Apples Diseases Insects Pest Management

Apple Update: June 22, 2016

Crop Stages

Apple fruitlets are increasing in size. At the University of Guelph Simcoe Research Station, they are 25-35 mm in diameter. Terminal buds have started to set in Essex County, which is much earlier than normal.


The weather continues to be dry, particularly in Niagara and Eastern Ontario. Trees would benefit from irrigation, especially the new plantings. If you don’t have your irrigation infrastructure installed, you may need to consider watering your new plantings manually with a water tank.  Agriculture and Agri-Food Canada has a Drought Watch webpage where you can retrieve maps of this season’s precipitation compared to a normal year.

Chemical thinning is showing variable results across the province. The efficacy depends on weather conditions. The apple growing regions during the window for chemical thinning experienced very hot temperatures for a  week which dropped down to cooler temperatures. Growers are just starting to hand thin. There is more benefit for increasing fruit size when hand thinning is done earlier.

Fire Blight

Fire blight continues to be an issue in many orchards across the province, including on less susceptible varieties and in orchards that have never had fire blight before. Signs of both blossom and shoot blight can be observed. OMAFRA’s plant pathologist, Mike Celetti has updated the fire blight risk maps with the actual infection risk that occurred during bloom across the province. It appears there were two period of potential infection. However, the first period was in the eastern regions from May 13-16 when trees were not yet in bloom. The second period began May 22 in the east and moved west across the province so that from May 25 to June 1, most apple growing regions were at high to extreme risk. Despite areas in the southwest that were no longer in full bloom during this period, there were still reports of extended or secondary bloom.

With the high humidity, ooze (see picture below) is actively present which increases risk of spread, particularly by insects but also wind, rain and even workers. According to George Sundin, Michigan State University, once fire blight infection occurs, about 2/3 of the pathogen cells migrate through the tree and the other 1/3 emerge as ooze. Each ooze droplet can contain approximately 1 BILLION cells while it only takes 100-1,000 cells to initiate shoot infection. That means a single ooze droplet could have the potential to infect every shoot in an orchard!

Ooze_with arrows
Bacterial oozing from fire blight infected shoot

So, now that there are strikes, what can be done about it? For more information, see previous ONfruit and Hort Matters articles. Another great resource is the MSU video, Fire Blight: Pruning Shoot Blight Strikes. In summary, management will depend on the age and vigour of the tree as excessive pruning can stimulate growth, potentially making the situation worse:

  • Young (<8 year old) tree with few strikes, prune.
  • Young (<8 year old) tree with many strikes, prune unless this will impact tree structure. Remove tree if this is the case.
  • Older (>8-10 year old) vigorous tree with few strikes, prune.
  • Older (>8-10 year old) vigorous tree with many strikes, prune when tree is dormant.
  • Older (>8-10 year old) low vigour tree or tree sprayed with Apogee, prune when tree is dormant.

Be sure to prune when there are 2-3 consecutive days of cooler temperatures and low humidity. Pruning cuts can be left in the row middles to dry up before removing or mulching them down. Do not drag exposed infected material through the orchard as this will increase the spread of infection.

Other Diseases

Scab can be found in orchards across the province. Most regions should be passed primary scab infection period by now. Any recent rains should have expelled the last of the ascospores from the leaf litter. It can take up to 14 days for lesions to appear after a scab infection period. Be sure to check the top of trees or anywhere where spray coverage may not have been adequate, such as a thick tree canopy. If primary scab was controlled, fungicide rates may be reduced and the interval between sprays may be lengthened for the remainder of the season. If scab lesions are found, maintaining a good protectant program will be critical to prevent secondary infection.

Powdery mildew, a hot and dry weather disease, has also been reported in numerous regions. This disease does not invade mature leaf tissue, so spread stops by terminal bud set. At this point in the season, especially with the high temperatures, sulphur at the labelled rate will likely cause burning and russeting of fruit. If using a product that is weak on fruit scab (eg., Fullback, Nova, Aprovia, Luna Tranquility) or if apple scab fungicide resistance is a concern, tank mix with a compatible protectant fungicide.

Now is the time to start looking for signs of bitter rot. The spores of the pathogen can infect fruit at any time during the growing season from as early as bloom right up until harvest. However, symptoms often show up mid to late season after a period of hot weather accompanied by rain or a thunderstorm. For identification and management of this disease, click here. Granuflo T, Allegro and Pristine are registered for control. However, some fungicides registered for management of scab and other summer diseases may provide some protection against bitter rot as well.


The spray window for 1st generation codling moth has closed with the exception of some later regions in the province. The biofix for obliquebanded leafroller has been set in most areas for early June. Degree days are quickly accumulating and spray timings will be coming up over the next few weeks.

Dogwood borer adult trap numbers are steadily increasing. If pheromone traps have not been placed in a problem orchard yet, these need to be installed as soon as possible since flight has begun. For orchards that are not using mating disruption (Isomate DWB should have been applied late May), trunk sprays of pyrethoids, Delegate, Rimon or Altacor can be applied a week following peak flight and re-applied at 2-week intervals. For more information, refer to the following Hort Matters article.

San Jose scale crawler (see picture below) activity has begun in orchards that are being monitored for this pest. Since emergence has just started, summer control options, such as Closer, TwinGuard or Sivanto Prime can be applied in the next week or so. If Movento is being used for this generation and has not been applied, now is the time to do so as it will take time to become active in the tissue. Activity will continue for 4-6 weeks during which time crawlers will damage new shoot growth and developing fruitlets. Due to the extended generation, a second application is recommended 10-14 days later.

Bacterial oozing from fire blight infected shoot

The second generation apple leafcurling midge adult flight has begun in the earlier regions of the province. In some orchards, eggs can be found in very high numbers on the newest growth (see picture below). Leafcurling from this generation will be expected to begin in the next 1-2 weeks.

Apple leafcurling midge eggs can be found on the newest growth.


Rose chafer activity has started in some orchards. This pest tends to stick to the same orchards or areas each year, causing defoliation and fruitlet damage. Management is relatively easy and many products used for other pests at this timing will have activity on rose chafer.

Mullein bug, plum curculio and European apple sawfly damage can be found on developing fruitlets.


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