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Ministry of Agriculture, Food and Rural Affairs

european red mite

European red mite adult and eggs European red mite adults and nymph European red mite European red mite European red mite nymph European red mite damage European red mite damage Click to enlarge.

Beginner

Scientific Name
            Panonychus ulmi

Identification 
Eggs:

  • Pale yellow when first laid and then turn red as they are about to hatch
  • Slightly flattened (onion-shaped)
  • Have a hair-like stalk protruding from the top

Nymphs:

  • Newly hatched nymphs have three pairs of legs
  • Older nymphs have four pairs of legs as do the adults
  • Feed on under surface of leaves

Immature Adults:

  • Typically reddish, but may appear green following molting
  • Develop darker colour as they feed more heavily
  • Feed on under surface of leaves

Adults:

  • Range in size from 0.15-0.4 mm, depending on life stage
  • Males and females are distinct from one another:
    • The adult female is a deep brown-red, about 0.40 mm in length and has rows of spots on her back with raised “spines”
    • The male is smaller (0.28 mm), lighter or drabber in colour with a pointed abdomen, and legs proportionately longer than the female
  • Feed on under surface of leaves

Damage:

  • Affected leaves have mild chlorotic spots and become bronzed if populations are sufficiently high
  • Severe infestations may result in defoliation
  • No direct fruit injury, however colour, soluble solids, firmness, size and weight of the berry at ripening can be affected due to reduced photosynthetic activity of leaves
  • Prolonged feeding may lead to reduced shoot growth and fruit bud set the following year

Often Confused With
Ozone injury - affected leaves usually darker brown; no mites visible

Period of Activity
European red mites rarely cause significant damage to grapes prior to mid-summer. Mites like hot, dry weather.

Scouting Notes
Mites are tiny and need magnification with 10X or greater hand lens or microscope to distinguish the life stages.
When monitoring for mite damage it is useful to consider previous infestation levels. Look at the underside of the leaves for their presence at the same time you are scouting your vineyard for leafhoppers and grape berry moth. If bronzing of the leaves is observed as you travel through the vineyard then confirm the presence of mites.
Moderate European red mite populations are likely to show injury on vines that are under stress (drought, excessive crop or growing after a winter of significant low temperature injury.) Cultivars with smaller leaves cannot support mite populations as those with larger leaves. Regular monitoring is essential.

Threshold
In some vineyards, this pest is kept at low levels by naturally occurring predatory mites and predaceous insects. Treatment is required when 50% of the shoots have obvious signs of bronzing at the mid-leaf level or above on shoots.  If the vines are under water stress, reduce this threshold to 25% of shoots with bronzing.  In all cases, the predominant developmental stage must be identified and must be in egg/nymphal (25/75) stage before treating. Because mite numbers can increase very rapidly, it is necessary to monitor grapes frequently during hot weather.

Advanced

Scientific Name
            Panonychus ulmi

Identification 
Eggs:

  • Pale yellow when first laid and then turn red as they are about to hatch
  • Slightly flattened (onion-shaped)
  • Have a hair-like stalk protruding from the top

Nymphs:

  • Newly hatched nymphs have three pairs of legs
  • Older nymphs have four pairs of legs as do the adults
  • Feed on under surface of leaves

Immature Adults:

  • Typically reddish, but may appear green following molting
  • Develop darker colour as they feed more heavily
  • Feed on under surface of leaves

Adults:

  • Range in size from 0.15-0.4 mm, depending on life stage
  • Males and females are distinct from one another:
    • The adult female is a deep brown-red, about 0.40 mm in length and has rows of spots on her back with raised “spines”
    • The male is smaller (0.28 mm), lighter or drabber in colour with a pointed abdomen, and legs proportionately longer than the female
  • Feed on under surface of leaves

Damage:

  • Affected leaves have mild chlorotic spots and become bronzed if populations are sufficiently high
  • Severe infestations may result in defoliation
  • No direct fruit injury, however colour, soluble solids, firmness, size and weight of the berry at ripening can be affected due to reduced photosynthetic activity of leaves
  • Prolonged feeding may lead to reduced shoot growth and fruit bud set the following year

