Petal fall in apple
Apples Diseases Insects Pest Management

Apple Pest Update: June 1, 2020

The latest update on insect and disease activity in apple orchards across the province.

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If you happened to turn your back for a second this week, you may have missed bloom. Even areas that were reaching pink just early last week are already in petal fall in many varieties. This quick bloom meant some missed key timings for certain applications such as Apogee. On the bright side, the week was fantastic weather for pollination.

There has been some concern that there may be more damage from the freezing temperatures we had in early May than originally thought. While bloom looked dazzling, getting up close suggested something different. Small king bloom, deformed petals and missing flower parts were just some indications I noticed. Only time will tell as fruit sets just what the crop will bring.


Fire Blight

Conditions for fire blight infection were high to extreme in most areas across the province this last week according to the fire blight prediction maps. These maps use the Cougar Blight forecasting model to determine infection risk. According to this model, some of the most damaging fire blight epidemics have occurred under these optimum conditions, including in orchards that have never experienced fire blight.

Growers running the Maryblyt model also saw the epiphytic infection potential (EIP) exceed the spray threshold of 100. It is important to remember with this model, the EIP resets back to zero when a bactericide has been applied. However, with high temperatures, it does not take long for the EIP to jump back up above 100. A benefit to this model is that it also predicts when fire blight symptoms will appear.

It seems as though the cooler temperatures will bring regional infection risk down for the remainder of the week. However, a cool forecast does not mean you are out of the woods entirely for fire blight blossom infection. The bacteria are capable of multiplying in temperatures ranging from 4⁰-32⁰C and will remain on the blossom until a wetting event occurs. As well, there is a possibility the day will be warmer than what was forecast or may be warmer in your orchard than elsewhere. In terms of fire blight infection risk, a few degrees can make a significant difference in disease pressure.

Secondary apple bloom following petal fall
Secondary apple bloom

Despite many regions seeing petal fall, secondary, or “rat-tail” blossoms are still possible. These late blooms are very susceptible to fire blight infection. Generally, continuing a protective program for a couple of weeks following petal fall will help ensure any late blooms are covered. If the day is dry and labour allows, pinching off these secondary blooms will also prevent the spread of infection. Little benefit comes from these blooms anyways.

Those that were able to get Apogee on in time applied at king bloom petal fall for management of fire blight shoot infection; however, some growers are applying Apogee earlier between pink to bloom if there is terminal growth. This product works by:

  1. Reducing vegetative growth of susceptible shoots and limiting spread of fire blight infection
  2. Thickening the cell wall to provide a physical barrier from bacterial infection
  3. Stimulating plant defense system and production of antimicrobial compounds to reduce infections.


Most areas are still within – though nearing the end of – the peak scab ascospore maturation period. Orchards that have seen a number of rain-free days could have a significant build-up of mature ascospores ready to be released during the next rainfall. Very little moisture – dew, rain or spray – is required to trigger spore release during this time. Protectant fungicide coverage is critical as most of the available mature spores are discharged within 2 hours after the start of the wetting event.

At the present time, there have been no reports of scab lesions. With the forecast weather, symptoms from mid-May infection events should start to develop on leaves where coverage was insufficient in the coming days. Keep an eye out for signs of lesions, especially in susceptible blocks or areas where coverage may not have been ideal.

Powdery Mildew

The hot, humid weather was ideal for powdery mildew development. Early signs of white fungal growth on developing terminals have been found , particularly on Paulareds which are known to be very susceptible to mildew. Most systemic fungicides applied for scab at this time of the year will have efficacy on powdery mildew. However, keep in mind, this disease likes warm, DRY weather. Keep foliage covered during these conditions even though the risk of scab infection is low.

White fungal growth of powdery mildew on apple leaf
White fungal growth of powdery mildew on apple leaf


Spring Feeding Caterpillar

Gypsy moth and other spring feeding caterpillars continue to be found along with terminal and cluster damage. Some orchards have reached threshold and growers will be applying a petal fall insecticide with activity on these pests.

