324 INSECTICIDES, FUNGICIDES, AND WEED KILLERS. 



Action on Funsfi and their Spores. — Fungi spores are very sensi- 

 tive to acetic acid (Wuthrich). Dilute acetic acid (0-06 per cent) still 

 destroys the zoospores of Plii/lupJithura i)ifesta)is, De By., and acts very 

 unfavourably on the germination of the conidia of Peronosiwra riticola, 

 De Bv. The spores of Ustilaijo car bo do not germinate after steeping 

 in acid of 0-06 per cent ; the uredospores of Piiccinia graminis, although 

 very sensitive to a solution of 0-06 per cent, are only destroyed by acid 

 of 0-6 per cent. The latter results agree with those obtained by 

 Hitchcock and Carleton on Piiccinia coronata. These spores do not 

 germinate after steeping in acid of O'l per cent. 



Use. — Coryneum Beycrinckii (gum of trees with stoned fruits, 

 Nectria ditissima). — Muller advises to overcome the gum of fruit 

 trees by the following treatment. After having removed the bark, 

 scraped and planed the wound with the knife, a rag, drenched with 

 50 per cent acetic acid, is introduced into the wound and covered 

 with a layer of grafting mastic. 



122. Oxalic Acid, COOH . COOH. — Preparation. — By oxidizing 

 wood sawdust niixed with a concentrated alkaline solution and heated 

 to 250^ C. (482° F.) in wrought-iron cylinders. The mass obtained is 

 treated with water, and milk of lime added. Oxalate of lime is pre- 

 cipitated and collected on a filter. The precipitate is decomposed by 

 dilute sulphuric acid, filtered, and the solution evaporated to crystal- 

 lizing point. 



Properties. — Oxalic acid forms white crystals soluble in 10 parts 

 of water at 20° C. and in alcohol. 



Action on Fungi. — The effect of oxalic acid on the spores of fungi 

 has been examined by Wuthrich. This acid behaves very like acetic acid. 

 The conidia of Peronospora viticola, De By., and of Phytophthora infes- 

 tans, do not germinate in an oxalic acid solution of 0-068 per cent ; the 

 movements of the zoospores of this latter fungus are arrested, as well 

 as their germination, by a 0-0063 per cent solution. The spores of 

 Ustilago carbo behave like the conidia of Pcronosp)ora ; however, the 

 m-edospores of Piiccinia graminis are more resistant and are not killed 

 by a 0-63 per cent solution. 



Use. — Nectria ditissima^ Tul. (canker of the pear-tree). — Ouvray 

 advises the use of oxalic acid to overcome the canker of fruit trees. 

 Clean the wound with a grafting knife, remove everything which is 

 torn or destroyed, then rub the wound several times with sorrel or 

 oxalic acid, then cover the wound with mastic or tallow to keep out 

 the air. 



Schizoneura lanigera, Hausm. (woolly aphis). — Oxalic acid appears 

 to be a specific against this aphis, for many scientific observers, such 

 as Taschenberg, Goethe, and Montillot, boast its good effects. It is as 

 energetic as Nessler's insecticide. A solution of 1-1-6 per cent pure 

 or mixed with a little soft soap, is used with the brush on the colonies 

 of w^ooUy aphis, for the first time in autumn after the ripening of the 

 fruit, a second time eight to ten days later, and a third time in the 

 spring. 



