Third Of Plants Research Articles

Spraying deposits using different nozzles and application volumes for pest management of cotton at reproductive stage

With the growing need for greater operational capacity, information about the effect of application volume and spray nozzles on the quality of pesticide application are essential to obtain greater efficiency in pest management in cotton crops. This study aimed to assess the effect of the spraying volume and nozzles on the deposition of spray solution on cotton crops at the reproductive stage. The treatments of the first experiment correspond to the 55, 67, 140 and 194 L ha-1 volumes obtained by variation of the displacement speed using the XR11004 flat fan nozzle. In the second assay the treatments corresponded to the applications of MGA9004 (hollow cone), XR11004 (flat fan), AIXR11004 (air induction flat fan) and CVIA04 (air induction hollow cone) nozzles with 120 L ha-1. An artificial brilliant blue food dye (FD&C 1) was used as a tracer (2.5 g L-1) to determine the deposited volumes on the leaves of the upper, middle and lower third of cotton plants. The results showed that increase in the application volume contributed to obtain the larger deposits in the upper third of the cotton crop during its reproductive phase, especially up to 140 L ha-1, but did not exhibit a significant increase of the deposition in the middle and lower thirds of the plants. The MGA9004, XR11004 and AIXR11004 nozzles provided the largest deposits in the three plant sectors. The flat fan nozzles resulted in greater uniformity of deposits in the upper and middle thirds of the plants.

Distribution of Bemisia tabaci within soybean plants and on individual leaflets

AbstractTo control whiteflies on soybean crops in an effective and economically viable way, it is necessary to quantify the occurrence and density of Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) on the leaflets. Estimating the number of B. tabaci cm‐2 on leaflets is difficult, because its distribution pattern on the various parts of the plant canopy and on the leaflet surface is unknown. The aim of this study was to evaluate the distribution of B. tabaci nymphs on soybean plants and leaflets, under greenhouse and field conditions. One hundred soybean plants infested with all nymph stages were randomly selected in a greenhouse, and 25 in a field. Of each plant, a trifoliate leaf of the middle third of the plant’s height was selected and its central leaflet was collected (greenhouse experiment), or a trifoliate leaf of each third layer (upper, middle, and lower), of which the left, central, and right leaflets were collected (field experiment). The collected leaflets were divided into 32 sections (1 cm2 per section), arranged in an array of eight rows and four columns to count whitefly nymphs. The Morisita index (Iδ), the negative binomial parameter k, and the dispersion index (I) were calculated for each leaflet, using the number of nymphs as variable. The highest population densities of whitefly nymphs were found in the middle third of the soybean plants. In leaflets from the middle third, the nymphs concentrated in the middle and bottom parts of the leaflets, whereas in the upper and lower thirds of the plant, they were randomly distributed on the leaflets.

Helicoverpa zea (Lepidoptera: Noctuidae) Preference for Plant Structures, and Their Location, Within Bt Cotton Under Different Nitrogen and Irrigation Regimes

Helicoverpa zea Boddie is a common economic pest of cotton (Gossypium hirsutum L.), including transgenic cotton varieties that express Bacillus thuringiensis (Bt). Helicoverpa zea oviposition is similar in Bt and non-Bt cotton, but behavior of H. zea larvae can be different in the presence of Bt, with neonates moving away from terminals faster in single-toxin Bt than non-Bt cotton or avoiding Bt-treated diet in the lab. We quantified H. zea oviposition and larval distribution on structures within cotton plants in small plot experiments of Cry1Ac + Cry1F cotton for 2 yr under different irrigation and nitrogen treatments. More eggs were oviposited on plants receiving nitrogen application during 2016 and on leaves in the top section of irrigated plants during 2017, but other treatment effects on eggs or larvae were minimal. Helicoverpa zea eggs were most common on leaves in the top third of plants at position zero and middle section of cotton plants throughout the season, but some oviposition occurred on fruiting structures as well. First and second instars were more common on squares in the top section of plants during 2016 and bolls in the middle and lower sections during 2017 due to oviposition lower in the canopy during 2017. During both years, third through fifth instars were more common on bolls in the middle and lower section of plants closer to the main stem. These findings have resistance management implications as extended larval feeding on bolls could optimize nutrition, decrease Bt susceptibility, and potentially influence behavioral resistance.

