Apples Diseases Insects Pest Management

Apple Update: June 8, 2017

In this update:

  • crop stages
  • thinners
  • disease: fire blight, scab, blister spot, sudden apple decline
  • insect: codling moth, San Jose scale, woolly apple aphid, leafcurling midge, dogwood borer

Crop Stages

  • In Southwestern Ontario apple fruitlets are 8-25 mm in diameter
  • In Grey County and east of Toronto, apple fruitlets are at petal fall to 10 mm in diameter


Fruitlet thinners are being applied across the province. Southwestern Ontario growersare applying their 2nd or 3rd thinning application while growers East of Toronto and in Grey County are at the beginning of their thinning program.  Second applications of Apogee are being applied in Grey County and East of Toronto. Fruit set is generally good across the province but there are blocks that show poor fruit set where trees were most stressed with heavy crop loads or on sandy knolls during last summer’s dry weather.

Eastern Ontario seemed to get most of the rainfall last week with 1-2 inches. There were reports of isolated incidences of hail in Essex, Wellington, Niagara, York and Durham.

With Sevin XLR (carbaryl) being applied for thinning, remember that the Restricted Entry Interval (REI) on the Sevin XLR label has changed as of September, 2016.

  • The REI for hand thinning and managing hand line irrigation is 14 days for high density, trellised orchards and 10 days for low density, traditional orchards
  • The REI for pruning scouting, pinching, tying and training is 4 days for high density trellised orchards and 12 hours for traditional, low density orchards.


The risk of blossom blight has passed in most orchards. However, particularly in the later regions of the province, growers should still be on the lookout for rat tail bloom or late bloom in young plantings. If ideal conditions continue and secondary bloom is not removed or protected, the bacteria can easily wash into the blossom initiating infection. This is likely where many growers got caught last year.

Monday, June 5th was the final update for the fire blight prediction maps. While the maps show predictions until June 11th, 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.

While fire blight has not been reported in commercial orchards in the province, strikes (Fig 1) are developing in the experimental block at Jordan Station (c.v. Gala/M9 rootstock). This indicates conditions were conducive to infection during bloom this year despite many cool days. Growers will be watching any problem blocks closely over the upcoming weeks for signs of blossom or shoot blight.

Figure 1. Blossom blight on Gala/M9 apple.

There is a very good chance that with the amount of precipitation the province has seen, the majority of orchards have had 100% mature ascospore release, signalling the end of the primary apple scab infection period. However, it is recommended to continue a protectant spray program for at least 3 weeks while monitoring for signs of scab lesions. Be sure to take a good look in the top part of the canopy. If nothing develops, a relaxed program can continue for the remainder of the season. Reports of scab continue to come in. However, infection has been light.

The warm, humid and wet weather has some growers thinking about blister spot (Fig 2) particularly in Mutsu but also Golden Delicious, Red Delicious, Jonagold and Cortland. Bacteria build up on leaf and plant surfaces including weeds in the orchard. These are then rain-splashed onto developing fruit where they infect through the lenticels. Young Mutsu fruit are most susceptible beginning 2 weeks after petal fall lasting for about 6 weeks or late July.

Blister spt
Figure 2. Blister spot on apples appear as small water-soaked blisters on the fruit surface often near the calyx end.

Reports of tree collapse continue with suspected Sudden/Rapid Apple Decline. The most common variety affected is Gala on M9 rootstock. However, collapse has also been observed in other varieties such as Honeycrisp, Ambrosia and Empire. The cause for this collapse is currently unknown. For more information, refer to the Dec 2016 Orchard Network Newsletter article Apple Tree Collapse: What We Know (And Don’t Know). If you are experiencing this collapse in your orchard, please contact Kristy Grigg-McGuffin, 519-426-4322 or


Most areas are at the tail end of oriental fruit moth egg hatch. Ideal spray timing would have been at petal fall/calyx. The next internal lepidopteran pest on growers’ radars is codling moth. Egg hatch is quickly approaching over the next few days in some of the earlier regions. Timing is very important as the larvae often tunnel into the fruitlets within 24 hours of hatch. 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.

San Jose scale adults have been trapped since the end of May in all monitoring orchards in the province. Based on degree days, 1st generation crawler emergence is predicted beginning June 15th/16th. Depending on the weather, crawler activity (ie., movement to new shoots and developing fruit) will continue for 4 – 6 weeks. Electrical tape wrapped sticky side out on a limb or trunk of an infested tree can be used to monitor for crawler movement (Fig 3). These insects are extremely small so a hand lens will definitely be needed!

SJS crawler on tape
Figure 3. San Jose scale crawlers are small, yellow-orange insects.

Registered products including Closer, TwinGuard and Sivanto Prime should be applied at the beginning of crawler activity and re-applied 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.

Woolly apple aphid colonies have been observed in some regions. Their characteristic cottony covering can be quite obvious along shoots. There are no thresholds for woolly apple aphid but management is often better when nymphs are young and colonies are just starting to form. If using Movento, the earlier the application, the better as control may not be apparent for 2-3 weeks. A well-timed application for San Jose scale would be an effective timing for woolly apple aphid as well. Early season control and good orchard management also allows for important natural enemy populations to build later in the summer, which growers should encourage for aphid control.

Figure 4. Apple leafcurling midge larva turn orange in colour prior to pupating.


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 (Fig 4). Second generation adult emergence has typically occurred in mid-June to early July in previous years.

Dogwood borer pupae can be found around graft unions and burr knots in problem blocks indicating adult flight will begin shortly (Fig 5). Flight will continue into September though peak flight typically occurs in July. Pheromone traps can be used to monitor flight.


Figure 5. Brown frass protruding from graft union is evidence of dogwood borer.

Mating disruption is available for this pest and offers effective control if used for multiple years. Painting the trunk with white latex paint will also help deter egg laying and (if applied thick enough) suffocate borers already in the wood. Pounce 384 EC, Perm-Up EC, Delegate, Rimon 10 EC and Altacor are registered as trunk sprays though needs to be applied at 2-week intervals following peak adult flight.

Rosy apple aphid colonies can still be found in some blocks as well as mullein bug. However, mullein bug activity seems to indicate they are predating on mites, aphids and leafcurling midge.

European red mite and two-spotted spider mite are active. Early miticide options were discussed in last week’s Apple Update: May 30, 2017.


0 comments on “Apple Update: June 8, 2017

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.

%d bloggers like this: