Improving red colouration in Honeycrisp apples under protective netting
Introduction
Apples grown in semi-arid regions (relatively dry regions with 25-50 cm of rainfall per year) are vulnerable to sunburn from intense sunlight and high temperatures, often resulting in fruit loss. Growers in Washington, USA have been adopting protective netting to reduce sun exposure and damage from hail, insects, birds, and other environmental factors. Nets block some of the sunlight, preventing the surface of fruits from getting too hot. However, reduced light exposure also limits red colour development in bi-coloured apples like Honeycrisp, Gala, and Ambrosia. This tradeoff presents a challenge for growers since red colouration is a key quality standard that determines grade and marketability. We conducted these two studies to identify strategies to maintain good red colour development in Honeycrisp apples grown under netting.
These strategies include:
- Netting retraction
- Protective netting was removed 10 days before harvest to allow full light exposure
- Reflective groundcover
- Two types of materials were tested, a woven plastic fabric (Extenday) and reflective film (Mylar)
About this brief
This brief was prepared by Nisa Chavez and Juliana Cao from the BC Food Web team, with the help of Lee Kalcsits, and is based on the following scientific journal articles:
- Mupambi, G., Valverdi, N. A., Camargo-Alvarez, H., Reid, M., Kalcsits, L., Schmidt, T., Castillo, F., & Toye, J. (2021). Reflective groundcover improves fruit skin colour in ‘Honeycrisp’ apples grown under protective netting. HortTechnology, 31(5), 607-614. https://doi.org/10.21273/HORTTECH04776-20
- Willsea, N., Blanco, V., Howe, O., Campbell, T., Biasuz, E. C., & Kalcsits, L. (2023). Retractable netting and evaporative cooling for sunburn control and increasing red colour for ‘Honeycrisp’ apple. HortScience, 58(11), 1341-1347. https://doi.org/10.21273/HORTSCI17339-23
Key Findings
We found 2 strategies to improve fruit colouration in Honeycrisp apples that are under protective netting:
- 1. Timing of net retraction improves red colour: Retracting protective nets 10 days before harvest increased the proportion of Honeycrisp apples meeting the “Washington Extra Fancy” standard (>33% red coverage) compared to leaving nets on until harvest.
- Sunburn risk with early exposure: While early net retraction improves colour, apples can be susceptible to sunburn if temperatures exceed 40 °C prior to harvest.
- 2. Reflective groundcovers enhance colour under netting: Installing reflective groundcover (woven plastic “Extenday” or reflective film “Mylar”) under protective nets increased the proportion of fruit with >25% red colour by improving light exposure.
- No negative impact on yield or fruit size: Since they were applied during final fruit maturation, both net retraction and reflective groundcover did not affect fruit weight or yield.
- These studies highlight the benefits of investing in additional materials for high-value apple varieties that rely on sun exposure for colour development.