Plant Whorls Research Articles

Defoliation level and timing affect popcorn yield traits in the Midwestern United States

Popcorn [Zea mays (L.) var. Everta] is an important field crop in the Midwestern United States. However, hailstorms are a major threat to ensuring high yield because of their effects on leaf photosynthesis, pollination, and stalk lodging. A multi-state study spanning six site-years (2020–2023) was conducted in two locations (Ohio and Nebraska) to determine how defoliation intensity at different stages affects yield loss in popcorn and compare these losses with current values in the National Crop Insurance Service (NCIS) Corn Loss Instructions. At each location the study was conducted in a randomized complete block design with four replicates. The treatments consisted of the combination of four levels of leaf loss (25, 50, 75 and 100 % leaf blade area removal) imposed at five developmental stages: V8 (10-leaf), V13 (15-leaf), VT, R2, and R4. The evaluated traits were plant population, grain yield, stalk lodging, and 100-kernel weight. All evaluated traits were affected by defoliation, except plant population. The treatments 100 % defoliation at VT and R2 stages were the most damaging in terms of grain yield reduction, number of ears per plant and 100-kernel weight for both locations. In Ohio, the greatest stalk lodging was observed at 100 %-R2 and in Nebraska, at 75 %-VT. For both locations, the actual yield losses in the defoliated treatments were lower than values currently listed in the NCIS Popcorn Leaf Loss Chart. These results indicate leaf loss chart values should be updated to accurately reflect yield losses from popcorn defoliation events. This evaluation did not impose damage to stalks (e.g., bruising) or to plant whorls as may be expected in natural events. Future research should incorporate other forms of plant damage such as those described to provide a better emulation of hail damage.

The Efficacy of Entomopathogenic Nematodes Plus an Adjuvant against Helicoverpa zea and Chrysodeixis includens in Aboveground Applications.

In the southern United States, corn earworm, Helicoverpa zea (Boddie), and soybean looper, Chrysodeixis includens (Walker) are economically important crop pests. Although Bt crops initially provided effective control of target pests such as H. zea, many insect pests have developed resistance to these Bt crops. Alternative approaches are needed, including biological control agents such as entomopathogenic nematodes (EPNs). However, the effectiveness of EPNs for aboveground applications can be limited due to issues such as desiccation and ultraviolet radiation. Effective adjuvants are needed to overcome these problems. Ten strains of EPNs were tested for virulence against eggs, first to fourth instars, fifth instars, and pupae of H. zea and C. includens in the laboratory. These 10 EPN strains were Heterorhabditis bacteriophora (HP88 and VS strains), H. floridensis (K22 strain), Hgkesha (Kesha strain), Steinernema carpocapsae (All and Cxrd strains), S. feltiae (SN strain), S. rarum (17c+e strain), and S. riobrave (355 and 7-12 strains). EPNs could infect eggs of H. zea or C. includens in the laboratory, but the infection was low. The mortality caused by 10 EPN strains in seven days was significantly higher for the first to fourth instars of H. zea compared to the control, as was the fifth instars of H. zea. Similarly, for the first to fourth and fifth instars of C. includens, the mortality was significantly higher compared to the controls, respectively. However, only S. riobrave (355) had significantly higher mortality than the control for the pupae of H. zea. For the pupae of C. includens, except for H. bacteriophora (HP88), S. rarum (17c+e), and H. floridensis (K22), the mortality of the other seven strains was significantly higher than the control. Subsequently, S. carpocapsae (All) and S. riobrave (7-12) were chosen for efficacy testing in the field with an adjuvant 0.066% Southern Ag Surfactant (SAg Surfactant). In field experiments, the SAg Surfactant treatment significantly increased the mortality and EPN infection for S. carpocapsae (All) on first instars of H. zea in corn plant whorls. On soybean plants, with the SAg Surfactant, S. carpocapsae (All) was more effective than S. riobrave (7-12) on fifth instars of C. includens. This study indicates that EPNs can control H. zea and C. includens, and SAg Surfactant can enhance EPN efficacy.

