Oystershell scale - cultural control

Oystershell scale occurs on a wide range of host plants as well as in the apple orchard itself. A significant part of fruit infestations in summer originate from wind-blown scale crawlers moving from shelter and other host plants. The presence of scale on the bark of these plants can be checked at any time of the year (it’s easiest in winter when deciduous plants have no foliage) to find those with the highest populations. Once this is known, there are four ways of reducing the problem:

1. Removal of the shelter or other host plants.
2. Topping of shelter. This can reduce the numbers of crawlers in the shelter, reduce the distance they are likely to be carried by the wind, and assist with ensuring better spray coverage if the shelter is sprayed.
3. Spraying of shelter in early spring and/or summer. Selective chemicals are available for use in IFP, and oils can be used by both IFP and organic growers. High volume spraying is vital to obtain good coverage. Shelter should be sprayed from both sides (or if this is not possible, from both directions on one side ).
4. Replacing shelter with a more scale-resistant tree or variety.

Some information is available on the resistance of different shelter species and selections to scale insects, and on the host plants most commonly infested with scale insects in the different regions of New Zealand. Significant risk of scale infestation in pipfruit orchards can come from neighbouring stonefruit, particularly if trees are left unsprayed. Stonefruit trees have been found highly infested with scale within some pipfruit orchards. Growers are strongly recommended to include scale control in stonefruit as part of their management plan for the whole orchard.