Florida Agricultural Experiment Station


to enable one to scrape in crotches and other restricted places.
In scraping old psorosis lesions, where a scraper jumps over the
hard, gum-infiltrated spots in the bark, a spokeshave sometimes
proves useful.
 SCALY BARK OR NAIL-HEAD RUST
 Causal organism not definitely known
 Scaly bark, or nail-head rust, as the disease on the fruit is
 termed in Florida, is a disease chiefly confined to the sweet
 orange. This disease has been termed leprosis by Fawcett and
 Lee. It was formerly thought to occur only in Florida but re-
 cently it has been found in southern China, the Philippines, and
 Mexico. Its present distribution in Florida is limited to a few
 of the citrus-growing sections of the state. While scaly bark
 was first observed in the Pinellas peninsula about 1860, it is re-
 ported to have spread very slowly and almost imperceptibly for
 several years and to have been known for at least 30 or 40 years
 before serious damage was reported. Scattering cases have
 also been found in the central part of the slate and in a few
 localities along the central portion of the East Coast.
 Scaly bark has caused serious damage in some of the older
 sweet seedling orange groves of Florida. It has been estimated
 by Fawcett that the annual loss of fruit alone from spotting as
 a result of this disease in the Pinellas peninsula has amounted
 to between 20,000 and 30,000 boxes, the loss from prematurely
 dropped fruit in badly infected groves in this section being
 estimated at from 35 to 75 percent of the total crop. In ad-
 dition to the fruit loss, there is a constant weakening of the
 trees from the scabbing and scaling of the bark and the dying
 back of the attacked twigs and branches.
 While scaly bark is confined almost entirely to the sweet
orange, it occasionally attacks other kinds of Citrus. It has been
found to occur on rough lemon trees in old neglected nurseries
and groves and also occurs on the sour orange. A very light in-
fection may be observed occasionally on grapefruit, tangerine,
and mandarin orange trees. The latter, however, are very re-
sistant to scaly bark, even when growing in close proximity to
badly diseased sweet orange trees.
 Scaly bark is a peculiar disease which is as yet but poorly
understood. It has been suggested that moisture at the right
season for infection is an important factor in the severity of this