Aphids (Sorghum)

Pests of Field Crops in Southern Africa

APHIDS (Sorghum)

(Hemiptera/Homoptera: Aphididae)

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Text Box: The main aphid species that attacks sorghum is Melanaphis sacchari, which can reach very high populations by the time of flowering. It is a small (1.25-2 mm), brownish-yellow aphid, which produces much honeydew. Rhopalosiphum maidis (maize aphid) may also occur in sorghum, but is quite distinct from the above species (see description under maize section). TOP

Text Box: Apart from grain sorghum, this pest has been found on various indigenous species of sorghum, sugar cane, some grasses and maize. TOP

Text Box: The sorghum aphid can reach very high populations by the time of flowering, particularly in warmer areas where dry-land sorghum is grown, or where the crop is late-planted. The aphids can appear on the crop from about 25 days after emergence, usually infesting the upper leaves and flag leaf, and later also the head. High infestations can cause substantial yield loss. The maize aphid may infest the whorl, lower leaves and head, and produce a great deal of honeydew, but has not been found to affect yield, and soon comes under reasonable natural control. TOP

Text Box: Winged and non-winged females produce live young by parthenogenesis and breeding may continue throughout the year. The young very rapidly pass through four instars, and many overlapping generations are produced. This very short life cycle enables huge populations to build up on sorghum in suitable conditions. TOP

Text Box: Although many predators, including ladybirds and Syrphid fly larvae, do become established alongside populations of sorghum aphid, their impact usually comes too late to prevent damage to the crop. Heavy or prolonged rainfall also has a good controlling effect, but may not be reliable in the drier areas where sorghum is often grown. For this reason, it is necessary to apply aphicides such as dimethoate or malathion when populations become heavy. Use of more selective insecticides if available, however, would be a better option to preserve the natural enemies, which will play a part in keeping renewed infestations under control. In the event of bollworm infestations occurring in the heads at the same time, it would be useful to use a chemical that does both jobs. TOP

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Sorghum aphid.