Biocontrol potential of entomopathogenic nematodes against invasive fall armyworm, Spodoptera frugiperda in India

The invasion of fall armyworm, Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae), has threatened the researchers to develop an effective biological control strategy at the global level. Larval stage remains in maize whorl, and precise placement of entomopathogenic nematodes (EPNs) opens up wide opportunity for biological control. The study evaluated the virulence of Heterorhabditis indica (Poinar) and Steinernema carpocapsae (Weiser) against all the developmental stages of S. frugiperda. The results revealed that both the tested EPNs had a high rate of ovicidal, larvicidal and pupicidal effects on S. frugiperda. The EPNs also significantly affected the adults, resulting in the deformation and death. The invasion efficiency and reproduction assays of EPNs revealed that H. indica had higher invasion efficiency and reproduction rates compared to S. carpocapsae on different larval stages and pupae. EPNs also reproduced in the adult cadavers of S. frugiperda emerged from the EPN-treated pupa. A preliminary study on the effect of EPN application on S. frugiperda was carried out under semi-field conditions by pre-releasing third instar larvae to whorl of corn plants. Application of H. indica and S. carpocapsae @ 500 IJs mixed with five gram of sand was applied manually to whorl led to mortality of 86.67 and 83.33%, respectively. The study demonstrated that both the EPN species tested showed high puissance as bio-control agents against S. frugiperda, having the potential for its successful management.

Efficacy of Selected Insecticides in Combination with Economic Thresholds in Managing Fall Armyworm (Lepidoptera: Noctuidae) Larvae in Maize Grown in Mexico

Abstract In Mexico, conventional insecticides are the main tools used to manage the fall armyworm, Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae), in maize, Zea mays L. This scenario results in the need to continually assess the biological efficacy of insecticides used to combat this pest. In this study, we evaluated the efficacy of insecticides with different modes of action in diverse locations under different levels of S. frugiperda larval infestation. The insecticides evaluated decreased larval density per plant to levels below the recommended economic threshold (ET) of 2.0 larvae per 10 plants (0.2/plant), resulting in decreased levels of damage to the plant whorl. When applied at infestation levels below the ET, larval numbers remained below the ET for at least 7–14 d after application. In contrast, when applied with infestation levels above the recommended ET, the performance of some insecticides in terms of effectively reducing larval density decreased. We, however, found that Coragen® (chlorantraniliprole; FMC Agroquímica de México), Clavis® (thiodicarb + triflumuron; Bayer de México), and Pleo® 50 EC (pyridalyl; Valent de México) can be used under these conditions to provide adequate protection up to 21 d after application. The information obtained in our experiments confirms the need to adjust the current ET depending on the type of compound to be used, since the insecticides used performed more efficiently and for a long time at densities lower than 2.0 larvae per 10 plants.

Laboratory and field trials reveal the potential of a gel formulation of entomopathogenic nematodes for the biological control of fall armyworm caterpillars (Spodoptera frugiperda)

