Practices that might help with alternate bearing were recently addressed in a report by Mary Sutton, University of Georgia (UGA) assistant professor and citrus Extension specialist. Alternate bearing, a common problem in many mandarin varieties, is the tendency of a tree to produce a heavy crop one year followed by a light crop the subsequent year.
A slightly edited version of Sutton’s report follows.
Unfortunately, there is very little that can be done to increase the crop load in an off-year. While certain plant growth regulators can be sprayed during flowering to increase fruit set, those fruit may still be subject to fruitlet and June drop in the weeks after they’ve set.
In particularly heavy years, cultural practices can be optimized to alleviate any deficiencies that may arise as a result of the heavy crop load. Likewise, in the off-year, cultural practices can be used to prep the trees for the heavy on-year that is likely to follow. However, this does little to prevent the alternate bearing pattern.
Reducing the crop load during a heavy year is the easiest way to alleviate the alternate bearing pattern. Removing flowers or fruit also removes the carbohydrates they’ve already imported and utilized. Therefore, the earlier flower or fruit thinning can occur, the better. This cuts down on the amount of wasted carbohydrates.
Thinning can be done by hand or through chemical thinners. Hand thinning is more labor intensive but ultimately provides better control over the quality and quantity of fruit remaining on the tree. Chemical thinners thin indiscriminately so you are more likely to run into issues of over- or under-thinning. A protocol for chemical thinning in Georgia citrus has not been developed yet, so it is not recommended yet.
Pruning, hedging and topping in on-years are also great ways of thinning out the crop load. Cutting back wood also removes all the fruitlets on that wood. While it seems counterintuitive, reserving these canopy management practices for heavy crop load years can help alleviate alternate bearing patterns.
The UGA is currently working on both pruning and fruit thinning recommendations that will hopefully help alleviate the severity of this pattern in the future.
Source: UGA
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