Eva Brusselman

Effect of the spray application technique on the deposition of entomopathogenic nematodes in vegetables

BACKGROUND The present study compared entomopathogenic nematode delivery at the base of savoy cabbage and cauliflower, at the lower side of savoy cabbage and cauliflower leaves and in leek stems and the ground deposition using a five-nozzle spray boom equipped with an ISO 08 flat fan, an air induction flat fan and Twinjet spray nozzles. Additionally, an air support system and a row application system were evaluated. RESULTS Approximately 40% of the applied nematodes did not reach the foot of the cabbage plants. The use of an air support system or a row application system improved nematode deposition at the savoy cabbage base. Relative nematode deposition on the lower side of savoy cabbage leaves was 27.20%, while only 2.64% of the applied nematodes reached the lower side of cauliflower leaves. After spraying leek with a standard boom, a low relative nematode deposition (26.64%) was measured in the leek stem. Nozzle type affected the distribution of nematodes in droplet spots. CONCLUSION Nozzle type has a minor effect on the number of entomopathogenic nematodes delivered on difficult-to-reach targets. The use of modified spray application techniques directing the spray to the target site are necessary to increase the chances of contact of entomopathogenic nematodes with their target.

Improving foliar applications of entomopathogenic nematodes by selecting adjuvants and spray nozzles

Abstract This study explores the influence of a selection of adjuvants and of three different nozzle sizes on the foliar application of entomopathogenic nematodes (EPNs). Two EPN species were studied: Steinernema feltiae and Steinernema carpocapsae. A viability test of EPNs suspended in different solutions of adjuvants showed that all selected alcohol ethoxylates and an alkyl polysaccharide have an immobilising effect on the selected nematode species. In a sedimentation test, xanthan gum proved to be the only adjuvant in a broad selection, capable of delaying sedimentation of EPNs in suspension. Without xanthan gum, sedimentation of S. carpocapsae and S. feltiae was noticeable after 20 and 10 minutes, respectively. When xanthan gum (0.3 g/L) was added to the suspension, no signs of sedimentation were noticed after 20 minutes with both EPN species. An ISO 02 flat fan nozzle can clog when spraying S. carpocapsae. A deposition test determined that an ISO 04 standard flat fan nozzle provides a higher relative deposition on cauliflower leaves and is therefore a better nozzle choice than the bigger ISO 08 standard flat fan nozzle for spraying S. carpocapsae. The addition of a spreading agent improved the deposition of S. carpocapsae. Adding xanthan gum to the EPN-spreading agent mixtures did not further improve deposition.

Evaluation of hydraulic, pneumatic and mechanical agitation for the spray application of Steinernema carpocapsae (Rhabditida: Steinernematidae)

Abstract The application of entomopathogenic nematodes (EPN) is generally done using standard spray application techniques. However, in contrast to chemical pesticides, these biological antagonists must remain viable during and after the application process. For the application of EPN, a good agitation system is indispensable as the nematodes tend to sediment fast in a spray tank without agitation. Three agitation systems, viz. mechanical, pneumatic and hydraulic agitation were tested for their ability to keep Steinernema carpocapsae (Rhabditida: Steinernematidae) suspended in an undamaged way. Hydraulic agitation was tested using a centrifugal and a diaphragm pump. Nematode damage was quantified based on viability and infectivity of the EPN. The ability of the agitation system to keep the nematodes in suspension was examined by comparing the nematode concentration observed in the samples taken at different agitation times. Only the hydraulic agitation using the centrifugal pump damaged the nematodes. After 120 min of recirculation, only 19.3% of the nematodes survived. Infectivity was even reduced to 0%. An additional experiment revealed that the temperature rise, from 21.7 to 45.4°C, was responsible for the observed nematode damage. The concentration measurements showed that the pneumatic agitation was unstable. Agitation during 120 min using the other agitation systems resulted in a significant loss of nematodes at 15 cm above the spray tank bottom. In conclusion, mechanical and hydraulic agitation using a diaphragm pump can be recommended when S. carpocapsae is applied, although attention should be paid to possible nematode loss during application.

An image processing technique for the observation of the viability of Steinernema carpocapsae in spray application research

Damage caused to entomopathogenic nematodes by spray application is generally assessed by observing the viability of the infective juveniles under the microscope. To improve the quality and speed of this observation we developed an image processing technique and tested the efficacy of acetic acid and sodium chloride as chemical stimulants. Because of the lower standard error on the results obtained (0.7 vs 1.7), sodium chloride was eventually selected for all subsequent observations. The viability as observed with the image processing technique rose significantly with the time after the nematodes were suspended in water; however, viability as observed under the microscope was not influenced by the time. These differences can be attributed to the difference in type of stimulant (mechanical vs chemical) used. After nematodes had been in suspension for 3.5 h, the viability as measured using the image processing system was still significantly lower than the viability as measured under the microscope. This difference did not disappear after 24 h at 4, 15 or 24°C. Maintaining nematodes for 24 h at 35°C significantly decreased the viability to 5.9% (microscope) or 11.0% (image processing technique). The decrease in viability as observed with the image processing system corresponded better with the decrease in infectivity (i.e., 13.8%). Our results support further use of the image processing technique, not only to observe the viability of entomopathogenic nematodes but also to count the mobile or total number of nematodes of any species.

Development of a reference method for airflow rate measurements through rectangular vents towards application in naturally ventilated animal houses

A naturally ventilated test facility was built.An airflow rate measuring method using 3D ultrasonic anemometers was developed.The method was successfully validated through the law of mass conservation.The effect of the wind incidence angle and speed on the airflow rate was studied.The necessity of measuring the 3D in-/outflow pattern was proven. In order to measure the airflow rate and emission rate of a naturally ventilated livestock building correctly, more reliable measuring techniques need to be developed. A test facility with a cross ventilated room was built at the Institute for Agricultural and Fisheries Research (Belgium) to study a new airflow rate measuring method. This method is based on an automated traverse movement of a 3D ultrasonic anemometer across 2 vents of 0.5mi?1.0m. To cope with the fluctuating wind velocity profile, a velocity measurement of 10s in 16 equally distributed measuring points is needed. Moreover, 10 traverse replicates are needed to obtain a representative average flow rate. Based on the law of mass conservation, the accuracy of the method was determined by calculating the relative deviation between the simultaneously measured airflow rates through both vents. A relative error of -1?11% was found, averaged over all wind incidence angles. However, wind angles parallel to the vent resulted in larger relative errors. A 3D velocity measurement in the in- or outlet opening of the test facility is necessary to obtain a correct flow rate. This was especially true in the outlet where up to 30% of the airflow rate was delivered by velocity components other than normal to the vent. The test facility and the developed ventilation rate measuring method can serve as a reference to study and validate new and existing ventilation rate measuring methods.

Effect of spray volume on the deposition, viability and infectivity of entomopathogenic nematodes in a foliar spray on vegetables

BACKGROUND Spray volume can influence the amount of free water on the leaf surface and subsequently the ability of entomopathogenic nematodes (EPNs) to move. In this study, an investigation was made of the effect of spray volume (548, 730 and 1095 L ha(-1) ) on the deposition, viability and infectivity of EPNs against Galleria mellonella on savoy cabbage, cauliflower and leek. RESULTS Increasing spray volume decreased nematode deposition on 7.1 cm2 leek leaf discs at a 15° angle with the spray nozzle. Although the number of living nematodes observed on leek after 240 min of exposure was not significantly different between the low-volume application (548 L ha(-1) ) and the high-volume application (1095 L ha(-1) ), a greater infectivity was obtained in the latter application. The higher number of droplets deposited on the leek discs in the high-volume application may have stimulated nematode movement. No significant effect of spray volume was observed on the relative deposition of Steinernema carpocapsae on the bottom side of cauliflower and savoy cabbage leaf discs. In spite of the low S. carpocapsae deposition on the bottom side of the savoy cabbage discs, high infectivity was obtained against G. mellonella. Using the lowest spray volume on savoy cabbage, infectivity decreased with increasing exposure time, while infectivity was not affected by exposure time when a spray volume of 730 L ha(-1) or more was used. CONCLUSION Spray volume is an important application parameter, as it affects nematode infectivity. Future research should investigate the effect of spray volume in the field and its influence on the effect of adjuvants.

Improving the biocontrol potential of entomopathogenic nematodes against Mamestra brassicae: effect of spray application technique, adjuvants and an attractant

BACKGROUND Steinernema carpocapsae Weiser, an entomopathogenic nematode (EPN), is a potential biological control agent for the cabbage moth (Mamestra brassicae L.). This research aimed to identify a suitable spray application technique, and to determine whether yeast extract added to an EPN spray has an attracting and/or a feeding stimulant effect on M. brassicae. The biological control capabilities of EPN against this pest were examined in the field. RESULTS Good coverage of the underside of cauliflower leaves, the habitat of young instar larvae (L1-L4) of M. brassicae was obtained using different spray boom configurations with vertical extensions that carried underleaf spraying nozzles. One of the configurations was selected for field testing with an EPN spray. Brewers yeast extract stimulated larval feeding on leaves, and increased the mortality of these larvae when exposed to EPN. The field trial showed that a spray application with S. carpocapsae, Addit and xanthan gum can effectively lower the numbers of cabbage heads damaged by M. brassicae. Brewers yeast extract did not significantly increase this field performance of EPN. CONCLUSION Steinernema carpocapsae, applied with an appropriate spray technique, can be used within biological control schemes as part of a resistance management programme for Bt.

The Spray Pattern of Entomopathogenic Nematodes

Application technology for biological insecticides like entomopathogenic nematodes (EPN) has been a relatively neglected area. One of the major considerations involved with the selection and use of an application system should be the application distribution pattern. While completely uniform distribution of the nematodes is not entirely essential to their success in soil applications, because there the nematodes can move short distances on their own, a uniform distribution is more important in foliar EPN applications. The present study examined the volumetric distribution pattern of Steinernema feltiae beneath a single standard flat fan, air induction, deflector and twinjet spray nozzle. A comparison with the distribution of a chemical tracer was made to reveal possible distribution problems. Droplet size spectra of the nozzles were measured and linked with the distribution results. A theoretical calculation of the coefficient of variation of the nematode distribution beneath a spray boom was performed. Finally, the actual spray pattern of the EPN on a horizontal surface beneath a spray boom was studied. We can conclude that the volumetric distribution pattern of EPN is influenced by nozzle type and is different from the volumetric distribution pattern of a chemical compound. By the spray overlap using a spray boom, differences in nematode distribution are however decreased to an acceptable level. Nozzle type significantly influences the number of nematodes deposited on a horizontal Petri dish and their distribution within the droplets. Future experiments are needed to reveal if the measured differences in coverage due to nozzle type will result in significant differences in pest control.