DisEAsEs OF VEGETABLES 1323 
For best results in spraying at least 100 pounds pressure must 
be used. It is usually impossible to obtain over 50 pounds pres- 
sure with hand sprayers. By expending much time and labor 
satisfactory spraying can be done on small areas with hand spray- 
ers, but they are out of the question for field work. Use a horse- 
drawn sprayer which derives power from the wheel or a gasoline 
engine. 
GENERAL DISEASES 
Damping Off. Seedlings and weak soft plants are subject to 
rotting off at the surface of the soil and consequent toppling over. 
Damping off is most injurious to plants grown indoors or under 
crowded conditions. The disease results from the attack of any 
one of several species of fungi. 
Injury can often be largely avoided by so regulating moisture, 
temperature, ventilation and spacing of plants as to produce as 
stocky, vigorous plants as possible. High temperatures and an 
excess of moisture favor the growth of the causal fungi and should 
be avoided. Where trouble with damping off has been experi- 
enced it may be expected that the same soil will continue to give 
more or less trouble. This can be overcome to a large extent by 
using new soil or by sterilizing, for which see soil sterilization. 
Root Knot or Nematode Galls. Root galls (Fig. 381), varying 
in diameter from one-thirty-second to one-half inch, occur on a 
great variety of plants, resulting in diminished vigor and de- 
creased yields. They are due to the entrance into the roots from 
the soil of microscopic worms. In this climate injury usually 
occurs only in greenhouses, for outside the worms are largely 
killed by the cold of winter. In badly infested houses lettuce 
and radishes are not appreciably injured, but the yield from 
tomatoes is noticeably lowered and cucumbers are almost a failure. 
Thorough steam sterilization of the soil is the only remedy that 
can be relied on to eradicate the disease. 
ASPARAGUS 
Rust (Puccinia asparagt DC.), Fig. 382. Rust is the most 
common disease of asparagus and very destructive in some sec- 
tions. Disease lesions do not occur on shoots cut for market but 
older bushy tops become covered with reddish or black pustules. 
