1920.] FBOGHOPPER BLIGHT OF SUGAB-CANE. 17 



{c.) Scattered small patches, mostly with no immediately recog- 

 nisable defect ill condition, but strictly local, usually 

 distinctly related to the contour of the ground, and surrounded 

 by large areas of healthy cultivation. 



These infestations are of a type approaching in local numbers and 

 severity the more general infestations of maximum froghopper years. 



28. There is undoubtedly deep significance in the fact of the 

 association between defects of soil condition and development of frog- 

 hopper blight. The relation has been frequently noted as being, in 

 general, characteiistic of the affection in any year, but it is usually 

 subject to rather striking exceptions. Keference was made to it, on 

 these lines, in my report of last year. In the present season, when the 

 froo-hopper has been reduced to its last strongholds, the association, as 

 would be expected, is most definite. 



29. A striking case was reported by INfr. Williams about the time I 

 arxived and was later visited several times. This was a field of third 

 ratoons on a slope, in which a rather large patch was completely blighted, 

 having been heavily infested with second brood froghoppers. The soil 

 of this patch was a red clay of putty-like consistency when moist, brick- 

 like when dry. On the margins of the patch, where it bounded on 

 friable black lo an, there was a sudden change to relatively uninfested, 

 and except for some leaf-spotting and young shoot injury, undamaged 

 canes. Marasmius and Odontia were abundant on the blighted patch 

 and were present in fair quantity in the surrounding parts of the field. 

 On the upper margin of the blighted patch there was a shallow weedy 

 oblong ]iond, and corresponding with its width a plainly defined strip 

 of cane extended down the slope, across the middle of the red clay, in 

 which the effects of the blight were much less severe, although the 

 leaf spotting was well-marked. This effect is believed to be in some 

 way due to the seepage from the pond. 



SO, The significance of the observations made on this case cannot as 

 vet be fully explain- d, but it was valuable as affording a clear instance 

 of the association of blight with soil conditions, and of the amelioration 

 of these conditions by greater regularity in the suj^ply of soil moistui'e. 

 The latter observation may be considei-ed as throwing some light on the 

 experience of the Princes Town district, in which the climate is more 

 uniform and froghopper infestations are less frequent and the damage ia 

 much less marked. 



31. That the prevalence of froghopper is dependent on other condi- 

 tions than the supply of its food-plant is self-evident when the discon- 

 tinuous nature of its distribution is con-sidered. Thei-e is a rapidly 

 increasing liability to infestation in the progress of fields from plant 

 canes to second or thi^rd ratoons. There is a similar increase in passing 

 through the various grades of soil from friable black loam to sticky red 

 clay, or the grades between good and poor tilth of any soil. But under 

 an_y of these conditions a local infestation can occur, when at the same 

 time the surl-ounding area, including fieMs of the same age and general 

 character, may be free, not only from the consequence of attack, bub 

 from the presence of the insect in any but trifling numbers. The other 



