80 INSECTICIDES, FUNGICIDES, AND WEED KILLERS. 



Puccinia Coronata, Corda (the crown rust of oats). — Wuthrich 

 made a comparative examination of these three rusts, by submitting 

 in turn their uredospores and their aicidiospores to the action of the 

 more or less dilute acid. The time of steeping was fifteen hours, and 

 the temperature 20°-21' C. (68°-69-8° F.). The uredospores resisted 

 an acid ten times stronger than the iecidiospores ; acid of 0-0049 per cent 

 does not act on uredospores of 0"049 per cent ; its action begins to make 

 itself felt, but it is not until 4-9 per cent acid is used that all vitality is 

 removed from the spores. The aicidiospores are completely destroyed, 

 and in the same conditions, by acid of 0'49 per cent strength. The 

 uredospores of the rust of cereals would appear to be the spores most 

 resistant to the action of sulphuric acid, as they likewise are to anti- 

 cryptogamic salts. Hitchcock and Carleton have, however, prevented 

 the uredospores from germinating, by steeping them for seventeen to 

 nineteen hours in O'l per cent acid. 



Claviceps jnirpurea, Tul. (ergot of rye).^The action of the acid 

 on this disease was examined by Wuthrich, who found that 0-049 

 per cent acid attenuated the germination of the conidia, but it required 

 steeping for fifteen hours at 20°-21° C. (68°-69-8" F.) in an acid of 0-49 

 per cent to stop this germination completely. Wuthrich, who examined 

 the action of the acid on the spores of PJiytojjhthora and of Pcro)iospora, 

 found these latter much more sensitive than those of the black and 

 red rust of cereals. 



Phytojjhthora infestans, De By. (potato disease). — Acid of 0-049 per 

 cent perceptibly diminishes the capacity of the conidia to form zoospores. 

 It may be entirely arrested by destroying the conidia, by using 0'049 

 per cent acid for fifteen hours at 19'-20' C. (66-2°-68° F.). 



Peronospora Viticola, De By. (vine mildew). — The conidia and the 

 zoospores of this parasite behave like those of the PliytopJithora ; acid 

 of 0-049 per cent completely annihilates them in fifteen hours at 20° C. 

 (68° F.). In ()-0049 per cent acid the formation of zoospores may 

 be restricted, and even suppressed, without the conidia being killed. 

 The latter then germinate and produce directly a germinative tube. 

 The deleterious action of sulphuric acid on the germs of mildew 

 has caused it to be used for the winter treatment of -wine stocks. 

 Bouchard got good results by treating the vines in the spring after 

 pruning with a 10 per cent acid. During three years the vines re- 

 ceived no other treatment than the above, and the disease did not re- 

 appear. Mc Alpine came to the same conclusion, and found this 

 treatment always to give good results. Millardet, on the other hand, 

 combats this opinion, and considers treatment with sulphuric acid as 

 very injurious to the vine. The author nevertheless sides in his opinion 

 with the first observers. Acidulated solutions of green vitriol used 

 everywhere against anthracnosis cause no injury to the stocks. 



Gloeosporium ampeloj)hagum, Sacc. (grape rot). — To combat this 

 disease the utility of the acid was found empirically. It is not, it 

 must be understood, a question of treating this disease during the 

 growing period, for sulphuric acid, or even the acid mixtures, would 

 have a deplorable action on the stocks. The acid is used exclusively 

 in winter to cauterize the spots hollowed out of the young wood, 



