Production and pest update brought to you by the OMAFRA Apple Team: 

Erika DeBrouwer, Tree Fruit Specialist and Kristy Grigg-McGuffin, IPM Specialist

Grower Grind

Ontario is finally seeing some sun and warm temperatures, which has been welcome across the province. Early regions have started chemically thinning, with growers in other regions preparing to utilize the warm weather to their benefit. Planting and mowing continues with some growers considering irrigation shortly.

Growth Stages

Across the province we are seeing variable fruit set and staging across multiple cultivars, this could be due to multiple reason, where most believe it is related to frost injury/damage, winter damage and potentially drought stress from last season.

• Essex & Chatham-Kent – Fruitlet sizing (8-18 mm)
• Lambton, Middlesex, Elgin – Petal fall to fruitlet sizing (8-14 mm)
• Norfolk – Petal fall to fruitlet sizing (8-12 mm)
• Brant, Wellington – Petal fall
• Niagara – Petal fall to fruitlet sizing (8-12 mm)
• Grey – Full bloom to petal fall
• Durham, Northumberland and Quinte – Full bloom to petal fall
• Ottawa Valley – Full bloom to petal fall

Terminal Growth & Fruitlet Sizing

Terminals are growing at the Simcoe Research Station with the following measurements and growth stages

Cultivar	Average ‘King’ Size (mm)	Average Terminal Measurements (cm)
Ambrosia	10.2	9.1
Brookfield Gala	10.9	10.9
Honeycrisp	9.9	11.6

Taxing Thinning

For information regarding thinning please refer to the article Chemically Thinning Apples, Bit by Bit. Here you will find information on weather implications, chemical thinning suppressors and promoters, along with a list of chemical thinning products available for apples. Below are a few highlights:

• Sunny weather increases carbohydrate reserves, making thinning more challenging. Watch the weather and take advantage when you can.
• If you have a light crop load, trees will hold on to their fruit more, suppressing thinner efficacy. Consider your block crop load and make changes based on the average tree.
• Consider nozzle adjustments (off/on) based on crop load, especially if there is frost damage on lower portions of trees. Frost damaged regions of trees can be easier to thin, but if a lot of crop load is on top, be sure to adjust rates and coverage accordingly.

If you have a window to thin, please use it to take off fruitlets incrementally.

Degree (Days) of Separation

Scale

Based on current degree day accumulations, the earliest regions of the province are reaching 1st generation San Jose scale crawler emergence (predicted emergence of 278 DDC).

Once crawler activity (ie., movement to new shoots and developing fruit) begins, this will continue for 4-6 weeks. Registered products including Closer and Sivanto Prime should be applied at the beginning of crawler activity and reapplied 10-14 days later due to the extended generation. Movento is a slow-acting product and should be applied ahead of predicted crawler emergence, again followed up 10-14 days later. Depending on the product, this timing may also have efficacy on woolly apple aphid and/or leafcurling midge.

For a full list of registered products, see San Jose Scale on the Ontario Crop Protection Hub.

Predicted emergence date of first generation San Jose scale, by region (biofix March 1st, base 10C)

Region	Current Degree Day Celsius (DDC)	Predicted Crawler Emergence (278 DDC)
Essex	251 DDC	June 1
Lambton, Middlesex, Elgin	149 DDC	June12
Norfolk	171 DDC	June 10
Wellington	110 DDC	>14 days
Niagara	158 DDC	June 13
Grey	129 DDC	>14 days
Durham, Northumberland	100 DDC	>14 days
Ottawa	111 DDC	>14 days

Apple leafcurling midge

First signs of egg laying was observed this week in the orchards we are monitoring.

Emergence predictions for the 1st generation adults are summarized below. Targeted prebloom products can be applied in blocks with a history of this pest. Otherwise, considering efficacy at petal fall. Target applications between 5 and 50% emergence.

• While Movento is registered for suppression, the timing for leafcurling midge is often earlier than for scale and woolly apple aphid so would have to be chosen based on which pest is of greater concern in your orchard.
• Other petal fall insecticides such as Delegate, Closer and Exirel (and for that matter, Minecto Pro) that may provide some efficacy as well, which could help delay the Movento application.
• Pyrethroids are registered but have greater efficacy earlier to target adult midges and can be very harsh on the numerous beneficial insects that are now active in the orchard.
• Summer oils will also help to smother eggs so long as good coverage is achieved to reach within the newest terminal leaves.

For a full list of registered products, see Leafcurling Midge on the Ontario Crop Protection Hub.

Predicted emergence date of first generation adult apple leafcurling midge, by region (biofix March 1st, base 9C)

Region	5% Gen 1 (76 DDC)	50% Gen 1 (132 DDC)	95% Gen 1 (235 DDC)
Essex	Passed	Passed	Passed
Lambton, Middlesex, Elgin	Passed	Passed	June 4
Norfolk	Passed	Passed	June 2
Wellington	Passed	Passed	June 8
Niagara	Passed	Passed	June 3
Grey	Passed	Passed	June 9
Durham, Northumberland	Passed	Passed	June 12
Ottawa	Passed	Passed	June 9