DEPOSITION AND COVERAGE OF SOYBEAN LEAF SURFACES BY SPRAYS APPLIED USING DIFFERENT ASSISTED BOOM SPRAYER SYSTEMS

ABSTRACT Maintaining homogeneity in the distribution of fungicidal sprays applied throughout the plant, minimizing the variation between the upper and lower third of the plant, is one of the main challenges for application technologies with regard to soybean crops. To increase the deposition and leaf coverage of sprayed compounds, especially in the middle and lower thirds of the plant, we developed and tested alternative assisted boom sprayer systems. In this study, three assisted boom sprayer systems (Vortex®, Dropleg®, and chain curtain) were evaluated, in addition to the conventional system, in terms of the deposition and coverage of the leaf surface they achieved in the upper, middle, and lower thirds of plants using the fluorescent tracer Helios SC 500™. The assisted boom sprayer systems allowed the sprayed mixture to be better distributed throughout the plant. With the conventional spray system (without assitance), the deposition in the upper third was approximately 26 times higher than that in the lower third, whereas with the use of the assisted boom sprayer systems, the difference in deposition between these thirds was 11 times higher. Among the evaluated systems, the Dropleg® system presented the lowest depositional variation, which was only 5.5 times higher in the upper than in the lower third, because of the increased deposition achieved in the lower third of the plant. Leaf coverage varied from 41% to 81% in the upper third, from 24% to 43% in the middle third, and from 4% to 13% in the lower third of the plant. Using the conventional spray system, the leaf surface coverage was approximately 13 times higher in the upper third than in the lower third of the plant, whereas with the use of the assisted boom sprayer systems, especially the Dropleg® system, this variation was reduced by 73%, and the coverage of the upper and lower thirds only differed by 3.5 times. Indeed, the Dropleg® system reached a leaf coverage of close to 13% in the lower third of the plant. The use of assisted boom sprayer systems improved the distribution of the mixture applied throughout the plant, reducing the differences among the thirds of the plant both in the levels of deposition and coverage of the leaf surfaces. The Dropleg® system increased the deposition and leaf coverage in the lower third of the plant the most, facilitating better distribution of the mixture.

Survey of imazethapyr-resistant common ragweed (Ambrosia artemisiifolia L.) in Quebec

Common ragweed (Ambrosia artemisiifolia L.) is widespread in soybean (Glycine max L.) fields in southern Québec. Biotypes resistant to ALS (group 2) herbicides are commonly reported in conventional crops where these herbicides are used. Reported cases are voluntary and potentially underestimate the occurrence of resistance. A survey was therefore undertaken in 2014 and 2015 in soybean fields treated with a Group 2 herbicide. Common ragweed seeds were collected from 123 fields. Seedlings were grown and tested for resistance using the recommended rate of imazethapyr (100.8 g a.e. ha-1). Weed populations were classified as susceptible, developing resistance (less than one third of plants classified as resistant) or resistant (at least one third of plants were resistant). Twenty populations were then selected based on these resistance levels and treated with four doses of the herbicide (0, 100.8, 201.6, and 403.2 g a.e. ha-1). Resistance to imazethapyr was detected in 81% of samples (21.1% were classified as developing resistance and 59.4% were classified as resistant). Populations classified as developing resistance had a resistance factor of 1.04, while populations classified as resistant had a resistance factor greater than 5. These results confirm the presence of multiple populations of imazethapyr-resistant common ragweed in Quebec.

