Orchard Outlook Newsletter Vol. 24, No 7

Today's newsletter reports stages ranging from petal fall of king blossoms to 6 mm king fruitlet diameter that should stir thoughts of thinning for many next week. Chemical thinners are discussed, including the role of temperature and fruit size - but stay tuned because carbohydrate status will be discussed next week. In terms of diseases, a heavy apple scab infection occurred and primary infections are still possible. In the cool temperatures, fire blight blossom blight risk is currently low but stay tuned for any risk on rattail flowers and flowering young trees. Thanks to the ongoing commitment of the Orchard Outlook Committee members. 

Table of Contents:

Weather

• 2024 Degree Day Accumulations
• Precipitation

Bud Development

• Apple Buds
• Pear and Stone Fruit Buds

Diseases

• Apple - Scab
• Apple - Powdery Mildew
• Fire Blight Prevention
• Apple and Pear - Fire Blight Blossom Blight
• Fire Blight - Shoot Blight Management
• Apple - Black Rot

Insects

• Do not spray insecticides during bloom!
• Post-Bloom Insecticides for Apple, Stone Fruit, and Pear

Fruitlet Thinning

• Influence of Weather
• Apple Fruitlet Thinning
• Defrosting Young Trees
• Pear Fruitlet Thinning

Horticulture

• Grafting
• Mowing
• Weed Management
• Pruning and Training
• Nursery Trees

Online Pest Management Guide

 

Weather

2024 Degree Day Accumulations

Due to the above-average temperatures over the previous two weeks, the degree day accumulations for base 5°C plant development and base 10°C insect development are more than the 5- and 10-year averages (Figure 1). 

Figure 1: Heating degree day accumulations for plant (above 5°C) and insect (above 10°C) development from March 1 to May 27 for the past 17 seasons. Provided by Jeff Franklin (AAFC).

• Approximately 15% more plant development heat units compared to the 5-year average, and 13% more compared to the 10-year average.
• Approximately 21% more plant development heat units compared to 2023, and 4% less compared with 2022.
• Approximately 24% more insect development heat units compared to the 5-year average, and 15% more compared to the 10-year average.

Precipitation

The Kentville area has received 25 mm of rain in May compared to the 25-year average of 75 mm. The current rain will contribute some but regardless it is clear that May will conclude with a precipitation deficit.

Bud Development

Apple Buds

An early region on Middle Dyke Road in the Kentville area is monitored to guide this newsletter. Yesterday on May 27, the Idared buds were at complete petal fall with king fruitlets already averaging 6 mm in diameter (Figure 2). Keep in mind that early varieties including Gravenstein may soon enter the thinning window. Honeycrisp was in the midst of petal fall with kings measuring 3-4 mm, and Ambrosia was at king bloom petal fall. Note that varieties known for protracted bloom like Gala still have unopened flower buds as flower on the tree range from pink to petal fall.

During bloom there appeared to be excellent pollination weather and bee activity. Temperatures were also theoretically conducive to good flower fertilization at a daily average of 15-19°C. 

If you want to target the early timing for Apogee/Kudos of 2.5 cm to 7.5 cm, note that shoots are already ranging from 5 cm to 9.5 cm (Figure 3). You may still apply Apogee/Kudos later but the efficacy is less. Over the last week, shoot growth essentially doubled in length again!

Figure 2: Fruit bud development in an early region on Middle Dyke Road in Kentville on May 27. Shown from left to right: Idared (6 mm), Honeycrisp (petal fall, 3-4 mm), and Ambrosia (king bloom petal fall).

Figure 3: Vegetative bud development in an early region on Middle Dyke Road in Kentville on May 27. Shown from left to right: Idared (9.5 cm), Honeycrisp (6.5 cm), and Ambrosia (5 cm).

Pear and Stone Fruit Buds

Yesterday on May 27 at an early region in Greenwich, the pear buds were at petal fall and the king fruitlets were already measuring 7 mm (Figure 5). Peach was beginning shuck split depending on the variety. European plum was at shuck split.

Figure 4: Bud development in an early region in Greenwich on May 27. Shown from left to right: pear (petal fall, 7 mm), peach (early shuck split depending on variety), and European plum (shuck split).

Diseases

Apple – Scab

Table 1: Apple scab infection events in Kentville from May 21 to May 28, based on the Modified Mills Table. 

