Diclofop resistance in sterile wild oat (Avena sterilis L.) in wheat fields in Greece and its management by other post-emergence herbicides

In 2009, a survey was conducted of cereal fields in five prefectures of Greece to establish the frequency and distribution of herbicide-resistant sterile wild oat (Avena sterilis L.). In total, 104 sterile wild oat accessions were collected and screened in a field experiment (conducted in 2009 and repeated in 2010) with several herbicides commonly used to control this weed. Most of the sterile wild oat accessions (89%) were classed as resistant (or developing resistant) to the ACCase-inhibiting herbicide diclofop, while resistance to other ACCase-inhibiting herbicides was markedly lower. The results of the pot experiments showed that some of the sterile wild oat accessions were found to have a very high level of diclofop resistance (resistance index up to 28.6), while cross-resistance with other herbicides was common. The levels of resistance and cross-resistance patterns varied among biotypes with different amount and time of selection pressure, indicating either more than one mechanism of resistance or different resistance mutations in these sterile wild oat biotypes. LA14, which had the highest diclofop resistance level (28.6 resistance index), showed resistance to all APP herbicides applied and non-ACCase inhibitors. Alternative ACCase-inhibiting herbicides, namely tralkoxydim and pinoxaden remain effective on 86 and 92% of the tested sterile wild oat populations, respectively. For the ALS-inhibiting herbicide mesosulfuron + iodosulfuron, nearly all the sterile wild oat accessions were susceptible (97%), with only 3 of them classed as developing resistance. Therefore, there is an opportunity to effectively control sterile wild oat by selecting from a wide range of herbicides and other cultural practices. Early post-emergence herbicide application is strongly suggested, since it could decrease the number of resistant seeds in the field and slow down the dispersal of this major problem.     

Trends of climatic potential and on-farm yields of rice and wheat in the Indo-Gangetic Plains

Rice and wheat are the two most important cereals in the Indo-Gangetic Plains (IGP) and are responsible for the food security of the region. To understand the productivity trends in the transects of the IGP: (1) the climatic potential yields of rice and wheat were simulated using a crop simulation modeling approach and (2) the long-term trends of potential and on-farm yields were compared. The potential yields of rice and wheat in the IGP ranged from 7.7 to 10.7 and 5.2 to 7.9 Mg ha⁻¹, respectively. The upper transects of the IGP are more productive and yield decreases by 27% for rice and by 32% for wheat from transect 2 to transect 5. The rate of change in the potential yield trend of rice from 1985 to 2000 ranged from −0.12 to 0.05 Mg ha⁻¹ per year. Negative yield trends were observed at six of the nine sites, four of which were statistically significant (P<0.05). The decrease in radiation and increase in minimum temperature were the reasons for the yield decline. The potential yield trend of wheat, however, appeared to be stable. On-farm yields of rice also showed a negative trend but for wheat the trend was mostly positive. The adverse changes in the weather parameters and declining trends of potential and on-farm yields of rice should be taken as an indication of a future problem. Regular on-farm monitoring of crops and climatic factors is urgently needed for predicting problems and allowing measures to be taken to improve productivity.     

Selectivity and weed control efficacy of pre- and post-emergence applications of clomazone in Southern Brazil

During the 2006/07 and 2008/09 growing seasons in Southern Brazil, we evaluated crop selectivity and weed control efficacy of clomazone on rice when applied alone or in a mixture with other pre- and post-emergence herbicides (BRS Querência variety). All herbicide treatments caused some degree of rice injury during both years; however, in no case was the injury still visible 21 days after application. Rice injuries were observed when application rates exceeded the recommended dose, and particularly when the herbicide was applied pre-emergence. Density reduction and panicle sterility served as measures of rice injury. Echinochloa crus-galli was the primary weed; it reduced rice yields by approximately 50% compared treated plots. In both growing seasons, clomazone herbicide (400 g ai ha⁻¹) controlled the weed 87.0%–99.6%, and it provided 8.06 t ha⁻¹ to 9.44 t ha⁻¹ of rice yield.     

Integrated effect of allelochemicals and herbicides on weed suppression and soil microbial activity in wheat (Triticum aestivum L.)

