Apple Pest Update: San Jose Scale

The second generation adult flight for San Jose scale is peaking in the early regions of the province. Based on degree day models, crawler emergence for this generation has started from Essex to Norfolk Counties. It is anticipated to begin east of Toronto and Georgian Bay in the coming weeks (Aug 19 and on).

In previous years, crawler emergence has generally begun late July to early August. This year, activity seems to be approximately one week behind average in some monitoring orchards. There has also been extended 1st generation crawler activity resulting in an overlap of generations. As a result, even those orchards that applied back-to-back sprays are seeing higher than expected fruit damage. It’s likely the residues from these sprays were depleted before the end of crawler emergence or were wash-off in those regions that have experienced heavy rain events.

Adult San Jose scale trap numbers are increasing across the province as the 2nd generation for this pest begins

Fruit damage caused by San Jose scale. Note the characteristic red halo surrounding the scale insect.

Those that have a history of damage from this pest may want to consider managing the 2nd generation to prevent fruit damage close to harvest, especially since activity can continue well into September. Registered products include:

• Movento – As this is a slow-acting product, it may be too late for early regions. However, those blocks in Georgian Bay and east of Toronto that didn’t use Movento earlier could apply over the next 2 weeks. Will also have efficacy on woolly apple aphid.
• Sivanto Prime – Use with oil (0.25% vol/vol)
• Closer – Use high labelled rate for effective control. Will also have efficacy on woolly apple aphid at high rate.
• TwinGuard – This product contains Delegate. Do not use if this was used previously for other pests active at this timing.

For good resistance management, always rotate to a different chemical group than what was used for the earlier generation.

As mentioned earlier, crawler activity is typically 4-6 weeks. In previous years, I have seen new scale damage on Ambrosia at the end of September. Applying two consecutive sprays 14-days apart will extend the length of coverage to avoid this late-season damage. However, be aware of the preharvest interval particularly on any early varieties. If you are planning to make one application only, you may want to consider holding off a week or two from start of predicted emergence timings to target peak crawler activity. There is the possibility of fruit damage occurring during the gap in spray timing, particularly in a year like this where generations are overlapping.