Orchard Outlook Newsletter Vol. 22, No 5

Today's newsletter discusses the outcome of the freezing temperatures recorded this past weekend. In advance of above-average temperatures in the forecast, we stress the importance of upcoming apple scab infection events and ideal conditions for powdery mildew. We also consider in advance the upcoming pre-bloom insect risks. Thanks to the ongoing commitment of the Orchard Outlook Committee members.

Table of Contents:

Weather

• 2022 Degree Day Accumulations
• Freezing Temperatures and Bud Injury
• Soil Temperature
• Precipitation

Bud Development

Diseases

• Apple - Scab
• Apple - Powdery Mildew
• Apple - Fire Blight Prevention
• Apple - Calyx or Blossom End Rot (Advance Notice)
• Stone Fruit - Brown Rot Blossom Blight

Insects

• European Red Mite
• Nematode (Pre-plant samples)
• Looking Ahead to Pre-Bloom Insecticides

Horticulture

• Weed Management
• Pollination
• Grafting
• Mowing
• Pruning
• Fertilizing
• Liming
• Planting
• On-farm Nursery

Pest Management Guides 2022

Events and Notices

 

Weather

2022 Degree Day Accumulations

The past week's cold temperatures continue to restrict degree day accumulation and cumulative totals are below average (Figure 1). A pattern change away from cold nights is in the forecast and above-average temperatures are expected in the coming week.

Figure 1: Heating degree day accumulations for plant (above 5°C) and insect (above 10°C) development from March 1 to May 9 for the past 17 seasons. Provided by Jeff Franklin (AAFC).

• Approximately 14% less plant development heat units compared to the 5-year average, and 12% less compared to the 10-year average.
• Approximately 26% less plant development heat units compared to 2021, and 37% more compared with 2020.
• Approximately 44% less insect development heat units compared to the 5-year average, and 45% less compared to the 10-year average.

Freezing Temperatures and Bud Injury

The slowed accumulation of degree days also slowed the bud development and maintained buds at a relatively hardy stage to freezing temperatures. Many apple buds were at the tight cluster stage when freezing temperatures were recorded on May 8 and 9. At the tight cluster stage, the critical temperature for 10% bud injury is at -2.8°C, and 90% injury at -6.1°C (see full chart).

On May 8, the lowest recorded temperatures for all regions being monitored in the Valley ranged from -0.1°C to -4.6°C. Most locations being monitored did exceed the critical temperature of -2.8°C that would be expected to produce minor bud injury. Temperatures that followed on May 9 approached but did not exceed -2.8°C.

Bud injury has been observed where the critical temperature was exceeded. An early assessment suggests that the central king buds were most prone to injury, as expected, because the king bud is most developed (Figure 2).   Occasionally, one or two of the side buds were also killed depending on the cold temperature and duration. Therefore, most five-fruit bud clusters still have two or three viable buds.

Figure 2: Cross sections of apple buds taken on May 9, 2022 following critical freezing temperatures. A vertical cross section of three buds showing browning in the central king flower indicative of injury (left). A horizontal cross section showing one dead king bud and four healthy side buds (centre). A horizontal cross section showing one dead king bud, one dead side bud and four living side buds (right).

Mostly I assessed buds in the lower canopy so it is possible that buds in the upper canopy are even less affected. Bud damage will vary based on microclimates and will be more pronounced in the frost pockets where cold air accumulates (in low elevations or near obstructions to air flow).

Apple trees usually set too many fruit so if the bud injury is minor then there will be plenty of buds for setting a crop. In most years, apples may need only 10-15% of the individual buds to set for a full crop. Just be aware that king apple fruit will be less frequent than usual.

Interestingly, stone fruit buds are more resistant to spring freezing temperatures than apple buds as you can see in the critical temperature chart. Minor injury is possible to peaches if temperatures exceeded -3.9°C but injury is less likely than in apple. 

Soil Temperature

Soil temperature has risen with heating from recent solar radiation. Currently, the temperature at 35 cm deep is around 9.5°C at the site being monitored (Figure 3, red line). For those of you waiting for spring fumigation or spring nematode sampling, the temperature of interest is 10°C at the site of interest. The site being monitored is expected to reach 10°C this week.

Anyone who wants fumigation should contact Chet Friesen directly (902-321-1436) by the end of the day on Wednesday, May 11 to let him know how land preparation is coming along.

Figure 3: Soil temperatures at 35 cm depth at the Kentville Research Station from 2017 to 2022. Provided by Jeff Franklin (AAFC).

Precipitation

Jeff Franklin (AAFC) reports that precipitation in the month of April was average at 87 mm. However, high winds might have contributed to more drying than usual.

