Click to enlarge.

Beginner

Scientific Name
Panonychus ulmi (Koch)

Identification
Eggs:

• Red,
• 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.

Immature Adults:

•  Typically reddish, but may appear green following molting.

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.

Damage:

• Bronzing on the leaves,
• Severe infestations may result in defoliation,
• Prolonged feeding leads to reduced shoot growth and fruit bud set the following year,
• Fruit colour, soluble solids, firmness, size and weight of the fruit are also affected.

Often Confused With

• Two-spotted spider mite- Damage from both mite appears as a bronzing of the leaves. Although they belong to the same family as two-spotted spider mites, European red mites produce less obvious webbing.

Period of Activity
European red mites are present from bloom to harvest. The first few generations are generally synchronous in development, but by mid summer generations overlap and all stages (eggs, nymphs, adults) are present at the same time. Females begin laying overwintering eggs in late August on twigs, branches and in the calyx end of fruit.
 
Scouting Notes
Begin weekly monitoring programs for European red mites in the dormant/tight cluster stage. Examine fruit spurs and twigs for overwintering mite eggs. From tight cluster through to petal fall, collect 2 fruit spurs from 25 random trees per block and examine the underside of the leaves using a dissecting microscope with a magnification of 25-40X for the presence of mite eggs, nymphs, adults and beneficial mites. Using a hand lens in the field may help experienced consultants and scouts obtain quick estimate of numbers, but does not provide accurate counts required for threshold numbers. 
  
After petal fall, collect 2 leaves from each of 25 well-spaced trees per block (50 leaves total). Pick leaves at arm’s length into the canopy. Include European red mite and twospotted spider mites in counts –total the number of mite eggs, nymphs and adults. Miticides vary in performance against different life stages and species.

Thresholds

For information on the timing of specific miticides, see OMAFRA Publication 360, Fruit Crop Protection Guide.

Advanced

European red mites are the most common mite found in Ontario apple orchards.

Scientific Name
Panonychus ulmi (Koch)

Identification
European red mite eggs are red, slightly flattened (onion-shaped) and have a hair-like stalk protruding from the top. Newly hatched nymphs have three pairs of legs. Older nymphs have four pairs of legs as do the adults. Immature mites are typically reddish, but may appear green following molting (the red colour develops with feeding). European red mites 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.

Immature mites feed primarily on the lower surface of the leaf near the veins and midrib. Adults feed on both the upper and lower surfaces of the leaf. Feeding on leaves causes characteristic leaf injury referred to as bronzing. Mites insert their needle-like mouthparts into leaf cells and suck out cell contents, including chlorophyll. Affected leaves appear stippled and may become bronzed if populations are sufficiently high. Severe infestations may result in defoliation.

Prolonged feeding by unmanaged mite populations stresses the tree, leading to reduced shoot growth and fruit bud set the following year. Fruit colour, soluble solids, firmness, size and weight of the fruit are also affected. In severe cases, mite-induced tree stress may result in death during harsh winters.

Often Confused With

• Two-spotted spider mite- Damage from both mite appears as a bronzing of the leaves. Although they belong to the same family as two-spotted spider mites, European red mites produce less obvious webbing.

Biology
Overwintering European red mite eggs are usually found on roughened bark around the bases of buds and spurs, and in the inner parts of the tree close to the main trunk and branches. Eggs begin to hatch around the tight cluster stage of apple.

As European red mite eggs hatch, nymphs move from the twigs to developing foliage where they begin feeding. Nymphs eventually become adults that mate and lay the first generation of “summer eggs.” There can be six to eight generations of European red mite each year.

Period of Activity
European red mites are present from tight cluster to harvest. The first few generations are generally synchronous in development, but by mid summer generations overlap and all stages (eggs, nymphs, adults) are present at the same time. Females begin laying winter eggs in late August on twigs, branches and in the calyx end of fruit.

Scouting Notes
Begin weekly monitoring programs for European red mites in the dormant stage. Examine fruit spurs and twigs for overwintering mite eggs. From tight cluster through to petal fall, collect 2 fruit spurs from 25 random trees per block and examine the underside of the leaves using a dissecting microscope with a magnification of 25-40X for the presence of mite eggs, nymphs, adults and beneficial mites. Using a hand lens in the field may help experienced consultants and scouts obtain quick estimate of numbers, but does not provide accurate counts required for threshold numbers.    

After petal fall, collect 2 leaves from each of 25 well-spaced trees per block (50 leaves total). Pick leaves at arm’s length into the canopy. Include European red mite and twospotted spider mites in counts –total the number of mite eggs, nymphs and adults. Miticides vary in performance against different life stages and species.

Sample leaves on a weekly basis, especially during hot summer months when numbers can increase and exceed thresholds very quickly. Although mites commonly occur in greater numbers on trees in sheltered areas and next to dusty roadways, always sample equally from all parts of blocks.

Take separate samples for each orchard block or treatable area. Red Delicious, Empire and Gala tend to support the largest mite populations. Sample these cultivars, along with orchard blocks with a history of mite problems. 

Beneficial mites can delay or prevent the need for a miticide application, so be sure to note their presence during monitoring.

Thresholds

For information on the timing of specific miticides, see OMAFRA Publication 360, Fruit Crop Protection Guide.

Management Notes

• Mite outbreaks in orchards are caused by:
  
  • conditions favourable to development,
    
  • poor groundcover management (providing overwintering sites for twospotted spider mites),
    
  • high nitrogen levels in leaves (resulting in higher mite fecundity),
    
  • loss of shelter and habit used by predators,
    
  • use of pesticides toxic to natural enemies.
    
• Natural enemies of mites include predatory mites and predators such as Stethorus punctillum (LeConte), minute pirate bugs (Orius spp.), predatory thrips, lacewings and mullein bugs Campylomma verbasci (Meyer).
  
• Beneficial mites can provide biological control of pest mites.
  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). A selective pesticide program may be less harmful to beneficial mites and prevent or delay the need for miticide applications.
  
• 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), and twospotted spider mite and apple rust mite (adults).
  
• Temperatures above 30°C negatively affect European red mite egg laying and development. Twospotted spider mites tolerate higher temperatures before suffering detrimental effects.
  
• Use well-managed cover crops between rows to limit dusty conditions that favour a buildup of pest mites. If ground cover dries, pest mites such as twospotted spider mites may move into trees.
  
• Use a delayed dormant oil (from tight cluster through pink) to effectively manage European red mite by smothering its eggs.
• These oils have little or no impact on twospotted spider mite and apple rust mite that overwinter as adults on the orchard floor.
• Dormant oils are an important part of any apple integrated pest management (IPM) program.
  
• Resistance to miticides is a serious concern in Ontario orchards.
• The long-term sustainability of mite resistance management programs requires judicious use of available products. Fortunately, Ontario growers have many different tools to manage mites and provide excellent options for a resistance management strategy. For more a resistance management strategy for miticides refer to OMAFRA Publication 360, Fruit Crop Protection Guide - Chapter 2 Apples or Apple Calendar only :
  • Recommendations for European red mite at Dormant, Half inch green, Pink, Bloom, Petal Fall/Calyx, First summer spray, Special sprays. as well as in Non-bearing orchards.