African armyworm (Spodoptera exempta)

The African armyworm can cause serious crop losses. Armyworms may cause indirect injury to the taproot by cutting stems and/or consuming foliage above ground.

Stemborers

Stemborers are the most important pests of sugarcane. Several species of stemborers attack sugarcane. The most important is the African stemborer.

1) The African sugarcane stalkborer (Eldana saccharina)
Adult moth has a wingspan of 30 to 40 mm. It has elongated, pale brown forewings, each with two small spots in the centre, and whitish hind wings with a short fringe. Adult moths congregate on the cane canopy at night, they are attracted to light and so populations can be sampled using light traps. Female moths lay batches of yellow, oval eggs behind the leaf sheath or in folds of dead leaves. Eggs become pink before hatching. Young caterpillars feed on the leaves eating away the upper layers of the tissue; this damage is known as windowing. Later, they penetrate into the stalks. Caterpillars usually burrow into single internodes. When burrowing in the stem, caterpillars push their excrement outside.

Large amounts of frass are often hanging from the exit hole made by caterpillars prior to pupation. Caterpillars are light brown to dark grey coloured with brown with very small dark coloured spots. Pupation takes place in the plants, in the stem or on the leaf sheath. At emergence, the moth leaves a large emergence hole in the stalk. Attacked plants are stunted; in severe attacks they may dry up and die. When very young plants are attacked "dead heart" results, followed by tillering of the plant.

Older plants or ratoon cane have internodes bored. Crop losses are hard to assess because they vary with the age of the cane. In unstressed, maturing cane, quite high numbers of borers may be present without serious crop loss, but where infested, stressed cane is left to stand from one season to the next, the loss may be total. This stemborer also attacks maize and sorghum.

2) The spotted cane borer (Chilo sacchariphagus)
It is a serious pest of sugarcane in the Indian Ocean Islands (Mauritius and Reunion), and also attacking sugarcane in Mozambique and South Africa.

Sugarcane scale (Aulacaspis tegalensis)

Adult scales are pear-shaped (females) to elongated (males). The scale mainly attacks stalks and leaf sheaths but can also be found on leaves as a result of crowding on the stalks. In the case of severe infestation, the cane stalks are almost entirely covered by scales. When gravid, the female's body is 1.8 mm long and 0.9 mm wide. After egg-laying, the female shrinks and loses her pink colouration. Eggs are laid under the females scale. Upon hatching the crawlers (young immature mobile stage) wander looking for a feeding site. They insert their needle-like mouthparts and suck plant sap and do not move again. They then develop a thick, waxy scale cover.

Crawlers can be dispersed considerable distances by wind or movement of vegetation by field workers and transport. This scale is a serious pest of sugarcane causing yield loss (both of canes and sugar content) and making extensive replanting necessary. Yields losses of over 30% percent have been reported in Tanzania (Bohlen, 1973).

Pink sugarcane mealybug (Saccharicoccus sacchari)

Adult female is pinkish and it is elongated, oval to round in shape, and about 7 mm long. This mealybug is usually found in colonies on the stem beneath the sheath but is sometimes found on the stem just below ground level, on the root crowns, on the stem buds, and underneath the leaves. The leaves often turn red at the bases as a result of mealybug attack. Sooty moulds often develop in severe infestations and ants feed on honey dew excreted by the mealybugs. This mealybug is often present in very large numbers, which excrete a considerable amount of honeydew.

Damage is partially caused by the insect sucking the plant sap, which may lead to stunting and yellowing, thin canes, death of young shoots and impaired growth when mealybugs are present in high numbers, but direct damage rarely causes yield loss in sugarcane. Most damage is caused by honeydew excreted by the mealybugs and the gums exuded from the wounded parts, which interfere with the synthesis of raw sugar juice leading to filtration and clarification problems, lower quality of the syrup and reduced crystallisation. Severe attacks decrease the general vitality of the plants, which become more susceptible to diseases.

Termites (Amitermes spp., Pseudacanthotermes spp., Macrotermesspp., Odontotermes spp., Microtermes spp. and Ancistrotermes spp.)

Occasionally termites can be a problem by attacking the seed pieces or the roots and stems of established plants. Yield losses can be very high. In Sudan losses of 18 % have been recorded and in Central Africa losses of 5-10% are common. In Nigeria plant germination failure of up to 28 % has been reported. The most common damage to sugar cane is the destruction of the planting material (setts).

Rats (Rattus spp.)

Every 5-6 years there are explosions in rat population size, mainly attacking food crops and sugarcane.

The sugarcane mosaic potyvirus (also called mosaic of abaca) (SCMV)

It causes systemic infection of the sugarcane plant: the whole plant, including roots, contains virus. The symptoms (mosaic and/or necrosis) are observed on the leaves and sometimes the stems. Sometimes the whole plant is stunted. The classical symptoms are contrasting shades of green on a background of paler green to yellow chlorotic areas. It is aphid transmitted and also through infected planting material.

Sugarcane common rust (Puccinia melanocephala)

Initial symptoms of sugarcane common rust are elongate yellowish leaf spots, 1-4 mm long. On susceptible plants, the spots increase in size and reddish-brown in colour. Typical rust pustules form on the leaves. The elongate pustules are parallel to the venation of the leaf and measure 2-20 mm by 1-4 mm. Multiple pustules on leaves give a reddish appearance to plants from a distance.

Red rot of sugarcane (Glomerella tucumanensis / Colletotrichum falcatum)

The fungus may infect any part of the sugarcane plant. It is most destructive as a rot of the stalk of standing cane, seed cuttings and/or stubble pieces remaining in the ground after the cane has been harvested. It produces long lesions on the leaf midribs. The lesions on the leaf midribs are dark or red. They may be short and discontinuous or long extending the length of the leaf. The centres become straw-coloured with age and are later covered with black powdery mass of spores of the fungus. However, the leaf lesions cause no serious injury to the plant but are important in the life cycle of the disease because they are sources of the spores that cause infection of the stalk.

Affected plants turn yellow, shrivel and the upper leaves die. On splitting the stalk or seed cutting, the normally white or creamy-white internal tissues are reddened and the reddened area is cross-barred with white or light patches. Any sort of wounding causes a reddening of the stalk tissues next to the wound, but when diseased the characteristic red discolouration extends beyond the point of the wound. In advanced stages of rotting, the interior of the stalk darkens and the tissues shrink, leaving a cavity, which may be filled with mycelium (growth) of the fungus.

The disease is spread by wind and rain. It is also spread by planting infected seed cuttings and it is enhanced by injuries by sugarcane borers and sugarcane weevils.

Pineapple disease (Ceratocystis paradoxa)

It is called pineapple disease because of the characteristic odour of the rotting cuttings, which is like that of decaying pineapples. The interior of affected seed pieces becomes sooty black. Eventually the vascular bundles (tissues conducting fluids in the plant) become fibrous strands in hollow blackened core.

In contrast to red rot (which is favoured by excessive soil moisture), pineapple disease is most destructive when cane is planted in dry soil. Another major difference is that the red rot fungus is not soil-borne and infection occurs before planting, whereas pineapple disease fungus lives in the soil.

Sugarcane smut (Ustilago scitaminea)

The main symptom of smut is a long whip-like shoot covered with black spores contained in a silver coloured membrane. It emerges at the top of the stem in place of the inflorescence. Other symptoms include stunting and production of thin horizontal leaves. Smut is spread by infected cuttings and spores released from the whip-like shoot. Infection takes place through seed pieces and through axillary buds of the growing plant.

Ratoon stunting disease (Clavibacter xyli subsp. xyli)

This disease does have overt symptoms: There is a decrease in plant vigour and decline in yields, both of which are noticeable in ratoon crops. Red spots can sometimes be seen in vascular tissues, especially in the nodes. It can be spread by infected planting material and also through mechanical operations.

Gummosis (Xanthomonas campestris pv. vasculorum)

It is a primarily a disease of the vascular system. It got its name from slimy gum that oozes from cut ends of infected stalks. Yellowish streaks, usually dotted with red or brownish spots are produced on the leaves near the tips. These spots often widen to a V-shape towards the leaf tip. Top rotting may result when the terminal bud is attacked resulting to shooting of the lateral buds. The disease is transmitted in infected cuttings used for seed, knife cuts and other means of physical contacts.

Leaf scald (Xanthomonas albilineans)

It is a vascular disease but differs from gummosis in that there is no oozing of gum from cut ends. Also leaf streaks due to leaf scald are different: they begin as sharply defined, narrow, white pencil stripes, which may extend the entire leaf length.

As the leaves grow older, the streaks tend to broaden and become more diffuse. There may be only one or several streaks on a leaf. Sometimes, instead of definite streaks, the entire shoot is chlorotic to nearly white. Affected plants become stunted and in advanced disease stage some shoots or the entire stool may suddenly wilt and die.