Plant Sanitation. 



398 



[Nov. 1906. 



The polyphagous habit of the moth is such that in August eggs are deposited 

 on the leaves of lebbek pear, plum, aristolochia fici, etc. Much remains to be learnt 

 of the natural habits of cotton pests, which in the field differ considerably from 

 those in captivity. 



EGG-DEPOSITS. 



One important point has been proved, viz., that the first great deposits of 

 eggs on the cotton plants occur between the 15th of June and the 15th of July, 

 the 20th of June to the 10th of July being the most critical period. Although the 

 pest is somewhat gregarious, the female moth prefers to deposit her eggs on cotton 

 a day or two after the irrigation of an]area. The eggs hatch in about three days. 

 They are not all deposited at one time ; thus the age and size of the worms of this 

 brood are very irregular. The writer has proved by experiments that early sown, 

 naturally grown cotton on average land will stand from 30 to 40 days without 

 water, and with excellent results in ripening the wood and producing an 

 unusually heavy crop, but on light sandy soils this period would probably 

 require some slight modification. 



From the foregoing remarks it will be seen that cotton which can be kept 

 dry during the egg-laying period is free from egg-deposits. Although it would 

 scarcely be possible to apply this method at one time throughout the whole area of 

 infected country, the irrigation of certain districts, by the present system of rota- 

 tions, creates suitable places or traps for the moth to deposit her eggs. By carefully 

 following up these rotations, the cost of labour Avould be considerably minimised, 

 and the valuable time now spent in searching unlikely places might be devoted to 

 the more thorough cleaning of egg deposits on traps formed by newly-irrigated 

 cotton-areas. 



EXTERMINATING YOUNG WORMS BY HEAT AND DRYNESS. 



The worms, after hatching on the leaf, lower themselves to the ground by 

 means of a web-like thread, and remain for a time under the soil of the ridges, feed 

 ing (during the first stake of their existence) chiefly at night on the lower leaves. 

 It is obvious from their various ages that several pickings of worms are thus 

 necessary to clear an infected area. In this it is impossible to prevent escapes, how- 

 ever carefully the work is done. Propagation from this source alone is capable of 

 much damage, and the complete extermination of this brood by a natural method is 

 therefore extremely important. 



The crux of the question of the extermination of cotton pests by the assist- 

 ance of nature, or at least the first stepping-stone to this object, is to counteract 

 unnatural conditions of shade and dampness, by dryness and heat. The successful 

 application of this method can only be l3arnt by continuous observation in the field. 

 It has been proved by experiment, that the heat of the mid-day sun on the surface 

 soil of unshaded ridges is often 120° to 130° F. Cotton, if allowed to flag from dryness, 

 contains no food in its foliage for the young larvse. It enables the sun to reach the 

 ridges, which is fatal to the existence of the worms and fungi disease. The produc- 

 tion of rank foliage is checked by the stoppage in the flow of sap. The green, 

 succulent wood ripens, and produces abundance of flowers and lint, and the quality 

 and quantity of the crop yield are considerably augmented. 



When once this natural method (which applies only to cotton controlled 

 by irrigation) has become known, and success more universally established, native 

 growers will see the advantage of taking the matter up. Reform will naturally be 

 slow, but the gain to the country would be enormous. The following are some of 

 the chief pests known to attack cotton cultivated in Egypt : — 



(1) Prodenia Littoralis— (The Egyptian Cotton Worm). Feeds on rank 

 foliage caused by overwatering, etc t 



