If the orchard predatory mite Typhlodromus pyri is established and there is a stable equilibrium between the predator and its prey, detailed monitoring of red spider mite populations is not necessary.
- It is prudent to keep an eye out for leaf damage on susceptible varieties (e.g. Discovery, Worcester, Gala).
- If the predator/prey equilibrium is not established, then careful monitoring of the pest is necessary, especially during hot weather when populations and damage can increase rapidly.
Overwintering populations
- Overwintering populations of eggs on spurs and shoots can be counted in winter.
- High numbers indicate high populations were present the previous season and that a balanced equilibrium between pest mites and the orchard predatory mite has not been established.
- An average of more than 5 eggs per fruit bud, or the presence of eggs round vegetative buds in the extension growth, indicates a possible problem.
- However, the percentage of eggs that hatch successfully is somewhat variable and sometimes damaging infestations do not develop even if high numbers of overwintering eggs are present.
In summer
- A sample of at least 25 (preferably 50) expanded leaves should be examined per orchard on each occasion when a pest assessment is done.
- The number of leaves with 4 or more mites (motile stages plus eggs) should be counted.
- If 7 or more leaves in a sample of 50 leaves have 4 or more mites per leaf (equating to a mean of 2 mites per leaf), treatment with an acaricide is justified, particularly if the orchard predatory mite Typhlodromus pyri is absent, or present in only small numbers.
Assessing numbers of Typhlodromus pyri
- When leaves are inspected for numbers of fruit tree red spider mite, the numbers of predatory mites present should be counted at the same time.
- The predatory mite often occurs along the main vein, particularly at the point where the main vein joins with a side vein, sheltering in the groove between the veins and the leaf lamella.
- The predatory mite is a pale whitish-straw colour, sometimes with red gut when a red spider mite has been consumed and is pear shaped with a smooth body with 17 pairs of setae.
- It often moves rapidly over the leaf.