Levels Of Defoliation Research Articles

English

Among the factors that may cause decreases in soybean yield there are the foliar diseases that despite control it can limit grain yield. The Asian soybean rust (Phakopsora pachyrhizi) is considered the most important disease of soybean in Brazil. The aim of this work was to simulate the progress of Asian rust in Brazilian soybean cultivars by removal of trifoliate leaves from the bottom to the top. The experimental design was a randomized complete block, in a 3x3x5 factorial scheme, with four replications. It was observed that there was significant interaction between cultivars and defoliation for all yield components and consequently in seed yield. Increase in the defoliation intensity towards the bottom to the top during the reproductive stages studied (R3, R5, R6) there is a linear decrease in grain productivity, reaching in the highest defoliation level, loss of 79.6, 77.7 and 38.6% in R3, R5 and R6 stages, respectively. The simulation of damage by soybean rust through defoliation cultivars showed severity in leaf area reduction and its consequent effect in grain seed yield.   Key words: Yield components, leaf area, reproductive stage, biotic stress.

Performance of the Forest Vegetation Simulator in Managed White Spruce Plantations Influenced by Eastern Spruce Budworm in Northern Minnesota

Silvicultural strategies such as thinning may minimize productivity losses from a variety of forest disturbances, including forest insects. This study analyzed the 10-year postthinning response of stands and individual trees in thinned white spruce (Picea glauca [Moench] Voss) plantations in northern Minnesota, USA, with light to moderate defoliation from eastern spruce budworm (Choristoneura fumiferana Clemens). Using the Forest Vegetation Simulator, model results suggested overprediction of stand basal area growth and tree diameter increment in these stands. Growth modifiers indicated that trees growing in unthinned stands and with greater defoliation levels (i.e., 20‐32%) would need the largest adjustment for diameter increment. Modifiers for height were similarly specified to compensate for the underprediction of height increment in these stands. Thinned stands continued to maintain target live crown ratios in excess of 0.40, suggesting long-term productivity. Results highlight the need for simulation models that represent appropriate responses to stands and trees affected by forest insects and diseases. Ultimately, accurate representations of growth and development in these models that account for influences of biotic disturbance agents are essential under future global change scenarios, particularly as silvicultural strategies are implemented to reduce the impacts of forest health threats and other stressors.

English

The aim of this study was to assess biomass production of pearl millet as a function of levels and phases of defoliation. The experiment was carried out in a protected environment at the Fazenda União experimental farm in the municipality of Nova Xavantina, MT, Brazil, in 8 dm3 capacity pots in soil classified as dystrophic red Latosol. The experimental design used was randomized blocks in a 5 × 3 + 1 factorial arrangement, with five phases of defoliation (three expanded leaves, six expanded leaves, flag leaf, booting, full flowering), three levels of defoliation (33, 66 and 99%), and an additional treatment without defoliation, with three replications. The pearl millet cultivar ADR 300 was used. Plant height, number of tillers, total dry biomass of the seed heads, and total dry biomass of the plants during the leaf rolling phase was assessed. It was observed that plant height at all levels and phases of defoliation was greater than the control. For number of tillers, a reduction was observed in the booting phase and full flowering phase at all levels of defoliation; and three expanded leaves and flag leaf phases for the levels of 66 and 99% defoliation. Total biomass of the panicle at all levels and phases of defoliation was less than the control. For total dry biomass, there was a statistical difference in relation to the control when the plants were subjected to 33% defoliation in the booting phase and full flowering phase, and 66 and 99% defoliation in all the phases. A fall in production of total dry biomass of the plant greater than 53% was observed with total elimination of the leaves during the flag leaf phase.   Key words: Leaf area, damage level, Pennisetum glaucum, no-till planting.

Impacts of insect outbreaks on tree mortality, productivity, and stand development

AbstractThe impacts of insect outbreaks on tree mortality, productivity, and stand development in Canada are reviewed, emphasising spruce budworm (Choristoneura fumiferana(Clemens), Lepidoptera: Tortricidae) and mountain pine beetle (Dendroctonus ponderosaeHopkins, Coleoptera: Curculionidae). Reduced growth and survival are a function of insect population and defoliation level. It is feasible to make short-term (annual) predictions of insect population and defoliation based upon sampling, but long-term, multi-year predictions are problematic. Given the historical record, it is expected that outbreaks will occur with relatively predictable frequency and basic host relationships and abiotic constraints will not change dramatically. However, the precision of predictions at fine scales is variable and reduced over time. Relationships between tree growth reduction, survival, and cumulative defoliation or beetle population level are available for major insect species. Understanding insect outbreak effects hinges on mortality, changes in interspecies competition, regeneration, and succession. Altered stand dynamics caused by insects can be interpreted for indicators such as wildlife habitat, old forest, riparian buffer cover, viewscapes, and connectivity. Anthropogenic changes are altering impacts via range expansions, northward shifts, and changes in forest composition. We can better understand effects of insect outbreaks and how best to ameliorate damage through a combination of empirical permanent plot studies, modelling, and manipulative experiments.

Defoliation percentage in two soybean cultivars at different growth stages

ABSTRACT The objective of this study was to evaluate the agronomic variables due to the effects of different levels of defoliation in the phenological phases of two soybean cultivars. The experiment was conducted during the 2011/2012 season, in a randomized block design with three replicates, in a 2 x 4 x 5 factorial scheme. Two cultivars were exposed to defoliations of 0, 25, 50, 75 and 100% at the stages of V4, V9, R3 and R5. The cultivar 'NK 7059RR' showed less sensitivity to defoliation than the cultivar 'IN 4990RG'. 25% defoliation levels reduced the yield of the cultivar 'IN 4990RG', while levels of 75 and 100% reduce the number of grains per pod in both cultivars. The defoliation performed in the V4 stage lead to lower grain yield than defoliation in V9. The most sensitive stages to defoliation are R3 and R5, where there is a greater reduction in the production potential of soybeans.

Levels of defoliation and regrowth dynamics in elephant grass swards

The morphogenetic and structural characteristics of forage plants and the processes of growth and senescence in tissues may vary according to the grazing management strategies used. This research aimed to assess the process of regrowth in elephant grass swards Cv. 'Pioneiro' submitted to two pre-grazing heights (90 and 120cm) combined with two levels of defoliation (50 and 70%). A reduction of the leaf elongation rate (LER) was observed during the regrowth stages, in addition to a reduction in the rate of leaf appearance (LAR) and aerial tiller population density (ATPD). In contrast, an increase was observed in leaf senescence (LSR) and stem and pseudo stem elongation rates (SER). The severe defoliation (70%) combined with a pre-grazing height of 120cm compromised the regrowth of elephant grass cv. 'Pioneiro', which must be managed with a maximum height of 90cm and maximum level of defoliation of 50% of the initial height.

Carbon allocation during defoliation: testing a defense-growth trade-off in balsam fir.

During repetitive defoliation events, carbon can become limiting for trees. To maintain growth and survival, the resources have to be shared more efficiently, which could result in a trade-off between the different physiological processes of a plant. The objective of this study was to assess the effect of defoliation in carbon allocation of balsam fir [Abies balsamea (L.) Mill.] to test the presence of a trade-off between allocation to growth, carbon storage, and defense. Three defoliation intensities [control (C-trees, 0% defoliation), moderately (M-trees, 41–60%), and heavily (H-trees, 61–80%) defoliated] were selected in order to monitor several variables related to stem growth (wood formation in xylem), carbon storage in stem and needle (non-structural soluble sugars and starch), and defense components in needles (terpenoids compound) from May to October 2011. The concentration of starch was drastically reduced in both wood and leaves of H-trees with a quasi-absence of carbon partitioning to storage in early summer. Fewer kinds of monoterpenes and sesquiterpenes were formed with an increasing level of defoliation indicating a lower carbon allocation for the production of defense. The carbon allocation to wood formation gradually reduced at increasing defoliation intensities, with a lower growth rate and fewer tracheids resulting in a reduced carbon sequestration in cell walls. The hypothesis of a trade-off between the allocations to defense components and to non-structural (NCS) and structural (growth) carbon was rejected as most of the measured variables decreased with increasing defoliation. The starch amount was highly indicative of the tree carbon status at different defoliation intensity and future research should focus on the mechanism of starch utilization for survival and growth following an outbreak.

