Production and pest update brought to you by the OMAFRA Apple Team: Erika DeBrouwer, Tree Fruit Specialist and Kristy Grigg-McGuffin, IPM Specialist
Fruitlets continue to size in all regions. Growers are noting that fruit is larger than normal across the province, with varieties and regions ranging in size, but most are around the 50mm size. Terminal bud set has begun.
The spring brought us some challenges regarding the minimal rainfall, while in the ‘heat’ of summer, we have seen a range of weather. Regions across the province have seen variable weather consisting of heavy rainfall, severe winds, and some hail. For more information on rainfastness of insecticides and fungicides, see the July 7th What the Crop?! update:
Growers continue to hand thin their trees. Generally, growers estimate harvest to be a few days ahead of normal, but as the season progresses this may change.
With apple fruitlets coming closer to harvest, some growers have noted concerns about sunburn. Therefore, here are rules of thumb regarding the topic.
When Sunburn Occurs
Sunburn can occur at various temperatures and is affected by many environmental factors but can be worse if there is a week of cool, windy, overcast weather followed by a hot (over 30°C) calm day with full sunshine. The fruit surface can be 14 to 17°C hotter than the air temperature, where sunlight, calm wind and low humidity contribute to this increase. Water stressed trees are even more prone to sunburn damage.
Types of Sunburn
Type of Sunburn
What Is It?
How Does It Happen?
What Happens to the Fruit?
When the fruit surface temperature exceeds 50°C for as little as 10 minutes, causing cell death.
Caused by excessive heat and is exacerbated by low humidity.
Cell death occurs, causing brown or black lesions.
Combination of UV-B radiation and high fruit surface temperature causing degradation of cell membranes.
Sunburn browning can contribute to storage/delayed sunburn.
Typically occurs between fruit surface temperatures of 45 – 49°C, although this can change based on the variety (i.e. Honeycrisp is more sensitive than Red Delicious or Braeburn).
Higher risk occurs between the hours of 11am and 5pm when maximum daily air temperature and mean maximum hourly temperature are high.
Yellow, bronze or brown spot develops on the sun-exposed side of the peel but may not appear for a few days.
Shock exposure to visible light due to light intensity, which can occur at low temperatures (17°C).
Risk factors include hand thinning, tree training, selective picking, summer pruning, branch movement and postharvest transit.
Photo-oxidative sunburn has been seen in the province where areas that have had ‘overcast’ conditions due to the smoke, with a sudden break and intense sunlight could have led to fruit sunburn.
Bleaching and eventual darkening of the peel.
Symptoms develop after harvest within the first few months of cold storage.
Exposure to excess heat and light stress during the growing season.
Fruit appears normal at harvest but develop brown discolouration during storage.
Strategies to Mitigate Sunburn
Definition & Use
Overhead irrigation that reduces air temperature due to water vapourization
– Water stains on fruit
– Root flooding
– Expensive to install, maintain and operate
– Access to water source during peaks
Overhead netting that reflects/absorbs sunlight
– Can reduce effects of wind / hail damage
– Colour of net can influence growth, colour and quality
– Learning curve for deployment and removal
– Colour of net can influence growth, colour and quality
Application of materials on fruit to create a physical barrier
– Spot treatment
– Not as effective as other options
– Reapplication often required
Other preventative measures include:
- Summer pruning – should be performed on cool days with 3 or 4 days remaining cool in the forecast.
- Adequate moisture – should be provided to trees to encourage resilience during periods of stress.
- Harvest management – fruit should be moved quickly out of the sun, preferably into storage as soon as possible.
With terminal bud set, the cell walls thicken, stomata on the shoot stem are no longer active and the base of the shoot starts to harden off and form bark. All of which results in a significant reduction in fire blight movement. This is a good time to start to prune out fire blight strikes if you haven’t been already. Choose days of dry weather and leave the pruning cuts in the row middles to dry up before mulching them down.
