Pests and Diseases 195 
another species (7'ychea brevicornis Hart.) has done con- 
siderable damage. This species also works on corn roots. 
No direct method of control is known for either of these 
insects. Sprays are impractical since the insects work 
under the ground. Prevention, the only known method 
of coping with the pest, can be practiced, however, in crop 
rotation and clean cultivation. Thorough tillage early 
in the spring is thought to help in controlling aphids. 
Sugar-beet nematode (Heterodera schachtii Schmidt). 
One of the pests that has done most damage to sugar- 
beets during the last few years is the nematode. This 
is not a true insect, but is an exceedingly fine, threadlike, 
colorless worm, so small that it is difficult to see with the 
naked eye. When these worms hatch from the egg, they 
enter the nearest rootlet and feed on the plant juices. 
This results in the formation of a dense mass of rootlets 
which cling to the beet when it is pulled up (Plate XXII). 
This has resulted in calling the trouble “bearded roots,” 
“hairy roots,” and other similar names. 
The first evidence of the pest is a change in the color 
of the foliage, which takes on a lighter tint when the beet 
is injured. The outer leaves gradually wilt and finally 
die. The inner ones are small and do not thrive. Often 
the plant dies and the infected land is left bare. Usually 
this condition appears as a spot in the field which gradu- 
ally enlarges. Since the pest is readily carried about in 
the soil, when it once becomes established in a district, 
it is likely to extend to all the fields unless its spread is 
checked. 
Rotation of crops seems to be the best method of 
