Percent Defoliation Research Articles

Mixing Elemental Sulfur or Chlorothalonil with QoI and DMI Fungicides for Management of Late Leaf Spot of Peanut.

Reduced sensitivity to demethylation inhibitor (DMI) and quinone outside inhibitor (QoI) fungicides in Nothopassalora personata, the cause of late leaf spot of peanut (Arachis hypogaea) complicates management of this disease in the southeastern U.S. Mixtures with protectant fungicides may help preserve the utility of members of both DMI and QoI fungicide groups for leaf spot management. Field experiments were conducted in Tifton, GA from 2019 to 2021 and in Plains, GA during 2019 and 2020. The primary objective was to determine the effects of mixtures of DMI fungicides, tebuconazole and mefentrifluconazole, and QoI fungicides, azoxystrobin and pyraclostrobin, with micronized elemental sulfur on late leaf spot in fields with populations of N. personata with suspected reduced sensitivity to DMI and QoI fungicides. In four of the experiments, the efficacies of elemental sulfur and chlorothalonil as mixing partners were also compared. In most cases, standardized area under the disease progress curve (sAUDPC) and final percent defoliation were less for all DMI and QoI fungicides mixed with sulfur or chlorothalonil than for the respective fungicides alone. In most cases, sAUDPC and final percent defoliation were similar for sulfur and chlorothalonil when mixed with the respective DMI or QoI fungicide. These results indicate that mixtures of DMI or QoI fungicides with either micronized sulfur or chlorothalonil can improve control of late leaf spot compared to the DMI or QoI fungicide alone. These results also indicate that elemental sulfur has potential as an alternative to chlorothalonil in tank mixes where that protectant fungicide is currently being used as a mixing partner to improve leaf spot control.

Free-feeding organisms and galling insects (Hymenoptera) interactions on Caryocar brasiliense (Malpighiales: Caryocaraceae) trees, a savanna plant from Brazil.

Galling insects are abundant in nature, found in many ecosystems globally, with species attacking plants of economic importance. We studied the effects of free-feeding organisms on the abundance of galling insects on Caryocar brasiliense (Caryocaraceae) trees in the Brazilian Cerrado (Savanna). Percentage of defoliation and the number of phytophagous mites or number of phytophagous Hemiptera correlated negatively with percentage of galled leaves and the parasitoid Eurytoma sp. (Hymenoptera: Eurytomidae) adults, respectively. Percentage of galled leaves and the numbers of Eurytoma sp. adults and phytophagous mites correlated positively with spiders. Numbers of mites and Hemiptera phytophagous correlated positively with those of lady beetles and Sycophila sp. (Hymenoptera: Eurytomidae), respectively. The number of Ablerus magistretti Blanchard (Hymenoptera: Aphelinidae) adults correlated negatively with Sycophila sp. The number of Agistemus sp. (Acari: Stigmaeidae) correlated, negatively and positively, with those of lady beetles and phytophagous mites, respectively. Free-feeding herbivores affected the presence of galling insects (Hymenoptera) on C. brasiliense trees, competing for food and space. The same was observed between two parasitoids of Eurytoma sp. galling insect, which can reduce the natural biological control of this pest.

Application of defoliants alters leaf growth and gas exchange parameters for cotton defoliation

The goal of the current study was to determine how different chemical defoliants and application timing affected defoliation in cotton variety CO 17. The studies were conducted using a split-plot design with three applications at three different times as the main plot and seven defoliants as the subplot. Thidiazuron + Diuron (0.03%) defoliant reduced the gas exchange parameters, photosynthetic rate, transpiration rate and stomatal conductance by reducing plant growth parameters, leaf area, leaf area index, specific leaf weight which significantly increased the defoliation percentage. The negative correlation of cotton growth and gas exchange parameters with defoliation percentage was observed in correlation studies. In conclusion, Thidiazuron + Diuron (0.03%) defoliant was found to be superior in action for improving leaf defoliation and its associated parameters. And also it may be a cost-effective cotton defoliant for aiding the mechanical picking of cotton bolls.

