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
Irrigation
This week is hot, hot, hot! Please review the following blogs for more information about proper irrigation timings and calculations.
Sunburn
When Sunburn Occurs
Sunburn can occur at various temperatures and is affected by many environmental factors but can be worse if there is a week of cool, windy, overcast weather followed by a hot (over 30°C) calm day with full sunshine. The fruit surface can be 14 to 17°C hotter than the air temperature, where sunlight, calm wind and low humidity contribute to this increase. Water stressed trees are even more prone to sunburn damage.
Types of Sunburn
Type of Sunburn | What Is It? | How Does It Happen? | What Happens to the Fruit? |
|---|---|---|---|
Sunburn necrosis (Fig 1A&B) | When the fruit surface temperature exceeds 50°C for as little as 10 minutes, causing cell death. | Caused by excessive heat and is exacerbated by low humidity. | Cell death occurs, causing brown or black lesions. |
Sunburn browning (Fig 1C&D) | Combination of UV-B radiation and high fruit surface temperature causing degradation of cell membranes. Sunburn browning can contribute to storage/delayed sunburn. | Typically occurs between fruit surface temperatures of 45 – 49°C, although this can change based on the variety (i.e. Honeycrisp is more sensitive than Red Delicious or Braeburn). Higher risk occurs between the hours of 11am and 5pm when maximum daily air temperature and mean maximum hourly temperature are high. | Yellow, bronze or brown spot develops on the sun-exposed side of the peel but may not appear for a few days. |
Photo-oxidative sunburn (Fig 1E&F) | Shock exposure to visible light due to light intensity, which can occur at low temperatures (17°C). | Risk factors include hand thinning, tree training, selective picking, summer pruning, branch movement and postharvest transit. Photo-oxidative sunburn has been seen in the province where areas that have had ‘overcast’ conditions due to the smoke, with a sudden break and intense sunlight could have led to fruit sunburn. | Bleaching and eventual darkening of the peel. |
Storage sunburn | Symptoms develop after harvest within the first few months of cold storage. | Exposure to excess heat and light stress during the growing season. | Fruit appears normal at harvest but develop brown discolouration during storage. |
Strategies to Mitigate Sunburn
Strategy | Definition & Use | Pros | Cons |
|---|---|---|---|
Evaporative cooling | Overhead irrigation that reduces air temperature due to water vapourization | – Water stains on fruit – Root flooding | – Expensive to install, maintain and operate – Access to water source during peaks |
Protective netting | Overhead netting that reflects/absorbs sunlight | – Can reduce effects of wind / hail damage – Colour of net can influence growth, colour and quality | – Expensive – Learning curve for deployment and removal – Colour of net can influence growth, colour and quality |
Sprayable protectants* | Application of materials on fruit to create a physical barrier | – Spot treatment | – Not as effective as other options – Reapplication often required |
Other preventative measures include:
- Summer pruning – should be performed on cool days with 3 or 4 days remaining cool in the forecast.
- Adequate moisture – should be provided to trees to encourage resilience during periods of stress.
- Harvest management – fruit should be moved quickly out of the sun, preferably into storage as soon as possible.
Hedging
Why or Why Not Should I Hedge?
Reasons why hedging is utilized:
- Filling in blind wood near the trunk
- Restricting canopy depth and height
- Light management in late winter/early spring, summer and close to harvest
It is possible to transition an existing block from strictly hand pruning to incorporate hedging. Big limbs should be removed manually over several dormant pruning seasons prior to hedging. Trial this new method on a small area first if you are unfamiliar with the results it will create. Note that some production will be lost, and that hedging is not practical and beneficial for every system.
Considerations:
- Hedging it easiest to execute when it is considered in the design of a new planting, but it can still be implemented to an existing block over time
- Hedging will ‘set the box’ for improved labour efficiency (harvest, pruning)
- Hedging will ‘set the box’ for improved uniformity of tree and fruit (colouration)
- Hedging does not necessarily need to be completed each year
- Hedging has a lack of selectivity compared to manual pruning
- You will still need to visit trees individually to remove unwanted branches, cut fruit, and to clean up hedging cuts
When Should I Hedge My Trees?
