Maize

Pests of Field Crops in Southern Africa

MAIZE

(Zea mays, Graminae)

Text Box: See general section. Helicoverpa armigera is a sporadic pest of maize, when it tends to be called “maize earworm”. It is capable of damaging cob tips and thus encouraging cob rots which can be a serious problem in wet seasons. Recent breeding work has resulted in varieties that produce cobs that turn downward as they mature, a favourable feature for this case since it prevents rainwater collecting in the opened and damaged tips. TOP

Text Box: See general section. Numerous small black or brown beetles can cause a good deal of tattering damage to leaves soon after the rainy season begins. The damage is mainly cosmetic and control is usually unnecessary. TOP

Text Box: See general section. Cutworms are usually a pest of newly-emerged maize, but serious damage has been observed on plants as tall as 30-40 cm, where the pest was detected boring into the stem at soil level, and the hearts of the plants were killed as a result. TOP

Þ Black Maize Beetle

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Dusty Surface Beetles

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Þ Maize Caterpillar

Þ Maize Rootworm

Pink Stem Borer

Þ Maize Storage Weevils

Þ Maize Streak Vector

Þ Pearly Scale

Text Box: See general section. Dusty surface beetles themselves can cause damage to sewn seed in drought years, eating out the germ of the seeds. The larval stages, false wireworms, tend to be a pest of heavier, red soils (unlike whitegrub), and they usually damage the adventitious (prop) roots, which may result in plants blowing over during windstorms. TOP

Dusty Surface Beetles

Þ Maize Stalk Borer

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Þ Termites (see general section)

Þ Whitegrubs (see general section)

Text Box: See general section. In any crop of maize in the “highveld” (above 1200 m altitude) this pest may constitute a small proportion of the stalk borers present, but it seldom reaches a significant level on is own. On occasion attack by this borer on very young crops does occur, however, and is a problem since it escapes the normal stalk borer controls which are carried out a little later. TOP

Pink Stem Borer

Text Box: See general section. In addition to the more common snout beetles discussed in the general section, damage is also occasionally caused to young maize plants by a weevil grub known as “Fat John” (Dereodus recticollis). The “Fat John” grub has a pale pinkish-orange colour, and unlike other snout beetle grubs, damages the young maize plants by boring into the underground stem bases. Damage is very similar to that described for maize rootworm. TOP

False wireworm.

Typical bollworm damage in a maize cob.

Young pink stem borer.

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Spotted Maize Beetle

Text Box: Spotted maize beetle, Astylus atromaculatus (Coleoptera, Melyridae), is an introduced pest occurring primarily in South Africa, where it is a minor pest of maize and some other crops. The beetles are about 10 mm long and distinctive, being variegated black and yellow in colour. The adults feed on pollen and may be quite abundant on flowering crops such as sunflower and maize. At the end of the summer they lay eggs amongst decaying leaves on the ground and their larvae are present in the soil in the winter, spring and early summer. Fully-grown larvae reach 15-20 mm in length, are brown in colour and covered in dark hairs and have two distinctive hooks at the end of the abdomen. It is the larval stage which may be responsible for damage to planted maize seed both before and after germination, in much the same way as snout beetle larvae and maize rootworms. TOP

Spotted Maize Beetle

Spotted maize beetle on sunflower. (above and below)