High dosage of mepiquat chloride delays defoliation of harvest aids in cotton

The plant growth regulator mepiquat chloride (MC) has been widely used to regulate cotton growth and development worldwide. However, little is known about whether MC application during cotton growing season affects defoliation efficiency of the harvest aids (TE), a novel product with the mixture of 10% thidiazuron and 40% ethephon. Here, a 3-year (2018–2020) field experiment was carried out in Hejian, Hebei province, China, involving six treatments as three different MC rates (MC free, farmers’ practice-conventional amount, high MC amount) and two defoliant rates (0 ml ha−1 [CK] and 2250 ml ha−1 [TE]). High MC rate delayed cotton leaf abscission and decreased the defoliation percentage at 7 days after TE treatment, but hardly affected harvest aids efficacy at harvest time. The delay of leaf abscission was due to an increase in auxin and cytokinin concentration of cotton leaves in MC treatment. The MC treatment accelerated the natural maturation of cotton, achieving a higher boll-opening percentage before defoliant spraying, and increased cotton lint yield. Over the 3-year period, compared to CK, the defoliant application TE increased the defoliation percentage by 43.4%, the boll-opening percentage by 10.4%, and the cotton lint yield by 9.1% due to an increase in opened boll number per unit land area. We concluded that the optimal MC dose (about 200 g ha−1) would decrease the risk of reducing defoliation and achieve higher cotton lint yield.

Health and Growth of Black Pine outside Its Natural Distribution Range in the Romanian Carpathians

In the last decade, coniferous stands outside their natural range in Romania have experienced declines in both their health and growth and, in tandem with global climate trends, these forests are becoming even more threatened. We studied the relationship between tree growth and defoliation as an indicator of tree health. The data came from black pine stands monitored from 2012 to 2021 in the Postăvarul Massif in the Romanian Carpathians. Analyses were carried out on 508 individual trees based on their defoliation and radial growth data and also at the stand level. The results revealed an increase in the percentage of tree defoliation from 17% to 38% during the studied decade, along with 13.5% tree mortality. Over the decade, radial growth showed a negative trend, driven significantly by defoliation. The biometric parameters of the trees did not influence their percentage of defoliation. In contrast, spring/summer droughts associated with high temperatures affect the health and growth of trees. Models generated from the temperature–defoliation–radial-growth relationship estimated a significant continuous reduction in the radial growth of the trees of 0.5%–0.6% for each 1% increase in defoliation. Under the site conditions of the investigated stands, an increase in basal area and stocking degree significantly increased stand defoliation. This was further accentuated when the pine stand included an understory of young trees. As a rule, in the interest of production, stands are kept dense to fully exploit the site, but thinning may become necessary to protect these stands and ensure their survival as the climate changes.

Drivers of twoneedle pinyon (Pinus edulis) cone productivity: Implication for wildlife

