Four years working as an agricultural engineer and 10 years on the farm have taught Rénald Radley not to take things for granted but rather to rely on research and proven results before implementing any practice. “I’m no one’s guinea pig. If a fertilisation or crop protection programme hasn’t been proven, then I am not interested. There is enough research being done on farming practices and there is an abundance of information out there. I don’t have to take anyone’s word for it, I rather do my own homework,” he advises.
Rénald’s thirst for knowledge is evident in his bookshelf packed with books on growing mangos. Quick to learn and quick to adapt, he is not set in his ways, but is always looking for methods to improve orchards and increase yield. “This is my secret to success.”
Radley Estate is situated near Malelane, Mpumalanga in an area where the mangos are harvested during peak mango season so Rénald can’t take advantage of premiums given for fruit coming onto the market earlier. His challenge is to ensure that what he puts on the market is of good quality. “Quality always sells better. I must have the right combination of cultivars to service the market.”
Rénald explains that ideally he should have three cultivars: early, mid- and late season. Radley Estate plants six cultivars, including 5ha Tommy Atkins (early season) yielding an average of 33t/ha, Joa (early mid-season) on 1ha averaging 18t/ha and Kent (late mid-season) on 8ha averaging 10t/ha. This cultivar should average 25t/ ha but the trees had to be pruned back vigorously after the previous season, compromising the yield. The average was also affected by two underperforming blocks as well as a high water table due to high rainfall over the period.
Heidi (mid-late season) on 10ha averages 16t/ha, but Rénald is aiming for an average of 22t/ha. Keitt (late season) on 3ha yields 25t/ha achar mangos and Sensation (late season) on 3ha averages 22t/ha. Rénald explains that Sensation is alternate bearing but can yield more when thinning half of the flowers when they are in full bloom in the good season. “At fruit set we have a second round of thinning by reducing the number of mangos to one per flower panicle. The result is a less alternate bearing pattern and a better, more popular fruit size.”
Because of the lower yield of Kent and Keitt, Rénald is in the process of switching these orchards to Tommy Atkins. “Our soil is very rich, but it makes Kent retain a green colour, making it less popular on the market.” Heidi is less susceptible to disease or fungi, but the yields are on average lower. “The trees will flower but fruit just won’t set. No one can seem to figure out what the problem is and no research is being done on it.
“The younger Heidi trees are four years old and doing well, but the older 16-year-old trees are struggling. At the end of this season I will prune them back quite drastically to see if that helps.” “Despite the problems, Heidi is still a good cultivar for me. I can’t pinpoint it, but there seems to be something on my farm that causes Heidi to produce better yields than on other farms. It could be a combination of the microclimate, soil, slope or day/night temperatures. The fruit also does well on the market and many customers will drive a bit further to buy these mangos from Radley Estate.”
Pine trees are wind breaks that protect the mango trees against bacterial black spot. As the wind blows, the mango leaves chafe the skin of the fruit, creating an entry point for the bacteria.
Mangos are harvested by hand and handled with care. Breaking the panicles when picking mangos releases the latex in the stem. The fruit is then left upside down so that the remaining latex can drip out and not cause latex burn on other fruit when packed into a crate.
Some 40% of Radley Estate’s mangos are marketed directly from the farm to hawkers and vegetable shops. Another 40% is sent to municipal markets and the remaining 20% is sent to a nearby dried mango and juice factory. “The hawkers are getting increasingly fussy over quality, but the advantage of this market is that they want a variety of sizes to fit into crates or to sell loose so it makes it easier to sell fruit that does not conform to formal market standards.”
Mango trees are pruned as soon as possible after harvest and all panicles are cut off. If the panicles remain they dry out and develop fungi, with a detrimental effect on the following year’s yield. Branches that don’t carry fruit during a season are pruned back in spring. They then become high potential branches the following season because of the reserves these branches have built up. Rénald explains that although mango trees tend to remain productive over the years, they must be pruned sufficiently to ensure good air movement and enough sunlight on the leaves.
