GROWTH CONDITIONS
Day length: most of the sorghums are short-day plants, but there is wide variation in
varietal response to photoperiodism (discussed in 1Ej, page 42).
Growth period: a vast range, from between about 70 and 220 days. Sometimes the
plants are cut down and harvested, then allowed to grow back up again as a ratoon
crop. This itself is then harvested, producing a second, normally smaller, crop of
grain and/or grazing.
Rainfall: some sorghum varieties are almost as drought resistant as pearl (bulrush)
millet. The optimum is 350–800 mm a year, while some early, short varieties can
produce a yield with no rain at all during the growth period if seed or seedlings are
planted into a cool, moist, retentive soil. One way to grow sorghum during the dry
season is to propagate seedlings in nurseries and transplant them into moist soil at
the end of the rainy season. In other situations, tall, late maturing varieties that are
growing in light soils may need 1000 mm or more during the growth period.
Temperature: 30 C is ideal for growth. Most sorghums are killed by frost. For
planting, the soil should be at least 17 C at sunrise.
Rotation: sorghum is often intercropped, normally with legumes such as different
types of beans, pigeon peas, etc. If it is monocropped, or rotated with maize or
another Graminae/Poaceae species, Striga weed (page 89) may become a big
problem.
Irrigation: sorghum responds well to irrigation, and can be grown under full
irrigation without any rain. If only irrigated once, the best time is just before heading
starts.
- Stalk Borer: may damage plants so much that whole seedheads break off, or the
whole plants are killed. Chemical control is not very effective as the larvae are well
protected within the stalk. All infected stalks should be destroyed.
normally serious.
- Sorghum Midge: eggs are laid in the flower, and the larvae feed on developing
seed. There are some resistant varieties available. - Sorghum Flies: there are several species. The shoot fly is about half the size of a
housefly; eggs are laid on young leaves, larvae eat the growing point. Not always a
problem, as young plants can recover with new tillers, though these also may be
attacked, resulting in bushy, stunted plants with few or no heads.
Beetle and the Grain Moth. Fumigation is often necessary. Seed should be stored at
less than 10% moisture, either as threshed grain in dry areas, or “in the head” in
more humid areas.
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- Corn Worms: young larvae eat the leaves and developing seed head. Not
- Storage Pests: Rice Weevil is the worst, often found together with the Flour
138 TONY WINCH
and other birds can cause devastating damage, so bad that sometimes farmers
have to abandon sorghum and grow other crops.
Pests: The small red-billed weaver or black-faced dioch (3 races of Quelea quelea)
Bird resistant varieties such as Seredo/ Sereno (an improved Serena) are avail-
able, but they have a high tannin content and so tend to be unequally unpalatable
to people and animals as to birds.