CAB129-37 — Page 350

Page 350.

Sorghums. Grain smut, Sphacelotheca sorghi, and Head smut, S. reiliana, were fairly common. Some heads infected with long smut, Telyposporium Ehrenbergii, were noted. Downy mildew, Sclerospora sorghi, and rust, Puccinia purpurea, were common, but in view of the severe attack by insects experienced by this crop it was not possible to assess the probable reduction in yield.

Other crops.

Streak was recorded in a small number of plants of maize on the Kongwa Experiment Station. Spotting of the leaves of Niger oil plants by Alternaria sp. was fairly common, but was not destructive. A leaf rust attacked a late sowing of castor oil. None of these diseases occurred on a serious scale..

Entomology

The results of a detailed survey appear in Section 14 of this report.

It is too early yet to decide what pests constitute definite threats to successful. agricultural production by the Corporation, but the following appear to merit close attention.

The most serious threat to groundnut production in the Central and Western provinces is the presence of Hilda patruelis in the area to be developed. Insecti- cidal measures against this pest might prove costly, and so cultural methods should be tried. This will mean the rigorous control of weeds on which the insect can feed, in fields and windrows.

In the Western and Southern provinces, Rosette disease of groundnuts is certain to be a major problem at least for a number of years. It is possible that when the bush is cleared infection may be limited to the boundaries. At present, the only counter measure which can be adopted is close planting. at least in the rows. It is hoped that research on the dry season host or hosts of the vector, on the natural reservoirs of the virus and on the epidemiology of the disease will provide further methods, such as selective felling of alternate hosts in wind breaks, drainage channels and uncleared areas of bush on steeply sloping ground.

Successful sorghum production in all areas may depend on the control of the central-shoot-fly, stem-borers and perhaps the blue bug, Calidea dregei. Control of the latter is again tied up with weed control, in this case of Hibiscus sp., which flourishes on cleared but unplanted land. Should commercial varieties of Hibiscus be grown the siting of the fields in relation to those of sorghum and sunflower will need careful consideration. It is possible that some varieties of sorghum may be able to produce high yields in spite of high stem-borer incidence and that cultural methods of limiting the population may be adequate, such as ploughing. in the stems as soon after harvest as possible to kill the hibernating caterpillars, and adjusting the planting date to a period when the number of egg-laying moths is at a minimum. Control of the central-shoot-fly may prove to be more diffi- cult, since it is quite possible that a high population exists in the indigenous grasses. Here again adequate weed control in fields and windrows may help.

In view of the importance of bees for pollinating sunflowers and the consider- able reduction of nesting sites and colony size as a result of extensive bush clearance, it is possible that special measures will have to be taken to ensure a sufficient supply of bees at the time when the sunflowers are in bloom.

9. MISCELLANEOUS ACTIVITIES

(a) Clearing Committee. In 1947 a committee was set up under the chairman-- ship of the Chief Scientific Officer to consider the technical problems of land: clearing at Kongwa and to conduct trials of the equipment available. The Unit and Area managers and the Chief Soil Conservation Officer were members. The following broad conclusions were reached :

(i) Initial flattening must be selective. The bulldozers should not attempt

special

Pafell, the large trees, but should leave them fagresiab treatment

can be reduced.

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