Bud Development

An early region on Middle Dyke Road in the Kentville area is monitored to guide this newsletter. Yesterday on May 9, the Idared buds were at tight cluster, Honeycrisp was at early tight cluster, and Ambrosia was at late half-inch green (Figure 4). Generally, many varieties and regions are around the tight cluster stage. 

Figure 4: Bud development in an early region on Middle Dyke Road in Kentville on May 9. Shown from left to right: Idared, Honeycrisp, Ambrosia.

Vegetative growth of the terminals is starting, which is worth noting in terms of protection from powdery mildew infections and to be aware for upcoming applications of prohexadione calcium (Apogee/Kudos).

Orchard Outlook committee members report that in the Morristown area, peach is at the stage of first pink and apricot is in full bloom. Pear is at the tight cluster stage.

Diseases

Apple – Scab

Table 1: Apple scab infection events in Kentville from May 3 to May 10, 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 Sunday, April 17th. Please use this as a guide because microclimates will cause conditions to vary on individual farms.

3 All forecasts are estimates. Observe forecasts daily for more accurate predictions.

Note: The environmental conditions for an infection are listed in the Modified Mills Table.

Upcoming Wetting Events:

• Rainfall is possible on Wednesday, May 11. At the forecast temperature of 12°C it would take around 11.5 hours of leaf wetness for an apple scab infection event to occur, according to the Modified Mills Table. Total ascospore maturity will be around 23.2%.
• A prolonged period of rainfall is currently forecast for the upcoming weekend. With the forecast temperatures being an average of 17°C, it would take around 10 hours of leaf wetness for an apple scab infection event to occur, according to the Modified Mills Table. Total ascospore maturity will be around 42.4%.
• Note that in the upcoming heat, ascospores are expected to mature rapidly by the weekend. Up to 31.5% of total ascospores could be released since the last infection on May 2. 

Recommendations:

• If you are due for a protectant fungicide, it is recommended that protection be maintained especially at this critical time in the season when the next rainfall will release ample spores. Otherwise, waiting for rain is a gamble with the hopes that protection is applied in time (and the possibility of relying on post-infection treatment).
• The heat later this week will produce rapid tissue growth that is not directly protected by fungicide that is applied prior to growth. However, Manzate redistributes in rain to help cover some additional tissue. In this case, following up after the rain with Manzate could also help with some kickback activity on any remaining unprotected tissue. Reportedly, the post-infection activity for Manzate would be 18 hrs in warm weather and extend to 48 hrs in cool weather.
• Re-apply a protectant fungicide to green tissue prior to an infection event on a 7-day interval, with a shorter interval after wet weather (cumulative 1-2” rain) or rapid tissue growth.
• Always tank mix single site fungicides with a group M for resistance management.

Apple – Powdery Mildew

Typically, conidia are released around the tight cluster stage. Powdery mildew infections can be expected when conditions are warm (10-25°C), humid and dry.

Addendum to the May 3 newsletter: 

Previously I reported that the protectant mildew fungicide prevents primary infections but, in fact, it prevents secondary infections. The primary infections are those that overwinter in buds and infect leaf tissue as soon as it emerges. These primary infections are known as flag shoots and they have a silvery grey appearance. 

The goal of a protectant fungicide is to prevent infection of healthy terminal shoots that are beginning to grow. Leaves on terminal shoots are susceptible for a few days after they emerge. Soon you will see flag shoots show up from overwintering infections and they are not a reflection of this season's powdery mildew management program. Flag shoots and infected clusters are a carry over from last year.

Recommendations:

• Ideal conditions for infection are occurring this week. Powdery mildew protection should go on prior to a period of warm and dry weather when infections are expected, and not prior to heavy rain. 
• Apply two sprays targeting powdery mildew prior to bloom on the re-application schedule noted on the product being used (usually 7-14 days). Coverage during the pink to bloom stage prevents fruit 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.
• Practice resistance management:
• Powdery mildew: Group Ms do not have activity on powdery mildew so they will not help prevent powdery mildew resistance development. Products in the groups 3, 7 and 11 are registered for control of PM. Resistance to group 11 products was reported in a survey in 2013. Therefore, whenever the remaining groups 3 & 7 are used, careful consideration must be given to rotating the groups to slow resistance development. Avoid more than two consecutive applications of a single group.
• Scab: The Group M fungicides (mancozeb and captan) provide scab control so tank mixing them with single-site fungicides is a great strategy to slow resistance development in the apple scab population. Although Group 3 fungicides Nova and Fullback are labeled for apple scab, they are not expected to provide control because of resistance in the scab population.

