Management of five stored-product insects in wheat with pirimiphos-methyl and pirimiphos-methyl plus synergized pyrethrins

Hard red winter wheat was treated with pirimiphos-methyl at 4, 6 and 8 mg kg(-1), synergized pyrethrins at 0.38, 0.75, 1.13 and 1.5 mg kg(-1), and combinations of the two insecticides, to conduct laboratory bioassays against four beetle pests of stored grain, red flour beetle Tribolium castaneum (Herbst), rusty grain beetle Cryptolestes ferrugineus (Stephens), lesser grain borer Rhyzopertha dominica (F), and rice weevil Sitophilus oryzae (L), and one moth pest, Indianmeal moth Plodia interpunctella (Hubner). Beetle adults and P interpunctella larvae survived well on control wheat, producing a large number of progeny (65-1037 insects per container). Kernel damage in control wheat among the insect species ranged from 9 to 99%. On pirimiphos-methyl-treated wheat, mortality of R dominica adults was > or =72%, but that of the other beetle species and P interpunctella larvae was 100%. Progeny were not produced on pirimiphos-methyl-treated wheat, and the kernel damage was negligible (< or =1%). Synergized pyrethrins were ineffective against the five insect pests. Pirimiphos-methyl combined with synergized pyrethrins was not superior to pirimiphos-methyl alone against the five insect pests. Pirimiphos-methyl is not registered in the USA for use on wheat, but our results suggest that it could be a viable grain protectant at rates of 4-8 mg kg(-1).     

Influence of vegetation parameters on runoff and sediment characteristics in patterned Artemisia capillaris plots

Vegetation patterns are important in the regulation of earth surface hydrological processes in arid and semi-arid areas. Laboratory-simulated rainfall experiments were used at the State Key Laboratory of Soil Erosion and Dryland Farming on the Loess Plateau, Yangling, northwestern China, to quantify the effects of Artemisia capillaris patterns on runoff and soil loss. The quantitative relationships between runoff/sediment yield and vegeta- tion parameters were also thoroughly analyzed using the path analysis method for identifying the reduction mechanism of vegetation on soil erosion. A simulated rainfall intensity of 90 mm/h was applied on a control plot without vegetation(C0) and on the other three different vegetation distribution patterns: a checkerboard pattern(CP), a banded pattern perpendicular to the slope direction(BP), and a single long strip parallel to the slope direction(LP). Each patterned plot received two sets of experiments, i.e. intact plants and roots only, respectively. All treatments had three replicates. The results showed that all the three other different patterns(CP, BP and LP) of A. capillaris could effectively reduce the runoff and sediment yield. Compared with C0, the other three intact plant plots had a 12%–25% less runoff and 58%–92% less sediment. Roots contributed more to sediment reduction(46%–70%), whereas shoots contributed more to runoff reduction(57%–81%). BP and CP exhibited preferable controlling effects on soil erosion compared with LP. Path analysis indicated that root length density and plant number were key pa- rameters influencing runoff rate, while root surface area density and root weight density were central indicators affecting sediment rate. The results indicated that an appropriate increase of sowing density has practical signifi- cance in conserving soil and water.     

Insecticide resistance in Bemisia tabaci (Homoptera: Aleyrodidae) populations from Crete

The resistance levels to alpha-cypermethrin, bifenthrin, pirimiphos-methyl, endosulfan and imidacloprid were determined in Bemisia tabaci (Gennadius) from Crete. Five B tabaci populations collected from greenhouse and outdoor crops were bioassayed and compared with a reference susceptible strain. Bemisia tabaci collected in a floriculture greenhouse exhibited the highest resistance against all insecticides: at LC50, resistance factors were 23-fold for bifenthrin, 80-fold for alpha-cypermethrin, 18-fold for pirimiphos-methyl, 58-fold for endosulfan and 730-fold for imidacloprid. A population collected on outdoor melons was more susceptible than the reference strain against all insecticides tested, suggesting the occurrence of local highly susceptible B tabaci populations in 'refugia'. In pairwise comparisons of resistance levels, correlation was observed between the LC50 values of the pyrethroid insecticides bifenthrin and alpha-cypermethrin.     

