Apples Diseases Insects Pest Management

Apple Update: June 20th, 2018

This post written by: Amanda Green, Tree Fruit Specialist, OMAFRA and Colleen Haskins, Acting Horticulture IPM Specialist, OMAFRA

In this update:

  • crop stages
  • thinning (chemical and hand)
  • irrigation
  • diseases (Scab, Fire blight, Powdery Mildew)
  • pest activity (Codling Moth, Oblique banded leaf roller, San Jose Scale, Brown Marmorated Stink Bug)

Crop Stages

Fruitlets are increasing in size and are in the cell division stage.  At the Simcoe Research station Honeycrisp are at 20mm and Ambrosia are at 24 mm diameter.

Chemical Thinning

Growers are applying their last thinner before fruit gets beyond the size where chemical thinners have little effect. Other growers have wrapped up chemical thinning and may be starting on early hand thinning.

With later chemical thinning, keep in mind the pre-harvest interval (PHI), as a few products PHIs are quite long and could potentially overlap with the harvest window of early varieties.

Pre-Harvest Interval (PHI)


Date which PHI is complete if you applied June 19th
86 days
September 14th
75 days
September 3rd
Cilis Plus
28 days
July 18th
5 days
June 25th

Hand Thinning

As you finish off chemical thinning and you may be considering starting on hand thinning. Please take note of the REI of Sevin XLR specifically for hand thinning:

  • 14 days for high density, trellised orchard
  • 10 days for traditional, medium to low density, non-trellised orchard.


Most of Western Ontario and  Durham have been getting quite dry over the last 30 days before the rain on Monday, receiving 40-60% of normal precipitation (See Agriculture Agri-Food Canada’s Agroclimate Maps).  Lambton, Middlesex, Kent and Elgin Counties and parts of Norfolk and Grey County have been especially dry with less than 40% of the normal rainfall in the last 30 days before Monday’s rain. Many growers have mentioned that they have had their irrigation already running.  This is a key time for irrigation as it during the time of cell division in the fruitlet which occurs from pollination until 5-6 weeks after bloom (Lakso 2003 and Palmer et al., 2003).  Water stress will have a greater impact on size at harvest during the cell division stage than at the cell expansion stage(Lakso 2003). For information on irrigation scheduling see the OMAFRA Irrigation Page and these two blog posts wrote by Rebecca Shortt, Engineer, Water Quantity, OMAFRA, during the dry year of 2016: Irrigation Update and How Long do I Run my Drip Lines


Lakso, A. N. 2003. Water Relations of Apples. p. 167-195. In: D. C.  Feree and I. J. Warrington (eds.) Apples: Botany, Production and Uses. CAB International

Palmer, J. W., J. P. Privé, and D. S. Tustin. 2003. Temperature, p. 217-237. In: D. C.  Feree and I. J. Warrington (eds.) Apples: Botany, Production and Uses. CAB International


Scab – Secondary scab lesions may start to appear over the next week or so.  Continue to monitor your orchards for scab and remain protected until you are confident you don’t have scab.

a) secondary scab a b) secondary scab b

Pictures:  a) & b) Secondary scab lesions on the top side of the leaf surface.
·Lesions on older leaves are raised and appear dark green to gray brown with distinct margins
Source: OMAFRA Crop IPM,


Maintaining a protectant fungicide program for scab will also help with other diseases such as powdery mildew, rust, sooty blotch, fly speck, bitter rot and black rot (*dependent on the protectant product used, as some provide suppression versus control of the fungal disease).

Fire Blight – Last week’s storm brought heavy rains, wind, and hail in some areas.  These conditions are very favorable to create trauma blight, and increase entry sites for Fire blight.  Be sure to have an extra look in your orchards for signs of fire blight.  If you see signs of shoot or other infection, prune out the infected tissue.

c) fb strikes  d) fb symptoms on leaves

Pictures: c) & d) Trees showing symptoms of fire blight strikes and infections
Picture credit: Michael Celetti, Pathologist-Horticulture, OMAFRA

Powdery Mildew – Although minimal, there are some reports in the various regions of powdery mildew.  Be sure to check your orchards for signs of powdery Mildew (e.g. cupping leaves, and “dusty, white appearance on the underside of leaves).

e)  pm cupping    f)  pm leaves

Pictures:  e) & f) Symptoms of powdery mildew
Leaves and terminals will curl upwards, and have a “powdery – dusty” look on the underside of the leaves.
Source: OMAFRA Crop IPM,

Pest Activity

Codling Moth (CM)
– Most areas applied control products this week.

Oblique Banded Leafroller (OBLR):  Western, Northern, and Central  areas have reported catch for this pest, with biofix occurring at the tail end of last week and the beginning of this week.  Central West and Eastern areas still have yet to catch OBLR and set their biofix for timing of sprays.

San Jose Scale (SJS):  Although we continue to catch adults in our traps, evidence of crawlers has not been observed at this time, but expect this event any day.

Brown Marmorated Stink Bug (BMSB): Traps for this pest have been placed in orchards over the past week.  We are monitoring for presence of both adults and nymphs.  Some orchards reported damage from this pest last season, which was evident during harvest.  We will report on any activity noted.



0 comments on “Apple Update: June 20th, 2018

Leave a Reply

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

%d bloggers like this: