Pruning for maximum benefit in litchi trees

Research conducted by HortResearch SA’s Dr Steve Oosthuyse shows that timely pruning of litchi trees can produce a rich flush and yield a greater harvest.

High yields can be obtained if the trees are pruned at the correct time.
Photo: Lindi van Rooyen

Mauritius litchi trees can vary significantly in flowering intensity and yield. The trees have a high flowering induction requirement and growers have a narrow window of opportunity in which to ensure a good litchi harvest. Dr Steve Oosthuyse, of HortResearch SA, has found that by pruning litchi trees at the right time, flowering occurs at a stage which is maximally inductive, resulting in a greater yield.

Mauritius litchi trees in Tzaneen were monitored for flowering intensity and cropping. “Flushing time after harvest determines flowering intensity and we have found that relatively small differences in flowering time in spring impacted greatly on tree yield,” says Dr Oosthuyse. He notes that while flushing shows variation between and within unpruned trees, it is directly influenced by the date of pruning. “Date of post-harvest flushing determines the terminal shoot maturation stage and bud break. Pruning must therefore be timed to ensure that shoot maturation takes place when conditions are maximally inductive in winter.”

Pruning
Dr Oosthuyse says that the first week of February is the best time to prune litchi trees in Tzaneen. “The terminal shoots will then be at the ideal stage for flowering.” Terminal bud development is required when conditions are maximally inductive. This generally occurs between August and September, just after temperatures are lowest and when the day temperatures start to increase.

Trees must be pruned by cutting back the terminal branches by 30cm to 40cm. This also ensures they maintain their allotted size in the orchard row.“ Our study found that generally, synchronous flushing occurred after pruning. The date of pruning effectively influenced the time of general flushing, and the maturation state of the shoots during July and August, when inflorescence development generally starts. “The approximate time between pruning and the first flush is about 14 days,” explains Dr Oosthuyse.

Results
Flowering intensity and cropping bore a strong relation to pruning date. “Trees pruned early enough, but not too soon after harvest, initiated only one flush after pruning and had terminal shoots that attained a stage of maturation during the flowering period. General bud development occurred when environmental conditions were sufficiently inductive.” Dr Oosthuyse says the terminal shoots on trees pruned later were not mature enough during the inductive period for sufficient bud development to occur. Consequently, flowering intensity and cropping was low in these trees.

“In pruning generally we force new shoot growth at the correct time for flowering to occur. Correct pruning can ensure that a farmer can produce a more stable income over two years.” Dr Oosthuyse notes that the effect of pruning dates on flowering intensity and cropping requires assessment in each of the major litchi growing regions in South Africa, before general recommendations can be made.

Contact Dr Steve Oosthuyse at [email protected]