Adsorption-desorption studies of alachlor, metolachlor, EPTC, chlorothalonil and pirimiphos-methyl in contrasting soils

Five soils with different organic matter contents ranging from 0.48 to 10.4% were used to study the adsorption and desorption of alachlor, metolachor, EPTC, chlorothalonil and pirimiphos-methyl in batch experiments. The isotherm shapes according to Giles classification were S-type for alachlor, metolachlor and chlorothalonil, changing to L-type for the latter as the level of soil organic matter increased, and L-type for EPTC and pirimiphos-methyl. The adsorption isotherms fitted the Freundlich equation x/m = KfCe1/n. The Kf values increased with the increase of organic matter content. The amounts of pesticides adsorbed over a range of concentrations of 0.1-20 mg litre-1 reached 63.1% for alachlor, 69.2% for metolachlor, 89.3% for EPTC, 98.4% for chlorothalonil and 96.3% for pirimiphos-methyl. The increase of the amounts desorbed with acetone indicated that the sorption of organic compounds onto organic matter occurred principally via weak London-type induction forces, or dispersion forces which are characteristics of the physical adsorption process.     

Current status of insecticide resistance in Q biotype Bemisia tabaci populations from Crete

BACKGROUND: A major problem of crop protection in Crete, Greece, is the control of Bemisia tabaci (Gennadius) (Homoptera: Aleyrodidae) with chemical insecticides owing to the rapid development of resistance. The aim of this study was to investigate the establishment of resistance and the underlying mechanisms to major insecticide classes with classical bioassays and known biochemical resistance markers. RESULTS: During a 2005–2007 survey, 53 Q biotype populations were collected. Application history records showed extensive use of neonicotinoids, organophosphates, carbamates and pyrethroids. High resistance levels were identified in the majority of populations (>80%) for imidacloprid (RF: 38–1958×) and α‐cypermethrin (RF: 30–600×). Low resistance levels (RF < 12) were observed for pirimiphos‐methyl. A strong correlation between resistance to imidacloprid and the number of applications with neonicotinoids was observed. Significant correlations were observed between COE and P450‐dependent monoxygenase activity with resistance to α‐cypermethrin and imidacloprid respectively. A propoxur‐based AChE diagnostic test indicated that iAChE was widespread in most populations. Resistance levels for α‐cypermethrin were increased when compared with a previous survey (2002–2003). Differentiation of LC₅₀ values between localities was observed for imidacloprid only. CONCLUSION: Bemisia tabaci resistance evolved differently in each of the three insecticides studied. Imidacloprid resistance seems less established and less persistent than α‐cypermethrin resistance. The low resistance levels for pirimiphos‐methyl suggest absence of cross‐resistance with other organophosphates or carbamates used. Copyright © 2008 Society of Chemical Industry     

诺敏河流域植被覆盖时空演变及其与径流的关系研究

基于GIMMS/NDVI数据对诺敏河流域1982-2006年间植被覆盖的时空演变特征进行了研究,并结合SCS模型模拟地表径流,在流域和像元尺度分析植被NDVI变化与径流的关系。研究表明:诺敏河流域植被NDVI值较高,但25a间整体呈下降趋势,NDVI减少的区域占总面积的82.5%,植被覆盖有所降低;NDVI空间差异明显,NDVI的高值区主要分布在中上游林区,而耕地分布较多的下游地区NDVI值相对较低。流域尺度上植被NDVI与径流不具有明显的相关性。但从像元尺度来看,植被NDVI和径流的正相关和负相关共存,流域不同空间位置的植被变化与径流的关系并不一致。     

施肥、起垄和品种对黄土高原新造耕地马铃薯氮磷钾吸收与分配的影响

于2019―2020年在黄土高原延安地区选择典型新造耕地,开展不同栽培措施和品种下马铃薯氮、磷和钾元素吸收量及其分配规律的研究.试验设7个处理,分别为克新1号+NPK(氮磷钾无机肥)+平作(CK)、克新1号+NPK+起垄(T1)、克新1号+NPKM(氮磷钾无机肥+有机肥)+平作(T2)、克新1号+NPKM+起垄(T3)...     

