Pest Management in Miombo Fruit Trees - Indigenous Fruit Trees in the Tropics: Domestication, Utilization and Commercialization - page 373

on miombo fruit trees. However, Phytophthora root rot is generally regarded as
the most serious soil-borne disease of citrus and avocados (Ploetz et al ., 1994).
In South Africa, different Phytophthora species attack Eucalyptus and Acacia
mearnsii (Roux and Wingfield, 1997) and in this way these exotics can be a
source of infection also for miombo fruit trees. Root damage caused by insects
can also give access to the tree root system for fungi which are not able to enter
through undamaged bark. For example, Fusarium

spp. can under such

circumstances cause substantial damage.

Insects

Termites are probably the most serious pests causing mortality of tree seedlings
after outplanting in the field. Termites attack plants at the base of the stem,
ring-barking or cutting them completely. Termites are not host-specific and most
often attack stressed plants (Sileshi, 2000). The most important termite pest
genera in Africa include Odontotermes , Macrotermes , Pseudacanthotermes ,
Microtermes , Ancistrotermes , Allodontermes , Amitermes , Trinervitermes and
Hodotermes (Uys, 2000). Damage is due to feeding either under soil sheeting
on the outer surface of the plants or on the roots. White grubs (larvae of
scarabaeid beetles) also affect roots of tree seedlings such as Sclerocarya birrea
(G. Sileshi, unpublished results).

Plant - parasitic nematodes

Nematodes are tiny, worm-like, animals mostly living freely in water and soil.
Plant-parasitic nematodes are major pests of fruit trees, interacting with
pathogenic microorganisms in disease complexes, and in some instances
constituting the main cause of damage to plants (Keetch, 1989; Kleynhans et al .,
1996). Much of the damage associated with nematodes goes unnoticed or is
attributed to other factors, mainly because growers are unaware of nematodes
(Kleynhans et al ., 1996). Plant-parasitic nematodes can affect fruit trees in a
variety of ways. Uptake of nutrients and water by a plant can be drastically
affected by direct feeding or root infestations of nematodes. Nematode feeding
also creates open wounds, which provide entry to a wide variety of plant-
pathogenic fungi and bacteria. These microbial infections may result in greater
losses than the damage from nematodes. Because nematodes damage roots,
any condition which stresses the plant, such as drought, flooding, nutrient
deficiencies or soil compaction, will tend to amplify the damage symptoms
noted above. Failure of plants to respond normally to fertilizers and slower than
normal recovery from wilting are signs of nematode infestation. Below-ground
attacks are mostly recognized as wilting of above-ground parts.
Little is known about root-attacking nematodes in the miombo forest.
Plant-parasitic nematodes have been found in soil samples from baobab
( Adansonia digitata ) in East Africa (Coleman et al ., 1991). In Senegal, the
baobab has been found to be a host of root-knot nematodes ( Meloidogyne sp.)
and

Rotylenchulus reniformis , and therefore baobab trees, although not