The mode of action of chlorsulfuron: A new herbicide for cereals

Chlorsulfuron (2-chloro-N-[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)aminocarbonyl]benzenesul-fonamide) is the active ingredient in DuPont “Glean” Weed Killer (formerly DPX-4189), a new herbicide for weed control in small grains as well as other uses. Continuous growth measurements of chlorsulfuron-sensitive seedlings demonstrated that the herbicide inhibits growth within 2 hr of application and by 8 hr reduces growth by 80%. This reduction in growth was closely associated with an inhibition of plant cell division. No significant effects were observed on auxin-, cytokinin-, or gibberellin-induced cell expansion. Photosynthesis, respiration, RNA synthesis, and protein synthesis were also initially unaffected under conditions where plant cell division is strongly inhibited.     

In vitro biomechanical comparison of cervical disk arthroplasty, ventral slot procedure, and smooth pins with polymethylmethacrylate fixation at treated and adjacent canine cervical motion units

Objective— To compare the biomechanical properties of cervical arthroplasty to a ventral slot procedure and pin‐polymethylmethacrylate (pin‐PMMA) fixation. Sample Population— Fresh cadaveric cervical (C2–T1) spines from 6 large dogs. Methods— Four spinal conditions were studied in each spinal specimen: intact, disk arthroplasty, ventral slot, and fixation with smooth pin‐PMMA at C5–C6 intervertebral space. Axial compression, torsion, flexion–extension, and lateral bending moments were sequentially tested on each specimen for the 4 spinal conditions. Data from the C3–C4, C4–C5, C5–C6, and C6–C7 vertebral motion units (VMUs) were compared among treatments. Results— In axial compression and torsion, the ventral slot procedure allowed significantly less motion than intact, pin‐PMMA, and arthroplasty groups at C5–C6. In lateral bending and flexion–extension, pin‐PMMA had the least motion of C5–C6, followed by the arthroplasty group, intact spine, and ventral slot, all of which were significantly different from each other. Overall, the artificial disk was better able to mimic the behavior of the intact specimens compared with the ventral slot and pin‐PMMA, producing similar displacements in axial compression and rotation in torsion, but more limited motion than intact in flexion–extension and in lateral bending. Conclusion— Cervical spine specimens with an implanted prosthesis have biomechanical behaviors more similar to an intact spine compared with spinal specimens with ventral slot and pin‐PMMA procedures. Cervical arthroplasty may then preserve some of the motion in the affected area after neural decompression while providing distraction. Clinical Relevance— Cervical arthroplasty should be further investigated in vivo to determine if it is a viable alternative to the ventral slot or pin‐PMMA procedures for surgical treatment of cervical diseases in dogs and in particular for treatment of disk‐associated caudal cervical spondylomyelopathy.     

The importance of economic injury levels in the development of integrated pest control programs

Summary Although economic injury levels have long been considered of importance in determining the needs for pest control measures, they take on added significance in integrated pest control programs. The designation of damage tolerance levels defines the goals of the integrated control effort. These management goals should be defined in terms of damage not numbers of pests. Although insect numbers and damage incidence are related they are not perfectly correlated and the relationship varies with changes in the ecological and economic environment. Many plants have the ability to tolerate or compensate for large amounts of injury without affecting yield or quality. Other plants have a limited capacity to produce a marketable crop; pest injury which does not reduce the capacity of the plant is not damage. These characteristics of plants, among others, and the limitations of artificial control measures permit the maintenance of subeconomic levels of pests in agricultural crop areas. These subeconomic pest populations foster an entomophagous fauna. It is very difficult to calculate precise cost/potential benefit ratios because of subtile long-term effects of artificial controls and the vagaries of estimates of potential economic value of the harvested crop.

---

Zusammenfassung Obwohl man die wirtschaftlichen Schadensgrenzen für die Feststellung der erforderlichen Schädlingsbekämpfungsmaßnahmen seit langem für wichtig hält, gewinnen sie in integrierten Programmen zusätzliche Bedeutung. Die Bestimmung der Schadenstoleranzgrenzen setzt die Ziele für den integrierten Bekämpfungseinsatz. Die Art der Behandlung sollte auf Grund des Schadens und nicht auf Grund der Zahl der Schädlinge festgelegt werden. Die Insektenzahl und die Häufigkeit des auftretenden Schadens stehen zwar miteinander im Zusammenhang, sind aber nicht vollständig korreliert. Ihr Verhältnis variiert mit Veränderungen der ökologischen und wirtschaftlichen Situation. Viele Pflanzen haben die Fähigkeit, großen Schaden zu ertragen oder zu kompensieren, ohne daß dadurch der Ertrag oder die Qualität beeinflußt werden. Andere Pflanzen besitzen eine begrenzte Fähigkeit, eine marktgerechte Ernte hervorzubringen. Ein Schädlingsbefall, der die Ertragsfähigkeit der Pflanze nicht beeinträchtigt, ist keine Schädigung. Diese und andere Merkmale der Pflanzen und die Einschränkung der künstlichen Bekämpfungsmaßnahmen gestatten die Erstellung subökonomischer Schadensgrenzen in landwirtschaftlichen Anbaugebieten. Diese subökonomischen Schädlingspopulationen sind in der Lage, eine entomophage Fauna zu fördern. Es ist sehr schwierig, ein genaues Verhältnis zwischen den exakten Kosten und dem potentiellen Nutzen zu berechnen, weil die subtile langfristige Wirkung der künstlichen Bekämpfung und die Zufälligkeiten bei Berechnungen des potentiellen wirtschaftlichen Wertes der Ernte berücksichtigt werden müssen.

