Phyllosticta leaf spot, fruit blotch, and canker of the apple : its etiology and control

Abstract

The increasing prevalence and seriousness of apple blotch in Illinois and thruout the United States, and the inadequacy of present control measures emphasize the need of detailed study of the life history and habits of the causal organism, Phyllosticta solitaria E. & E. Since the first published account of the disease on the commercial apple in 1902, valuable observations and isolated facts have been presented by many investigators. Existing publications on the disease, however, show a lack of knowledge of many important phases of nje organism necessary for its successful control. THE DISEASE NAMES APPLIED Before anything definite was known about apple blotch, fruit growers regarded it as an unusual stage of apple scab or apple bitter rot. Up to 1907, the disease was known variously as "apple blotch," ' ' fruit blotch, " ' ' dry rot, " ' < black scab, "" late scab, " " cancer, " ' ' tar blotch," "Phyllosticta," ' ' Phyllostictose, " "star fungus," "Phyllosticta spot," or ' ' Phyllosticta on the apple." As more was known about the disease it came generally to be referred to as apple blotch, and this is the name that will be used in this bulletin. HISTORICAL **' $> Specimens of fhe disease were first collected in October, 1893, by L. M. Underwood 92 on the leaves of the American crab apple (Pyrus coronaria L.) in Montgomery county, Indiana. They were submitted for examination to J. B. Ellis, who determined the causal organism to be a Phyllosticta, to which he gave the name Phyllosticta solitaria; in 1895, he furnished a meagre description of it. A few months previous to the publication of the description of Phyllosticta solitaria, by Ellis and Everhart, 30 M. B. Waite, pathologist of the Bureau of Plant Industry, U. S. Department of Agriculture, photographed blotched a The results presented in this bulletin form part of a thesis submitted by the author to the Graduate School of the University of Illinois in partial fulfilment of the requirements for the degree of doctor of philosophy in botany, May, 1923.

Pest categorisation of Phyllosticta solitaria

“…The second type of symptoms consists of pinhead‐sized, yellowish‐green spots in the interveinal areas (Yoder, ). Pycnidia appear on leaf lesions early in the season, whereas pycnosclerotia are formed late in the season (Guba, ). Pycnosclerotia are more common in the lesions formed on the petioles than on the leaves.…”

“…In the available literature, the only documented reports of Pyrus spp. being hosts of the pest are those of Sheldon () and Guba (), according to which, the original host of P . solitaria was probably Pyrus coronaria (crab apple), a wild Pyrus species.…”

“…lancifolia and M . angustifolia (Guba, ) and Crataegus (Seaver, ) also become affected by the pest. The latter is reported as an incidental host by EPPO () and as a wild host by CABI (online).…”

Phyllosticta solitaria Ell. & Ev.: Fungi Imperfecti: Sphaeropsidales

“…Identification (4,5,8,9) Symptoms O n leaves: tiny white spots, 1.5-3 mm in diameter, first appear between or on the veins and petioles. The spots enlarge, up to 6 mm, and become elliptical, sunken, tan or buff lesions with a black spot (pycnidium) forming in the centre.…”

“…Fung,al mycelium can overwinter indefinitely in twig cankers of some varieties while, in others, natural excision occurs within Disease incidence and severity are directly correlated with rainfall ; in years with frequent rain, 50 % or more of the fruits in many orchards may be affected. There are varying reports on effects of temperature on the fungus (1,4,5 ) and the temperature requirements observed do not explain the distribution of P. solitarin in nature.…”