Apple Pest Update: Aug 14, 2020

Table of Contents

San Jose scale

The second generation adult flight for San Jose scale has peaked in Norfolk orchards being monitored. Based on degree day models, crawler emergence for this generation has started in all areas of the province.

Damage from the 1st generation crawler activity can be found. It is possible that there may be overlap of the generations due to a rather extended crawler activity of that 1st generation. As a result, even those orchards that applied back-to-back sprays could see higher than expected fruit damage. It’s possible 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.

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 week to target peak crawler emergence. 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.
If Purespray Green Spray Oil is still being used for summer mite control, this may provide some suppression of scale crawlers.

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.

Apple maggot

Apple maggot activity continues in many orchards. See the July 25th Apple Pest Update for more information on biology and characteristics of apple maggot products. Consider the residue length, especially with late-maturing varieties to ensure protection is maintained until harvest. Also keep in mind, Imidan is the only maggot product where efficacy has been studied using border sprays. This approach is not recommended for other products.

Fruit rot

Fruit rot lesions have started to develop in some varieties such as Empire, Idared, Gala and Ambrosia. A high rate of Supra Captan/Maestro will provide efficacy against black rot and bitter rot. Pristine, Allegro and Granuflo-T are also registered; however, other fungicides registered for scab may also provide efficacy on fruit rot including Senator and Flint. Watch preharvest interval restrictions for some of these products.

Applications should be made every 10-14 days if there is a history of rot in the orchard, but shortened to 7 days if frequent rain is experienced. If possible, time an effective fungicide application just prior to a rain to prevent fruit from rain-splashed spores. Always rotate products to reduce the potential for resistance development.

Black rot lesions developing on Idared apples.

Scab

Apple scab lesions can be found in some orchards. New leaf infection has been found in some of these blocks. Be sure to maintain a regular program until harvest if scab has been an issue. With rain showers, spores can be splashed to new tissue. Pinpoint scab becomes a particular concern at this time.