Effects of surface treatments and application shanks on nematode, pathogen and weed control with 1,3-dichloropropene

BACKGROUND: Preplant fumigation with methyl bromide (MeBr) has been used for control of soilborne pests in high‐value annual, perennial and nursery crops, but is being phased out. In 2007 and 2008, research trials were conducted to evaluate the effects of surface treatments and two application shanks on pest control with 1,3‐dicloropropene (1,3‐D) in perennial crop nurseries. RESULTS: All 1,3‐D treatments controlled nematodes similarly to MeBr. Application of 1,3‐D with virtually impermeable film (VIF) reduced Fusarium oxysporum compared with unfumigated plots, but was not as effective as MeBr. Applications of 1,3‐D with VIF or 1,3‐D followed by metam sodium reduced Pythium spp., but 1,3‐D followed by intermittent water seals was comparable with the untreated plots. When sealed with high‐density polyethylene (HDPE) film or VIF, 1,3‐D generally was as effective as MeBr for reducing weed density and total weed biomass, but weed control was reduced by intermittent water seals and in unsealed plots subsequently re‐treated with additional 1,3‐D or metam sodium. CONCLUSION: Applications of 1,3‐D sealed with HDPE or VIF film or with intermittent water seals can control nematodes similarly to MeBr. However, additional management practices may be needed for effective pathogen and weed control if plastic film is not used. Copyright © 2011 Society of Chemical Industry     

Molecular characterization of Ralstonia solanacearum strains from Ethiopia and tracing potential source of bacterial wilt disease outbreak in seed potatoes

Bacterial wilt, caused by Ralstonia solanacearum, is emerging as a major threat to potato production in Ethiopia, reaching epidemic proportions in the Chencha district recently, with a prevalence of 97% of potato fields in 2015. The recent disease outbreak in the district coincided with a significant introduction of seed potatoes. This research was therefore initiated to genetically characterize the pathogen so as to trace its source, identify its relationship with outbreaks in the rest of the country, and make intervention recommendations. Ralstonia solanacearum isolates were sampled both from seed and ware potato fields in Chencha and from seed potato fields in production regions suspected of being potential sources of the pathogen. Multiplex PCR and phylogenetic analysis of partial endoglucanase gene sequences identified all of the isolates as phylotype IIB sequevar 1. VNTR sequence analysis distinguished 11 different haplotypes, nine of which were unique to the Chencha district. However, one of the haplotypes was common to all seed potato producer regions of Ethiopia except for the Shashemene area. The unique and diverse VNTR haplotypes of the pathogen in Chencha indicates that it is well established in the district. When a geographical map of the VNTR haplotypes was superimposed with the main cross‐regional seed potato distribution pattern of the country, it became evident that the pathogen was being disseminated via latently infected seed from the Holeta‐Jeldu area in the Central Highlands of Ethiopia. Identification of largely uninfected highland districts and multiplication of high‐grade seed potato exclusively in those districts should be given priority.     

Development of natural late blight epidemics in pure and mixed plots of potato cultivars with different levels of partial resistance

Late blight, caused by Phytophthora infestans , is the most severe disease of potato worldwide. Controlling late blight epidemics is difficult, and resistance of host cultivars is either not effective enough, or too easily overcome by the pathogen to be used alone. In field trials conducted for 3 years under natural epidemics, late blight severity was significantly lower in a susceptible cultivar growing in rows alternating with partially resistant cultivars (mixtures) than in unmixed plots of the susceptible cultivar alone. Partially resistant cultivars behaved similarly in unmixed and mixed plots. Mixtures of cultivars reduced disease progress rates and sometimes delayed disease onset over unmixed plots, but did so significantly only for the slowest epidemic. This suggests that reduction of area under the disease progress curve (AUDPC) in mixtures resulted from the cumulative action of minor effects. Disease distribution was focal in all plots at all dates, as shown by Morisita's index values significantly exceeding 1. Significant yield increases for the susceptible cultivar, and occasionally for the partially resistant ones, were observed in mixed-cultivar plots compared with single-cultivar plots. These results show that cultivar mixtures can significantly reduce natural, polycyclic epidemics in broadleaved plants attacked by pathogens causing rapidly expanding lesions.     

