Orchard Outlook Newsletter Vol. 24, No 15

Tuesday, November 12, 2024

*Updated on Nov 13 to add two bullet points about glyphosate to the fall herbicide section.

Today's newsletter is the final issue for Volume 24 in the year 2024. In the last issue of the season I review a summary of the weather, tree health, crop load, pest pressures and fruit quality which can all be useful information to reference in the future. With hopefully a little rest after harvest, consider November an opportunity to winterize orchards so you have a head start next season. Cheers to you all for wrapping up another harvest season!


Table of Contents:


  • Degree Days
  • Precipitation
  • Tree Health
  • Crop Load
  • Review of Disease Pressure
  • Harvest and Fruit Quality
  • Fall herbicide application
  • Fall soil pH adjustments
  • Orchard rodent control
  • Reducing the risk of apple scab
  • Peach leaf curl
  • Three Commodities to Create Climate Adaptation Strategies
  • Upcoming Conferences


2024 Growing Season Summary


Degree Days

The growing degree day models indicated that this past season the base 5°C plant development and base 10°C insect development degree days were above the five- and ten-year averages. Jeff Franklin explains that although we have had some warmer than average days through the fall, they have been offset by periods of cooler than average temperatures. This year was the fifth warmest growing season on record in terms of base 5°C degree days. 
Figure 1: Heating degree day accumulations for plant (above 5°C) and insect (above 10°C) development from March 1st to Oct 31st for the past 17 seasons. Provided by Jeff Franklin (AAFC).
  • Approximately 4% more plant development heat units compared to the 5-year average, and 4% more compared to the 10-year average.
  • Approximately 3% more plant development heat units compared to 2023, and 1% less compared with 2022.
  • Approximately 4% more insect development heat units compared to the 5-year average, and 5% more compared to the 10-year average.

Precipitation

The season was also dry except for a handful of heavy rain events. The total seasonal precipitation was about 100 mm less than the 25-year average. 

Table 1: Monthly precipitation totals for the Kentville Research and Development Centre in 2024 compared with the 10- and 25-year averages. Data provided by Jeff Franklin (AAFC).


Tree Health

There were some reports of bark peeling, bark cracks, tree decline, and occasional tree collapse that are suspected to be a sign of lingering effects from the polar vortex. A Cornell researcher Jason Londo is exploring similar damage in New York and is hearing of damage in the Northeastern US as well. He explains that, “Cold damage to the rootstock shank causes sublethal damage and while the tree can repair some, eventually the tree collapses as the canopy water requirements exceed what the old xylem can supply.” Susceptible trees may also exhibit less productivity for a time.

By turning our attention to tree health and graft unions, it was noticed that bark was peeling and shedding on rootstocks and in particular the Geneva rootstocks. Through exploring this concern, it was explained that many Geneva rootstocks have a genetic characteristic of the outer (dead) bark peeling off but the interior bark which contains the phloem and cambium is still alive. This explanation made sense where live tissue was found and the foliage was healthy even through warm and dry weather. In such situations, the bark peeling and cracking is not a concern.

Crop Load

In late April, soon after green tissue began to grow there were freezing temperatures recorded. Frost damage caused some crop loss on early apple varieties such as Gravenstein and in many cases damaged the king bloom of the main varieties. Then there was a snowball bloom with good pollination weather but early fruit set from flower fertilization was less than expected. The widespread variability in fruit set does not correlate with our typical cold pockets so it seems that other factors are at play. 

The reasons are unclear and may have included a combination of 1) sublethal injury from freezing temperatures in late April, 2) lack of sunlight in the later part of 2023, and 3) a heavy bloom resulting in heavy drop.

Furthermore, there were reports from AAFC of low populations of natural pollinators and this year the bee boxes were removed from orchards early to be placed in wild blueberry crops. By harvest time, there also seemed to be more parthenocarpic fruit (seedless) than usual indicating a possible role of pollination failure. It serves as a reminder to rethink pollination plans for next year including bringing in bees and having pollinator varieties nearby as insurance for pollination success.

The current year experienced a strong response to the standard thinning program resulting in near-target crop load as fruitlets thinned easily. It is believed that the trees were under a carbohydrate deficit based on weather observations and more information will be discussed this coming winter with regard to thinning models being trialed in our region. Later in the season as fruit sized, it was reportedly common to realize there were more fruit on the trees than originally anticipated.

The stone fruit crop was good for the first time in several years. Buds were initiated in the 2023 season during weak shoot growth from the polar vortex so some buds were weak and died, however, many buds survived.


Review of Disease Pressure

Apple Scab

Above-average temperatures in early spring led to early maturing ascospores and wetting periods produced infection events that occurred roughly every week. Of the spores that were released during infection events, a light to moderate amount were capable of causing infection. This season a total of 8-10 primary infection events were recorded, which is slightly less than has been occurred in recent years. The event on May 26/27 was notable because it released an incredible 74.5% of the total spore load.

