ENCLOSURE TO PART IV. |
of cotton in South Africa for some years (see occasional notes in the
Journal of the Department of Agriculture.)
With regard to the other injuries attributed to Dysdercus it would
be interesting to obtain the opinion of the delegates concerning the
importance under field conditions of boll shedding due to stainer
puncture, failure of the bolls to open normally and loss of lint due to
injury to the seed by the same insects. Injury to seeds, affecting
germination, appears to be of considerable importance in Southern
Rhodesia during the present season. The seeds become very hard and
shrivel to a noticeable extent. Whether the injury is purely direct or
associated with the development of organisms has not yet been
ascertained. The market value of the seed for crushing purposes is
stated to be very seriously impaired, and much of it will apparently
be unsaleable. It is thought that Dysdercus is responsible for this
injury, but the question calls for investigation. It appears to have
been generally noted that the first infestation of a cotton field with
Dysdercus develops with great rapidity, and is due to invasion by
adults which have matured elsewhere. Notes concerning the stage
of development of the crop when this invasion takes place are not
altogether in agreement. Thus Pomeroy and Golding in Nigeria state
that the invasion commences as soon as the plants flower (R.A.E.
XII., p. 67). Withycombe in Trinidad states that the stainers
generally appear when the bolls are ripening and not before (R.A.E.
XII., p. 548) and, elsewhere, that they are not attracted to the cotton
plants in appreciable numbers until the bolls commence to open (Bull.
Ent. Res., XV., p. 171). Observations in Southern Rhodesia to date
are generally in accordance with the last two statements.
Heavy shedding of the very young bolls, of course, commonly
takes place previous to heavy invasion of the fields by Dysdercus.
This shedding appears to be due to physiological causes, possibly of
a similar nature to those causing the well-known *‘ June Drop ”’ of
oranges in California, a phenomenon which occurs also in Southern
Rhodesia in the corresponding season. Shedding due to Dysdercus
attack must clearly occur at a later stage and the experience of the
delegates as to its regular occurrence or otherwise, following the
Dysdercus invasion, and its economic significance would be instructive.
The points on which an expression of opinion by the Conference
would be specially appreciated include the following:
Have any of the delegates any experience of lint-staining
occurring. under conditions where the agency of Dysdercus,
or of other sucking insects, is not indicated ?
- Have any of the delegates any experience of lint-staining
which is apparently not due to either Bacteria or Fungi?
Are any extensive outbreaks of bollrot, due to Bacillus
malvacearum, Smith, in American ‘“ Upland ’* varieties on
record ?
What is the present position in reference to the association
of Bacillus gossypii, Stedman, with Bollrot?
Have any careful mycological studies been made of bollrot
and lint-staining as occurring in Africa, apart from Marsh's
work on stained Nyasaland cotton ?

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