Production and pest update brought to you by the OMAFA Apple Team:
Erika DeBrouwer, Tree Fruit Specialist and Kristy Grigg-McGuffin, IPM Specialist
August has arrived, bringing with it the final stretch of summer and a noticeable shift in the orchard. For Ontario apple growers, this month marks a critical transition – from monitoring and maintenance to preparing for harvest. The fruit is sizing up, colour is beginning to show, and the results of this season’s hard work are finally becoming visible. Continue to fine-tune insect and disease management strategies, and keep a close eye on weather that can either help or hinder the final push to harvest.
Table of Contents
Growth Stages
Terminal bud set continues. With the on-going heat, some cultivars like Ambroisa are showing signs of reverting. Not only is water critical at this time for floral induction, but also fruit sizing. Be sure to provide your trees with enough water and nutrients for this season and the next.
At the Simcoe Research Station, fruitlets and terminals are sitting at the following:
Honeycrisp | Ambrosia | Gala | |
|---|---|---|---|
Fruitlet Size | 71.3 mm | 62.1 mm | 62.1 mm |
Terminal Growth | 30.5 cm | 24.9 cm | 35.4 cm |
Paint It Red (With Science)
With harvest closely upon us, the push for fruit colour also intensifies.
The best option for ideal colouration is to have an open canopy to allow light penetration throughout the tree.
Although having an open canopy aids significantly in colouration, sometimes a boost is needed. Options that may be of interest include:
- Leaf Removal: whether that be manual (pruning) or mechanical (defoliator)
- Nutrients: phosphorus, magnesium, and boron have shown to aid in colour development, along with nutrients like calcium, zinc and manganese indirectly affecting colour.
- Plant Growth Regulators: in the form of colour enhancers and fruit maturation inhibitors
- Reflective Ground Cover: this includes various materials that are laid beneath the tree and in the alley to reflect the sun
For more specifics on apple colour aids check out the Rouge Regime article.
Remember that:
timing is critical for all colouring technologies
AND
cool nights are still needed for the success of any colour aid.
iClouds Not Synching
Continued dryness throughout the province (Figure 1) over the past few weeks and/or months depending on the location, has growers irrigating regularly.
Maps of current agroclimate conditions – Agriculture and Agri-Food Canada
Thirst Things First
Knowing how much water is needed for your trees, based on your soil, temperature, relative humidity, wind speed, and solar radiation, is important before making any decisions. If rainfall isn’t meeting the demands needed by your trees irrigate if possible.
Learn how to calculate your trees needs based on evapotranspiration here: Drip Irrigation Scheduling
An example calculation of evapotranspiration can be found here: Using ET Data to Make Irrigation Decisions
If water resources need to be dispersed due to limitation of water levels consider the steps below:
- Prioritize newly planted and young trees due to their minimal root system in comparison to mature tree root systems.
- Monitor for signs of drought stress. Pale, wilted or scorched leaves, along with early leaf senescence or drop. Trigger water if these symptoms are seen.
- Other considerations, such as weed management to encourage water be directed to your crop, and purchasing of rain gauges and/or soil moisture monitors to aid in water management.
Alternatives to Irrigation Systems
For growers that do not have an irrigation system, here are some alternatives:
Purchase water from a water hauling company
Water can be held in tanks until needed. This can be costly over time and requires additional infrastructure (holding tanks and delivery access).
Purchase municipal water from hydrants
This can also be costly, and may not be an option for all locations.
Access water from a neighbour
A written agreement may help to ensure the sharing arrangement is clear for both parties and help avoid disputes.
- Ensure that the total withdrawal complies with the Permit To Take Water (PTTW) issued by the Ministry of Environment Conservation and Parks (MECP).
- A PTTW is required for takings of 50,000L or more on any one day from any water supply, either groundwater (wells) or surface water (pond, stream, wet area, ditch etc.). 50,000L is equivalent to approximately half an acre irrigated with one inch of water.
- For more information about PTTWs see https://www.ontario.ca/page/permits-take-water or call 1-800-461-6290
Best Practices for Manual Watering
- Keep water close to the root zone. Wet only around the base and avoid flooding beyond that zone.
- Water frequently but in reasonable amounts. Mimic drip irrigation by watering in smaller doses more often.
- Let the soil dry slightly between watering. This encourages deeper root development and improves drought resilience.
- Water during the cooler parts of the day. Early morning is best as it reduces evaporation losses.
For more detailed information regarding irrigation check out the links below
- Watering Strategies for Grape Growers without irrigation
- Drought monitoring and irrigation for apples and grapes
- Agricultural irrigation
Last Bite
As harvest approaches, pest management decisions shift from protecting developing fruit to ensuring fruit quality and minimizing residues. Even though the bulk of your pest worries may have lessened, late season pressure from both insects and pathogens can still downgrade fruit and complicate storage.
Keep the following in mind over the next few weeks leading up to harvest:
The PHI Files
This is a critical time to double-check the preharvest interval (PHI) of any product you’re considering, or the minimum number of days between the last application and planned harvest. Spraying too close to harvest can lead to unacceptable residue levels which could result in:
- Detectable residue or compliance violations
- Rejected loads, especially for export or processing markets
- Loss of certifications (e.g., CanadaGAP)
- Regulatory penalties
Check the PHI of every product used between now and harvest. PHIs can vary between active ingredient, formulations, and market (domestic vs export). Note, PHI compliance is still required even if the fruit is going into long-term storage. You can’t wait out a PHI in the cooler – the harvest date is the legal reference point.
