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

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

Grower Grind

Apple continue to grow, with anticipated lower croploads than the norm due to the cold winter and the challenging spring. Fruitlets are hanging on, and thinning had been successful in some areas, but not so much in others. The weather has been cooler across the province, with terminal buds beginning to set in early regions.

Growth Stages

Fruitlets continue to grow with some drop occurring. Ambrosia is light, Honeycrisp is temperamental and mixed for cropload (as always), while Gala seems to have a decent crop.

Terminals are starting to show bud set at the Simcoe Research Station, although this could revert, considering the season has been full of surprises.

At the Simcoe Research Station, king fruitlets and terminals measuring the following:

	Honeycrisp	Ambrosia	Gala
Fruitlet Size	38.0mm	37.2mm	36.9mm
Terminal Growth	18.1cm	26.5cm	24.8cm

To Hedge, or not to Hedge?

If wanting to hedge, or are considering hedging, timing is critical as your goal and result change. Goals surrounding hedging are commonly one or two of the following:

• Reducing tree height
• Maintaining alley space
• Improving light penetration
• Reducing labour requirements
• Fruiting wall goals, potentially for mechanization integration

It is important to remember that hedging:

• Is non-selective.
• It changes canopy architecture.
• It changes light distribution.
• It changes vigor distribution.

Dormant Hedging

This timing provides trees with keeping the canopy narrow and the ability to see the whole tree structure. If dormant pruning, expect vigorous growth the following spring. This is great for trees that need a flush of growth, are weaker trees and/or need to fill space.

Early Summer Hedging

This timing is during active shoot growth and often has the the strongest regrowth response. Trees will try to replace the cut portions, resulting in multiple replacement shoots. Early summer hedging makes sense when multiple passes are going to occur and the grower is aware the growth is stimulated.

Post-Solstice or Post-Terminal Set Hedging

Shoot growth has slowed at this point, which is great for managing the canopy as regrowth isn’t as substantial compared to early summer or dormant hedging. In Ontario, this timing works well because of our latitude, as:

• Light interception is often limiting.
• Canopy shading reduces bud quality.
• Growing seasons are shorter.
• Late-season regrowth can be problematic.

Always follow-up with pruning to clean up your hedging cuts. This allows for double checking cuts for better tree sealing and more resilient to pests.

Feeling Scabby?

With apple scab now present in several orchards, management has shifted to limiting further spread, especially to fruit and reducing sporulation from existing lesions. At this stage, “burnout” activity is aimed at suppressing viable spores and slowing secondary infection cycles.

The table Characteristics of Apple Scab Fungicides provides an overview of some of the scab products available and their post-symptom, or burnout activity.

Unfortunately, this information has not been made available to me for all products which is why you may not find the product you are looking for on this list.

• Products like Buran or Cyclone Plus act as dessicants and dry up the lesions, reducing spore viability.
• Surface sterilents such as Oxidate will kill any active spores on the tissue surface immediately on contact.
• Where active lesions are present, use of resistance-prone fungicide groups (e.g., Group 1, 3, 7 and 11) should be avoided, where possible. If used, tank-mix with a protectant fungicide like a Group M, BM or 29, and rotated with other modes of action as part of a strong resistance management program.

Syllit is registered on apples and historically provided strong post-infection activity. However, there is well-documented resistance to Group U12 (dodine) in Ontario scab populations, and its use beyond tight cluster is not recommended.

Finally, where lesions are present, orchards remain at risk of secondary infection. Conidia produced from existing lesions can continue to infect leaves and fruit throughout the season during wetting events. Keep a consistent protectant program, particularly when conditions are conducive to infection. The goal is to contain existing infections while preventing new ones.

Barking Up the Wrong Tree

Dogwood borer trap catch has started to increase in early regions this week in orchards with a history of problems with this pest. Adult emergence of this single generation will continue through to early September but management often targets peak flight or shortly after, as explained below.

Dogwood borer is a clearwing moth whose larvae feed beneath the bark of weakened or injured areas on the tree. Throughout their activity, females will lay eggs on the surface of burr knot formations, pruning cuts, cankers, and wounded bark. This pest overwinters as partially developed larvae within these feeding sites.

As a result, finding larvae in trees at this time of year is expected – they are not the result of recent egg laying, but rather individuals from last year’s generation that survived the winter within the tree.

Over the coming weeks, these larvae will resume feeding briefly before pupating within their galleries and emerging as adult moths.

In Ontario, adult flight commonly begins in June with trap catch increasing through July and into August. The increase in trap catch being observed now reflects this ongoing adult emergence and indicates active egg laying is underway or imminent. Eggs are laid on bark surfaces, particularly near burr knots or wounds, and newly hatched larvae quickly bore into these protected sites to begin feeding. Because of the extended emergence period, there can be overlap between the overwintering generation and summer generation of larvae at different developmental stages throughout the summer.

Currently, pyrethroids, Altacor, Delegate and Rimon are registered for trunk application for control of borers:

• Pyrethroids at this timing can have significant impacts on the natural enemy complex. If used, these products act primarily by contact, with some secondary action by ingestion and have a fairly short residual. For this reason, application should be made at the beginning of egg hatch, or a few weeks following peak flight.
• Rimon 10 EC is an insect growth regulator (IGR) that must be absorbed by eggs or ingested by larvae to be fully effective. The optimal timing for this product is around 25-75% egg laying, or approximately peak flight.
• Delegate and Altacor must be ingested by the larva in order to work; therefore it must be applied at the beginning of egg hatch, or a few weeks following peak flight.
• With all products, a repeat application 14 days later is recommended.

For more information on registered products for dogwood borer, see the Dogwood Borer on Ontario Crop Protection Hub.

An alternative management option for dogwood borer next year is the mating disruption product, Isomate DWB. Dispensers (250-375 dispensers/ha) should be applied before adult borer emergence, or approximately the end of May. Researchers from Rutgers and Cornell University feel that Isomate DWB can adequately control light to medium dogwood borer infestations and give equal control to trunk drenches after multiple years of use.

Degree (Days) of Separation

Scale

Crawlers have been observed on monitoring tape in Norfolk County. At this point, all regions have reached the degree day timing for crawler activity (predicted emergence of 278 DDC). The second generation crawler emergence is predicted to begin at 806 DDC, which is typically early to mid August.

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	503 DDC	Passed
Lambton, Middlesex, Elgin	371 DDC	Passed
Norfolk	401 DDC	Passed
Wellington	297 DDC	Passed
Niagara	395 DDC	Passed
Grey	320 DDC	Passed
Durham, Northumberland	312 DDC	Passed
Ottawa	336 DDC	Passed

Apple leafcurling midge

Adult flight for the second generation of apple leafcurling midge will begin in all regions over the next week. Emergence predictions for the 2nd generation adults are summarized below. If leafcurling midge is an ongoing issue in your orchard, consider products that have efficacy for this pest. Ideally timing is between 5-50% emergence.

For a full list of products with efficacy on leafcurling midge, see Leafcurling Midge on the Ontario Crop Protection Hub.

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

Region	Current Degree Day (DDC)	5% Gen 2 (430 DDC)	50% Gen 2 (556 DDC)	95% Gen 2 (701 DDC)
Essex	581	Passed	Passed	July 2
Lambton, Middlesex, Elgin	431	Passed	July 3	>14 days
Norfolk	466	Passed	July 1	>14 days
Wellington	355	June 30	>14 days	>14 days
Niagara	461	Passed	July 2	>14 days
Grey	376	June 29	July 8	>14 days
Durham, Northumberland	364	June 30	>14 days	>14 days
Ottawa	392	June 27	July 7	>14 days