“Branches in the middle of the tree that start drying out from age or lack of sunlight must be removed. If only the outside of the tree is pruned, the new fruit-bearing branches are concentrated on the outside. The tree volume is not fully utilised to produce mangos if it only bears on the edges. “If the older, dry branches are removed and the tree is also pruned on the inside, the new leaf flush is equally distributed and the tree also stays alive in the middle.” After pruning, Rénald applies a copper spray to keep the leaves free from pests and disease.
Feeding the orchards
In November, soil analysis is done and the fertilisation programme planned, to be applied once the harvest has been completed. Nitrogen is added directly after harvest, according to the analysis. Rénald says that most blocks don’t need any nitrogen, while some average 30g urea per tree. Only three blocks need between 280g and 340g urea per tree. “Our leaf analysis shows that we don’t really need to add much nitrogen, as too much deters fruit colouration.”
Although Radley Estate has its own packhouse, due to the size of the orchards, the packhouse can’t be run continuously throughout the season. The only way to overcome this is to double the area planted to mangos.
Phosphorus is added in March at an average rate of 100g/tree to 150g/tree. Varying from block to block, potassium is added in May at an average rate of 200g/tree. “We add around 300g sulphur to each tree directly after harvest to reduce the pH as it is somewhat high and reduces the absorption of trace elements. “The pH of the soil is between 7,5 and 8, with some blocks below 7. It should be between 6 and 7,2,” Rénald explains.
Each tree receives between 100g and 430g of potassium sulphate in May. Rainfall on the farm averages 650mm per annum so the orchards are irrigated. After being pruned, the orchards are irrigated according to tensiometer readings. In May, induced drought places the trees under stress. “If the trees are not stressed they don’t flower. However, if the trees are really suffering I give them a bit of water.”
A cold winter stimulates optimal flower bud development. Because of the unpredictable weather, the trees are placed under further water stress during warmer winters. “If by mid-July the flower buds look like they want to break, I start irrigation and reduce any other stress the tree might experience so that it will go into a strong growth phase.” Orchards are drip irrigated once a day, twice on hot days, with two dripper lines per row of trees. Irrigation lasts up to a maximum of four hours, ensuring that the whole soil profile is wet.
Rénald follows Syngenta’s MangoPack crop protection programme, starting when the flower panicles are 5cm. He sprays for powdery mildew, soft brown spot, bacterial black spot, stem end rot and anthracnose. “Bacterial black spot is a problem on the farm. As the wind blows, the leaves chafe the skin of the fruit, creating an entry point for the bacteria. We prevent it with a copper oxychloride spray.”
Radley Estate produces 600t to 700t of compost annually from pruned branches and twigs from the orchards, orchard chippings, sickle bush and organic waste from around the farm.
In November, Rénald sprays for weevils and mealy bugs with Fenthion and Methomyl respectively. Scouting identifies weevils or mealy bugs; if a high concentration is found, insecticide is applied. But these chemicals are kept to a minimum and only spot spraying is done where the infestation is. “If wet weather prevails during flowering time, anthracnose becomes a problem. Kent really took a beating this year so we have had to pick the entire crop for achar.”
The Syngenta programme advises a spray rotation of Tilt, sulphur and Tilt, and then sulphur again. “But I think one of the sulphur sprays must be replaced with Ortiva, or a carbendazim-containing product, because it works better for anthracnose in a wet year.” To keep infestations to a minimum, Rénald keeps the orchard clean of fallen and rotten mangos. “Fruit falls off the trees all the time and removing the fruits prevent the mango seed weevil, because it lays its eggs on the fruit and then bores into the pip and feeds on it. It then survives through the winter and affects the mangos the next season.”
Fallen mangos are ground finely to ensure that the weevils don’t survive.
Contact Rénald Radley on 082 388 3643.