Table of Contents:
- Preharvest Management of Apple Storage Rots and Fungi
- Apple maggot
- Defoliation from Necrotic Leaf Blotch?
- Tree Health
- On Farm Nursery
- Revisit Crop Load and Hand Thinning
- Bitter Pit and Calcium
- Preharvest Management Strategies - ReTain and Harvista
- Summer Pruning and Hedging
- Reflective Mulch
- Using a Delta Absorbance (DA) Meter
- Reducing bruising
- Considering watercore
- Avoiding internal browning
Late Season Diseases
Preharvest Management of Apple Storage Rots and Fungi
A well-timed preharvest chemical control can go a long way to prevent storage rots. Pinpoint scab, black rot, flyspeck, sooty blotch and brooks spot are preharvest issues that infect fruit in the orchard. Fungal spores that land on unprotected fruit can germinate and show up as infections in storage. Preharvest fungicide is your only protection going into storage.Recommendations:
- The group 7 & 11 products Pristine and Merivon can be applied up to 5 days before harvest (and preferably within 2 weeks). They are labelled for the control of scab, black rot, flyspeck, and sooty blotch. The short PHI and good activity are especially helpful for protecting apples being placed in long-term storage.
- Don't put away the sprayer too early! Late varieties benefit from a preharvest spray too. Growers who stop their fungicide program early see early symptoms of diseases in storage.
- However, be very aware of fungicide preharvest intervals. This year may be an early harvest season so plan for an early harvest when considering chemical PHIs.
- Of course, avoid bruising or wounding to prevent infections of blue and gray moulds. Take the time to educate staff on the proper way to handle fruit.
Insects
Apple Maggot
- Clean maggot traps 7 to 10 days after treating a block for maggot and monitor for new trap captures. Retreat if new maggot flies are caught. Flies emerge over a period of time so for satisfactory maggot control, monitor the presence of apple maggot flies to inform treatment programs. Remember, a single female can lay hundreds of eggs so do not stop treatment prematurely.
- Re-treatment is required after 10-14 days or cumulative rainfall of 12.5-25 mm (0.5-1 inch). Danitol and products registered for suppression are expected to have a relatively shorter field residual life of 7-10 days. Insecticide residue should be maintained through to the end of August.
- Apple maggot flies are weak flyers so a border/perimeter spray of Imidan near known hotspots may be an approach to help kill adult flies from the source. (Being cognizant of the 22-day PHI and REI restrictions).
- In organic orchards, Surround can be used to deter egg laying and GF 120 fruit fly bait can be used for suppression of adult flies.
- Apple maggots pupate in the soil and may not emerge until up to four years later. Therefore, several years of diligent management are required to reduce the resident insect population.
Horticulture
Defoliation from Necrotic Leaf Blotch?
Earlier this season in newsletter #12, I mentioned widespread leaf spotting on Ambrosia that led to leaf drop in severe cases. AAFC is working with leaf samples to explore if the symptoms are disease-related. However, my ongoing theory has been necrotic leaf blotch - a weather related disorder. We had the weather earlier this summer that fits the description for necrotic leaf blotch being, ‘a cool, rainy period for 4-5 days that proceeds several hot, sunny days’. This weather is thought to trigger a hormonal imbalance in susceptible varieties.
I mention this now because I wonder if some of the defoliation we are observing is from necrotic leaf blotch. Necrotic leaf blotch shows up in only ‘Golden Delicious and its strains and seedlings’. Defoliation during the drought has been severe in some cases on Ambrosia, Gala, and Red Prince which all have Golden Delicious parentage. Some of these cases of defoliation seem to happen where leaves are not even wilting yet.
The blotches form rapidly in a day or two on the oldest leaves and then defoliation of affected leaves happens within 4-7 days. Most of the affected leaves turn yellow before falling off. This disorder tends to show up in two to four distinct 'waves' during the growing season typically midseason to late season. Severity varies quite a bit between orchards and growing seasons. Necrotic leaf blotch can cause up to 75% defoliation.
