Termite damage has been recorded on the majority of crops grown in the southern African region. All stages of the growth cycle are subject to attack and post-harvest loss is common on many small-scale farms. Seed is destroyed in the ground by a number of genera of the fungus-growing sub-family, Macrotermitinae, resulting in poor stands.
INTRODUCTION
Termite damage has been recorded on the majority of crops grown in the southern African region. All stages of the growth cycle are subject to attack and post-harvest loss is common on many small-scale farms. Seed is destroyed in the ground by a number of genera of the fungus-growing sub-family, Macrotermitinae, resulting in poor stands. Specialist grass-feeder harvester termites, such as Hodotermes mossambicus and Microhodotermes viator, may be responsible for severe damage to vigorously growing seedlings and young plants through defoliation or by cutting through at the base of the stems and carrying them away piecemeal. Where seedlings, young and mature plants are attacked, externally at or just below the soil surface, it is usually due to larger Macrotermitinae such as Macrotermes spp., Odontotermes spp., and Pseudacanthotermes spp. Plants may be completely or partially severed at the base. Felled plants are then consumed under cover of a soil canopy. Roots of mature ripening plants are attacked and hollowed out, the excavation often extending upwards into the plant stem. Internal attack such as this is generally the work of smaller termites such as Microtermes spp., Allodontermes spp. and Ancistrotermes spp. Plants may be attacked externally, the outside of the stem being covered with soil sheeting and the still actively growing or mature plant being consumed under this cover. This mode of attack is largely associated with Odontotermes spp. Underground tubers, such as yams, potatoes, and sweet potatoes are attacked and hollowed out while crops grown from stem cuttings, such as cassava and sugar cane, may be damaged both as seed pieces and when they mature. Occurrence of termite damage is always patchy, reflecting a similar distribution of termite colonies. A tendency for termites to work their way along rows in cultivated lands has also been noted.
CEREAL CROPS
Maize, the major staple cereal crop grown throughout the region, frequently suffers serious damage by termites. In the drier areas of both South Africa and Zimbabwe the harvester termite, H. mossambicus, may cause severe damage to a young maize crop at the seedling stage either by partial defoliation, in which case the plants can recover, or by cutting down and consuming the entire plant. This species does not attack the roots.
Generally the incidence of damage by termites of the fungus-growing sub-family Macrotermitinae, is low during the early phases of the growth cycle while plants are growing vigorously. Attack becomes increasingly severe from about 9-11 weeks, until plants reach maturity (ca.16 weeks) and senescence sets in. Plants may either remain standing or lodge (fall over). Lodged plants are subject to further attack by termites resulting in partial or total destruction of cobs. Incomplete harvesting of lodged plants in commercial agriculture where the crop is mechanically harvested leads to high loss of yield (up to 100%) unless cobs are harvested by hand incurring added costs. In small-scale enterprises, where harvesting is undertaken solely by hand, losses are considerably lower.
In the Southern and Central Provinces of Zambia, southern Tanzania and Malawi 20 - 30% of pre-harvest loss in maize is due to termites. Losses as high as 90% have been recorded on individual plots. In the warmer Bushveld areas of northern and eastern South Africa, 10-50% of plants may be attacked resulting in crop losses of between 3-30%. This attack is predominantly by the small fungus-growers. Records in the North West Province of South Africa over a period of six years, showed incidence of lodging due to termite attack varied between 20%-100% by the time the crop was ready for harvest.
Sorghum and millet generally show resistance to termite attack, but this has been recorded in Zimbabwe, Tanzania, Malawi and South Africa. Crop loss estimates have been in the order of 7%.
- Wheat and other small grains
The harvester termite, H. mossambicus, may be responsible for severe damage to young cereal crops such as wheat, oats, rye and barley in both South Africa and Zimbabwe. Occasional damage to wheat by Microhodotermes viator also occurs in the Western Cape Province of South Africa. Maturing cereals such as wheat, particularly in drier areas, may be attacked by Allodontermes spp., Microtermes spp. and Ancistrotermes latinotus; the base of the central stem being hollowed out which results in premature whitening of the grain head.
Cassava is an important staple food crop in some countries in the region is attacked by a variety of Macrotermitinae. The cuttings are hollowed below ground or at ground level and the stems fall over.
