Plant Sanitation. 



314 



[October, 1910. 



noticeable way when a spell of wet 

 weather recurs after a few days' sun- 

 shine. Little damage may be done or 

 the blight may become worse and worse 

 both mature leaves and flushing shoots 

 becoming affected, then blackening and 

 dying till leaf pickiug is stopped. 



The spores of the parasite are distri- 

 buted by the wind and the quick dis- 

 tribution can be understood when one 

 remembers the fairly strong breezes that 

 occur here. On days in which there are 

 a few hours of dry weather or sunshine, 

 the wind will blow the light dry powdery- 

 spores about, and they may be borne a 

 considerable way and scattered over a 

 comparatively wide area. Iu the Balasan 

 valley strong breezes blow _ up the 

 valley, especially in the evening of a 

 hot day, and the blight has travelled 

 much more rapidly and is more severe 

 towards the head waters than down- 

 wards towards the plains. In this 

 valley the disease is severe on slopes 

 exposed to the wind, i.e., on southern 

 slopes. On the Tukvar side of Senchal 

 the winds are not so steady and more 

 irregular in direction, and here the 

 distribution of the disease is erratic. 



The blight attacks the high quality 

 Assam and hybrid jats most severely, 

 while China and Manipuri are not so 

 much affected. It is quite interesting to 

 see, in some China blocks where Assam 

 or hybrid bushes have been used to reset 

 empty places, how the leaves of the two 

 high quality jats are well infected with 

 blister whereas the leaves of the China 

 are almost free: Yet in some gardens 

 China is very badly affected and the 

 bushes have a woeful white or black 

 appearance according to the stage of 

 the disease. 



With respect to heavy pruned, lightly 

 pruned and unpruned tea it is difficult 

 to say definitely that one is attacked 

 more often than another, but, when once 

 the blight has come, the damage done is 

 in the order of mention. In the young, 

 succulent rapidly growing leaves of the 

 heavy pruned tea the blight develops 

 vigorously and may destroy nearly 

 all the leaves that ought to go to form 

 growth leaves. Now for a good frame- 

 work of new wood a heavy pruned bush 

 depends mainly on the growth made 

 in the first year after heavy pruning. 

 If, then, iu the first season much damage 

 is done to the leaves growth is checked, 

 thus causing serious loss in crop in the 

 following season. 



The blight is worse on places with a 

 high rainfall and worst about that ele- 

 vation where rainfalls nearly every day 

 and mists are constantly hanging about. 



Thus on the slopes of the Rungbag and 

 Balasan Valleys facing the plains the 

 blight is on the whole worse than on the 

 Darjeeling side of the Senchal. The 

 blight seems to be more severe at high 

 elevation and worst between 4,000 and 

 5,500 feet. Not elevation, however, but 

 moisture is the real factor with regard 

 to severity. In this district high ele- 

 vation means, within certain limits, 

 high and evenly distributed rainfall. 

 The three worst blocks and the only 

 extremely bad cases ou a large area seen 

 by me were on gardens between 5,000 

 and 5,500 feet- Whereas in a low ele- 

 vation garden in the Rangit Valley, the 

 blight came late in the season of 1909 and 

 was only very slight ; one had to search 

 to get blistered leaves. Too much shade, 

 whether artificial from planted trees 

 or from proximity to jnugle, favours the 

 blight and it is worse, too, on damp, 

 shady hollows. It was found that the 

 bushes under the trees grown for shade 

 in the garden were often affected when 

 the surrounding unshaded bushes were 

 free from blight, and when both were 

 affected the shaded bushes were more 

 severely blistered. This occurred under 

 old trees that were giving more shade 

 than was really necessary, and suggests 

 the thinning of jungle trees near the tea, 

 and lopping off branches where shade- 

 trees have become too dense. 



The amount of damage done by blister- 

 blight this season is difficult to gauge. 

 Fortunately for the industry weather 

 conditions were favourable from April 

 to June and gardens flushed well, get- 

 ting thus well ahead of their usual 

 average. They have, however, since 

 gone down and some gardens are well 

 behind. The greater loss is attributable 

 to wet, unfavourable weather in July 

 and August and a consider able portion 

 to blister-bligbt. The worst damaged 

 piece of tea was a heavy pruned block. 

 Ninety per cent, of the plants had lost 

 all their leaves or the leaves were all 

 blistered. As soon as a bud sent forth a 

 leaf it was attacked. The year's growth 

 had failed, and most of the bushes will 

 start next spring as if they had been 

 just pruned unless, as is more likely, 

 they start weakened by the lack of 

 growth this season. In new extension 

 young plants often suffer badly. In one 

 seed bed, all the seedlings were destroy- 

 ed by blister-blight, and as the cost of the 

 seed and of upkeep amounted to Rs. 770, 

 this was dead loss. On Dooteriah Divi- 

 sion in the two seasons over 900 maunds 

 of blistered leaves were picked and des- 

 troyed of which about one-sixth might 

 have been made into tea, the remainder 

 being mature leaf. The cost of collect- 



