Assessment of the impact of mid-season late blight infection on disease development and yield of potato variety Russet Norkotah in Maine

Development of late blight of potatoes caused by Phytophthora infestans (US 8 fungal genotype, A2 mating type) was monitored in two Russet Norkotah commercial fields at Fort Fairfield in 1996 and Duncan Farm in 1997. Experimental plots representing various disease treatments (low, moderate, high and random late blight severity levels) were established in two fields in 1996. In 1997, only low and high disease treatments were established. The application of fungicides for late blight control was conducted in both years. Late blight incidence and severity were assessed in each plot of each treatment. Components of late blight disease development, tuber blight incidence and tuber yields were determined from each plot. Progress of late blight disease was rapid in 1996 but not in 1997. During the 1996 cropping season, mean disease incidence and severity in the random disease treatment plots were 84 and 21% respectively within 10 days of disease detection. In 1997, low levels of late blight severity were detected in the field plots. Average numbers of late blight leaf and stem lesions on infected plant and fungal sporangia on the diseased leaf were not significantly affected by disease treatment. Late blight foliar severity significantly affected potato tuber yields. Lowest tuber yield was obtained in plots with high disease levels and highest yields were recorded in plots with low late blight severity in 1996. Late blight severity was significantly correlated with tuber yield but not with per cent tuber blight.     

Measurement of healthy and diseased haulm area for assessing late blight epidemics in potatoes

The advantages of assessing disease severity by visual grading and by measuring healthy and diseased plant area were compared in four mild to moderate late blight epidemics during spring and in two severe epidemics during autumn in Israel. Disease progress curves obtained through visual grading showed a continuous increase, but the area of lesions tended to fluctuate during the cropping season and often reached a maximum in plots in which the total amount of foliage was also largest. The healthy haulm area differed with disease intensity and undefined seasonal and cultural influences. The decrease in healthy haulm area was not related to expansion of the blighted area only, but also to the breaking of plants at stem lesions. This phenomenon was especially evident in the warm spring season and was not determined by visual grading of disease severity. Each kind of assessment revealed different features of the epidemics and suited different applications. Visual grading enabled the easiest comparison of epidemic patterns. Lesion areas reflected patterns of inoculum potential, while healthy haulm areas reflected the integrated influences of factors affecting the crop and disease and thus provided useful data for simulating epidemics and for estimating yield losses.     

Resistance to benzimidazoles in Pseudocercosporella herpotrichoides1

In a long-term monitoring experiment in winter wheat between 1976 and 1980 no substantial change in the benzimidazole resistance of Pseudocercosporella herpotrichoides was observed; carbendazim or related chemicals were applied twice a year. In 1982, a high percentage of the fungus population was benzimidazole-resistant. There is no conclusive explanation for this sudden change. Paralleling this development, since 1982 farmers in northern Germany complain about failures in eyespot control with benzimidazole-type fungicides. In a survey in 1983 (52 fields from all over the country; 10 haulms per field), spore germination tests (on 2 ppm carbendazim) in nearly 50% of the fields showed the fungus population to be carbendazim-resistant. This result was confirmed by other findings (disease assessment, yield data). In 1984, plants were again taken from more than 150 unsprayed plots all over the country. This time benzimidazole resistance was expressed by the frequency of isolates on carbendazim-containing medium (100 haulms per field). The previous results were confirmed. Benzimidazole resistance is still much more a problem in northern than in southern Germany. There seems to be some relationship between benzimidazole resistance in the field and the history of benzimidazole-type applications on the plot.     

Yield reduction in wheat by simulated rat damage

Abstract

A study of simulated rat damage was done to determine the loss of wheat yield when O (control). 10, 30 and 50% ot the wheat stems were cut at tillering, booting, dough and mature crop stages. The yields at harvest from each of 128 1‐m² plots were compared by analysis of variance and least significant difference tests. Yield at the tillering stages was not significantly different from the controls but yields at all other stages differed significantly. Yield losses in tillering and booting stages were not significant for the different damage levels except for 50% stem cutting at the booting stage. The yields from dough and mature crop stages at all damage levels were significantly lower than yields from controls. No significant differences in yield at all growth stages were observed between control plots and those receiving 10% damage, but 30 and 50% damage gave significant losses.     

