Annona Species Monograph.pdf - Crops for the Future

Chapter 10. Agronomy
water to be applied during each irrigation event depends on the amount of
water per tree and number of trees per orchard unit. In addition, the time
taken to apply the required amount of water depends on the number of
emitters per tree and their outlet volumes. If the watering calculations suggest
a time that is longer than 3 hours, it is recommended that the irrigation be
split into 2 or 3 applications to avoid excessive wetness around the root
system and loss of water due to percolation (Santos, 1997). Irrigation at night
avoids evaporation losses. Growers should seek expert advice on developing
any irrigation strategy.
Water quality is as important as the amount of water and the time of its
application. The presence of certain nutrients, such as calcium, can
precipitate phosphates and provoke clogging of the emitters (Pinto and Silva,
1994). The presence of sodium in irrigation water can cause concern, as this
can result in salinization, especially in shallow soils without drainage
systems. Needless to say, salinization is extremely detrimental to plant
growth and fruit yield. Irrigation water containing NaCl, CaCl 2
or CaC0 2
causes depressed growth rate and reduced dry weight of all annona trees,
especially above 3,000 ppm (Galila et al., 1991, cited by Mansour, 1997),
leading to leaf burn and defoliation of the seedling leaves. High boron and
chloride contents in irrigation water also promote phytotoxicity and injury to
the leaves and fruits (Pinto and Silva, 1994).
10.3.7 Pest and disease management
Annona trees are attacked by a large number of insect pests and numerous
diseases. Peña and Bennet (1995) described 296 species of insects associated
with annonas, although many of them are not economically important. Nava-
Díaz et al. (2000) reported that, world-wide, 106 insects, 91 fungi, 5
nematodes, 2 bacteria and 1 virus have been recorded attacking Annona
species. In Venezuela, Marin Acosta (1973) described 27 species of pests
attacking annona trees. A full biological description of each pest, with
management information, would be a very difficult task with limited
applicability here, therefore only the major and regionally important
secondary pests and diseases will be described below. Pest and disease
control in commercial orchards has traditionally relied on the use of chemical
products. With increasing awareness of the human and environmental
hazards in pesticide use, alternative methods of control are suggested. In
small scale plantings, the potential for rapid increase in pest or disease
incidence is less, and the capability to monitor any outbreak is easier.
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