Looking for a quick refresher for pruning fire blight? An oldie, but a goodie – check out this video from Dr George Sundin, Michigan State University:
The unsettled weather we are experiencing may continue to bring hail, strong winds or heavy rains that could still trigger trauma blight from terminal set until harvest. These could be very isolated events, occurring in one area but not another nearby. Assess for signs of damage in all blocks following any storm.
Be sure to apply Streptomycin (PHI 50 days) or 0.5-0.8% Cueva as soon as possible after the trauma event, especially if foliage damage is extensive or fire blight is known to be active in the orchard (ie., cankers, etc). New research is now suggesting ideal timing is 4 to 12 hours after a storm. Anything applied later runs the risk that the bacteria will have already established and begun to grow, reducing the efficacy of the product.
These hot, humid days and sporadic storms are also ideal conditions for summer disease, such as bitter rot, fly speck and sooty blotch. Be sure to keep up with regular fungicide applications while these conditions last. For more information on summer disease management, see the July 7 What the Crop?! update.
Apple maggot have been caught throughout the province, though catch is very sporadic for many. Emergence is closely linked to soil moisture with flushes in flight often following periods of significant rainfall loosening soil. Those areas receiving good amounts of rain with the events rolling through may see a flush of apple maggot emergence in the coming days to weeks.
With catch on yellow sticky boards, it is important to differentiate between male and female adult flies. Males generally begin emerging before the females, but by peak emergence (August), the sex ratio is about 1 to 1.
Timing for management depends on the type of trap:
- Sexually immature males and females are attracted to the yellow sticky boards, which mimic nectar sources. Insecticides are not needed until 7-10 days after first fly, particularly a female, is captured.
- Sexually mature females ready to lay their eggs are attracted to red spheres, which mimic ripe apples and indicate an insecticide should be applied immediately as damage is imminent.
Imidan has worked well for years as a border spray option for many growers. However, with the new label changes, all hand thinning activities must be finished before Imidan can be used. The main reason why Imidan can be used effecively as a border spray is its activity as a contact adulticide, killing adults as they fly into the orchard from surrounding areas. Not all alternative products registered for apple maggot have this same activity and therefore are not recommended in a border spray program.
In the table below, adapted from Dr John Wise at Michigan State University (2021), summarizes the characteristics of apple maggot products. Organophosphates (Imidan) and neonicotinoids (Assail, Calypso) are the only insecticide groups that have strong long-lasting activity on the adults as well as a curative effect on the eggs and larvae due to their ability to penetrate into the flesh of the fruit.
Summary of Insecticides Used to Control Apple Maggot
Mite Flaring Potential
egg, larva, adult
Ambush, Danitol, Perm-Up, Pounce, Ship, Up-Cyde
Aceta, Assail, Calypso, Cormoran, Theme
Egg, larva, adult
Good – Excellent
Delegate, TwinGuard, GF-120 Fruit Fly Bait
Altacor, Exirel, Harvanta, Vayego
Japanese beetle damage can also be easily found now in many regions. The characteristic leaf skeletonization is quite distinct. Look for damage and congregations of this pest at the top of the canopy as damage often moves down the tree. Honeycrisp is often the most preferred variety.
Most insecticides applied for codling moth should have good efficacy on Japanese beetle; however, the tendency of these beetles to move in from surrounding areas may make multiple applications necessary. If applying a control product, target timing for early morning while beetles are still relatively inactive on the tree. Once feeding begins, the sex pheromones emitted by females combined with what numerous studies believe to be feeding-induced plant volatiles attract more beetles to congregate in the feeding area. Achieving knockdown before this occurs could help reduce the number of individuals coming into the orchard from surrounding areas.
Good weed control in and around the orchard will also help reduce Japanese beetle pressure. Populations tend to be more abundant in orchards where there is poor control of wild raspberry, blackberry, Virginia creeper and wild grape.