6 



BULLETIN 734, U. S. DEPARTMENT OF AGRICULTURE. 



migrating through the soil, attack the wheat seedlings, penetrating 

 between the leaf sheaths, causing them to become wrinkled, distorted, 

 and swollen. The larva} so adjust their zone of infection that almost 

 all remain near the young growing portion of the plant. In this 

 way. as the plant grows they are elevated toward the flowering parts. 

 When the plant blossoms, the larvae, which up to 

 this time appear not to have taken nourishment, 

 enter the flowering parts, from which they ob- 

 tain food. Here they develop sexuality, pair, lay 

 eggs, and die. These eggs hatch and produce 

 larvae. When the wheat plant matures these 

 larva? become coiled and dried up, forming the 

 inner yellowish-white portion of the black gall 

 as is shown in figure 5. The nematodes have great 

 tenacity of life, and in many respects are analo- 

 ; gous to the well-known Trichinae of pork. They 

 bear a temperature of 125° F. and are also very 

 j resistant to frost and low temperature. 



Heads infected with the nematode disease re- 

 semble heads infected with the stinking smut of 

 wheat. They are usually thicker and shorter than 

 > normal heads, the glumes of the spikelet are 

 spread somewhat, and in place of the normal seed, 

 dark galls, incapable of germination and full of 

 larvae, are to be found. 



Information gathered from those whose crops 

 of grain have been infected with this disease is to 

 the effect that it is easily recognized in the field 

 on account of the darker green appearance of the 

 heads and their somewhat longer maturing period. 

 The plants are smaller, having a blighted and 

 blackened appearance. Sometimes only one side 

 of the spike is affected, while the other side is 

 normal. There may also be some sound grains in 

 the infected spikelet, and in some instances the 

 head may not be infected at all, the only apparent 

 infection being the formation of tumor-like or 

 abcess-like elevations on the leaves of the plant. 

 Figure 6 shows the similarity between wheat 

 heads infected with the nematode disease and with the stinking-smut 

 disease of wheat in comparison with an unaffected wheat head. 



Soil conditions seem to have an important bearing on the disease. 

 Spots in fields which become water-logged, or parts of the field where 

 trash has accumulated, show the greatest percentage of infected 

 plants. 



