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Apples Diseases Insects Pest Management

Apple Pest Update: June 17, 2020

The latest update on insect and disease activity in apple orchards across the province.

Listen to audio article here:

Despite the predicted rainfall during last week’s storm, few areas saw much precipitation at all and orchards remain pretty dry. Unfortunately, it doesn’t look like the next week will bring much relief either. Fruit are sizing well overall though I have been noticing low to moderate amounts of misshapen and russeted fruit this week likely from the May frost.


Fire Blight

Secondary bloom adjacent to developing fruitlets on apple branch
Secondary bloom can pose as a threat for fire blight infection

The risk of blossom blight has passed in most orchards. However, growers should still be on the lookout for rat-tail bloom or late bloom in spring planted blocks.

Friday, June 12th was the final update for the fire blight prediction maps. While the maps show predictions until June 18th, keep in mind this model is using forecast data which may change over the week. Presently, the maps are being updated with the actual infection risk that occurred during bloom across the province. This will be posted shortly.

There have been a number of reports of fire blight, both blossom and shoot blight. Conditions during bloom were extremely conducive to infection this year with the hot, humid weather:

  • While bloom happened quickly, this may have actually left the blooms at greater risk of infection.
  • Blooms were opening rapidly so if antibiotics were only applied every few days, this left a significant window (in bacterial infection terms) where new – and highly susceptible – blossoms were unprotected.
  • With the hot weather, the bacterial populations would have been multiplying rapidly to the point where very little moisture would be needed to wash large amounts of this bacteria into the floral cup.

While the storm last week may not have brought much rain, it did have very strong and damaging winds. These winds continued for more than a day after the storm which meant rescue treatments of streptomycin could not be applied as planned for some. These sprays need to be applied less than 24 hours after a trauma event, ideally 4-12 hours before bacterial growth progresses beyond streptomycin’s ability to control. Signs of trauma blight are now beginning to develop.

For more information on pruning out fire blight strikes, see this previous ONfruit article or the following video from Michigan State University:

Important points to remember:

  • Continue managing fire blight throughout the season as infection can still occur through open wounds caused by strong winds, heavy rain and hail, insect feeding, pruning or mechanical damage.
  • Inoculum can be spread large distances throughout a region during storms.
  • Cueva and Double Nickel are registered for the control of shoot blight following a trauma event.
  • Like all coppers, there is the risk of russeting with Cueva. However, if fire blight is active in your orchard at the time of trauma, better to lose some fruit this season than trees later.
  • The preharvest intervals for Streptomycin and Kasumin are 50 and 90 days, respectively.

Continue to watch any problem blocks closely over the upcoming weeks for signs of blossom or shoot blight. It is best to do any hand labour activities such as thinning, pruning or removing suckers in dry conditions in these blocks to avoid the potential spread of bacteria.

Apple Scab

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.

Powdery Mildew

The warm, humid weather has really favoured the development of powdery mildew in some orchard blocks. Continue to protect susceptible varieties such as Gala, Honeycrisp, Cortland, Idared, Crimson Crisp, Goldrush, Russet, Fuji and Spy. This disease does not invade mature leaf tissue, so spread stops by terminal bud set.

Summer Disease

With many growers now 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 (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.

Interestingly, a number of varieties have been holding onto their petals following fruit set including Ambrosia, Honeycrisp, Golden Delicious, Cortland and Crimson Crisp. Fruit can be susceptible to calyx rots by moving into the sepal and developing fruit through the withered petals.

Consider fly speck, sooty blotch and fruit rot efficacy when selecting petal fall and first cover sprays and continue to keep fruit protected throughout the summer with 14-21 day intervals after primary scab is over. Shorten application intervals 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.


Internal Feeders

Most areas that control for oriental fruit moth have passed the spray window. Ideal timing would have been at petal fall/calyx when most growers would have used a product effective against fruit moth.

The next internal lepidopteran pest on growers’ radars is codling moth. Insecticides targeting egg hatch have begun this week in the early regions. Timing is very important with codling moth as the larvae often tunnel into the fruitlets within 24 hours of hatch. For early regions, it is too late for insect growth regulators, such as Rimon (petal fall timing) or Intrepid (83-111 DDC) as they need to be on early to interrupt regular development. Contact or ingestion larvicides are applied typically around 138 DDC.

This timing may also help with early obliquebanded leafroller hatch, too. However, obliquebanded leafroller catch has only just started in most areas so control timing will begin over the next couple of weeks across the province.

San Jose Scale

San Jose scale crawlers on apple branch
Look for signs of small, yellow San Jose scale crawlers on infested apple limbs

San Jose scale adult flight has declined this week. First generation crawler emergence is predicted to begin over the next week. Based on degree-day models, earlier regions should start to see activity this week while later regions should see activity picking up the week of June 22. This is about 10 days ahead of last year’s model.

As of Tuesday, June 16, no crawlers have been found in orchards that I am actively monitoring.

Crawler activity (ie., movement to new shoots and developing fruit) will continue for 4-6 weeks. Registered products including Closer, TwinGuard 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. 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.

Depending on the product, this timing may also have efficacy on leafcurling midge and/or woolly apple aphid.

Plum Curculio

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 similar to what we saw throughout and shortly after bloom. Activity is believed to be linked to weather patterns, so could be as long as 6 weeks during cooler conditions. However, peak activity is typically within the first couple of weeks after petal fall.

Mullein Bug

Mullein bug populations remain high in some orchards despite a targeted petal fall insecticide being applied. The critical time for damage from mullein bug is generally dime to quarter-sized fruit. Up to this point, very little damage has been reported.

Interestingly, a significantly high number of mullein bug can be found in apple leafcurling midge terminal damage. It is possible mullein bug are feeding on these larvae.

Apple Leafcurling Midge

Leafcurl damage from apple leafcurling midge can be easily found in many orchards. Larvae within the rolled leaves are beginning to turn orange in early regions, which is a sign of late instar stages just prior to pupating. Second generation adult emergence has typically occurred in mid-June to early July in previous years.

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.

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