Avocado Production in Asia and the Pacific - United Nations in ...

Irrigation
Avocado is very sensitive to dry soil. Soil moisture should be maintained in the root
zone. Moisture stress gives rise to physiological hindrance, resulting in weak vigour and
even defoliation and fruit drop. Avocado sets flowers and bears fruit during December to
May, the dry season in most of the southern part of China, hence irrigation is very important.
Avocado orchards give a high and stable yield when irrigation is available. Improved
irrigation systems such as sprinkle and drip are not used at present. For the orchards with
easy access to water, flooding is achieved by water pumping. For the orchards far away from
water source, irrigation is carried out using tractors with water tanks.
Control of pests and diseases
Diseases
There are more than ten diseases, such as root rot, collar rot, phytophthora canker,
anthracnose (Colletotrichum gloeosporioides), stem-end rot (Dothiorella aromatica), scab
(Sphaceloma perseae), etc. Of the diseases, root rot and collar rot are the most serious.
Root rot is the most serious disease of avocado in mature orchards, caused by a
fungus, Phytophthora cinnamomi. It attacks small roots, thereby causing leaf fall, dieback of
branches and tree collapse. The trees infected show symptoms of weak vigour with withered
and sagged leaves, yellowish-green leaves, dead twigs and branches, small fruit and
seriously scalded branches. The cortex of the infected roots turns black, rots and dies. Some
seriously infected trees wither and die. Root rot is aggravated by waterlogged and poorly
drained soils. Chemicals such as Alliette, Ridomil, etc. are used as a soil drench, or Alliette
as a trunk injection at 0.3 grams/square metre. Phytophthora-resistant rootstocks are also
being selected, such as Thomas, Duke 7, etc, but they are not yet used commercially.
Collar rot, caused by Phytophthora citricola, is another serious disease of avocado in
young orchards in Hainan. It attacks the collar, resulting in retarded growth without flushing
and then tree decline or collapse. The affected trees show a symptom of shallow
honeycombed rot at the early stage, which then spreads, resulting in exudation of white
foam-like or pasty sticky liquid (attracting a mass of ants) and, finally, a ringlike rot and
death. The disease occurs after heavy rain caused by typhoon. A survey carried out on 4
hectares of affected plantations in 1989 indicated that the incidence was as high as 22
percent.
For the control of collar rot it is very important to drain the water after heavy rain,
prune regularly the drooping branches and maintain good ventilation of the plantations.
Alliette (1%) is applied at a solution rate of some 2.5 kg to the base of the trees in the
orchards of high incidence, or to those affected by typhoon. For the affected trees, the soil
around the tree base is removed in clear day, and the affected parts are washed by spraying
with tap water and, when dry, painted with Alliette paste 2% and refilled with soil.
Satisfactory results were obtained by using this method (Shang, Liu, et al., 1996).
Pests
The insect pests include scale insects, mealy bugs and mites, Mexican leaf rollers,
aphids, fruit flies, burrowing nematodes, etc. Serica sp. is the most important insect
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