1 For a high inoculum orchard, a significant number of spores can be released during darkness, so begin calculating leaf wetting regardless of the time of day when the wetting event started. An orchard is considered to have a high inoculum load if last season it had 100 or more scabby leaves observed over 600 shoots.
2 Assuming a green tip date of Saturday, April 15th. Please use this as a guide because microclimates will cause conditions to vary on individual farms.
Note: The environmental conditions for an infection are listed in the Modified Mills Table.

• Kaboom! This past week's wetting event released a very large spore load of 74.5% and an apple scab infection event would have occurred on unprotected tissue. 
• The ongoing rainfall may produce another infection event. Today the total seasonal ascospore load is mature to 96.6% with 3% of the spore load available since the last release.

Recommendations:

• According to the forecast, total seasonal ascospores are expected to mature to 99.7% within the next week. Therefore, primary infections are still a risk according to the model and leaf tissue should stay protected on 5-7 day intervals.
• Let's review some considerations for product options at this time of the year:
• Mancozeb (Manzate/Penncozeb) can be used only 4 times/year. Mancozeb is compatible with oil and may be used around the same time as streptomycin/kasumin + Agral 90 or it may be used as the spreader-sticker. If it is necessary to include mancozeb with your antibiotic, reduce your rate of Agral 90 by at least half to avoid strep burn.
• Captan is not recommended for application with an antibiotic. Firstly, Captan is not compatible with oil so it CANNOT be combined with Agral 90. Secondly, Captan does not act as a spreader-sticker so using it with your antibiotic would sacrifice coverage and efficacy which is not recommended. Do not apply captan within 7-14 days of an oil such as Agral 90 (worse if applied after oil that preconditions leaves).
• Allegro may be applied as long as oil has not been applied within 3 days (including Fontelis and Agral 90). The REI is short at 24 hrs. 
• Do not apply: Folpan/Follow and Syllit should NOT be applied between tight cluster and 30 days after petal fall to avoid fruit russeting. 
• Note that single site products in group 3 are not expected to provide control of apple scab due to resistance. For other single site products, check the label for rates required for apple scab control because for Luna Tranquility the high rate is needed unless it is tank mixed with another product for scab control.
• Apply a protectant fungicide to green tissue prior to an infection event and reapply on a 7-day interval, with a shorter interval after wet weather (cumulative 1-2” rain) or rapid tissue growth.
• Pears: For pear scab, Allegro and mancozeb are NOT registered uses. Captan may be used 2 times for low density and 10 times for high density. Note that for pears, Scala and Luna Tranquility have a 72 day preharvest interval. The registered products are listed in the online guide under Tree Fruit and Pears.

Apple – Powdery Mildew

Powdery mildew infections can be expected when conditions are warm (10-25°C), humid and dry.

Recommendations:

• The petal fall timing is another opportunity for applying a mildew protectant.
• If you're using Luna Tranquility for powdery mildew, concurrent activity for scab control is only provided at the high rate. If you're using a full rate of Nova, Fullback or Cevya, no scab activity is expected due to resistance. If using Nova, the water soluble packaging should not be mixed with oil or boron.
• Avoid more than two consecutive applications of products with a group 3, 7, or 11. Powdery mildew resistance to group 11 products was reported in a survey done in 2013 so success is unlikely. Group M products do not have activity on powdery mildew. 
• Buran is registered for control of powdery mildew in apples under low to moderate disease pressure and local research is ongoing. Apply with 0.1% Agral 90. This product does not have protectant scab activity so will only provide scab protection post-infection.
• Remember to treat young plantings because severe infections can reduce shoot growth, which is most concerning for young, non-bearing orchards.
• Pay particular attention to susceptible and high-value varieties such as Honeycrisp and Gala.

Fire Blight Prevention

Recommendations:

• Pruning practices should be done on dry and sunny days, especially in high risk blocks. Wounds can take about 2 days to heal. Do not work in trees when they are wet from dew.
• Even if bacterial EIP populations are low, do not pinch flowers in wet weather. Pinching causes open wounds like a trauma event and bacteria are transported to wounds in wet weather. Remember that any remaining flowers are susceptible to infection if the EIP becomes high.

Apple and Pear – Fire Blight Blossom Blight

Current and Forecast Blossom Blight Risk

• Industry alerts will continue while rattail bloom and bloom in young plantings is present. 
• The risk of bacterial growth on flowers is low for now and into the foreseeable future. Stay tuned because predictions can change on short notice.
• Ideally you can monitor your own farm-specific conditions and improve your management decisions using PomeBlight that was developed for Nova Scotia apple and pear growers.

Recommendations:

• Note that varieties known for protracted bloom like Gala still have unopened flower buds. Their long bloom period is one of the reasons why they are high risk for fire blight. Do not underestimate the risk of infections on late flowers.

Fire Blight - Shoot Blight Management

Recommendations:

• Apogee/Kudos (prohexadione calcium) supress shoot blight. Their use is highly recommended this year because there was a high risk of fire blight infection during full bloom. When Apogee/Kudos are applied after 10 cm of new shoot growth, the vegetative growth reduction is less but the product will still slow fire blight progression.
• Follow up with a second application applied around 14 days later. 
• Apogee should be put on with higher water volumes to cover all new leaves and growing tips.
• Include Agral 90 at 500 mL per 1000 L of water. Do not exceed this amount of surfactant. If applying Agral 90 there may be a risk of burn if using Captan.
• Apogee should also be applied with spray grade ammonium sulphate (AMS) in an equal 1:1 ratio with the amount of Apogee used (e.g. 500 g Apogee = 500 g or 0.5 L of ammonium sulphate). This is not the blossom thinning product ammonium thiosulphate (ATS)!

Apple – Black Rot

Recommendations:

• Based on our limited knowledge, the highest risk of infections is theoretically between petal fall and 4-6 weeks after bloom.
• A 10 hr wetting period at 16°C to 32°C allows infection. 
• The optimum temperature for infection is 20°C to 24°C. 
• There are few management options to cover such a long risk period. Captan has activity but note the REI for orchard activities. Merivon has activity but this group 7 + 11 product should not be used more than 4 times each year. Folpan has activity but should not be applied until 30 days after petal fall to avoid russet. We do not have a model for black rot infection but protection would need to be targeted prior to wetting and ideal weather conditions.
• The fruit cuticle is sensitive at this stage. Be cautious with spray mixtures (calcium, foliar nutrients). 

Insects

BE RESPONSIBLE FOR POLLINATORS – DO NOT SPRAY INSECTICIDES DURING BLOOM!

• Fungicide, antibiotic, and growth regulator sprays are best applied early morning or late evening when bees are not actively foraging. Be aware that dandelion blooms are open until about dusk.

Apple Insects

Pesticide options for post-bloom insects are listed in the table. Choose insecticides by considering what you are targeting and what the products control. Often your hardest to control pest will determine what you need to use, then check the label of that product for all pests that are also controlled by the product. Please refer to the petal fall insecticide decision table for a quick overview of your choices for apple trees.

(Click image to access full size PDF file for printing)

In addition:

• Monitor for white apple leafhopper. Sevin XLR applications for thinning in mature blocks will control leafhopper but monitor non-bearing plants for leafhopper. If treatment is required, a neonicotinoid, Sivanto Prime, or Exirel would control leafhopper.
• Monitor for rosy apple aphid and green aphid in young trees and nursery plantings where feeding can disrupt shoot growth. If leaves are curling, high water volumes are needed for effectiveness.

Stone Fruit Insects

Recommendations:

• Treatment for plum curculio should be applied at petal fall before shuck split to obtain optimal control. Treat between petal fall and shuck split. A second application is usually needed about 10 days later.
• The insecticides available for managing plum curculio include Malathion, Pounce, Assail (Neonicotinoid) and Exirel (Diamide). The neonicotinoids kill plum curculio on contact, and they are also systemic so they deter egg laying and feeding. Their systemic activity will also kill eggs and larvae that are present in the fruit.
• Plum curculio will target apples if stone fruit are nearby.
• Be aware of bee toxicity warnings on pesticide labels and take precautions while nearby crops are in bloom.
• For stone fruit, monitor for green peach aphids and black cherry aphid.
• Tarnished plant bug and stinging bugs cause catfacing of peaches. This stinging takes place around shuck split/fall and one to two insecticide applications may be required to reduce the incidence of catfacing if pressure is high. Apply one to two applications of one of the pyrethroids listed in the Online Pest Guide for peaches. Repeat treatment in 5-7 days if additional stings are detected. Note that pyrethroids are best used at moderate temperatures (20°C or less) and lose efficacy at around 25°C.

