October. 1910. 



KNOWLEDGE. 



395 



on vounsr charlock 



rough leaf" stage caused them 



sulphate of ammonia sprayed 

 plants in the early 



to begin to wither in a couple of 

 hours. Chloride of potassium is said 

 to have a similar effect on charlock 

 when applied in solution. 



About seven years ago Mr. G. F. 

 Strawson stated * in regard to copper 

 sulphate that : "" It is now admitted 

 that mangolds, as well as beans, peas, 

 tares, wheat, oats, and barle\' can be 

 spraved without injur\-, and the char- 

 lock among them destroyed, and that 

 the spraving does no harm to the 

 voung grass seeds, clover, sainfoin, 

 and so on, growing in the crop." 

 Evidence on this point, however, is 

 conflicting, as we shall see, and in 

 Germanv, \'. Riimker, only last year, 

 held that spraying sugar beets with 

 sulphate of iron is hazardous. ^ (There 

 may be some difference in sensitiveness 

 between mangolds and sugar beets, and 

 also in the methods of spra\ing). Only 

 this summer Mr. Strawson repeats that 

 mangolds have been constantly spraved 

 during the last seven or eight years, 

 and that he has never heard of a single 

 instance where the crop was appre- 

 ciabh' injured. He also repeats that 

 corn, tares, sainfoin, clover, beans 

 (and peas in most cases), can be safely 

 spraved with pure copper sulphate 

 to eradicate charlock.' The statement 

 regarding mangolds was confirmed a 

 week later in the same journal bv 

 another writer. 



A good deal of experimental work in 

 spra\ing has been conducted at the 

 North Dakota .Agricultural Experiment Station bv 

 Mr. H. L. Bollev, and some of his results are 



and weeds are making rapid 

 that slow-growing weeds are 



l-ram a photograph by H. C. Long. 



Figure 9. 

 Yorkshire Fog. {HoJciis 

 I an at us L.) A great troubk- 

 in many pastures. Very 

 common and widely distri- 

 buted. 



bv stock. 



interesting. ? His experiments commenced in 1896 

 with copper sulphate and mercuric bichloride, and 

 the results in killing charlock without 

 injurv to wheat are described as sur- 

 prisingly successful. Bolley found 

 that the best time to spray is when 

 the crop 

 growth, 



hard to kill, and that the more suc- 

 culent the weeds the more easily are 

 the\- destroyed. Sodium arsenite in 

 preliminary experiments was usually 

 much more efficient as a weed de- 

 stroN'er than the sulphates of iron and 

 copper : it acts quickly, destroying 

 the weeds (apparently charlock and 

 ■■ king-head "') even though rain follows 

 w ithin a few hours. Referring to the 

 two sulphates Bollev concludes (in 

 Press Bulletin No. 27, 1907) : "These 

 substances are recommended here for 

 mustard and king-head, and will dis- 

 pose of other annual weeds which thev 

 thoroughly wet. including Red-River 

 weed, common rag weed and pepper 

 grass, and will much weaken and retard 

 the development of the French weed, 

 wild buck wheat, black bindweed, rose 

 bushes, wild docks. Canada thistle and 

 many other of the destructive weeds 

 which in\ade cereal crops." In Bulletin 

 No. 80 (1908) Bolley shows that at the 

 North Dakota Station they have success 

 fully used, in various sorts of weed eradi- 

 cation work, common salt, sulphate of 

 iron, sulphate of copper, corrosive sub- 

 limate and sodium arsenite, but because 

 of its cost and its extremely poisonous 

 character the corrosive sublimate (mer- 

 curic bichloride) is not recommended for weed killing, 

 while the arsenite must be used with great caution. 



(To he continued.) 



THK HABITS OF CATERPILLARS. 



B\- L. 



\vinti:k iovnlr. 



W'itli Illitstratioiis from Photographs hy the Writer. 



Both the subjects of the following notes are 

 American, from the State of New York. 



The very singular caterpillar (seen in Figure 1), 

 with the white ivory spots, is that of the Emperor 

 Moth I Dryoeanipa iniperiali.s i. 



The moth is a large purple-banded, buff-colored 

 insect : but it is most remarkable for the very 

 singular manner in which it feeds in its lars'al 

 condition. In spite of its generic name of Dryoeanipa 

 meaning, primariK". oak caterpillar, the creature is 



usually found on the pine, preferring perhaps Finns 

 .strulni.<i to all other pines. Seen in the branches and 

 looked at from under the tree the grub, from its dark 

 olive-green complexion, more than a little resembles 

 the voung cones of this pine, but any doubts of its 

 identity may be dispelled by the presence of recenth- 

 dropped '" frass," which is of a colour not readily 

 distinguishable from that of the carpet of dead pine 

 needles beneath the tree. 



In the accompanying photograph, especially in the 



Fifth Annual Report on the Destruction of Charlock in Corn Crops in 1903. ' Dent. Laiidu-. Presse, Feb. 6th, 1909. 

 Farmer aiul Stock Breeder. ]une 13th, 1910. i Press Bulletin No. 9. 1903 ; Press Bulletin No. 27, 1907; Bulletin No. SO, 1908. 