All of this to say... that I hope some cases of defoliation are a hormonal imbalance rather than a representation of tree health. The disorder is not well understood but it is influenced by air temperature, light intensity, and soil moisture.
Tree Health
- This is a reminder that any activities to protect trees from the wind are valuable at this time of the year as trees are carrying the extra weight of fruit.
- Check the height of the graft union above the soil line. If frost heaving has occurred it is recommended that you hill soil to cover exposed roots and an overexposed rootstock shank. An overexposed rootstock shank may be more susceptible to winter injury during fluctuating warm winter temperatures. Exposed roots are susceptible to herbicide sprays.
- Top dressing with nutrients is not recommended after the end of June. Late release will prevent trees from hardening off before the winter.
- Around July the trees are storing reserves in the roots for next year’s growth. When they are storing reserves, late glyphosate applications can be damaging if taken up by root suckers and transported to the root system. Avoid the risk by avoiding glyphosate applications after the end of June.
- Remove root suckers. Suckers compete with the main tree for water and nutrients. They harbour pests, and they are an entry point for fire blight. Pull or break off suckers because otherwise cutting them would let them rebound.
On-Farm Nursery
- It is highly recommended that you water your nursery before and after budding to encourage callus formation and a healthy union.
- Find a source of budwood that does not have a history of fire blight strikes. Trees that have shown signs of fire blight strikes or that are situated near fire blight infections should be eliminated as a source of budwood. Cut budwood fresh every morning if possible.
- Occasionally sanitize all tools used for budwood collection, storage, and budding by washing in detergent and water and disinfecting with sodium hypochlorite bleach. During bud wood collection and budding, frequently spray hand tools with fresh sodium hypochlorite bleach solution.
- The general recommendation is one part bleach to ten parts of water.
- If bleach is too tough on tools, Lysol and Pinesol at one part product to ten parts of water are good alternatives.
- Do NOT use rubbing alcohol because even at 70% to 99% concentration it allows bacteria to survive (California Agriculture 1991).
Honeycrisp Fruit Maturity Report
Important Note - The following information is for general industry purposes only. Growers are encouraged to use their own discretion to harvest trees that are exhibiting delayed colour development or exhibiting maturity indices that disagree with what is being reported here. Values were measured on an average of fruit that were representative of the block's crop load and tree vigour. Fruit representative of size and colour were taken from all sides but not from the interior of the canopy where maturity is expected to be delayed and is most likely targeted for a second pick timing.
- Similar to last year, Perennia will give short weekly updates as indicators of Honeycrisp and Ambrosia maturity.
- Like last year, I started sampling Honeycrisp very early to track the rate of change leading up to harvest. I'll share some preliminary information at this time.
- I will be away next week, so reports will resume on the week of Sept 2.
Summarized notes based on my first samples of the season in Lakeville, Rockland, and North Medford:
- As is typical for this time of year, the starch has not yet started to convert to sugars.
- The DA value at most sites ranges from 1.3 to 1.5 on moderate crop loads. So far, these readings are at a value indicating they are less mature than they were at this same time last year. (But weather conditions might influence the accuracy of DA values).
- For Honeycrisp, values above 0.60 are immature, values 0.6 to 0.36 are ideal for long term storage, and values below 0.35 are best for short term storage because they are more prone to storage disorders.
- Typically the DA value changes at a rate of -0.1 units per week.
- Red blush colour is not developing as early as it did last year. However, there has been a notable gain in red colour over the last few days during the cool weather.
- Soluble solids that represent sugar content are higher than this same time last year. The sugars vary with crop load but all sites have a measurably higher sugar content, likely related to the dry weather.
- Low crop loads mature faster than high crop loads. A low crop load had a DA reading of 1.0.
- Fruit on trees with the least drought stress weighed 141 g and measured 69 mm (2.7") in diameter. Fruit on trees with drought stress weighed 102 g and measured 62 mm (2.4") in diameter.
Harvest Fruit Quality
Revisit Crop Load and Hand Thinning
- If you have unused labour resources, consider additional thinning on healthy trees where fruit size appears small.
- Remove the smallest fruit that you know will not reach minimum size anyway. Leave the rest of the resources for the best fruit.