---

Résumé Bien que le niveau de dégâts économiques ait depuis longtemps été d'une grande importance pour déterminer quelles étaient les mesures de lutte antiparasitaires à prendre, il joue un rôle encore plus significatif dans l'élaboration de programmes de lutte intégrée. C'est la fixation du niveau de dégâts admissible qui établit les buts des efforts à fournir en matière de lutte intégrée. Ces buts devraient être définis en termes de dommages et non de nombres de parasites. Bien qu'il y ait une relation entre le nombre d'insectes et les dommages causés, la corrélation n'est pas parfaite et les rapports varient avec les changements du milieu écologique et économique. Beaucoup de plantes sont capables de tolérer ou de compenser une grande partie des dommages subis sans que le rendement ni la qualité ne s'en trouvent affectés. D'autres plantes au contraire ont une capacité limitée de produire une récolte susceptible d'être commercialisée; du moment que les insectes ne réduisent pas la capacité de production de la plante, on ne peut pas parler de dégâts. Ces caractéristiques que possèdent, entre autres, les plantes et la restriction des mesures de lutte phytosanitaire ont pour résultat le maintien des parasites infestant les récoltes agricoles à des niveaux qui ne menacent pas le rendement, et qui nourrissent la faune insectivore. Il est très difficile de calculer les rapports précis qui existent entre le prix de revient et le bénéfice possible étant donné les effets à long terme non tangibles d'une lutte artificielle et les difficultés à évaluer exactement la valeur virtuelle des récoltes.

     

Susceptibility of potato varieties and advanced breeding lines (Solanum tuberosum L.) toPhytophthora infestans (Mont.) de Bary in greenhouse screenings

Late blight (Phytophthora infestons (Mont.) de Bary) has re-emerged as an important pathogen of the cultivated potato (Solanum tuberosum subsp.tubero-sum L.) in North America. The purpose of this study was to evaluate the relative susceptibility of potato germplasm in the greenhouse in order to initiate a breeding program for resistance to the US-8/A2 mating type which is the more aggressive and prevalent strain of late blight. Whole plants of 147 cultivars and breeding lines were evaluated. Percent plant area infection was visually assessed. Seven days after inoculation, infection ranged from 0 to 100% and the overall mean was greater than 50%. Two-thirds of the cultivars and breeding lines tested were very susceptible to the US-8 genotype. The highest resistance was identified in the somatic hybrids betweenS. tuberosum andS. bulbocastanum and their backcross derivatives. Pike and Snowden were less susceptible than the other North American cultivars. Zarevo was most resistant among the European cultivars. Seven of the advanced breeding lines were equivalent to Zarevo in infection levels. The host plant resistance identified among the material tested in this study can be used by breeding programs to develop improved cultivars with resistance to US-8 genotypes of late blight.     

Integrated nutrient management (INM) on yield trends and sustainability,nutrient balance and soil fertility in a long-term (30 years) rice-wheat system in the Indo-Gangetic plains of India

We analyzed data from a long-term rice–wheat cropping sequence to evaluate the effects of integrated nutrient management (INM) on yield trends and sustainability, nutrient balance and soil fertility of the system. After 30th cycle, grain yield of both the crops significantly declined under control and highest rice and wheat grain yields were obtained when 50% N supplied through green manure and farm yard manure, respectively. The magnitude of yield slope under INM was found considerably higher than 100% recommended fertilizer (RDF). Sustainable yield index (SYI) for both the crops were found lower in control but considerably higher with the 100% RDF and under INM. The soils under all the treatments suffered an apparent loss of K and N (except where organics replacing 50% N). Correlation study also reveals K is the sole factor for the yield sustainability as apparent K balance was negatively correlated with SYI and yield slope.     

Long-term irrigation with zinc smelter effluent affects important soil properties and heavy metal content in food crops and soil in Rajasthan,India

Use of wastewater for irrigating agricultural crops is on the rise, particularly in the developing countries. The present study was undertaken to assess the long-term effect of irrigation with zinc smelter effluent on important soil properties including heavy metal status. Metal concentration in the edible parts of the crops grown on smelter effluent-irrigated soils was also measured. For this purpose, the agricultural lands which have been receiving the zinc smelter effluent irrigation for about five decades at Debari, Udaipur, India were selected. The adjacent tubewell water-irrigated fields were selected as reference. Long-term irrigation with smelter effluent resulted into significant buildup of ethylenediaminetetraacetic acid extractable Zn (57.7 fold), Cu (4.51 fold), Fe (3.35 fold), Mn (1.77 fold), Ni (1.20 fold), Pb (45.1 fold), and Cd (79.2 fold) in soils over tubewell water-irrigated fields. Total Zn, Cu, Mn, Ni, Pb, and Cd content in effluent-irrigated soils was also increased by 27.0, 1.60, 1.40, 1.30, 26.2, and 167 fold, respectively. Risk assessment indicated a very high to moderate potential ecological risk due to Cd, Pb, and Zn in soils close to the immediate vicinity of the smelter plant. Cadmium and Pb concentrations in edible parts of almost all the crops grown on effluent-irrigated soils were above the safe limit of CODEX commission. On an average, soil pH dropped by 0.31 units due to smelter effluent irrigation. Smelter effluent irrigation resulted into significant increase in soil organic carbon, electrical conductivity, and CaCO₃ content. On an average, there was decrease in available N (21.0%) and P (20.8%) content in effluent-irrigated soils over the tubewell water-irrigated ones. An increase in available K (102%) and S (26.0 fold) was recorded in effluent-irrigated soils. Long-term irrigation with zinc smelter effluent resulted into reduced microbial activities in soil as evidenced from the level of microbial biomass carbon and dehydrogenase activity. In view of the buildup of heavy metals and subsequent imbalance in essential plant nutrients in smelter effluent-irrigated soils, appropriate remediation-cum-fertilization strategy needs to be adopted for better soil health and plant nutrition.