English

®according to the stages of reproductive development of the plant at defoliation and the levels of defoliation. A randomized block experimental design was used in a 6 × 3 + 1 factorial arrangement, composed of six reproductive stages at the time of defoliation [R1 (Beginning flowering), R2 (Full flowering), R3 (Beginning pod formation), R4 (Full pod formation), R5 (Beginning seed filling), R6 (Full seed filling -100% pod filling), and three levels of defoliation (33, 66 and 99%), as well as one additional treatment without defoliation, with three replications. The following features were evaluated: Plant height, number of pods per plant, number of grains per pod, harvest index, thousand seed weight, and grain yield. It was observed that all the levels of defoliation had a significant effect on the other variables studied, with the exception of plant height. The phenological stages at the time of defoliation had a significant effect on plant height, number of pods per plant, harvest index, and grain yield. There was a decline in grain yield with levels of defoliation as of 66%, and this decline was more significant with defoliation at the more advanced stages of the crop reproductive cycle.

A simple tentative model of the losses caused by the Senegalese grasshopper, Oedaleus senegalensis (Krauss 1877) to millet in the Sahel

Oedaleus senegalensis is a serious pest of millet in the Sahel, but the correlation to crop loss remains largely unknown. Therefore, the correlation between densities of O. senegalensis, defoliation level and millet yields was investigated in Niger in 2008, and a simple model to foresee the yield based on these parameters was developed. The yield was significantly correlated to both the density of O. senegalensis and the defoliation level on 17 September. The best model to foresee millet yield involved grasshopper density and cumulated rainfall and may be regarded a tentative method in O. senegalensis control.

Shea (<i>Vitellaria paradoxa</i> C. F. Gaertn.) Seedlings Showed Impressive Recovery after Defoliation

Experiments to determine the effect of seed size, watering interval and defoliation on growth and dry matter attributes of seedlings of shea butter tree were conducted at Makurdi, Nigeria, from July 2010 to April, 2012. In the first experiment, treatments were made up of three seed size categories described as small (5-10g), medium (11-15g) and large (16-20g) and three watering intervals of 3, 6 and 9 days. In the second experiment, treatments comprised three watering intervals of 3, 6 and 9 days and three levels of defoliation – 0, 50 and 100%. In both experiments, factorial combinations of the treatments were laid out in completely randomized design (CRD) and replicated three times. Results of analysis of variance showed that in the first experiment seed size significantly influenced root length with the medium and large seeds producing seedlings with comparatively longer roots than the small seeds. The most frequently watered seedlings (3 and 6 days) produced more leaves than those watered less frequently (9 days). Seed size influenced dry weight of root and total (whole plant) dry weight with the medium and large seeds recording significantly higher values than the small seeds. Watering interval however did not significantly influence any of the other traits. Seed weight exerted significant influence on amount of dry matter partitioned to the stem and the root. More dry matter was partitioned to the stem by the small seeds. Conversely, medium and large seeds allocated more dry matter to the root than to the stem. In the second experiment, defoliation level only influenced total fresh weight, dry weight of root and total dry weight in favour of plants with half their leaves removed. None of the traits examined were significantly influenced by watering regime. Interaction between defoliation level and watering regime significantly influenced total fresh weight, dry weight of root and total dry weight. Generally seed size had more influence on seedling characters than watering interval. Seedlings also demonstrated remarkable ability to overcome effects of defoliation.

Shea (<i>Vitellaria paradoxa</i> C. F. Gaertn.) Seedlings Showed Impressive Recovery after Defoliation

