Differences In Yield Loss Research Articles

Effects of Hybrid Susceptibility and Inoculation Timing on Goss's Bacterial Wilt and Leaf Blight Severity and Corn Yield.

Goss's bacterial wilt and leaf blight (Goss's wilt) of corn is the most important corn disease in North Dakota (ND), and yield loss due to the disease has not been reliably quantified in northern corn growing regions. To help quantify the amount of yield loss caused by Goss's wilt, a total of six field experiments were conducted from 2015 to 2017. Experiments were designed in a randomized complete block with a split plot arrangement. Hybrids served as main plots and Clavibacter nebraskensis inoculation timings as subplots. Three hybrids were used and classified as susceptible, moderately susceptible, and resistant. Inoculation timings included a noninoculated control, six to 10 leaf collars (V6 to V10), reproductive silk stage (R1), or a sequential combination of V6 to V10 and R1. A high level of disease (greater than 50% on susceptible hybrid) occurred in three experiments, a low level of disease (less than 5% on susceptible hybrid) in one experiment, and no disease was reported in two experiments. A combined analysis of the high disease experiments indicated yield losses of 34 to 41% on the susceptible hybrid when C. nebraskensis inoculation occurred at V6 to V10. Yield losses of 22 to 25% occurred on the moderately susceptible hybrid when C. nebraskensis inoculation occurred at V6 to V10, and statistical differences in yield loss were not found among inoculations timings on the resistant hybrid. Correlation analyses suggest that for every 1% increase in R1 disease severity on the susceptible hybrid, yield was reduced by 117 kg/ha (1.9 bu/acre). The current study further demonstrates the importance of hybrid resistance and provides updated yield loss information on Goss's wilt in a northern corn growing region.

Tolerance to rice water weevil, Lissorhoptrus oryzophilus Kuschel (Coleoptera: Curculionidae), infestations among hybrid and inbred rice cultivars in the Southern U.S.

The rice water weevil, Lissorhoptrus oryzophilus Kuschel, is the most destructive insect pest of rice in the U.S. This insect poses a global threat to rice production, having invaded rice-producing regions of Asia and Europe. Tolerance is a type of plant resistance that allows crop plants to maintain yield in spite of injury by herbivores. This study was conducted to test the hypothesis that tolerance to L. oryzophilus infestations differs between hybrid and inbred rice cultivars. Field experiments were conducted in Louisiana in 2016–2017 and in multiple locations (Texas, Mississippi, and Louisiana) in 2018. Plant tolerance was assessed by evaluating L. oryzophilus infestations and yields from insecticide-protected and unprotected plots of hybrid and inbred rice cultivars. Infestations of L. oryzophilus negatively affected rice yields, with losses across cultivars ranging from 16.4 to 48.0% in 2016 and 4.2–29.2% in 2017. In the multiple location experiment in 2018, yield losses ranged from 4.1 to 29.7, 7.7–17.2, and 4.5–12.2% in Louisiana, Texas, and Mississippi, respectively. Comparisons of yields between insecticide-protected and unprotected plots indicated that hybrid cultivars exhibited higher tolerance to L. oryzophilus infestations than inbred cultivars in 2016 and 2017. Moreover, in the multiple location experiment in 2018, yield losses were lower in hybrid compared to inbred cultivars in Texas, but no differences in yield losses across cultivars were observed in Louisiana and Mississippi. Rice cultivars expressing tolerance to L. oryzophilus could be used to reduce pest damage in situations where use of insecticides is not practical, too expensive, or only partially effective.

Genotypic differences in yield loss of irrigated soybean attributable to charcoal rot

ABSTRACT Charcoal rot, caused by the fungus Macrophomina phaseolina (Tassi) Goid., is a disease of soybean (Glycine max (L.) Merr.) that causes yield loss worldwide. The purpose of this research was to determine the effects of charcoal rot on the yield loss of six individual soybean genotypes grown in infested, irrigated plots. Overall, colony-forming unit (CFU) levels were low (≤5,500). Even so, regression analysis indicated a significant (P ≤ 0.05) negative linear relationship of CFUs with seed yield for one genotype in two out of 3 years (2011, r 2 = 0.43, P = 0.0403; 2013, r 2 = 0.71, P = 0.0023) at levels of CFUs that ranged from zero to 1,300. At low CFU levels, none of the other five genotypes showed a significant (P ≤ 0.05) linear relationship. Hence, not all genotypes that were colonized by M. phaseolina lost seed yield. These results indicated that yield loss was dependent on both genotype and environment.

