Ambrosia apple in late July
Apples Diseases Insects Pest Management

Apple Pest Update: July 25, 2020

Terminal bud set slowing down fire blight and powdery mildew activity, conditions ideal for bitter rot infection, apple maggot flight remain low and mite pressure continues to build across the province.

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Dry, hot weather continues across the province. Some areas have received a few days of rainfall while others have seen very little since June.

For information on irrigation, check out some of these resources from Rebecca Shortt, Water Quantity Engineer:

Evapotranspiration data can be found at ONpotatoes and FarmWest websites. Note, Farmwest may have some missing rainfall data from July 3 to present.


Terminal buds have set in most regions by now. Without new shoot growth, there is no longer a risk of powdery mildew. It is possible to see a flush of new growth later in the season, especially if these dry conditions change and we get some moisture back into the trees.

Fire blight

Fire blight strikes throughout canopy of Empire

With terminal bud set, the cell walls thicken, stomata on the shoot stem are no longer active and the base of the shoot starts to harden off and form bark.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.

Extreme weather events like hail or strong winds can still result in fire blight infection from terminal bud set until harvest. If you have had active fire blight in your orchard this year or know of a neighbouring orchard dealing with issues, consider an application of 0.5% Cueva following the trauma event. Efficacy may be increased with the addition of Double Nickel.

Bitter rot

In periods of high heat and humidity followed by a rain storm, there is the risk of bitter rot infection. With hand thinning continuing, be sure to toss thinned fruitlets to the row middle and mulch. These fruit have been known to cause infection of remaining fruit on the tree by splashing spores during rain events.

While Allegro (PHI 28 days), Pristine (PHI 5 days) and Granuflo T (PHI 28 days) are registered for control of bitter rot, some other scab fungicides may also provide protection. Summer applications should be made every 10-14 days if there is a history of rot in the orchard, but shortened to 7 days if frequent rain is experienced. If possible, time an effective fungicide application just prior to a rain to prevent fruit from rain-splashed spores. Always rotate products to reduce the potential for resistance development.



The hot, humid weather has resulted in an increased activity of European red mite (ERM), two-spotted spider mite (TSSM) and apple rust mite (ARM) in many orchards. Those growers that are seeing populations reach threshold quickly are opting for miticides with relatively quick knock-down.

Keep in mind, thresholds for mites increases through the season as the tree canopy becomes more dense. From June to mid/late July, the threshold for most products is 7-10 active mites/leaf. Consider 5 mites/leaf for products like Nealta or Kopa. However, late July to August, the threshold for most products can be delayed to 10-15 active mites/leaf.

The table below lists registered miticides for summer managment. When choosing a product, consider the abundant life stages that are present in your orchard. For instance, if you are seeing mainly eggs, Envidor may be an option as it is slower acting. However, if the population is mainly nymphs or adults, you may opt for a product that offers a faster knock-down. As mentioned earlier, products like Nealta or Kopa should be applied as populations are building.

Target Species
Life Stage Affected
Knock-Down Activity
Acramite 50 WS
nymphs, adults
Envidor 240 SC
eggs, nymphs, adults (female)
Kanemite 15 SC
all life stages
Kopa (soap)
nymphs, adults
all life stages
nymphs, adults (ERM, ARM)
nymphs (TSSM)
Purespray Green
Spray Oil 13 E
ERM (suppression)
eggs, some nymphs
Activity of Summer Miticides Registered on Apple in Ontario

Despite the lush, dense foliage this time of year, do not let mite populations cause extensive damage. Late-season mite pressure and leaf bronzing can result in poor fruit finish and reduce winter hardiness.

Apple Maggot

Apple maggot have been caught in most regions of 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. In dry years such as this, pupae can remain within the soil until conditions improve, even remaining until the following year.

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.

Male and female apple maggot
Apple maggot flies. Note the rounded abdomen of the male (left) and pointed abdomen of the female (right). (Photo: Dr. Rob Smith, retired, AAFC Kentville)

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.

Many growers make use of an Imidan border spray at this point in the year when the longer re-entry restrictions won’t interfere as much with work that needs to be done. Border sprays are not recommended for other registered apple maggot products.

The following table, adapted from John Wise, Michigan State University (2019), summarizes the characteristics of apple maggot products. Organophosphates (Imidan) and neonicotinoids (Assail, Calypso) are the only insecticide groups that have 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.

Product Name
Chemical Group
Life-Stage Activity
Residual Activity
Mite Flaring Potential
Eggs, larvae, adults
14+ days
Ambush, Mako, Perm-Up, Pounce, Up-Cyde
7-10 days
Delegate, TwinGuard, GF-120 Fruit Fly Bait
7-10 days
Assail, Calypso
Eggs, larvae, adults
10-14 days
Altacor, Exirel, Harvanta
10-14 days
Not classified
Adults (deterrent)
7-10 days
Summary of Insecticides Used to Control Apple Maggot
(Adapted from John Wise, MSU:

Codling Moth

We are now reaching second generation spray timing for codling moth in most regions. When the timing for apple maggot control coincides with timing for codling moth control, one insecticide can often manage both of these pests. However some chemistries (Altacor, Harvanta, Delegate, TwinGuard), that provide effective management of codling moth, only provide suppression of apple maggot in low pressure orchards.

Those areas that are seeing some rain should keep in mind that heavy rains can lead to residue wash-off. In general, 2 inches of rain will removed residues for all products and require immediate re-application. With less rain, there are some insecticide classes such as the spinosyns (Delegate, TwinGuard) and diamides (Altacor, Exirel, Harvanta) that have a high rainfast rating. Check out the recent ONfruit article, Rainfastness of Insecticides on Fruit Crops – A Reprise for more information.

It’s important to note for resistance management, if re-application is required for control of a pest with discrete generations, use the same product within a generation. Rotate to another insecticide class for the 2nd generation to ensure each generation is only exposed to one active ingredient.

Potato Leafhopper

Potato leafhopper are quite active. Hopper burn and leaf cupping can be easily found in many orchards. This is caused by a toxin in the leafhopper’s saliva that blocks vascular system flow, preventing normal movement of water and nutrients to the affected area.

In most high vigour blocks, leafhopper damage is manageable, particularly once terminals harden off. However, nursery trees and non-bearing blocks require control at first sign of injury since vigour and shoot growth can be significantly impacted.

Japanese Beetle

Japanese beetle damage can 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.

San Jose Scale damage on developing apple fruitlet

San Jose Scale

The second generation adult flight for San Jose scale is on the upswing in the early regions of the province. In previous years, crawler emergence has generally begun late July to early August. Based on degree days, we seem to be on track this year to see crawlers are early August in most areas.

Fruit damage from San Jose scale has been relatively low to date this year, especially compared to the high pressure in many blocks in previous years. Those that have a history of damage from this pest may want to consider managing this generation to prevent fruit damage close to harvest. Registered products include Movento, Sivanto Prime, Closer and TwinGuard. For good resistance management, rotate to a different chemical group than what was used for the first generation. If using two consecutive sprays applied 14-days apart, be aware of the preharvest interval particularly on any early varieties.

Apple Leafcurling Midge

Orchards that still have not seen terminal set or are experiencing secondary growth may be noticing more apple leafcurling midge damage on the newest leaves. So long as there is new growth on either shoots or root suckers, leafcurling midge activity will continue into the fall. Watch young trees as this damage will impact growth and tree vigour.

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