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96
GRAANGIDS
2016
GRAIN GUIDE
Tank mixtures may have a different
effect from what you think
Most of the time producers underestimate the impact a tank mixture of agrochemicals has on
crop production.
There are a multitude of seed treatments, herbicides, insecticides, fungicides, nematicides as well
as plant growth regulators on the market that can be used by producers. However, these products
must be mixed strictly according to registration prescriptions. This means that every product label
contains a section that addresses ‘mixability/mixing instruction’, and that agrochemicals cannot
be mixed with each other randomly. The effect and impact of a tank mixture usually cannot be
perceived immediately, but only at the end of a season when you harvest, or even only the next
season if the agrochemicals have a long aftereffect and residue remained in the soil.
When chemicals are mixed randomly, they can either inhibit or increase the action of the various
products, which can lead to crop damage and/or ineffective control. It is therefore not the prod-
ucts that are defective, but the tank mixture. The so-called hardness and pH of water also play a
major role when chemicals are mixed. When so-called hard water (an indication of, among other
things, CaCO
3
in the water) or water with a too low pH (<4) is used to mix agrochemicals, the
active ingredients can precipitate, form an emulsion (a gel-like liquid) or bind to other molecules
and not dissolve – the right active ingredient is then not available to do its work.
There is also a definite sequence in which agrochemicals must be mixed in tank mixtures. Firstly,
the water must be corrected. When the pH is too low, a buffer must be added to the tank water
first. A product like ammonium sulphate can then be added (if required and as prescribed on
the product label) to correct hard water. The formula (which is an indication of the solubility of a
product in water) of agrochemicals also plays a role in the mixing of products. This is indicated on
the label, or sometimes in the name of a product. Roundup PowerMax™ or Guardian S® EC, for
example, are soluble concentrates (SL), which indicates that they are emulsifiable concentrates.
The correct sequence of certain formulations is the following: WG>GR>WP>SC>CS>EC>SL.
When the product has to be mixed in the tank water, it is advisable to first dissolve the product in
a little water and then mix it with the rest of the tank water (which has been prepared), particularly
when the product consists of granules. Certain herbicides can be successfully (and in accord-
ance with registration) mixed with an insecticide, but as a rule fungicides cannot be mixed with
herbicides. The addition of any other products like growth regulators and additives (penetrators,
wetting agents) must be done very carefully. Only registered products with indications on their
labels may be added and mixing instruction must be followed at all times. Producers can cause
considerable harm by randomly mixing any chemicals with agrochemicals.
For further enquiries, contact dr Elbé Hugo at 018 299 6298 or send an email
to
HugoE@arc.agric.za.
Elbé Hugo: ARC-GCI