Durian tree phenology and the control of phytophthora diseases of durian using phosphonate trunk injection

Abstract

We have identified phenological patterns of mature durian trees grown in the north of Queensland, Australia, and monitored the distribution of phosphonate following trunk injection at three distinct phenological periods, to identify the injection period which results in maximum uptake in all tree organs. Durian cultivars Gumpun, Parung and Gob Yaow were injected with 16 g a.i. phosphonate at each of three injection periods (early flowering fruit/fruit-set, mid-fruit-set, and immediately after harvest). In northern Queensland, durian shoot and root development appears to be active throughout the year despite the relatively cool conditions that occur during winter. Shoot-flushing activity often occurs in parts of the tree rather then uniformly over the canopy. Phosphonate was detected within two days of injection in all organs sampled and reached a peak between four and eight days after injection. The highest levels of phosphonate were recorded in leaves and flowers (mean value of 60 and 40 μg/g dry weight). Phosphonate levels either declined or increased with sampling date, depending on organ and injection time, but persisted in all tissues for at least 128 days. Phosphonate trunk injection trials were also carried out on local durian varieties in Vietnam. Under moderate disease pressure, annual injections of 16 g a.i. per tree gave superior control of canker compared with recommended sprays of metalaxyl or Aliette. Under high disease pressure, 48 g a.i., injected at 3 three-monthly intervals, gave the best disease control. Results presented in this paper demonstrate the efficacy of phosphonate in controlling phytophthora diseases in durian when applied as a trunk injection.