Natural Availability of Oak Wilt Inocula

Abstract

Need for information that would be useful in explaining the spread of oak wilt prompted an intensive study of the availability of oak wilt inocula. This study was made in five major wilt areas in Illinois and covered the 10-month period from October, 1952, through July, 1953.  A total of 649 typical mycelial mats,
each with a pad in the center, were found on 31 selected trees, some of the mats in each month of the 10-month study period.  Spore counts from mat samples indicated that the highest concentration of conidia on mats was reached in December, after which there was a steady decrease during a period of low winter and spring temperatures until April, when a sharp rise occurred with the rise in temperature.  In the laboratory, best germination was obtained from conidia that were collected in April and good germination from those collected in October, November, and March. The highest average number of conidia was obtained from mature mats but the highest germination rate of conidia was obtained from immature mats. The significance of mat size, as well as numbers of mats, in accounting for the concentration of conidia in an oak wilt area was demonstrated from sample data.  A mat that measured 24 by 10 cm was estimated to contain 1,650,000,000 conidia.  Twenty-three per cent of 393 mats (which were presumed to be old enough to have perithecia) contained perithecia.  Mats with perithecia were found in all months of the study except July, and the highest average number of perithecia per mat sample was found on aging mats in May.