SOURCE: Lindi Botha, Farmers Weekly
Any crop can be seen as ‘easy’ or ‘difficult’ to cultivate, depending on how you manage it and your yield expectations. This is especially true of mangoes,” says Johann du Preez, general manager of Bavaria Fruit Estates in Hoedspruit, Limpopo.
“You can leave mangoes to follow their own natural cycle with minimal interference, and still get a crop. But with profit margins being so narrow, it’s crucial to get the best crop and a consistent yield. This is why I constantly try to improve the crop.”
Du Preez, who has over 30 years’ experience as a mango farmer, emphasises the need to produce a consistent harvest, rather than a bumper harvest one year, but with inevitably smaller fruit, and a small harvest with larger fruit the following season. This is a particular problem with the mango, which is an alternate-bearing tree.
“Inconsistency makes marketing fruit more difficult. Markets want to know what they’re getting and where it fits into their marketing plan. So it’s better to get a similar yield and the same-sized fruit year after year.”
Du Preez walks the talk: in an industry where yields have fluctuated dramatically from one year to the next, he has achieved approximately 27t/ ha consistently over the past four years. He is also the winner of the South African Mango Growers’ Association’s coveted Golden Mango Award in 2018 for his contribution to mango research.
The key to managing mangoes, explains Du Preez, lies in understanding them. “We’re farming a tropical crop in a subtropical environment, so tree and environmental manipulation is necessary.”
Because mangoes are terminal-bearing, the fruit is borne only on new growth.
“This means waiting for new branches to sprout and harden before flowering. But new branches sprout only after harvesting, and all the fruit must be harvested. Even with a big harvest on a late cultivar such as Keitt or Brookes and all the branches bearing fruit, everything must be picked before we can prune and get new growth.
“The problem is that the time between new growth and flowering is 40 days, so if the harvest ends only at the beginning of April, there’s not enough time for the new branches to grow and harden before the flower induction window in May and June.”
This, he explains, is the optimal time of the year, as the temperatures are just right for flowering.
“July is too cold and August too hot, so if the trees flower then, they don’t set fruit. We’ve also noticed that flower malformation, which has become a big problem industry-wide, is more prevalent on later flowers, so we try to get our trees flowering as early as possible.”
This is where Du Preez’s experience at tree manipulation comes into its own. In December, he prunes those flower stems that have not borne fruit, so that the tree sprouts new growth. This will ensure a good crop the next year. The branches that don’t bear in one season can then bear the next.
“On the Brookes cultivar in particular, you need to intervene, because it’s prone to a high yield one year and a low one the next. By thinning out fruit and pruning the non-bearing branches early, we even out the yield over two years. On the later cultivars, we thin out the fruit when we see the trees are bearing too heavily. The green fruit is then sent for achar.”
Hardening of the new leaves is a sign that inflorescence is due to take place.
“I squash the leaves in my hand. If they crunch, not just bend, they’re mature and the
tree is ready for flowering and fruit set. If the branches don’t mature in time and flowering takes place after that, the flowers will be weak and won’t set properly.”
Several factors are required to get the flowering period right: the correct hormone levels in the trees, the optimal timing and volume of irrigation, the ideal air temperature, and the energy reserves in the tree. This is a complicated process and requires careful management.
The climate is the main factor that determines when and how well a mango tree flowers, says Du Preez. As mangoes originated in the monsoonal tropics, where it rains for six months of the year and there are only minor variations in temperature, the trees have evolved to flower all year round. This means that trees in subtropical areas must be stressed to induce flowering at the ideal time.
Withholding water prevents vegetative growth, he explains. “The key is to irrigate at the right time to wake the tree up and ensure that flowering takes place when required.
“We start reducing irrigation after flush, which enables the new leaves to start hardening. We stop irrigation altogether after they’ve hardened, which forces the tree into flower and stops all new leaf growth. Getting the timing of this second phase just right is especially tricky. If vegetative growth doesn’t occur when the tree should start flowering, the tree will flower later, when it’s not ideal.”
Du Preez adds that although new buds are present on the tree, the climate determines whether they turn into vegetative growth or fruit.
“So every effort must be made to manipulate the tree into producing flowers and not new leaves. At the same time, we try to ensure that when the time comes for the buds to flower, the tree has enough energy reserves to push everything it can into producing fruit.
After the leaves have hardened, we apply a phosphate nitrate foliar spray. The salt in the phosphate draws out moisture, so the tree senses drought, which induces stress and hence flowering. The tree also absorbs the nitrates, which deliver nitrogen to the plant and boost flower development.”
A balancing act
Bavaria Fruit Estates has been blessed with mild winters over the past few years, which has made production management easier.
“The weather is the biggest challenge. You can apply all the practices mentioned, but with a long, cold spell, everything goes out the window. You can never fully manipulate the trees into doing what you wish. But mango is a long-term crop, so if you can achieve success in four out of five years, you’re doing well,” says Du Preez.
He adds that when water is scarce, mangoes can keep a mixed farming operation going.
“We also farm citrus, which can’t handle drought. So when water is scarce, we divert
what we have to the citrus, away from the mangoes. But the mango trees keep going, and when water is available again, we irrigate and get a harvest. The combination of the two works out well.”