Fig. 105. Oat smut 



This is common in oat fields wherever oats are grown. 



It is easily controlled by disinfecting the seed. The 



illustration shows one good head and three diseased 



heads. (Photograph by L. E. Melchers) 



EXERCISE 68 

 CONTROLLING PLANT DISEASES 



Statement. Much of the great loss due to bacterial plant 

 diseases may be controlled by disinfecting the seed. One of 

 the most efficient substances for this purpose is formalin. 

 This disinfectant is used successfully in the case of stinking 

 smut of wheat, smut of oats, barley, sorghums, and potato 

 scab. 



Object. To treat seed by the formalin method for bacte- 

 rial disease. 



Materials. Pint of formalin ; peck samples of wheat and 

 oats which are smut infested ; pails for immersing the seed. 



Directions. Buy a pound of formalin from the drug 

 store, and secure samples of wheat and oats which contain 

 smut from the. elevator or from the farm and a sample of 

 potatoes from a field which suffered from potato scab. Pre- 

 pare the formalin mixture, using one pound of formalin in 

 forty-five gallons of water. Place each sample to be treated 

 in a cloth bag and immerse it in the formalin solution. Leave 

 it immersed for ten minutes and then spread out to dry. Plant 

 the seed as soon as possible after receiving the treatment. If 

 you live on the farm apply treatments at home to seed to be 

 used on the farm. It will be necessary to figure out the exact quantity of solution needed for treating 

 a small lot of seed or potatoes. Do not use a stronger or weaker strength than recommended. After 

 treating, plant the seed and ob- 

 serve results, as compared with the 

 results from untreated seed planted 

 alongside or in the fields of the 

 neighborhood. 



Questions. What are the most 

 destructive plant diseases in your 

 community ? How are bacteria and 

 fungi distributed ? Where may they 

 be found ? What is the value of 

 treating seed for smut? In what 

 form is smut present on seed ? 

 Name as many methods of control 

 of plant diseases as you can. Is it 

 much trouble to treat seed with 

 formalin? Is it expensive? If 5 

 per cent of the crop is saved by 

 treating the seed, does it pay? 



References. Waters, H.J. Essentials of Agriculture, pp. 287-298. Ginn and Company. Duggar, B. M. 

 Fungous Diseases of Plants, pp. 372-380. Ginn and Company. Stevens and Hall. Diseases of Economic 

 Plants, p. 346. The Macmillan Company. 



[ 135 ] 



Treating seed oats for smut prevention 



The method shown is the new "dry" method, concentrated formaldehyde solution being 

 used. Every shovelful of grain is given one "shot " of very fine spray. (Photograph by 



L. E. Melchers) 