The fall armyworm (FAW), Spodoptera frugiperda Smith (Lepidoptera: Noctuidae) can cause tremendous yield losses in maize. Its invasion into Africa and Asia has dramatically increased the use of insecticides in maize agro-ecosystems. Safe, effective and readily available alternatives are urgently needed. Entomopathogenic nematodes (EPN) represent a promising and sustainable option to control fall armyworm caterpillars on maize. Commonly used against soil insect pests, EPN can also be applied to control above-ground pests if formulated appropriately. We explored the possibility to control FAW by incorporating the EPN species Steinernema carpocapsae into protective formulations that can be easily applied into the whorl of maize plants, where the caterpillars mostly feed. We tested this approach in laboratory cage experiments as well as in field trials. In the laboratory, treating maize plants with a low dose of S. carpocapsae (3000 infective juveniles per plant) formulated in a carboxymethyl cellulose (CMC) gel caused 100% mortality of FAW caterpillars and substantially reduced plant damage, whereas EPN applied in water or a surfactant-polymer-formulation (SPF) caused 72% and 94% mortality, respectively. Under field conditions, one-time treatments with S. carpocapsae applied in water, SPF or CMC decreased plant damage, but only the EPN-gel formulation significantly reduced FAW infestation. As compared to control, about 40% fewer caterpillars were found on plants treated with EPN formulated in the gel. Notably, the EPN-gel formulation was as effective as a standard dose of cypermethrin, a pyrethroid insecticide commonly used against FAW, in reducing FAW infestation. Repeated applications may be needed to reduce re-infestations by FAW across a whole cropping season depending on the local maize phenology and pest dynamics. These findings demonstrate that EPN, when properly formulated, are excellent candidates for the biological control of FAW, and can be a safe and sustainable alternative to synthetic insecticides.

Evaluation of a Subset of Ethiopia Sorghum Collection Germplasm from the National Genetic Resources Program of the United States Department of Agriculture for Anthracnose Resistance

Globally, one of the most devastating diseases of sorghum is anthracnose incited by Colletotrichum sublineola. During the 2019 and 2020 growing seasons, 94 and 64 accessions from the Ethiopian sorghum germplasm collection maintained by the National Genetic Resources Program of the United States Department of Agriculture were evaluated for anthracnose resistance. Seeds were planted in 1.8 m rows with 0.9 m row spacing in a randomized complete block design. The accessions and checks were replicated three times and 30 days after planting, inoculated by placing C. sublineola-colonized grains in the plant whorls. A total of 30 accessions, including PI533918, PI533923, PI534131 and PI534151 were resistant to the disease in both years. These identified resistant sources can be used in breeding programs to develop anthracnose-resistant lines and hybrids.

Broadcasting of tiny granules by drone to mimic liquid spraying for the control of fall armyworm (Spodoptera frugiperda).

The fall armyworm (FAW), Spodoptera frugiperda (J. E. Smith), is an invasive pest. Maize is one of its preferred host plants. The traditional application of granules has been effective for the control of FAW. Nevertheless, the challenge is to develop an application method that is less labor-intensive and also efficient. Tiny granules in the size range of 0.38-0.55 mm were prepared by the centrifugal granulation method for drone application. The in-swath distribution patterns of granules deposited on sticky tapes were similar to the distribution of aqueous droplets through drone spraying. In the range of 1.5-3.5m, a relatively higher aircraft height of flight can provide a more uniform distribution pattern of deposited granules, but resulted in less deposit of tiny granules in the whorl of maize plants. Similarly, the deposit of granules in the whorl of maize plants significantly decreased when the flight speed increased from 4 to 6m s-1 . Granules gathered in the whorl accounted for 50.8-58.7% of total granules deposited in the maize canopy. The field experiment demonstrates granular formulations (containing 0.25% chlorantraniliprole +0.15% emamectin benzoate, or higher concentrations) can provide better and longer duration of FAW control than the aqueous spray formulation at the whorl stage of maize plants. Broadcasting of tiny granules by drone can provide better FAW control than liquid spray. The architecture of the maize plant and the downward airstream of the drone create favorable conditions for the deposition of granules in whorls. © 2021 Society of Chemical Industry.

