Pedestrian sprayers: equipment for ultra-low and very-low volume spraying1

Plant protection products often need to be applied to small areas, inaccessible to vehicular equipment, hence the need for manually carried equipment. While there are lever-operated knapsack and compression sprayers using conventional hydraulic nozzles, reduced-volume applications have been developed in combination with the use of rotary atomizers to provide a narrow droplet spectrum. Most of the initial development of these hand-carried battery-operated spinning disc sprayers was for their use in the semi-arid tropics to apply insecticides to cotton in the absence of plentiful water supplies. This continues to be the main market for these sprayers, although the trend recently has been away from oil-based ultra-low volume formulations to very-low volume spraying (typically 5-1 5 litre ha¹) of water-based formulations to reduce costs and allow greater flexibility in choice of insecticide in integrated pest management programmes. Changes in equipment design have been made to suit this change in spray volume and formulation. Air-assisted sprayers have also been used in glasshouses. Subsequent development of rotary atomizers operated at slower speeds has led to the equipment being used for herbicide application. especially in forestry and urban situations where low weight of equipment and drift reduction have been important considerations. Formulations prepacked in containers to connect directly to the sprayers have been used to reduce operator contamination.     

Influence of environmental conditions on dispersal of Botrytis cinerea conidia and on post-harvest infection of gerbera flowers grown under glass

Dispersal of Botrytis cinerea in a gerbera crop grown in two glasshouses 30 km apart was studied over a period of 18 months, in 1988 and 1989. Conidia were caught in spore traps consisting of agar in petri dishes exposed at different heights in the crop in each glasshouse. No seasonal patterns could be identified in the spore catches, assessed as colonies on the agar traps after incubation. The number of lesions caused by conidial infection of gerbera flowers following incubation, however, showed a distinct pattern. In spring and early summer few lesions were recorded whereas at other times of the year many lesions appeared. In linear regression analysis, variation in numbers of colonies (spore catches) could not be explained by environmental factors recorded during the experiments. Linear regression accounted for 77% and 81% of the variation in the number of lesions on flowers in the two glasshouses, in terms of relative humidity (postively correlated), global radiation outside the glasshouse (negatively correlated) and age of the crop (positively correlated). Despite differences in the systems by which the gerbera crop was produced and in the spore catches, the numbers of lesions on gerbera flowers in the two glasshouses were significantly correlated though not significantly different from each other.     

Epidemiological aspects of Didymella bryoniae,the cause of stem and fruit rot of cucumber

The survival ofDidymella bryoniae and the incidence of ascospores in glasshouses, outdoors and under controlled conditions were studied. The fungus was able to overwinter in the open as dormant mycelium. Dry and undecomposed crop residues remained a source of infection for more than one year. Moisture and a minimum temperature between 5 and 10°C were needed for fructification. For ascospore release a high relative humidity was not sufficient, the substrate had to be moist during a short period. Ascospores could be trapped throughout day and night both outdoors and in glasshouses, but there was a marked peak during a period of 3 h in the evening. Both on days with and without rain about the same numbers of ascospores were trapped from crop residues in the open. Ascospore release was favoured by watering the plants in the glasshouse. Under controlled conditions the release of ascospores was determined by humidity and not by light or darkness. In a cucumber crop in the glasshouse the first ascospores were trapped at about the same time the first symptoms on the plants appeared. In the glasshouse with introduced diseased plant debris, particularly when the debris became wet when the plants were watered, the disease was more severe and yield was less than in a glasshouse without introduced plant debris. Airborne ascospores may cause the primary infection of a cucumber crop. Therefore, hygienic measures must be taken to eliminate plant debris as source of infection, both in glasshouses and outdoors.     

Influence of environmental conditions in a glasshouse on conidia ofBotrytis cinerea and on post-harvest infection of rose flowers