Seeds of twoneedle pinyon (Pinus edulis) serve as a nutritionally dense food resource for a myriad of wildlife. Pinyons exhibit synchronist masting with high cone production occurring every 4–7 years. Per-tree cone abundance may be influenced by tree-level and site-level features. Our goal was to identify features that influence pinyon cone abundance and determine how cone production relates to habitat selection by the Oscura Mountains Colorado chipmunk (Neotamias quadrivittatus oscuraensis), an old growth pinyon-juniper specialist and seed-caching rodent. We hypothesized increased cone abundance would be exhibited by older trees and at sites with increased water availability. We hypothesized that the chipmunk would select sites exhibiting increased 8-year cone production and annual cone abundance. We used double observer abscission scar counts on five branches per tree averaged between observers to estimate tree cone abundance for the most recent eight years. We used linear modeling to determine tree- and site-level features influencing per tree cone abundance, incorporating site as a random-intercept for tree-level models. The most influential tree-level feature was diameter, with larger diameter trees having greatest cone abundance. Percent defoliation in the living tree canopy exhibited an inverse relationship with cone abundance. Water availability of a site was represented by reproductive tree density and heat load, both of which inversely influenced per-tree cone abundance. However, reproductive tree density exhibited a positive relationship with cone production across a stand. Our data did not support the prediction that the chipmunk would select sites based on mean 8-year cone production, although there was a suggestion that it preferentially used sites with higher annual cone abundance during a high mast year. Though it requires further testing, sites that produce high cone abundance might be important for maintaining chipmunk metapopulations. We encourage management of pinyon-juniper woodlands to consider drivers of pinyon cone productivity and influence of cone production on wildlife. We urge the protection of old growth stands of pinyon-juniper woodland to support wildlife, as older trees are the most influential determinant of cone abundance and concurrently provide structural complexity important for wildlife. Lastly, our study indicates thinning of pinyon-juniper woodlands as unwarranted for the goal of increasing cone production. Maximizing pinyon cone production would be best met by maintaining dense old growth stands.

A Novel Simplified Protocol for Pre-Processing Whole Wood Samples for Stable Isotope Analysis in Tree Rings

In the context of climate change, the stable isotope analysis of tree rings may play a crucial role in deciphering the eco-physiological mechanisms underlying forest decline and dieback phenomena. However, this technique is often considered expensive, time-consuming, and with several methodological constraints. Specifically, milling and transferring the material from jars to vials during the different steps of sample preparation involve risk of contamination among samples and loss of sample material. When dealing with declining trees (i.e., trees affected by loss of vitality with strong percentage of defoliation and reduction in growth) and trees subjected to extreme events or negative pointer years (characterized by extremely narrow ring) the sample preparation is particularly difficult because of scarce amount of wood material. In such a case, pooling rings from several years to achieve the minimum weight of wood is often necessary, thus losing information at the annual resolution. In order to overcome such limitations, we developed a novel protocol for quick and accurate whole-wood pre-processing, testing it on oak tree rings of different widths taken from living trees. The main novelty introduced by our protocol was freezing tree-ring samples at −80 °C and milling multiple samples at a time by using a 24-tube plate. The results showed that our novel simplified protocol significantly reduced the pre-processing time with respect to the standard protocol (12 vs. 284 sec/sample), while achieving the same wood particle size, limiting the loss of wood material and reducing the risk of contamination among samples.

Effect of defoliants on percent defoliation and yield of American cotton (Gossypium hirsutum)

Cotton production is labour intensive in almost all the developing countries where it is picked by hand. However, due to acute labour shortage in recent times, mechanized harvesting is gaining momentum. It requires the application of defoliants, which reduces the cost of labour and maximum cotton can be picked in a single pick (one picking) and consequently provide timely sowing of next crop. The farmers can get benefit of two crops instead of one single long duration cotton crop. Therefore, a two year study conducted at Agricultural College Farm, Bapatla, Andhra Pradesh, during the kharif of 2018–19 and 2019–20 to know the the effect of different defoliants and their time of application on per cent defoliation and seed cotton yield in High Density Planting American Cotton (HDPS).Three defoliants Dropp ultra, mepiquat chloride and etherel and three times of application 80% of boll opening, Node Above Cracked Boll and Node Above White Flower were included in this research in split plot design with four replications. Per cent defoliation was significantly influenced by different defoliant treatments, as well as time of application. At 21 days after defoliant spray, there was significant increase in per cent defoliation with Dropp Ultra 540 SC (Thidiazuron 360 + Diuron 180) @ 250 mL/ha (91.5%) over other defoliants and at 80% Boll Opening (88.3%), which was on par with NACB (86.9%). Higher seed cotton yield was obtained with application of Dropp Ultra @ 250 mL/ha and found on par with Etherel @ 3000 ppm (D3) and regarding times of application, defoliants applied at 80% Boll Opening recorded maximum yield, which was found at par with NACB method.

