Bulletin 229, Diseases of Citrus in Florida


recovery. Unscraped lesions continued to increase in size and
at the same rate whether disinfected or not.
 The bark-scraping method for the control of psorosis has been
tried out extensively in Florida by the senior author and has
given excellent results. Since gummosis and psorosis usually
have not yielded to the haphazard methods of treatment formerly
used by growers, many growers simply have become resigned to
the occurrence of these bark diseases and consider it useless to
attempt to control them. Like gummosis, however, psorosis can
be cured fairly readily by the proper method of treatment, if it
has not progressed beyond the intermediate stages, although
the ease of treatment and likelihood of cure are decreased when
the disease has been allowed to go unchecked for several years.
When psorosis has progressed to such an extent as to involve
more than one-half of the circumference of the trunk or branch
and has begun to involve the cambium but has not seriously in-
jured the wood, the disease may still be checked and frequently
cured by careful scraping, although the cure is more uncertain.
Where the disease has been present for a number of years, or
until the greater part of the bark of the trunk or limb is af-
fected and the wood underneath is killed and discolored, there is
little hope for a permanent recovery. If the bark on the trunk
is badly killed or the top of the tree as a whole appears stunted
or unproductive, the tree should be removed.
 Since the bark-scraping method of treatment applied equally
 well to both gummosis and psorosis and since Florida growers
 usually do not distinguish between these two bark diseases, the
 method of treatment for both these diseases is here described.
 The principle governing the treatment of these bark diseases by
 this method is the elimination of the diseased outer bark tissue
 without interfering with the production of new, healthy bark
 from the cambium, or growing layer. This is accomplished by
 scraping off the outermost, diseased layer of bark and applying
 some good disinfectant paste or wash, such as lime-sulphur paste
 or wash or bordeaux paste, as soon as the bark lesions on each
 tree have been thoroughly scraped. This allows the remaining
 outer, corky layers of bark to dry out and checks the development
 of the disease. This part of the bark will. slough off later in
 flakes or scales of variable size. The slight exudation of gum
 from season checks that develop in the freshly scraped bark sur-
 faces is no indication that the treatment will not be successful,