164 Journal of Agricultural Research /oi. x, no. 4 



larly those of the root system, affords a reliable basis for diagnosis. 

 The first indications of an attack of rootrot are seen in the foliage. 

 The leaves are paler in color than the normal green and have a yellow 

 cast, an appearance of unthriftiness, and are smaller than normal. The 

 thinness of the foliage later attracts attention (PI. 15, A, B). This 

 appearance is produced by a failure of many of the lateral buds to 

 develop and by a check in length of the terminal growths. In later 

 stages one or more of the main branches may die, while others may 

 appear normal, but more commonly the general death of the tree 

 results. 



Trees of bearing age in late stages of rootrot have a tendency to 

 heavy bearing, the fruit being small and poor in quality. One of the 

 most reliable signs is an inclination of the trunk, the lean being directed 

 away from the most seriously affected roots. Affected trees appear to 

 die rather suddenly, but in most cases symptoms of rootrot have been 

 present for a year or more; trees are rarely, if ever, killed within a 

 single season from the time of infection. This is shown by a marked 

 check in the terminal growth of branches which usually extends back 

 over a period of two or more years and indicates the cumulative effect 

 of a comparatively slow-acting parasite. Measurements of the length 

 of terminal growths of two contiguous 6-year-old York Imperial apple 

 trees, one healthy and the other affected with rootrot, gave the averages 

 shown in Table I. The affected tree shows a marked check in growth 

 beginningin 1915. Plate 15, E, shows representative terminal growths 

 of these trees; the check in growth, the suppression of lateral buds, and 

 the decrease in number and size of the leaves are apparent. 



Table I. — Average terminal growth of healthy and of diseased York Imperial apple trees 



Healthy tree. Rootrot tree, 



1913- 

 1914. 



1915- 

 1916. 



Death from rootrot may result at any stage in seasonal development, 

 but the majority of trees probably succumb during the fall or winter. 

 When death takes place during the growing season, the leaves brown and 

 shrivel and hang on for sometime. Trees of any age may be subject to 

 attack. The greater percentage dies between the ages of 12 and 20 years; 

 a few may die as early as five years or younger. Trees on newly cleared 

 land from which the stumps of forest trees have been removed shortly 

 before planting usually die more rapidly and in greater numbers than 

 those planted on cultivated land. A high percentage of the replants set 

 where trees affected by rootrot have been removed die from the same 

 disease (PI. 17, B). Replant death commonly begins at three years of 



