Apples Diseases Insects Pest Management

Apple Update: June 21, 2017

Crop Stages

  • In Southwestern Ontario, apple fruitlets are 20-35 mm in diameter, terminal buds are starting to set in older trees in Essex County
  • In Grey County and east of Toronto, apple fruitlets are at 15-20 mm in diameter


June drop is starting to occur up in Southwestern Ontario.  Growers in Grey County and East of Toronto are applying their final fruitlet thinner. Growers will be starting to hand thin after June drop. Field work at this time of year includes cleaning up leaders by removing competing shoots and constructing trellises for new orchards.

Really hot temperatures were experienced in the early part of last week with records for high temperatures being broken for temperatures in some parts of the province. Rainfall was variable on Thursday with apple growing areas receiving 5-25 mm on Thursday. This was following a period of no rain for 10-14 days, so this week’s rainfall is very welcome.


Very little fire blight has been reported. However, those orchards with active cankers can observe oozing in the high humidity.

Apple scab continues to develop in some orchards. Most lesions can be found on oldest leaves suggesting infection likely occurred during the extended wet periods late April. Fruit scab can also be found (Fig 1). In these orchards, a protective fungicide program should continue during periods of potential scab infection. Spores will be released from existing lesions during rain/wetting events and infect surrounding leaf and fruit tissue. This secondary infection period will continue through to harvest.

Figure 1. Apple scab on leaves and developing fruitlet.

Based on prediction models, if symptoms from primary scab infection are to develop, this window will be closing over the next week or so. After this time, if a thorough check of the orchard determines no scab is present, fungicide rates and intervals can be relaxed for the remainder of the summer.

Summer fruit rots are on the minds of many growers. In periods of high heat and humidity followed by a rain storm, there is the risk of bitter rot infection. While Allegro (PHI 28 days), Pristine (PHI 5 days) and Granuflo T (PHI 28 days) are registered for control of bitter rot, some other scab fungicides may also provide protection. Summer applications should be made every 10-14 days if there is a history of rot in the orchard, but shortened 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.


The spray timing for 1st generation codling moth egg hatch has passed in most areas. There have been no reports of fruitlet damage yet. In regions that have had rain recently, some growers are concerned about rainfastness of cover sprays. The following chart by John Wise, Michigan State University summarizes the general rainfast characteristics for common insecticide classes. To read the full article, see Rainfast Characteristics of Insecticides on Fruit.

Obliquebanded leafroller control timing has begun in early regions and will continue over the next couple of weeks across the province.

San Jose scale crawlers have been observed this week (Fig 2), signalling the start of 1st generation crawler emergence. Activity is predicted to begin later this week in Georgian Bay and east of Toronto. 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.

Figure 2. Small, yellow San Jose scale crawlers on white electrical tape.

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.

Rosy apple aphid pressure is higher than normal in many orchards across the province and significant leaf curling/crinkling can be found around fruit clusters (Fig 3). Chemically thinning fruit around infested clusters can be very difficult.

Woolly apple aphid colonies have been building. Still more commonly found inside the canopy around pruning cuts, cankers or split bark (Fig 4), 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. Many beneficial insects such as lady beetle can be found feeding on colonies.

Mullein bug stings on developing fruitlets (Fig 5) have been reported in orchards including varieties such as Honeycrisp and Ambrosia. In some of these orchards, low numbers of mullein bug nymphs were actually tapped out during weekly monitoring. At this point in the season, damage is not a concern as most mullein bugs are late stage nymphs (with wing pads) or adults and fruit is larger than dime- to quarter-sized.

Damage from leafcurling midge, tarnished plant bug (Fig 6) and plum curculio (Fig 7) continue to be found. Both European red mite and two-spotted spider mite are active.


The Ontario Apple Orchard Tour will be held in the Niagara area on July 5th. For more information and to register, click here.

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