Toxicological and biochemical response to azinphos-methyl in Cydia pomonella L. (Lepidoptera: Tortricidae) among orchards from the Argentinian Patagonia

BACKGROUND: Azinphos‐methyl is the main insecticide used to control codling moth on apple and pears in Northern Patagonia. The aim of this study was to evaluate the toxicological and biochemical response of diapausing larvae of codling moth in orchards subjected to different insecticide selection pressure. RESULTS: Dose–mortality assays with azinphos‐methyl in diapausing larvae of Cydia pomonella L. showed significant differences between the LD₉₅ from a population collected in one untreated orchard (2.52 µg moth^?1) compared with that in a laboratory‐susceptible population (0.33 µg moth^?1). Toxicity to azinphos‐methyl in field populations of diapausing larvae collected during 2003–2005 was evaluated by topical application of a discriminating dose (2.5 µg moth^?1) that was obtained from larvae collected in the untreated orchard (field reference strain). Significantly lower mortality (37.71–84.21%) was observed in three out of eight field populations compared with that in the field reference strain. Most of the field populations showed higher esterase activity than that determined in both the laboratory susceptible and the field reference strains. Moreover, there was a high association between esterase activity and mortality (R² = 0.64) among the field populations. On the other hand, a poor correlation was observed between glutathione S‐transferase activity and mortality (R² = 0.33) among larvae collected from different orchards. CONCLUSIONS: All the field populations evaluated exhibited some degree of azinphos‐methyl tolerance in relation to the laboratory susceptible strain. Biochemical results demonstrated that esterases are at least one of the principal mechanisms involved in tolerance to this insecticide. Copyright © 2008 Society of Chemical Industry     

Effects of strip intercropping of potatoes with non‐hosts on late blight severity and tuber yield in organic production

The effects of strip cropping of potatoes with cereals or a grass‐clover mix in and perpendicular to the main wind direction on foliar late blight severity and tuber yield were studied in large‐scale field experiments in Germany. Disease progress was assessed in 12–18 sections per plot and yields determined from the same sections. In 2000, plot size was 3 × 10 m and there were no disease reductions apparently due to interplot interference. In 2001 and 2002, with plot sizes of 6 × 18 and 6 × 36 m in strip‐cropped potatoes, disease was significantly reduced by 9–20% and 4–12%, respectively, compared to pure stands of potato, with the greatest reductions in plots planted perpendicular to the wind and neighboured by grass‐clover. The most important factors contributing to disease reduction were loss of inoculum outside of the plots and barrier effects of neighbouring non‐potato hosts. Only 0–20% of the overall yield variation could be explained by the area under the disease progress curve, depending on cultivar and year. In one year disease effects on the yield of a moderately resistant cultivar were higher than on the yield of a susceptible cultivar. This was probably caused by differences in bulking behaviour. Nutrient limitation appeared to be more important than disease in reducing yields. Yields in the edge potato rows directly neighboured by cereals were significantly reduced in all 3 years, but competition by cereals did not change the disease–yield‐loss relationship. Strip intercropping might be a useful component in an overall management strategy to reduce incoming late blight inoculum.     

Resistance of codling moth, Cydia pomonella (L.) (Lepidoptera: Tortricidae), larvae in Michigan to insecticides with different modes of action and the impact on field residual activity