To evaluate the allelopathic effects of major crops and weeds, studies were conducted during 2011–12 and 2012–13 by utilizing water extracts of allelopathic plants namely rice (Oryza sativa L.), Parthenium hysterophorus L., Phragmites australis Cav., and Datura alba L. with reduced rates of fenoxaprop-p-ethyl and bromoxynil plus MCPA to control weeds. Application of Phragmites australis and Parthenium hysterophorus along with lower rates of fenoxaprop-p-ethyl and bromoxynil plus MCPA showed promising results by controlling weeds and improving yield. Parthenium hysterophorus extract with half of the recommended dose of fenoxaprop-p-ethyl and bromoxynil plus MCPA reduced weed density by 51 and 50% during year 1 and year 2, respectively, compared with the control. Phragmites australis extract with half of the recommended dose of fenoxaprop-p-ethyl produced grain yield (5.7 and 6.1 t ha⁻¹ during year 1 and 2, respectively) in wheat. However, these results were also at par with Parthenium hysterophorus and Datura alba extracts in combinations with half the recommended doses of the above mentioned herbicides. The study of microbial activity showed higher amount of mineralizable carbon in D. alba with half the recommended dose of fenoxaprop-p-ethyl treated plots (0.073 g during both the years). The lowest amount of mineralizable carbon (0.035 and 0.030 g during year 1 and 2, respectively) was observed in the control plots. The presence of allelopathic plants in field crops and subsequent mixing in soil by tillage may create problems in crop production. Therefore, further studies are suggested to fully explore all the possible interactions among allelochemicals and herbicides.     

Control of Helminthosporium leaf blight of spring wheat using seed treatments and single foliar spray in Indo-Gangetic Plains of Nepal

Four fungicides for seed treatments and one as foliar spray were tested in replicated field experiments in a strip plot design to determine the effect of fungicides on Helminthosporium leaf blight (caused by Cochliobolus sativus and Pyrenophora tritici-repentis) severity and grain yield of wheat. Wheat seed cv. RR 21 was treated with fungicides, carbendazim (Areestin), triadimenol (Baytan), tebuconazole (Raxil), and carboxin + thiram (Vitavax 200B). Single foliar application of propiconazole (Tilt) was sprayed at flowering stage. Controls were included for both factors and treatments were replicated four times. Triadimenol and carboxin + thiram increased seed germination in both years. Triadimenol, tebuconazole, and carboxin + thiram reduced the number of infected seedlings and seedling root rot severity in both years. Number of tillers was higher in carboxin + thiram treated plots compared to other seed treatments. Compared to the control, carboxin + thiram increased grain yield by 9% and 8% in 2004 and 2005, respectively, and triadimenol by 6% in both years. The foliar spray of propiconazole significantly reduced Helminthosporium leaf blight severity and increased thousand-kernel weights. Propiconazole spray increased grain yield by 15% and 14% in 2004 and 2005, respectively. Therefore, seed treatment either with triadimenol or carboxin + thiram in combination with single post-flowering foliar spray of fungicides should minimize grain yield loss due to wheat foliar blight in South Asia. The findings of this study could be useful in developing strategies to manage Helminthosporium leaf blight in South Asia and other warm wheat growing regions of the world.     

影响大豆田除草剂防除效果因素及对策

概述了影响北部大豆田化学除草剂应用效果的自然气候,杂草演变,施用技术,人为因素等,就影响因素进一步提出了相应解决对策。     

Evaluation of post-emergence herbicides for the control of wild oat (Avena fatua L.) in wheat and barley in Argentina

Wild oat (Avena fatua L.) is the most troublesome weed in cereal crops in Argentina. With the aim of studying the effects of different herbicides, doses, and wild oat growth stage at application on weed control and crop yield, field experiments were conducted in wheat and barley crops during three growing seasons in the south of Buenos Aires Province, Argentina. Treatments were post-emergence applications of new herbicide, pinoxaden + cloquintocet mexyl (5%-1.25%), at doses that ranged from 20 g to 60 g a.i. pinoxaden ha⁻¹, applied at two to three leaves and the beginning of tillering of wild oat. In addition, standard treatments were included and applied at the same wild oat growth stages. Diclofop methyl at 511 g a.i. ha⁻¹ and fenoxaprop-p-ethyl at 55 g a.i. ha⁻¹ were applied in barley. In wheat, diclofop methyl was replaced by clodinafop-propargyl + cloquintocet mexyl (24%-6%) at 36 g a.i. clodinafop-propargyl + 9 g cloquintocet mexyl ha⁻¹ and in 2008/09 wheat experiments, iodosulfuron plus metsulfuron methyl (5%-60%) at 3.75 g a.i. ha⁻¹ + 3 g a.i. ha⁻¹ also was included. In both crops, pinoxaden at 30 g a.i. ha⁻¹ and at higher rates, fenoxaprop-p-ethyl and clodinafop-propargyl gave the best control of wild oat. In 2006/07 wheat crops, treatments applied at tiller initiation provided better control than the early timing averaged across herbicides. However, wheat yield generally was greater with early application. In barley, wild oat control and crop yield were similar regarding time of application. Variations in crop yield were correlated with grain number m⁻² both in wheat and barley, but relationships between both grain number and spikes m⁻² and with grains per spike were identified only in wheat.     

