Application Technology

Application technology aims at minimum loss during transfer of active ingredient, i.e. entomopathogenic nematodes from the mixing tank to the target insect. Several factors affect the ability to deliver infective juveniles in close proximity to the target insect for achieving optimal results at the minimal possible cost. Since formulations of entomopathogenic nematodes have live, delicate and tiny organisms, a careful handling is required during its application so that the adverse effects of the surrounding are minimized in order to achieve the desired activity and efficiency. Survival of nematodes during and after application is also an important aspect to be considered. Application of nematodes is mostly targeted to the soil and cryptic habitats of insects (Hussaini 2001). The choice of application equipment, and manner in which the nematodes are applied, can have substantial impact on pest control efficacy (Shapiro-Ilan et al. 2006).While selecting an application system, some points, which need special attention are volume of the sprayer, agitation system, pressure, recycling time, environmental conditions and spray distribution pattern (Shetlar 1999). A high- or low-volume sprayer can be used to dispose the nematodes, but care should be taken that the pressure in the spray tank should not be too high (300 psi or 2,070 kPa); otherwise, it will prove detrimental to the nematodes. Repeated recirculation of the tank mix also decrease viability as the mechanical stress from the pump and nozzles may lead to the rise of temperature in the liquid (Nilsson and Gripwall 1999). Therefore, the best way is to maintain the temperature below 30°C within the pump, tank and nozzles (Grewal 2002) and this can be done by the use of lower-capacity pumps, such as diaphragm or roller pump. When applied in aqueous suspension the water should neither be too hot nor heavily chlorinated. At higher temperature, the solubility of oxygen decreases ultimately making the nematodes inactive. Another important issue is settling or sedimentation. When the density of infective juveniles to be used is 1.05 g/cm2, it becomes heavier than the water and settles in spray tank (Wright et al. 2005). Infective juveniles larger in size settle faster than the smaller one. Sedimentation results in unequal distribution of nematodes particularly when used under irrigation system. Increasing the viscosity of water by adding carboxymethyl cellulose may reduce the sedimentation speed (Peters and Backes 2003). Above all, the right choice of nematode species or strain for a particular target insect pest is also very important (Shapiro-Ilan et al. 2008).

For soil application, larger capacity hydraulic nozzle is usually recommended. Nozzles with largest orifice create relatively the lowest shear stress on nematodes. Any obstacle such as smaller particles in the spray suspension may partly block the nozzle orifice, leading to a reduction in viability of the nematodes passing through the nozzle (Gwynn et al. 1999). When entomopathogenic nematode is to be applied in soil, pre- and post-application irrigation is usually recommended. This will help in going down the nematode deeper in soil and work efficiently against the target insect. Also the nematodes remain protected from the environmental extremities (Ali et al. 2005b).

Foliar application is also an interesting option, which requires careful handling of the nematodes as well as equipment to be used. Droplet size and spray distribution system are the other two important considerations for foliar application of entomo-pathogenic nematodes (Grewal 2002). Solid cone nozzle and flat fan nozzle deposit greater number of entomopathogenic nematode on leaves and give higher mortality of target insect (Lello et al. 1996). Addition of adjuvant to spray solution can also help in increasing the deposition of entomopathogenic nematode on foliage. However, surface application on foliage faces hindrance as entomopathogenic nema-todes cannot tolerate the effect of extreme temperature and ultraviolet radiation. Use of antidesiccant to retard evaporation of the nematode suspension on foliage and to prevent desiccation of nematodes has led to a great chance of success (Glazer and Novan 1990). Glycerine 10% has proved to be a more effective adjuvant for increasing survival and activity of nematodes on foliage (Nash and Fox 1969). But high cost of glycerine and risk of phytotoxicity at higher temperature limit its application. A better alternative for an effective protection against these external factors can be achieved by addition of fluorescent brightener and application during the period of moderate temperature and high humidity or late in the evening (Ali et al. 2005b). With some exceptions foliar applications have been less successful than soil applications due to nematode susceptibility to desiccation and ultraviolet rays, however, frequent low-rate applications of nematodes to foliage can result in substantial suppression of green house pests such as thrips (Shapiro-Ilan et al. 2006).

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