Table 1: Summary of apple scab primary infection periods recorded in Kentville in 2024, based on the Modified Mills Table and assuming a green tip date of April 15.

Powdery Mildew

Wet weather diseases were less of a risk than usual but on the other hand the dry, warm and humid weather conditions were conducive to powdery mildew. Newly expanding leaves on terminal shoots were frequently at risk of infection in midsummer. Susceptible varieties like Cortland and Honeycrisp that were unprotected had plenty of infections on new leaf tissue. Buds are infected this year and will overwinter to cause infection pressure next year. More discussion about management options will occur this winter as we reflect on local trial results. 

Fire Blight

The first blossoms in the Valley opened around May 15 with early regions in full bloom by about a week later.  Above-average heat during the bloom period caused multiple successive high risk periods for fire blight blossom blight although the wetting requirement might not have always been realized. According to the Maryblyt model, high EIP values were first noted on May 17 and then there was an especially challenging high risk period from May 22 through to May 25. The EIP was again high on open blossoms in new plantings throughout most of the month of June and July. Wetting events including rainfall and dew during high EIP periods were conducive to bacterial infection, unless antibiotic protection was applied. New fire blight infections developed where protection was not achieved. In some cases the late season flush of terminal growth following a heavy rainfall in July was prone to shoot infections.

Harvest and Fruit Quality

Red colour progressed very well this past season. The excellent colour development is owing to a nighttime cooling trend in mid-August that continued to bring consistently cool nights followed by warm and sunny days. The weather was excellent for the red pigment anthocyanin to develop on the sun exposed sides of the fruit. Meanwhile, the sugar content of the fruit was optimal by harvest maturity and the flavour was excellent in my opinion!

However, the challenge during harvest was that the early season and cool temperatures hastened harvest maturity. Depending on the variety the window of maturity was either a few days advanced or similar to historically early harvest dates. The cool weather and hastened maturity may influence the prevalence of storage disorders like internal breakdown. In October, high winds coincided with the beginning of the harvest window for Ambrosia and resulted in some crop loss.


Winterizing Orchards


Fall Herbicide Application

Fall is prime germination time for winter annuals, and perennials are susceptible to treatment because they’re actively storing reserves in their roots. Those of you that attended the Growing Good Growers tailgate meeting this past summer about weed management with guest Sonny Murray heard discussion about treating weeds at the end of the season. End of season treatment approaches so here are some reminders.

To get out of the cycle of trying to manage large weeds with post-emergent herbicides:
  • Think about residual/pre-emergent herbicides as filling windows of time. Most residual products will give about 4-6 weeks of weed control. Some products have longer-lasting control like Alion (trees >3 yrs old) and Sinbar.
  • Use residual herbicides through periods of high weed germination (spring and early fall). 
  • Early fall is when perennial and difficult winter annuals germinate. You may want to clean up what does germinate before they get too large by doing a late fall cleanup with a post-emergent herbicide. Consider targeting some tough perennials with glyphosate in mature plantings in late November to early December when trees are dormant and while the ground is not yet frozen. 
    • If using glyphosate, set up the weed sprayer to minimize the amount getting on the bark and just spray two bands next to the tree and avoid the row middles.
    • As long as the weeds aren’t frozen and you can travel without making a mess, glyphosate can be applied. Ideally apply it after a couple of relatively warm nighttime lows above 1.6C. Roundup will work slowly in cool temperatures but should take out the weeds by spring.
  • Sencor and Sinbar give suppression of quackgrass and have some pre-emergent activity on bluegrass.
  • Consider Prowl H2O and Dual II Magnum (pre-emergent) and Venture (post-emergent) options to improve your grass control spectrum. However, these products won't work for bluegrass species.
  • Be aware that Chateau has activity on ragweed whereas Authority does not.
  • Sinbar is a good option for fall application of a residual herbicide that is labelled in first year fruit trees. It will have good control of pre-emergent grasses. Next spring, consider Prowl H2O and Chateau in young plantings. Later in the program could include Ignite with Sandea.

Key points:

  • Summer and winter annual species have populations that germinate in both fall and spring and therefore troublesome weeds may need to be managed at both times.
  • After harvest, consider using a post-emerge herbicide to clean up weeds along with a residual product to save time early next season. Orchards without fall application of residual herbicides are expected to exceed weed thresholds in early spring before those treated with residuals.
  • If planning to apply glyphosate, wait until trees are dormant (late November to early December) or late in spring to avoid translocation to fruit tree root systems.
  • Even if you are not set up to perform weed control in the fall, now is a good opportunity to identify what weed species are present to inform herbicide choices for early next year.

Fall Soil pH Adjustments

Soils in the valley are naturally acidic, and nitrogen fertilizers will slowly acidify soils over time. As soils acidify, nutrients such as calcium, potassium and phosphorus are less available for uptake by fruit trees. Other nutrients such as manganese and aluminum become more available and uptake by fruit trees can become excessive.