Does yield loss due to weed competition differ between organic and conventional cropping systems?

SummaryHigh weed abundance in organic crops is thought to be a key factor contributing to the greater yield loss in organic as compared with conventional cropping systems. However, even with greater weed densities than conventional systems, some organic systems have yields comparable to conventional systems, suggesting that cropping systems might differ in yield loss due to weed competition. The diversity in soil nutrient resources due to diversity in crop rotations and variable inputs might enhance crop tolerance to weed competition. We assessed the long‐term effects of contrasting levels of crop rotations (low, medium and high diversity) on weed density, weed biomass and wheat yield loss in organic and no‐till conventional cropping systems using a microplot study within a long‐term cropping systems trial at Scott, Saskatchewan, Canada. Weed density and biomass were found to be four times higher in the organic systems than in the conventional systems. Under standard weed management practices, organic had 44% lower yield than the conventional system. Lower yields in organic, even without weed competition, suggest that the lower yields are due to low soil productivity rather than weed competition. No differences in yield loss were observed among the organic and conventional systems or among the diverse crop rotations. We conclude that the organic management practices and/or increased crop rotation diversity did not enhance yield or reduce yield loss due to weed competition, due to the factors associated with lower soil fertility.

A meta-analysis of severity and yield loss from ascochyta blight on field pea in Western Australia

A meta-analysis of severity and yield loss from ascochyta blight (AB) on field pea was performed using 18 field experiments conducted over eight seasons in 13 locations in Western Australia (WA). The severity of AB, across the WA grain-belt, reached its maximum limit (AB severity 5) during mid-April sowing and linearly declined to almost nil by mid-July sowing. Pre-sowing rainfall had a significant effect on AB severity: the more rainfall events that occurred the less was the disease severity. The regional and seasonal difference in the rate of decline of the AB severity (slope of the regression line) with delay in sowing was not significant, whereas the intercepts were largely significant indicating there were differences in the initial AB severity status between the regions and seasons. Fungicide control [Impact® in-furrow (flutriafol) application or fortnightly sprays of Bravo® (chlorothalonil)] did not reduce the disease severity in early sowing (week ending 7 May). The yield loss due to AB was calculated as 10.3% per AB severity unit, indicating that a loss of ≥50% could occur with the highest severity. Magnet showed significantly higher yield loss compared to all other varieties. The differences in yield loss between the five regions were not significant. On the other hand, a dry finishing season resulted in significantly higher yield loss than a wet finishing season. These analyses will help design improved strategies for AB management in field pea in Western Australia.

Comparison of Track and Tire Effects of Planter Tractors on Corn Yield and Soil Properties

Soil compaction remains a serious concern throughout crop production areas of the world because of its deleterious effects on crop yield and soil quality. Many studies indicate significant yield losses due to compaction, others indicate significant differences in yield loss between tires and track, yet others show no differences at all for reasons that have not been fully explained. To investigate tractive method effects on corn (Zea mays L.) yield, Clarion-Nicollet-Webster soil was compacted with four-wheel drive and mechanical front-wheel drive class tractors equipped with both tires and tracks. The planter centerline was offset from the tractor drawbar to obtain plant data from crop rows with a range of distance values from the tire centerline. Plant emergence, grain yield, and penetrometer resistance were analyzed to determine compaction treatment and distance effects, and no significant treatment differences were found. A method for estimating critical soil stress levels required to cause structural degradation was also implemented; these results similarly suggest that treatment differences should not be observed.