Bio-efficacy of egg parasitoid, Trichogramma chilonis (Ishii) against spotted stem borer, Chilo partellus (Swinhoe) in Kharif maize

Maize stem borer, Chilo partellus, is the most serious and ubiquitous pest of maize not only in India but also throughout the Asian countries where it is a constant threat. The larvae, after hatching, enter the plant whorl and feed inside the plant for rest of the life. Owing to its cryptic behavior, insecticides are not the right choice. Moreover, unwarranted use of pesticides has directly increased the cost of cultivation and accounted for many health as well as environmental hazards. Use of biological control agents is far better than harmful agro-chemicals in terms of health benefits and ecosystem stability, provided they are effective enough to suppress the pest population. Egg parasitoid, Trichogramma chilonis, has proven its worth against many lepidopteran borers and provided satisfactory control in many crops. With this view, an experiment was conducted to evaluate the potency of T. chilonis against spotted stem borer, Chilo partellus at laboratory and research area of CCS Haryana Agricultural University, Regional Research Station, Karnal during Kharif, 2017. In our study, maximum egg parasitization (62.40%) was recorded in treatment with two releases of T. chilonis parasitized eggs @ 1,25,000/ha at 7 and 14 days after germination (DAG) which was at par with two releases of T. chilonis parasitized eggs @ 1,00,000/ha at 7 and 14 DAG (60%) whereas treatment with one spray of Dimethoate 30 EC @ 660 ml/ha had minimal T. chilonis activity (3.5% parasitization). Lower leaf injury rating (LIR), plant infestation and dead hearts were recorded in treatments with two release of T. chilonis parasitized @ 1,25,000 and 1,00,000 eggs/ha at 7 and 14 DAG which were statistically comparable with Dimethoate 30 EC treated plots. Whereas treatments with single release of T. chilonis parasitized eggs did not provide satisfactory control. Treatment with two releases of T. chilonis parasitized eggs @ 1,00,000/ha at 7 and 14 DAG was the most economically remunerative with the highest incremental cost: benefit ratio (1:32.48) and benefit: cost ratio (1.41). Although, pesticide treated plots (Dimethoate 30 EC @ 660 ml/ha at 7 DAG) provided satisfactory monetary return but it is not environmentally compatible and ecologically viable for long run.

Relationship between Leaf and Fibre Characteristics of Agave sisalana

With decrease in wood from the forest, non-wood fibres have attracted interest in the production of pulp and paper products in recent times due to their short growth cycles, moderate irrigation and fertilizer requirements as well as their low lignin content. The use of these plants will aid sustainable development in the pulp and paper industry. This study investigated leaf dimensions and fibre characteristics of Agave sisalana and how the leaf dimensions relates to its fibre characteristics. Leaves were collected from three sisal plant stands in Oyo State, Nigeria. The plant whorl was divided systematically into bottom, middle and top from which five leaves were randomly collected from each whorl position. The fibres of the leaves were extracted from which 2cm of fibres were taken from three positions on the leaf (top, middle and base). Extracted fibres were macerated and 3375 fibres were measured. The result shows that Agave sisalana leaves collected at the top had the longest length and was also widest at the base and middle. The average fibre length was 1.69 mm, while the fibre diameter, lumen width and cell wall thickness of Agave sisalana were 16.98 µm, 12.33 µm and 2.32 µm respectively. The slenderness ratio averaged 99.4 while the coefficient of flexibility averaged 72.61. The highest value of the runkel ratio of Agave sisalana was 0.42. There was significant negative correlation between leaf characteristics and fibre characteristics. Young sisal (Agave sisalana) leaves produced the best fibre characteristics suitable for the production of high quality paper.

Screening Sorghum Accessions for Resistance against Anthracnose and Grain Mold through Inoculating with Pathogens