Assessing Forest Vitality and Forest Structure Using 3D Data: A Case Study From the Hainich National Park, Germany

The adaptation of forest management to changing environmental conditions due to climate change relies on information on the current forest and tree vitality. In common practice, the percentage of crown defoliation is used as a proxy for tree vitality, an approach that has several drawbacks. By performing laser scanning on a forest plot in the Hainich National Park, we tested a new approach to quantifying tree vitality. Based on the difference in structural complexity measured between summer and winter, assessed via the box-dimension, the new approach provides an objective and reproducible method that does not only allow the quantification of the defoliation, but also includes the effects of branch diebacks. In addition, we assessed the change in box-dimension and branch lengths between 2013 and 2021 and studied the overall structural development of the trees to analyze the alteration of their vitality. On average, we found a decrease in overall structural complexity, as well as in branch lengths for most trees in the investigated forest. Further, the mean difference in box-dimension (summer minus winter) decreased with ascending vitality class. We conclude that the vitality of the trees was negatively affected over the period of 8 years, and we argue the newly proposed method based on the box-dimension holds potential to be used as a measure for tree vitality in deciduous forests.

Impact of Adult Popillia japonica (Coleoptera: Scarabaeidae) Foliar Feeding Injury on Fruit Yield and Quality of a Temperate, Cold-Hardy Wine Grape, 'Frontenac'.

Popillia japonica (Newman), is a highly polyphagous, invasive species, first recorded in the U.S. in 1916, and detected in Minnesota in the late 1960s. Historically, research on this pest in the Midwest U.S. has focused primarily on ornamental and turf crops, with little attention placed on adult feeding damage to fruit crops. Recently, wine grape producers in the region noted substantial increases in defoliation from P. japonica feeding, confirming concerns for this perennial high value crop. To address these concerns, studies were conducted during the summers of 2020-2021 to understand the impact of P. japonica foliar feeding on the quality and yield of wine grapes. Trials utilized vines of the wine grape variety, 'Frontenac.' In addition to open plots, whole vines were caged within fine mesh netting and infested with P. japonica at 0, 25, 50, and 100 beetles per meter-row of vine. Beetles used for infestations were collected from natural field populations of P. japonica and left to feed until grapes were ready for harvest. During harvest, data collection included leaf samples for obtaining average percent defoliation, cluster weights, and berry subsamples for soluble solid content, pH, titratable acidity, and phenolic compound measurements. Results from these studies demonstrated that as beetle population density and defoliation per m-row increases, at-harvest measurements of quality parameters are significantly and negatively affected (P < 0.05) when compared with uninfested vines. The negative impacts to fruit quality exhibited in these studies will be important in the development of future management strategies for P. japonica in 'Frontenac.'

Efficacy of Helicoverpa Armigera Nucleopolyhedrovirus on Soybean for Control of Helicoverpa zea (Boddie) (Lepidoptera: Noctuidae) in Arkansas Agriculture.

Simple SummaryHelicoverpa zea is a major pest of soybean, and has developed resistance to many insecticides. This has led to an exploration of alternative control tactics. One such tactic is Helicoverpa armigera nucleopolyhedrovirus (HearNPV). Although using a biological agent as a control tactic has limitations, the purpose of this study was to address the effectiveness of HearNPV in controlling each H. zea larval instar by simulating a field application on soybean and observing mortality. Furthermore, this study addresses the potential for infection in one generation to lead to infection in a sequential generation. Our results indicate that HearNPV is effective at controlling 1st–3rd instar larvae, but does not effectively control 4th or 5th instar larvae. Also, a sequential generation of 2nd instar larvae succumbed to viral infection faster than the previous infestation. Therefore, HearNPV is capable of cross-generational infection, and could be a useful tool in producer’s management tactics for H. zea.Helicoverpa armigera nucleopolyhedrovirus (HearNPV) is a naturally occurring virus commercially produced for control of Heliothines, including Helicoverpa zea. One drawback with using this virus for control has been the slower time to mortality compared with synthetic insecticides. However, a new formulation (Heligen®) has anecdotally been thought to result in quicker mortality than previously observed. The objective of this study was to evaluate percent defoliation, the efficacy of HearNPV on mortality for each H. zea larval instar, and the potential for control of a second infestation. Fourteen days after the first infestation, all plants were re-infested with a second instar larva to simulate a second infestation. Helicoverpa armigera nucleopolyhedrovirus was effective at killing 1st–3rd instars, resulting in 99% mortality over 4–6 days. However, 4th and 5th instar mortality only reached 35%. Second infestation larvae died between 3.4 and 3.8 days, significantly faster than the 1st infestation of 2nd instars, which had a mean time to mortality of 4.9 days. An increase in mortality rate is probably due to increasing viral concentrations after viral replication within the first hosts. Final defoliation percentages were significantly smaller in the treated plants versus the untreated plants. Only 3rd and 4th instar larvae caused percent defoliation to exceed the current Arkansas action threshold of 40%. Helicoverpa armigera nucleopolyhedrovirus in the Heligen formulation can control 1st–3rd instars within 4–6 days, while keeping defoliation below the action threshold of 40%.

Cotton maturity and responses to harvest aids following chemical topping with mepiquat chloride during bloom period

Early maturity, complete defoliation and boll opening are essential for the efficient machine harvesting of cotton. Chemical topping, involving one extra application of mepiquat chloride (MC) in addition to its traditional multiple-application strategy, may be able to replace manual topping. However, it is not known whether this chemical topping technique will influence maturity or cotton responses to harvest aids. In this 2-yr field study, we determined the effects of the timing of chemical topping using various rates of MC on boll opening percentage (BOP) before application of harvest aids (50% thidiazuron·ethephon suspension concentrate, referred to as TE), and the defoliation percentage (DP) and BOP 14 days after TE application. The results indicated that late chemical topping (near the physiological cutout, when the nodes above white flower is equal to 5.0) significantly decreased BOP before TE by 5.9–11.2% compared with early (at peak bloom) or middle (seven days after peak bloom) treatments in 2019, which was a relatively normal year based on crop condition. Also, a high MC rate (270 g ha−1) showed a significantly lower (22.0%) BOP before TE than low (90 g ha−1) or medium (180 g ha−1) rates. In 2020, which was characterized by stronger vegetative growth in the late season, the late chemical topping reduced the number of leaves before TE application relative to early or middle treatments, but had lower DP (23.2–27.2%) 14 days after TE application. The high MC rate showed a leaf count before TE application that was similar to the low and medium rates, but it showed the most leaves after TE and much lower (15.0–21.7%) DP in 2020. These results suggest that late timing of chemical topping and a high MC rate decreased the sensitivity of leaves to harvest aids. Further analysis indicated that the late chemical topping mainly affected the leaf drop from the mainstem and fruiting branches where the late regrowth occurred, and the high MC rate reduced leaf shedding from these parts and also from the vegetative branches. In conclusion, chemical topping with MC during the bloom period affected cotton maturity and responses to harvest aids in different ways according to the crop condition. To avoid the risks of delayed maturity and poor defoliation after the application of harvest aids, chemical topping should not be performed too late (i.e., near the physiological cutout) by using MC at more than 180 g ha−1. The optimum timing of chemical topping probably varies from peak bloom to around seven days later, and the safest MC rates for chemical topping should be less than 180 g ha−1.

