Apples Diseases Insects Pest Management

Apple Pest Update: June 26, 2021 (with audio)

Terminal growth continues to favour powdery mildew and fire blight, San Jose scale damage appearing on developing fruitlets, and recent rain across the province ideal for summer disease

Listen to the audio article here:

While there has been a bit of a break in the hot, humid temperatures recently, most areas still remain quite dry. Irrigation continues where it can. The latest Vegetable Crop Report for June 24, 2021 gives a great overview of growing degree days (GDD) and precipitation across Ontario.

Overall, most regions continue to have a similar growth rate as their respective 10-year averages but are still ahead of the average by roughly 100 degree days. Most apple growing regions, particularly Georgian Bay and Eastern Ontario, lag behind the 10 year average for precipitation. However, Essex has been the exception, having surpassed its 10-year precipitation average for the month of June.

With the high humidex predicted over the coming days, this could bring unsettled weather to some areas including heavy rains, thunderstorms and/or damaging winds. These conditions at this time of year are ideal for disease development.


Powdery mildew

The warm, humid weather has really favoured the development of powdery mildew in many orchard blocks. Continue to protect susceptible varieties such as Gala, Honeycrisp, Cortland, Idared, Crimson Crisp, Goldrush, Russet, Fuji and Spy. Powdery mildew requires actively growing tissue to complete its cycle so fungicides with efficacy against this disease should continue until terminal growth stops.

Infected shoots will not cause damage to fruit at this point in the season. Fruit damage is a result of early infection that occurred in the flower buds and during bloom. However, infected shoots will be the inoculum source for next year. Prune out any strikes that are present.

Fire blight

While many orchards may have got through bloom period without signs of fire blight, infection can still occur through open wounds caused by strong winds, heavy rain and hail, insect feeding, pruning or mechanical damage, or even microtears during rapid growth. Blossom blight does not need to be present for other parts of the tree to be affected such as shoots or rootstock. In fact, inoculum can be spread large distances throughout a region during storms.

Until terminal bud set, young shoots can be easily damaged during summer storms. Fire blight is active in a number of orchards across the province, which means the potential for shoot or trauma blight can be quite high during these hot, humid conditions.

I’ve had a number of questions about what can be done to manage fire blight this time of year. In the April 2021 Orchard Network Newsletter article Putting Out The Fire – Part 2: Managing Blossom and Shoot Blight, I included a number of tips for management.

The following video from Michigan State University also provides some good tips for pruning out fire blight strikes:

Other disease

Low levels of apple scab infection can be found in some orchards across the province. Though overall, many orchards still appear to be clean at this time. While primary infection period may be over according to the ascospore maturity model, it is important to wait a few weeks after the last infection event before backing off of a scab program. Monitor for signs of scab lesions. Be sure to take a good look in the top part of the canopy as coverage can often be inadequate there. Before reducing fungicide rates, be sure your orchard is completely free from primary scab.

When beginning to relax back on scab management for the summer, it is important to still consider fungicide sprays for summer diseases. While often considered mid- to late summer diseases, now is the time to start thinking about management of fly speck, sooty blotch, bitter rot and black rot.

Frog-eye leaf spot on Gala.

Frog-eye leaf spot (black rot) can already be found in orchards. The developing fruitlets are now at risk of infection by these fungi despite symptoms not actually appearing until mid-summer.

Moving back into some hot and humid weather, we could see some ideal bitter rot infection conditions, especially when followed by a rain storm like what many regions experienced at the end of last week. Spread can be extensive with bitter rot as spores are produced on the fruit surface and rain splashed to other fruit resulting in further infections as the season progresses. Wounds do not need to be present for bitter rot infection unlike black rot.

Infection timing for fly speck and sooty blotch should also be considered. In wet years, infection typically begins 2-3 weeks after petal fall. With this season being so dry, it’s likely to be later than this. There is a fly speck forecasting model that predicts the start of infection at 185-190 leaf wetting hours after petal fall.

For management of summer diseases, follow a 14-21-day application interval until harvest to ensure fruit remains protected. Pristine can provide reasonable residual control of summer disease up to 3 weeks at the labelled rate in ideal conditions; however, captan should not be pushed further than 14-days between sprays particularly since it is not as strong on fly speck and sooty blotch as other control products. In all cases, reduce interval to 7 days during times of hot, wet weather.

Important cultural management recommendations include:

  • Prune and thin clustered fruit to facilitate drying and improve fungicide coverage.
  • Remove potential sources of inoculum such as dead branches, fruit mummies (where possible), infected fruit on the orchard floor and alternate hosts including brambles (blackberry, raspberry) from surrounding hedgerows or woodlots.
  • Toss pruning cuts and thinned fruit in the row middle and mulch.
  • Reduce tree stress by irrigating and/or applying a sun protectant, especially ahead of a heat wave.


San Jose scale

San Jose scale crawler activity for the 1st generation has begun. To spot these small yellow-orange nymphs, you’ll need to get close to the trunk with a hand lens as you can see in the picture below. While emergence may be slow at first, activity can pick up quickly, generally peaking early July. This generation will be active, however, for 4-6 weeks as crawlers move to new shoots and developing fruitlets. Once attached and starting to feed, these immature scales will form waxy coverings that protect them from insecticides. Red halos surrounding these feeding scale have been found already this year in high pressure orchard blocks.

Targeting sprays during the vulnerable time when crawlers are exposed will maximize the efficacy of products such as Closer, TwinGuard and Sivanto Prime. Since Movento is slow-acting, ideal application timing is 1-2 weeks prior to crawler emergence. If planning to use this product and it has not gone on yet, applying as soon as possible may still provide some efficacy for later emergence due to the extended pest activity. While Purespray Green Spray Oil is registered for summer use on mites and aphids only, trials in Ontario have found weekly oil applications may provide some suppression of scale during the crawler stage.

Internal feeders

Egg hatch for 1st generation codling moth is on-going. There have been no reports of fruitlet damage yet.

Following egg hatch, codling moth larvae search out the fruit where they begin to tunnel in. This can happen as quickly as 24 hours after egg hatch which is why timing of control strategies are so important. After entering fruit, the larvae will feed for approximately 3 weeks before leaving the fruit to pupate (usually on tree trunk or larger branch of the tree). Pupation generally lasts 14-21 days. Some larvae do not pupate at this time, but remain as larvae until the next year. Second generation adults begin to appear in orchards as early as July and lay eggs over two months.

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. For instance, codling moth is still in the first generation window. Second generation larvae activity will not begin for another few weeks – typically early August. Rotate to another insecticide class at that time to ensure each generation is only exposed to one active ingredient.

Terminal flagging caused by oriental fruit moth damage. Note brown frass at terminal tip.

Control timing for 2nd generation oriental fruit moth is still a couple weeks away. This generation more commonly feeds on developing fruit. I have been in a few orchards in the province with terminal damage caused by oriental fruit moth. The 1st generation larva often enter growing terminals when other fruit sources (fruit) are still not present. Once terminal set occurs, this risk is reduced but can impact growth of new plantings. This damage can also be misidentified with shoot blight. Look for presence of brown frass and an entry hole at terminal tip.

Trap catch still remains quite low for obliquebanded leafroller. Biofix has been set for some but not all regions. Control timing will begin over the next couple for weeks across the province.

Apple maggot traps are currently going up ahead of adult emergence. Emergence is closely linked to soil moisture levels. Those regions seeing drier than normal conditions may see a delayed emergence or sudden flush following a rain event. Apple maggot are even able to remain dormant until the following year if conditions are not favourable.


This has been quite the year for aphids, in particular rosy apple aphid. Overall, activity seems to have declined with petal fall and first cover sprays as well as increased beneficial insect populations. Keep an eye on fruit clusters as feeding damage by rosy apple aphid can cause deformed fruit.

Woolly apple aphid colonies have been building. Still more commonly found inside the canopy around pruning cuts, cankers or split bark, there are some cottony masses that are beginning to move throughout the canopy. Most products timed for San Jose scale should have some efficacy on woolly apple aphid as well.


Potato leafhopper adult on apple leaf.

Potato leafhopper are quite active though little hopper burn and leaf cupping have been reported. This damage 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. With the first cut of hay happening in many regions, there may be a flush of potato leafhopper moving into orchards in the coming weeks.

Dogwood Borer

Dogwood borer trap catch is beginning in early regions in orchards with a history of problems with this pest. However, adult emergence will continue through to early September with peak flight typically occurring mid-July. During this time, females lay eggs on the surface of burr knot formations, pruning cuts, cankers, and wounded bark, after which the larvae use as entry points to bore into the tissue to begin feeding.

If pheromone traps have not been placed in the problem orchard yet, these need to be installed as soon as possible since adult flight has begun. Four traps per site, placed in low scaffold limbs, are recommended. Use a minimum distance of 50 m between traps, and monitor twice a week. Record the number of adults captured – graphing the results – to identify peak flight time. This information can be used to time trunk applications of a registered insecticide.

Currently, pyrethroids, Altacor, Delegate and Rimon are registered 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.

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.

Japanese beetle

The first Japanese beetles have been found in some orchards in the earlier parts of the province. Damage by these beetles is rather characteristic, causing distinct leaf skeletonization (leaving margins and veins only). 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.

Other insects

Mullein bug stings on developing fruitlets have been reported in orchards. However, overall damage from this pest has been fairly low. This is especially surprising in some orchards especially given the high numbers of mullein bug nymphs were tapped out during weekly monitoring. At this point in the season, damage is not a concern as most mullein bugs are adults and fruit is larger than dime- to quarter-sized. In fact, mullein bugs are very effective predators of many orchard pests so supporting these populations from this point on in the season is encouraged.

Low levels of plum curculio damage has been found on developing fruitlets. Often movement into the orchard follows a period of sustained warm weather and rain. Activity is believed to be linked to weather patterns, so could be as long as 6 weeks during cooler, more dry conditions.

Adult flight for the 2nd generation of leafcurling midge has begun and egg laying can be found in growing terminals. New leaf curls will likely start developing in the coming week or so. Damage will continue until terminal set.

Overall, mite pressure continues to remain relatively low in most orchards in the province, despite the hot, dry weather.

Beneficial insects can be easily found in orchards now. Just this week, my counts have included lady beetle larva, mullein bugs, lacewings, hoverfly larva, assassin bug egg masses and evidence of aphid parasitism (see the enlarged remains of rosy apple aphid, including exit hole caused by parasitic wasp emergence in photo below). Keep an eye out for these good guys. They’re doing a great job in the orchard this year.

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