Experiments to determine the effect of seed size, watering interval and defoliation on growth and dry matter attributes of seedlings of shea butter tree were conducted at Makurdi, Nigeria, from July 2010 to April, 2012. In the first experiment, treatments were made up of three seed size categories described as small (5-10g), medium (11-15g) and large (16-20g) and three watering intervals of 3, 6 and 9 days. In the second experiment, treatments comprised three watering intervals of 3, 6 and 9 days and three levels of defoliation – 0, 50 and 100%. In both experiments, factorial combinations of the treatments were laid out in completely randomized design (CRD) and replicated three times. Results of analysis of variance showed that in the first experiment seed size significantly influenced root length with the medium and large seeds producing seedlings with comparatively longer roots than the small seeds. The most frequently watered seedlings (3 and 6 days) produced more leaves than those watered less frequently (9 days). Seed size influenced dry weight of root and total (whole plant) dry weight with the medium and large seeds recording significantly higher values than the small seeds. Watering interval however did not significantly influence any of the other traits. Seed weight exerted significant influence on amount of dry matter partitioned to the stem and the root. More dry matter was partitioned to the stem by the small seeds. Conversely, medium and large seeds allocated more dry matter to the root than to the stem. In the second experiment, defoliation level only influenced total fresh weight, dry weight of root and total dry weight in favour of plants with half their leaves removed. None of the traits examined were significantly influenced by watering regime. Interaction between defoliation level and watering regime significantly influenced total fresh weight, dry weight of root and total dry weight. Generally seed size had more influence on seedling characters than watering interval. Seedlings also demonstrated remarkable ability to overcome effects of defoliation.

Stand structure and height-diameter relationship of a degraded Populus euphratica forest in the lower reaches of the Tarim River, Northwest China

Understanding stand structure and height-diameter relationship of trees provides very useful information to establish appropriate countermeasures for sustainable management of endangered forests. Populus euphratica, a dominant tree species along the Tarim River watershed, plays an irreplaceable role in the sustainable development of regional ecology, economy and society. However, as the result of climate changes and human activities, the natural riparian ecosystems within the whole river basin were degraded enormously, particularly in the lower reaches of the river where about 320 km of the riparian forests were either highly degraded or dead. In this study, we presented one of the main criteria for the assessment of vitality of P. euphratica forests by estimating the defoliation level, and analyzed forest structure and determined the height-diameter (height means the height of a tree and diameter means the diameter at breast height (DBH) of a tree) relationship of trees in different vitality classes (i.e. healthy, good, medium, senesced, dying, dead and fallen). Trees classified as healthy and good accounted for approximately 40% of all sample trees, while slightly and highly degraded trees took up nearly 60% of total sample trees. The values of TH (tree height) and DBH ranged from 0–19 m and 0–125 cm, respectively. Trees more than 15 m in TH and 60 cm in DBH appeared sporadically. Trees in different vitality classes had different distribution patterns. Healthy trees were mainly composed more of relatively younger trees than of degraded tress. The height-diameter relationships differed greatly among tress in different vitality classes, with the coefficients ranging from 0.1653 to 0.6942. Correlation coefficients of TH and DBH in healthy and good trees were higher than those in trees of other vitality classes. The correlation between TH and DBH decreased with the decline of tree vitality. Our results suggested that it might be able to differentiate degraded P. euphratica trees from healthy trees by determining the height-diameter correlation coefficient, and the coefficient would be a new parameter for detecting degradation and assessing sustainable management of floodplain forests in arid regions. In addition, tree vitality should be taken into account to make an accurate height-diameter model for tree height prediction.

Analysis of Unmanned Aerial System-Based CIR Images in Forestry—A New Perspective to Monitor Pest Infestation Levels

The detection of pest infestation is an important aspect of forest management. In the case of the oak splendour beetle (Agrilus biguttatus) infestation, the affected oaks (Quercus sp.) show high levels of defoliation and altered canopy reflection signature. These critical features can be identified in high-resolution colour infrared (CIR) images of the tree crown and branches level captured by Unmanned Aerial Systems (UAS). In this study, we used a small UAS equipped with a compact digital camera which has been calibrated and modified to record not only the visual but also the near infrared reflection (NIR) of possibly infested oaks. The flight campaigns were realized in August 2013, covering two study sites which are located in a rural area in western Germany. Both locations represent small-scale, privately managed commercial forests in which oaks are economically valuable species. Our workflow includes the CIR/NIR image acquisition, mosaicking, georeferencing and pixel-based image enhancement followed by object-based image classification techniques. A modified Normalized Difference Vegetation Index (NDVImod) derived classification was used to distinguish between five vegetation health classes, i.e., infested, healthy or dead branches, other vegetation and canopy gaps. We achieved an overall Kappa Index of Agreement (KIA) of 0.81 and 0.77 for each study site, respectively. This approach offers a low-cost alternative to private forest owners who pursue a sustainable management strategy.