BACKGROUND: The codling moth is one of the principal pests of apple in the world. Resistance monitoring is crucial to the effective management of resistance in codling moth. Three populations of codling moth in neonate larvae were evaluated for resistance to seven insecticides via diet bioassays, and compared with a susceptible population. In addition, apple plots were treated with labeled field rate doses of four insecticides. Treated fruit were exposed to neonate larvae of two populations from commercial orchards. RESULTS: Two populations of codling moth expressed two‐ and fivefold resistance to azinphos‐methyl, seven‐ and eightfold resistance to phosmet, six‐ and tenfold resistance to lambda‐cyhalothrin, 14‐ and 16‐fold resistance to methoxyfenozide and sixfold resistance to indoxacarb, but no resistance to acetamiprid and spinosad. The impact of the resistance to azinphos‐methyl, measured as fruit damage, increased as the insecticide residues aged in the field. In contrast, fruit damage in methoxyfenozide‐ and lambda‐cyhalothrin‐treated fruit was observed earlier for resistant codling moth. No differences in efficacy were found for acetamiprid. CONCLUSIONS: Broad‐spectrum insecticide resistance was detected for codling moth. Resistance to azinphos‐methyl, lambda‐cyhalothrin and methoxyfenozide was associated with reduced residual activity in the field. Broad‐spectrum resistance presents serious problems for management of the codling moth in Michigan. Copyright © 2008 Society of Chemical Industry     

Isolation and characterization of Streptomyces species from potato common scab lesions in Norway

The present survey was conducted to isolate and characterize Streptomyces species from common scab lesions of potato in Norway. Bacteria were isolated from scab lesions on tubers sampled in two consecutive years at different locations in Norway spanning ～1400 km from south to north. In total, 957 independent isolations from individual tubers were performed, with 223 putative pathogenic isolates obtained from 29 different potato cultivars and 130 different fields. Streptomyces europaeiscabiei was the most abundant species isolated from common scab lesions (69%), while 31% of the isolates obtained were S. turgidiscabies. Streptomyces scabies was not found. Pathogenicity of selected Streptomyces isolates was tested on potato. The ability of the bacterial isolates to infect potato was consistent with the presence of the txtAB operon. The results revealed no pattern in geographical distribution of S. europaeiscabiei and S. turgidiscabies; both could be found in the same field and even the same lesion. Four different pathogenicity island (PAI) genotypes were detected amongst the txtAB positive isolates: nec1+/tomA+, nec1–/tomA+, nec1+/tomA? and nec1?/tomA?. The current findings demonstrate that there is genetic variability within species and that the species are not spread solely by clonal expansion. This is thought to be the most comprehensive survey of Streptomyces species that cause common scab of potato in a European country.     

A psbA mutation in Kochia scoparia (L) Schrad from railroad rights-of-way with resistance to diuron, tebuthiuron and metribuzin

Kochia [Kochia scoparia (L) Schrad] has become resistant to many herbicides used in cropland and railroad rights-of-way in North Dakota and Minnesota. Kochia scoparia plants that had survived annual treatments with diuron and tebuthiuron were sampled along railroad rights-of-way in North Dakota and Minnesota. The samples were screened in the greenhouse for resistance to diuron, tebuthiuron, metribuzin and bromoxynil from 0.5x to 32x the recommended use rates. A resistant K scoparia accession (MN-3R) was confirmed with resistance up to 16-fold higher than recommended use rates for tebuthiuron and diuron and up to 4-fold higher for metribuzin. However, the resistant K scoparia accession was susceptible to bromoxynil even at 50% of the recommended use rate. The herbicide binding region of the psbA gene fragment of eight resistant (R) and seven susceptible (S) K scoparia accessions was PCR-amplified and sequenced for detection of mutations. The psbA gene of four R K scoparia accessions was mutated at residue 219 with substitution of isoleucine for valine (GenBank accession number AY251265). The seven S K scoparia accession sequences were wild-type at this residue (GenBank accession number AY251266). The other four R accessions sequences showed a previously known triazine R mutation with substitution of glycine for serine at residue 264. All 15 K scoparia accessions were wild-type at all other psbA residues within the region analyzed. Resistance to diuron, tebuthiuron and metribuzin among the railroad rights-of-way K scoparia is probably due to the mutation at residue 219 of the psbA gene in some plants, but due to the previously reported Ser(264)Gly substitution in other plants. Target-site resistance associated with a change of valine to isoleucine at residue 219 of the psbA target-site in weeds has previously been reported for Poa annua L selected in diuron-treated grass seed fields, and for Amaranthus powelli S Wats selected in linuron-treated carrot fields. This is the first report of the mutation in herbicide-resistant K scoparia.