Apples Diseases Insects Pest Management Weeds

What the Crop?! Apple Update: April 28, 2023

Cooler temperature across the province has slowed growth and pest activity this week, but could see a significant scab infection period over the weekend

Production and pest update brought to you by the OMAFRA Apple Team: Erika DeBrouwer, Tree Fruit Specialist and Kristy Grigg-McGuffin, IPM Specialist

Growth Stages

The sudden pop of warm weather early April pushed apples forward in certain regions of the province, but with the cool weather these past few weeks, things have really slowed down and levelled out growth staging throughout Ontario. Most orchards are at tight cluster, while the earliest regions are showing signs of pink.


Some growers may notice discolouration (reddish/purple perimeter) in the leaves of various cultivars. This can most likely be attributed to the cool weather we have been experiencing. Extension specialists and consultants have referenced the accumulation of anthocyanin (reddish/purple colour) as a trees natural process to further withstand cooler temperatures.

Various regional study groups in the province held their first meetings of the season recently. Some points of discussion included:

  • Pre-emergent herbicide applications for new plantings – stay tuned for an article on this topic by OMAFRA’s Weed Specialist, Kristen Obeid.
  • Pruning and planting continues throughout the province.
  • Frost protection was also a hot topic, where growers stated the use of zinc and stress protectant products would be used, along with fans, drains, etc.
  • Most regions stated that cropload isn’t nearly as high as last year, but still good overall. Honeycrisp seem to have a decent cropload as well throughout Ontario.


Most areas have now reached (or are very near) the accumulation of 125 degree days since green tip where we start to see rapid maturation of ascospores. With the forecasted weather predicting rains over the weekend and into early next week, we are entering into a potentially major apple scab infection period. Average temperatures look to be around 6 to 10C, which only requires 11-18 hours of leaf wetness for a primary infection to occur. For more information, check out Relationship of Temperature and Moisture to Apple Scab Infection.

Keep good fungicide coverage throughout this infection period. If there are any concerns about residue wash-off, you may want to consider going in after the rains have stopped with a post-infection, or kickback product. Refer to Characteristics of Apple Scab Fungicides for more information.

  • Cooler weather products that may offer some kickback protection include Syllit (do not use beyond tight cluster), Scala, Inspire Super, Luna Tranquility and Buran.
  • Other products belonging to Groups 3, 7 or 11 can also be used, especially if things are further along in development and more broad-spectrum disease control is needed.
  • Where possible, tank-mix systemic fungicides with a protectant such as a Group M (mancozeb, captan, folpet).
  • Allegro does not offer post-infection activity.

Fire Blight

With bloom quickly approaching, the Ontario fire blight prediction maps are now being updated 3 times per week until petal fall is over in all areas of the province.

These interactive maps show the 7-day predicted risk based on the Cougar Blight model. Growth stage is not considered in this prediction – if there are no open blossoms in the orchard, there is no risk of infection!

Now is the time to apply prebloom fire blight protection products such as Lifegard or Regalia Rx (replacing Regalia Maxx) if these are being considered. These products work by boosting the immune response of the tree to better fight off disease, also known as System Acquired Resistance (SAR) or Induced Systemic Resistance (ISR). Because of this mode of action, these products should be proactively applied in advance to conditions conducive for disease development to allow time for the immune response to kick in. Note, Lifegard is toxic to bees so cannot be applied during bloom or if hives have already been brought into the orchard.

Spring-Feeding Caterpillar

For the most part, the cool weather has kept insect activity very low. However, this week there have been a few signs of early spring-feeding caterpillar damage, in particular leafrollers. Look for signs of leaf feeding, rolled terminal leaves and webbing.

When scouting between tight cluster to petal fall, check 5 terminal shoots and 5 fruit buds in 10 trees (50 terminals and 50 fruit buds in total). Control is typically warranted when 12-15 terminals and buds are infested. Click here for registered prebloom control products for spring-feeding caterpillar.

Apple Leafcurling Midge

Another insect pest we commonly start to see an increase in activity at tight cluster to pink is apple leafcurling midge. With the rains and cool weather, adult emergence has been quite low to date. Even in the earliest regions of the province, based on the degree day model for leafcurling midge, 50% adult emergence of the first generation will not be reached by the time we are likely seeing bloom (as shown in table below).

While in other years, a prebloom insecticide may have provided some efficacy against this pest, emergence may be too delayed for a targeted application to be worthwhile. Instead, consider leafcurling midge efficacy when selecting your petal fall insecticides.

Predicted emergence date of first generation adult apple leafcurling midge, by region (biofix March 1st, base 9C)
5% Gen 1
(76 DDC)
50% Gen 1
(132 DDC)
95% Gen 1
(235 DDC)
May 10
>14 days
>14 days
May 12
>14 days
>14 days
May 13
>14 days
>14 days
>14 days
>14 days
>14 days
>14 days
>14 days
>14 days
>14 days
>14 days
>14 days

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