Pear Insects

• If you are planning to use Agri-Mek + Oil for pear psylla control, it is best to apply it at petal fall or ideally within 2 weeks. Agri-Mek has better residual control when applied to younger tissues. 
• Do not apply Agri-Mek with any bloom around as this product is highly toxic to bees. 
• Do not use Captan/Maestro as a fungicide for pear scab within 14 days of Agri-Mek + Oil. 
• Do not use MaxCel in close proximity to AgriMek because the oil will increase thinning activity.
• Minecto Pro (Abamectin and Cyantraniliprole) is a new formulation that is registered for control of pear psylla with the same recommended application time.
• Petal fall is the ideal treatment timing for winter moth and fruit worm in pear. Treatment should be based on need determined by monitoring.
• Apple curculio is difficult to monitor for and its presence often is not observed until damage on fruitlets shows up. Treatments for this pest should go on when pears have reached petal fall. Use of one of the products registered for plum curculio should also control apple curculio.

Fruitlet Thinning

Influence of Weather

Temperature and sunlight on the 2 days before and more importantly the 4 days after applying thinners determine thinner response. The relationship has been explained in terms of the carbohydrate status of the tree. During sunny days the tree is photosynthesizing unimpaired and when matched with cool nights (<18°C) it is respiring slowly, meaning carbohydrates are plentiful. Reversing the conditions, cloudy days impair photosynthesis and when coupled with warm nights the respiration uses many carbohydrates making them in short supply, causing stress to weak fruitlets.

Apple Fruitlet Thinning

• Please note that the timing of chemical thinning is based on the average size of the king fruitlet. The size of the side fruitlets is irrelevant. After petal fall, fruitlets typically grow about 1 mm each day in average temperatures. Chemical thinning occurs when king fruit are 5 to 18 mm in diameter and is most effective from 7-12 mm. 
• This year a new thinner called Accede is registered and has activity at up to 25 mm fruitlet diameter but supposedly works best at 18 mm.  Product supply is limited but you may wish to try it on a small scale.

Product Overviews:

Sevin XLR

• Does not overthin so it is mild and reliable.
• Undissolved Sevin remains active. Damp and drizzly weather that keeps tissue wet but does not wash off product results in more thinning.
• Often combined with Fruitone for a synergistic effect resulting in more thinning than either product used alone.
• Temperatures at application should be above 17°C.
• Note that the PHI for Sevin is 75 days and this may be challenging for early varieties like Paula Red. The REI is 0.5-17 days depending on the activity.
• When using Sevin in high density orchard do not exceed 3.22 L of product/ha/year. In low density orchard do not exceed 2.15 L of product/ha/year. Sevin is a thinner but note that it is also an insecticide and care should be taken to avoid contact with bees.

Fruitone L

• Strong thinner that is very effective in Nova Scotia and is rate-responsive. Higher rates thin more.
• Unabsorbed residue on leaves is inactivated by sunlight. Slow drying conditions cause more absorption. Therefore, nighttime applications are usually more effective.
• Temperatures at application should be above 16°C.

MaxCel/Cilis Plus

• Product is most likely effective when weather conditions cause a carbohydrate deficit. The thinning effectiveness has been limited in Nova Scotia and it may be because in many years the trees are not stressed during chemical thinner application.
• This product can be used to increase fruit size (20g/fruit) beyond the influence of thinning by stimulating cell division but the timing matters. According to research:
• When applied at 10-15 mm, it increases fruit weight 80% of the time.
• When applied at 5 mm, it increases fruit weight 25% of the time.
• When applied at petal fall, there is generally no increase in fruit size.
• Temperatures at application should be above 18°C.

Recommendations:

• Next week during the thinning window I will comment on the suspected carbohydrate status of the trees. (During the recent heat, trees were expected to have a carbohydrate deficit and currently are expected to accumulate a surplus according to the forecast.)
• The optimal temperature for thinner activity is between 21-24°C. In cooler temperatures the thinning activity is less and in warmer temperatures the thinning activity is more. At thinning time, consider the weather and then you may adjust your usual rate +/- 20%. 
• Have a block with trees on and off? Thin according to trees with the heaviest fruit set. Trees with less flowers are less likely to thin anyway because holding onto well-supplied fruitlets.
• Varieties prone to biennial bearing that had a low crop load last year should be thinned adequately and early enough this year to enable bud initiation (for Honeycrisp this is within 45 days after bloom).

