The phytotoxicity of narrow distillation range petroleum spraying oils to valencia orange trees in South Australia. Part II: The influence of distillation temperature and spray timing on fruit quality

Petroleum oils sprays are used as pesticides on citrus in South Australia to control California red scale (Aonidiella aurantii Maskell), but may have phytotoxic effects on trees and fruit. As part of a programme to establish improved specifications for spray oils for South Australia, three oils with different 50 %-distillation temperatures were applied to trees each month from October to May for two seasons in order to observe their effects on fruit quality. The 50 %-distillation temperatures of the three oils were 211, 224 and 240°C at 10 mmHg (in order of increasing molecular weight) and the oils are subsequently referred to as the 211, 224 and 240 oils. The 224 and 240 oils significantly reduced the amounts of sugar and acid in the juice, and delayed and inhibited colouring. These effects increased in severity, the closer to harvest the trees were sprayed and the higher the distillation temperature of the oil. The 240 oil prevented full colour development, and caused ‘re-greening’ if sprayed later than February. Oil sprays applied to the same trees in the following season caused similar effects. However, if oil sprays were omitted in the following season, there was no residual effect, of the previous season's spray, on the sugar and acid contents or the colour of the fruit. Individual fruit weight was not affected in the first spraying season, but there was an increase in the average individual fruit weight in the second season, regardless of whether a second spray was applied that season or not. The effect was more severe, the closer to harvest the trees were sprayed and the greater the distillation temperature of the oil. The effects on yield resulted from a change in the number of fruit per tree.     

The phytotoxicity of narrow distillation range petroleum spraying oils to valencia orange trees in South Australia. Part I: The influence of distillation temperature and spray timing on yield and alternate cropping

Petroleum oil sprays are used on citrus to control California red scale (Aonidiella aurantii Maskell), but may have phytotoxic effects on trees and fruit. As part of a programme to establish improved specifications for spray oils for South Australia, three oils with various 50%-distillation temperatures were applied to trees each month from October to May to observe their effects on crop yield. Some treatments were applied once in each of three consecutive seasons while others were applied only once in the first season. The 50%-distillation temperatures of the three oils were 211, 224 and 240°C at 10 mmHg. The oils caused significant reductions in yield, and caused or accentuated alternate cropping cycles. The higher the 50%-distillation temperature of the oil, the greater the effect. The time of application was also important. The greatest yield reductions (expressed as two averages) occurred when the oils were sprayed in November; the tendency to alternate cropping increased with the month of application from December to May. For the oil with the highest 50%-distillation temperature, the yield reductions were about 30%, and the yields from trees in a severe alternate cropping cycle, in the ‘light crop’ year, were as low as 25% of those on unsprayed trees.     

荔枝、龙眼园使用机油乳剂的安全性及其对荔枝蒂蛀虫的防治研究

利用机油乳剂对果树进行安全性和防治荔枝蒂蛀虫Conopomorpha sinensis Bradley研究试验，结果表明，喷施机油乳剂后荔枝和龙眼的落果率与对照树4无差异，喷清水的对照树其蒂蛀虫蛀果率比喷机油乳剂的处理树高，分别为150、200和250倍机油乳剂处理的2.8、3.0和2.7倍。在荔枝、龙眼园应用机油乳剂防治害虫不会导致落叶、落果、畸形叶和畸形果，也不会延缓果实的生长和成熟及降低单果重，而有利于控制介壳虫、螨类、蛀果类等害虫。机油乳剂可替代广谱性化学农药的使用，减少化学农药的污染，有利于果园天敌的生存、繁殖，提高生物多样性，改善果园生态环境。     

Properties of Banana Spray Oils in Relation to Sigatoka Disease Control and Phytotoxicity on Banana Leaves

Abstract

The properties of banana spray oils have been investigated by a number of researchers. The results of these investigations are reviewed in this paper, and include information on volatility (distillation range, flash point); flow characteristics (viscosity, pour point); other physical properties (specific gravity, colour, aniline point); and chemical properties (unsulphonated mineral residues, aromatics, paraffins and naphthenes).

