252 Diseases of Truck Crops 



stem longitudinally, it wiU be found that the bundles 

 from which the yellow slime oozes out are browned 

 or bright yellow. This shows that the germ is con- 

 fined to the fibrovascular bundles of the stem and 

 leaves. 



The Organism. Psevdomonas Stewarti is a short 

 rod with rounded ends (fig. 45 b). It occurs singly, 

 in pairs, or fours, and moves about by means of polar 

 flageUa. It grows slowly on gelatine without lique- 

 faction. On agar plates it grows slowly, forming 

 small round colonies. It produces no gas and is 

 strictly aerobic ; the organism is very sensitive to Ught. 



Control. It is likely that the disease is carried with 

 the seed. Hence the latter should be secured from 

 localities free from wilt. Before planting, seed 

 should be disinfected in formaldehyde, see p. 99. 

 Not all varieties of sweet com are equally subject to 

 wilt; hence truckers are advised to try to develop 

 a resistant strain or strains of commercial varieties. 

 On the methods of selection for resistance, see p. 374. 

 Finally, fields badly infected should be rotated and 

 devoted to other crops for about three to four years. 

 As far as is known the disease only attacks com, 

 so other cereals may be used in the system of ro- 

 tation. 



Smut 



Caused by Ustilago zecB (Beck.) Ung. 



Com smut is different from any smut which at- 

 tacks other cereals. The greatest damage is experi- 



