PLANT PROTECTION 1 – Pests, Diseases and Weeds

PLANT PROTECTION 1 – Pests, Diseases and Weeds
Scientific name
Peach leaf curl (Taphrina deformans, Phylum
Ascomycota).
Host range
Ornamental and flowering stone fruits.
Mainly peaches and nectarines, but almonds,
apricots and plum may also be attacked.
Symptoms
Leaves.
In spring, spores germinate and the spore
tubes penetrate directly through the cuticle or
stomata of leaves. The mycelium then grows
between the cells and invades tissue increasing
cell enlargement and cell division causing
abnormal growth and distortion of leaves.
Leaves infected throughout lose most of
their green colour and become very thick and
pale. Partially infected leaves become
distorted because growth is more rapid in the
infected parts than in the healthy sections.
Affected leaf areas are pale green
initially but develop a deep pink or purplish
colour. Later a white bloom appears on the
surface and leaves shrivel, brown, die and fall.
Severe attack can completely defoliate a tree.
Trees usually produce new leaves that
remain healthy as the season advances. However,
if cool, wet weather persists during spring,
infections may continue to appear on new leaves
for several months.
Peach leaf curl
Curly leaf, leaf curl
Shoots.
Infected peach shoots are less obvious than
infected leaves. Shoots become swollen, stunted,
pale green to yellow, gum may ooze from them.
In apricot trees a witches' broom
develops (densely bunched curled growth).
Infected shoots usually die. This is the common
symptom of peach leaf curl on apricot trees; it is
rare to find an isolated infected leaf.
Flowers and fruit.
Infected flowers usually fall from the tree.
Partial or complete defoliation after leaf
infection usually results in heavy shedding of
developing fruit.
Infected peach fruits show raised,
irregularly-shaped areas which may develop a
pinkish or reddish color long before normal fruit
show any colour change.
Small infected fruits usually die and fall.
General.
Defoliation in consecutive seasons seriously
weakens tree growth.
Nursery stock which has suffered severe
defoliation rarely develops satisfactorily after
such a setback.
Diagnostics.
Do not confuse symptoms of peach leaf curl, with
those caused by green peach aphids (page 152).
This can be a common mistake.
Peaches and some other stone fruits may be
affected by both peach leaf curl and green peach
aphid injury at the same time.
Fig. 199. Peach leaf curl
(Taphrina deformans). Affected
parts of the fruit are blistered.
PhotoCIT, Canberra (P.W.Unger).
Fig. 200. Peach leaf curl (Taphrina deformans). Affected
parts of leaves are thickened distorted and covered with a white
bloom of spores. PhotoNSW Dept of Industry and Investment (M.Senior).
358 Fungal diseases - Examples of fungal diseases