Improving nitrogen and phosphorus use efficiencies through inclusion of forage cowpea in the rice–wheat systems in the Indo-Gangetic Plains of India

In high productivity zones of Indo-Gangetic Plains in south Asia, the rice–wheat system is stressed due to production fatigue as evidenced by declining soil organic matter content, low efficiency of fertilizer use and diminishing rates of factor productivity. We, therefore, conducted field experiments at Modipuram, India, to conserve soil organic carbon, improve N and P use efficiency, and increase yields of rice–wheat system through inclusion of forage cowpea during the summer before cultivating the rice–wheat system. Cowpea forage harvested at 50 days removed greater amounts of N and P through aboveground biomass than those recycled through belowground roots and nodules. The NO₃-N in soil profile below 45 cm depth after wheat harvest was greater under fallow during summer than under cowpea, suggesting that cowpea minimized NO₃-N leaching beyond 45 cm depth. Similarly, in the treatments receiving both 120 kg N and 26 kg P ha⁻¹, NO₃-N in soil below 45 cm depth was lower compared to those receiving N or P alone. After three crop cycles, soil OC content in 0–15 and 15–30 cm depths was greater compared to initial OC in plots having cowpea. P applied at 26 kg ha⁻¹ increased available P content over initial P content, and also over P content of soil under no P treatments. The available P content was, however, invariably low under summer cowpea plots as compared to that under no cowpea ones. With continuous rice–wheat cropping, the bulk density (BD) of soil increased over the initial BD at different profile-depths, more so at 30–45 cm depth in no cowpea plots, but inclusion of summer cowpea helped decreasing the BD in the surface (0–15 cm) and sub-surface (15–30 and 30–45 cm) soil layers. Summer cowpea grown on residual fertility after wheat harvest did not influence rice yield, but increased wheat grain yield (P<0.05 during the terminal year), when both the crops received fertilizer N and P at recommended rates. Skipping of N or P or both, however, resulted in consistently low yield of these crops under summer cowpea treatments than those under no cowpea treatments, although the differences were not necessarily significant every year. The use efficiency of applied N and P fertilizers in rice and wheat, measured as agronomic efficiency and apparent recovery, was increased with the use of fertilizer N and P at recommended rates, and also with inclusion of summer cowpea.     

Prevention of berry formation in potato plants (Solanum tuberosum L.) by single foliar applications of herbicides or growth regulators

Summary Thre seed production in potato plants (Solanum tuberosum L.) may contribute to the persistence of potato cyst nematodes and of viruses, fungi and bacteria. In four experiments MCPA, ethephon, 2,4D-amine, naphtylacetamide, metoxuron and gibberellic acid were tested for their potential to reduce berry formation. MCPA (500 or 750 g a.i. ha⁻¹ and ethephon (144 or 192 g a.i. ha⁻¹) reduced or almost completely prevented berry set and their effect was strongly influenced by the crop growth stage at the time of application. For both chemicals application at early bud stage was the most effective and, whereas MCPA showed no adverse effects on tuber yield, size, dry matter content and fry colour, ethephon substantially reduced the percentage of large tubers over 50 mm.     

Zn distribution and bioavailability in whole grain and grain fractions of winter wheat as affected by applications of soil N and foliar Zn combined with N or P

A two-year field experiment was conducted to investigate the effects of foliar Zn combined with N or P on Zn concentration and bioavailability in wheat grain and its milling fractions under different soil N levels. At maturity, grains were harvested and fractionated into flour and bran for nutrient analysis. Both high soil N supply and foliar Zn-enriched fertilizer applications greatly increased Zn concentration and bioavailability in both whole grain and grain fractions. Compared with foliar Zn alone, foliar Zn combined with N increased Zn concentration and bioavailability, whereas foliar Zn combined with P decreased Zn concentration and bioavailability. However, foliar Zn combined with P slightly increased the protein concentration compared to foliar Zn alone. Protein concentration significantly increased, whereas phytate concentration decreased, in whole grain and flour, both in soil N and foliar Zn-enriched N treatments. Therefore, foliar Zn plus N (with appropriate soil N management) may be a promising strategy for addressing dietary Zn micronutrient deficiencies, especially in countries where flour is a significant component of the daily diet.