Parka Provides Hassle-Free Sunburn Protection to Apples

Parka supplements the cuticle of the fruit and leaf with a clear, hydrophobic, and elastic lipid bi-layer that expands as they develop. Parka reduces sunburn incidence and increases stress tolerance by enhancing the plant’s antioxidant capacity and the amount of chlorophyll and pheophytinboth essential tools the plant needs to manage light energy during photosynthesis. When conditions arise that would normally cause sunburn damage, the excess light energy can be used for growth, rather than damaging the photosynthetically active tissue.  

Supplementing the cuticle with Parka during the early stages of fruit development and through the season reduces the incidence of other cosmetic disorders such as stem bowl cracking, lenticel breakdown, and russeting in sensitive cultivars. 

Apple Sunburn
Apple Comparison
Fig. 3 Parka does not leave white residue on fruit (right) unlike kaolin clay products.

Why use Parka on Apples?

  • Proven to reduce sunburn damage by up to 42% over control, and 9% more than traditional calcium carbonate-based products.
  • Increases fruit quality.
  • Increases plant tolerance to environmental extremes.
  • Easily tank mixed with foliar nutrients and pesticides.
  • Leaves no visible residue.
  • Exempt from maximum residue levels.
  • Zero preharvest interval, zero worker reentry interval.

How to Use Parka in a Program

Once sunburn occurs, the damage cannot be undone, so apply Parka early in the season. The first application should be at the 12-15 mm fruit size and be repeated every 21 to 30 days for a total of 3 to 4 applications, depending on variety sensitivity and season length.

To reduce the impact of sunburn, growers are encouraged to use an integrative approach where orchard management practices are combined with different protective strategies such as evaporative cooling, netting, and the application of protective sprays.

Because Parka is exempt from MRLs, has an excellent worker safety profile and does not have visible residue, it can be applied near harvest if necessary.


What Causes Sunburn in Apples? 

Sunburn is caused by excess solar radiation and heat. Too much light energy can overwhelm the light absorption capacity of fruit by exceeding its photosynthetic ability. Heat exacerbates the problem, and in some cases is the sole cause of it. Sunburn can be classified into three types:

Sunburn necrosis is when fruit tissue dies due to excessive heat – when the temperature of the fruit surface is greater than 126°F. This can happen even when the ambient temperature is just 90°F, since the fruit surface can be up to 30°F hotter than the air.

Sunburn browning is the most prevalent, and thus the most costly type of sunburn. It is causes cell membrane degradation and is a function of both light and temperature. It occurs when the fruit surface temperature is between 114°F-120°F and is exposed to UV radiation for approximately one hour. The degradation can continue through post-harvest storage, causing “storage” sunburn.

Photo-oxidative sunburn occurs when young fruit (or foliage) that has not been acclimated gradually is suddenly exposed to intense light. This type of damage can occur at low temperatures, and affected areas appear as bleached spots that turn dark over time.

Apple Sunburn
Sunburn damage occurs when too much light energy overwhelms the light absorption capacity of fruit.

How Does Parka Prevent Sunburn Damage?

Chlorophyll captures the energy from the sun in the first phase of photosynthesis (the PSII complex) which is used to split a water molecule. The “excited” electron released from this splitting is received by a molecule called pheophytin and is used in the rest of the photosynthetic process. Both chlorophyll and pheophytin are necessary tools plant cells need to deal with energy from the sun. Parka-treated trees have been shown to contain higher concentration of both components in leaves and fruits, which means the cells have a better capability to use the excess light energy for photosynthesis instead of allowing it to cause photo-oxidative damage.

Parka-treated trees also have an improved overall tree performance, exhibiting improved transpiration rates, CO2 exchange and stomatal conductance. This suggests trees treated with Parka have better resistance to stress conditions and are able to yield more and better quality fruit.

What Do Growers Like About Parka? 

Growers like Parka for its for its efficacy in sunburn protection in apples. It is grower-friendly in other significant ways, as well, particularly its flexibility in tank mixing. Parka can be tank mixed with a wide variety of other foliar inputs, including both fertilizers and pesticides, saving the cost of an additional pass in the field. Harvest crews like Parka, because it does not have the white residue that can be an irritant during picking. Finally, Parka’s exemption from maximum residue levels and a zero worker reentry interval allow growers maximum flexibility.

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