A comparison of distillation curves is of greater significance than comparison of individual boiling points. Such a comparison will show whether any one oil product is a homogeneous oil or a mixture of heavy and light oils. Disease control is closely related to volatility of the spray oil; the lower the volatility of the oil the better the disease control. Phytotoxicity (leaf-flecking) increases as the percentage volatility of the spray oil decreases. Oil volatility governs the amount of oil remaining on the leaf after application. The initial amount of oil applied to the leaf is of less significance in the fungistatic effect than is the amount of oil remaining on or in the leaf. From a viewpoint of Sigatoka disease control, flash points are of little significance, but must be considered from the viewpoint of safety in storage, transportation and use.

As the viscosity of spray oils increases [in the range 35-100 Saybolt Universal Seconds (SUS) at 100[ddot]F] disease incidence decreases and phytotoxicity increases on sprayed banana leaves. The naphthenic oils are superior to the paraffinic oils, particularly in the viscosity range of 75-85 SUS at 100[ddot]F, for spraying bananas.

The performance of banana spray oils is related to the proportions of the major hydrocarbon groups (aromatics, naphthenes and paraffins) present in the oil. Properties such as specific gravity and aniline point are indicative of the proportions of the major hydrocarbon groups in a spray oil.

Colour of mineral oils is of no significance in the control of Sigatoka disease. Light mineral oils with unsulphonated mineral residue (U.M.R.) in the range of 70-99.9 are equally effective in Sigatoka disease control regardless of U.M.R. However, the degree of leaf damage (phytotoxicity) is directly related to U.M.R. value. The oils of high U.M.R. cause the least damage. The aromatic fraction of four spray oils tested (heavy paraffinic, light paraffinic, heavy naphthenic and light naphthenic) caused abundant phytotoxicity at a deposit level of 3 US gal/ac. There was little or no phytotoxicity and no appreciable disease control at a deposit level of 1.5 US gal/ac. Paraffinic and naphthenic oils of comparable U.M.R. value (94-95%) and viscosity (74-75 SUS at 100[ddot]F) provide good disease control within the deposit range 1.4-2.1 US gal/ac. At these deposit levels the naphthenic oil causes only 20 and 50% respectively as much phytotoxic flecking as the paraffinic oil. Photosynthesis is inhibited by the application of petroleum oil to banana leaves.

It is the opinion of the writer that a long-term trial (a minimum of two years) should be conducted to evaluate the effect of a comparable naphthenic and paraffinic oil on Sigatoka disease control and banana yield.     

Measurements of atmospheric deterioration of citrus spray oils

Autoxidative deterioration of three commercial mineral spray oils was studied by measuring oxygen absorption under atmospheric conditions and by an accelerated method in the laboratory. The outdoor experiment showed an absorption of 0.02-0.25 moles of oxygen per mole of oil during the first 5 days, which increased to 0.13-0.42 moles after 20 days of exposure. The oxygen absorption was accompanied by separation of insoluble tar-like substances. The relative rates of the autoxidation of the three oils were found to be in agreement with their tendency to cause excessive fruit drop. Accelerated autoxidation was performed under controlled conditions of temperature, light spectrum and relative light intensity; it was accomplished in several hours and gave approximately the same results as the outdoor experiment. The accelerated procedure is closely correlated with the atmospheric one and thus is suitable as a routine test for spray oils, for mineral oil fraction or formu-lations, and for mixtures of oils with other pesticides.     

Efficacy and phytotoxicity of multiple petroleum oil sprays on sweet orange (Citrus sinensis (L.)) and pummelo (C. grandis (L.)) in Southern China

The efficacy of pest control of three different oil formulations in multiple low-concentration spray programmes on sweet orange and pummelo were compared with unsprayed and normal farmer-treatments over three years. Phytotoxicity of sprays was assessed in terms of fruit and leafdrop, fruityield and external fruitquality. Trees sprayed with any type of oil had lower pest numbers than unsprayed trees. On sweet orange, the heaviest oil was better than the normal farm practice at controlling chaff scale on fruit and red mite and whitefly on leaves. On pummelo it provided the best control of red mite on leaves. All three oils were as effective as the normal farm practice in control of rust mite on sweet orange fruit and leaves and red mite, rust mite and red scale on pummelo fruit. On sweet orange trees there was no evidence of phytotoxicity, and the external quality of fruit generally improved over time. On pummelo trees, oil sprays were unable to improve the external fruitquality. The number of pummelo per tree was reduced in three of the oil spray schedules in 1995 and one in 1996, but the total weight of fruit harvested per tree was unaffected.     

