DISEASES OF CULTIVATED PLANTS 615 



smut in his fields. This course will largely prevent the spread of 

 both kinds of smut. 



(5) Maintain a quarantine against any handlers of machinery 

 who allow their machinery to become or remain contaminated with 

 smut spores. This would be effective against the grain smut. It 

 would probably have no effect on the head smut, however. 



(6) Milo has not yet been reported as subject to either smut, 

 and hence may probably be safely grown without treatment. (B. 

 P. I. 374; Cir. 8.) 



RICE DISEASES. 



Rice Blast. This disease is variously known as blast, blight 

 and rotten-neck. It is, in all probability, the same as the disease of 

 rice known in Italy as brusone, and in Japan as imotsi. Blast is 

 caused by the attack of a particular species of fungus known as 

 Pincularia oryzsc. The most conspicuous lesions are found at the 

 sheath-nodes just above the joints of the stem, at the region where 

 the stem comes to be the axis of the head (the neck region), and at 

 the points where the blades of the upper leaves join their sheaths. 

 The first indication of disease is apt to be a small, pale, somewhat 

 watery spot; this increases in size, passing through shades of brown 

 and finally becomes quite dark. The lesion extends more rapidly 

 in an upward direction ; at the neck it may involve as much as two 

 inches of the axis, or it may completely encircle a sheath-node. In 

 the later stages a nodal area frequently shows transverse fissures due 

 to the contraction and cracking of the dead tissues. At the junction 

 of leaf-blade and leaf-sheath there is a breaking, as a result of which 

 the blade hangs downward, it having given indication before this of 

 its general unhealthy condition by a paling of color and drying. 

 At the neck the diseased area is weak, and as the head becomes 

 heavy in maturing, it gives way and the head hangs down or falls to 

 the ground. 



The more general effects of blast are seen in the extensive 



Ealing and drying of leaf and stem, and in the poor condition of the 

 ead. The worst effects on the head are seen when infection of the 

 plant is early and the fungus is well established before the head 

 shoots up from the last leaf-sheath. In such cases none of the 

 grains fill out; and the erect heads with their light colored empty 

 glumes can be distinguished at a distance. Such a condition caused 

 by blast must not be confused with the white blast following the 

 attack of the larvae of a moth w T hich bore into the straw above the 

 last node and cause the death of the head usually before flowering. 

 The two conditions are somewhat similar in appearance, but are 

 quite different in their nature. 



If the attack of Piricularia at the neck is later and less severe, 

 the head will fill out to a greater or less extent, but there will always 

 be a considerable proportion of poorly formed grains. Many such 

 heads will break at the weakened neck region while the rice is 

 standing, and many others during harvesting. The circumstance 

 that the heads that break are apt to be the heavier of the affected 

 ones, makes this source of loss especially heavy. In threshing, much 