Influence of canopy structure on sheath blight epidemics in rice

Sheath blight (caused by Rhizoctonia solani) is one of the most important constraints in achieving high grain yield in intensive rice production systems. Canopy structure can influence the development of sheath blight epidemics. The objective of this study was to determine the effect of canopy structure parameters such as shoot number, leaf area index, biomass production, contact frequency, light transmittance and plant height on the development of sheath blight epidemics in commercial fields. Field experiments were conducted in both early and late seasons of 2009 and 2010 in Wuxue, Hubei province, China. The effects of nitrogen (N) rate and hill density on structure and production parameters and sheath blight severity were investigated. Sheath blight severity was recorded as a sheath blight index or relative lesion height on inoculated and uninoculated plants in each crop. Lesion length was measured on inoculated plants in 2010. The results showed that the sheath blight index increased with an increase of N rate and hill density in uninoculated plots in each trial. Stepwise multiple regression analysis demonstrated that contact frequency was consistently related to sheath blight. Lesion length on inoculated plants was not correlated with canopy structure. These results indicate that canopy structure influences sheath blight epidemics. A ‘healthy’ canopy resulting from appropriate crop management practices can be used to suppress sheath blight epidemics in rice.     

Modelling the economics of herbicide treatment in wheat and barley using data on prevented grain yield losses

Losses in grain yield prevented by controlling weeds were measured in 59 fields of (southern hemisphere) spring-sown wheat (Triticum aestivum L.) (cv, Otane) and 45 fields of spring-sown barley (Hordeum vulgare L.) (cv. Corniche) in five consecutive growing seasons from 1988/89 until 1992/93 in the Canterbury region of New Zealand. The losses were measured as the differences in yield between weeded and non-weeded plots located in randomly positioned pairs in the fields. In the first 2 years, the weeding was by push hoe in‘organically grown crops. For the last 3 years, the fields were under prophylactic herbicide regimens with nonweeded plots created by excluding commercial herbicide applications (made mostly in October for wheat and November for barley) with polyethylene sheets placed temporarily over the plots. For each season the distributions of yield losses were modelled using the normal distribution and probabilities of ‘breaking even’ on herbicide use derived by substituting cumulative probability density functions into a simple break-even model for herbicide use. The model assumed that herbicide application in the current crop has no flow-on economic effect for succeeding crops. The mean annual yield losses prevented by herbicide application were positively correlated with September and October rainfall for wheat and bailey respectively. As a consequence, the probabilities of breaking even on herbicide use increased with increasing spring rainfall. Using historical rainfall records, probabilities of breaking even were estimated for each of the 48 years from 1947 to 1994. Averaging over these years, the analysis revealed that at current grain prices prophylactic use of the commonly applied herbicides is likely to be uneconomic in 24% (95% confidence limits 6% and 50%) of fields of average-yielding Otane wheat and in 26% (95% confidence limits 1% and 91 %) of fields of average-yielding Corniche barley in Canterbury. It was concluded that there is potential for withholding herbicide treatments without jeopardizing profitability in these crops, particularly in seasons with low spring rainfall.     

Leaf and Flower Blight Caused by Monilinia vaccinii-corymbosi on Lowbush Blueberry: Effects on Yield and Relationship to Bud Phenology

ABSTRACT Naturally established lowbush blueberry clones in four fields were evaluated for the incidence of leaf and flower blight, proportion of mummy berries, and yield reductions caused by Monilinia vacciniicorymbosi. The relationship between the phenology of flower and leaf bud development and susceptibility also was examined. Three fields were examined over one crop year and one field was studied in two subsequent crop years. The incidence of stems with blight was correlated to incidence of leaf blight in all fields and to incidence of flower blight in one field. Incidence of leaf and flower blight and the proportion of mummy berries produced were not correlated. Lowbush blueberry clones with higher incidence levels of leaf blight had reduced fruit set and lower berry weights. For healthy stems, leaf-to-fruit ratios had no effect on berry weight in most fields. In contrast, blighted stems with higher leaf-to-fruit ratios had higher berry weights in three fields. Stems with slowerdeveloping leaf and flower buds had less leaf and flower blight, respectively, than stems with faster bud development. Some blueberry clones may avoid infection by delaying production of susceptible tissue until after ascospore release by M. vaccinii-corymbosi.     

