Plant Sanitation. 



42 



[July, 1911. 



the past century, and to contrast it with 

 the comparatively small annual toll 

 exacted by the root fungus of that crop, 

 or by the pod diseases of cacao, in order 

 to realize fully how different may be the 

 effects produced. In the first instance, 

 the colonies were threatened with the 

 complete annihilation of their staple 

 industry ; while, with the other two, 

 though the yield is reduced to a greater 

 or less extent by the parasites, some 

 return may always be expected from 

 the crops. 



Since the attacks of endemic fungi, 

 such as those causing pod diseases of 

 cacao, are much less immediate in their 

 economic effect, and consequently of a 

 considerably less alarming nature to the 

 community in general, ample time is 

 afforded to the mycologist in which to 

 perfect his means of combating them, 

 and to the practical agriculturist in 

 which to realize the importance of such 

 means and to apply them to his crops. 

 Moieover, endemic fungi are frequently 

 in their nature more easy of control 

 than the epidemic. The majority of 

 plant diseases are of an endemic nature, 

 and this fact, taken in conjunction with 

 their extended scientific study, has 

 resulted for the greater part in the 

 formation of fairly efficient means for 

 reducing the damage they inflict, and 

 the recognition of the nature and import- 

 ance of these diseases has called into 

 being a body of men specially trained in 

 the knowledge of this subject. 



Now, since common experience has 

 shown in many cases that such trained 

 men are able to give advice which, if 

 followed, will result in the extensive 

 reduction of the losses formerly incurred 

 owing to the attacks of parasites, a 

 natural belief is tending to arise that 

 mycologists can always afford advice 

 of a simple kind for controlling or 

 eradicating all fungus diseases. In 

 reality, this is far from being the case. 

 Much depends on the nature of the host 

 plant, on general external conditions, 

 and on the co-operation of large numbers 

 of persons whose crops are attacked by 

 any given disease. Even then the 

 position may appear almost hopeless, 

 and may only be saved by the inter- 

 vention of some unforeseen external 

 circumstance. A good illustration of 

 what is meant is afforded by the out- 

 break of canker on the chestnut trees of 

 the United States, which only attracted 

 attention in the year 1904, and has now 

 become a serious epidemic, so far impos- 

 sible to control. 



The disease is due to a wound fungus 

 identified as Diaporthe parasitica, Mur- 

 rill, which lives in the inner bark and 



cambium of the stem and all woody 

 branches of the chestnut. On limbs 

 with smooth bark, the parasite pro- 

 duces pale brown, sunken patches on the 

 Outer bark. These become more or less 

 thickly covered with the yellow orange 

 or reddish brown pustules of the fungus, 

 which break through the lenticels. In a 

 damp atmosphere, the summer form of 

 spore is extruded in a yellow or greenish 

 tendril, which becomes brown as it grow3 

 older. The fungus grows so fast that it 

 can completely girdle a branch or small 

 trunk, and thus kill it in from one to 

 two years. Even large trunks are 

 girdled as a rule in four years. 



The native American chestnut (Cas- 

 tanea dentata) is the plant most subject 

 to attack, but the chinquapin (Castanea 

 pumila), found native from New Jersey 

 to Florida, is also affected, while the 

 disease has been found, as well on the 

 Japanese chestnut (Castanea crenata). 

 Indeed, it is suggested that imported 

 plants of this foreign variety growing 

 at Long Island may well have served as 

 the original source of the disease- This 

 point has not, however, been definitely 

 established. 



Instances of a disease which may have 

 been this were noted as early as 1902, but 

 it was not until 1904 that it attracted at- 

 tention ; while it did not receive full in- 

 vestigation by a mycologist until 1905. 

 At that time it had assumed serious pro- 

 portions, and by 1909 over fifty per cent, 

 of the trees within a radius of twenty- 

 five miles of New York had been com- 

 pletely killed out. In addition to this, 

 the disease had appeared at various 

 points in a number of states, and its 

 rapid spread throughout the whole of 

 the chestnut and chinquapin-growing 

 area of the United States appeared im- 

 minent. Another very serious consider- 

 ation was that all the preventive 

 measures tried within the area of serious 

 infection had failed absolutely to pro- 

 duce any effect, though these had been 

 carried out on a fairly extensive scale 

 by trained men, and though support was 

 given to the work by the United States 

 Department of Agriculture. There was, 

 moreover, no lack of co-operation on 

 the part of individuals, and no want of 

 money. Everything possible was done 

 in many instances, but absolutely no re- 

 sult was achieved. At the present time, 

 practically every tree within the infect- 

 ed area is doomed, while the possibility 

 of the complete destruction of the native 

 American chestnut and of the chinqua- 

 pin must be faced. It is needless to state 

 that this destruction represents a loss 

 of economic products aggregating in 

 value several hundred million dollars. 



