172 JuuiiKAL oi HIE Dki'aktmknt of Agriculture. — Aug., 1922. 



tubers also aft'eets the keepiuf^' properties; iut'ested tu})ers will not 

 keep as lon<^ as healthy ones, and are more liable to destruction by 

 bacteria] and fungous diseases. 



Life-liistoii). — The life-history of this worm has not \ et been 

 complete^'y elucidated in South Africa, and need not be discussed 

 here. For our purpose it will suffice to note a few points. 



The adult gravid females occur in the "trails" or "knots" of 

 IIm' roots of infested plants; the irritation caused by their presence 

 briuf^'s al)Out a rapid multiplication of the surroundino- cells, and this 

 t'N'entnally leads to the formation of the root yalls. By nieans (d' a 

 spear-like structure situated in the head-end of Uie hody the larva 

 is able to pierce its way out of a root into the soil. There li may lie 

 dormant for some time, and then seek out and penetrate another 

 rootlet, or if conditions are favourable it may not abandon the root 

 within which it was hatched, but may mi<?rate to adjacent healthy 

 tissues and undei'go sexual differentiation there. 



American studies show that the time required for the eompletioii 

 of the life-cycle may be four weeks or more, according to the tempera- 

 ture of the soil. The winter is passed probably most frequently in 

 the larval stage in the soil, but in the case of galls on perennial roots 

 the worms may overwinter in these in a more advanced stage, even as 

 practically mature and perhaps already fertilized females. 



Cofifrol. — It may be stated at once that an efficient and practical 

 method of control is not known. Hence the measures adopted are 

 largely of a preventive nature. For infested lands which do not beai' 

 perennial crops the following measures are advised: — 



(1) Keep the land absolutely fiee from all vegetation for two 

 years; this is the most efficient method, but is usually not practicable. 

 If the land can be kept free from all vegetation for a shorter period, 

 say three or six months, during the hottest part of the year, this will 

 undoubtedly be of some assistance. 



(2) Do not plant susceptible crops on infested lauds for two or 

 three years. The following are more or less immune to loot -knot : — 

 Velvet bean, peanut, most varieties of winter oats, Johnson grass, 

 crab grass, Japanese barnyard millet, broomcorn millet, pearl millet, 

 timothy, rye, sorghum, kaffir corn, wheat and maize. 



(3) In gardens it is a useful measure to uproot woithles.s plants 

 and to destroy them by burning. If such plants are lett until the tops 

 have dried up and are then broken off, the soil will become infested 

 with worms which are liberated when the roots decay. 



(4) Rotate susceptible crops, such as the potato, with nioj«> or 

 less immune crops. 



(5) Avoid the use of seed-potatoes siiowing nodules. 



(6) Heavy applications of potash fertilizers often greatly reduce 

 eelworm injury. Unless the soil already contains an abundance of 

 potash, potatoes will respond well to such treatment. 



<7) In Europe trap-crops have been used successfully against a 

 related species of gall-worm known as the beet-nematode (H. Schachtil 

 Schmidt). It appears that few experiments have been conducted to, 

 test the value of trap-crops against H. ladicicola, and these weie not. 



