PART IV. ‘73
in abundance depending on certain factors as to weather, soil, ete.
The only possible exception is the Sudan boll worm, which has not yet
been reported from parts of the Cape Province where cotton is grown.
A wider survey of our cotton areas is necessary before any definite
statements can be made.
There is evidence that cultivation, rotations, and size of field
has some effect on the occurrence of the major cotton pests; but so
many exceptions have arisen, that I have no statement to make until
the matter is more thoroughly studied. Experiments along these lines
will be conducted next season.’
(f) APHIDES AND JASSIDS.{
The questions raised by the Empire Cotton Growing Corporation
were left in abeyance more or less for the consideration of this
combined session, as far as the matter of formulating replies thereto
is concerned.
For the information of this meeting I beg to submit the following
observations : —
1. Mr. Haines (contributed): (a) Natural enemies are
numerous in South Africa, as everywhere, on Aphides, and special
mention need not be made of them. No study of the natural enemies
of the jassid has been made. (b) The question of plant selection for
resistance will be dealt with by Mr. Parnell, but I might add that long
ago we noticed that certain cotton plants resisted the jassid, especially
those with hairy leaves and stems. We also noticed that the growing
plant was more resistant than the matured plant; and also, that there
is a definite relationship between jassid attack and rainfall, i.e.,
prolonged periods of wet weather, which seem to hasten jassid attacks.
Jassid occurs, so far as we know, all over the cotton areas, but it has
never given serious trouble in the higher altitudes of these areas, and
has only under certain conditions become pestiferous in certain parts
of our low-veld. (¢) Nicotine dust kills the jassid if applied strong
enough, but the effect is only transient, as the plants very soon become
infested again. Calcium cyanide dust gave very unsatisfactory results.
Bordeaux mixture, as a dust and a spray, was the only substance that
gave results at all lasting, but it is doubtful if it would pay to use it.
It is certainly not advisable to recommend spraying or dusting as a
satisfactory control measure for jassid, as it seems certain that jassidresistant
 strains of cotton will be found. (d) We have no direct
evidence that cultivation makes any difference as to jassid outbreaks
vn cotton, except that well-drained cotton fields seem to delay the
attacks somewhat. In general, it seems to hold true that h:althy,
well-grown cotton plants withstand jassid attack longer than those
plants which are poorly and slowly grown.
2. Mr. Hargreaves stated that in Uganda the Aphides was
perhaps the most serious pest on Cotton; certainly the accumulated
effect appeared to be greater than that of any other insect.
3. Mr. Ritchie suggested that the control of Aphides and
Jassids by fungi might be further investigated; a fungus was the most
potent controlling factor of Aphis in Tanganyika, and he instanced the
success of a fungus as the controlling factor of West Indian Cane
I See also pages 180 and 181.

I