Minimise sun damage and heat stress in your fruit by spraying your trees with a thin layer of kaolin clay.
Few results are as credible as those from successful farm trials run by farmers themselves. In the case of Simon Baty from Matrozefontein in South Africa’s Sandveld region in the Western Cape Province, trials are a familiar teacher and are one of the reasons for his successful cultivation of citrus fruit in this hot, dry area.
Trials at Matrozefontein were conducted to determine how successfully citrus can be produced in the region and included different irrigation systems, cultivars and rootstock, and even the application of shade netting to mitigate heat damage and utilise resources like water most efficiently.
One of the trials that have yielded good results was the application of kaolin to decrease leaf temperature, heat stress and sun damage to plants.
“In the first 2 years we used an infrared thermometer to test the product and observed a 4˚C decrease in leaf temperature on trees that were sprayed as opposed to the trees that weren’t. We also did trials with shade netting and the leaf temperature beneath the nets was up to 8˚C lower than on trees that received no treatment.
“The trees experience less heat stress during critical times due to lower leaf temperatures. An additional advantage is that the fruit are also protected against sunburn. The kaolin clay is white and forms a thin layer on the fruit that reflect sunlight, and thus keeps leaves and fruit cooler.”
70% LESS SUNBURN
“We used to experience as much as 10% sunburn damage on our fruit before we used kaolin. With the clay, this damage has been brought down to an average of 3% on our navel oranges. The efficiency of the kaolin against sunburn on naartjies and lemons isn’t as dramatic.
“The effect of the kaolin on the health and productivity of the tree cannot be doubted. We tested kaolin on our Midknight Valencia 3 years ago, but didn’t get a noteworthy result. When I returned to the trial block during the next season, the rows where we tested the kaolin were much healthier and lusher than the untreated trees. The kaolin, thus, brings a much better summer-flush, which results in sustained production levels.
“We took leaf samples from treated and untreated trees from this block. The nutrient content of the treated leaves were significantly higher than that of untreated leaves,” Batey explains.
There are some negative aspects to using kaolin clay as it adheres strongly to the leaves and peels of the fruit, which leaves white marks on the fruit, even after washing and waxing. According to Robert Paterson, a fruit farmer near Clanwilliam who uses kaolin on his citrus fruits and avocados, it is possible for the clay to extend the withholding period for some chemicals.
“This is still under debate and is unproven, but it may be better to err to the side of caution. If you apply chemicals before you apply the kaolin, it’s safe, but the argument is that chemicals cling to the kaolin and then take longer to break down.”
Both Batey and Paterson spray kaolin as a preventative measure when a heatwave is predicted. Batey sprays the first application of the product at 2.5 kg/100 l water with high volume applications (between 1 000 l and 1 200 l per ha). Paterson sprays 30 kg/ha with high volume application for his first spray.
The second and third applications for these producers varies between 2.5 kg and 2 kg per 100 l of water for Batey and 15 kg/ha for Paterson. Neither will exceed 3 applications per season.