Pre- and post-harvest control of mango anthracnose in the Philippines

Two field trials were conducted in the Philippines in successive years to compare the effectiveness of different pre- and post-harvest treatments on the development of anthracnose on mango fruits caused by Colletoirichum gloeosporioides. In one experiment, the pre-harvest application of benomyl (250 mg/l a.i.) significantly reduced the number of conidia sampled in tree canopies compared with control trees (no fungicide) and was associated with a significant reduction in the post-harvest development of anthracnose on fruits. A hot-benomyl dip (850 mg/l a.i. at 52 55 C for 10 min) completely eradicated anthracnose on fruit treated on the day of harvest. In a second experiment, pre-harvest applications of prochloraz (500 mg/l a.i.) either within a pre-planned spray schedule or applied strategically (when 18 h or more continual leaf wetness was recorded by a sensor placed within a tree canopy) gave the best control of anthracnose on fruits. A hot-benomyl dip was again the most effective post-harvest treatment for fruit treated on the day of harvest and on the day after. There was no significant difference, however, between hot-benomyl dips or prochloraz dips (500 mg/l a.i. for 10 min) at ambient temperatures when fruit were treated on the third day after harvest. The implications of these results for the production and treatment of Carabao mangoes in the Philippines are discussed.     

The efficacy of a petroleum spray oil against Aphis gossypii Glover on cotton. Part 2: indirect effects of oil deposits

The primary mode of action of petroleum spray oils (PSOs) on pest insects is through direct contact. Indirect effects are, however, also possible, and deposits of the oils may influence pest populations by killing insects and/or by influencing their behaviour. The indirect effects of deposits of a new nC24 oil against the cotton aphid, Aphis gossypii Glover, were therefore determined. The effects of oil deposits on the acceptance of cotton as host plant by the aphids were assessed, as well as aphid mortality rates and their success in the establishment of colonies. The efficacy of deposits of a heavier oil (nC27) was also evaluated. Deposits of PSO were toxic to A. gossypii and remained effective until 8 days after spraying. Mortality decreased with time, so that, the older the deposit, the lower was the mortality. Significantly higher aphid mortalities were achieved on younger leaves than on mature ones. Thus, leaf age proved a significant factor in the efficacy of the deposits. Consecutive prophylactic applications (at 9 day intervals) did not have a cumulative effect, and their killing power proved to be independent of one another. Thus, applying the oil prior to aphid infestations would confer only minimal protection. The mortality inflicted by the deposits was not improved by increasing the molecular mass of the oil used (nC27 oil), but the toxic life of the oil deposit was increased. Oil deposits did not deter alates from landing on oil-sprayed plants. Oil deposits did, however, affect subsequent alate and nymphal survival, and thus the establishment of aphid colonies. The impact that the oils could have on the longer-term development of aphid populations in the field was thus demonstrated. First- and second-instar nymphs were the most susceptible life stages, with > 50% mortality compared with < 10% for the other stages. These nymphs did not show the typical signs of oil-induced mortality observed in aphids killed by direct oil applications, which suggests an alternative mode of action to that of the directly applied oil. Anoxia does not seem to be involved in either process, and alternative modes of action of the oil deposits are discussed. The implications of these findings for cotton aphid control are also considered, primarily in relation to the timing and frequency of oil application.     

