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
Grower Grind
This weekend is finally calling for some warm weather and sun! Minimal progression from a staging standpoint has happened over the past week, but with the forecast of heat, things could move quickly! Planting, pruning and spraying are ongoing across the province.
Growth Stages
Southern regions are pushing petal fall, where late regions are hold strong at tight cluster.
- Essex & Chatham-Kent – Bloom to petal fall
- Lambton, Middlesex, Elgin – Bloom to petal fall
- Norfolk – Bloom
- Brant, Wellington, Halton – Bloom
- Niagara – Bloom
- Grey – Tight cluster to pink
- Durham, Northumberland and Quinte – Tight cluster to pink
- Ottawa Valley – Tight cluster
Terminal Growth
We’re just starting to get a bit more heat (and hoping it continues). Terminals are growing at the Simcoe Research Station with the following measurements and growth stages:
Cultivar | Growth Stage | Terminal Measurements (cm) |
|---|---|---|
Ambrosia | King Bloom | 3.2 |
Brookfield Gala | King Bloom | 5.7 |
Honeycrisp | Full Bloom | 5.9 |
Cold Confusion: Purple, Pale and/or Puckered Leaves
Certain areas have been noticing damage to floral parts from the recent cold events – but we have yet to showcase leaf injury and damage. If you are seeing the following, it could mean your trees are experiencing abiotic stress/damage caused by cold temperatures:
- Necrotic or dark lesions between leaf veins
- Pale new leaves
- Purpling on the underside and/or along leaf margins
- Puckering and/or cupping between leaf veins
These symptoms can arise from cold weather because of the physiological processes that aid in protecting the tree. Below are symptoms and reasons how cold weather affects leaf processes:
- Purpling: purpling of leaf margins and undersides after prolonged cool temperatures can be caused by (i) the temporary restriction of phosphorus, as cold soils reduce root activity and (ii) the accumulation of anthocyanin pigment, as sugars accumulate rather than being transferred.
- Paleness: pale leaves can occurs in cold temperatures due to (i) slower chlorophyll production and (ii) restricted nitrogen uptake.
- Puckering: puckering/cupping of leaves occurs from cool weather when cells are expanding and water movement is restricted.
These symptoms will usually rebound once warmer weather comes, but if portions of leaves are dead – brown or blackened patches (photo below) – this will not be remedied.
Thinning After the Cold
When deciding chemical thinner application, make sure you assess for frost damage before making any decisions and follow suggestions laid out by Dr. John Cline, Professor, Pomology and Tree Fruit Physiology, Dept. of Plant Agriculture, University of Guelph, Simcoe Research Station.
- If flower injury is light (less than 30% brown, damaged buds), the potential for a good crop is certainly still there.
- But if injury is in the moderate to severe range (greater than 50%) growers should keep a close eye on the important fruit-set period following petal fall.
- Certainly, significant frost/freeze injury (>60%) will make thinning decisions more complex.
If the king-bloom is killed leaving several viable lateral fruitlets, thinning may become more difficult due to less differentiation in size and greater inter competition between lateral fruitlets. In this instance, it may be prudent to wait until fruit sizes differ within the cluster, and once fruit set is more apparent. Apply thinners before the largest fruit is no more than 14-15 mm.
When the lower part of the tree canopy is more affected, apply 65-90 % of water volume to the top half of the tree canopy and consider turning off the lower nozzles on the sprayer. Reliance on some hand thinning may be necessary to selectively remove fruit with frost markings or misshappen fruit. Remember, only approximately 5% of flowers are required to set a full commercial crop.
If the frost has resulted in significant crop reduction, then you may want to seriously consider controlling growth for the growing season using Apogee/Kudos. Sprays for this begin at petal fall.
Fungus Amoung Us (*And Bacteria)
Fire blight
Fire blight infection risk will be HIGH to EXTREME in many regions over the next few days with the warmer weather and potential for rains. Keep open blossoms protected! For those earlier regions that have reached petal fall, be on the look out for delayed bloom.
If you’re not already watching the Ontario fire blight prediction maps, now is the time to key an eye out.