Apple – Fire Blight Prevention

Recommendations:

• Fire blight ooze is being reported. 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.
• Not sure if it's fire blight? If in doubt, take it out! No cankers are helpful and they harbour diseases. If you need a second opinion, I can take a look.
• Be cautious when applying post-emergent herbicides to prevent injury to young trees. 
• Apogee/Kudos (prohexadione calcium) supress shoot blight. The timing of the first application at 2.5-7.5 cm of new shoot growth is critical to success.
• If interested in pinching buds on young trees the practice can begin around the bud separation stage when it's possible to avoid removing the terminal shoot. Pinching buds becomes risky as bloom begins because fire blight bacteria grow on the flower stigma and are expected to be present in high numbers in warm weather. Do not pinch flowers when tissues are wet. This practice is time-consuming.

Apple – Calyx or Blossom End Rot (Advance Notice)

Infections develop toward the end of bloom and appear about one month after petal fall as a brown discolouration surrounded by red on the calyx end of the fruit. The lesion is usually sunken and a corky rot develops in the flesh. When in storage, blossom end rot can lead to moldy core.

Blossom end rot is more likely in years when the weather is warm (15 to 25°C) and wet during and shortly after bloom. The disease is most common on Paulared, Delicious, Cortland, Honeycrisp and McIntosh.

Recommendations:

• Captan is a good product for blossom end rot and black rot management. Note the new WSP formulation changes to REI and maximum number of applications if using the product.
• If calyx or blossom end rot has been an issue in the past, consider using a captan product during full bloom. 
• If applying Streptomycin with Agral 90 there is a risk of burn if using captan. Prioritize fire blight over blossom end rot.

Stone Fruit – Brown Rot Blossom Blight

Brown rot infection of the flowers during bloom provides secondary inoculum for fruit infections later on.

Recommendations:

• Fungicide protection from brown rot should begin just prior to bloom and be maintained during periods of warm, wet weather. 
• Rotating classes of brown rot fungicides is key to slow resistance development. There are many options in the management guide.
• The new formulation of Captan limits the number of applications to one per year on stone fruit.

Insects

European Red Mite

To be most effective, oil application for European red mite should be targeted close to egg hatch – around tight cluster and before pink. Erika Bent (APM) notes that egg hatch has begun with first nymphs found on Monday afternoon.

Avoid oil if freezing temperatures occurs within 48 hrs and no captan within 7-14 days. Oil should not be applied to young trees at less than 3 years old, and the risk on varieties with Delicious parentage (Ambrosia, Gala) increases after tight cluster.

Nematode (pre-plant samples)

Root and soil samples are best collected in the spring (May-June) or during the fall (September-October), both of which avoid the heat or drought conditions in summer. Soil temperatures at sampling should be above 10°C for adequate nematode presence in the upper soil levels.

Looking Ahead to Pre-Bloom Insecticides

Depending on the heat in the forecast, your region, and monitoring reports, action may be needed during the upcoming full pink stage.

Spring Caterpillar Complex

(winter moth, green pug moth, eyespotted bud moth, speckled green fruitworm, obliquebanded leafroller)

Recommendations:

• Treatments for spring caterpillars should not be applied too early because product must enter the developing flower clusters where the larvae like to feed to be effective. Treatments should be applied pre-bloom so target the full pink stage. 
• Evidence of feeding includes tiny holes in new leaves and flower buds, and black specks of frass. Begin scouting procedures described in Perennia’s Best Management Practices. Monitor your scouting reports for notes on WM, GPM, and other caterpillars for those with scouting services. Dr. Suzanne Blatt reports from KRDC that the pug moth stripe is not yet visible.
• Note that there is a lower tolerance for WM than GPM. Green Pug Moth do not feed directly on developing fruitlets.
• If a treatment for just WM is required, then a Bt product (e.g. Dipel or Bioprotec) with Mako applied at bud separation is effective with a minimum impact on beneficial insects.

European Apple Sawfly

Recommendations:

• In orchards with a history of damage and high numbers of EAS catches, an application of Altacor, Assail, Calypso, or Exirel at full pink is recommended to control the adults prior to egg laying.
• In blocks with low to moderate pressure, control of EAS can occur at petal fall.

Tarnished Plant Bug

Recommendations:

• If history of tarnished plant bug damage indicates that pressure is moderate to high, an application of insecticide at full pink can be beneficial.
• Pyrethroids (group 3) and the sulfoximine product Closer (group 4), are registered for control.

General Notes

• Monitor for rosy apple aphid populations that exceed thresholds when aphid stem mothers start producing offspring.
• If treatments for OBLR are required at pink, the treatments will also have some activity on WM and GPM. 
• If a pyrethroid is applied for tarnished plant bug at pink, it will also have activity on WM and GPM. Similarly, pyrethroids are expected to have some activity on EAS if being applied for other pests.
• As a reminder, pyrethroids are best used at moderate temperatures (20°C or less) and are harsh on beneficial insects and predator mites. They should only be used where potential losses justify their application.

