A survey was conducted to determine the incidence of an annual stem canker of plantation-grown black walnut in Illinois, Iowa, Minnesota, Missouri, and Wisconsin. Regionwide, walnut canker was observed in 84% of the 183 plantations surveyed, and 9.7% of the 19,340 trees examined were cankered. Canker incidence was significantly higher on bottomland sites (12.2%) than on upland sites (7.2%). Fusarium solani was the Fusarium sp. most frequently isolated from cankers. Regionwide, 30% of the cankers were associated with wounds; pruning wounds were the most frequently observed wounds associated with cankers. Only 1.6% of the cankers were associated with signs of attack by ambrosia beetles. Minimizing wounding may reduce the chances of canker formation. North. J. Appl. For. 10(1):10-13.
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Carlson et al. (1993) studied this question.