Page 7 - Vol.36-No.6 issue

CROP PROTECTION

FUNGICIDE SEED DRESSING

FOR RICE

sprayed a ‘home-made concoction’ onto
the vines to prevent thieves from steal-
ing the grapes. The ‘concoction’ used
was a mixture of blue, hydrated copper
DR. TERRY MABBETT sulphate (CuS04.5H2O) and calcium hy-
droxide - Ca(OH)2) and mixed in water
Application of fungicide to control
crop disease caused by pathogenic fun- to give a thick, gelatinous precipitate.
gi is most commonly carried out by foli- The spray deposit failed to deter
ar spraying in which liquid spray drop- thieves but did control highly damaging
lets carrying the fungicide particles are downy mildew disease of grapes caused
generated and propelled onto the crop by the fungus-like pathogen called Plas-
target. Water is the most frequently used mopara viticola. Millardet was subse- Disease-free plants grown in
carrier liquid although non-evaporative quently able to patent his discovery as nursery beds ensures healthy
mineral and vegetable oils may be used ‘Bordeaux mixture’ which is still used and vigorous-growth seedlings
through ultra-low volume spraying sys- today to control a range of fungal, fun- for transplanting into the field
tems that use very small droplets. Use of gus-like and even bacterial pathogens
non-evaporative oils as carrier liquids of crops. (Picture courtesy Omex)
minimises in-flight evaporation of drop- The history books generally say Millar-
lets. det was first to discover chemical fungi- subsequently adhered to the seed. It re-
mained on the planted seed grain and
cide action although a Swiss mycologist from there controlled the Tilletia caries
called Benedict Prevost had achieved fungus which is a seed-borne fungal
the very same thing some 75 years ear- pathogen of wheat. Prevost’s action was
lier in 1807. Benedict Prevost left some the very first albeit inadvertent example
wheat seed in a copper pannier (basket) of a fungicide seed dressing being used
over the winter months before sowing to control plant disease.
the seed in the following spring.
The active fungicide principle in both
To his surprise the growing wheat Millardet’s Bordeaux mixture and in the
plants were largely free of bunt dis- oxychlorides of copper formed on the
ease a particularly damaging disease of surface of Prevost’s copper basket was
wheat panicles and ears and caused by the divalent copper ion or Cu2+. In the
the fungal pathogen Tilletia caries. Me- 1900’s other copper-containing fungi-
Seed is admixed with a solid tallic copper on the surface of the pan- cides were developed but with the em-
powder formulation containing nier (basket) had been oxidised (cor- phasis now on fixed copper compounds.
the fungicide – wheat seed roded) to form the green-coloured and
is seen here and dressed powdery oxychlorides of copper which First example was copper oxychloride
with ‘turmeric powder’ for in 1908. Cuprous oxide was subsequent-
demonstration purposes ly reported in 1932 by J.G. Horsfall the
legendary North American plant pathol-
(Picture Dr Terry Mabbett)
ogist for its fungicidal properties when
used as a seed protectant, although it
Seed dressing preceded would later be used on a much wider
scale for foliar spraying. The word ‘fixed’
foliar spraying which is used to describe cuprous oxide
Be that as it may, foliar spraying is not refers to the sparingly soluble nature of
the only vehicle used to deliver fungi- the compound. This means the active in-
cide to crops. Seed dressing as a solid gredient is solubilised very slowly over
delivery system was the first instance of a period of time which helps to make
a fungicidal chemical controlling a crop cuprous oxide an ideal protectant fungi-
disease. This event happened almost cide.
one hundred years before the first ex-
ample of a fungicide spray controlling a Requirements for seed
crop plant disease, although both events Whether rice grain is seeded dressings
happened ‘by accident rather than by in nursery beds or directly into
design’. the field conditions will be moist Seed dressings are used to control the
First documented example of a liq- and humid, which also favours myriad of seed-borne and soil-borne
uid fungicide spray controlling a plant seedling blight or damping off crop pathogens at source (on or inside
disease took place in a French vineyard disease caused by a range the seed, or in the soil) before they can
in the 1880’s when Professor Pierre-Ma- of fungal and fungus-like infect highly vulnerable plant seedlings
rie-Alexis Millardet, a botanist and my- pathogens as they emerge and establish during
cologist at the University of Bordeaux, (Picture courtesy Omex) germination. Requirements are for a sol-

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