Differences in Susceptibility to Phomopsis Blight of Seven Eggplant Cultivars with Different Fruit Types

Phomopsis blight caused by Diaporthe vexans is a serious disease on fall eggplant crops in the southeastern United States. The objective was to compare seven eggplant cultivars, representing seven horticultural fruit types, for susceptibility to D. vexans. Eggplant transplanted in April 2018 and 2019 was cut back in late summer and harvested in September and October. Leaf area under the disease progress curve and percentage defoliation were greater on Black Beauty (globe type) than Patio Baby (Indian), Millionaire (Japanese), Rosa Bianca (Italian), and Gretel (white). Cankered stem length was greater on Black Beauty and Fairy Tale than on Gretel. Hansel (Chinese) and Gretel produced the most healthy, unblemished marketable fruit; Patio Baby, Millionaire, and Fairy Tale had a moderate number; and Black Beauty and Rosa Bianca produced the fewest fruit. Percentage fruit rot both years was greater (P ≤ 0.01) on Black Beauty than Hansel, Gretel, Patio Baby, and Rosa Bianca. Several eggplant cultivars, such as Hansel and Gretel, are less susceptible to Phomopsis fruit rot than Black Beauty and produce more marketable fruit than several other specialty eggplant cultivars.

Optimizing the application of a novel harvest aid to improve the quality of mechanically harvested cotton in the North China Plain

Defoliation is an indispensable step in cotton production with mechanical harvesting, especially in the North China Plain (NCP) where mechanical harvesting is limited by a large proportion of green leaves and unopened bolls at harvest time due to insufficient thermal resources. It is essential to quantify the optimal use of defoliation products while minimizing yield and quality loss in China. The objective of this study was to test the effect of a new defoliant Xinsaili (XSL, a compound of 10% thidiazuron and 40% ethephon) on the spatial distribution of cotton leaves and bolls, yield and quality in the NCP. There were four treatments: XSL 1800 mL ha–1, XSL 2700 mL ha–1, XSL splitted into two equal applications (1350 mL ha–1 for each), and XSL-free (water) control. Field experiments were conducted in Hebei, China in 2016–2017. All the defoliant treatments did not significantly affect cotton yield and fiber quality compared with the water control. At harvest time, the rate of open bolls under XSL 2700 mL ha–1 was 13.5% higher than that under XSL-free control, while the other two treatments showed no significant difference, across the two years. Defoliation percentage of the three XSL treatments showed no difference, but they were on average 42.2% higher than that of XSL-free control. The year-round effect of the defoliant XSL was significant, indicating that climate factors would affect its application. It was concluded that the optimal dose of XSL in the NCP was 2700 mL ha–1, and it was unnecessary to split it into two applications. These results would promote cotton mechanical harvesting and reduce the labor cost of cotton production in China.

Appraisal of the performance of peanut genotypes (Arachis hypogaea L.) from the ICRISAT collection in India

Peanut (Arachis hypogaea L.) is a worldwide popular oilseed. In Burkina Faso, production fluctuates from year to year. This fluctuation in yield is linked to the biotic factors which constitute the major constraints of peanuts. To this end, many breeding programs have been set up to select disease-resistant varieties to improve yields. It is with this in mind that this work focused a genetic analysis of traits related to leaf spot resistance of groundnuts. This study was to evaluate the performance of groundnut genotypes of Indian origin, through field screening to identify leafs spot resistant genotypes with good performance. The experimental device was in a completely randomized Fisher block with three repetitions. After setting up the trial, severity of the disease, percentage of defoliation and yield components were noted. Data from all observations were analyzed using the XLSTAT Pro.1 static analysis software. Statistical analysis of the obtained results showed a significant difference between the obtained values in the different genotypes evaluated for all of the above parameters except the yield. At the end of this study, nineteen (19) resistant genotypes and twenty-three (23) genotypes moderately resistant to leaf spot were identified. These resistant genotypes constitute an additional list of resistant varieties and can be used as a source of resistance in a varietal improvement program.Keywords: Performance, Arachis hypogaea L., ICRISAT collection, India.

Can inoculation with diazotrophic bacteria decrease the productivity loss of defoliated Vigna unguiculata (L.) Walp?