Horticulture

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.
• Timing is becoming important so apply a post-emerge to knock down weeds. Timing is becoming important and something will be better than nothing.
• Note that residual herbicides can damage single tree replacements. 
• Residuals need an activating rain of 0.5 inches within 7-10 days of application.
• When mixing residual herbicides, agitation is important to keep the product in solution. If the herbicide settles in the tank then it can be delivered in a high concentration and possibly result in crop injury.
• If weeds are already present, add a post-emerge to a residual herbicide to achieve control. 

Pollination

• Consider that it is near the time that honeybees should be moved into the orchard for pollination when king flowers open.

Grafting

• Bark typically slips from pink to bloom but can be checked early if you plan to get a head start.

Mowing

• Keeping the orchard floor cover mowed pre-bloom will minimize dandelion flowers that attract bees, which increases the safety of pre-bloom insecticide applications.

Pruning

• If pruning is delayed, plan a strategy to get the most value for your time. Prioritize young blocks and high value varieties and then return to low value areas.
• Ensure that youngest blocks are pruned first so growth is directed into desirable leader and terminal extension. Prune early to encourage vigour or delay pruning to remove vigour.
• Mature blocks can be pruned later and are best when pruned prior to bloom.

Fertilizing

• Bud break to bloom is the ideal time for granular fertilizer application to maximize tree growth.
• Foliar nutrients to correct nutrient deficiencies:
• Boron: Applied pre-pink. Do not use water soluble pesticide bags in a tank mix with boron and rinse the tank well before and after boron. Do not use boron with oil or Epsom salts.
• Magnesium: Epsom salts are applied starting at pink. Do not use with oil or boron.
• Nitrogen: Urea may be used from pre-pink to mid-June as a nitrogen supplement. Sprays near bloom give a boost of nitrogen when it is needed most. Urea used from tight cluster to mid-July can remedy a nitrogen shortage.
• When foliar nutrients are applied in slow drying conditions, about 40% is absorbed in 6 hours. When applied in dry and winter conditions, about 75% can be lost in 48 hours.
• Foliar nutrients are not well-absorbed at below 10°C.

Liming

• Be cautious because a lime spreader intended for fields with tall beaters at high speeds can damage the leaf tissue and buds on tree fruit.
• Lime especially if a site is being planted this year. When applied in spring the lime works best when applied as soon as possible to get the product working in the top layer of soil. 
• Surface applied lime will take a number of years to adjust pH of the soil profile so it is best to apply annually or biannually where needed. If soil testing for pH, measure during the same time each year as pH can change over the growing season. 
• The provincial limestone trucking assistance program is open.

Planting

More information was provided in the May 3 newsletter.

• Remember to document the quality of your nursery trees with pictures and notes. 
• Avoid letting trees dry out.
• Bundles of trees sitting in water awaiting planting can asphyxiate, especially in stagnant water and/or warmish water.
• Tilth should be friable enough to avoid air pockets for good root to soil contact.
• If you fumigated last fall, remember to practice tillage within the same direction as fumigated rows and not across.
• If fumigating in the spring, remember the importance of soil preparation to get the most out of the fumigant.
• Remember the risk of dipping roots in a shared water solution.
• Keep newly planted trees supplied with water for the first few weeks after planting if dry conditions prevail. Watering-in or rainfall soon after planting can help to fill air gaps.

On-Farm Nursery

• Remember the importance of weed control in nurseries. Management practices now will impact the outcome of the final tree. Encourage the growing point to be successful!

Pest Management Guides 2022

All changes new to 2022 are made in red text directly on the guides. The information on all changes was summarized in a blog post on April 8th.

• Download the 2022 Pome Fruit Management Guide
• Download the 2022 Organic Apple Management Guide
• Download the 2022 Stone Fruit Management Guide
• Download the 2022 Thinners and Growth Regulators Guide
• Download the 2022 Tree Fruit Weed Management Guide

Events and Notices

For upcoming events, visit the ‘Events’ tab on the NS Tree Fruit Blog. Specific events will be described here when available.

This Orchard Outlook has been published with the input of the Orchard Outlook Committee including this week's participants: Larry Lutz, Dr. Suzanne Blatt, Colin Hirtle, Jeff Wentzell, Dr. Mathew Vankoughnett, Danny Davison, Joan Hebb, Jeff Franklin, Dr. Bob Prange, Dr. Ian Willick, and Dustin MacLean.

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