Similar to last year, I will give short weekly updates on degree day accumulations and indicators of Honeycrisp maturity.
Update on 2022 Degree Day Accumulations
Figure 1: Heating degree day accumulations for plant (above 5°C) and insect (above 10°C) development from March 1st to Sept 13th for the past 17 seasons. Provided by Jeff Franklin (AAFC).
- Approximately 5% more plant development heat units compared to the 5-year average, and 5% more compared to the 10-year average.
- Approximately 1% more plant development heat units compared to 2020, and 4% more compared with 2019.
- Approximately 6% more insect development heat units compared to the 5-year average, and 5% more compared to the 10-year average.
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 where maturity is expected to be delayed.
Table 1: Maturity indices for Honeycrisp fruit sampled in four regions on September 13, 2021.
The average DA value for fruit measured in all regions has not reached the target of 0.60. DA values will be noticeably different between the most mature and least mature fruit on a tree. Next week's measurements will show how maturity progresses.
About each 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 both the red and green sides.
Firmness - Measured using a handheld penetrometer with a 7/16 inch diameter plunger on ten representative fruit.
