This is the fourth maturity update for Honeycrisp using the example regions. At the current rate of change, first pick fruit are expected to be optimally mature in a few days' time at the example regions being monitored. An update is shared on the rate of change of starch, sugars, colour, mass and diameter etc. Please note that the DA meter is misaligned with maturity indices this year and that the tool is predicting maturity prior to actual maturity. Please refer to the update for more details.
Total degree day accumulations are still slightly warmer than average and the trend has not changed significantly in recent weeks. This year ranks in the top few years of heat accumulation in the historical record. Interestingly, even though the overall growing season has been above-average, August temperatures have been on average. In August, temperatures did not exceed 30°C and therefore did not impede colour development. Also, below average nighttime temperatures and many sunny days may be contributing to good fruit colouration.
Figure 1: Heating degree day accumulations for plant (above 5°C) and insect (above 10°C) development from March 1 to September 15 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.
Seasonal Precipitation
The precipitation events have been erratic with a few large precipitation events contributing much of the total. The precipitation total is average but likely some of the rainfall was lost as runoff.
Figure 2: Monthly precipitation totals in 2024 compared with the 10-year average. Provided by Jeff Franklin (AAFC) using the Kentville weather station data.
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 1: Maturity indices for regular Honeycrisp fruit sampled in the current year on Sept 16, 2024. Values are compared with the samples taken last week on Sept 9 in Rockland and Lakeville, and Sept 10, 2024 in North Medford.
Table 1 Discussion:
- The rate of starch conversion to sugars increased over the last week leading to current starch index values near 4. At the current rate of change, first pick fruit are expected to be optimally mature in a few days' time and should be monitored.
- 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 but are approaching 5.0. When harvested early, the fruit are at greater risk of developing bitter pit in storage.
- Where ReTain was used, starch index values are relatively lower near 2-3.
- Please note that the DA meter values suggest that fruit are optimally mature right now BUT... we suspect a misalignment this year in using the predictive DA meter tool. The average DA value is currently reading 0.47 to 0.57 for tested fruit not treated with ReTain. The other maturity indices (starch, sugars etc.) show that maturity is not yet optimal. The DA meter was developed as a tool based on the relationship between chlorophyll degradation and the rate of change of maturity indices and in some years such as this with atypically warm weather the relationship may not align. I recommend relying on the starch-iodine test.
- Soluble solids values in our region for Honeycrisp tend to be 11% at around optimum harvest maturity but again it depends on crop load. The soluble solids are currently not yet optimal.
More observations (data not shown):
- Red blush colour is progressing well this year. Red colour on fruit not treated with ReTain is averaging around 60-70% in the outer canopy that would be targeted for a first pick, which is a 10-20% increase from last week.
- See Figure 3 for an example of blush (top photos) and ground colour (bottom photos) progression over time on the indicated dates.
- 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 starch 7.5 results in more soft scald.
- Fruit treated with ReTain generally have less colour (-10%) but are also correspondingly at an earlier stage of maturity.
- 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 215 g and growing at a rate of +11.5g/wk. The diameter was an average of 79 mm/3.11 inches and growing at a rate of +2 mm/+0.08 inches/wk. However, this information is highly dependent on the crop load in a particular block.
- Side note: Some fruit have fewer or no seeds this year and it will be monitored. There is some speculation the lack of seeds may relate to cool April temperatures and possibly shed some light on the fruit drop this past season. It may be difficult to prove but is an interesting theory at this time.
Figure 3: Progression of red blush colour (top photos) and ground colour (bottom photos) change over time in 2024.
Table 2: 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 2 Discussion:
- Starch index continues to be 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 but note comments above about possible misalignment with actual fruit 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.
New Resource - Video about Starch-Iodine Test
For those of you doing your own starch-iodine test, there is a short 3-minute video to guide you through the process.
This Orchard Outlook has been published with the input of the Orchard Outlook Committee including this week's contributors: Jeff Franklin, Joan Hebb, Bob Prange, Harrison Wright, Heather Rand, and Kari Brown.
Perennia Food and Agriculture Corp.
Edited by Michelle Cortens, Tree Fruit Specialist
Edited by Michelle Cortens, Tree Fruit Specialist
