Two-Spotted Spider Mite
Beginner
This pest affects:
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Scientific Name
Tetranychus urticae
Identification
Eggs
- clear and spherical, becoming milky-white over time
Nymphs
- Newly hatched individuals are colourless, with spots appear following feeding
- 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
- Produces 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
- Mottling and bronzing to the leaves
- Characteristic webbing on the under surface of the leaf
Often Confused With
European red mite- Nymphs and adults are reddish brown; no webbing produced
Period of Activity
The two-spotted spider mite can be found in peach orchards from the mid- to late- summer.
Scouting Notes
Begin weekly monitoring programs for two spotted spider mites after bloom.
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 two spotted spider mites in counts –total the number of mite eggs, nymphs and adults. Miticides vary in performance against different life stages and species.
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.
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.
Beneficial mites can delay or prevent the need for a miticide application, so be sure to note their presence during monitoring.
Two spotted spider mites are commonly encountered where growers have interplanted strawberries with young peach trees or have peaches adjacent to strawberries.
Thresholds
Spray if 5-10 active mites pest mites are present in July and few beneficial mites are present.
Advanced
This pest affects:
|
|
|
|
|
|
Scientific Name
Tetranychus urticae
Identification
Eggs
- clear and spherical, becoming milky-white over time
Nymphs
- Newly hatched individuals are colourless, with spots appear following feeding
- 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
- Produces 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
- Mottling and bronzing to the leaves
- Characteristic webbing on the under surface of the leaf
Often Confused With
European red mite- Nymphs and adults are reddish brown; no webbing produced
Biology
Two-spotted 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. The rate of development is temperature dependent, being slower in the spring and fall and more rapid during the hot summer months. Hot dry weather conditions favour mite development and populations can increase rapidly under optimum conditions. There are from 5 to 9 generations in the orchard each season, depending on weather conditions.
Although two-spotted 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. Two-spotted spider mite populations continue to thrive until cool, late summer weather reduces population activity. Webbing gives mites and their eggs protection from natural enemies and environmental fluctuations. 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 two-spotted spider mite generally occur later than European red mite infestations.
Natural enemies of mites include predatory mites such as Typhlodromus pyri, T. caudiglans, Amblyseius(=Neoseiulus) fallacis, Zetzellia mali , Agistemus fleschneriand Balaustium spp.
Other important predators of mites include Stethorus punctillum, minute pirate bugs, predatory thrips, lacewings and mullein bugs. Beneficial mites can provide biological control of pest mites. Heavy rain can physically remove and kill many mites, and remove dust that collects on foliage and interferes with mite predators.
Period of Activity
The two-spotted spider mite can be found in peach orchards from the mid- to late- summer.
Scouting Notes
Begin weekly monitoring programs for two spotted spider mites after bloom.
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 two spotted spider mites in counts –total the number of mite eggs, nymphs and adults. Miticides vary in performance against different life stages and species.
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.
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.
Beneficial mites can delay or prevent the need for a miticide application, so be sure to note their presence during monitoring.
Two spotted spider mites are commonly encountered where growers have interplanted strawberries with young peach trees or have peaches adjacent to strawberries.
Thresholds
Spray if 5-10 active mites pest mites are present in July and few beneficial mites are present.
Management Notes
Do not over-fertilize with nitrogen.
Maintain 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 two-spotted spider mites may move into trees. Cover crops will also provide shelter and habitat for predators.
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.
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, Fruit Crop Protection Guide.
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.
For more information on control for two-spotted spider mite, see OMAFRA Publication 360, Fruit Crop Protection Guide:
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Chapter 5 - Tender Fruit calendar: Recommendations for two-spotted spider mites for peaches at Special sprays |