With early bloom, some growers have opted for antibiotic alternatives such as Buran, Serifel, Serenade, Blossom Protect, Double Nickel or Cueva, especially with risk being lower until now. This helps to save Streptomycin or Kasumin for full bloom and when risk is high.
As bloom progresses, frequent protective sprays may be needed if risk remains high as new blossoms are opening daily and will not be protected by sprays made while these blooms were closed. As well, antibiotics degrade rapidly in sunlight so are only active for 2-3 days MAXIMUM. Apply these products as close to a wetting event as possible. For resistance management with antibiotics, rotate between Streptomycin and Kasumin.
If there are any concerns about missing a potential infection event or potential trauma during a rain or wind storm, Streptomycin provides kickback activity but should be applied within 12 hours after the event. Kasumin does not provide kickback activity.
Those at king bloom petal fall are also applying Apogee/Kudos (typically when growth is 2.2 – 5.5 cm long) to help with shoot blight management.
For a full list of registered products, see Fire Blight on the Ontario Crop Protection Hub.
Scab
Most areas are still within – though nearing the end of – the primary apple scab 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.
The small, periodic rains that some regions have been getting may be helpful to release any newly matured ascospores without causing infection. Many of the wetting events haven’t been long enough to meet those infection requirements. However, continue to keep good coverage with each potential infection event until the end of primary infection period when all ascospores have matured and released. With temperatures above 15C, only 6 hours of leaf wetness (from start of wetting event until leaves are fully dry, or relative humidity drops below 90%) are required for germination to occur.
Now is the time to start looking for signs of infection from the previous weeks. 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. Be sure to look carefully at the underside of older leaves, which would have been present at time of infection.
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+ | – |
Other diseases
On a good note, the cooler spring has kept powdery mildew pressure relatively low. Mildew thrives in dry weather and high relative humidity.
Very little signs of frog-eye leaf spot (foliar symptoms of black rot) have developed as of yet this year. Optimum temperature for leaf infection is 26⁰C. However, infection can occur any time above 10⁰C but will just require a longer leaf wetting period (more than 24 hours at 10⁰C).
As mentioned above, dark spots on leaves caused by frost damage can look similar to frog-eye leaf spot. Note any accompanying symptoms like leaf discolouration or puckering/cupping that may give some indication this damage is environmental, not fungal. Frog-eye leaf spot will appear as distinct round lesions with light tan centers.
Bugs Behaving Badly
Insect activity has been eerily quiet so far this season. With the warmer temperatures coming, be prepared for this to change. Keep up with regular monitoring to keep ahead of any development!
Apple leafcurling midge
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.
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 | May 19 |
Chatham-Kent | May 17 | May 24 | >14 days |
Lambton, Middlesex, Elgin | Passed | May 18 | >14 days |
Norfolk | Passed | May 18 | >14 days |
Wellington | May 17 | May 26 | >14 days |
Niagara | Passed | May 19 | >14 days |
Grey | May 16 | May 28 | >14 days |
Durham, Northumberland | May 20 | >14 days | >14 days |
Ottawa | May 18 | May 26 | >14 days |
Scale
Based on current degree day accumulations, the 1st generation San Jose scale crawler emergence is predicted to begin across the province in several weeks (predicted emergence of 278 DDC).
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 | 156 DDC | >14 days |
Chatham-Kent | 37 DDC | >14 days |
Lambton, Middlesex, Elgin | 75 DDC | >14 days |
Norfolk | 80 DDC | >14 days |
Wellington | 43 DDC | >14 days |
Niagara | 74 DDC | >14 days |
Grey | 54 DDC | >14 days |
Durham, Northumberland | 27 DDC | >14 days |
Ottawa | 31 DDC | >14 days |
Mites
European red mite activity has begun though overall populations remain fairly low likely due to the cooler weather. Those orchards that did not apply an early season oil should be monitoring and be aware of the appropriate timing for whichever product you use as some can only be applied within weeks of petal fall (eg., AgriMek, Minecto Pro), require earlier application as populations build (eg., Nealta) or have a slow knock-down (eg., Envidor).