1918.] 



DISEASES OF PLANTS. 755 



produced in other vines by tlie heavy rain (100 mm.) of May 20. The grapes 

 showed the contamination three days later than did the leaves. 



The length of tlie interval between contamination and the evidences of attack 

 (inoculation period) depends upon the temperature and humidity of the air, 

 being shortest when these are 25° C. (77° F.) and 100 per cent, respectively. 

 The conditions prevalent in early spring usually give an incubation period of 

 seven days. From the first appearance of the white spots, each good rain pro- 

 duces an invasion seven days after the precipitation occurs. Spraying must 

 be done about the end of this period to be effective. Applications made during 

 a rain, except perhaps just at the beginning, are lost, the fungicide being 

 washed away. 



Rainfall and grape downy mildew, A. Cadoret {Prog. Agr. et Vit. {Ed. 

 TEst-Centre), 38 {1917), No. 25, pp. 588, 589).— A comparison in tabular form 

 as regards precipitation is made between years of serious mildew attack (1910 

 and 1915) and years of relative freedom from such attack. 



Spraying for grape downy mildew in rainy weather, A. Cadobet {Prog. 

 Agr. et Vit. {Ed. I'Est-Centre), 38 {1917), No. 2^, pp. 565-567).— The author 

 reviews opinions regarding the advisability of the prfictice of spraying grape- 

 vines for doAvny mildew during humid and rainy weather. 



The treatment for downy mildew, L. Taboureau {Prog. Agr. et Vit. {Ed. 

 VEst-Centre), 38 {1917), No. 11, pp. 255-258, fig. i).— This is a discussion of 

 spraying experience and observations of the biological and meteorological phe- 

 nomena connected with the development of grape downy mildew. 



It is stated that years of serious mildew outbreaks are not always years of 

 heavy precipitation. Treatment is not effective if delayed for several days 

 after a rain or after the general occurrence of conditions favoring spore 

 germination. 



Treatment of grape downy mildew in southwest France, J. Capus {Prog. 

 Agr. et Vit. {Ed. I'Est-Centre), SB {1917), No. 19, pp. Wh U5).—lt is said that 

 in soils naturally dry in spring, as in those of Medoc or Graves (in Gironde), 

 the invasions of downy mildew which ordinarily occur in regions of moister 

 soils do not appear. The latter part of May or the first of June is usually 

 sufficiently early for the first sprayings. The most important period of con- 

 tamination is about June 10, the corresponding invasion occurring about ten 

 days later. 



In other soils of the southwest of France the most important period for 

 treatment is from May 15 to 31, though in case of very humid soils May 1 is 

 late enough for the first treatment. Certain localities are supplied from the 

 stations with special instructions regarding the time to spray. It is said to be 

 impossible to fix the exact dates when spraying is required, as these vary from 

 year to year, according to circumstances. Success in spraying depends upon 

 thoroughness and care in applying 2 per cent copper sulphate. 



Treatment of grape downy mildew, J. Capus {Rev. Vit, 46 {1917), Nos. 

 1191, pp. 265-269; 1192, pp. 282-285) .—For the information of growers not so 

 situated as to be supplied with information from stations regarding the time 

 to spray in order to prevent outbreaks of grape downy mildew (see preceding 

 abstract), the author states that the proper moment for the application of the 

 spray is the most important question arising in this connection. The develop- 

 ment of an outbreak presents three phases, namely, contamination, or pene- 

 tration by the fungus, after its germination, into the plant tissue; incuba- 

 tion, or development of the fungus within the host, with little or no outward 

 indication of its presence; and the appearance of the oil spots popularly 

 termed the invasion. This development may require from 6 to 28 days, accord- 

 62077°— 18 5 



