July, 1912 



THE CANADIAN HOETICULTURIST 



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Celery Sprayed Nine Timas with Bordeaux Mixture on the Left. Not Sprayed on the Right. 



border ; but when the spots become 

 numerous on a leaf, the latter begins to 

 turn yellow, and subsequently the fungus 

 develops abundantly its fruiting growth 

 in indefinite areas thus giving the char- 

 acteristic ashen spots of indiscriminate 

 form. This "early blight," Cercospora 

 Apii, is seen on the leaf only, while "late 

 blight" may occur on any part of the 

 plant. 



The "late blight" Septoria Petroselini 

 Des, var. Apii, begins by attacking the 

 lower outside leaves, where it is seen in 

 small brown spots, which later turn 

 black. These spots often form in clus- 

 ters, but where the leaves are badly 

 affected the clusters cover the entire leaf 

 surface and these leaves soon fail to 

 perform their natural function and die. 

 In many cases, however, the blight does 

 not confine its ravages to the leaves (leaf 

 blades), but attacks the stalks (petioles) 

 also-. Here, again, it is seen in small 

 black spots. The stalks soon turn brown, 

 soften and finally shrivel up. Shortly 

 after the appearance of the characteristic 

 blight spots upon the leaves and stems. 

 there may be seen small black pustules in 

 the centre of the dead area. By referring 

 to figures one and two an idea of the 

 appearance of the two blights may be 

 obtained. 



THE SPOT 



A minute study of the "spots" shows 

 great differences. In the early blight, a 

 section through the spot simply shows 

 the threads of fungus ramifying through 

 the tissue, the fertile filaments, or hy- 

 phae, protruding through the pores or 

 stomates of the leaf. These fertile hy- 

 phae, as seen under the microscope, are 

 Illustrated in figure three. It will also 

 be seen that these bear transparent re- 

 productive bodies, or spores. In late 

 blight pustules or pycnidia are found, 

 and the spores are contained in these 

 These pustules are visible to the naked 

 eye and appear as black specks. Under 

 the microscope they appear as figure 

 four. 



The spores of early and late blight re- 



semble each other. In both cases they 

 are long and narrow, and may or may 

 not be slightly curved. They are trans- 

 parent (hyaline) and usually have cross 

 partitions (Septae). Usually the spores 

 of early blight are more club-shaped, and 

 have not as many septae as in the late 

 blight. These spores appear as threads. 

 In both cases they are very light, are 

 blown by the wind and under favourable 

 conditions germinate quickly. Figures 

 five and six show the spores, and also 

 their manner of germination. 

 THE PLANTS 



The character of the entire plant is 

 also very different in the two diseases. In 

 the early blight the plant may have a 

 gnarled stunted appearance, but never 

 loses its stability ; while in Septoria the 

 stalk becomes soft, wilted, and eventu- 

 ally dries up. 



Considerable confusion exists regard- 

 ing the nature of the season during 

 which this early blight is most prevalent. 

 It has been reported most abundant dur- 

 ing hot dry periods, and also most in- 

 jurious during warm "muggy" days. In 

 my own experience the disease develops 

 best during hot weather, and is not much 

 dependent on moisture. The ordinary 

 dews are quite sufficient for its rapid 

 development. As autumn approaches 

 with cooler rains, the fungus disappears 

 to a great extent. At Macdonald Col- 

 lege this disease was followed by the late 

 blight. This latter malady was not 

 serious in the field, but the fungus is 

 still active in the cellar, and is causing 

 considerable injury. 



CONTEOL 



Despite the failure of Bordeaux mix- 

 ture as a preventive in the field for Cer- 

 cospora Apii in many localities, we are 

 satisfied that, when faithfully applied, 

 the disease may be controlled by Bor- 

 deaux. The accompanying photographs 

 show plants from the field sprayed nine 

 times with Bordeaux, and beside them 

 some plants not sprayed at all. The re- 

 sults are striking. The unsprayed plants 

 are useless. 



The spores of the fungus have been 

 found to germinate after passing the 

 winter on the dead leaves of the previous 

 growth. This will suggest the necessity 

 of destroying all refuse matter and dis- 

 eased material as far as possible. The 

 same disease is said to grow on the wild 

 parsnip, so it may be as well to rid the 

 fence corners of this plant. 



CONTROLLING LATE BLIGHT 



The late blight can be controlled in 

 the field by fungicides and without 

 greater trouble than in the case of the 

 other. A nozzle with a large opening 

 and high pressure should be used, so that 

 plenty of the spray mixture may be forc- 

 ed right into the centre of the plant 

 This spraying for Septoria is impHDrtant 

 if celery is to be stored, so that a mini- 

 mum of disease will be carried to the 

 cellar. Badly affected leaves should be 

 stripped away before consigning to the 

 storage. The temperature should be 

 low, so as to hinder the rapid develop- 

 ment of any remaining spores. Good 

 ventilation seems to be an important pre- 

 ventive factor, and the best evidence of 

 this is. afforded by the observation that 

 the blight is less injurious along the cen- 

 tral gangways of the cellar. 



The usual Bordeaux mixture four-four- 

 forty was used here, and we believe it 

 to-be as good as any. It has been urged 

 by someone that Bordeaux mixture 

 should not be used on celery in view of 

 the fact that the leaf stems are eaten . 

 It has been shown that a man must needs 

 eat from one hundred and sixty-six to 

 one thousand three hundred and twenty- 

 eight heads of celery at one time to get 

 a tonic dose of copper, and sixty-six 

 thousand four hundred and forty plants 

 would be required to kill, so the danger 

 is not great. 



USE GOOD SEED 



As before referred to, in late blight the 

 pustules containing spores may occur on 

 any aerial part of the plant including the 

 seeds (seed coats) and the pedicels on 

 which they are borne. To the naked 

 eye they appear as black specks. It is 

 believed that the introduction and rapid 

 distribution of the disease in this coun- 

 try is due to the importation of infected 

 seed. One thing we know, the fungus 

 often appears on seedlings. Good seed 

 with celery is as important as good seed 

 in other garden croRs. Celery seed on 

 which the pycnidia can be seen ought, of 

 course, to be rejected ; but diseased seed 

 cannot always be identified at a glance. 

 We believe that the time is coming when 

 gardeners will pay more attention to 

 saving their own seed. When this is 

 done and seed saved from healthy plants 

 and the Ijest possible, we shall have 

 made a long step in advance. We need 

 not blame the weather when we intro- 

 duce disease into the field in the blem- 

 ished infected .seed. This is usually the 

 beginning of the end. 



