Larvae occur in two principle forms: the gregarious (gregaria) form characteristic of high-density populations and the solitarious (solitaria) form found at low larval densities. Intermediate, 'transiens' forms may also be present. Gregarious larvae have a velvety-black upper surface with pale lateral lines, a green or yellow ventral surface, and no hairs on the body. There are three parallel lines on the dorsal surface of the prothoracic (first body) segment and a stripe running longitudinally down the mid-dorsal surface of the body is always paler than the black pigmentation on either side of it. The head is always shiny-black. Solitarious larvae are cryptically coloured in a variety of shades of green-brown or pink, appear fat, and are extremely sluggish. They are difficult to distinguish from other grass-feeding caterpillars. The pupa are mahogany-brown, 10-14 mm long, with a smooth, shiny surface. They are difficult to distinguish from pupae of other Spodoptera species. They may be sexed by examining markings on the ventral surface of the terminal abdominal segments. Adult S. exempta are stout-bodied moths of typical noctuid appearance, 14-18 mm long and with a 29-32 mm wing span. The abdomen is covered with pale grey-brown scales except for the tip in the female which has black hair-scales characteristic for this species. Forewings are dark-brown with distinctive grey-black markings.
Weed-free maize crops greater than 50 cm high are unlikely to become infested by newly hatched larvae of S. exempta because the leaves are too tough to allow them to establish. However, if larvae are able to develop on grass weeds, subsequent infestation of the crop may occur. Farmers are advised to keep crops free of grass weeds but, if fields do become infested, to leave the weeds until the larvae have pupated or been controlled. Chemical control includes Indoxacarb 15 SC, Nemesis, Mac-Ten.
Indoxacarb 15 SC (Indoxacarb 15%) - Classified green
Mac-Ten (Emmamectin Benzoate 50g/kg) - Classified green
Nemesis (Acetamiprid 64 gr/lt + Emamectin benzoate 48 gr/lt) - Classified green