- Revisit trees to remove fruit where it has become clear that the first round of hand thinning was not enough. Reduce those high crop loads to reduce pressure for resource supply.
- Even if there are no benefits to fruit size, at the very least it will help to promote tree health.
- Research shows that tree water stress is influenced by crop load. I continue to observe that trees carrying less crop load this year appear less water stressed.
Bitter Pit and Calcium
- Bitter pit can occur during a dry year because calcium uptake from the roots is reduced. Bitter pit is also known to occur during a wet year when other nutrients compete with calcium and when vigorous shoots compete with fruit for calcium. Foliar calcium applications during this dry year are a very good idea to supply calcium directly to the fruit skin to be absorbed.
- The recommended rate is 4.5 to 15.5 kg elemental calcium per ha (4 to 14 lbs of elemental calcium per acre) over an entire season spread over six to eight cover sprays. Keep it up!
Preharvest Management Strategies - ReTain and Harvista
- I'm currently exploring any concerns with using ReTain and Harvista on drought stressed trees and fruit. I'll follow up if I find answers. However, if you rely on harvest management tools to manage labour resources then they are likely needed regardless to successfully harvest your crop.
- It probably goes without saying, but if trees are wilting and defoliating then ReTain and Harvista will not provide any benefits to those fruit.
- For local rates and timing, visit our resource on ReTain and Harvista for Gala and Honeycrisp.
- Harvista blocks ethylene action in fruit, even after ethylene has been produced by fruit so it can be applied within a few days of harvest. ReTain requires a timely application to fruit before ethylene production escalates so it is applied several weeks prior to anticipated harvest.
- This is not the year to experiment with using ReTain and Harvista if you have not used them previously. The results will likely be variable.
- These products are not expected to prevent the structural stem damage that is associated with broken stem windfalls due to high winds.
Summer Pruning and Hedging
- An article by Cornell states that summer pruning or hedging can reduce leaf area during drought. Removing young, exposed leaves can reduce transpiration and reduce water stress. Summer pruning is unlikely to improve fruit growth but may help with tree water status. However, I suspect that the summer pruning strategy is only helpful in trees that are not yet wilting. Pruning forces the trees to expend energy to mend wounds and that can be an additional stress to an already stressed tree.
- Summer pruning should involve making the pruning cuts to one- and two-year old wood. Remove vigorous shoots in the entire canopy but especially at the top.
- Leave the weaker side laterals to supply the fruit with carbohydrates. If you over prune you could end up reducing fruit size.
- Hedging done after terminal bud set is not expected to result in regrowth this season.
Reflective Mulch
My theory would be that the additional sunlight exposure would heat plant surfaces and increase transpiration and water loss, so using reflective mulch this year is discouraged. Furthermore, sunlight is not lacking this year so the benefits of improving fruit colour using reflective mulch might not be observed this year. I suspect that the greatest opportunities for using reflective mulch are during years of scarce sunlight exposure when every chance to capture sunlight matters.
Using a Delta Absorbance (DA) Meter
The DA meter is a handheld device used to monitor the chlorophyll content of the apple peel as an indication of fruit maturity. Chlorophyll degrades as the fruit matures so the reading correlates with other changes that happen during the ripening process.
PLEASE NOTE: Drought conditions may influence the accuracy of DA meter readings this year. Other maturity indicators should be used simultaneously. Also, during years of above-average heat we have noted that the DA meter can be misaligned with other maturity indices so stay tuned for when starch degradation begins.
What you need to know:
- Varieties have a unique set of DA meter values associated with them that are the boundaries of when to begin and end harvest, based on local research by AAFC. This means that you cannot test a Gala and expect it to match values set for Honeycrisp. McIntosh and Cortland do not work well with the DA meter.
- DA meter values become smaller as fruit matures. Typically the readings will change by 0.1 units in one week (ex. from 0.6 to 0.5). There may be daily fluctuations so do not take daily readings as the time scale is too frequent.
- The late Dr. John DeLong who spearheaded local research on the topic recorded a podcast with us in 2019 on 'Sensing Fruit Maturity'.
