In sun-soaked growing regions, such as Central Washington or Chile, the sun’s damaging rays pose a risk of sunburn and delayed sunscald in apples.
The damage is driven by exposure to high light and hot weather, so researchers are working to develop tools to detect crop stress and exposure levels to help growers predict and prevent damage.
While sunburn shows itself in the field, delayed sunburn, also known as sunscald, appears after storage and poses a particularly difficult problem for growers because it cuts packout rates seemingly without warning.
Chilean researchers aim to fix the problem by identifying the subtle warning signs in sun-exposed apples, so that growers can take steps to prevent damage in the first place and so fruit that’s likely to develop damage in storage can be sold quickly.
The sunscald problem is “fruit that looks healthy, it looks fine when it goes into storage, but then it will develop this surface browning,” said Carolina Torres, a professor of horticulture at the Universdad de Talca in Chile.
She spoke to Washington growers at a field day in Quincy in May. “So we’re trying to predict its appearance, and we know that the more sunburn we see pre-harvest, the more sunscald we will have after 30 days in cold storage.”
And there is no postharvest control for sunscald. That’s why Torres says it’s important to break through the typical separation between postharvest practices and orchard management to address this disorder, which is estimated to cost about $100 million in losses every year in both Washington state and in Chile.
“This is a postharvest problem, but we need to work to correct it in the field. We know conditions in the field where fruit was produced will directly affect how fruit will do postharvest.” Torres said. “We have a very bad climate for sunburn in Grannies in Chile, and with climate change, it’s getting worse.”