泰安市核桃园主要病虫害发生情况及其化学防治用药流程

为明确山东省泰安市核桃园主要病虫害的发生情况及其化学防治的用药流程，于2017—2018年采用田间调查法进行主要病虫害的调查，于2019年采用常规喷雾法对不同防治对象进行化学防治，研究不同用药时间及用药次数下3种农药对核桃的保果效果及对主要病虫害的防治效果，确定用药流程。结果表明，2017年泰安市核桃园主要病虫害以核桃细菌性黑斑病、核桃炭疽病和核桃举肢蛾Atrijuglans aristata为主，造成的病虫果率达83.25%。5月中旬至6月下旬，以核桃细菌性黑斑病和核桃举肢蛾单独发生为主；7月上旬至8月上旬，以核桃细菌性黑斑病和核桃炭疽病单独发生为主；8月中旬至下旬，以核桃炭疽病单独发生和核桃炭疽病+核桃细菌性黑斑病共同发生为主。2018年3种病虫害造成核桃的总体落果率为79.84%，共出现2次落果高峰，即在6月下旬以核桃举肢蛾造成的落果和在8月下旬以核桃炭疽病单独发生和核桃炭疽病+核桃细菌性黑斑病共同发生造成的落果。针对以上3种主要病虫害，在核桃生长期应至少喷药6次，其总体的保果效果和防治效果分别达到96.58%和93.70%，分别显著高于喷药4次的83.72%和70.56%，与喷药8次处理差异不显著。在实际生产中，建议对核桃细菌性黑斑病自5月上旬至8月上旬，每15~20 d用药1次，至少用药6次；对核桃炭疽病自6月下旬至8月上旬，每15~20 d用药1次，至少用药4次；对核桃举肢蛾在5月下旬和7月下旬各用药1次。     

Eradication of apple powdery mildew (Podosphaera leucotricha) with dormant-season sprays of surface-active agents

Of twenty non-ionic surfactant formulations tested in 1974–75 several were successful as eradicants of overwintering apple mildew as were two ionic materials. The incidence of Nectria canker was increased by sprays applied in October but less so by the same materials applied in January or February when phytoxicity measured in terms of fruit yield was also less. PP 222, a non-ionic surfactant introduced in 1975, proved to be an efficient eradicant of mildew in 1976. Although the yield of fruit from most sprayed trees was greater than from controls, the best mildew eradicants did not produce greatest yields in the same year, perhaps indicating adverse effects of treatments on the trees. However, significantly better yields of fruit obtained in the year following the dormant season eradication of primary mildew, suggest long term beneficial effects of these treatments.     

Spray treatments combined with climate modification for the management of Leveillula taurica in sweet pepper

The effects of several spray and climate treatments on Leveillula taurica were tested under controlled and commercial greenhouse conditions either alone or combined with a climate treatment. Ampelomyces quisqualis AQ10 inhibited the germination of conidia on leaves, but not on glass. Trichoderma harzianum T39 inhibited germination on both surfaces. Neither the examined biological control agents (BCAs) nor the two tested mineral oils (AddQ and JMS Stylet-Oil) affected the viability of conidia. Sulphur drastically limited the germination and viability of L. taurica. In experiments at 15–25°C, AQ10 alone reduced hyphal leaf colonisation at 25°C. T. harzianum T39 significantly reduced leaf colonisation at all temperatures but significantly reduced disease only at 20–25°C. The oils significantly reduced leaf colonisation and sulphur reduced both leaf colonisation and disease at all temperatures. Results were confirmed in an experimental greenhouse. In a field experiment, azoxystrobin, polyoxin AL, neem extract, and T39 were effective; sulphur was superior to them. Under severe epidemic conditions the disease had a negative impact on yield; late fungicide treatments at spring-time were found unnecessary. Chemical sprays applied in alternation was compared with the ‘friendly’ spray regime (alternation of Heliosoufre, T. harzianum T39 + JMS Stylet oil, A. quisqualis AQ10+AddQ oil and Neemgard) in two climates i.e. (i.) day warm climate and (ii.) regular (cool) day climate regimes. In the warm climate, there was no significant difference in the performance of the ‘friendly’ spray regime and the chemical spray regime. However, in the cooler climate, the ‘friendly’ spray programme was not as effective as the chemical spray programme. It was concluded that a change in the greenhouse climate may affect the development of powdery mildew and, at the same time, promote the activity of BCAs and render a pathogen more vulnerable to these control agents, allowing for better disease suppression.     