Defruiting Young Trees

• Defruiting young trees can be accomplished with a combination of Sevin XLR at 2.5 L plus Maxcel/Cilis Plus at 5.0 L per 1000 L of water applied using dilute nozzles to the point of drip. A few litres of oil (10.6 L/1000 L water) can also be added as a spreader sticker to this combination unless the variety is sensitive to oil (avoid Gala, Ambrosia, Golden Delicious, Red Delicious). 
• This mixture should cover more than an acre of young trees. 
• Apply from petal fall until 8-10 mm. A second application can be done before 18 mm if additional thinning is needed. A second application will likely still miss some fruit so consider that hand thinning may still be required anyway.
• Choosing to use Fruitone (NAA) in this mixture instead of MaxCel will result in chemical pinch at the terminal bud that stunts growth.
• Using currently available products, the amount of product that would be needed to completely defruit trees in our climate would likely negatively affect tree growth. Therefore, expect that hand thinning will still be required.

Pear Fruitlet Thinning

• The Maxcel thinning window is 8-14 mm and early treatments are most effective.

Horticulture

Grafting

• Bark typically slips from pink to bloom at which point grafting can begin. The local business Maple Grove Nursery made a video this year about top working young trees. The video is available on their website called, “Reworking Young Orchard Trees (slow motion)” https://www.maplegrovenursery.ca/grafting-supplies

Mowing

• Keeping the orchard floor cover mowed to minimize dandelion flowers that attract bees, which increases the safety of insecticide applications.
• Mowing and herbicide strips help to prevent issues with two-spotted spider mite (John Michael Hardman).

Weed Management

• Studies have shown maintaining weed free strips from bud break to 30-days after full bloom has the greatest impact on tree growth and yield. Timely herbicide application will ensure you make the most of the weed free window.
  • Create a plan for the whole year. Put on residual products before weeds emerge and use the post-emerge products as backup.
• If using glyphosate alone, consider coarse droplets and low pressure to reduce drift. Use Ignite during hot days in full sun if possible.
• In young plantings, weed control is essential. If newly planted trees have received a settling rain then you may consider a residual herbicide before the next rain.
• Understand and consider using more Venture for grass control in young orchard. Venture is slow to work (2-3 wks) but you can check for activity by removing the flag leaf on treated grass and examining the base of that shoot for rot.
• Add Prowl H2O or Dual II Magnum to improve your grass control spectrum in young orchard. These pre-emerge products won’t work for bluegrass species however.
• Sinbar is good for pre-emerge grasses in young orchard.
• Lontrel is a great post-emergent for vetch, clovers, and sheep sorrel.
• Chateau has activity on Ragweed whereas Authority does not.

Pruning and Training

• Start selecting strong terminals on young trees and remove competing terminals to single the tops if there are no re-entry intervals active.
• Pruning and training practices should be done on dry and sunny days, especially in blocks with high risk of fire blight. Wounds can take about 2 days to heal. Do not work in trees when they are wet from dew.
• Ensure that deer fencing is installed as soon as possible to protect new growth on young trees. Prior to deer fencing, the product Bobbex may be used as a deer repellent but it requires frequent application to new growth and after rainfall.
• Newly planted trees should be pruned for tree structure and supported as early as possible after planting. Prioritize trees that are known to be brittle at the union, including many of the new Geneva rootstocks (G.11, G.41, G.16 etc).

Nursery Trees

• Consider staking to prevent blowouts. Even if not tied, the rod acts as a physical barrier to mechanical injury.
• Treat for tarnished plant bug and green aphids.
• Remove rootstock leaves when they are tender and before shoots become woody. 
• For bench grafts, leave some shoots on the rootstock to feed the scion as the callus tissue develops. Locally, rootstock leaves have been stripped when the scion has 8-10 leaves. Early in the season, leave at least an extra scion leader for insurance.
• Remember the importance of weed control in nurseries. Management practices now will impact the outcome of the final tree.

Online Pest Management Guide

Beginning this year, all of the pest management guides are available from an online tool. On the tool you will find guides for organic and conventional apples, pears, peaches/nectarines, plums, and sour/sweet cherries. You can search and filter the information and/or print. If you wish to view growth regulators only, then under the 'Advance Search' for 'Pesticide Type' choose growth regulator. To help you navigate the guide, we have developed a brief tutorial video as well as a how to use guide.

This Orchard Outlook has been published with the input of the Orchard Outlook Committee including this week's participants: Jeff Franklin, Larry Lutz, Danny Davison, Keith Fuller, Suzanne Blatt, Joan Hebb, Dustin MacLean, Mathew Vankoughnett, Ian Willick, Heather Rand, Jill MacDonald and Jessica D'Entremont.

Edited by Michelle Cortens, Tree Fruit Specialist
Perennia Food and Agriculture Corp.