616 INSECTS AFFECTING VEGETATION 



of the grain from affected heads is of such light weight as to be 

 blown out in the cleaning. Because the damage caused by blast is 

 apt to appear late, it is a frequent thing for the disease to occasion 

 considerable miscalculation in regard to yield. Up to the heading 

 period and even beyond it, indications may point to a good yield; 

 and there is surprise and disappointment when the number of sacks 

 turns out to be very many fewer than the expectation. 



The destructive effects of the rice blast fungus may be seen at 

 times upon quite young plants less than six inches high. The first 

 indications of attack are brown spots which come to have ashy gray 

 centers and involve the whole thickness of the leaf. These spots 

 enlarge and coalesce until practically the entire leaf is involved. 

 The lower and older leaves of the plant suffer first, and become 

 entirely brown and dry and shriveled ; afterward the younger leaves 

 are destroyed, and the plant appears dead. But even in such severe 

 cases a small percentage of the plants may have the closely wrapped 

 bud portion unaffected, and under proper conditions may send up 

 new shoots and continue growing. This blight of young rice seems 

 to be infrequent, but it may be quite destructive when it does occur. 



Spotting caused by Piricularia may occur on the leaves of plants 

 almost or quite mature; but in such situations the effects are local- 

 ized, and there is no such general dying as follows leaf infection 

 of quite young plants. 



Preventive Measures. 1. In the South Carolina experiments 

 it was found that spraying with Bordeaux mixture while the heads 

 are still in barrel prevented serious damage from blast. Unfortu- 

 nately the spraying of rice at such a stage is not a practicable meas- 

 ure. It is interesting to note that this treatment has been recom- 

 mended for brusone in Italy ; the efficacy of it would tend to support 

 the contention that brusone is due primarily to the attacks of a para- 

 sitic organism rather than to a condition of the root system. 



2. In the Carolina experiments it was found that applications 

 of lime to the soil reduced blast and greatly increased yields. While 

 this treatment seemed at first quite promising, further tests under a 

 wider range of conditions have not been altogether satisfactory, and 

 lime is not to be recommended as a general preventive of blast. 



3. The idea has prevailed in some quarters that the withdrawal 

 of water at the time of heading up will prevent blast. Insofar as 

 the writer has been able to learn the experience of rice growers in 

 this matter, the evidence is rather conflicting. As has been indi- 

 cated already, the whole matter of the treatment of rice at about this 

 period, and for that matter at all periods, ought to have careful study 

 with the purpose of determining the relation to the spread of blast. 



4. Immune varieties. It is of interest to know that the variety 

 of rice known as bertone in Italy was, at the time of its introduction 

 into that country in 1828, almost if not absolutely immune to bru- 

 sone. But in the years that have followed bertone rice has lost to a 

 great extent its resisting powers, and at the same time there has been 

 marked general deterioration in the variety. Nevertheless this gives 

 indication that it may be possible to discover or to originate varieties 



