Report from the Sub-comittee on the environment and health

Product mixtures in
preparations and sprayer
tanks
70
is at present of greatest relevance for fungicides. The side effects are
particularly effects on harmless fungi and <strong>the</strong> derivative effects of
reduced fungus densities.
In a study of <strong>the</strong> effect of split dosing of a leaf fungicide, <strong>the</strong> effect of 1/3
dose proved to be relatively high, and particularly <strong>the</strong> effect of <strong>the</strong> first
two (beginning-end May) applications. Depending on <strong>the</strong> year, 3 x 1/3
dose often has a greater effect on both harmless and harmful fungi than a
single full dose. (Reddersen et al. 1998). The results of such comparisons
must be expected to depend on <strong>the</strong> year (<strong>the</strong> wea<strong>the</strong>r) and <strong>the</strong> actual and
relative times when <strong>the</strong> individual applications are carried out. It is
probable that <strong>the</strong> same applies to fungicides as to herbicides: <strong>the</strong>
recommended dose is normally more than enough to achieve <strong>the</strong> desired
effect. Placed optimally, <strong>the</strong> effect of 3 x 1/3 dose on sensitive fungi will
<strong>the</strong>refore be more comparable to 3 x full dose than 1 x full dose.
Clear analyses of <strong>the</strong> importance of split dosing, reduced dosages,
spraying time, and wea<strong>the</strong>r conditions require simulation models and
sensitivity analyses. Such tools are only now being developed.
Since <strong>the</strong> beginning of <strong>the</strong> 1980s, farmers have traditionally sprayed
winter cereals twice with fungicides. Ten years ago, <strong>the</strong>y used two full
doses. Today, optimisation of <strong>the</strong> application time and falling grain
prices have made two applications of 1/3 of <strong>the</strong> dose <strong>the</strong> most
economically optimum and, on average, that has replaced two
applications of <strong>the</strong> full dose. Depending on <strong>the</strong> product, <strong>the</strong> reduced
dosages produce a varying dosage response. Split dosing has not
increased <strong>the</strong> risk of routine application of insecticides. However, when
traditional spraying with fungicides is carried out around earing, many
farmers are tempted to add an insecticide if <strong>the</strong>y have seen a few aphids
in order to avoid perhaps having to spray again one week later, when <strong>the</strong>
damage threshold has been exceeded. All else being equal, <strong>the</strong> direct
effects of pesticides will be less with use of reduced dosages.
The effect of product mixtures is an unknown factor in <strong>the</strong> assessment of
<strong>the</strong> effects on <strong>the</strong> pests and non-target organisms. That is because <strong>the</strong>
substances can affect each o<strong>the</strong>r’s toxicity. In many crops <strong>the</strong> usual thing
is to apply several active ingredients in one go, ei<strong>the</strong>r as finished
preparations or by mixing <strong>the</strong>m in <strong>the</strong> tank. In Denmark, <strong>the</strong> extent to
which tank mixtures are used in practice has not been investigated. The
substances can have an additive, intensifying or impeding effect. It is not
possible to get a picture of which substances intensify each o<strong>the</strong>r’s effect,
partly because <strong>the</strong>re are many possible combinations and partly because
it depends on <strong>the</strong> species on which <strong>the</strong> mixture is tested, <strong>the</strong> dosages
used, and <strong>the</strong> timing of <strong>the</strong> test. It has been proven that <strong>the</strong> effect of many
insecticides is intensified by <strong>the</strong> presence of o<strong>the</strong>r substances with an
entirely different toxic effect. The intensifying effect may be due to <strong>the</strong>
fact that <strong>the</strong> substances act on <strong>the</strong> enzymatic degradation of <strong>the</strong> toxin, on
<strong>the</strong> penetration of <strong>the</strong> substance or on <strong>the</strong> adsorption of <strong>the</strong> substance. In
some cases, an up to 100 times increase in toxicity has been observed,
which can radically change a substance’s hazard classification. In 32% of
<strong>the</strong> cases found, where an insecticide is involved, <strong>the</strong> effect on mammals
increases by a factor of 10 or more.