- DA meter readings after Harvista/ReTain might not actually represent maturity. Changes to chlorophyll content caused by these products might not be synchronous with other maturity indicators. Do not take DA meter readings on fruit treated with ReTain or Harvista and instead use other maturity indicators.
Using the DA meter:
- Years ago Joan Hebb created a handy Quickstart Guide. Follow the instructions for calibrating and clearing the mean values.
- Leave the fruit on the tree but ensure that leaves are not caught between the LED sensors and the fruit surface.
- Take a reading on the average sides of each apple (imagine an apple has four sides, ignore the sun-exposed and shade-exposed sides and use the remaining two sides).
- Test a minimum of 20 apple samples randomly from each block by measuring 10 apples from one side of the row and 10 apples from the other side (10 apples x 2 fruit sides x 2 row sides = 40 readings).
- Record the average result calculated by the device then clear the mean value to start over in the next block. Keep your mean values because it will be helpful to compare blocks over time and between years. Record the block name and successive dates of measurement.
Recommendations:
- Take weekly observations on the same day to analyze the rate of change. Start taking sample readings 3-4 weeks before the predicted harvest date to anticipate the rate of change and the approaching start time. One of the major benefits of the DA meter is using the readings to chart the progression of maturity and to compare blocks so that more mature blocks can be harvested before others.
- The DA meter values for optimum harvest may vary each year so it is still important to regularly do a taste test and starch test. The DA meter helps to increase the frequency of sample testing and the sample size.
Reducing Bruising
Recommendations:
- Let fruit warm up before harvesting. Apples picked in the cool weather of early morning bruise more easily than those picked in the day’s warmth. Generally, susceptibility to bruising decreases gradually from 0 to 15°C.
- Take the time to educate staff about the proper way to perform harvest activities that reduce bruising. For example, pick the bottom of the tree first, don’t overfill the picking bag, avoid long harnesses that let the bag bump against knees when walking, explain the difference between varieties etc.
- Re-grade orchard roads prior to harvest to lessen bumps that would jostle fruit being transported in bins.
- Have an inspector sample fruit from various positions in the bin two times each week and leave at room temperature for 24 hours to check for signs of bruise development.
- If bins of fruit will sit in the orchard during overnight freezing temperatures, place the bins where they will be shaded from direct morning sun. Direct sun will warm the fruit too quickly and can lead to deep and lasting bruises.
Considering Watercore
Watercore is a fruit disorder closely associated with over-mature apples along with several other factors. It happens most frequently in years with high sunshine and lack of cloudy, rainy days. Also, highly coloured and large fruit are most prone to the disorder. Fruit with the disorder have an appearance of water-soaked flesh because the spaces between the cells become concentrated with sugars instead of air. Small signs of watercore can disappear in storage and add sweetness to fruit. However, more serious watercore can reduce gas exchange in the fruit and lead to internal breakdown.Recommendations:
- Mature fruit are more likely to develop the disorder because as fruit mature the starches are converted to sugars. The sugar solution builds up in the fruit. Blocks that have a history of watercore should be harvested before other blocks.
- Consider products to delay harvest maturity. Both ReTain and Harvista labels state delayed onset and incidence of watercore.
Avoiding Internal Browning
Internal browning is likely related to carbon dioxide injury. The disorder frequently occurs in overmature and large fruit that have high carbon dioxide concentrations. In particular, fruit harvested late in the harvest window are most susceptible because as fruit mature their ability to diffuse internal carbon dioxide concentrations decreases. The internal carbon dioxide builds up and increases the chance of injury. Consider using products that delay harvest maturity.Pest Management Guide
We offer printable PDFs of the guides from our website:
Online pest guides are also available without login (https://www.perennia.ca/pest-guides/) and with login on your Perennia account (https://www.farmdatatools.perennia.ca/). Using the online tool you can filter for organic and conventional options, search for key information, and sort based on information of interest.
Edited by Michelle Cortens, Tree Fruit Specialist
Perennia Food and Agriculture Corp.
Perennia Food and Agriculture Corp.