Aims: The aim of this study was to identify resistant accessions against pathogens, causing anthracnose and grain mold.
 Study Design: Study was laid out in a randomized complete block design with three replications. Data for anthracnose rating, grain mold severity, seed weight, and percent germination rate were analyzed using the command PROC GLM.
 Place and Duration of Study: The study was carried out at the Texas AgriLife Research Farm, Burleson County, Texas, in 2010, 2014, and 2015 growing seasons.
 Methodology: Forty-seven accessions were planted in 6 m rows 0.31 m spacing. Plants were inoculated by placing Colletotrichum sublineola colonized grain in the plant whorls 30 days after planting. Disease evaluation was initiated 30 days post-inoculation and thereafter on a weekly basis for three consecutive weeks. Grain mold experiment: Three treatments were used: 1) plants sprayed with A. alternata alone, 2) a mixture of A. alternata, F. thapsinum and C. lunata, 3) control plants sprayed with sterilized water and exposed to natural infection. At 50% bloom, three panicles per line within replication were inoculated for each treatment.
 Results: Eleven accessions, including PI641874, PI656070, PI656115, and PI534167 were consistently resistant when challenged with the anthracnose pathogen, C. sublineola. Accessions PI534047 and PI574455, exhibited resistance to moderately resistance grain mold response when challenged with the treatments. Seed weight, germination rate, and mycoflora analysis which are factors in determining grain mold resistance also were measured. Across the accessions, mean seed weight ranged from1.4 g to 4.3 g per 100 kernel and germination rate ranged from 26 to 87%. 
 Conclusion: The resistant accessions identified in this study can be used in breeding programs to develop anthracnose and grain mold resistance lines.

Water in maize whorl enhances the control of Spodoptera frugiperda with insecticides

ABSTRACT The fall armyworm Spodoptera frugiperda is among the main insect-pests on maize crops, due to its damaging potential and control issues related to the larval habit of concealing itself within the plant whorl. This study aimed to evaluate the effect of water in the maize whorl, combined with insecticides and spray sets, on the damage caused by S. frugiperda and the grain yield. The experiments were carried out under field conditions, at two cropping seasons, both with Bt-maize hybrids, in a 2 × 2 × 5 + 1 factorial scheme, testing the presence or absence of water inside the plant whorl, two insecticides and five spray sets (combinations of spray volumes, nozzle types, pressures and spraying speed), plus a control without water and insecticide. The presence of water inside the whorl reduced the damage caused by S. frugiperda during the early growth stages, especially in the plants sprayed with the insecticide chlorantraniliprole. The spray sets with 200 L ha1/20.3 psi or 250 L ha1/33.4 psi provided the highest reductions in the percentage of damaged plants and damage scores, regardless of the insecticide. Therefore, the spraying of insecticides, when there is water from irrigation, dew or rainfall inside the maize whorl, improves the control of S. frugiperda in maize crops, especially in Bt-maize.

Great Plains Yucca (Yucca glauca) Control on Shortgrass Rangelands

AbstractGreat Plains yucca is a native species that competes with forage plants for space and water and at high densities may warrant control. The objective of this study was to determine the efficacy of seven herbicides applied in the spring or fall for Great Plains yucca control. Six foliar herbicides applied by ground application at 187 L ha−1 spray volume, one herbicide applied to individual plant whorls, and a nontreated check were established in June and September of 2009 and 2011. Percent mortality was determined 12 to 16 mo after herbicide application. Most herbicides gave similar control between the 2 yr, with triclopyr in diesel applied to individual plant whorls at 10 g L−1 providing the greatest control at 83%. Most herbicides applied in June near the blooming stage of Great Plains yucca were more effective than September treatments. June treatments providing the greatest reduction in yucca densities were metsulfuron + dicamba + 2,4-D amine + 2,4-D low volatile ester (LVE) at 21 + 113 + 325 + 431 g ae ha−1, metsulfuron + aminopyralid + triclopyr at 49 + 9 + 227 g ha−1, metsulfuron + chlorsulfuron + 2,4-D LVE at 34 + 11 + 431 g ha−1, and metsulfuron + aminopyralid + 2,4-D LVE at 49 + 9 + 431 g ha−1. A single application of a foliar herbicide provided a maximum of 72% mortality of Great Plains yucca, suggesting that repeat application may be necessary to achieve optimum control.

