Production and pest update brought to you by the OMAFRA Apple Team:
Erika DeBrouwer, Tree Fruit Specialist and Kristy Grigg-McGuffin, IPM Specialist
Table of Contents
Growth Stages
We are seeing mixed staging on the tree, meaning bloom hasn’t been uniform. This will make for a difficult thinning season, along with potential future challenges with late bloom.
Regionally, growth stages are fairly spread out depending on cultivar and proximity to water:
- In Essex, Chatham-Kent, Lambton, Middlesex, Elgin, Norfolk, Brant and Niagara, most cultivars are at king bloom, or will be shortly. In early areas, more inland sites are full pink to full bloom.
- In Grey, most cultivars are at early pink.
- In Durham, Northumberland and Quinte, most cultivars are at tight cluster with some pink on early varieties.
- Further along the St. Lawrence and into the Ottawa Valley, apples are at tight cluster, just starting to show pink.
Frost Update
Areas across the province have reported frost damage from last week’s low temperatures. Parts of the province reached as low as -6 °C, where most areas experienced between -1 and -3 °C. Damage has mostly been seen in the pistils, specifically in flowers at lower parts of the tree, affecting areas and varieties that were further advanced. We have a few more weeks until we are out of the frost-free days, but the forecast looks mild and hopefully it stays as such.
Disease Development
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.
The risk of fire blight infection is possible if the following conditions are met:
- 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.
- 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.
- 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.
Pre- and early bloom management options
Consider alternatives to antibiotics during the early bloom period, especially if risk remains low to moderate but fire blight has been an issue in your orchard before. These include:
- Biologicals – eg., Blossom Protect, Buran, Serenade, Regalia or Double Nickel
- Surface sterilant – eg., Oxidate
- Copper labelled for in-season use – eg., Cueva – note that copper and some fungicides are not compatible with certain biologicals. Check the label before use.
Pink is also an important timing if using the Bacillus product, Lifeguard. This product works by activating the tree’s defense mechanism and is most effective when it is applied before infection occurs or when added to a fungicide rotation. A few notes of importance:
- This is a biological product and should not be tank-mixed with antibiotics such as Streptomycin and Kasumin.
- Initial inducement of plant defense response occurs soon after application but 3-5 days are required to attain maximum level of protection.
- Avoid application during bloom as this product is toxic to bees. Applications can pick up again at petal fall after hives have been removed.
Insects of Interest
Spring-feeding caterpillar
The first signs of caterpillar damage can be found on growing terminals and fruit buds. In general, an insecticide is usually recommended when the action threshold of 12-15 larvae per 100 terminals and fruit buds is observed. If spring-feeding caterpillar such as leafrollers, spongy moth, budmoth or green fruitworm have been a problem in previous years, keep an eye out for damage and consider management if pressure is high. Click here for registered prebloom control products for spring-feeding caterpillar.
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.
Rosy apple aphid
If this spring continues to be on the cooler, 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 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 are considering a prebloom insecticide.
Plum curculio
The first adult plum curculios were found in monitoring traps placed outside the perimeter of orchards this week with the sunny, warm days that followed the weekend rains. This indicates the start of curculio movement into the orchard from adjacent overwintering sites in nearby woodlots and shelters. Activity will continue into petal fall.
Monitor for signs of oviposition or feeding scars on the flower bud or developing fruitlet.
Apple leafcurling midge
Adult leafcurling midge flight has begun. With the warm weather this week, emergence has spiked. Egg laying is likely to begin over the next week in the earlier regions of the province. Emergence predictions for the 1st generation are summarized below.
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) |
|---|---|---|---|
Harrow | Passed | May 7 | >14 days |
London | May 4 | May 10 | >14 days |
Delhi | May 4 | May 11 | >14 days |
Grimsby | May 5 | May 11 | >14 days |
Collingwood | May 12 | >14 days | >14 days |
Durham | May 13 | >14 days | >14 days |
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.
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.
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