ABSTRACT The objective of this study was to evaluate the effect of artificial defoliation on vegetative and productive stages of cowpea inoculated with diazotrophic bacteria, in two experiments. The first experiment was performed in a greenhouse with 5 × 5 factorial (five defoliation percentages and five N sources), with four repetitions. N sources consisted of bacterial inoculation with strains INPA 03-11B, UFLA 03-84, UFRB FA34C2-2, and two control treatments: i - with N fertilization and ii - blank control, without N fertilization and without inoculation. The second experiment was performed in the field, in a 3 × 5 factorial scheme, with three repetitions. Treatments consisted of three N sources: with N fertilization, with bacterial strain INPA 03-11B that was selected in the first experiment, and five percentages of artificial defoliation. Defoliation percentages for both experiments were 0, 25, 50, 75, and 100%. Artificial defoliation during the vegetative stage caused reduction in the dry mass of bacterial nodules. Inoculation increased plant tolerance to defoliation and enhanced grain nutrient concentration (N and P). Inoculation with the strain INPA 03-11B allowed cowpea plants to tolerate 50% defoliation in the vegetative stage. The mean productivity of cowpea was reduced under &gt; 50% defoliation during the productive stage; therefore, control of defoliating pests until the productive stage is not necessary under field conditions.

Photoprotective compounds as early markers to predict holm oak crown defoliation in declining Mediterranean savannahs.

Dehesas, human-shaped savannah-like ecosystems, where the overstorey is mainly dominated by the evergreen holm oak (Quercus ilex L. subsp. ballota (Desf.) Samp.), are classified as a global conservation priority. Despite being Q. ilex a species adapted to the harsh Mediterranean environmental conditions, recent decades have witnessed worrisome trends of climate-change-induced holm oak mortality. Holm oak decline is evidenced by tree vigour loss, gradual defoliation and ultimately, death. However, before losing leaves, trees undergo leaf-level physiological adjustments in response to stress that may represent a promising field to develop biochemical early markers of holm oak decline. This study explored holm oak photoprotective responses (pigments, tocopherols and photosynthetic performance) in 144 mature holm oak trees with different health statuses (i.e., crown defoliation percentages) from healthy to first-stage declining individuals. Our results indicate differential photochemical performance and photoprotective compounds concentration depending on the trees' health status. Declining trees showed higher energy dissipation yield, lower photochemical efficiency and enhanced photoprotective compounds. In the case of total violaxanthin cycle pigments (VAZ) and tocopherols, shifts in leaf contents were significant at very early stages of crown defoliation, even before visual symptoms of decline were evident, supporting the value of these biochemical compounds as early stress markers. Linear mixed-effects models results showed an acute response, both in the photosynthesis performance index and in the concentration of foliar tocopherols, during the onset of tree decline, whereas VAZ showed a more gradual response along the defoliation gradient of the crown. These results collectively demonstrate that once a certain threshold of leaf physiological damage is surpassed, that leaf cannot counteract oxidative stress and progressive loss of leaves occurs. Therefore, the use of both photosynthesis performance indexes and the leaf tocopherols concentration as early diagnostic tools might predict declining trends, facilitating the implementation of preventive measures to counteract crown defoliation.

Effectiveness of Trichogramma pretiosum in controlling lepidopterous pests of soybean crops

Controlling lepidopteran pests in soybean in Uruguay usually involves the application of chemical insecticides with risks to health and the environment. As part of an inundative biological control program using Trichogramma pretiosum, a plot trial at three sites located in the department of Soriano (Uruguay), in the 2019-2020 growing season, compared this conventional practice with different doses of the egg parasitoid, number of release capsules per hectare, different number of releases in the culture cycle and ground and aerial releases (with or without release capsules). Using the cloth method, the number of larvae per linear meter and the defoliation percentage were evaluated over 6 weekly samplings. Although the best results were obtained with the application of chemical insecticides, two releases of T. pretiosum by terrestrial methods, 20 days apart, or 4 weekly applications by means of a drone, reached the best results below the thresholds of sanitary intervention, both options with 200,000 parasitoids per hectare. This biological tool can differentiate and value Uruguayan agricultural production.

