By Fernando Alferez
Five years of University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) data in trials across the state have shown that individual protective covers (IPCs) are effective in preventing HLB until they are removed. This has been shown in sweet orange varieties such as Valencia and Hamlin. In these varieties, it has been demonstrated that the covers can protect the trees for as long as 30 months after planting. This provides an advantage resulting in better fruit quality as the tree is already producing fruit when the IPC is removed. As a result, there are now trees of bearing age that are free from HLB in Florida for the first time in years.
However, one aspect of IPC use is often overlooked. Varietal differences may dictate IPC feasibility or the time the covers can be maintained on the tree. With this idea in mind, a UF/IFAS research project began more than three years ago using three promising mandarin varieties (Sugar Belle, Early Pride and Tango) grafted on two different rootstocks, sour orange and US-942. Trees were covered with 6-foot IPCs.
The trial results may help to make informed decisions when deciding to adopt IPCs in newly planted mandarin groves. Early Pride did not perform well under cover regardless of the rootstock. A large percentage of trees were affected by branch dieback during the second year, and some trees died after the third year.
Sugar Belle performance was very interesting. By the first and the second year, trees under IPCs grew larger and more uniformly than unprotected trees. But after the second year, these differences were lost. By the third year, non-covered trees were larger with better defined canopies. This effect was more visible in trees on US-942 than on sour orange, probably because of more vigorous growth. It was remarkable also that covered Sugar Belle trees did not set almost any fruit, in contrast with non-covered trees.
Finally, Tango trees, irrespective of the rootstock, performed much better under IPCs than the non-covered trees, showing better canopy density, larger and greener leaves, and taller trees that were able to set fruit.
In summary, the research shows that IPCs are a great tool to protect sweet orange and Tango mandarin trees for about three years. IPC use on Sugar Belle should be limited to the first two years after planting. Other varieties affected by branch dieback, such as Early Pride, should not be covered by IPCs.
Fernando Alferez is an assistant professor at the UF/IFAS Southwest Florida Research and Education Center in Immokalee.
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