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

Not much has changed from our previous blog post. Growers are early planting and are in the later stages of pruning. Fertilizers are being applied and spray season continues; where early areas have multiple applications, and later districts have begun as tree growth progresses and warm temperatures move in. Thinning strategies are top of mind as growth staging progresses.

Growth Stages

This time of year is showing some variation across the province in growth staging due to the ever-changing weather. Cool temperatures have slowed progression of growth over the past week, although with warm conditions and sunshine may push things quickly.

• Essex & Chatham-Kent – king bloom to petal fall
• Lambton, Middlesex, Elgin – Tight cluster to early bloom
• Norfolk – Tight cluster to early bloom
• Brant, Wellington – Tight cluster to early pink
• Niagara – Tight cluster to early bloom
• Grey – Tight cluster to early pink
• Durham, Northumberland and Quinte – Tight cluster to early pink
• Ottawa Valley – tight cluster

Frosty the Threshold

Some murmurs of cooler nights have sparked discussion on critical temperatures. Here is a refresher chart, along with resources for frost mitigation and assessment.

Apples	Silver Tip	Green Tip	½ inch Green	Tight Cluster	First Pink	Full Pink	First Bloom	Full Bloom	Post Bloom
Old temp	-8.9	-8.9	-5.6	-2.8	-2.8	-2.2	-2.2	-1.7	-1.7
10% kill	-9.4	-7.8	-5.0	-2.8	-2.2	-2.2	-2.2	-2.2	-2.2
90% kill	-16.7	-12.2	-9.4	-6.1	-4.4	-3.9	-3.9	-3.9	-3.9

Frost Mitigation and Assessment Resources

• Freeze protection methods for crops | ontario.ca
• Frost Warnings and Tools for Frost Protection in Apples and Pears – ONfruit
• Reducing Frost Damage in Tree Fruit – ONfruit
• Evaluating Frost Damage on Buds in Tree Fruit – ONfruit

Fungus Amoung Us (*And Bacteria)

Scab

Most areas have experienced multiple apple scab infection events over the last couple of weeks. Earlier regions of the province are beyond 50% ascospore maturation, while later regions are at about 30-50% of ascospores matured. This means that for future rain events, expect large ascospore release and keep good fungicide coverage on those rapidly growing leaves. With temperatures above 15C, only 6 hours of leaf wetness are required for germination to occur.

With the extended wetting periods last week, coverage was certainly a concern. Many growers opted for kickback products such as Scala, Inspire Super, Luna Tranquility, Cevya and Buran to provide extra protection.

Monitor blocks where coverage may have been inconsistent to look for signs of lesions. 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. At the predicted time, begin looking on the top and underside of leaves for velvety brown lesions with indistinct margins.

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

If you’re not already watching the Ontario fire blight prediction maps, now is the time to key an eye out. As of yet this year, low heat unit accumulations have kept risk relatively low (see more details below), which is why most areas remain at Low to Caution risk ratings. With the warm weather, potential rains and the start of bloom for many in the coming days, fire blight risk may also take a big jump.

Fire Blight Prediction Maps

A reminder, the risk of fire blight infection is possible if the following conditions are met:

1. Flowers are opened and/or are opening – There is no risk of infection if bloom is not present in the orchard despite the fire blight maps stating caution to extreme; however, keep an eye on any early signs of bloom as it can happen quickly.
2. Enough heat units have accumulate based on forecasting models – The fire blight maps use Cougarblight but this applies to MaryBlyt as well. Similar to degree days, daily temperature is accumulated and must reach a certain point before risk increases.
3. A wetting event is predicted – Any type of wetting event will wash the bacteria into the open bloom including rain, dew or even the artificial rain shower you create with the sprayer during critical infection periods.

**Frost-injured blooms can still be at risk of infection. Damage to pistil and ovary does not likely have an effect on entry of the bacteria into the flower as bacteria are washed into the nectaries, or flower cups. As well, frost can cause wounding and damage to the base of the petals or tender wood surrounding blooms. This wounding creates another point of entry for the fire blight pathogen should bacterial cells be transferred to this surface via rain, wind, insects or contaminated equipment.

Bugs Behaving Badly

Spring-Feeding Caterpillar

For the most part, insect activity has been low. However, this week there have been a few signs of early spring-feeding caterpillar damage, in particular leafrollers. Look for signs of leaf feeding, rolled terminal leaves and webbing.

When scouting between tight cluster to petal fall, check 5 terminal shoots and 5 fruit buds in 10 trees (50 terminals and 50 fruit buds in total). Control is typically warranted when 12-15 terminals and buds are infested. Click here for registered prebloom control products for spring-feeding caterpillar.

Apple Leafcurling Midge

Another insect pest we commonly start to see an increase in activity at tight cluster to pink is apple leafcurling midge. Despite the cooler weather, leafcurling midge flight has started to kick off. There are still no signs of egg laying but I imagine this will begin in the coming weeks. I will continue to provide updates on egg laying as well as regional degree day predictions.

Aphids

If this spring continues to be on the cool, wet side, be prepared for rosy apple aphid populations to build. Egg hatch is likely on-going currently but infestations really start to be observed into tight cluster to bloom. Pay particular attention to fruit clusters of susceptible cultivars like Cortland, Idared, Golden Delicious and Ambrosia.

Tarnished plant bug

Adult tarnished plant bug activity has been reported in various regions of the province. Feeding damage can occur on the developing flowers and early-stage fruitlets resulting in dimpled or sunken areas on the fruit. Those orchards that have had a historical issue with this pest and are still at tight cluster to pink are considering a prebloom insecticide.

Oriental Fruit Moth

Oriental fruit moth trap catch has jumped this week in early regions of the province. This will be used to determine peak flight or to kick off degree day modelling (first sustained moth catch) for targeting first generation timing. Terminal flagging, especially on young plantings can be an issue early season by this pest. 

Mites

European red mite egg hatch has started. At this point, the use of a delayed dormant oil will no longer be as effective. Click here for registered petal fall miticide options for European red mites. More information on the activity and target life stages of miticides can be found in the table, Activity of Miticides Registered on Apple and/or Pear in Ontario.

Beneficial insects

Many beneficial insects can be found out in orchards now including lady beetles, assassin bugs, spiders and ground beetles. To support these populations, choose control products that are softer on beneficial insects. This information can be found in the “View Details” section of products listed in the Fruit Crop Protection Search.