DROPLET DISTRIBUTION AS A FUNCTION OF COTTON INTERROW SPACING AND ANGLES OF SPRAYER DISPLACEMENT

ABSTRACT Application technology factors may be influenced by changes in plant architecture, such as height and leaf area. This study aimed to evaluate which angle of sprayer displacement in the application of pesticides in relation to the direction of cotton sowing, cultivated in the ultra-narrow row, narrow row, and conventional systems, provides the best application quality characteristics in the different thirds of plants. The experiment was installed in a split-plot design with four replications in the 3 × 4 factorial scheme, composed of three cotton cultivation systems and four angles of sprayer displacement in relation to the direction of the sowing rows. The evaluated characteristics were mean volumetric diameter, density and coverage of droplets, number of droplets, and open area in the interrows without leaf. The upper third presented the highest values of mean volumetric diameter, number of droplets, and density and coverage of droplets for all interrow spacing and application angles. The angle of displacement of 30° in relation to the sowing row presented the best results in relation to the number and density of droplets. The spacing of 0.90 m in the interrows increased the number of droplets, droplet density, and coverage in the lower third of plants.

Dispersion and Persistence of Trichogrammatoidea bactrae (Nagaraja) over Tuta absoluta (Meyrick), in Tomato Greenhouses.

Inundative biological control depends on the ability of natural enemies to disperse and persist in the environment. The objective was to evaluate the dispersion and persistence of Trichogrammatoidea bactrae (Nagaraja) on Tuta absoluta (Meyrick) eggs. Inundative releases of this parasitoid were performed in experimental tomato greenhouses. For vertical dispersion, leaves of the upper and middle third of plants were artificially infested with T. absoluta eggs; for horizontal dispersion, plants at increasing distances from a release point were infested. These eggs were renewed at days 2 and 4 to evaluate persistence. The amount of parasitized patches was registered. Logistic regression analysis was used. The position of the eggs in the plant did not affect the DE (discovery efficiency: proportion of parasitized patches). Time since release negatively affected the DE, while distance affected it only when plants were higher. These results could be used to adjust the release methodology of T. bactrae.

Neonicotinoid insecticide systemicity in soybean plants and its effect on brown stink bugs

ABSTRACT During the application of pesticides on soybean fields, a vertical deposition gradient of the product can occur throughout the canopy, resulting in difficulties for controlling stink bugs that are in the middle and lower thirds of plants. This study aimed at evaluating the systemicity of thiamethoxam insecticide in different soybean phenological stages, using brown stink bugs as bioindicators of the pesticide efficacy. The study combined product application sites (lower, middle and upper third) and stink bugs infestation areas at five soybean phenological stages (R2, R3, R4, R5.2 and R6). For the R2 and R5.2 stages, plants presented acropetal translocation of the product, being the effect more evident in the R2 stage. For the R3, R4 and R6 stages, the product translocation was not sufficient for controlling the stink bugs. In all stages, for treatments with direct exposure (same infestation and spraying place), stink bugs were satisfactorily controlled.

Diagnostic leaf to evaluate the nutritional status of Jatropha

ABSTRACT The analytical determination of nutrient levels in recently mature leaves in order to diagnose nutritional status is based on the fact that leaves are metabolically active and more sensitive to variation in nutrients of the soil. In most of cases, there is a direct well known between foliar content and the development and yield of the plant. However, for a more accurate interpretation, it is essential to establish the index leaf. There are few published studies about Jatropha with contrasting results. In order to establish the index leaf, in adult plants, the macronutrient levels were evaluated in samples collected in experimental plots, in which doses of nitrogen and phosphorus were applied, in two parts of the floral branches (in the top and in the middle thirds); and in three positions of leaves of the floral branch (between the 1st and 3rd, 6th and 8th, and 13th and 15th leaves below the inflorescence). The location of the leaf on the plant significantly affects nutrient contents. Nitrogen, phosphorus, potassium and sulfur tend to have higher concentration in young tissues. Calcium and magnesium showed higher levels in the basal leaves of floral branches. Samples collected in the top third of plants (between the 6th and 15th leaves of the floral branch) are more sensitive to variations of nitrogen and phosphorus fertilization. Therefore, we indicate the 6th to 15th leaves of the top third plants as index leaves estimate nutritional status of Jatropha.

