a result of the lack of diversity in the weed management plan which should include crop and herbicide rotation. Field testing showed pre-emergence applications of mesotrione combinations (Lumax ® , Lexar ® ) provided good control of this A. tuberculatus population. In addition alternative herbicides to control this population have been identified: Glyphosate, glufosinate, paraquat, PPGO-inhibitors, auxins, and triazinones were very effective. Keywords: Amaranthus tuberculatus , inbred corn, mesotrione, waterhemp Amarant entwickelt Resistenz gegen HPPD-Hemmer in Saatmais Produktionsfeldern - ein weiteres Beispiel fur fehlende Vielfalt in den Unkrautbekampfungsverfahren In 2010 wurde in McLean County, Illinois, in einem Maissaatgutproduktionsfeld eine Amaranthus tuberculatus Population bestatigt, die nicht mit Nachauflaufbehandlungen von HPPD-Hemmern bekampft werden konnte. In Gewachshaus- und Feldstudien wurde die Resistenz gegen Nachauflaufbehandlungen der HPPD-Hemmer Mesotrione, Tembotrione and Topramezone gezeigt. Zusatzlich wurde eine Kreuzresistenz gegen ALS-Hemmer und gegen Triazine festgestellt. A. tuberculatus ist ein sehr konkurrenzstarkes Unkraut, das in hoher Populationsdichte auftreten und sogar noch sehr spat in der Saison auflaufen kann. Es ist ein zweihausiges Unkraut und daher ein obligater Fremdbestauber, welches zu hoher genetischer Variabilitat in der Population fuhrt. Diese biologischen Charakteristika erhohen das Risiko einer Resistenzentwicklung gegen Herbizide. In dem Feld in dem die resistente Population gefunden wurde, wurde fur mindestens sieben aufeinanderfolgende Jahre Hybridsaatmais aus Inzuchtlinien produziert. Inzuchtlinien sind im Vergleich zu Hybridmais sehr konkurrenzschwach gegenuber Unkrautern und zusatzlich existieren nur begrenzte Moglichkeiten der chemischen Unkrautbekampfung. Da diese A. tuberculatus Population eine Resistenz gegen Triazine aufwies, war der HPPD-Hemmer fur mehr als sieben aufeinander folgende Jahre der einzige effektive Wirkmechanismus in der Nachauflaufbehandlung. Die Entwicklung der Resistenz gegenuber HPPD-Hemmern ist daher eine klare Folge von einer nicht vorhandenen Diversitat im Unkrautmanagement, welches ackerbauliche Massnahmen und Herbizidwechsel beinhalten sollte. Feldversuche haben gezeigt, dass alternative Bekampfungsmoglichkeiten dieser Population bestehen. So waren im Mais Vorauflaufbehandlungen von mesotrionehaltigen Kombinationsmitteln (Lumax ® , Lexar ® ) erfolgreich in der Bekampfung dieser Population. Zusatzlich wurden weitere Herbizide mit guter Wirkung gegen diese Population identifiziert: Glyphosat, Glufosinat, Paraquat, PPO-Hemmer, Auxine und Triazinone waren sehr wirkungsvoll. Stichworter: Amaranthus tuberculatus , Herbiziresistenz, Inzuchtlinien, Mesotrione

Analysis of Soil Fertility and Management Effects on Yields of Wheat and Corn in the Rolling Pampa of Argentina

AbstractThe Rolling Pampa is the most productive region of the Argentine Humid Pampa comprising around 10 Mha. Wheat (Triticum aestivum L.), corn (Zea mays L.), and soya bean [Glycine max (L.) Merr.] are the main grain crops produced. To develop sound cropping strategies, a better understanding of the impact of soil fertility and management on crops is needed. The objective of this study was to develop models for estimating the effects of growing season precipitation, soil fertility and management on wheat and corn yields. Data from 347 wheat and 323 corn field experiments and production fields over six growing seasons were used. Soil, management and weather characteristics were determined and yields were then evaluated. Data were analysed using linear and quadratic models and a quadratic polynomial surface model. Soil fertility, management and rainfall and interactions were analysed. Growing season precipitation correlated with wheat (R2 = 0.42) and corn (R2 = 0.25) yield. Maximum wheat yield was achieved with 350–400 mm rainfall and corn yield reached a plateau around 700 mm. Soil fertility accounted for 33 % of wheat yield variability and 5 % of corn yield variability. Management accounted for 48 and 9 % respectively. Whole polynomial models integrating rainfall, fertilizer N and P rates, soil N and P, previous crop and tillage system accounted for 67 % of wheat yield variability and 51 % of corn yield variability. Soil organic matter was not included in the models but an indirect effect on yield was detected as organic matter correlated with initial soil N levels for both crops. Soya bean as a previous crop had a positive effect on wheat and corn yields. Wheat was insensitive to tillage system but corn yield was higher under no till. N and P fertilization had a two‐ to three‐fold greater impact on yield than soil nutrient levels. As this region is considered to be of high soil fertility and has a history of very low fertilizer consumption, adequate use of N and P fertilization will be essential to maintaining high wheat and corn yields.

