Vol. VIII. No. 198. 



THE AGRICULTURAL NEWS. 



379 



FUNGUS NOTES. 



HOW FUNGICIDES SHOULD BE 



EMPLOYED. 



The substance of the following article is taken 

 -from Bulletin No. 155 of the Bureau of Plaiit Industry 

 of the United States Department of Agriculture 

 -entitled Tlie Control <if Blacl- Hot of the Grape, by 

 ■C. L. Shear, G. F. Miles, and L. A. Hawkins. 



Tlie disease is cau.sed by a fungii.s, Guignardm BidwMil, 

 -which produces dirty white spots on the grapes; these spread 

 until the whole berry is shrivelled and becomes covered with 

 minute black pustules which are the spore-bearing organs of 

 the fungus. When the grapes are attacked in the early 

 stages, they turn black and soon dro]) off. The disease also 

 attacks the leaves and young .shoots. The fungus can produce 

 Itself in two ways. During the summer small black pycnidia 

 are formed under the skin of the diseased portions. These 

 are more or less si)herical, with a small beak-shaped opening, 

 and in tbem white unicellular spores are produced, borne on 

 the end of fine thread-like stalks. During the winter, an 

 ascigerous form of fructification is produced. 



One of the obvious methods to be employed for the 

 control erf this disease is the removal of all the fallen 

 pieces of vine, leaves branches or fruits, during the winter, 

 either by raking them up and burying them, or ploughing 

 them in with a deep plough. The other is to keep the vines 

 covered with a tine layer of fungicide until the grapes have 

 reached maturity; that is to .spray them well at suitable 

 intervals. 



Experiments were undertaken, in Pennsylvania, from 1906 

 to 1908, New York and Michigan, 1907 and 1908, and in New 

 -Jersey in 1 908. The object of the experiments was to deter- 

 mine the best fungicide to employ under any given set of 

 conditions, and the minimum number of applications that 

 would keep the vineyards more or less entirely free from 

 black rot. In addition to this, a careful account was kept 

 of the increased profits obtained on sprayed plots, as com- 

 pared with those obtained from unsprayecl plots, and of the 

 total cost of the siiraying, in material and labour. By 

 subtracting the cost of .spraying from the gross additional 

 profits, the net increase in profit derived from the sprayed 

 plot was obtained. 



Various strengths of Bordeaux mixture were tried, from 

 a mixture containing 6 Bo. of copper sulphate and 3 tt). of lime 

 to every 50 gallons of water, to one containing 3 lb. of copper 

 sulphate and 2 S). of lime to the same quantity of water. In 

 addition, rosin and whale-Oil soap compound was added in 

 some cases, in order to determine if the extra adhesive 

 quality which it gave to the weaker mixtures was sufficiently 

 effective to justify the additional trouble and expense. Various 

 modifications of Bordeaux mixture made with sodium car- 

 bonate, and a nnxture of sodium carboiiate and sodium 

 benzoate, instead of lime, were also tried,' as well as other 

 insecticides, such as various forms of lime-sulphur wash. 



The percentage of rot jiresent was determined by actually 

 ■counting the number of diseased grapes in 1,000 average 

 bunches from each of the plots under observation, and com- 

 paring this number with the average number of berries 

 u.sually produced upon the same number of biinches. 



On some of the plots, eight applications of fungicide 

 were made, and on others five. Where eight were made, the 

 first spraying was carried out when the vines were quite 



dormant, and continued at intervals of about ten days to 

 a fortnight, until the grapes were nearly full grown. AVhen 

 there were only five applications, the first was made when the 

 shoots were about 8 inches long, and the fungicide for the 

 first application, was not <juite so strong as that used when 

 the vines were dormant. In all cases, a weaker Bordeaux 

 mixture, or a non-staining fungicide such as neutral copper 

 acetate solution, was u,sed in the final spraying, to avoid 

 injury to the grapes. 



The following were some of the conclusions arrived at, 

 as a result of the.se experiments. Tlie Bordeaux mixture 

 prepared with 1 lb. of copper sulphate and 3 Bj. of lime to 

 50 gallons of water was quite as effective in preventing this 

 disease as mixtures contain larger proportions of copper 

 sulphate and lime. Tt was also found that when fresh stone 

 lime is used, 3 B). of lime is ample to niore than neutralize 

 1 ft. of copper sulphate, and this quantity is preferarble; a.s, 

 according to recent investigations, excess of lime is likely to 

 prove a disadvantage. None of the other mixtures tried 

 were as successful as Bordeaux mixture, though neutral 

 copper acetate and ammoniacal .solution of copper carbonate 

 were valuable as non-staining fungicides for final spraying. 

 The first of these is made by dissolving 1 fc. of neutral 

 copper acetate in 50 gallons of water, and the second by 

 mixing 5 oz. of copper carbonate and 3 pints of ammonia 

 solution with 50 gallons of water. The addition of ro.siii 

 and whale-oil soap compound to weaker Bordeaux mixtures 

 was not of sufficient advantage to justify the extra expense. 

 Lime-sulphur washes in the proportions generally employed 

 were not as effective as Bordeaux mixture, and were found 

 to cause severe scorching of the foliage. 



Five applications of fungicide were sufficient, beginning 

 after the shoots were about 8 inches long. There was no 

 additional advantage to be derived from an earlier applica- 

 tion. 



Where unsprayed grapes were a total loss in 1907, the 

 rot on sprayed plots was reduced to 28-3 percent. In the- 

 next season, when the rot was equally bad on unsprayed vine- 

 yards, the rot on sprayed plots was reduced to much less 

 tlian 1 per cent. This indicates the cumulative effect of the 

 spraying. The net profits, after deducting the expenses of 

 labour and materials, .showed an increase of !?10-G0 to .?62'30 

 per acre over unsprayed plots, and this does not take into 

 account the very considerable improvement in the general 

 health of the vines which would become more manifest in 

 succeeding seasons. 



In carrying out such experiments, the materials must be 

 thoroughly and carefully mixed, the best method being to. 

 well mix the lime, and to completely dissolve the copper 

 sulphate before adding them to one another. 



Another very important point is the necessity of 

 thoroughly covering the plants sprayed with a thin film of 

 the fungicide. This necessitates careful application, and 

 when the plants are leafy, a movable nozzle on the end of 

 a hose pipe must be emi>loyed, so that it can be manipulated 

 by hand and directed on to all parts of the plant. It is only 

 by very careful attention to the.se points that reliable results 

 can be obtained. 



The chief conclusion to be drawn from the above 

 experiments is that, if spraying is to be successful, 

 definite knowledge is necessary on the following points: 

 (1) the best fungicide fco employ, (2) the best propor- 

 tions in which its ingredients should be mixed, and (3) 

 the minimum number of applications that can be 

 profitably made. These points can only be determined 

 by carefully organized field-work. 



