Honeycrisp Fruit Maturity Report - Sept 10

This is the third maturity update for Honeycrisp using the example regions. Starch is beginning to convert to sugars and other maturity indices are discussed including new comments on fruit weight and diameter. There are also comparisons with last week and indices for this same time on the past two years. This report includes some information on using iodine solution.

Weather

Degree Day Accumulations

Total degree day accumulations are still slightly warmer than average and the trend has not changed significantly in recent weeks.

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

• Approximately 4% more plant development heat units compared to the 5-year average, and 5% more compared to the 10-year average.
• Approximately 5% more plant development heat units compared to 2023, and equal with 2022.
• Approximately 5% more insect development heat units compared to the 5-year average, and 6% more compared to the 10-year average.

Mean Temperatures and Precipitation

Table 1 shows monthly temperature and precipitation totals for the growing season in comparison to the 25-year averages. The accumulation of heat over the last month of August was near-average. Jeff Franklin shares that, "The mean daily temperature for August was 20.0 °C compared to the 10-year and 25-year means of 20.1 °C and 19.9 °C respectively."

Apart from a few large precipitation events, we have not been receiving very much rain. Jeff Franklin summarizes that, "Precipitation total for August was 30.1mm compared to the 10-year and 25-year means of 101.2 mm and 91.6 mm."

Table 1. Mean monthly temperatures and precipitation totals for the current year compared with the 25-year averages. Provided by Jeff Franklin (AAFC).

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.

Table 2: Maturity indices for regular Honeycrisp fruit sampled in the current year on Sept 9, 2024 in Rockland and Lakeville, and Sept 10, 2024 in North Medford. Values are compared with the samples taken last week on September 3, 2024.

Table 2 Discussion:

• The starch has begun to convert to sugars so the starch index is higher than the base level of 1.0. Local research by John Delong et al. 2013 showed that optimal values of the starch index for long-term storage for Honeycrisp are between 5.0 and 7.5. Starch index values are currently below 5.0. When harvested early, the fruit are at greater risk of developing bitter pit in storage.
• The average DA value is currently 0.72-0.75 for tested fruit not treated with ReTain. The DA value may come within the acceptable range within a week or a week and a half (Sept 20)(at an average rate of loss of 0.1 units per week). However, note that starch index is lagging behind and that the DA meter may be misaligned in this atypically warm year. I will update again next week.
• Soluble solids values in our region for Honeycrisp tend to be 11% at around optimum harvest maturity but again it depends on crop load.

More observations (data not shown):

• There is 4-14% more red colour at this time than at this same time the last 2 harvest seasons.
• Red colour is averaging around 50% in the outer canopy that would be targeted for a first pick (fruit not treated with ReTain). 
• This year if colour is progressing better than it has in recent years, just be cautious about harvest maturity. In some cases high colour encourages harvest of immature fruit. Use all maturity indices in your decision whether to begin harvest. There are always tradeoffs though, including labour resources. Just be aware that early harvest of Honeycrisp can lead to more bitter pit in storage whereas late harvest beyond DA 0.36 or starch 7.5 results in more soft scald.
• Fruit treated with ReTain generally have less colour but are also correspondingly at an earlier stage of maturity.
• Background green colour has become noticeably more yellow over the last week.
• If you feel that fruit size is ahead of normal at this point, consider more bins in your bin estimate. The fruit size in my samples averaged 203 g and 77 mm (3 inches) in diameter however this information is highly dependent on the crop load in a particular block.

Table 3: Maturity indices for regular Honeycrisp fruit relative to the past 2-yr average (combined years 2022 and 2023) sampled on a similar calendar date.

Table 3 Discussion:

• Starch index is higher this year meaning that maturity is slightly ahead.
• Soluble solids vary, likely related to crop load.
• The DA meter values are lower this year meaning that the DA meter also predicts advanced maturity.

About each maturity measurement:

Starch Index - Starch is converted to sugars as ripening progresses. The starch-iodine test is used because iodine binds to starch molecules turning them blue/black, whereas sugars are not stained and remain clear. The Cornell chart on a scale of 1 to 8 was used above and values are an average of ten representative samples from each block.

Soluble Solids - Approximates the percentage of sugar content of the fruit. Measured using a digital refractometer. Values are an average of ten representative samples from each block.

DA Meter - The delta absorbance (DA) value is related to the chlorophyll content of the peel. AAFC researchers in Kentville developed a protocol 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. Values shown above are the average of twenty fruit taken throughout a block, with readings taken on the transition area between the sun and shade exposed sides. DA values will be noticeably different between the most mature and least mature fruit on a tree. 

Using Iodine Solution for Maturity Testing

For those of you doing your own iodine testing please note:

• Generic iodine chart created for McIntosh is used as guidance.
• Consult your packinghouse for suggested starch index values used to determine the first acceptable harvest date of specific apple varieties.
• Local research by John Delong et al. 2013 and 2016 showed that optimal values for long-term storage are as follows: Honeycrisp between index 5.0 and 7.5 and Ambrosia between index 2.8 and 5.0
• The correct starch-iodine index numbers for the first acceptable harvest date will vary depending on region so be careful of numbers that you use from other regions. Typically more northern regions such as ours will have relatively higher starch index values than southern apple growing regions for the first acceptable harvest date because low temperatures preceding harvest favour the conversion of starch to sugar.
• Charts for varieties are available online but please note that the generic chart is the industry standard. The variety-specific charts just tend to show the variety-specific pattern of starch staining better than the figures developed using McIntosh. Just be cautious of the index values they report for long-term storage.
• If you signed up for an iodine solution kit from Perennia, you should have received an email stating that it is now available for pick up at the Perennia office at 28 Aberdeen Street in Kentville.

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