Assessment of Soil Potassium Sufficiency as Related to Quantity‐Intensity in Montmorillonitic Soils

No studies have been conducted to evaluate the potassium (K) quantity‐intensity (Q/I) relationships that exist in eastern South Dakota soils and how that may affect K fertility interpretations. The objectives of this study were to i) evaluate the K status of smectite‐dominant soils through quantity‐intensity relationships and (ii) relate the findings to current research on soil K release and plant availability. Soil and plant tissue samples were collected from eight different corn production fields across east‐central South Dakota. Samples were collected from areas where corn plants did or did not exhibit K deficiency symptoms. Quantity‐intensity plots were developed and used to derive the typical Q/I parameters. Little difference existed in Q/I parameters and the form of Q/I plots among field sites. The ARe K and ΔK0 values ranged from 0.0013 to 0.0113, and −0.47 to 0.18 cmolc kg−1, respectively, and most sites were considered K insufficient. The predominant phyllosilicate present in the clay‐sized fraction was montmorillonite with an estimated 17% tetrahedral charge. These soils would not be expected to contribute much plant‐available, nonexchangeable K and would be in need of frequent K fertilization. Presumably, these and similar soils, upon K exhaustion, rely heavily on K released from K‐bearing silt‐sized particles and may be highly dependent on surface‐controlled dissolution processes for labile K replenishment. Additional research needs to be conducted concerning the release kinetics of K from K‐bearing minerals of these soils.

Spatial Variability of Measured Soil Properties across Site‐Specific Management Zones

The spatial variation of productivity across farm fields can be classified by delineating site‐specific management zones. Since productivity is influenced by soil characteristics, the spatial pattern of productivity could be caused by a corresponding variation in certain soil properties. Determining the source of variation in productivity can help achieve more effective site‐specific management. The objectives of this study were (i) to characterize the spatial variability of soil physical properties across irrigated corn (Zea Mays L.) production fields and (ii) to determine if soil physical properties could explain the variability in productivity between site‐specific management zones. The study was conducted over three study sites in northeastern Colorado. The soil properties measured were bulk density, cone index, surface soil color, organic C, texture, sorptivity, and surface water content. A multi‐response permutation procedure was used to test for significant differences among soil properties between management zones. Box plots of soil physical properties were created for each management zone within each study site to determine if trends in soil physical properties corresponded to the productivity potential of the management zones. Overall, this study showed that soil physical properties exhibited significant spatial variability across production fields. The trends observed for the measured soil physical properties corresponded to the productivity potential of the management zones. Utilizing site‐specific management zones could help manage the in‐field variability of yield‐limiting soil physical properties.

Nitrogen Uptake across Site Specific Management Zones in Irrigated Corn Production Systems

Development of improved fertilizer management practices has the potential to increase fertilizer use efficiency and improve environmental quality. The objectives of this study were (i) to characterize the within field spatial variability of N uptake across irrigated corn production fields, (ii) to quantify and compare N uptake and grain yield across three site specific management zones (SSMZs), and (iii) to compare grain yield response to applied N between management zones. This study was conducted on continuous corn (Zea mays L.) in irrigated fields in northeastern Colorado. Fields were classified into high, medium, and low site specific management zones. Treatments consisted of a control and two uniform N application rates over 2 site‐years (one field over 2 consecutive yr and another field over 1 yr). Nitrogen fertilizer rates varied with site‐year and ranged from 56 to 268 kg N ha−1. Aboveground biomass samples were collected at physiological maturity and analyzed for total N. Between management zones, N uptake, grain yield, and grain yield response to applied N were found to be statistically different (p &lt; 0.05). Management zones were found to be less spatially variable than the whole field. The SSMZs accurately characterized variability in N uptake as well as grain yield response to applied N. Thus, variation in N uptake and grain yield can potentially be managed using SSMZs.

How good is your weed map? A comparison of spatial interpolators

Recent interest in describing the spatial distribution of weeds and studying their association with site properties has increased the use of interpolation to estimate weed seedling density from spatially referenced data. In addition, farmers and consultants adopting elements of site-specific farming practices are using interpolation methods for mapping weed densities as well as soil properties. This study was conducted to compare the performance of four interpolation methods, namely inverse-distance weighting (IDW), ordinary point kriging (OPK), minimum surface curvature (MC), and multiquadric radial basis function (MUL), with respect to their ability to map weed-seedling densities. These methods were evaluated on data from four weed species, velvetleaf, hemp dogbane, common sunflower, and foxtail species, of contrasting biology and infestation levels in corn and soybean production fields in Nebraska. Mean absolute difference (MAD) and root mean square (RMS) between the observed point sample data and the estimated weed seedling density surfaces were used to evaluate the performance of the interpolation methods. Four neighborhood search types were compared within each interpolation method, and Search3 (12 to 16 neighboring locations) generated an interpolated surface with the smallest MAD and RMS indicating the highest precision. IDW with a power coefficient of p = 4 gave the smallest MAD and RMS, as did a test with an elliptical search and no anisotropy. The level of precision of all four interpolation methods was very poor for weed species with low infestation levels (&gt; 75% of field weed-free; MAD ranged from 100 to 187% of the observed mean density), whereas precision was improved for weed species with high infestation levels (&lt; 25% of field weed-free; MAD ranged from 45 to 85%). No single interpolator appears to be more precise than another. Implications of this study indicate that grid sample spacing and quadrat size are more important than the specific interpolation method chosen.