Validation of decision support systems for tomato early blight and potato late blight, under Brazilian conditions

Early and late blight are the most important foliar diseases of tomato and potato crops in Brazil. Decision support systems (DSS) are important tools in reducing the large amount of fungicides applied to suppress disease intensity. Systems developed for early or late blight were validated in two cropping seasons under Brazilian conditions. For tomato early blight, FAST, CUFAST, and TOMCAST systems were compared in the spring–summer (September–December) (SS) 2002 and summer–autumn (January–April) (SA) 2003. In both seasons, area under disease progress curve (AUDPC) values for FAST (123.2 and 340.3, respectively) and CUFAST (64.0 and 359.2, respectively) did not differ from calendar-based treated plots (82.5 and 225.7, respectively). Plots treated according to TOMCAST were sprayed once and AUDPC values (369.9 and 697.8) in SS and SA seasons, respectively, did not differ from the control plots (397.5 and 836.0, respectively). In SS, four fungicide sprays were recommended by CUFAST and FAST, whereas five were set by fixed calendar treatment; there were no differences in yield loss among treatments. In SA, FAST, CUFAST and calendar, recommended 4, 9, and 11 sprays, respectively. Higher yields were recorded in plots sprayed according to the calendar system compared to control plots, but there were no significant differences between the DSS and the calendar system. For potato late blight, BLITECAST, SIMCAST, NegFry, and Wallin systems were compared in the summer (December–March) and in the autumn (March–June). Despite no late blight developing in the summer, all systems recommended fungicide sprays. In the autumn–winter, late blight was severe but was reduced by fungicide applications according to all DSS, but the number of sprays was similar to the calendar. The AUDPC values in control plots (1193.5) were higher than BLITECAST (19.5), SIMCAST (97.7), NegFry (193.1), Wallin (69.7), and calendar (63.5) but there were no differences among AUDPC values in plots treated according to DSS. The NegFry and Wallin systems recommended five and the calendar six sprays. All DSS were as effective as the calendar treatment in reducing AUDPC. FAST and Wallin were the most effective systems in forecasting tomato early blight and potato late blight, respectively. Decision support systems are potentially useful tools for integrated management of both diseases in Brazil.

Reliability of higher seeding rates of wheat for increased competitiveness with weeds in low rainfall environments

Increasing crop competitiveness using higher seeding rates is a possible technique for weed management in low input and organic farming systems or when herbicide resistance develops in weeds. A range of wheat seeding rates were sown and resulted in crop densities between 50–400 plants/m2 (current recommendations are 100–150 plants/m2) in the presence and absence of annual ryegrass (Lolium rigidum Gaud.) in three wheat cultivars at nine experiments in southern Australia. Wheat densities of at least 200 plants/m2 were required to suppress L. rigidum and to a lesser extent increase crop yield across a wide range of environments (seasonal rainfall between 200–420 mm) and weed densities (50–450 L. rigidum plants/m2). Doubling crop density of all cultivars from 100 to 200 plants/m2 halved L. rigidum dry weight (averaged over all experiments) from 100 g/m2 to about 50 g/m2. Higher crop densities gave diminishing marginal reductions in weed biomass, while cultivar differences in weed suppression were small. Grain yields ranged from 0·5 t/ha to over 5 t/ha depending on site and season. Maximum yields in the weed-free plots (averaged over environments and cultivars) were at 200 crop plants/m2, and yield declined only slightly by 4–5% at densities up to 425 plants/m2. In the weedy plots grain yield continued to increase up to the highest density but at a slower rate. The percentage yield loss from weed competition was of a smaller magnitude than the suppression of L. rigidum by wheat. For example, 100 wheat plants/m2 led to an average 23% yield loss compared with 17% at 200 plants/m2, and the probability of reduced crop grain size and increased proportion of small seeds was negligible at these densities. Cultivar differences in yield loss from weed competition were small compared with differences due to crop density. Adoption of higher wheat seed rates as part of integrated weed management is now strongly promoted to farmers.