The effect of Busseola fusca infestation, fungal inoculation and mechanical wounding on Fusarium ear rot development and fumonisin production in maize

Fusarium verticillioides and Busseola fusca are among the most significant biotic constraints to maize production in South Africa. In this study, the effect of B. fusca damage and mechanical wounding to maize ears on Fusarium ear rot development and fumonisin production was investigated. The effect of the interaction on Fusarium ear rot and B. fusca damage was studied by inoculating maize ears with F. verticillioides isolate MRC826 and infesting plant whorls with aliquots of 10–15 neonate larvae at the 12th leaf stage prior to tasselling. To simulate hail damage, maize ears were mechanically wounded at the blister stage with cork borers of different sizes and number of wounds, with and without F. verticillioides inoculation. Uninoculated, uninfested and undamaged control treatments were included. Field trials were conducted over three seasons using a randomised complete block design with six replicates per treatment. In all seasons, most Fusarium ear rot developed on ears inoculated with F. verticillioides. This study indicated that B. fusca infestation was not associated with higher Fusarium ear rot incidence in two of the three seasons. Moreover, B. fusca infestation was not associated with high fumonisin production in any season. This indicates that the presence of B. fusca was not highly associated with Fusarium ear rot or fumonisin production, possibly due to its characteristic feeding nature that causes sporadic wounds on maize ears, but also the strong impact of weather variability. Fusarium ear rot development and fumonisin production by F. verticillioides inoculum varied seasonally indicating the importance of environmental conditions on Fusarium ear rot and fumonisin production. Fusarium ear rot and fumonisin production significantly increased with the severity of cork borer wounding in both naturally infected and artificially inoculated maize ears. Therefore, the prevention of severe injuries to kernels, whether by mechanical damage or insects, should be considered as important in reducing Fusarium ear rot and fumonisin production in maize.

First Report of Corn Whorl Rot Caused by Serratia marcescens in China

AbstractWhorl rot is a novel disease of corn found in the Huang‐Huai‐Hai Plain, China. Common symptoms of the disease in fields include yellowing and water‐soaked brown necrosis of young leaves in the whorl of corn plants, which often results in rot of the whorl. Bacterial streaming was always observed from diseased samples. Bacterial isolates were obtained from symptomatic tissue and further confirmed to be the casual agent of the disease using Koch's Postulates. Sequence analysis of 16S rDNA, housekeeping gene groES‐groEL and BIOLOG tests revealed that the isolate B3R3 belongs to the bacterium Serratia marcescens. None of the corn cultivars evaluated showed acceptable resistance to the disease. To our knowledge, this is the first report on corn whorl rot caused by Serratia marcescens.

Larval survival and plant injury of Cry1F-susceptible, -resistant, and -heterozygous fall armyworm (Lepidoptera: Noctuidae) on non-Bt and Bt corn containing single or pyramided genes

The fall armyworm, Spodoptera frugiperda (J.E. Smith), is a major target of transgenic corn, Zea mays L., expressing Bacillus thuringiensis (Bt) proteins in both North and South America. A highly Cry1F-resistant strain of S. frugiperda was established from a field collection in Puerto Rico in 2011. In this study, three greenhouse trials were conducted to evaluate larval survival and leaf injury of Cry1F-susceptible, -resistant, and -heterozygous genotypes of S. frugiperda on whole plants of five non-Bt and eight Bt corn hybrids. The Bt corn products included two single-gene Bt corn hybrids containing Herculex®I (Cry1F) and YieldGard® (Cry1Ab) traits and six pyramided Bt corn hybrids representing four traits: Genuity® VT Double Pro™, Genuity®VT Triple Pro™, Genuity® SmartStax™, and Agrisure® Viptera™ 3111. In each trial, neonates of S. frugiperda were placed into the plant whorls at vegetative plant stages (V6–V10). Larvae of the three insect genotypes on non-Bt corn hybrids survived well and caused serious plant injury. Cry1Ab corn was ineffective against all three insect genotypes. On Cry1F corn plants, resistant larvae survived on 72.9% plants after 12–15 d and caused a leaf injury rating (Davis' 1 to 9 scales) of 5.7 after 7 d and 7.6 after 12–15 d. Both the larval survivorship and leaf injury rates of the resistant larvae on Cry1F corn plants were not significantly different from those observed on non-Bt corn hybrids. In contrast, no live larvae and little or no leaf injury were observed on the Cry1F corn plants that were infested with susceptible or heterozygous genotypes, or on the pyramided Bt plants. The results demonstrated that the Cry1F-resistant S. frugiperda was highly resistant to whole plants of Cry1F corn and the resistance was recessive. Hybrids that contained one of the four pyramided Bt traits were effective for managing the Cry1F resistance in S. frugiperda.