Quantification and horizontal distribution of air-borne inoculum ofBotrytis cinerea in a rose crop in a glasshouse of 300 m² was studied in 1991 and 1992. Conidia ofB. cinerea were caught in spore traps consisting of an agar medium selective forB. cinerea in Petri dishes placed within the crop, at flower height 1 m above the ground. Spore catches were counted as colonies, after incubation. Lesions due to conidial infection were counted on petals of rose flowers, also after incubation. Relative humidity (RH) and temperature within the glasshouse and global radiation and windspeed outside were recorded during the experiments. The horizontal distribution ofB. cinerea in a rose crop grown under glass was fairly uniform in both years. In 1991 a clear seasonal pattern in the number of colonies could not be found. In 1992 the number of colonies were high in August, September and October. The number of lesions on rose flowers showed a distinct pattern in both years. In August, September and October many lesions were counted whereas in the other months few lesions appeared. In linear regression analysis, variation in numbers of colonies (spore catches) could not be explained by environmental factors recorded during the experiments. Linear regression accounted for 76 and 63% of the variation in the number of lesions on rose flowers in 1991 and 1992, in terms of relative humidity (positively correlated), global radiation outside the glasshouse (negatively correlated) and, numbers of colonies on spore traps (positively correlated). The results in the rose crop suggest that RH, global radiation and spore density in glasshouses are important variables in regulating the numbers of lesions during storage and transport. The numbers of spores in glasshouses are dependent on the production system. A glasshouse with a system resulting in wet dead tissue on the ground give higher amount of spores in the glasshouse air and through that high numbers of lesions on flowers. On roses outside the glasshouses very high numbers of lesions were counted sometimes, mostly during and after rain showers, as a result of rain-deposition of spores onto the flowers.     

Plant protection equipment in glasshouses1

The use of pedestrian equiprnent such as sprayers, blast sprayers and fogging machines in glasshouses of dilferent size is still very common. Hand-held sprayers or those carried by straps on the back or on one shoulder are well known. Fogging machines are in use as pedestrian or stationary equipment. For pedestrian sprayers, the quality of distribution and the accuracy ofdosing depend very much on the qualification of the operator. As to the use of stationary cold fogging, a summary is given of a research programme to investigate various influences on the quality of distribution and recovery. To guarantee reproducible results in distribution quality, the model of the cold-fogging machine has to be adjusted to the size of the glasshouse. In big cold houses, it is important to have sufficient circulation of the airstream. The force of the circulating airstream depends on droplet size and on the size of the glasshouse. Good distribution quality and high recovery rate cannot be achieved at the same time.     

Extent and Economics of Biological Control of Tetranychus urticae and Trialeurodes vaporariorum in Danish Glasshouses1

A survey was conducted among Danish tomato and cucumber growers concerning the use of biological and chemical control in Danish glasshouse crops in 1982. The survey revealed a widespread use of biological control of Tetranychus urticae and Trialeurodes vaporariorum on glasshouse crops of cucumber and tomato (87 and 77 % of the area, respectively). The growers estimated biological control to be cheaper than chemical control, and showed a pronounced preference for biological control (82 % of the replies). In cucumber crops, the area on which biological control was uninterrupted throughout the growing season was greater than in tomato crops, despite the fact that more chemical applications against other pests and diseases were necessary on cucumber crops. A list of the pesticides most commonly used in glasshouses in conjunction with successful biological control of spider mite is presented. Guidelines for biological and chemical control of spider mite on cucumber and whitefly on tomato are given.     

Stability of insecticide resistance in the peach-potato aphid,Myzus persicae (Sulzer)

Anholocyclic Myzus persicae (Sulz.) from the glasshouse and field can be classified into six variants, each with a characteristic carboxylesterase activity and consequent resistance to carbamate and organophosphorus insecticides. Overlapping activity distributions prevent unequivocal identification of an individual from measurements of its enzyme activity, but this may be done by cloning and measuring the frequency distribution of the enzyme activity in its progeny. Although each of the four lowest esterase variants has a frequency distribution with a single peak, only the susceptible (USLL) is best described by a single Normal distribution. Those of the other three clones (MSIG, French R and T1V) correspond better with two Normally-distributed components. However, these are not well separated and the lower component accounts for only 10-25% of the individuals. The very resistant clones from glasshouses have higher mean activities but with very broad distributions covering the whole range observed in this aphid. These broad distributions have peaks corresponding to those of the less resistant variants and arise from the appearance at each generation of a small proportion of individuals with much less active enzyme than their parents. Careful monitoring of the changes in activity between parents and offspring of the most resistant variant (clone G6) showed that complete loss of resistance can occur either in a single step or over several generations, and that below a threshold value, reversion to higher levels is very rare. Such reversion could only be detected by selection, with insecticide, of large clonal populations from an individual that had lost activity. High esterase activity was not stabilised by breeding for 16 generations only from individuals with high esterase activity, and is probably maintained in glasshouses by continuous exposure to insecticides. Spontaneous loss of esterase activity and resistance was observed only in glasshouse populations.     

