Production and pest update brought to you by the OMAFRA Apple Team: 

Erika DeBrouwer, Tree Fruit Specialist and Kristy Grigg-McGuffin, IPM Specialist

Grower Grind

A warm start to the week rapidly pushed bloom ahead across much of the province and provided several good pollination days. Cooler, unsettled weather returned, unfortunately, with wind creating the biggest challenge for timely spray applications. As orchards move through bloom and petal fall, primary management has been focused on preventative fungicide applications, petal fall insecticides, and assessing chemical thinner strategies under such variable conditions.

Growth Stages

Southern regions are pushing quickly in fruit set, while other regions are just hitting bloom. Cooler temperatures are expected to continue into next week, so keep this in mind for chemical thinner applications.

• Essex & Chatham-Kent – Fruitlet sizing (8-12 mm)
• Lambton, Middlesex, Elgin – Petal fall to fruitlet sizing (8 mm)
• Norfolk – Bloom to petal fall
• Brant, Wellington – Bloom to petal fall
• Niagara – Bloom to petal fall
• Grey – King bloom to full bloom
• Durham, Northumberland and Quinte – King bloom to full bloom
• Ottawa Valley – King bloom

Fungus Amoung Us (*And Bacteria)

Scab

Many regions are nearing the end of the ascospore maturation period. This means that for future rain events, still expect that primary infection is a risk and keep good fungicide coverage on those rapidly growing leaves – and more importantly now, developing fruitlets!

Early signs of scab lesion development have been found. The table Relationship of Temperature and Moisture to Apple Scab Infection (also summarized below) provides the number of days after infection before lesions will become visible.

Now is the time to start monitoring blocks for signs of lesions. Take a good look at the top AND underside of leaves for velvety brown lesions with indistinct margins. Overwintering spores are coming from the orchard floor, so most early season infections typically start on the underside first. Things have also been fairly windy this season which could impact spray coverage, particularly in the upper canopy. Look at all parts of the canopy to ensure there are no escapes.

If lesions are present, continue a regular protectant program to prevent secondary infection on developing fruitlets.

Number of days required for apple scab lesions to appear following an infection event

Average temperature (C)	Lesion appearance (days)
0-5	–
6-9	17
10	16
11	15
12-13	14
14-15	12-13
16-24	9-10
25+	–

Fire blight

Blossom blight

The Ontario fire blight prediction maps continue to be updated regularly. Right now, they’re showing low to moderate risk thanks to the cooler temperatures. That said, this dip in risk is likely temporary – warmer weather next week could push things back up again.

Fire Blight Prediction Maps

It’s also important to remember that just because the model shows lower risk, it doesn’t mean the bacteria is gone. The warm temperatures earlier this week would have helped build up bacterial levels (which can survive on surfaces for a couple of days), especially in orchards with a history of fire blight. Keep fire blight on your radar and be ready to act if needed.

For more information on fire blight, check out last Monday’s post Fire Blight Risk Increases Across Province.

Extended bloom

As bloom winds down, pay close attention to staggered or irregular bloom. With different bloom stages occurring within an orchard (or even on a tree), the window of infection risk is extended until the last blossom falls. This also includes delayed bloom on young trees and secondary, or rat-tail bloom.

Trauma blight

This week’s storm also raises concern for trauma blight. Strong winds, hail, and driving rain can spread inoculum and create entry points for bacteria independent of flower infection. Assess for signs of damage in all blocks following any storm.

Be sure to apply Streptomycin (PHI 50 days) or 0.5-0.8% Cueva as soon as possible after the trauma event, especially if foliage damage is extensive or fire blight is known to be active in the orchard (ie., cankers, etc). Ideal timing is 4 to 12 hours after a storm. Anything applied later runs the risk that the bacteria will have already established and begun to grow, reducing the efficacy of the product.

For registered control options, see the Ontario Crop Protection Hub.

Bugs Behaving Badly

Insect activity has been fairly quiet so far this season. However, the warmer temperatures brought about more sightings. Keep up with regular monitoring to keep ahead of any development!

Petal fall insecticide sprays are beginning to go on in the earlier regions of the province.

