PAR IV:
populations were dependent to a certain extent on Tembo Tamu for
food purposes. In view of the experience in Zanzibar, the question
‘might now be re-opened in Kenya.
CHAPTER V.
MYCOLOGICAL QUESTIONS.
CONTROL OF STREAK DISEASE ON MAIZE AND SUGAR
CANE.
The CHAIRMAN (Mr. Fuller) read the following note contributed
by Mr. H. Storey, Mycologist, Union of South Africa: —
MAi1zE.
(1) We find this disease to be naturally controlled climatically,
its occurrence being rare above 4,000 feet. Generally the incidence
of infection is greater the lower the altitude.
(2) In the coastal region (and, to a variable extent, inland) the
incidence of infection increases as the season advances.
(3) Where a succession of maize crops is planted at intervals in
an area, streak is generally more prevalent than where the whole crop
is planted at one time.
(4) We have been able to prove that the insect-vector (Balclutha
mbila Naude) may survive in an infective condition through the
winter. from one season’s maize crop to the next. We believe that
this is the important manner of over-wintering of the disease virus,
and that secondary host-plants play an unimportant part.
(5) Our recommendations for streak control aim at curtailing
the over-wintering and preventing the building up of infection before
the main crop is planted by: —
(a) Destroying all over-wintering volunteer maize plants.
(b) Avoiding any early spring planting before the main crop.
(6) Our trials have failed to show any marked resistance in
standard varieties, and only slight indications of individual resistance
within varieties.
SuGAR CANE.
(1) The deleterious effect of this disease is now generally
admitted by cane planters, Even where secondary infection takes
place rapidly the advantages of planting healthy seed is shown in
tonnage return.
(2) This disease is firmly established in South Africa, probably
309 of the Uba cane now growing being diseased. = There is great
regional variation in the incidence of secondary infection, which we
have been unable to correlate with any known factor.
(3) . Control by selection and roguing has been successful in
regions not subject to severe secondary infection, but has generally
failed elsewhere. It is as yet uncertain whether the transport of
planting material from the favoured areas will be generally adopted
as a means of reducing losses from streak disease.
(4) It is clear that many varieties of sugar cane are ab present
immune or highly resistant to streak disease. In particular, the
P 0O.J. Chunnee-Cheribon crosses and D.1185 have proved immune
under local conditions.

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