Magazine: Adjuvants Part.2
By Jerry Spencer in Consultancy on 20th Nov 2007 10:40
Part 2 of Adjuvants by Jerry Spencer
If you missed Part 1 click on the link.
http://www.pitchcare.com.au/magazine/article/238
WETTER-SPREADERS.
A spray drop must be able to wet the foliage and spread out or cover an area of the leaf for the pesticide to perform its pest control function. In some situations, (very waxy or hairy leaves or insufficient surfactant in the pesticide concentrate formulation), additional adjuvant is needed for good coverage. The surfactant acts here by reducing the surface tension of the water on the surface of the spray drop and by reducing the interfacial tension between the spray drop and surface of the leaf. This requires a surfactant that will preferentially aggregate at these surfaces. This may not be done effectively by the surfactants that form and stabilize the oil/water emulsion from the concentrate formulation.
STICKERS.
A sticker can perform four types of functions.
a) It can increase the adhesion or "stickiness" of solid particles that otherwise might be easily dislodged from a leaf surface.
b) It can also reduce evaporation of the pesticide.
c) It can be provide a waterproof coating. If a pesticide is fairly water soluble, it may be washed off the leaf during heavy rainfalls that follow
deposition. If the sticker is not water soluble, it can provide a degree of protection from this form of loss.
d) The final function is that they can slow UV degradation of pesticides.
Many of the stickers contain surfactants as their principal functioning agent and are sold as spreader-stickers, which give both a sticker action and a wetter-spreader action. These will perform the first two functions quite well. But since the surfactants that provide wetter-spreader action must be somewhat water soluble, they may not provide good protection from rain. This will be provided by products that contain latex (rubber) such as Bind- R.
EMULSIFIABLE OIL ACTIVATORS.
Petroleum oils will enhance the penetration of some pesticides through the waxy layer of cuticle on a leaf surface and thus increase the rate of penetration.
Surfactants will also enhance penetration of some pesticides into plants, A surfactant may increase penetration for a pesticide on one species of plant but not another, or for one pesticide but not another. It is best to consider specific data on each surfactant/pesticide/plant combination in drawing conclusions about a product's efficacy as a penetrant. Systemic insecticides, auxin herbicides and some other types, and translocatable fungicides can have their activity increased as a result of increased penetration. However, too much increase may result in loss of specificity between the weed and the crop from the action of herbicides.
COMPATIBILITY AGENTS.
Pesticides can sometimes be combined with liquid fertilizers for application. The disadvantages of this are that there may be unequal distribution of the pesticide and that the pesticide formulation may break under the influence of the strong salt solutions in liquid fertilizers. There is a special class of emulsifiers known as Compatability Agents that are designed to prevent formulations from breaking when combined with liquid fertilizers. Unless the pesticide concentrate formulation specifically states that it is compatible with liquid fertilizers, it will probably be necessary to add a compatibility agent to ensure that the pesticide will not either cream or sink. If you have not had prior experience with the mixture of pesticide/liquid fertilizer/compatibility agent in question, small scale tests compatibility tests should be carried out to determine stability prior to mixing in a spray tank .
DRIFT RETARDANTS.
Drift is a function of drop size. Drops with diameters of 100 microns (0.1 mm) or less contribute the bulk of the drift off site from the treated fields. Chemicals that increase the viscosity and the "tensile" strength of water will decrease the proportion of these smaller drops in a spray system.
FOAM RETARDANTS.
Some formulations will create foam, in some spray tanks. This is usually a result of both the surfactants used in the concentrate formulation and the type of spray tank agitation. This foam can be reduced or eliminated by a small amount of foam inhibitor.
BUFFERS.
Some water used for diluting pesticide formulations is alkaline (high pH). If the pH is sufficiently high and the pesticide is subject to degradation by alkaline hydrolysis, it may be necessary to lower the pH of the mix water. The efficacy of any buffer product depends on the degree of alkalinity or "hardness" of the mixing water that is being neutralized. The more alkaline the water, the greater the amount of buffer that will be required. An excellent option worth considering is Quatrabuff which contains a coloured dye indicator which indicated the tank pH when applied.
Spray additives.
Various other spray additives may increase the effectiveness of insecticides. Ammonium sulphate solves hard water antagonism of calcium, magnesium, zinc, sodium, Aluminium and iron and also aids pesticide uptake by what is called ‘ion trapping’.
Too often Turf managers are tempted to cut corners and save money by using the cheapest adjuvant they can find. However, the key issues when choosing an adjuvant should be quality, environment and proper adjuvant selection.
Thanks to Jerry for the informative article, to find out more about ETP click on the logo.
References for the part 2 articles are:
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Adjuvants Product Guide Nufarm 2002
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Adjuvants for enhancing herbicide performance Agronomy Facts 37 Penn State College of Agricultural Sciences • Cooperative Extension
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Bakke D, Analysis of Issues Surrounding the Use of Spray Adjuvants With Herbicides
Pacific Southwest Regional Pesticide Use Specialist December 2002 Revised, January 2007
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Bayer, D.E. and C.L. Foy. 1982. Action and fate of adjuvants in soils. In: Adjuvants for
Herbicides, WSSA, Champaign, IL. Pp. 84-92.
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Hull, H.M., Davis, D.G. and G.E. Stolzenberg. 1982. Action of adjuvants on plant surfaces. In:
Adjuvants for Herbicides, WSSA, Champaign, IL. Pgs. 26-67.
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Perkins SW, Surfactants -A Primer, Dyeing, Printing & Finishing, AT1 August 1998
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Tu M & Randall JM Weed Control Methods Handbook, The Nature Conservancy
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Understanding surfactants, http://www.sacoa.com.au/L3_tech/L3_understanding_adjuvants.php
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Woodhall K, Spray adjuvants 1996
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| There are 2 comments on this article |
20 Nov 07 by KeepitSharp\\\
Top article Jerry i learn something every article of yours i read.
Keep up the good work and cheers.
20 Nov 07 by Anthony Asquith
Great article jerry i totally agree with the last paragraph about using the very best wetting agents.
Here in the UK out of about 50 (ish) surfectants only a small handfull are any good so for maximum results purchase quality - like anything in life you get what you pay for!
However when talking of turf wicket soils in which high BD and binding strength is trying to be acheived the application of such products might (and only might) affect the drying process during wicket preperation.
I've trialed a few and this seems to be the case!
However i do use them during wicket recovery and aftercare (once wickets have been used during the season) and i use the cheaper ones as i only want it in the soil for a limited amount of time.
In all other cases buy quality for max results!
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Part 2 of Adjuvants by Jerry Spencer
