11 



the territory may become infested, and that the pest will flour- 

 ish greatly under the conditions there provided. This is unfor- 

 tunate, because these useful vleis occur on many good tobacco 

 farms, and are very liable to be planted with potatoes for an 

 early crop. Seed potatoes are, without doubt, the chief agent 

 by which gallworm is transported, although nursery stock may 

 also play an important part. Once the pest has been intro- 

 duced to a farm, it is liable to be carried about by farm imple- 

 ments, the boots and feet of labourers and others, including 

 animals and birds, by flood w r ater, by drains, by irrigation, and 

 perhaps even by the wind. Once a suitable soil has become 

 infested with gallworm, it is likely to remain so as long as suit- 

 able plants are provided for its use. The variety of plants 

 attacked is very great, and includes nearly all the crops that 

 can be grown profitably in Southern Khodesia, with the for- 

 tunate exception of cereals, including maize. The damage 

 done to the plants is due, in the main, to the irritation set up 

 in the tissues, which stimulates the formation of swellings or 

 galls. The thickening of the tissues of the root interferes 

 seriously with the functions of the plant, causing a feeble 

 growth, wilting and frequently death. Seeing that remedial 

 measures against this pest are hardly practicable on tobacco 

 lands in this territory, it is obvious that great care is necessary 

 to prevent the introduction of the pest. As already mentioned , 

 seed potatoes constitute the most likely vehicle by which the 

 pest may be brought to the farm, and on this account a potato 

 tuber shewing galls caused by a gallworm is shewn in the 

 adjoining plate, in order to enable growers to recognise the 

 trouble, and to discard such infested tubers for seed purposes. 

 Every endeavour is made in South Africa to prevent the spread 

 of this trouble with nursery stock by means of the Government 

 inspection of nurseries. Burning the seed beds acts as a pre- 

 caution against infestation of the transplants, and should 

 always be carried out, in spite of the fact that some growers 

 express doubts as to whether the work and expense involved are 

 justified. Land that has become infested should be discarded 

 for tobacco and planted to maize or another cereal for several 

 seasons. 



CATERPILLARS. Two species of caterpillars have been 

 reported as injurious to tobacco in Southern Khodesia. One 

 is Laphygma (Caradrina] exigua, a cosmopolitan pest known 



