PLANT PROTECTION 1 – Pests, Diseases and Weeds

PLANT PROTECTION 1 – Pests, Diseases and Weeds
Non-living agents (contd)
NUTRIENT DEFICIENCIES & TOXICITIES, PESTICIDE INJURY, ACID SOIL.
Fig. 228.
Soil acidity. ACID ALKALINE
PH. 1 2 3 4 5 6 7 8 9 10 11 12 13 14
Aim for a pH of about 6.5
Soil acidity is a major agricultural and turf problem in Australia. Soil acidification is a
gradual lowering of soil pH. It is a natural process which can be accelerated by
agricultural practices, especially:
When large quantities of biomass are harvested and removed from the land.
Where recycling of nutrients is inefficient and nitrate is allowed to leach into soil.
Where ammonium-based fertilizers are used.
Soil acidification results in increased availability of aluminum and manganese
which become toxic. Phosphates and molybdenum become less available while
leaching may deplete cations such as calcium, magnesium and potassium.
More than 70% of the continent is covered with soils that have either a pH < 5.5
(acidic) or > 8.5 (alkaline) in which chemical toxicities and deficiencies abound.
Soil alkalinity may occur if soil is naturally alkaline or if there is prolonged irrigation
with alkaline bore water, recycled household water, etc. Trace elements may be
unavailable in alkaline soils, eg iron, zinc and manganese.
Fig. 229. Magnesium deficiency
on Valencia orange leaves, note yellow
V-shaped pattern on leaves. PhotoNSW Dept.
of Industry and Investment. (M.Senior).
Fig. 230. Iron deficiency
on citrus leaf, note yellowing
between green veins. PhotoCIT,
Canberra (P.W.Unger).
Fig. 231. Whiptail (molybdenum
deficiency) on small heart leaves of
cauliflower. PhotoNSW Dept. of Industry and
Investment.
Fig. 232. Blossom-end rot of tomato
due to a calcium deficiency in the blossom
end of the developing fruit, favored by
inadequate calcium in the soil, high salt
concentrations in the soil, dry soil, hot windy
conditions, vigorous vegetative growth,
uneven watering, etc. Do not confuse with
sunscald injury (Fig. 218). PhotoCIT, Canberra
(P.W.Unger).
Fig. 233. Simazine injury to Prunus sp. Leaves
yellowed but veins remained green. New growth the
following spring was normal. A heavy thunderstorm
after application washed the simazine down hill. Do
not confuse with deficiencies. PhotoCIT, Canberra (P.W.Unger).
Non-parasitic pests and diseases 395