Apple Rust Mite (Aculus schlechtentali (Nalepa))
Apple rust mite on leaf
Overwintering apple rust mite in crescent of hairs behind bud
Apple rust mite damage to Bramley rosette leaf at mouse ear
Russeting damage to fruits caused by apple rust mite
Apple rust mite is an important secondary pest of apple. A similar species, the pear rust mite, is an important and frequently damaging pest of pear.
Apple rust mite is seldom a problem in orchards where the orchard predatory mite, Typhlodromus pyri, is established The predatory mite should be introduced, by transferring summer prunings in summer to newly planted orchards and to orchards where it is absent.
Pesticides harmful to the orchard predatory mite should not be used except as a last resort, as they cause outbreaks of rust and spider mites.
Rust mites are minute but can be seen with a x20 hand lens and are then readily recognised. They have a simple life cycle, overwintering behind buds in the previous season’s extension growth. Monitoring the number overwintering behind buds in the previous season’s extension growth is important in orchards where a satisfactory and stable balance between the mite and the orchard predatory mite has not been established.
They invade rosette leaves at bud burst and green cluster, causing shrivelling and puckering damage to the outer rosette leaves if present in high numbers.
They colonise the outer surface of the receptacle during flowering and the surface of young fruitlets round the calyx during early fruitlet development. This damage is most important and occurs at low to moderate population densities (1 mite per flower or young fruitlet).
Feeding on developing fruitlets causes russeting round the calyx and on the cheek of the fruit.
Feeding on the undersides of leaves in summer causes browning.
- Diflubenzuron (Dimilin) is specifically recommended for control of apple rust mite but it is at best only partially effective and is unlikely to control severe infestations adequately.
- Spirodiclofen (Envidor) is specifically recommended for control of apple rust mite. Young larval stages are most susceptible.
- A programme of sulphur sprays (various products) at reduced rate (3-5 kg a.i. / ha), applied to control mildew on apple, will suppress rust mite and fruit tree red spider mite. Some apple varieties are sulphur shy (consult the label for details) but are often safe at low rates. However, multiple sprays of sulphur are likely to be harmful to orchard predatory mites, so such an approach is not ideal.
- Clofentezine (Apollo) and tebufenpyrad (Masai) are approved for control of fruit tree red spider mite on apple but are not specifically recommended for control of apple rust mite. When applied for control of fruit tree red spider mite, they may give partial control of rust mite but should not be relied on to control damaging infestations.
- A full approval for spirotetramat (Batavia) on apples for the control of sucking insect pests will help to suppress apple rust mite. It must be applied after flowering and works best when pests are moving from brown wood to green tissue. It will prevent population build-up but does not offer pest ‘knockdown’.
Insecticides, acaricides and fungicides approved for use on apple which are recommended to control apple rust mite, or will offer some incidental control when applied to control other pests.
Choice of insecticides – efficacy factors
|Active ingredient||Trade name (examples)||Class||Selectivity||Recommended for control of||Safety to Typhs|
|clofentezine||Apollo||acaricide, ovicidal||selective||Winter eggs of fruit tree red spider mite on apple||safe|
|diflubenzuron||Dimilin||CSI*||selective||Rust mite in apples and pears, codling, tortrix and winter moth||safe|
|pyrethrins||Spruzit||extract from pyrethrum||broad spectrum||Aphids, apple blossom weevil, caterpillars, spider mites, scale insects||harmful|
|spirodiclofen||Envidor||ketoenol acaricide||selective||Red spider mite, two-spotted spider mite, rust mite, mussel scale||harmful|
|spirotetramat||Batavia||tetramic acid derivative||selective||Sucking insect pests||unclassified|
|sulphur||various||fungicide & acaricide||selective||Scab and mildew on apples and pears. Gall mite on black-currants.||inter-mediate|
|tebufenpyrad||Masai||acaricide and aphicide||selective||Red spider mite in apples and pears. Damson hop aphid||u|
*CSI=chitin synthesis inhibitor
METI = mitochondrial electron transport inhibitor
Choice of acaricides – Safety factors
Read and follow the label before applying any sprays
|Hazards2||Harvest interval(days)||Max. no. sprays or dose||Buffer zoneWidth (m)|
|Anticholin-esterase?||Humans||Fish & aquatic life||Bees|
|spirotetramat||no||h, i||t||u||Start of ripening||2||sm|
|sulphur||no||u||u||u||0||Varies with product||u|
|Keys: d=dangerous, ed=extremely dangerous, h=harmful, i=irritant, t=toxic, u=unspecified or unclassified, sm= statutory minimum*CSI=chitin synthesis inhibitor not recommended for use with hand-held sprayers|
Control in organic orchards
Emphasis should be placed on natural control by the orchard predatory mite Typhlodromus pyri. Application of foliar sprays of fatty acids (potassium soap) (Savona) or pyrethrum (various products), which are harmful to the predatory mite, should be avoided unless absolutely necessary.
- Programmes of sprays of sulphur are often applied for scab and mildew control in organic apple orchards and these suppress apple rust mite.
- Sulphur-tolerant strains of the orchard predatory mite develop eventually but the use of sulphur can lead to outbreaks of fruit tree red spider mite.