10 Florida Agricultural Experiment Station
to wilt is sometimes lessened in fields also infested with nematodes
or root-knot. Some varieties of cotton seem to be resistant to
nematodes as well as to wilt but no definite recommendations can
be made on this score at this time. Consequently, it is better not
to plant cotton at all in fields heavily infested with both wilt and
nematodes. Such fields can be used satisfactorily for small grains,
corn, Iron or Brabham cowpeas, or other crops that are not sus-
ceptible to root-knot.
 Applications of potash are sometimes said to be effective in con-
 trolling wilt, but in a number of experiments at Gainesville no
 great difference could be seen in plots that had the usual amount
 of potash, 4 percent, and those that had extremely large amounts
 of potash. Since wilt can be easily controlled by the use of resist-
 ant varieties of cotton, of which there are a large number to select
 from, it is not advisable to content oneself with makeshifts.
 Some wilt-resistant varieties of cotton suitable to Florida con-
ditions are: Willis, Lightning Express No. 7, Rhyne's Cook,
Cook 307-6, Miller, Cleveland 54, and Council Toole. This list of
varieties contains representatives of all the principal types of
cotton grown in Florida, and substitutions of resistant varieties
can be made without sacrificing a favorite type.

 ROOT-KNOT OR NEMATODE DISEASE

 The root-knot disease is caused by minute worms or nematodes
which are ordinarily very slender and thread-like, though the
adult female becomes almost spherical in shape. These worms
are known scientifically as Caconema radicicola (Greef) Cobb,
formerly as Heterodera radicicola (Greef) Muller.
 Root-knot is a widespread and injurious disease of cotton as
well as of a large number of other plants, particularly the truck
crops. In addition to severe damage caused by the disease itself,
other parasites gain entrance through the galls on the roots, and
further the injury. Cotton wilt is much worse where root-knot
occurs. Root-knot of cotton occurs in Florida and, though cotton
is not so badly attacked as some other hosts, considerable damage
is done in some fields. The loss for the state as a whole, however,
probably does not exceed 1 percent. For the entire cotton belt,
the United States Department of Agriculture estimates the loss
at between 100,000 and 150,000 bales a year. Root-knot is more
common and injurious on the lighter soils, but it may also occur
in the heavier soil types. The application of large amounts of