Comparison of Two Inoculation Methods for Evaluating Maize for Resistance toAspergillus flavusInfection and Aflatoxin Accumulation

Aflatoxin, the most potent carcinogen found in nature, is produced by the fungusAspergillus flavusand occurs naturally in maize,Zea maysL. Growing maize hybrids with genetic resistance to aflatoxin contamination are generally considered a highly desirable way to reduce losses to aflatoxin. Developing resistant hybrids requires reliable inoculation methods for screening maize germplasm for resistance toA. flavusinfection and aflatoxin accumulation. The side-needle technique is a widely used inoculation technique: anA. flavusconidial suspension is injected underneath the husks into the side of the ear. This wounds the ear and limits expression of resistance associated with husk coverage, pericarp thickness, and seed coat integrity. In this investigation, the side-needle technique was compared with a second inoculation method that involved dispensing wheat kernels infected withA. flavusinto plant whorls at 35 and 49 days after planting. Results showed that although the side-needle technique produced higher levels of aflatoxin accumulation, differences inA. flavusbiomass produced by the two inoculation techniques were not significant. Both inoculation techniques were effective in differentiating resistant and susceptible single cross hybrids irrespective of the use ofA. flavusinfection or aflatoxin accumulation as a basis to define resistance.

Technique to Assess Effectiveness of Control Tactics Against <I>Ostrinia nubilalis</I> (Lepidoptera: Crambidae) in Whorl-Stage Corn

Ostrinia nubilalis (Hübner) (Lepidoptera: Crambidae) is one of the most damaging insect pests of corn. Studies were conducted to determine whether live larval counts obtained from corn whorls were predictive of the amount of larval tunneling that would result in the stalk of the plant 40 d later at the end of larval development. Whorls from plants treated with Dipel 10G (6,400 IU per whorl) and untreated controls, both infested with O. nubilalis neonates, were evaluated for the number of live larvae in 50 whorls 5, 7, 9, and 12 d after Bacillus thuringiensis (Berliner) (Bacillales: Bacillaceae) application. Forty days after larval infestation, 25 plants from each plot were split from tassel to base, and the length of larval tunneling was recorded. There was a strong relationship between numbers of live larvae in the plant whorl and the length of larval tunneling that resulted. While linear at each location, there was significant variation in the relationship among locations, indicating that comparisons could not be made between years or locations within a year. Blocks within a location on a given year did not vary significantly and reproducible results were obtained each year within a given location as well as on any of the whorl pulling dates evaluated. Because of its ease of use, predictability, and rapid return of results, we propose this technique as an additional method to shot-hole feeding and stalk splitting to evaluate the effectiveness of O. nubilalis management strategies.

Biological control of aflatoxin contamination in corn using a nontoxigenic strain of Aspergillus flavus.

