Apples Diseases Insects Pest Management

Apple Pest Update: June 5, 2019

Warmer weather seems to be on the horizon as petal fall pest management begins

Crop Stages

  • In southwestern regions of the province, apples are at 3 to 15 mm fruitlet size
  • In Grey County and east of Toronto, orchards are at full bloom to petal fall


Fire Blight

Cool weather has kept the risk for fire blight infection low in orchards still in bloom. However, for many regions, the fire blight prediction maps are predicting high risk of infection for the later part of this week as temperatures warm up slightly.

Secondary apple bloom following petal fall
Secondary apple bloom

While bloom has passed in many regions of the province, growers should be aware of blossoms still open, particularly young trees or rat-tail bloom. Protecting these open blossoms from infection will be critical during times of high risk. Antibiotics will break down quickly in sunlight, likely only providing 24-72 hours of protection before a re-application would be required. This means any antibiotics applied last week during the main bloom period will have already degraded away. If time and labour are available, it may be best to go through the orchard every couple of days and remove the rat-tail blossoms by hand. Be sure to remove blossoms in dry weather to prevent the spread of infection.

Some areas experienced extreme weather over the weekend including heavy rain, hail and high winds. These events can cause trauma blight. If there is concern, Streptomycin or Cueva and/or Double Nickel can protect against spread of infection if used immediately following a trauma event.

Vegetative growth is very lush this year. Applications of Apogee continue to help manage growth and protect against shoot blight.

Apple Scab

Most regions in the province have reached – or very near – the end of the primary apple scab period. With the frequent rains, it is very likely ascospores have been released quickly following maturation throughout the spring. However, it’s best to err on the side of caution and keep good fungicide coverage for a few more weeks to be sure all ascospores have been released and monitor for scab lesions.

Apple scab lesions on underside of leaf
Early apple scab lesions on underside of leaf

With the cooler weather, lesions can take upwards of 15+ days to develop in temperatures less than 12⁰C. Be sure to take a good look in the top part of the canopy. Prolonged and/or heavy rains may have reduced fungicide residue or spraying in not ideal conditions may have limited full canopy coverage. If no lesions develop over the next 2-3 weeks, a relaxed program can continue for the remainder of the season. However, reports of scab continue to come in. Keep a tight interval and high rate program if this is the case in your orchard as developing fruit are now at risk of secondary infection so long as conditions are conducive to infection.

Powdery Mildew

Despite the frequent rains, there have been enough breaks with warmer, humid weather to have allowed for powdery mildew to germinate in some susceptible blocks. This risk will continue until terminal bud set. Continue to consider scab products that offer efficacy against powdery mildew until such time.

Black Rot

Frog-eye leaf spot has been found in varieties that tend to be more susceptible to black rot such as Gala, which holds on to fruit mummies that act as a source of inoculum. These early lesions appear as small purple to reddish flecks with light centers.

Frog eye leaf spot on apple
First symptoms of frog eye leaf spot appear as purple flecks with light centers

While the optimum temperature for leaf infection is 26⁰C, infection can occur any time above 10⁰C but will just require a longer leaf wetting period (more than 24 hours at 10⁰C). With the frequent rains and overcast conditions, this hasn’t been out of the question.

If you are seeing frog-eye leaf spot now, you now know inoculum is present in the orchard or coming from a sporulating nearby source such as dead or decaying wood in an adjacent woodlot. Black rot produces 2 types of inoculum – ascospores (sexual spores), which are wind blown and conidia (asexual spores), which require a wet period and rain splash for release. Both begin to release shortly after bud break; however, the heaviest ascospore release occurs for a 4-6 week period following petal fall and fruit infection can occur at 20-24⁰C with 9 hours of wetting. In other words, if your protectant program considerations haven’t included black rot yet, now is the time! Registered products include captan and Pristine but efficacy of other scab products can be found in Table 2-3. Activity of Fungicides on Apple Diseases in the 2018-2019 Publication 360, Fruit Crop Protection Guide. While Allegro provides good control of bitter rot, it is not as effective against black rot.

Phytophthora Root Rot

The saturated soils this spring have created ideal conditions for Phytophthora crown and root rot. While symptoms may develop this year on young trees especially in heavy or water-logged soil, it is also possible infected trees may decline slowly over several years. Typically, purplish cankers can be found at the base of the tree at and/or below the soil line. Tissue necrosis under the bark is often reddish-orange with distinct margins. For more information, see Monitor for Phytophthora root, Collar and Crown Rot Diseases in Fruit Trees in the May 17, 2017 Hort Matters issue.

Newly planted apple tree in standing water
Newly planted apple tree in water-logged soil

Symptoms of Phythophthora can often be confused with rootstock fire blight as well as rapid/sudden apple decline. Submitting samples to a pest diagnostic laboratory will help you determine the appropriate management required. If you’d like assistance with this, please contact me at 519-420-9422 or

Blister Spot

It’s time to start thinking about blister spot in problem/susceptible blocks. The warm, humid and wet weather predicted may increase risk of blister spot 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.


Petal fall insecticide application have begun. Some growers are concerned with rainfastness and the extent of rainfall in many areas. 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.