Besteht das Risiko der Verschleppung der Bakteriellen Ringfäule der Kartoffel durch den Krautschläger?

In 2001 and 2002, two field trials were performed by the Plant Protection Service (PPS) of the Landwirtschaftskammer Weser-Ems in Oldenburg and the Institute for Plant Protection of the Bavarian State Research Center for Agriculture (LfL) in Freising respectively to examine the transmission of the bacterial ring rot pathogen of potato (Clavibacter michiganensis ssp. sepedonicus) by haulm cutting. In the experiment conducted by the PPS in Oldenburg a lawn-trimmer was used to simulate haulm cutting, before a bacterial suspension was sprayed on the ends of the cut haulms. Two cultivars (early and late) were tested and also the effect of an additional chemical measure for haulm destruction on the transmission of the pathogen was determined. In the trial performed at the LfL in Freising plots with infected plants for the contamination of the haulm cutter were treated immediately prior to plots with healthy plants. Infections of stems (re-growth) and tubers of the plants were determined by polymerase chain reaction (PCR) and indirect immunofluorescence antibody staining (IFAS). In the trials conducted with the haulm cutter, ring rot could be detected in the re-growth of 60% of the plants derived from healthy tubers 4 weeks after haulm cutting. It was confirmed in a bioassay, that the isolated pathogens were viable and virulent. Although the ring rot pathogen was transmitted to a great extent to the leaf material, no infection of progeny tubers occurred in a total of 450 tested plants. However in general a migration of the transmitted pathogen to the tubers cannot be excluded. Therefore further on it is advisable to clean and disinfect the haulm cutter before each use.     

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.     

Stability of partial resistance in potato cultivars exposed to aggressive strains of Phytophthora infestans

Potato cultivars were evaluated for their resistance responses to aggressive strains of Phytophthora infestans in field and laboratory experiments. Analysis of variance revealed differential cultivar-by-isolate interactions for both foliar and tuber blight resistance. Differential responses occur as revealed by specific susceptibilities of cultivars to certain pathogen genotypes and changing rank order. In general, severity of late blight epidemics as observed in the haulms did not correlate well with foliar blight resistance ratings as presented in the National List of Recommended Potato Varieties. No significant correlation was found between tuber blight incidence under field conditions and the tuber blight rating in the National List. Also, there was no relation between the field and laboratory tuber blight resistance assessments. A significant association was demonstrated between late blight infection in the foliage and tuber blight incidence under field conditions. The presence of differential interaction, independent of R-gene-based resistance, indicates some adaptation of P. infestans to partial resistance and consequently adverse effects on the stability and durability of partial resistance to potato late blight.     

再生稻二化螟防治指标的研究

在福建省,二化螟是再生稻的重要害虫。作者对第二代二化螟为害前季稻造成的产量损失结构进行了通径分析。通过田间调查和小区试验,建立了再生稻二化螟防治指标模型: ET=(100C·F-P·E(0.0037N_1 0.1207N_2))/(P·E(0.0123N_1 0.0098N_2)) (卵块密度) ET=(100C·F-P·E(0.0097N_1 0.1258N_2))/(P·E(0.7077N_1 0.5601N_2)) (枯鞘株率) 按照防治指标模型,制定出不同产量水平的防治指标。     

Relationships between disease and yield in cotton fields affected byAlternaria macrospora

Application of various fungicides to cotton plots (Gossypium barbadense cv. Pima) affected byAlternaria macrospora resulted in a yield increase from 3955 kg/ha in unsprayed plots to 5207 kg/ha in plots treated with fentin acetate. Pathogen, host and disease parameters were estimated by a key of grades in the field and by precise measurements of detached plants. Measurements included the number of spores present in the field and numbers and/or areas of healthy, lesioned and shed leaves and bolls. No significant differences were found between the number of healthy bolls on variously treated plants and the number of lesioned bolls on the same plants. Disease incidence was relatively low in treated plots, with no significant difference between treatments and no correlation with the size of the pathogen population or the yield level in variously treated plots. The low proportion of lesioned leaves resulted from their tendency to shed and from the emergence of new leaves, which masked the damage. Rate of shedding was correlated with the respective yield and with the size of the pathogen population in the same plot. Leaf shedding was induced by lesions occupying an average of 1 to 3% of the leaf area. Shedding was affected by leaf position on the plant, being most frequent for the lowest leaves despite their being the least lesioned, and least frequent for the upper leaves even though these were the most lesioned.     

玉米小斑病对玉米产量损失影响的初步研究

玉米小斑病(Helminthosporium maydis Nishikodo and Miyake)对玉米产量损失的影响,迄今所知甚少。1977年作者开始对此进行研究,采用中等感病品种洛阳白马牙,在自然发病条件下,间隔不同时期喷施敌菌灵保护叶面,人为地造成不同程度发病。结果表明,至流行终止期,各处理间有显著不同的病情差别,并相应地引致明显不同的产量差异。病情与产量呈极显著的负相关关系,进面推导出一个经验回归方程。(?)=28.26-0.1351x0.1446x2。经统计分析,此方程具有高度概括性,用试验中各组病情数值推算理论产量(?),误差均在允许的范围之内,说明本试验的经验方程具有相当高的精确度。     

Field evaluation of a supervised control system forBotrytis leaf blight in spring sown onions in the Netherlands

Between 1988 and 1992 two existing weather based advisory models to control leaf blight in onions, were evaluated in the Netherlands. The first model, BOTCAST, can be used to time the initial spray while the second model, SIV, can be used to advise on every subsequent spraying. The evaluation based on field trials showed that application of both BOTCAST and SIV can reduce the number of sprays by 54% compared to a weekly spraying program without any yield loss or a higher disease severity. There was no relation between yield losses of untreated plots and disease severity expressed as lesion counts or leaf dieback. Relative disease growth rate was significantly but not closely related to weather based model characteristics or the observed crop micro-climate using linear regression analysis. The model characteristics did not yield better regressions than the climatological characteristics. Two changes to improve BOTCAST are proposed. Introduction of a supervised control system based on BOTCAST and SIV seems only economically feasible when the system is used as a regional warning system.     

Competition between annual weeds and vining peas grown at a range of population densities: effects on the crop

Competition between annual weeds and vining peas (Pisum sativum L.) at five target population densities between 11 and 194 plants/m² was examined by means of periodic destructive sampling of weedy and weed-free plots. A further area of each plot was cut and vined to assess yields. Weeds impaired vegetative development, particularly by reducing tillering in low density crops. This resulted in weedy plots having fewer pods per plant at harvest but a lower proportion of flat pods than weed-free plots. Weeds had no effect on numbers or weights of peas in full pods nor on tenderometer values of samples of vined peas. Adverse effects of weeds on the growth of individual crop plants decreased with increasing crop density. However, at lower crop densities many of the additional pods on weed-free plots contributed little to vined yield, while at higher densities, direct or indirect effects of weeds increased the problem of maintaining sufficient photosynthetic area during pod swelling to prevent pod abscission and poor ovule development. Regression analysis of yield on crop density and of yield on numbers of pods per plant showed that vined yield per hectare was reduced by weeds by a constant amount across the range of densities and numbers of pods examined. Vining throughput was also reduced in weedy as compared with weed-free crops, even on high density plots where little or no weed vegetation remained at harvest. In general, weed presence had effects similar to those caused by increasing crop density, but without the additional contribution to yield made by extra plants. Higher density crops suppressed weeds very effectively but were no less vulnerable to yield loss than those of lower density; they therefore merit just as much attention to effective weed control as crops suffering more visibly from competition by weeds.     

Weed control in squash and tomato fields by soil solarization in the Jordan Valley

Black (BPE) and clear polyethylene mulches (CPE), 0.08 and 0.06 mm thick, respectively, were compared for their effectiveness for soil solarization over three seasons during 1986–1989 in weedy fields. Solarization for 6 weeks reduced weed growth and enhanced crop yields. However, further mulching with BPE after solarization with either BPE or CPE gave the best results. Not all weeds were sensitive to solarization. Some weed species were completely controlled; others were reduced to varying degrees; yet other weed species seemed to be enhanced by solarization. Solarization without further mulching was no better than farmer-practice in reducing weed growth or in increasing crop yield. Weeds required further removal after the middle of the growing season. Any soil disturbance after solarization reduced the weed control effect of solarization. Crops grew best in plots after solarization with BPE if they were planted in the same mulch after it was perforated.     

Het vaststellen van de door de erwteknopmade (Contarinia pisi) veroorzaakte schade en de bestrijding van dit insekt

Summary The preceding paper deals with the damage caused byContarinia pisi. The technique used to determine the losses of yield is discussed. Heuver (1960) is of the opinion, that the cutting of flowerbuds (in fact flowers and young pods) of the pea plant is comparable to an infestation byContarinia pisi. However, according to the present authors' investigations these injuries are not comparable. It is also impossible to investigate the exact damage by treating small plots in larger untreated pea fields because reinfestation of the treated plots will occur.The most feasible method to determine crop losses is by comparing average yields in a well treated area with the yields obtained in untreated fields in the same area.The accuracy of this method is greatest in years when damage is heavy.The damage to both canning peas and harvesting peas may be serious.     

Critical period of weed competition in three vegetable crops in relation to management practices

The critical period of weed competition was determined in three vegetable crops: early cabbage (Brassica oleracea var. capitata L.), pickling cucumbers (Cucumis sativus L.), and field-seeded processing tomatoes (Lycopersicon esculentum L.). There were significant interactions between weed-removal treatments, year, and row width. Cabbage yields were reduced if plots were not kept weed-free for at least 3 weeks after transplanting or if weeds which emerged with the crop were allowed to remain longer than 4–5 weeks, Cucumber yields were reduced if plots were not kept weed-free for up to 4 weeks after seeding or if plots remained weed-infested longer than 3–4 weeks. Higher crop population densities (narrower row widths) in cabbage and cucumbers resulted in smaller plants, earlier competition from weeds, and therefore a shorter period that the crop could remain weed-infested without suffering reduced yields. Yields of direct-seeded tomatoes were reduced if plots were not kept weed-free for up to 9 weeks after seeding or if weeds which emerged with the crop were allowed to remain longer than 5 weeks. In each crop the timing of the critical period of competition was verified by weed removal only during this interval. There was a true critical period in direct-seeded tomatoes, but not in cabbage or cucumbers where a single weeding was sufficient to prevent yield losses.     

Potato production and protection in Poland in the 1990s1

Potato is an important crop for Polish agriculture, now grown on an area of 1.8 million ha, with an annual production of about 35 million t. The crop is used for fodder (pork production), human consumption and as a raw material for various branches of industry. High quantity and quality are essential for proper utilization. The main limiting factors in Polish potato production are: water (shortage or excess), seed potato quality, cultivation practices, and damage by pests, diseases and weeds. Improving the economics of potato production depends on decreasing the acreage and increasing the extent of proper protection. The major constraint is late blight (Phytophthora infestans) which causes yield losses estimated at 22.8%. Blight control is indispensable. The level of resistance among Polish cultivars, both in haulm and tuber, is not satisfactory, so more intensive resistance breeding is needed. Chemical control has increased in popularity, but improper use of phenylamides has created new problems. Further progress will depend on cost-effective methods of control and reliable use of fungicides.