PLANT PROTECTION 1 – Pests, Diseases and Weeds

PLANT PROTECTION 1 – Pests, Diseases and Weeds
Non-living agents
ENVIRONMENT.
Fig. 216. Water stress. If the problem is too little water,
tips and margins become brown and brittle. If the problem it
too much water, tips and margins become brown and soft;
also caused by excessively high concentrations of salts, or by
chemical injury. The whole leaf may be affected and die.
Fig. 217. Sunscorch. Camellia leaf
showing symptoms of sunscorch injury.
Brown scorched areas often start within
the leaf margin but not always so. The whole
leaf may become scorched.
Fig. 218. Sunscald injury. Left: Capsicum, affected
areas are bleached and sunken. Right: Affected area on
the shoulder of an immature tomato is grayish-white and
has a paper-like surface. Compare with blossom-end rot
(see Fig. 232). PhotoNSW Dept. of Industry and Investment.
Fig. 219. Sunburn
injury on a tree
branch. Cracking of
bark and discoloration
of the wood beneath
the dead bark where it
was peeled back.
Sunburnt areas are entry
points for wood rot fungi.
Photo NSW Dept. of Industry
and Investment.
Fig. 220. Rind splitting in orange. Some strains of
Washington Navel orange are prone to split due to the
internal pressure of the pulp. It often occurs after a drop in
average maximum day temperature with the approach of
winter and an increase in relative humidity when the
rate of fruit growth is decreasing. PhotoNSW Dept. of Industry and
Investment.
Fig. 221. Cracking in tomato fruit is due to rapid
growth following favorable weather conditions of high
temperatures and good soil moisture just prior to harvest.
PhotoNSW Dept. of Industry and Investment.
392 Non-parasitic pests and diseases