Post-trial monitoring produces timely advice for orange growers
Citrus growers are now armed with information to combat a potential future threat to production.
The results of long term scientific trials by the South Australian Research and Development Institute (SARDI), a division of PIRSA, show some orchard trees that were healthy at ten years old are now dying at the 15 year mark.
The original trials included the combination of C35 citrange rootstock with Navelina 7.5 scion. These specific trees were initially successful up to ten years of age, but now are shown to be incompatible.
SARDI research scientist Mark Skewes said the trial was planted by SARDI at Loxton Research Centre in 1997 to compare the performance of three different Navel orange scions on eight rootstocks.
“The trial went from 1997 to 2007, looking at tree size and yield, and was then maintained as a commercial planting,” Mr Skewes said.
“It was then revisited by SARDI in 2015 and we found that some of the trees that were healthy at 10 years old are now dying, and all of the dead trees had one of three identified scion/rootstock combinations.
“It’s estimated that Navelina makes up around 6% of the SA Orange industry, and 4% nationwide. Probably less than 25% of that group would be on C35, but it’s important not to invest further in this combination when we know that premature die-off is likely.
“All of the dead trees had Navelina 7.5 as the scion, and in all cases this was budded onto F80-5 citrumelo, F80-7 citrumelo or C35 citrange.
“Based on the evidence found at this trial site, C35 citrange should not be used in combination with Navelina 7.5 scion. In addition, due to their close genetic similarity, caution is advised in budding other varieties such as M7, Navelina 315 and FJ Navel (a recent Navelina sport) onto these rootstocks, as similar problems are possible.”