The effect of pyraclostrobin on soybean plant health, yield, and profitability in Ontario

Mahoney, K. J., Vyn, R. J. and Gillard, C. L. 2015. The effect of pyraclostrobin on soybean plant health, yield, and profitability in Ontario. Can. J. Plant Sci. 95: 285–292. Prophylactic fungicides have been advocated to manage foliar diseases, optimize plant heath, and increase yields. Studies were conducted in 2009, 2010, and 2011 using 20 soybean cultivars to determine if pyraclostrobin, a strobilurin, induced plant health effects to increase yield and profitability under conditions with low levels of foliar disease. Pyraclostrobin applied at the R3 stage significantly reduced leaf defoliation caused by brown spot (Septoria glycines Hemmi) compared with the untreated control with 27 and 45% defoliation, respectively, across all cultivars. Pyraclostrobin delayed maturity, but the response varied among cultivars. For example, cultivars with low levels of leaf defoliation responded with an increase in the number of days to maturity, whereas cultivars with high levels of defoliation generally did not. Pyraclostrobin increased yield by 4.1% compared with the untreated control across all cultivars with 4.49 and 4.31 t ha−1 harvested, respectively. Increased revenue from increased yield was offset by increased fungicide costs, resulting in a negligible effect on profitability; however, effects of pyraclostrobin application on profit margins in individual environments ranged from -$50.02 ha−1 in 2009 to $53.73 ha−1 in 2011. Overall, these results suggest that if environmental conditions are conducive for foliar disease, a pyraclostrobin application could be warranted.

Desenvolvimento e produtividade de grãos de milho submetido a níveis de desfolha

O objetivo deste trabalho foi avaliar a influência da desfolha do milho no desenvolvimento e na produtividade de grãos. Seis ensaios foram conduzidos em diferentes safras e locais e em dois níveis de produtividade. Utilizou-se o delineamento de blocos ao acaso, com sete repetições. A desfolha foi realizada no estádio vegetativo V4 do milho (quatro folhas expandidas), e os tratamentos foram: remoção das duas folhas basais, remoção das quatro folhas expandidas, remoção total das folhas (secção da parte aérea) e testemunha (sem desfolha). Foram avaliados: duração do período vegetativo; e, em pré-colheita, altura de planta, altura de espiga, percentagem de plantas acamadas, força de quebramento de colmo, força de arranquio da planta e produtividade. A remoção das quatro folhas e a remoção total aumentaram a duração do período vegetativo e reduziram a altura de planta, a altura de espiga e a resistência do colmo ao quebramento. Esses níveis de desfolha também reduziram a produtividade, principalmente com a remoção total das folhas. A força de arranquio da planta não foi influenciada pela desfolha. A retirada de quatro folhas e do total das folhas reduz a produtividade de grãos, respectivamente, em 6,25 a 14,05% nos híbridos avaliados.

Moth outbreaks alter root-associated fungal communities in subarctic mountain birch forests.

Climate change has important implications on the abundance and range of insect pests in forest ecosystems. We studied responses of root-associated fungal communities to defoliation of mountain birch hosts by a massive geometrid moth outbreak through 454 pyrosequencing of tagged amplicons of the ITS2 rDNA region. We compared fungal diversity and community composition at three levels of moth defoliation (intact control, full defoliation in one season, full defoliation in two or more seasons), replicated in three localities. Defoliation caused dramatic shifts in functional and taxonomic community composition of root-associated fungi. Differentially defoliated mountain birch roots harbored distinct fungal communities, which correlated with increasing soil nutrients and decreasing amount of host trees with green foliar mass. Ectomycorrhizal fungi (EMF) abundance and richness declined by 70-80% with increasing defoliation intensity, while saprotrophic and endophytic fungi seemed to benefit from defoliation. Moth herbivory also reduced dominance of Basidiomycota in the roots due to loss of basidiomycete EMF and increases in functionally unknown Ascomycota. Our results demonstrate the top-down control of belowground fungal communities by aboveground herbivory and suggest a marked reduction in the carbon flow from plants to soil fungi following defoliation. These results are among the first to provide evidence on cascading effects of natural herbivory on tree root-associated fungi at an ecosystem scale.