Control of the Olive Moth in Cyprus

Damage caused by larvae of Prays oleae has great economic impact for the olive growers in many of the chief olive-growing areas of Cyprus. P. oleae has three generations per year affecting successively the flowers, the fruit and the leaves. The fruit generation is the most destructive, the larvae living inside the stone of the fruits and the attacked fruit falling prematurely from the tree either in late June of in late August. The trials reported in this paper were aiming to find the best time to spray for more effective control of the fruit generation. Olive trees were sprayed four times at weekly intervals using the insecticide formothion. The treatments which started on 25 May were completed by 16 June 1976. The best period was found to be that particular stage of fruit growth at which the fertilized fruit started to grow normally and they can easily be distinguished from the non-fertilized. Having found the best time to control the fruit generation in 1976, three insecticides were tested in 1978. These were cypermethrin, formothion and triazophos.     

采用果园喷雾施药机械施药时农药有效沉积率的计算方法

针对传统农药沉积率测算方法无法精确反映果园中农药实际利用率的问题,提出一种结合果树冠层特征与叶面沉积量直接测算农药药液在果树靶标上有效沉积率的方法,以期建立一种适用于不同栽种模式的果园通用农药沉积率计算方法。首先采用传统方法计算采用风送式自走喷雾机喷雾后农药在乔化稀植型果园的地面流失率,将其结果与采用果树冠层特征与叶面沉积量相结合的方法计算的有效沉积率进行比较,再通过计算采用风送式自走喷雾机喷雾后农药在矮砧密植型果园的有效沉积率以及采用担架柱塞泵式喷雾机和植保无人飞机喷雾后农药的有效沉积率,验证本研究所提出的将果树冠层特征与叶面沉积量相结合计算农药有效沉积率方法的准确性及适用性。结果表明:基于叶面沉积量结合果树冠层特征方法计算得到的农药有效沉积率与采用传统方法计算得到的农药地面流失率结果基本一致,均能体现施药机械的农药利用率,但比较而言,本研究所提出的方法在果园植保机械喷雾施药有效利用率的影响因素方面考虑更全面,兼顾了叶面沉积量和果树冠层结构的影响,且对于不同栽种模式下的果园更具适应性。将果树冠层特征与叶面沉积量相结合进行果园农药有效沉积率的计算,可以更加真实地反映出果园农药的实际利用情况,同时通过将果树冠层结构量化为叶面积指数、冠层阴影面积等指标,可以为不同栽种模式下的果园选择适宜的植保机械,结合地面流失率的测量,计算出果园农药的飘移量,从而通过调整喷雾角度、雾滴大小、喷雾流量等参数,实现对植保机械的优化,达到精准施药的目的。     

Control of the spread of tulip breaking virus in tulips with mineral-oil sprays

Several mineral-oil sprays used to curtail the spread of stylet-borne tulip breaking virus (TBV) in tulips ‘Elmus’ were tested. The similarly concentrated sprays prepared with summer oil, winter oil, Albolineum, and Asepthion oil, decreased the spread of TBV considerably. Control was improved by the more concentrated Albolineum sprays (2.5, 5, 10%), and spread was reduced more effectively, when variable quantities of emulsions providing good leaf coverage were used (2.5, 5%). The weight ratios of the bulb yields of plots given a 2.5% spray in all years and a 5% spray in 1972 and 1973 fluctuated closely (0–6%) around the value for the untreated plots, which was taken as 100. These ratios dropped by 11–19% after more concentrated sprays were used in variable quantities in 1971. Spraying was slightly more effective at weekly than at fortnightly intervals, but the weight ratios scarcely differed. Better control of TBV spread was obtained when spraying was started at the beginning of May; when started in June, the sprays were not effective. The weight ratios were not clearly influenced differentially except when spraying was begun in the first week of May. The efficacy of mineral-oil sprays is discussed in relation to tulips and lilies, with reference to comparable experiments. The application of mineral-oil sprays for curtailing TBV spread in commercial tulip culture is discussed.     

Field effectiveness of fosetyl-AI against citrus foot rot and brown rot1

The effectiveness of fosetyl-A1 against citrus foot rot caused by Phytophthora citrophthora has been evaluated in a 25-year-old orchard of sweet orange cv. Tarocco, showing severe symptoms of the disease and in a 10-year-old orchard of the clementine-type mandarin cv. Monreal, apparently healthy. All the trees were grafted on sour orange. In both orchards, three sprays at 200 g a.i. per 100 1 were applied in May, July and September for 3 years. The results were evaluated on the basis of yield and fruit quality. Trees of cv. Tarocco had yield increased by 25–44% whereas cv. Monreal yielded 3–16% higher than the unsprayed trees. Fruits of orange cv. Tarocco were collected from trees sprayed with fosetyl-A1 and plunged in a water suspension of P. citrophthora. Fruits treated 11 days before inoculation showed an infection rate of 8.7%) whereas those unsprayed were 77% infected. Fruits inoculated 21 days after the treatment with fosetyl-A1 were 32% infected whereas those unsprayed were 91%, infected. In other trials, trees of volkamer lemon were sprayed with a conidial and mycelial suspension of P. citrophthora at different times after application of fosetyl-A1. The number of infected fruits and leaves in the unsprayed trees was very high (up to total leaf drop) and decreased sharply with the number of sprays (1 to 3).     

Crop loss and control of Pseudocercospora fruit and leaf spot of citrus in Ghana

Pseudocercospora fruit and leaf spot (PFLS) of citrus, caused by Pseudocercospora angolensis, was recently described in Ghana and has spread in most citrus-growing areas of the country. A survey of PFLS incidence was conducted in the Eastern Region. Orchards were georeferenced and data on altitude, annual mean temperature, and annual precipitation were obtained from the WorldClim database. Fruit drop due to PFLS and other pests and diseases was evaluated in three orchards. Field efficacies of 4-week, 6-week and 8-week schedules with carbendazim + mancozeb were evaluated in the major and minor fruit production seasons. Ordinal logistic regression and generalized linear models were fitted in each case according to the nature of the data and possible overdispersion. Disease incidence in the sweet orange orchards surveyed was 25–100 %, with higher values in higher altitude areas exposed to lower temperatures and higher rainfall. PFLS was the main problem causing yield losses, associated with 84–87 % of fruit dropped on the orchard floor. PFLS severity on shoots and incidence on fruit 12 weeks after full bloom was significantly reduced by all fungicide schedules evaluated. The effects of fungicides on PFLS severity in fruit at harvest were not substantial because of intense fruit drop. The 8-week schedule showed the lowest effectiveness in reducing fruit drop and thus the 6-week schedule is preferred. Further research is needed for an integrated management of PFLS in Ghana.     

喷施锌肥对渭北旱塬苹果生长及产量品质的影响

在陕西渭北旱塬果园,于苹果膨大期喷施不同浓度的锌肥,观测分析锌对果树生长和苹果品质的影响.结果表明,施锌可以抑制新梢生长速率,对果实直径生长速率、百叶干重、叶面积生长有显著的促进作用.其中,喷施0.5%浓度的锌肥,株产量比对照增加24.7%,可溶性固形物含量增加10.5%,还原糖增加27.5%,硬度提高了23.6%;喷施1%浓度的锌肥,株产量比对照增加40.2%,Vc含量提高了20.4%,可溶性糖增加了26.7%,花青苷含量提高了75%.综合考虑苹果生长与品质因素,该地区果园以喷施0.5%～1%浓度的锌为宜.     

Enhancement of Postharvest Disease Resistance in Ya Li Pear (Pyrus bretschneideri) Fruit by Salicylic Acid Sprays on the Trees during Fruit Growth

