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/ PRODUCTION AND TECHNOLOGY

nowledge about the cotton plant’s beetle (Syagrus) could damage this seedling
development is very important in stage, but it rarely happens.
order to apply effective integrated As the seedling develops into the first true
pest-management and resistance- leaf stage (see Figure 1c), usually after seven
K management programmes for pests days, some pests can occur from the first- to
and herbicides as well as for the spraying of fourth-leaf stage, like thrips and various leaf
growth regulators and defoliants. This article miners. However, most plants “grow out of the
will deal with midseason pests in relation to problem” and control is rarely necessary. Thrip
plant development. damage shows as silvery leaf damage, with
tattered leaves (personal communication, late
The cotton plant goes through the following SW Broodryk). Wind damage can often occur
development stages: on seedlings, but they recover well.

GERMINATION AND SEEDLING VEGETATIVE GROWTH STAGES
DEVELOPMENT The four-leaf stage of cotton is often seen after
Planting should take place when the soil three weeks and is used to indicate glyphosate
®
temperature, at 30 mm deep, is between spraying on Roundup Ready cotton. It is also
16 °C and 18 °C for longer than 10 the stage where other sporadic pests occurring
consecutive days (ARC, 2004). The hypocotyl in some areas, can be present, e.g.:
emerges from the seed and forms the stem, • the cotton stem weevil (Apion), causing pin
while the radicle forms the root (see Figure 1a). holes in leaves and larvae boring into the
The hypocotyl straightens at the soil surface and stem;
pulls the folded cotyledons (first leaves/“false • aphids (honeydew on leaves and sooty
rounded leaves”) out of the soil (see Figure 1b). mould);
The plant starts its active growing period. • black cotton beetle (Sygrus) causing holes in
leaves not reaching leaf edge; and
COTYLEDONS AND FIRST TRUE • leaf eaters causing random holes in leaves
past the leaf edges.
LEAF STAGE
Cotyledons are the first two rounded leaves. Start scouting for aphids and whitefly at this
They are storage organs that form in the seed stage. Use the threshold for aphids by scouting
and emerge from the soil as leaf-like structures. three leaves per plant in the top, middle and
The apical meristem emerges from between bottom of the plant. If more than three leaves
the leaves and starts forming other leaves. per plant have more than 30 aphids in total
Cutworm, false wire-worm and black cotton on at least 15 plants per 24 plants scouted,

Figure 1: Development of the seed to the cotyledon and first true leaf stages.

Volume 21 No 1 March 2019 | 23