Zucchini yellow mosaic virus; two outbreaks in the Netherlands and seed transmissibility

In 1983 and 1987/88 two limited outbreaks of zucchini yellow mosaic virus in cucumber and zucchini squash occurred in the Westland glasshouse district in the Netherlands, mainly in glasshouses. The disease could be eradicated and has not recurred so far. In both cases a relatively mild but still highly pathogenic strain of the virus was involved. Diseased plants of zucchini yielded severely distorted or no fruits and it was difficult to obtain seeds from infected plants. Two out of 4196 seedlings grown in isolation from seed from inoculated zucchini plants showed symptoms and contained the virus, indicating that the virus can be transmitted via seed but at very low rate. This explains the erratic incidence and international distribution of the virus.     

Prediction of herbicide activity

The performance of a herbicide is influenced by a number of factors, such as temperature, humidity, weed species and stage of development of the weed. Trials in glasshouses and climatic chambers have shown that the shape of the dose-response curve of a herbicide is dependent only on the mode of action of the herbicide. Therefore, the performance of a herbicide under different climatic conditions can be described as a parallel displacement of the dose-response curve. The same seems to be the case regarding the performance of a herbicide against different weed species or against one weed species at different growth stages. The trial programme is in an introductory phase, but the intention is, on the basis of trials where the influence of the above mentioned factors are quantified, to build up a simulation model that adjusts the dose to the conditions prevailing at the time of spraying. In this paper, the results from trials in climatic chambers to test the effect of a herbicide under different climatic conditions, and glasshouse trials with three weed species at three stages of development, are summarized.     

Effect of chlorothalonil on resistance of Botrytis cinerea to dicarboximides in cucumber glasshouses1

Failures to control grey mould by dicarboximides on winter-grown cucumbers in glasshouses in Israel were attributed to the development of resistance to these fungicides in populations of Botrytis cinerea. A survey of 18 glasshouses in the winter of 1983-84 revealed that resistance is widespread where dicarboximides have been used extensively. During the summer, resistant B. cinerea populations often shift back to sensitivity; however, following few dicarboximide sprays in the subsequent winter, resistant strains reappear, increase rapidly and become dominant in the pathogen population. In two out of three glasshouse experiments, combination of chlorothalonil and dicarboximides in spray programmes slowed down the increase of resistant strains, whereas in a third experiment such a programme had no effect. The usefulness of chlorothalonil in fungicide-alternation programme to suppress dicarboximide resistance is dicussed in relation to the fitness properties of established versus newly-appearing resistant mutants.     

Variation in response to neonicotinoid insecticides in peach-potato aphids,Myzus persicae (Hemiptera: Aphididae)

Laboratory bioassays applying the neonicotinoid insecticides imidacloprid, acetamiprid and nitenpyram against clones of the peach-potato aphid Myzus persicae (Sulzer) demonstrated that these compounds effectively circumvent the known carboxylesterase, modified acetylcholinesterase (MACE) and knock-down (kdr) insecticide resistance mechanisms in this species. However, some clones showed cross-tolerance (up to 18-fold) of these compounds relative to susceptible standards. A survey assessing the frequency of neonicotinoid tolerance in M persicae in the UK, based on samples collected from the field and glasshouses between 1997 and 2000, showed that such tolerance is still rare. Experiments on neonicotinoid-susceptible and -tolerant populations of M persicae under simulated field conditions in the laboratory showed that, although the latter were well controlled by imidacloprid applied at recommended application rates, they were more likely to survive and reproduce when this compound was applied at lower concentrations. Such conditions are probably periodically present in imidacloprid-treated field and glasshouse crops. Selection favouring tolerant forms of M persicae could lead to increases in their frequency and the evolution of more potent resistance to neonicotinoids.     

Occurrence of yellowing viruses (Beet pseudo-yellows virus, Cucurbit yellow stunting disorder virus and Cucurbit aphid-borne yellows virus) affecting cucurbits in Greece

A survey of the incidence of yellowing viruses in Greek glasshouse (and occasional field) cucumber and melon crops was carried out during 2000–03. In most cases disease incidence ranged from 50 to 80%. Simplex RT-PCR was used for the detection of Beet pseudo-yellows virus (BPYV) and Cucurbit yellow stunting disorder virus (CYSDV), and DAS-ELISA for the detection of Cucurbit aphid-borne yellows virus (CABYV). The results showed that BPYV was the predominant virus in cucumber and melon crops, whereas CYSDV, reported for first time in Greece, was isolated only in three regions of southern Greece: Rhodes, Crete and Arkadia. CABYV was detected only in three cucumber glasshouses in Pella (Macedonia). A simplified triplex RT-PCR method using a simple sample-preparation protocol was developed to allow rapid, sensitive and simultaneous detection of the three viruses. Sequence comparisons of the PCR products of BPYV and CYSDV revealed 98·7 and 100% amino acid identity, respectively, with previously reported sequences. The arable weed species Amaranthus retroflexus , Selosia cristata , Sonchus oleraceus and Sonchus sp. were identified as potential BPYV reservoirs.     