A 2-year study was conducted to determine the efficacy of different applications of a nontoxigenic strain of Aspergillus flavus for reducing aflatoxin contamination in corn. Treatments consisted of the nontoxigenic strain in the form of (i) conidia-coated hulled barley applied to soil when corn was about 0.8 m tall, (ii) conidia-coated hulled barley applied in plant whorls prior to tasseling, (iii) multiple applications of a spray formulation of conidia during silking, and (iv) untreated control. Treatments were replicated eight times in individual plots consisting of four rows of 18 m each. In year 1, no significant differences were associated with treatments for aflatoxin, total A. flavus colonization, or incidence of nontoxigenic isolates of A. flavus in corn, which were all relatively high, ranging from 83.8 to 93.1%. In year 2, the whorl application produced a significantly lower mean aflatoxin concentration of 49.5 ppb compared with all other treatments, while both the soil (108.3 ppb) and spray applications (173.7 ppb) were significantly reduced compared with the control (191.6 ppb). The whorl application was the only treatment that had a significantly higher incidence (86.5%) of nontoxigenic isolates of A. flavus than the control had, which was still relatively high at 69.1%. Data indicated that applications of the nontoxigenic strain influenced untreated corn, thus reducing the apparent effect of the biocontrol treatments. Larger-scale studies with greater separation between treated and untreated fields are warranted.

The effect of the adjuvant, Break-Thru S240, on whorl penetration and efficacy of foliar insecticide applications against Chilo partellus

Insecticide sprays registered for the control of maize stem borers are all intended for whorl application. Chemical control of these pests is complicated by their cryptic feeding habit inside plant whorls. The aim of this study was to investigate whether addition of the organosilicone adjuvant, Break-Thru S240, to insecticide sprays would result in improved stem borer control. In one experiment the position of stem borer feeding damage inside plant whorls was quantified to have a standard for comparison and evaluation of the effective distances of downwards movement of spray applications into whorls. The distance of movement of spray applications at five adjuvant rates (50, 100, 200, 400 & 600 ml ha−1) into whorl leaves was determined. A colorant was added to spray applications to facilitate measuring the distances of downwards movement of water into each whorl leaf. A 14% increase in downwards movement of sprays into the target zone was observed with addition of the adjuvant. Efficacy of insecticide sprays for control of C. partellus with and without the adjuvant was evaluated under field conditions. Increased levels of efficacy were observed with addition of the adjuvant but not with all the insecticides.

Identification of QTL for maize resistance to common smut by using recombinant inbred lines developed from the Chinese hybrid Yuyu22

Common smut in maize, caused by Ustilago maydis, reduces grain yield greatly. Agronomic and chemical approaches to control such diseases are often impractical or ineffective. Resistance breeding could be an efficient approach to minimize the losses caused by common smut. In this study, quantitative trait loci (QTL) for resistance to common smut in maize were identified. In 2005, a recombinant inbred line (RIL) population along with the resistant (Zong 3) and susceptible (87-1) parents were planted in Beijing and Zhengzhou. Significant genotypic variation in resistance to common smut was observed at both locations after artificial inoculation by injecting inoculum into the whorl of plants with a modified hog vaccinator. Basing on a genetic map containing 246 polymorphic SSR markers with an average linkage distance of 9.11 cM, resistance QTL were analysed by composite interval mapping. Six additive-effect QTL associated with resistance to common smut were identified on chromosomes 3 (three QTL), 5 (one QTL) and 8 (two QTL), and explained 3.2% to 12.4% of the phenotypic variation. Among the 6 QTL, 4 showed significant QTL x environment (Q x E) interaction effects, which accounted for 1.2% to 2.5% of the phenotypic variation. Nine pairs of epistatic interactions were also detected, involving 18 loci distributed on all chromosomes except 2, 6 and 10, which contributed 0.8% to 3.0% of the observed phenotypic variation. However, no significant epistasis x environment interactions were detected. In total, additive QTL effects and Q x E interactions explained 38.8% and 8.0% of the phenotypic variation, respectively. Epistatic effects contributed 15% of the phenotypic variation. The results showed that besides the additive QTL, both epistasis and Q x E interactions formed an important genetic basis for the resistance to Ustilago maydis in maize.