Testing the reliability and stability of the internal accuracy assessment of random forest for classifying tree defoliation levels using different validation methods

In this study, the strength and reliability of internal accuracy estimate built in random forest (RF) ensemble classifier was evaluated. Specifically, we compared the reliability of the internal validation methods of RF with independent data-sets of different splitting options for defoliation classification. Furthermore, we set out to statistically validate the best independent split option for image classification using RF and multispectral Rapideye imagery. Results show that the internal accuracy measure yields comparable results with those derived from an independent test data-set. More important, it was observed that the errors produced by the internal validation methods of RF were relatively stable as statistically shown by the lower confidence interval obtained as compared to the independent test data. Results also showed that the 70–30% split option had the lowest mean standard errors (0.2351) and hence highest accuracy when compared to the other split options. The study confirms the reliability and stability of the internal bootstrapping estimate of accuracy built within the random forest algorithm.

Effect of artificial defoliation on cane regrowth and fruit development in ‘Jecy Gold’ kiwifruit

Leaves of kiwifruit have long petiole and large size, so that they are easily damaged by strong wind. This study was performed to evaluate the effect of leaves loss by typhoon damage on fruit quality and yield and new cane growth with artificial defoliation. Five-year-old ‘Jecy Gold’ kiwifruit vines grown in a plastic house were used in this study. Artificial defoliation was done on August 23 (100 days after anthesis) at the different defoliation levels, such as 0 (control), 50, 75, and 100%. Cane regrowth by axillary bud burst, cane bark carbohydrate reserve, and fruit quality and yield were investigated. Severe defoliation at 75 and 100% level showed significantly higher axillary budburst than the control and the 50% defoliation. Especially, the 100% defoliation induced a few abnormal off-season flowering. Starch and sucrose contents were significantly declined during the first 2 weeks after defoliation at the 75 and 100% defoliation. However, other soluble carbohydrate reserves including fructose, glucose, and myo-inositol were not affected significantly. Fruit drop was promoted and the mean fruit weight, firmness, and soluble solid concentrations were lower by the defoliation. Our results indicated that the loss of leaves above 50% would induce a transient shortage of assimilate supply and reduce fruit quality and yield significantly.

Outbreaking herbivore escapes parasitoid by attaining only a small body size

The reason why parasitoids are often unable to control insect herbivores during outbreak years has remained unclear to modern ecologists. Here I show that the blue willow beetle (Phratora vulgatissima) can escape parasitoids (Perilitus brevicollis) by reaching only a small body size during the increased competition which coincides with outbreaks. Different phases of outbreaks were simulated by allowing leaf‐beetle larvae to develop at different densities on willow. The denser the herbivore populations, the smaller body sizes they attained. In the field too, herbivore body size decreased when the level of defoliation increased. The parasitoids were clearly limited by herbivore body size, exhibiting reduced survival in parallel with decreasing herbivore size, with none of them surviving in beetles from larvae reared at the highest density. The results demonstrate how bottom‐up control of the herbivore becomes more important as outbreaks intensify, while top‐down control gradually becomes less important and collapses during the outbreak peak. Because the mechanism limiting P. brevicollis parasitoids involves herbivore body size, which is reduced at high densities, I anticipate that these parasitoids are unable to terminate herbivore outbreaks.

English

The cotton leafworm, Alabama argillacea (Hubner, 1818) (Lepidoptera: Noctuidae) is a major defoliating pest that reduces yield and quality of the crop. The purpose of this study was to evaluate the effect of different levels of defoliation caused by different larval densities of A. argillacea on four cotton cultivars in three different plant ages. The experiment was conducted at an experimental station of the Agencia Paulista de Tecnologia dos Agronegocios (APTA), Polo Centro Norte, in Pindorama, SP, Brazil. The experiment was arranged in a factorial randomized block design with 4 replicates: four cultivars (DeltaOPAL, IAC-25, Fibermax 996 and Fibermax 993) x four larval densities (0, 2, 4, and 6 larvae per plant) x three infestation times (30, 60 and 90 days after plant emergence). Fortnightly evaluations carried out based on the production of squares, flowers, fruits and bolls per plant. It was found that the higher infestation level of A. argillacea , the lower was the production of buds per plant and consequently the production of fruits and bolls of the four varieties. Early infestation (30 and 60 DAE) reduced the production of reproductive structures per plant in cultivars more than late infestation (90 DAE).