Mycorrhizal inoculation and/or selenium application affect post-harvest performance of snapdragon flowers

The effect of mycorrhizal inoculation and/or selenium (Se) application as possible agents to improve post-harvest performance of cut snapdragon (Antirrhinum majus L.) flowers had been studied. Rhizophagus intraradices was inoculated to half of plants at the seedling stage. One third of non-inoculated plants and one third of plants inoculated with R. intraradices were not supplied with Se. One third of non-inoculated and inoculated plants were foliar-sprayed with either 100 or 200 μg of seleninic acid per plant before flowering. Flowers were harvested at dawn, packed dry or placed in water and stored in darkness at 5 °C. Afterwards, the vase-life of cut flowers was evaluated. Plant growth and water parameters as well as photosynthetic pigments and organic solutes in leaves were determined at harvesting. The results showed that mycorrhizal inoculation improved plant height, length and basal diameter of flowering stems. In plants untreated with Se, mycorrhizal inoculation increased starch, phenolics, chlorophylls and carotenoids but decreased soluble sugars and proline in leaves. Mycorrhizal inoculation counteracted the reductions in carbohydrates, proline and proteins caused by Se in non-inoculated plants. Type of storage strongly influenced post-harvest performance of cut flowers, being dry storage the most beneficial for delaying senescence. In comparison with non-inoculated plants untreated with Se, neither mycorrhizal inoculation nor the foliar application of Se, alone or combined, prolonged the vase-life of cut flowers. High dose of Se decreased the vase-life of flowers from non-inoculated snapdragons and mycorrhizal inoculation counteracted this negative effect. Changes in water status and carbohydrate metabolism in plants inoculated or not with R. intraradices may have resulted in unusual development of flowering stems and post-harvest performance of flowers after spraying high dose of Se. Further research is needed to confirm this hypothesis.

Danos da Mosca-Branca Bemisia Tabaci (Genn.) e distribuição vertical das ninfas em cultivares de soja em casa de vegetação

A mosca-branca Bemisia tabaci causa danos em plantas de soja em decorrência da sucção de seiva, transmissão de vírus e favorecimento da fumagina, que afetam o desenvolvimento e a produção da cultura. O objetivo deste trabalho foi avaliar os danos diretos da mosca-branca e a distribuição vertical de ninfas em cultivares de soja em condições de casa de vegetação. O delineamento experimental foi de blocos ao acaso, com 10 cultivares no esquema fatorial 10 x 2 (com e sem infestação) e 4 repetições. Contabilizou-se o número de ovos e ninfas em todos os folíolos e, separadamente, em um folíolo do terços superior, médio e inferior das plantas Os índices de produtividade analisados foram: número de vagens por planta e de grãos por vagem, massa de 100 grãos e massa total de duas plantas. Os dados foram submetidos à análise de variância e ao teste F (α < 0,05) e as médias comparadas pelo teste de Tukey ao nível de 5% de probabilidade, obtendo-se as diferenças mínimas significativas entre os tratamentos. As cultivares estudadas não foram afetadas pelo ataque de B. tabaci nos níveis de infestação registrados. CD 219 RR foi o cultivar mais infestada por ninfas de mosca-branca. Para melhorar a eficiência e o uso de tempo nas avaliações, em estudos em casa de vegetação, indica-se que estas sejam realizadas nos terços superior e médio das plantas.

