i68 



THE CANADIAN HORTICULTURIST 



July, 1911 



The Cdcry Blights 



Prol. £. M. Strcight, Macdonald College, Que. 



WHEN a farmer says "My potatoes 

 have been struck by rust "or "My 

 celery is going with the blight," 

 what does he mean? When he speaks of 

 controlling "blights" and "rusts," what 

 does he hope to do? I find the greatest 

 amount of misconception concerning the 

 Whole subject of plant disease, and when 

 the expert explains the difficulty in the 

 language of mycelium, conidiophore, 

 uredospore, and teleutospore, he has not 

 added much to the gardener's conception 

 of the difficulty or the most approved 

 method of combating the same. 



We shall have made much advance 

 when all men realize that every plant 

 disease is also a plant. True, these forms 

 are low down, but just as truly plants as 

 the potato, celery, or other plant which 

 they attack. These plants are not so 

 much unlike other plants as many sup- 

 pose, except that they are very minute 

 — so minute that they are seldom seen 

 with the naked eye, unless very many 

 are aggregated together. 



Early Blight on Celery Leaf. Fig. 1 



The plant body is a mass of threads, 

 vi/hich wind themselves back and forth 

 through the tissue of the host, either 

 through the cells or between them, and 

 constantly suck up the elaborated food 

 which the host plant manufactured for its 

 own use, and which the fungus had not 

 the power of manufacturing for itself. 



Very soon, usually, after the attack, 

 the plant causing disease acquires the 

 power of sending up little stalks. These 

 little stalks bear spores, either singly 

 or massed together. These spores, which 

 correspond to seeds in the higher plants, 

 are the common forms of reproduction. 

 They are so lig'ht that they are easily 

 blown by the wind from place to place, 

 where they fall on other plants, germin- 



Late Blight on Celery Leaf. Fig. 2 



ate, attack the plant, and the whole life 

 history is gone over again. 



A MISCONCEPTION 



We must get away from the idea that 

 warm, moist weather causes rust and 

 blights. Climatic conditions, moist and 

 warm, are usually favorable to the ger- 

 mination and proper development of the 

 fungus, but it would be just as reason- 

 able to say that warm, moist weather 

 caused the oat crop. The truth is that 

 heat and moisture are usually as neces- 

 sary for the germination of the spore as 

 for the germination of celery seed, but in 

 neither case does it cause the plant. 



If a seed of one of the higher plants 

 were put in kerosene oil it would not 

 germinate. In just the same way, there 

 are many substances in which the spores 

 of plant diseases cannot grow. One of 

 the best of these is Bordeaux mixture. 

 If a fungus is already within the tissue 

 it is evident that the application of a 

 fungicide, such as Bordeaux mixture, is 

 of little avail so far as curing the malady 



goes ; but even 

 then it may Ivn 

 der the spread 

 of the disease. 

 Prevention is 

 the watchword. 



If the leaves 

 of plants are 

 covered with 

 some substance 

 in which spores 

 cannot germin- 

 ate, it matters 

 little how much 

 . .. _, L, t c- 1 disease there 



Section Thronih Leal. rig. i , • , 



mav be m the 



Early b'i;ht. (Section, ',.. , 



through spot). Fruiting locality, or how 



bodies arising through f,^;,ny spores 



stomate of leaf, bearing ,. /^ 



Bpores. alight On your 



'^^ 







SuBple Spoti. Fi(. 4 



plants, so long 

 as their armour 

 is complete. 

 True, the spores 

 often work in 

 between the 

 joints of the ar- 

 mour. This ne- This shown an enlarged 



cessiiates care- might of Oeicry, showing 



ful and continu- ^^e Dustulee or pycnldia. 

 ous spraying so that there may be protec- 

 tion for every part. Bordeaux mixture 

 alfords such protection. 



It is well in this connection to remem- 

 ber that bluestone is the important and 

 essential thing, but because of its solu- 

 bility, we dare not use it in a pure state, 

 as it would kill the plants on which it was 

 sprayed, along with the fungus which 

 attacked it. The lime of Bordeaux is 

 simply to bring the bluestone in such a 

 condition that it is no longer soluble in 

 water. In this condition it simply forms 

 a coating on the leaves without injury 

 to the host plant, and at the same time 

 hinders the germination of the spores. 

 With these preliminary considerations 

 we shall proceed more particularly tr) 

 Celery Blights and their control. 



TWO CELEET BLIGHTS 



As with potatoes we have two blights 

 of celery which are of great importance 



Germinating Spores of Early Sporei of Late Blight 

 Blight. Fig. 5 on Celery. Fig. 6 



— the Early and the Late. The one is 

 often mistaken for the other. At certain 

 seasons both are present at one time. As 

 a rule the early blight is most destruc- 

 tive early in the season, and the late 

 occurs in autumn. Its destructiveness 

 does not end in the field, for the storage 

 cellars often furnish conditions favour- 

 able for its rapid development, and the 

 losses in many sections have been heavy. 

 The early blight begins on the outer- 

 most green leaves and rapidly spreads 

 to the younger leaves as they unfold in 

 freshness and vigour. It appears in 

 spots more or less circular, greyish-green 

 at first, and becoming brown and ashen. 

 In the early stages of the disease there 

 is a well defined spot with slightly raised 