All PHI are listed on the product label and can be found under ‘View Details’ for each product on the Ontario Crop Protection Hub. If using List View, be sure to select a pest for the PHI to appear.
As harvest approaches, ask:
- Is the block within the PHI window already?
- Will weather or pest pressure force you to spray after that window?
- Will spraying a produce with a long PHI force you to delay harvest?
Plan sprays backwards from your expected harvest date. Build in a few extra days if the weather may accelerate ripening.
Different cultivars = different harvest dates = different PHI cutoffs
Early cultivars like Paulared or Ginger Gold need shorter PHI products, whereas late cultivars like Fuji or Cortland allow more time – but also more potential for late-season issues like pinpoint scab, codling moth or fruit rot.
Keep block-specific spray and harvest plans to avoid any accidental residue issues.
No Worm Left Behind
Certain insect pests remain active well into the harvest window. The critical ones to manage are those that will cause direct damage to the fruit. At this point in the season, foliar insect pests can impact winter hardiness and tree vigour but are not priority for management.
- Codling moth – Second or third generation larvae may still be tunneling into fruit. Use degree-day models to time your final sprays, especially for later cultivars.
- Apple maggot – Adults can be active right up until the first frost. Keep monitoring and consider controls is you’re still getting catch.
- Obliquebanded leafroller – The overwintering generation of OBLR larva will continue activity into September. A late flush can damage fruit surfaces. However, management of OBLR at this timing is tricky. Be prepared for springtime emergence instead.
- Fall webworm – These can be sporadic around edges near hedgerows and often look worse than they are. Prune out and burn the limbs if you see them. Pay particular attention to young trees as this can affect their development.
- Stink bug – In the fall, adults of species like brown marmorated stink bug move into orchards to feed and prepare for overwintering. Late season damage close to harvest can lead to internal browning and corking, often only visible post-harvest.
- San Jose scale – Second generation crawler emergence is on-going in all areas of the province (see table below). This activity can continue well into September. Applying two consecutive sprays 14-days apart will extend the length of coverage to avoid this late-season damage.
Rot & Roll
Rain, humidity and heavy dews in late summer can trigger infection from a few key diseases, especially if fungicide coverage is lacking. Preventative fungicide applications are still warranted, especially in high-risk blocks (can anyone say Ambrosia?!), when rain is forecast and if harvest is still more than 2 weeks away.
- Fly speck & sooty blotch – Risk increases with prolonged wetness and high canopy humidity. This infection can sit latent (aka no symptoms) until scab fungicide residues become minimal late season.
- Black rot – Warm, humid weather can lead to fruit infections, especially on trees with or near cankered wood or following trauma damage (hail, bird, insect, etc). Enlarged lenticels are also prone to secondary infection by black rot and may appear in storage.
- Bitter rot – This one loves to sneak in late summer following a heat wave and thunderstorm. Often symptoms don’t develop until fruit comes out of storage.
- Pinpoint scab – Even orchards that looked clean all season can show tiny black dots at harvest caused by pinpoint scab infection. Risk increases when fungicide coverage lapse near harvest. If possible, try to get a preharvest spray on that have good efficacy on scab.
- Powdery mildew – This might come as a surprise but late season infection can occur on shoot where terminal bud set reverts and new growth is present. This won’t infect fruit but will increase overwintering pressure for next year.
Hygiene Matters
Even at harvest, orchard sanitation plays a role in pest management:
- Remove or mulch dropped fruit to prevent overwintering sites for pests such as rot or larva.
- Clean bins before bringing them into the orchard to avoid introducing pathogens or insects from other blocks or previous years.
- Minimize bruising and wounding during harvest to reduce postharvest rots.
Degree (Days) of Separation
Based on the degree day model, crawler emergence for second generation San Jose scale is on-going across the province.
San Jose scale degree day accumulations based on March 1st biofix and base temperature 10C
| Region | Current Degree Day Celsius (DDC) | Predicted Crawler Emergence 2nd Gen (806 DDC) |
|---|---|---|
| Harrow | 1056 DDC | on-going |
| London | 887 DDC | on-going |
| Delhi | 1029 DDC | on-going |
| Grimsby | 966 DDC | on-going |
| Clarksburg | 784 DDC | Aug 8 |
| Durham | 843 DDC | on-going |
| * as of August 6, 2025 |
For more information on registered products or those with efficacy against scale, see San Jose scale on Ontario Crop Protection Hub.
For good resistance management, always rotate to a different chemical group than what was used for the earlier generation.
Have You Been Tested?
A reminder that there is FREE molecular herbicide resistance testing available to Ontario growers. This service allows Ontario farmers to submit leaf tissue samples and receive quick, accurate confirmation of herbicide resistance, often within 10 business days.
If you have noticed weed issues this season and suspect resistance may be a problem, check out the post below for more information on how to submit a sample. Take advantage of this service while it is still available!