The Ya Li pear (Pyrus bretschneideri) trees were sprayed three times with 2.5 mM salicylic acid (SA) around 30, 60 and 90 days after full flowering. The fruit were harvested at commercial maturity (about 120 days after full flowering), inoculated with Penicillium expansum, and incubated at 20 °C, 95–100% RH. The results showed that resistance to the pathogen of the mature pear fruit was remarkably enhanced by the SA sprays. Disease incidence in the SA-treated fruit was 58.0% or 26.5%, and lesion diameter on SA-treated fruit was 58.4% or 29.0% lower than that in/on fruit without SA treatment (control) on day 12 or 17 after incubation, respectively. The SA spray applied to the trees around 30 days after full flowering notably enhanced accumulation of hydrogen peroxide in the young fruit. Meanwhile, activities of defense enzymes, including peroxidase, phenylalanine ammonia-lyase (PAL), chitinase or β-1,3-glucanase in the young fruit from SA-treated trees was 29.5%, 60.0%, 24.4% or 35.7% higher than that in the control fruit 4 days after the SA spraying. Furthermore, after harvest, activities of PAL, chitinase and β-1,3-glucanase were still significantly higher in the mature pear fruit from the trees sprayed three times with SA than those of the control fruit. Activities of the antioxidant enzymes including catalase and ascorbate peroxidase in the young fruit were significantly reduced by SA spraying. However, the activity of another antioxidant enzyme, glutathione reductase in the young fruit was significantly enhanced by SA spraying. These results suggest that enzymes exerting their functions in different ways may be coordinately regulated by SA in the pear fruit. Our study indicates that treatment of SA sprays on the trees may provide further protection against postharvest disease of Ya Li pear fruit in practice and could be used as an alternative and economical approach to reduce application of chemical fungicides.     

The efficacy of a petroleum spray oil against Aphis gossypii Glover on cotton. Part 1: mortality rates and sources of variation

Petroleum spray oils (PSOs) kill insect pests on contact, and the composition of modern PSOs is substantially different from the ones introduced earlier. The effects of direct application of a new nC24 PSO on the cotton aphid, Aphis gossypii Glover, were therefore determined. This covered not only aphid mortality rates but also the way in which the oils affected aphid behaviour at the time of contact with the oil. Direct application of the nC24 oil proved to be highly effective in controlling A. gossypii at a range of concentrations between 1 and 10% v/v. The oil killed cotton aphids quickly, with most of the mortality occurring within the first 10 min of spraying. The fast killing action of the oils prevented any behavioural responses by the aphids. Aphids killed by the oils became flaccid and their legs and antennae extended horizontally relative to the body axis. With time, their cuticle became very shiny and began to darken. The quick death of the aphids suggested a contact mode of action of the oils, an interpretation supported by the lack of any negative effect on aphids not initially reached by the oils. However, those aphids not hit by the oils, but that subsequently encountered oil-treated areas when they moved elsewhere, also died, indicating that the oil deposits are also toxic to the aphids. The mode of action of the oil thus seems to be versatile, and the means by which it kills the aphids may be more complex than anoxia, which is the widely claimed mechanism attributed to PSOs. This oil now needs to be tested for any possible indirect effects on the cotton aphid (e.g. through its host-plant acceptance behaviour). The implications of the present findings for cotton aphid control and assessment of PSO efficacy in the field are discussed.     

Accumulation and distribution of pp′-DDT and related compounds in an apple orchard. II. Residues in trees and herbage

DDT residues in or on the roots and leaves of the herbage and the roots, bark, leaves and fruit of the trees are given for an apple orchard sprayed annually (1953–1969). The distribution of DDT in both the grass and the grass roots was in circular areas of residues, with maximum values at each trunk and decreasing radially to each alley. Of the spray applied at the green cluster stage 80% was deposited on the grass sward and very little, if any, directly on the soil surface. The pp′-DDT content of the grass fell rapidly with successive mowings (from which the cuttings remained in situ) from 400 μg/g at spraying to 2 μg/g after nine months. 33 g/ha pp′-DDT was found in the herbage roots (0.87% of the total residues in the soil). The residues in the bark (87.5 g/ha) were much lower than expected after 13 years spray application. There were increased amounts of pp′-DDE, pp′-TDE and pp′-TDEE relative to pp′-DDT, indicating some breakdown on the bark, but the chief losses were attributed to volatilisation and to removal by wind and rain. The residue content of root bark varied from 3 μg/g near the emerging trunk to 0.05 μg/g at a depth of 90 cm. The pp′-DDT content of leaves at leaf fall rose from <1 ng/g after a single spring spray to 8.33 μg/g following an additional spray in late June. There was a large loss of DDT from the canopy between the June spray and leaf fall (440–480 g/ha down to 25 g/ha), attributed to volatilisation. The amount of pp′-DDT on the fruit, after a single spray, was 3 ng/g fresh weight (80.9 mg/ha out of a total of 1.0–1.5 kg/ha used).