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

Fruitlets continue to drop, with most growers having to hand thin to clean up particular cultivars. Most areas across the province were looking dry with many regions irrigating, but with the sporadic storm certain areas were able to shut off their irrigation for the time being.

Growth Stages

Growers are noting fruit drop across the province, with some going in to hand thin – specifically hard to thin cultivars like Gala.

• Essex & Chatham-Kent – Fruit set (20+ mm)
• Lambton, Middlesex, Elgin – Fruit set (20+ mm)
• Norfolk – Fruit set (20+ mm))
• Brant, Wellington – Fruit set (20+ mm)
• Niagara – Fruit set (20+ mm)
• Grey – Fruit set (20+ mm)
• Durham – Fruit set (20+ mm)
• Northumberland and Quinte – Fruit set (20+ mm)
• Ottawa Valley – Fruit set (20+ mm)

At the Simcoe Research Station, king fruitlets and terminals are sitting at the following:

	Honeycrisp	Ambrosia	Gala
King Fruitlet Size	34.8mm	28.6mm	29.7mm
Terminal Growth	15.7cm	15.8cm	18.1cm

The Heat Is On (Or Is It?)

Growing Degree Day Springs Into Action

Thankfully we have recently seen brighter days compared to the previous month. GDDs have been slow to accrue due to the low temperatures across the province at the end of May and into June.

Delving into the GDDs with a baseline temperature of 5°C and using Brantford as an example (Figure 1), we note the following:

• April followed typical GDD accumulation
• May was above average for accumulation, until the end of the month (around Julian day 145)
• June was lower than the 5- and 10-year GDD accumulation
• Currently, Brantford is 16 GDD lower than the 5 year average, but is on par with the 10-year average (Table 1)

Julian Day	2025	2024	2023	5-year	10-year
90	26	33	2	24	16
120	131	134	114	110	91
151	349	460	360	374	360
170	603	704	595	619	604

Looking at the GDDs with a baseline temperature of 10°C (Brantford as an example, Figure 2) we note the following:

• April followed typical GDD accumulation
• May was above average for accumulation, until the end of the month (around Julian day 140)
• June continues to be lower than the 5- and 10-year averages
• Currently, Brantford is 30 GDD lower than the 5-year average, and 25 GDD lower than the 10-year average (Table 2)

Julian Day	2025	2024	2023	5-year	10-year
90	4	5	0	3	2
120	35	28	46	26	20
151	119	200	156	157	154
170	278	349	295	309	303

Be sure to check out a more in-depth and wider provincial review in the Spring Issue of ONcore (to be released shortly)!

Breezy Does It

Strong winds continue to persist over the growing season, which can cause damage of leaders, limbs, fruit drop, and even breakage of the graft union.

The best way to address wind issues is by understanding your landscape and how it can affect your orchard

Hills, valleys, dense vegetation, and fencing all factor into wind patterns and aerodynamics. Be sure to factor these in before planning or making changes to your orchard.

To mitigate wind issues consider the following:

• Windbreaks on windward side of orchard trees
• Orientation of rows, along the path of prevailing winds
• Support trees directly after planting
• Maximize strength of trellis systems and anchors
• Prune trees to fruit to hang away from limbs
• Prune limbs that may cause rubbing

For more information check out the following resources

• Weather Risks: strategies to Mitigate Wind Damage
• Designing and Caring For Windbreaks

Feelin’ the Burn

With reports of fire blight continuing to come in, a quick reminder on managing trauma blight during times of unsettled weather.

Check out last week’s ‘What the Crop?! Apple Update: June 13, 2025’ for strategies to manage fire blight once it’s in the orchard.

The unsettled weather we are experiencing may continue to bring hail, strong winds or heavy rains that could trigger trauma blight, especially with the amount of bacterial-laden ooze out there.

Be sure to apply Streptomycin (PHI 50 days), 0.5-0.8% Cueva, or Oxidate as soon as possible after the trauma event (ideally 4-12 hours after), especially if foliage damage is extensive or fire blight is known to be active in the orchard (ie., cankers, etc). Anything applied later runs the risk that the bacteria will have already established and begun to grow, reducing the efficacy of the product.

Streptomycin will provide kickback activity for any infection already in the tree – to an extent, of course – whereas, Cueva and Oxidate are surface sterilants only (ie., will just kill the bacteria on the tissue surface before infection occurs).

Following a trauma event, continue with an immune boosting program, using products such as Regalia or Lifegard to help the tree better fight off infection. Other products such as Buran or Cyclone Plus can help as dessicants to slow the spread of shoot infection.

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

Barking Up the Wrong Tree

Dogwood borer trap catch has started to peak in early regions this week in orchards with a history of problems with this pest. Adult emergence will continue through to early September but management often targets peak flight or shortly after, as explained below. Throughout their activity, females will lay eggs on the surface of burr knot formations, pruning cuts, cankers, and wounded bark, after which the larvae use these as entry points to bore into the tissue to begin feeding.

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.
• 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

For more information on registered products or those with efficacy against scale, see the San Jose scale on Ontario Crop Protection Hub.

San Jose scale degree day accumulations based on March 1st biofix and base temperature 10C

Region	Current Degree Day Celsius (DDC)	Predicted Crawler Emergence (278 DDC)
Harrow	410 DDC	Passed
London	301 DDC	Passed
Delhi	341 DDC	Passed
Grimsby	310 DDC	Passed
Clarksburg	226 DDC	June 23
Durham	257 DDC	June 22
* as of June 19, 2025

Crawlers have been observed on monitoring tape in Norfolk County this week, which aligns with the forecasted emergence.

Apple leafcurling midge

Early regions are entering into the second generation adult flight. Emergence predictions for the 2nd generation adults are summarized below. See May 23rd What The Crop?! for management options.

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

Region	5% Gen 2 (430 DDC)	50% Gen 2 (556 DDC)	95% Gen 2 (701 DDC)
Harrow	Passed	June 24	July 2
London	June 24	July 2	>14 days
Delhi	June 21	June 29	>14 days
Grimsby	June 23	July 1	>14 days
Clarksburg	July 2	>14 days	>14 days
Durham	June 29	>14 days	>14 days
*as of June 19, 2025