Over a five year period loss of stand as a consequence of the activities of the small fungus growers, Microtermes spp., Allodontermes tenax (Silv.), and Ancistrotermes latinotus, averaged 33% in Tanzania with losses of more than 80% being recorded on individual plots. Termites gain access to stems at, or just below, ground level, remove the internal tissues causing weakened plants to collapse. Attack took place from crop emergence onwards, with losses increasing rapidly once the crop reached maturity.
Termites are a serious groundnut pest throughout the southern African region.
The smaller fungus-growers in particular, attack and invade actively growing groundnut plants through the roots and stem near ground level, hollowing them out and causing the plants to wilt and die with a consequent reduction in crop stand. Roots damaged by other soil pests, such as white grubs, are also liable to invasion by termites. Apart from this form of attack, stem bases are sometimes severed by species such as Macrotermes spp. and the harvester termite H. mossambicus, with 25-100% of plants being lost in this way. As the crop ripens the outer layers of the pods are scarified (removal of soft corky tissue between the veins of the pod) by termites allowing contamination of the seed with soil fungi, such as Aspergillus flavus, which produce lethal ‘aflatoxins’. Infected plants are not obviously diseased and are frequently harvested with and contaminate the rest of the crop. Scarification as high as 30% has been reported. In large-scale plantings, damaged pods cannot be satisfactorily harvested mechanically. Species such as Microtermes spp. also penetrate the shell to feed off the soft inner lining, filling the pod with soil. This form of attack leads to additional loss through premature germination of kernels. Stacks of plants left drying in the fields are also frequently attacked by species such as Odontotermes spp. with farmers losing between 30-40% of their crop at this stage. Termite damage is generally most serious towards the end of the growing season just prior to harvesting with drought being an aggravating factor.
Cotton is a crop that is frequently damaged by termites, particularly in drier areas of the sub-continent. Smaller termite species damage young plants by attacking the root collar, entering the stem and hollowing out the centre, causing the plants to wilt and eventually die. Larger species cut through the plants at ground level. In drier parts of Tanzania, Malawi and Zimbabwe seedlings may also be cut down and carried away piecemeal and older plants may be severely defoliated by the harvester termite H. mossambicus.
Sugar cane is sporadically severely damaged by termites. Cane is grown from short lengths of cane (setts). The most common damage to the crop is when these setts are first planted out in the fields. Attack at this stage prevents germination, resulting in a poor stand. Termites also attack the crop as it begins to mature as well as the cut stumps following harvest. Secondary attack can also occur when termites gain access to the soft pith through sites damaged by rodents, stem borers or other agents. In South Africa and Swaziland attack is generally associated with infertile soils or with dry conditions in sandy soils.
Tea is generally grown in high rainfall areas, often at high altitudes where termites are less common and it is only in marginal areas that the crop becomes subject to sporadic termite attack. As with other crops, drought appears to be an aggravating factor. Attack takes the form of ring-barking mature plants. Various species of Odontotermes are responsible for much damage in Malawi, Tanzania and Zimbabwe where Ancistrotermes latinotus, and Macrotermes spp. are also implicated. In the Western Cape Province of South Africa, the herbal "rooibos" tea is occasionally attacked by the harvester termite, Microhodotermes viator.
Large commercial orchards of citrus, mangoes, avocados, guavas, bananas, macadamia and pecans and fields of pineapples, particularly those planted to newly cleared and prepared lands, are vulnerable to attack by termites, sometimes resulting in the total destruction of entire orchards. Damage to fruit trees by termites is similar to that described for trees grown for timber. The termites implicated are Macrotermes spp., Odontotermes spp., and Ancistrotermes latinotus.
Tobacco in both South Africa and Zimbabwe is attacked both in the field and in seed beds by Macrotermes spp., Odontotermes spp. and A. latinotus. Termite damage to sunflower has on occasions made mechanical harvesting impossible and greatly reduced yields. In Zimbabwe, Macrotermes. natalensis has been reported attacking bambara groundnuts. Incidence of termite attack on pigeon pea varies substantially in different areas with a steady loss of up to 45% stand loss being reported. Termite attack increases gradually as the dry season progresses, with no sudden increase following the end of the rains. As with pigeon pea, termite attack on cow pea varies in different areas and different varieties, with up to 80% of plants being severely damaged at crop emergence on occasions.