Epidemiologic Study of Ramularia areola under Different Soil Covers and Spacings, for Cotton Crops

The objective of this work was to evaluate the progress of the areolate mildew of cotton under different soil cover and spacing conditions. The experiment was carried out using randomized blocks and a 2 × 3 factorial design, with two spacings (0.45 m and 0.90 m) and three soil covers (no cover, Pennisetum glaucum and Crotalaria spectabilis) with four replications. The plants were inoculated with R. areola, sixty DAS. A total of 14 evaluations of disease severity were performed. At the lower, middle and upper thirds of plants, a diagram scale with nine levels of severity was used and the resulting data were converted into the AUDPC. Gompertz, logistic, and monomolecular mathematical models were tested in the disease severity curves for each third. Agronomics characteristics were evaluated as well. Significant differences of AUDPC were found for the cotton plants thirds, and the middle third was the highest AUDPC. Significant difference for the lower and upper thirds, whose AUDPC were highest on 0.90 m spacing, was observed too. The disease progress curves of the thirds did not fit the tested models. Significant results to the both covers situations, where the treatments grown on crotalária cover and without cover had highest AUDPC, were evidenced. The treatments with C. spectabilis cover were taller than other treatments. Significant data were observed for the cover crops used and in the treatments grown at 0.90 m spacing, to residual cover and crop yield, respectively.

Effect of nucleopolyhedrovirus concentration in soil on viral transport to cotton (Gossypium hirsutum L.) plants

Soil-to-plant abiotic transport of a recombinant nucleopolyhedrovirus (HzSNPV.LqhIT2) was studied to quantify the proportion of different concentrations of soil virus transported to specific parts of cotton plants under controlled greenhouse conditions; these results were related to transport in the field where wind, rain, and soil type were not controlled. Under conducive precipitation conditions in the greenhouse, the estimated number of viral occlusion bodies (OB) transported ranged from 7 OB (to the top third of the plant, 40–60 cm above the soil, at the low virus concentration, 250 OB/g soil) to 629 OB (to the bottom third of the plant, 0–20 cm, at the high virus concentration, 12,500 OB/g soil). Under conducive wind conditions in the greenhouse, the estimated number of OB transported ranged from 8 OB (to the top third of the plant at the low concentration) to 94 OB (to the bottom third of the plant at the high concentration). The overall proportion of OB transported from soil to plant was greatest, ranging from 2.1–6.2 × 10−6, from the lowest soil concentration to the lowest 40 cm of the plant. Only 5 × 10−8 of the soil OB were transported from the high-concentration soil to a height of 40–60 cm on the plants. In the field experiment, the estimated number of OB on each cotton plant depended on the concentration of OB in soil in June and July, but this effect was no longer significant in August. There were significantly more OB on the lower third of plants than on the top third in July, but not in June or August. Significantly more OB were detected on cotton leaves than on buds or squares in July, and there were more OB on leaves than on buds, squares, bracts, or bolls in August. The amount of HzSNPV.LqhIT2 naturally transported from soil to cotton plants was sufficient to infect 6–11% (low to high soil concentration) of first instar Heliothis virescens (Fabricius) (Lepidoptera: Noctuidae) in June, 2–6% in July, and 1–3% in August. These results fill gaps in understanding NPV epizootiology that are important to biological control and risk assessment.

Distribution of eggs, larvae and adults of Sternechus subsignatus Boheman on soybean plants in no-till system

Soybean [(Glycine max (L.) Merrill] commercial fields, maintained under a no-till system, were sampled during the crop seasons 1990/91 and 1996/97, in Cruz Alta and Júlio de Castilhos, Rio Grande do Sul State, to determine the distribution of eggs, larvae and adults of Sternechus subsignatus Boheman (Coleoptera : Curculionidae). Soybean plants and soil were examined at different time schedules. Eggs and larvae were recorded in main stems, lateral branches and leaf petioles, divided into the upper third, medium and lower third of soybean plants. Eggs (87%), and larvae (79%) were mainly observed in the main stem and in the medium plant sections (87% and 78%, respectively). Larval movement was not observed because larvae remained inside the galls, in the same area where the eggs were laid. Adults were located in different places depending on the sampling time. At night, adults were observed to move to the upper third of the plant and, during the day, down to the lower third of the plant and to the soil. The insects are normally concealed during their pre- and post- embryonic stage throughout most of the day.

