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Ministry of Agriculture, Food and Rural Affairs

Twospotted spider mite

Twospotted spider mite adult and eggs Male and female twospotted spider mites Overwintering twospotted spider mite adults
Click to enlarge.

Beginner

Scientific Name
Tetranychus urticae

Identification
Eggs:

  • Clear, becoming milky-white over time,
  • Spherical.

Nymphs:

  • Newly hatched individuals are colourless, with spots appearing following feeding.
  • Progress through several immature stages including a six-legged larva and eight-legged nymph.

Adults:

  • Pale green or straw-coloured with two dark spots on the back,
  • Produce dense webbing to coat the surface of leaves,
  • Overwintering females usually turn reddish-orange, and are often found near the calyx and stem of fruit near harvest. 

Damage:

  • Bronzing on the leaves,
  • Characteristic webbing on the under surface of the leaf,
  • Prolonged feeding by unmanaged mite populations stresses the tree, and reduces 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

  • European red mite and apple rust mite- These mites cause similar bronzing to leaves. However twospotted spider mites are associated with webbing on the leaves.  Twospotted spider mite adults and nymphs are easily distinguished from European red mites. They are pale green or straw-coloured with two dark spots on the back and more elongated than European red mite.

Period of Activity
The twospotted spider mite can be found in apple orchards from the end of tight cluster through harvest. Generally they do not appear in high numbers in orchards until early to midsummer when they move into the trees from nearby dying weeds.

Scouting Notes
Begin weekly monitoring programs for mites (twospotted spider mite and European red mite) at the tight cluster stage. 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

Stage of growth

Spray threshold and timing*

Dormant to tight cluster

Eggs present

Petal fall to 21 days after calyx

1st egg hatch and before more than 3 nymphs/leaf

 

5-7 active mites/leaf timed for 50% egg hatch

June to mid July

7-10 active mites/leaf, when approximately 50% of population are nymphs

Mid July to August

10-15 active mites/leaf when approximately 50% of population are nymphs

*Some recently registered miticides are applied slightly earlier than conventional products, at 5 mites/leaf.

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

Advanced

Twospotted spider mites are usually found in lower numbers in orchards, and appear later in the season than European red mites. Production areas including Georgian Bay and east of Toronto often have more problems with twospotted spider mites than European red mite.

Scientific Name
Tetranychus urticae

Identification
Twospotted spider mite eggs are clear and spherical, becoming milky-white over time. Newly hatched individuals are colourless, with spots appear following feeding. As with European red mite, twospotted spider mites progress through several immature stages including a six-legged larva and eight-legged nymph. Twospotted spider mite adults and nymphs are easily distinguished from European red mites. They are pale green or straw-coloured with two dark spots on the back and more elongated than European red mite. Twospotted spider mites produce dense webbing to coat the surface of leaves. Overwintering females usually turn reddish-orange, and are often found near the calyx and stem of fruit near harvest. 

Twospotted spider mites cause bronzing on the leaves. Spider mites create a characteristic webbing on the under surface of the leaf. Webbing gives mites and their eggs protection from natural enemies and environmental fluctuations. Prolonged feeding by unmanaged mite populations stresses the tree, and reduces 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

  • European red mite and apple rust mite- These mites cause similar bronzing to leaves. However twospotted spider mites are associated with webbing on the leaves.  Twospotted spider mite adults and nymphs are easily distinguished from European red mites. They are pale green or straw-coloured with two dark spots on the back and more elongated than European red mite.

Biology
Twospotted spider mites overwinter as orange-coloured adults under bark or on weeds beneath the tree. Populations often build up on broadleaf weeds, brambles and sucker growth beneath the tree and adjacent areas in the spring. Although twospotted spider mites can overwinter successfully on trees, large numbers often migrate into the tree canopy from the orchard floor in mid to late summer when weeds and other plants on the orchard floor dry up. Twospotted spider mite populations continue to thrive until cool, late summer weather reduces population activity. There are three to five generations each year. These mites are able to disperse over wide areas and from orchard to orchard by wind and air currents. Severe infestations of twospotted spider mite generally occur later than European red mite infestations.

Period of Activity
The twospotted spider mite can be found in apple orchards from the end of tight cluster through harvest.

Scouting Notes
Begin weekly monitoring programs for twospotted spider mites at the 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.

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

Stage of growth

Spray threshold and timing*

Dormant to tight cluster

Eggs present

Petal fall to 21 days after calyx

1st egg hatch and before more than 3 nymphs/leaf

 

5-7 active mites/leaf timed for 50% egg hatch

June to mid July

7-10 active mites/leaf, when approximately 50% of population are nymphs

Mid July to August

10-15 active mites/leaf when approximately 50% of population are nymphs

*Some recently registered miticides are applied slightly earlier than conventional products, at 5 mites/leaf.

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

Management Notes

  • Mite outbreaks in orchards are caused by:
    • Hot dry weather conditions that are favourable to mite 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 such as Typhlodromus pyri (Scheuten), T. caudiglans (Schuster), Amblyseius(=Neoseiulus) fallacis (Garman), Zetzellia mali (Ewing), Agistemus fleschneri (Summers) and Balaustium spp.
  • Other important predators of mites include 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. 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 twospotted spider mite adults.
  • 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.  
  • 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. Consider the following information when managing mites:
    • Miticides are often highly selective. Some may only affect certain types of mites at certain life stages. Be aware of this when selecting a product.
    • Miticides are most effective when applied alone, using recommended rates and high water volumes (>1,000 L of water/ha). 
    • Apply each miticide only once per season to delay the development of resistance. If miticides are needed two years in a row, use products from different chemical families to avoid the development of pesticide resistance.  For more information on the chemical families of miticides, see OMAFRA Publication 360, Guide to Fruit Production.
    • Some newer miticides are slower acting – remember this when applying products and for follow up assessments.  For products with slow knockdown, wait one to two weeks after spraying to determine if the product was effective.
    • See OMAFRA Publication 360, Guide to Fruit Production - Chapter 4 Apples (PDF) or Apple Calendar only (PDF) :