Page 35 - Agriculture_Form_3

Agriculture for Secondary Schools

Maize lethal necrosis: Maize Lethal Necrosis (MLN) is a viral disease that
causes yellowing and drying of the leaves. It also leads to poor plant growth and
empty cobs, which causes a big loss in the harvest. The disease can be managed
by planting maize varieties that resist MLN, controlling insect vectors such as
thrips and aphids that spread the virus, and practising crop rotation with non-
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host crops. To reduce the risk of spreading the disease, maize should not be
planted near fields where infected plants were grown before. Figure 2.8 shows
the symptoms of MLN.

Figure 2.8: Symptoms of maize lethal necrosis

Common rust: This is a fungal disease that affects maize during cool and wet
weather. It shows up as reddish-brown spots or raised areas on the leaves, stems
and sheath or husks. As the disease gets worse, the leaves dry out, and the plant
becomes weak because it cannot make enough food through photosynthesis. The
disease spreads quickly through tiny spores carried by the wind. Maize rust can
be controlled by using resistant varieties, avoiding late planting, and applying
fungicides in severe cases. Figure 2.9 shows the symptoms of common rust in
maize.

Figure 2.9: Symptoms of common rust in maize

26 Student’s Book Form Three

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