PLANT PROTECTION 1 – Pests, Diseases and Weeds

PLANT PROTECTION 1 – Pests, Diseases and Weeds
Grapeleaf blister mite
Example of an eriophyid mite
Generally speaking, this mite is not considered to
be a serious pest, but if most of the leaves are
attacked, the cropping of vines may be affected
and sunburn of berries may occur. This only
occurs in localized and limited areas where there
are extremely heavy infestations on some vines
and not others. Eriophyid mite damage in
grapevine in Australia is considered to be the
common cause of the widespread “Restricted
Spring Growth” syndrome (Bernard et al 2005).
Scientific name
Colomerus vitis (Class Arachnida, Order Acarina,
Family Eriophyidae). There are two forms of this
mite, one which infests leaves and another which
infests growth buds. They look identical.
Host range
Grapevines (Vitis vinifera).
Description & damage
Adult eriophyid mites are 0.2 mm long
and less than half the size of spider mites. Under
a x10 hand lens eriophyid mites will only look like
specks of dust. You will need at least a x40
magnification to see their shape. They are white or
creamy in colour and worm-like with 2 pairs of
legs situated near the head end. They may be
found in the felt-like areas on the undersurface of
the blistered areas of the leaves during the growing
season and in the buds during winter.
Blister mite form.
– Leaf undersurfaces. Mites suck plant sap from
leaf undersurfaces in spring. Initially small yellow
areas up to 6 mm or more across develop on the leaf
undersurface. These areas have a felt-like appearance
(erinose) due to the production by the host plant of
densely packed fine hairs. This mat of hairs becomes
darker and rusty brown with age. Mites may be seen
in amongst the hairs with the aid of a microscope.
– Leaf upper surfaces. The upper surfaces of the
felty areas develop blisters (page 207, Fig. 127). In
severe infestations the raised blisters may run together
and most of the leaf surface may be covered.
– Fruit. If leaves are severely damaged bunches may
be sunburnt.
Bud mite form.
– Buds, shoots and canes. There is stunting of
the canes, shortened internodes at the base, zigzagged
shoots, dead ‘overwintering’ buds and
abnormal development of buds. Failure of buds to
develop normally causes some reduction in yield. In
severe infestations buds may fail to burst. Bud mites
spend most of their lives in the buds. Feeding in the
bud results in a bubbling or wart-like appearance of
plant tissue. The amount of shoot damage apparent
in spring depends on the level of infestation of new
buds during the previous season(s). Shoots that
develop from infested buds may have distorted
basal leaves, shortened internodes and more
extensive ‘bubbling’ of the tissue around the base of
shoots. If bunch primordials are attacked clusters
will be deformed.
Diagnostics.
Morphology of the mites. Bud mite and
blister mite are identical in appearance so it is
difficult to distinguish blister and bud mite forms.
Mites are difficult to see, you need a compound
microscope and even then can be hard to find.
Placing affected leaves in a paper in a plastic bag
for day or so at room temperature can make them
more active, bring them out of the erinose and
easier to see.
Damage.
– Blister mite damage. During the growing
season the blister-like distortion (Table 42) on
young foliage may misdiagnosed as:
Downy mildew.
Pubescence (having fine short hairs).
Powdery mildew.
– Bud mite damage can be determined in winter
by examining dormant winter buds for mites or
‘bubbling’ of the tissue inside the outer bud scales
using a microscope. Bud mites tend to infest basal
buds so sampling should focus on these. Soon after
budburst, at the leaf rosette stage bud mites may be
found in leaf axils and internodes of growing
shoots. Small newly developing buds can contain
mites almost as soon as they begin to develop when
2-3 leaves are separated. Often misdiagnosed as:
Boron deficiency or toxicity.
Bud mite damage is generally patchy, rust mite
damage is commonly spread across a whole
block or vineyard).
Phomopsis damage.
Cold damage.
Restricted spring growth (RSG).
Symptoms of fan leaf virus.
Herbicide injury.
Table 42. Comparing blister mite damage to leaves with fungal diseases and pubescence.
LEAVES
BLISTER MITE
DAMAGE
NATURAL
PUBSCENCE
(on some varieties)
DOWNY MILDEW
SYMPTOMS
UPPER SURFACE Blisters Healthy appearance Flat oily areas,
leaves may wither
UNDER SURFACE
White or reddish
patches of
White hairs dispersed
evenly all over leaf.
Many varieties
smooth/glossy, not
pubescent
White patches of
fungal spores in
humid weather
POWDERY MILDEW
SYMPTOMS
White powdery patches
Occasionally white
powdery patches
206 Insects and allied pests – Mites (Arachnida, Acarina)