Important Note - This 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.
Table 1: Maturity indices for Honeycrisp fruit sampled across four regions on October 5, 2021.
Note that all blocks being monitored are at various stages of spot picking. Where DA values are higher than they were the previous week, the increase in DA value is largely a result of measuring fruit that were left behind during early picks that are by nature less mature.
The average DA value for fruit measured in all regions following spot picking is above 0.35, which is ideal for long term storage. Over the last week, starch conversion to sugars has progressed (Figure 1).
The block with ReTain treated fruit that is being monitored anecdotally has now crossed the threshold for the DA value recommendation by measuring an average of 0.54. Fruit in the block has maintained average starch levels around 5.6.
Comments on Colouring
Colouring has been slow to develop on certain varieties this year. An article by Penn State notes this varietal difference explaining the different temperature requirements for colouring, "McIntosh requires temperatures below 70 degrees (21.1°C), Fuji requires temperatures in the low 60s (15.5°C), and Redchief Delicious requires temperatures in the low 50s (10°C), but one day at 90 degrees (32.2°C) will negate the effects of several cool nights."Anthocyanin is the pigment responsible for red colour in apples. Studies on detached apples show that the precursors for anthocyanin development are formed at temperatures below 15°C and the conversion to anthocyanins is completed at higher temperatures around 20-25°C during sunlight hours (Steyn 2005). Warm temperatures earlier this harvest season slowed down the process of colouring by slowing down anthocyanin production.
Anecdotally, it seems that colouring has improved within the last week in the ReTain treated Honeycrisp block that's being reported on, which could be due to the recently cool nights. Typically colouring will noticeably improve after several cool nights followed by warm, sunny days.
About each measurement:
Starch Index - Starch is converted to sugars as ripening progresses. The starch-iodine test is used as a visual indicator 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 (immature) to 8 (most mature) was used above and values are an average of five 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 five 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 0.60 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.