Melhoria da qualidade da uva ‘Primitivo’ por desfolha manual e aplicação de ácido abscísico

As condições climáticas têm uma forte influência no cultivo da videira. A alta precipitação e as baixas temperaturas, por exemplo, podem fazer com que as uvas não atinjam índices de maturação adequados. Com o objetivo de verificar o efeito da desfolha e da aplicação de ácido abscísico (S-ABA) na melhoria da qualidade da uva, foi realizado um experimento em um vinhedo comercial da uva ‘Primitivo’, no Sul do Brasil, durante duas safras. Os tratamentos foram os seguintes: 1) controle; 2) desfolha manual no início da maturação ('veraison'); 3) 15 dias após a primeira desfolha manual; 4) ácido abscísico 200 mg L-1; 5) ácido abscísico 400 mg L-1; 6) ácido abscísico 600 mg L-1. Foram avaliadas as variáveis ​​sólidos solúveis, acidez titulável, polifenóis totais e antocianinas, intensidade de cor nas bagas, radiação fotossinteticamente ativa, índice de clorofila, porcentagem de desfolha e clorose. A desfolha manual realizada 15 dias após a primeira desfolha aumentou os sólidos solúveis e reduziu a acidez titulável, enquanto a aplicação de 400 mg L-1 de S-ABA aumentou a acidez titulável do mosto de uva. Houve uma maior radiação fotossinteticamente ativa próximo ao cacho para tratamentos de desfolha e S-ABA. A aplicação de S-ABA proporcionou clorose nas folhas, seguida de baixo teor de clorofila, causando a senescência. Portanto, a desfolha 15 dias após a primeira desfolha manual influenciou os sólidos solúveis e a acidez titulável, e a aplicação de ácido abscísico aumentou os níveis de polifenóis totais, antocianinas e a intensidade da cor nas cascas das bagas ‘Primitivo’.

Influence of Heat Units on Defoliation, Physiology and Yield of Cotton during Defoliants Application

Aims: A study was conducted to determine the effect of temperature on defoliation process, physiology and yield of cotton during defoliants application.&#x0D; Study Design: The experiment was laid out in split-plot design with four replications.&#x0D; Place and Duration of Study: Field experiment was conducted at Department of Crop Physiology, Tamil Nadu Agricultural University, Coimbatore during 2018 to 2019.&#x0D; Methodology: The main plot comprised of three stage of defoliants spray (120 DAS, 127 DAS and 134 DAS) and the sub-plots were seven defoliant treatments (Control, 2, 4 D (0.5%), Ethephon (0.5%), Ethephon (0.5%) + Triiodbenzoic acid (TIBA) (450 ppm), Sodium chlorate (0.9%), 6 benzylaminopurine (BAP) (0.1%), Thidiazuron + Diuron (0.03%).&#x0D; Results: After 15 days of defoliants spray, Thidiazuron + Diuron (0.03 %) recorded highest defoliation percentage (99.3, 98.1 and 96.8%) followed by Sodium chlorate (0.9 %) (91.9, 94.6 and 93.6%) at three different stage of defoliants spray. Although a significant effect was observed on chlorophyll index value (SPAD) due to the favorable weather condition like minimum temperature of 14.3, 16.9 and 19.3°C and maximum average temperature of 30.8, 31.8 and 33.23°C (120, 127 and 134 DAS respectively) during defoliants spray to 15 days after defoliants spray. Sodium chlorate (0.9%) and 6-BAP (0.1%) recorded higher (95.8 and 95.4) per cent boll opening at 120 DAS when comparing to 127 DAS and 134 DAS. Heat units accumulated during defoliants spray to 15 days after defoliants spray was 113.54, 140.52 and 169.57°C days (120, 127 and 134 DAS respectively).&#x0D; Conclusion: Therefore, the minimum and maximum temperatures of 14.3 and 33.3°C, respectively conducive for inducing defoliation process and boll opening in cotton.