The pH of orchard soil should be between 5.5 and 6.6 (target 6.0) because nutrient availability is best within this range. Fall is the ideal time to make soil pH adjustments because it gives time for limestone to neutralize the acidity before the next growing season. Also in the fall, the dust from limestone applications will not interfere with growth or bloom.

Recommendations:

  • The results of a soil test will give a lime requirement based on your soil type and pH.
  • Apply calcitic limestome unless magnesium is needed from dolomitic limestone.
  • A surface application of no more than 3 tonnes/ha of limestone in any one year is recommended because higher volumes could be washed away and are ineffective.
  • If the lime is being worked into soil then you can follow the recommended rate on your soil report. Incorporating lime into soil will show benefits sooner than a surface application. A surface application moves down at a rate of about 1 inch per year.
  • If you have ongoing issues with lack of calcium in established plantings, consider banding gypsum at a rate of 4 tons per acre under trees. Annual applications have been shown to reduce bitter pit and senescent breakdown. Gypsum can also improve soil structure and improve water infiltration. Be aware that gypsum can reduce magnesium uptake. Gypsum will not replace the need for lime for pH adjustment.

Orchard Rodent Control

Rodents feed on tree bark in the fall and winter when other food supplies are scarce. The most common issue is when rodent feeding girdles the trunk of young trees at or near the ground surface or at the height of snow accumulation.

Recommendations:

  • Mow ground cover and maintain a weed-free strip to expose mice to predators.
  • Clean up drop apples from the tree row and alleyways to remove attractive food sources.
  • Be aware that using straw mulch can harbour mice.
  • If rodent activity is observed (mouse tunnels, droppings and chewed apples), consider the use of rodenticide. Bait stations manage the risk of poisoning other species and the control is long-lasting.
  • Bait stations placed on the perimeter of the orchard target mice moving into the orchard from bordering fields, fence lines or ditches. Pay particular attention to orchard blocks that neighbour corn and soybean fields.
  • Install tree guards, if feasible, on young trees. Remove after snow melt in spring to avoid fungal problems at the base of the trunks.


Diseases


Reducing the Risk of Apple Scab

Scab spores can be reduced for the next growing season by accelerating the decay of infected leaves in the fall of the current season. The benefit is less disease pressure next spring that can help to reduce the risk of primary scab infections. All efforts to reduce primary inoculum for next year will be helpful for scab control under recent fungicide restrictions.

Recommendations:

  • Spraying urea (46-0-0) onto leaves on the ground can reduce spores by about 66%. The recommended rate is 50 kg/ha in 1000 L/ha of water. The solution can alternatively be applied to full trees as leaf fall begins. Urea should be dissolved in warm water before putting it in the tank. The 50 kg/ha rate will supply approximately 23 kg/ha of nitrogen to the ground, so nitrogen application next spring should be adjusted accordingly.
  • Flail chopping all plant matter on the orchard floor in November can reduce the number of scab spores by as much as 85%. Flail chopping in only the alleyway can reduce scab spores by as much as 50%. Why does chopping work? Dr. Gordon Braun explained in a year 2000 publication that:
    • "By chopping up leaves finely, they are more easily broken down by bacteria and molds to be consumed by earthworms."
    • "The apple scab fungus needs to mate with the opposite mating type and smaller leaf pieces reduces the likelihood of the two meeting."
    • "The smaller fragments also fall deeper into the grass and have a greater probability of resting in a position which is less than horizontal which reduces the ability of the ascosopres being successfully discharged into the air currents and carried to susceptible leaves."
  • Using a combination of both shredding and urea applications can produce the best results.

Peach Leaf Curl

Peach leaf curl is a fungal disease of peaches and nectarines that is usually well-controlled by a fungicide application in spring or late fall. Infections occur in the spring at bud swell when overwintering spores are washed from the surfaces of the bark. Therefore, a fungicide application prior to bud swell in the spring is preferred. However, occasionally early warm temperatures combined with extended snow cover can make spring applications challenging.

Recommendations:

  • The spores overwinter on the bark, so fall applications for peach leaf curl should be tailored to provide complete coverage of trunks and branches. Fall application should be made after 75-100% of leaf drop has occurred and when the temperature is above freezing.
  • Unusually wet winter weather with heavy rain can wash off a protectant fungicide applied in fall. If residues are washed off, re-treatment in spring before buds swell is recommended. 
  • Chlorothalonil (Bravo/Echo) has been the most effective fungicide in Nova Scotia. Only 1 spray of Bravo/Echo may be applied per year, meaning it cannot be applied in both spring and fall. Other products registered for control in the fall are fixed copper products.

Events


Upcoming Conferences


Perennia Food and Agriculture Corp.
Edited by Michelle Cortens, Tree Fruit Specialist
By Michelle Cortens at November 12, 2024
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