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

Not much has changed from our previous post (other than maybe a bit more sunshine and some double digit weather – finally!). The cool temperatures have continued over the past week, with some cold night in certain regions and pockets within orchards. There has been some movement in growth staging, but it has slowed due to the cool temperatures. Regions are starting to even out in staging given the continued cool weather over past week.

Growth Stages

• Essex – Early bloom
• Chatham-Kent – Pink to early bloom
• Lambton, Middlesex, Elgin – Pink to early bloom
• Norfolk – Pink to early bloom
• Wellington – Pink to early bloom
• Niagara – Pink to early bloom
• Grey – Tight cluster
• Durham, Northumberland and Quinte – Tight cluster to pink
• Ottawa Valley – Tight cluster

Cool Progression

Temperatures across the province over the past week have been variable, below are values and a map showcasing the minimum temperatures reached across the province:

• Essex – low of +1.2°C, May 2
• Chatham-Kent – low of +2.9°C, May 2
• Lambton, Middlesex, Elgin – low of +0.4°C, May 3
• Norfolk – low of +1.1°C, May 2
• Wellington – low of -3.8°C, May 3
• Niagara – low of +0.5°C, May 3
• Grey – low of +3.2°C, May 2
• Durham, Northumberland and Quinte – low of -3.3°C, May 3
• Ottawa Valley – low of +0.2°C, May 1

Although cool temperatures have been the recent norm, GDDs are still accumulating, check out what’s happening across the province in the chart below.

GDD Over Time (base 5^oC, starting January 1 as of Julian Day 127)

Region	2026 Cumulative GDD	5-year Average GDD	10-year Average GDD
Essex	337	219	200
Chatham-Kent	178	–	–
Lambton, Middlesex, Elgin	216	174	158
Norfolk	229	213	247
Wellington	154	136	114
Niagara	210	–	–
Grey	133	144	119
Durham, Northumberland and Quinte	117	133	109
Ottawa Valley	130	115	108

The F Update

Frost damage has been noted in multiple regions given challenges over the weekend with lower kings and laterals showing dead tissues.

Consider evaluating for frost damage utilizing the methods found here: Evaluating Frost Damage on Buds in Tree Fruits

A Blight Idea

If you’re not already watching the ONTARIO FIRE BLIGHT PREDICTION MAPS, now is the time to key an eye out. As of yet this year, low heat unit accumulations have kept risk relatively low (see more details below), which is why most areas remain at Low to Caution risk ratings. There is potential things will start to warm up by the end of next week and with potential rains plus the start of bloom for many in the coming days, fire blight risk may also take a big jump.

Fire Blight Prediction Maps

A reminder, the risk of fire blight infection is possible if the following conditions are met:

1. Flowers are opened and/or are opening – There is no risk of infection if bloom is not present in the orchard despite the fire blight maps stating caution to extreme; however, keep an eye on any early signs of bloom as it can happen quickly.
2. Enough heat units have accumulate based on forecasting models – The fire blight maps use Cougarblight but this applies to MaryBlyt as well. Similar to degree days, daily temperature is accumulated and must reach a certain point before risk increases.
3. A wetting event is predicted – Any type of wetting event will wash the bacteria into the open bloom including rain, dew or even the artificial rain shower you create with the sprayer during critical infection periods.

**Frost-injured blooms can still be at risk of infection. Damage to pistil and ovary does not likely have an effect on entry of the bacteria into the flower as bacteria are washed into the nectaries, or flower cups. As well, frost can cause wounding and damage to the base of the petals or tender wood surrounding blooms. This wounding creates another point of entry for the fire blight pathogen should bacterial cells be transferred to this surface via rain, wind, insects or contaminated equipment.

Very Hungry Caterpillar

As mentioned in last week’s What the Crop?! Apple Update: May 1, 2026, the first signs of caterpillar damage can be found on growing terminals and fruit buds. In general, an insecticide is usually recommended when the action threshold of 12-15% infested terminals or buds is observed. For obliquebanded leafroller, this threshold is lower at 1-2% infested terminals or buds. Management is most effective when larvae are young.

Degree (Days) of Separation

Apple leafcurling midge

Overall, first generation apple leafcurling midge has had a slow start. Some of the early areas are just beginning to see flight pick up, but still no signs of egg laying have been observed yet this year.

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.

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	May 20
Chatham-Kent	May 17	>14 days	>14 days
Lambton, Middlesex, Elgin	Passed	May 20	>14 days
Norfolk	Passed	May 20	>14 days
Wellington	May 18	>14 days	>14 days
Niagara	Passed	>14 days	>14 days
Grey	May 18	>14 days	>14 days
Durham, Northumberland	>14 days	>14 days	>14 days
Ottawa	May 20	>14 days	>14 days

Scale

Based on current degree day accumulations, the 1st generation San Jose scale crawler emergence is predicted to begin across the province in several weeks (predicted emergence of 278 DDC).

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	147 DDC	>14 days
Chatham-Kent	33.5 DDC	>14 days
Lambton, Middlesex, Elgin	74 DDC	>14 days
Norfolk	77.5 DDC	>14 days
Wellington	43 DDC	>14 days
Niagara	68 DDC	>14 days
Grey	53 DDC	>14 days
Durham, Northumberland	26 DDC	>14 days
Ottawa	29.5 DDC	>14 days

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 at least 1 week prior to 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.

San Jose scale is not the only scale pest that can be found in orchards. Oystershell scale populations have been increasing in a number of blocks across the province. Crawler activity for this species is often about 1 week prior to San Jose scale emergence, occuring 2-3 weeks after petal fall. There is only one generation of oystershell scale per year, but crawler activity can continue throughout the summer. Management options would be similar to San Jose scale.