Importance of plant size, distribution of egg masses, and weather conditions on egg parasitism of the European corn borer, Ostrinia nubilalis by Trichogramma ostriniae in sweet corn

Abstract Trichogramma ostriniae (Hym: Trichogrammatidae), an egg parasitoid of the European corn borer, Ostrinia nubilalis (Lep: Pyralidae), were released into sweet corn (Zea mays L.) fields to study the effects of weather, plant size and distribution of egg masses on egg parasitism by the wasp. Sentinel European corn borer eggs were stapled onto leaves located in the upper, middle and lower third of sweet corn plants 5 to 35 meters away from the wasp release point in either a radial or grid manner. Weather conditions and plant architecture were monitored during the experiments. Logistic regression was used to analyze the data. The results indicated that percentage of eggs parasitized was negatively related to an increase in leaf area as well as an increase in distance eggs were located from the point of release of wasps. Eggs distributed on plants at different directions from the release point received different levels of parasitism. Eggs that were stapled onto leaves in the upper third of a corn plant received much less parasitism than those on the middle and lower third of the plant. Higher mean temperature adversely affected the level of parasitism during hotter times of the season and conversely, lower temperatures (<17 °C ) reduced the egg parasitism during cooler times of the season. The longer the exposure of eggs to wasps, the higher the level of egg parasitism. However, the levels of egg parasitism for 2 day's exposure were almost the same as that for 3 day's exposure due to the limited longevity and egg‐laying behavior of the wasp. These results suggest that inundative releases of T. ostriniae should be made every two to three days, with multiple release points per hectare. In addition, weather conditions and plant architecture, especially temperature, plant height and leaf area must be taken into consideration to optimize levels of parasitism.

Associations of Plant Symptoms and Pod Position with Phomopsis sojae Seed Infection and Damage in Soybean1

The frequency and severity of infections of Phomopsis sojae (Leh.), pod and stem blight fungus, were inversely related to pod height on soybean [Glycine max (L.) Merr.] plants for the cultivars ‘Chippewa 64’ ‘Hark’, and ‘Wells’. Phomopsis sojae seed damage was primarily found in the bottom third of plants and distribution of damaged seed was heavily skewed to the lowest bearing node. Overall USDA soybean grades were lowered for Chippewa 64 and Wells due to seed damage caused by P sojae. Disease ratings based on stem, pod, and seed symptoms were tested for their association with seed infection rates. Visible symptoms rating for seed was highly associated with rates of seed infection for all cultivars. Pod and stem symptom ratings were highly associated with seed infection rates in Chippewa 64 and Wells but not for Hark. Selective harvest of upper plant portions improved seed quality.

The B-chromosome system of Allium schoenoprasum

Nine morphologically distinct euchromatic B-chromosomes have been identified in Allium schoenoprasum from the River Wye, South Wales. The most common type (89%) is telocentric (Bt−1) and it is likely that the non-standard Bs are derivatives of Bt−1 by deletion, centric shift and/or centric misdivision. New B-types have also been produced from standard Bs in controlled crosses. In general, the Bs are mitotically extremely stable, although occasional plants, particularly those carrying non-standard Bs, are conspicuously variable in their B-constitution between root-tip cells. In addition, B-chromosome number is enhanced in some anthers of about one third of plants. Behaviour of B-chromosomes during meiosis is described. Although there is little bivalent formation, less than 5% of the Bs are lost during meiosis in anthers. There is, however, no evidence of B-chromosome accumulation in the offspring of controlled crosses, usually a slight loss, and Bs have deleterious effects on aspects of vigour and fertility. Thus, no satisfactory explanation for populations with up to 65% B-containing individuals has yet been found.