Research in Europe and in the U.S. has shown that precise timing of hedging can achieve different results. Each grower may choose different timing for ages of trees or cropping histories. For example:
- Dormant to early spring hedging can stimulate growth on weaker trees.
- Late June hedging as fruit bud initiation begins can minimize regrowth and encourage fruit bud formation.
- Hedging in August can expose fruit to the sun to improve fruit colour.
Caution must be taken to prevent several potential problems:
- Freshly exposed fruitlets can quickly sunburn. Apply sunshade products before hedging.
- Fire blight bacteria can infect open wounds. Do not hedge if fire blight is present, and choose warm, dry days to hedge for quick wound healing.
- Trellises must be straight, and drive rows need to be smooth to avoid damage to hedging equipment or trellis.
What Type of Hedger Should I Use?
Most effective hedging has been accomplished with maneuverable cutter bars. This limits the size of cut that can be made and confines hedging to removal of young wood.
How To Make Hedging Worth It?
The main hindrance for hedging to be implemented in orchards is the lack of branch selectivity. Hedging cannot replace hand pruning entirely but allows for more efficient detailed work. The most effective use of hedgers is in orchard systems that are approaching their desired optimum size. This allows for establishment and maintenance of tree shape.
Disease Concerns in Unsettled Weather
Fire Blight
The unsettled weather we are experiencing may bring hail, strong winds or heavy rains that could trigger trauma blight. These could be very isolated events, occurring in one area but not another nearby. 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, strikes, 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.
Summer Disease
Now is the time to start considering summer disease management. While symptom development doesn’t really start to appear for fruit rots, fly speck and sooty blotch until later in the summer or into the fall, infection actually happens now.
We have had ideal bitter rot infection conditions over the last week with the hot, humid weather followed by rain. With hand thinning beginning, be sure to toss thinned fruitlets to the row middle and mulch. These fruit have been known to cause infection of remaining fruit on the tree by splashing spores during rain events.
Infection timing for fly speck and sooty blotch should also be considered. In wet years, infection typically begins 2-3 weeks after petal fall. There is a fly speck forecasting model that predicts the start of infection beginning 175 leaf wetting hours after petal fall.
Table 3 summarizes activity of fungicides that could be used for summer disease control. Residual protection will vary depending on the product used. For example, Pristine can provide reasonable residual control of summer disease up to 3 weeks at the labelled rate in ideal conditions; however, captan should not be pushed further than 14-days between sprays particularly since it is not as strong on fly speck and sooty blotch as other control products. In all cases, reduce interval to 7 days during times of hot, wet weather.
Table 3. Activity of registered fungicides on fly speck/sooty blotch, black rot and bitter rot
Product | Group | PHI | Scab | Fly speck / sooty blotch | Black rot | Bitter rot |
|---|---|---|---|---|---|---|
captan | M | 19 days* | +++(+) | ++(+) | +++(+) | +++ |
Folpan (NR) | M | 1 day | ++(+) | ++(+) | ++(+) | +++ |
Senator (NR) | 1 | 1 day | +++ | ++++ | +++ | + |
Aprovia Top | 3+7 | 30 days | ++++ | +++ | — | — |
Inspire Super | 3+9 | 14 days | ++++ | +++(+) | — | — |
Pristine | 7+11 | 5 days | +++(+) | +++(+) | +++(+) | +++(+) |
Merivon | 7+11 | 0 days | +++(+) | +++(+) | +++(+) | +++(+) |
Flint | 11 | 14 days | ++++ | ++++ | +++ | ++(+) |
Allegro | 29 | 28 days | ++ | +++ | + | +++ |
Phostrol | 33 | 1 day | — | ++ | — | — |
Regalia | P5 | 0 days | +(+) | +(+) | ++ | +(+) |
— = activity is unknown for this pest
Important cultural management recommendations include:
- Prune and thin clustered fruit to facilitate drying and improve fungicide coverage.
- Remove potential sources of inoculum such as dead branches, fruit mummies (where possible), infected fruit on the orchard floor and alternate hosts including brambles (blackberry, raspberry) from surrounding hedgerows or woodlots.
- Toss pruning cuts and thinned fruit in the row middle and mulch.
- Reduce tree stress by irrigating and/or applying a sun protectant, especially ahead of a heat wave.