Gypsy moths tend to have boom and bust life cycles, building to huge numbers every few years before predators and pathogens catch up to them and their numbers crash to very low levels for several years.  Judging by numbers in tree fruit, hazelnuts and other landscape trees, this is definitely a boom year for gypsy moths.

Mullein Bug

Mullein bug activity has begun in some orchards, exceeding threshold of 7-9 per 25 taps in some blocks. A targeted spray may be required particularly on susceptible varieties, such as Red Delicious, Spartan, Spy, Empire, Cortland, Ambrosia, Gala, Jonagold and Golden Delicious. The critical time for damage from this pest is generally from dime to quarter sized fruit. However, mullein bug is also a very effective orchard predator for mites, aphids and leafcurling midge. It’s possible if other food sources are abundant, fruit injury may be minimal despite having high numbers tapped out. The opposite, however, could be said if alternative food sources are scarce with damage found without mullein bug populations really found.

If planning to use Minecto Pro (pre-mix of AgriMek and Exirel) at petal fall, keep in mind Exirel does not have efficacy on mullein bug. Continue monitoring following application and apply a targeted control if populations exceed threshold.

A recent label expansion for Closer now included control of mullein bug, woolly apple aphid and tarnished plant bug at the high rate. The Closer/Delegate pre-mix TwinGuard also now includes these pests on the label.

Plum Curculio & Other Weevils

I have had a number of reports of plum curculio activity kicking off. Adult migration into the orchard typically begins following sustained warm weather (mean temperatures of 15.5ºC or higher) and light rain. This usually occurs around bloom and lasts for up to six weeks, with the greatest migration occurring within the period of up to 14 days after petal fall. Females start to lay eggs a few weeks after activity begins, once fruit set has occurred.

Interestingly, I’ve been noticing another weevil in the mix while scouting at a number of orchards during bloom. I believe it may be the apple blossom weevil, Anthonomus pomorum. Damage from this insect creates “capped blossoms” as a result of larva feeding on the base of the petals.

Weevil on apple blossom

Rosy Apple Aphid

Leaf curling and puckering typical of rosy apple aphid has been observed around bloom clusters. Colonies still remain in relatively low numbers. The most serious rosy apple aphid damage occurs when a toxin found in its saliva translocates from the leaves to fruit, causing apples to remain small, deformed (pigmy fruit) and unmarketable. Control is recommended if more than 5% of fruit clusters are infested.

Apple Leafcurling Midge

Apple leafcurling midge egg counts are increasing and can be found near leaf folds or margins of young, developing leaves. Leafcurling caused by cream-colored larvae can be found in orchards with high midge pressure. This damage is expected to increase in the next week or two.

Currently, only pyrethroids (Mako, Matador, Silencer, Decis) are registered for prebloom control of this pest. Movento is registered for suppression but can only be used postbloom. However, Ontario trials have found other products such as Purespray Green Spray Oil, Closer, Exirel and Delegate may also have efficacy when application timing is early in egg hatch/leafcurl stage.

San Jose Scale

Orchards in the Norfolk regions that are monitoring for San Jose scale observed the start of adult flight. Interestingly, this typically aligns with 1st generation codling moth biofix for the region but moth activity has been delayed. Degree days for San Jose scale have begun to be accumulated to predict crawler emergence. Typically, 1st generation crawlers emerge mid- to late June in Ontario and are active for 4-6 weeks.

Control is rather targeted as most petal fall insecticides will be too early for scale. One option is back-to-back sprays of Movento starting 10-14 days after petal fall, or early June. This is a slower-acting product and requires a couple of weeks to see control so timing is best before crawler activity begins. Another option is a back-to-back spray of Sivanto Prime, Closer or TwinGuard (pre-mix of Delegate and Closer) starting at crawler emergence.


Mite activity increased during the hot spell last week. Be sure to keep mite pressure under control, especially if spur leaves are looking rather small.

Beneficial insect activity has also been increasing including spiders, lacewing and lady beetles.

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