Often Confused With
Ozone injury - affected leaves usually darker brown; no mites visible

Biology
European red mites survive the winter as eggs laid on vine canes and trunks. As eggs hatch, nymphs move to developing foliage where they begin feeding. Nymphs develop into adults that mate and lay eggs on the undersides of leaves. Females are capable of producing 200 or more eggs each and development can be rapid during warm weather. Mite populations can, therefore, explode rapidly under favourable conditions (temperatures of 22 to 27°C).  Temperatures above 30°C negatively affect European red mite egg laying and development.
 There can be multiple  overlapping generations of European red mite each growing season. and all stages can be found on grapes at any time during the summer months.  During late summer and early fall, eggs are laid around cane nodes and on the rough bark of trunks and permanent cordons, where they overwinter.  
Both adults and nymphs feed by piercing individual leaf cells and removing the fluid contents. Healthy grapevines can tolerate moderate numbers of european red mites, which may cause mild chlorotic spots on the leaves. Heavy feeding results in bronzed leaves that fall prematurely, reducing photosynthetic activity and vine vigour. Heavy feeding damage can delay ripening of the berries.
Heavy rain can physically remove and kill many mites, and remove dust that collects on foliage and interferes with mite predators.
Extreme winter weather or adverse conditions during hatch can negatively affect survival of overwintering European red mite eggs.


Period of Activity
European red mites rarely cause significant damage to grapes prior to mid-summer. Mites like hot, dry weather.

Scouting Notes
Mites are tiny and need magnification with 10X or greater hand lens or microscope to distinguish the life stages.
When monitoring for mite damage it is useful to consider previous infestation levels. Look at the underside of the leaves for their presence at the same time you are scouting your vineyard for leafhoppers and grape berry moth. If bronzing of the leaves is observed as you travel through the vineyard then confirm the presence of mites.
Moderate European red mite populations are likely to show injury on vines that are under stress (drought, excessive crop or growing after a winter of significant low temperature injury.) Cultivars with smaller leaves cannot support mite populations as those with larger leaves. Regular monitoring is essential.

Threshold
In some vineyards, this pest is kept at low levels by naturally occurring predatory mites and predaceous insects. Treatment is required when 50% of the shoots have obvious signs of bronzing at the mid-leaf level or above on shoots.  If the vines are under water stress, reduce this threshold to 25% of shoots with bronzing.  In all cases, the predominant developmental stage must be identified and must be in egg/nymphal (25/75) stage before treating. Because mite numbers can increase very rapidly, it is necessary to monitor grapes frequently during hot weather.

Management Notes

  • Mite outbreaks in vineyards are caused by:
    • conditions favourable to development
    • high nitrogen levels in leaves (resulting in higher mite fecundity),
    • loss of shelter and habitat used by predators,
    • use of pesticides toxic to natural enemies.
    • Leaves with dense lower surface hair will have higher mite populations
  • Beneficial mites can provide biological control of pest mites. Natural enemies of mites include predatory mites and predators such as predatory mites,  minute pirate bugs , predatory thrips, and lacewings.
  •  Use a selective pesticide program to preserve mite predators. Some pesticides are toxic to beneficial mites and act as a repellent or irritant to European red mite (pyrethroids), while others can increase egg laying (some neonicotinoids). Repeated use of sulphur used for powdery mildew control can flare mites. A selective pesticide program may be less harmful to beneficial mites and prevent or delay the need for miticide applications.
  • A permanent mixed groundcover will support greater numbers of beneficial insects and predaceous mites.
  •  High populations may require treatment with an effective miticide – good coverage with sufficient water volume is important

A miticide may be required if bronzing and mites reach threshold levels.  See OMAFRA Publication 360, Guide to Fruit Production - Chapter 5 Grapes : Recommendations for European red mite at Berry touch to cluster closure.