General Rainfastness Characteristics for Common Insecticide Chemical Groups (PDF / Word)

Insecticide groupRainfastness
≤ 0.5 inch (fruit)
≤ 0.5 inch (leaf)
≤ 1.0 inch (fruit)
≤ 1.0 inch (leaf)
≤ 2.0 inch (fruit)
≤ 2.0 inch (leaf)
Persistence (residual on plant)Penetration characteristics
Carbamates (1A)MM/HMMLLShortCuticle penetration
Organophosphates (1B)LMLMLLMedium-LongSurface
Pyrethroids (3A)M/HM/HMMLLShortCuticle penetration
Neonicotinoids (4)M,SH,SL,SL,SL,SL,SMediumTranslaminar*, acropetal
Spinosyns (5)HHHMMLShort-MediumTranslaminar
Avermectins (6)M,SH,SL,SM,SLLMediumTranslaminar
IGRs (15, 18)MM/HMMLLMedium-LongTranslaminar
Diamides (28)HHHMMLMedium-LongTranslaminar

H = Highly rainfast ≤ 30% residue wash-off; M = Moderately rainfast ≤ 50% residue wash-off; L = Low rainfast ≤ 70% residue wash-off; S = Systemic residues remain within plant tissue

* = Translaminar materials require 24 hours of drying prior to a rain to fully move into the developing fruit and leaf cuticle.

Adapted from John Wise, Michigan State University (2018)


The spray window for oriental fruit moth will be over in most early regions in the next 10 days. Some growers have selected insecticides with good efficacy on mullein bug, spring feeding caterpillars, European apple sawfly and/or apple leafcurling midge if monitoring had indicated they had reached threshold or had high pest pressure.

In other insect traps, codling moth catch has been increasing.  However, spray timing for 1st generation egg hatch is still more than 10 days in some regions. Obliquebanded leafroller traps are up. A significant number of redbanded leafroller and lesser appleworm have been caught at sites monitoring for these moths as well.

Leafroller larvae can still be found in rolled foliage. As well, damage from gypsy moth and pug moth have been found in some orchards.

European apple sawfly catch has been relatively low likely due to the cool weather during bloom. None the less, growers in areas where this is a pest of concern are applying – or planning to apply – a petal fall insecticide that has efficacy on sawfly.

San Jose Scale

San Jose scale adult flight continues in orchards that are being monitored. Pressure is very high in some blocks. Degree day models using first adult catch as the biofix have started to be accumulated. Early estimates are predicting 1st generation crawler emergence late June. The cooler nighttime temperatures are delaying development.

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. These insects are extremely small so a hand lens will definitely be needed!

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.

Mullein Bug

High numbers of mullein bugs are being tapped out in various orchards across the province, exceeding the threshold of 7-9 nymphs per 25 taps. No damage has been reported yet. Growers seeing numbers above threshold are applying insecticides with activity against this pest particularly on susceptible varieties such as Red Delicious, Spartan, Spy, Ambrosia, Empire, Cortland, Gala, Jonagold and Golden Delicious.

Mullein bug nymph
Mullein bug nymph

It’s recommended to continue monitoring after the insecticide has been applied to determine if a follow-up spray is required. Delegate, Minecto Pro, Altacor and Exirel do not have efficacy on this pest.

The critical time for damage from mullein bug is generally dime to quarter-sized fruit. Cooler temperatures are slowing fruitlet development which could result in an extended time the fruit is at risk of damage by this pest.

Despite high pressure in some orchards in recent years, very little damage was actually observed. These pests are also very good predators of mites, aphids and leafcurling midge. It is possible if there is enough other food available in the orchard, it can keep the mullein bug from feeding on developing fruitlets. On-going assessments of leafcurling midge terminal damage are already finding significant amounts of mullein bug predation.

Apple leafcurling midge

Apple leafcurling midge egg hatch continues. Infested terminals are becoming quite apparent already in many orchards with a history of this pest. Terminal damage will result in stunted shoot growth, reduced photosynthesis and poor root establishment of young trees.

Apple leafcurling midge infested terminal
Apple leafcurling midge infested terminal

While Movento is registered for suppression, the timing for leafcurling midge this year may be earlier in many regions than for scale and woolly apple aphid. However, there are other petal fall insecticides such as Delegate, Closer, Twinguard and Exirel that may provide some efficacy as well, which could help delay the Movento application. Summer oils will also help to smother eggs so long as good coverage is achieved to reach within the newest terminal leaves.

Woolly apple aphid

Woolly apple aphid colonies have started to be found along the trunk and in sheltered areas of the tree. 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 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 woolly apple aphid control.


Despite the cool weather, the appearance of potato leafhopper has been earlier than usual. These were likely blown in on the storms in recent weeks since this pest does not overwinter in Ontario. No sign of hopperburn has been reported yet. However, scouts and growers are monitoring young trees in orchards where potato leafhopper has been observed as damage can stunt growth.

1 comment on “Apple Pest Update: June 5, 2019

  1. Have just started following this blog and love the detailed info! A great additional resource for us. Thanks.

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