Status of resistance of sorghum hybrids to the aphid, Melanaphis sacchari (Zehntner) (Homoptera: Aphididae)

Four field trials were conducted over four seasons during the period from 1996/97 to 2000/2001 to determine the status of resistance of South African sorghum hybrids to natural infestation by the aphid Melanaphis sacchari. Aphid damage symptoms were evaluated on a scale of 1 to 5. Pronounced differences were observed in levels of resistance of hybrids. However, hybrid reaction was in many cases not similar over seasons. PAN8446, SNK3939 and NS5511 exhibited medium to severe damage symptoms in some seasons but only light to medium damage was observed in others. The hybrid NK283, which is the most commonly planted in South Africa, was highly susceptible to aphid damage and exhibited severe damage symptoms in most of the seasons. In the 2000/2001 season, yield of hybrids was determined under aphid infestation as well as in a trial that was protected from aphid infestation by means of insecticide application. Significant differences in yield loss between hybrids were observed in the 2000/2001 season, ranging from 24 to 73%. Tolerance to aphid damage was identified in some hybrids. Results can be applied for selection of hybrids to be planted in areas where aphid infestation is likely.

Response of local maize varieties and commercial hybrids to natural infestation by Busseola fusca (Fuller) (Lepidoptera: Noctuidae) in Lesotho

The response of farmers' varieties and maize hybrids commonly grown in Lesotho was evaluated in field trials under natural infestations of Busseola fusca (Fuller). Plant response of varieties and hybrids was evaluated in relation to a susceptible and resistant maize hybrid. The incidence of infested plants, number of damaged inter- nodes and number of B. fusca individuals that successfully colonised plants of different varieties as well as yield loss was determined. All the local varieties and commercial hybrids were susceptible to damage by B. fusca and sustained yield losses higher than that of the experimental resistant check hybrid. Maize varieties generally suffered lower yield losses than hybrids. Differences in yield losses between hybrids and farmers' varieties were ascribed to differences in length of growing season requirements (days to 50% flowering) and the incidence of damage to maize ears. Results indicate that Lesotho farmers can benefit from a stem borer resistance breeding programme and that adaptation of planting date can lead to escape of damage and reduced yield losses.

A basis for predictive modelling of the relationship of potato yields to population density of the potato cyst nematode, Globodera pallida

The relationship between initial population density of Globodera pallida and yield was examined for five genotypes of potato at four different experimental sites; two in Scotland and two in England. The experiments at each site were conducted in two stages. The experimental area was first manipulated using resistant and susceptible potato cultivars to give plots with different nematode population densities to act as the initial populations (Pi) for the second stage. The main experiment was conducted using a range of host genotypes that differed in their tolerance and susceptibility. The utility of an inverse linear model relating yield to initial population density was confirmed as were differences in cultivar tolerance. Site differences in yield loss were also observed. It was found that the model could be modified to include the partitioning of genotype and site effects. The implications of this in terms of developing further models to predict yield loss and nematode population dynamics are discussed.

Smut Incidence and Yield Losses of Corn Cultivars under Different Plant Population Densities

AbstractSix corn cultivars were grown, under field conditions, at two population densities of 14285 and 22875 plants/ acre. All were subjected to an artificial infection at 6‐leaf growth stage to determine their reactions to smut disease and yield losses. Changes in plant chemical composition, including K and N contents of ear‐leaf, were performed at silking stage. The results showed that corn cultivars imposed wide variations to smut reaction. Susceptibility to smut disease was less prevalent on D.H 204 and 3‐way cross 310 and more abundant on D.H 215, Iskandria 11 and El‐Kabera 1. The corn cultivar Giza 2 appeared an intermediate reaction. Smut incidence at high population density was markedly depressed by 6.6 % below the comparable level at low population rate. Differences in yield losses between low and high plant population densities were actually limited for smut resistant cultivars, while the opposite was true for the more susceptible ones. On average, the yield losses at the low population density varied from 2.5 % for D.H 204 to 14.4 % for Iskandria 11. The calculated losses of the respective cultivars declined to 2.3 and 9.2 % at the thicker stand. The overall effect of increasing smut infection on yield losses, as revealed from the regression coefficients of the response curves, was clearly pronounced at the higher plant population, whereas the yield was substantially improved by 9.7 %. Varietal response to smut performance was explained on the basis of vigor growth and K/N ratio of ear‐leaf.

Yield losses of soybeans due to Phytophthora megasperma f.sp. Glycinea

Field trials were conducted in two seasons to determine the influence of Phytophthora megasperma f.sp. glycinea on seed yields of soybean genotypes with different levels of resistance. The fungicide metalaxyl, applied as a seed dressing and soil drenches, was used to control the disease. The cultivar Davis, which has high field resistance, did not suffer significant losses in either year. whereas the yield depression of less resistant genotypes ranged up to 72%, depending on the genotype and year. In 198 1 - 82 high death rate of plants occurred early in the season, but yield losses were less than in 1982-83 when mortality occurred late in the season. The declining ability of surviving plants to compensate for disease losses during the latter growth stages may account for the differences in yield losses between seasons.Genotypes with immunity to P. megasperma f.sp. glycinea have been widely grown in the United States because they offer complete protection against some races. However, new pathogenic races have developed quickly, and previously immune genotypes have then suffered severe yield losses. The results of these trials demonstrate that yield losses can be prevented without resorting to fungicide treatments. It is likely that a stable long-term solution to phytophthora root and stem rot will be conferred by field resistance.

Modelling the effects of weeds on crop production

SummaryIn most quantitative studies on interplant competition, static regression models are used to describe experimental data. However, the generality of these models is limited. More mechanistic models for interplant competition, which simulate growth and production of species in mixtures on the basis of the underlying physiological processes, have been developed in the past decade. Recently, simulation models for competition between species for light and water were improved and a detailed version was developed for sugarbeet and fat hen (Chenopodium album L.). The model was validated with data sets of five field experiments, in which the effect of fat hen on sugarbeet production was analysed. About 98% of the variation in yield loss between the experiments (which ranged from –6 to 96%) could be explained with the model. Further analysis with the model showed that the period between crop and weed emergence was the main factor causing differences in yield loss between the experiments. Sensitivity analysis showed a strong interaction between the effect of the variables weed density and the period between crop and weed emergence on yield reduction. Different quantitative approaches to crop‐weed competition are discussed in view of their practical applicability. Simulations of experiments, where both the weed density and the period between crop and weed emergence were varied over a wide range, showed a close relation between relative leaf cover of the weeds shortly after crop emergence and yield loss. This relation indicates that relative leaf cover of the weeds accounts for both the effect of weed density and the period between crop and weed emergence. This relation has the potential to be developed into a powerful tool for weed‐control advisory systems.

Field experiments comparing ammonium nitrate and urea top-dressing for winter cereals and grassland in the U.K.

SummaryThe results of 173 field experiments carried out between 1957 and 1986 are presented comparing ammonium nitrate and urea as top-dressings for winter cereals and grassland.The trials show that urea was an inferior nitrogen source to ammonium nitrate. The yield from ammonium nitrate was significantly greater than that from urea for winter wheat, winter barley and for first, second and third cut silage. The results suggest (a) that winter wheat and winter barley respond differently to the two nitrogen sources and (b) that yield losses from urea are just as likely on first cut silage as second or third cut.A breakdown of results according to soil texture, soil pH and region showed no consistent differences in yield loss. This indicates that broad generalizations based on soil characters and geographical location are not helpful in distinguishing situations where urea performance may be either better or worse than average.

FLUE-CURED TOBACCO LOSSES CAUSED BY THE TOMATO HORNWORM, MANDUCA QUINQUEMACULATA (LEPIDOPTERA: SPHINGIDAE), AT VARIOUS INFESTATION LEVELS IN ONTARIO

AbstractStudies on the flue-cured tobacco losses caused by the natural tomato hornworm, Manduca quinquemaculata (Haworth), were conducted in the field at Delhi, Ont., during 1973, 1974, and 1975. The feeding habits of the larval stage were observed and data on the subsequent damage to tobacco were recorded Two to six leaves per plant, depending on leaf size, were unmarketable due to damage caused by one hornworm larva. The most severe damage by the larva was due to destruction of terminal buds.The tobacco yield was significantly related, negatively, to the tomato hornworm infestation levels. All infestation levels influenced quantitative tobacco losses, but no qualitative differences were apparent when compared with the yield in the insect-free plots. Maximum yield losses occurred at the highest level of infestation. There were no significant differences in yield losses per larva among the infestation levels or among the years. The average yield reduction per larva for all of the population densities and years was 0.70 oz of cured leaves. A prediction equation to establish the relationship between hornworm infestation levels and tobacco yield losses was calculated. A theoretical economic-injury level for the tomato hornworm on tobacco in Ontario was established.