The following link is a summary of efficacy of registered products for common petal fall pests. Efficacy will be based on rate used.

Caterpillars

The spray window for oriental fruit moth is quickly approaching in most early regions. Some growers are opting for insecticides with good efficacy on mullein bug, plum curculio, spring-feeding caterpillars and/or apple leafcurling midge, if monitoring had indicated they had reached threshold or have high pest pressure.

Spring-feeding caterpillar activity can still be found. Of the caterpillar complex, leafroller and spongy moth can be found causing significant damage in some parts of the province, especially those orchards that saw high pressure in the last two years.

Mullein bug

Low numbers of mullein bugs are being tapped out in various orchards across the province. Controls are warranted when threshold reaches 7-9 nymphs per 25 taps. Continue to monitor as populations can jump quickly, especially on susceptible varieties such as Red Delicious, Spartan, Spy, Ambrosia, Empire, Cortland, Gala, Jonagold and Golden Delicious.

Plum curculio

Plum curculio have been found in monitoring traps within high pressure orchards, indicating they are beginning to migrate from surrounding overwintering sites. Keep an eye out for damage to the blossoms and developing fruitlets, especially once sunny days come back. During cooler weather, these weevils tend to move slower, opting to crawl in from surrounding woodlots; however, on warmer days, they’ll fly in which is often when there is an increase in observed damage during these periods.

Degree (Days) of Separation

Apple leafcurling midge

Adult flight has picked up this week but there are still little signs of egg laying and leaf curl in the orchards we are monitoring.

Emergence predictions for the 1st generation adults are summarized below. Targeted prebloom products can be applied in blocks with a history of this pest. Otherwise, considering efficacy at petal fall. Target applications between 5 and 50% emergence.

• While Movento is registered for suppression, the timing for leafcurling midge is often earlier than for scale and woolly apple aphid so would have to be chosen based on which pest is of greater concern in your orchard.
• Other petal fall insecticides such as Delegate, Closer and Exirel (and for that matter, Minecto Pro) that may provide some efficacy as well, which could help delay the Movento application.
• Pyrethroids are registered but have greater efficacy earlier to target adult midges and can be very harsh on the numerous beneficial insects that are now active in the orchard.
• Summer oils will also help to smother eggs so long as good coverage is achieved to reach within the newest terminal leaves.

For a full list of registered products, see Leafcurling Midge on the Ontario Crop Protection Hub.

Predicted emergence date of first generation adult apple leafcurling midge, by region (biofix March 1st, base 9C)

Region	5% Gen 1 (76 DDC)	50% Gen 1 (132 DDC)	95% Gen 1 (235 DDC)
Essex	Passed	Passed	Passed
Lambton, Middlesex, Elgin	Passed	Passed	June 2
Norfolk	Passed	Passed	June 1
Wellington	Passed	May 26	>14 days
Niagara	Passed	Passed	June 3
Grey	Passed	May 26	>14 days
Durham, Northumberland	Passed	May 31	>14 days
Ottawa	Passed	May 27	>14 days

Scale

Based on current degree day accumulations, the 1st generation San Jose scale crawler emergence is predicted to begin in the earliest regions of the province in the next 14 days (predicted emergence of 278 DDC).

Once crawler activity (ie., movement to new shoots and developing fruit) begins, this will continue for 4-6 weeks. Registered products including Closer 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. Depending on the product, this timing may also have efficacy on woolly apple aphid and/or leafcurling midge.

For a full list of registered products, see San Jose Scale on the Ontario Crop Protection Hub.

Predicted emergence date of first generation San Jose scale, by region (biofix March 1st, base 10C)

Region	Current Degree Day Celsius (DDC)	Predicted Crawler Emergence (278 DDC)
Essex	210 DDC	May 30
Lambton, Middlesex, Elgin	112 DDC	>14 days
Norfolk	129 DDC	>14 days
Wellington	82 DDC	>14 days
Niagara	128 DDC	>14 days
Grey	93 DDC	>14 days
Durham, Northumberland	66 DDC	>14 days
Ottawa	72 DDC	>14 days