Influence of particle size and type of formulation on phytotoxicity and persistence of atrazine

The initial and residual activities of wettable powder formulations of atrazine comprising different particle sizes were investigated in field and glasshouse experiments. A flowable formulation was also compared with these. Oats were used as the test species for the glasshouse studies while in field trials effects on control of broadleaf weeds in maize were studied. No marked differences were noted in the activity of wettable powders of different particle sizes in the glasshouse as pre-emergence applications. As a post-emergence treatment the fine particle size was more phytotoxic than the coarse material, especially when a wetting agent was added to the spray solution. In the field trials, no appreciable differences in weed control or crop tolerance could be established regardless of the time or rate of application. The flowable formulation was less active than the wettable powders in some glasshouse experiments but no such trend was apparent in field trials. Bioassays showed that the residual activity of the flowable formulation was lower than wettable powder formulations in both glasshouse and field studies but no consistent differences were noted in the persistence of the three forms of wettable powders.     

Predators with a future as bioagents against glasshouse pests1

As a result of the application of Encarsia formosa, Phytoseiulus persimilis and Bacillus thuringiensis, and of the decreased use of pesticides, we have observed the spontaneous appearance of natural enemies not normally present in Bulgarian glasshouses. Clitostethus arcuatus has proved a competitive species with E. formosa on Nicotiana glauca, green capsicum and Hibiscus syriacus, attacked by Trialeurodes vaporariorum. On cucumber and capsicum plants infested respectively by Aphis gossypii and Myzus persicae, Cryptolaemus montrouzieri was established after spontaneously entering an experimental glasshouse. Some trials were carried out with the polyphagous bug Podisus maculiventris under laboratory conditions. It was able to use larvae of T. vaporariorum, M. persicae and A. gossypii as prey. On this basis, it seems quite promising to include this predator in IPM programmes as an additional bioagent against certain glasshouse pests during the autumn-winter-spring period.     

Horizontal and vertical distribution of airborne conidia of Botrytis cinerea in a gerbera crop grown under glass

The horizontal and vertical distribution of airborne conidia ofBotrytis cinerea in a gerbera crop in two glasshouses (100 m² and 350 m²) was studied during 18 months in 1988 and 1989. Conidia ofB. cinerea were caught in simple spore traps consisting of agar in Petri dishes placed in a regular pattern at three different heights in the glasshouse and counted as colonies, after incubation. Lesions due to conidial infection were counted on gerbera petals. The horizontal and vertical distribution of conidia ofB. cinerea in a gerbera crop grown under glass was fairly uniform in both distinct glass-houses. Conidia ofB. cinerea trapped in a glasshouse can originate from sources inside and outside the glasshouse. No significant interaction was found between location and time for the colony counts and for the log transformed (ln(N+1)) lesion counts. The results of this study suggest that spore trapping at one height and at a limited number of locations and dates is sufficient for efficient monitoring ofB. cinerea in a glasshouse.     

New developments in insecticide resistance in the glasshouse whitefly (Trialeurodes vaporariorum) and the two-spotted spider mite (Tetranychus urticae) in the UK

A recent survey of insecticide resistance in two of the most problematic pests in UK glasshouses revealed some new developments. At least some individuals in all UK samples of Trialeurodes vaporariorum that were tested resisted the insect growth regulator (IGR) buprofezin. The most strongly resistant strains were unaffected by the field application rate of this compound, and even samples from populations that had never been exposed to buprofezin contained individuals that survived the highest concentration applied (10,000 mg litre-1). The field rate of buprofezin was shown to select for resistance through vapour action alone. The benzophenylurea teflubenzuron, an unrelated IGR, was cross-resisted by buprofezin-resistant individuals. There was no evidence of resistance to imidacloprid, but all T vaporariorum strains tested, regardless of origin, exhibited a high innate tolerance to nicotine, when compared with another whitefly species, Bemisia tabaci. Marked resistance to fenbutatin oxide and tebufenpyrad was found in single glasshouse populations of Tetranychus urticae, but these compounds and abamectin appeared to remain highly effective against all other strains collected.     

