Role of physical factors on pesticide performance in forestry: An overview

Abstract

Most modern pesticides are expensive. Application of excessive dosage rates is likely to cause undesirable biological side-effects and is economically wasteful.Non-uniform distribution of the spray cloud, or application at the wrong time, may result in failure to control the pest. It is the responsibility of the field operator to acquire sufficient knowledge and skill to ensure proper use of the control agents, to increase efficiency of 115 116 SUNDARAM AND SUNDARAM their usage and to reduce unwanted side-effects. To achieve this goal, he must take into consideration the various physical factors that govern field performance of pesticides. A simple relationship exists between the spray volume and emission rate used, and droplet size produced. The use of extremely low spray volumes (i.e., those less than 2.0 litre per ha) for forest insect control in Canada, as opposed to higher volumes used in agriculture, necessitates the release of fine droplets (ranging from 20 to 70 μm in diameter) to obtain adequate coverage of the target area. These droplets take a long time to sediment downwards, evaporate in-flight, become smaller in size and/or form powdery residues, thus contributing to off-target drift and impaired droplet adhesion to target surfaces. Physical factors such as rain washing, degradation by sunlight and erosion by wind also influence the longevity of pesticide deposits on foliage which is crucial during the critical period of pest control. Factors affecting the mode of entry into insects are related to the type of ingredients used in formulation. If a pesticide acts via crawling contact, formulations which would provide surface deposits would be more beneficial than emulsions or oil-based mixes which tend to undergo penetration into foliar cuticle. Physical factors that affect field performance of a pesticide tank mix are Downloaded by [McGill University Library] at 12:51 13 December 2014 PESTICIDE PERFORMANCE IN FORESTRY 117 related to phase separation and 'breakdown of emulsions' in the application equipment; 'agglomeration and caking' of wettable powder dispersions at the bottom of the tank; impaired flow behaviour of highly viscous formulations;and coarse atomization of high-viscosity tank mixes leading to poor target cover.

Aerial ULV control of Aedes aegypti with naled (Dibrom) inside simulated rural village and urban cryptic habitats

“…The vapor produced from the droplets must consist of the solvent (and possibly other inactive ingredients), the active ingredient or its derivatives, or a combination of all the volatile constituents of the formulation. Other processes that affect droplets and vapor products include the oxidation or other reaction of the active ingredient with compounds already present in the atmosphere such as CO 2 , or physical breakdown for instance from UV radiation from sunlight [ 37 ]. Certainly, naled is known to break down in the air and soil into vaporous DDVP [ 15 , 38 ] which is highly effective against mosquitoes.…”

Quantitative impact assessment of spray coverage and pest behavior on contact pesticide performance

“…Spray coverage studies involving water‐sensitive spray cards have shown that it is not uncommon, especially with aerial fixed‐wing applications, for leaf deposition to be below 1% in the lower portion of a sprayed crop canopy 24, 25, 27. Several studies have shown how weather conditions, in particular, can markedly influence the actual coverage when pesticides are applied 25, 28…”

An investigation of droplets and films falling over horizontal tubes

“…(Field and Hutchings, 1984), the distribution of pesticides on plant foliage, e.g. (Sundaram and Sundaram, 1991;Sundaram, 1992;Sundaram et al, 1994), filtration of aerosols, e.g. (Dickson and Addlesee, 1984;Douglas and Ilias, 1987;Michaels and Goren, 1987;Wang and Kasper, 1991;Huang and Tsai, 2003), the effect of rain on the environment of bodies of water, e.g.…”