Effects of adjuvants on the performance of a novel powdery mildew fungicide, 1-(4-chlorobenzyl)-4-phenylpiperidine

The effects of adjuvants on the performance of a dispersible concentrate formulation (DCI) of a novel powdery mildew fungicide, 1-(4-chlorobenzyl)-4-phenylpiperidine (I) were investigated. The method involved assessment, under glasshouse conditions, of the therapeutic (curative) control of infections of powdery mildew (Erysiphe graminis DC f.sp. hordei Marchal) on barley (Hordeum vulgare, L.) eight to nine days after spray application to plants that had been inoculated one day prior to spraying. The results from the first trial showed that marked improvements (∽five-fold) in the performance of DCI could be obtained by the spray tank addition of some types of surfactant adjuvants and a series of further trials investigating a wide range of adjuvants was conducted. Nonylphenol, alkylamine and alcohol ethoxylates varying in mean ethylene oxide content between 5 and 20 moles were highly effective. There were indications that optimum performance enhancements were obtained with these surfactants containing between 5 and 10 moles ethylene oxide. Lower enhancements, sometimes only marginal, were obtained from trisiloxane, phosphate ester, propylene oxide, alkylamine-propylene oxide and castor oil ethoxylates and also alkyl polyglucoside biosurfactants. Negligible adjuvant enhancements were observed with emulsifiable paraffinic/naphthenic and rape seed oils, though slightly better enhancements were seen with an emulsifiable transmethylated rape seed oil and, interestingly, larger enhancements with an emulsifiable lipophilic alcohol. A final trial identified the alcohol ethoxylate, ‘Dobanol’ 91-6, as the most effective adjuvant and that its optimum application rate under glasshouse conditions was 250 g ha^-1. This information will be used to guide the design of field trials. © 1997 SCI     

Control of root-knot nematodes (Meloidogyne spp.) in Hungary1

Under Hungarian climatic conditions, root-knot nematodes, and other phytoparasitic nematodes, generally cause damage in certain plant growing areas. These pests are present in glasshouses throughout the country. In the field the nematodes occur in sandy soil in the vegetable-growing areas of southern and central Hungary. The following species of root-knot nematodes have so far been reported to occur in Hungary: Meloidogyne incognita, M. arenaria, M. hapla, M. javanica, M. incognita acrita, M. thamesi and M. naasi. There are 10 specific nematicides registered for nematode control in the country. These chemicals are mainly applied in glasshouses where their use produces most economic return. Nematoderesistant cultivars are only available in the case of tomato. The nematodes cause the heaviest damage on glasshouse cucumber.     

New Atomizer Developments in the Hungarian Aviation Service1

In the practice of aerial application of chemicals in Hungary, the need arose in the mid-70's to solve the spray atomization problem for the ULV range. First experiments were carried out with imported equipment, in view of the lack of Hungarian-manufactured equipment. Unfavourable practical experiences impelled the Air Service in Hungary to develop and manufacture new spraying equipment, specially adapted to local requirements. The Unirot-4 electrically driven rotary drum became the first successful atomizer, which was put into large-scale operation in recent years. This multi-purpose spraying equipment is now essential on helicopters used for ULV and LV applications. The X-2 fan-driven rotary drum is being developed for fixed-wing aircraft.     

Modern Technology for Aerial Application of Agrochemicals1

Most pesticides and fertilizers are applied by aerial techniques in the agricultural farms of Hungary. The importance of the work done by plane or helicopter is characterized by the following data: in regions having many planes more than 50% of the plant protection activity is carried out by aerial application. Another characteristic feature of Hungarian agricultural aviation is the fact that almost 35% of the total spraying involves the application of herbicides, defoliants and desiccants. Large-scale use of formulations dangerous for the environment has made it necessary to take some important measures, such as directed spraying, regulation of drop sizes etc. With the development of these methods and the transformation of spraying equipment it became possible to carry out spraying under optimal biological conditions. Nowadays aircraft are used in at least one production process for crops such as cereals, rice, maize, sunflower, sugar beet, potato and vegetables and vines (chemical weed control, spraying for the control of fungi or insects, desiccation). Finally it should be mentioned that all equipment is mounted with the membrane-lock nozzles developed by the Aviation Service of the Ministry of Agriculture and Food to meet the requirements of modern technology. A very promising part of this activity is the development of rotating nozzles for helicopters (electrically driven) and for planes (wind driven).