Recovery frequency of P. ramorum inoculum at different depths (open symbols: 0 cm, grayed symbols: 5 cm, closed symbols: 15 cm) and gravel thickness treatments (circle: 0 cm, triangle: 2.5 cm, square: 7.5 cm) in trial 2, CA during solarization (A: solarized, B: non-solarized). Means ± standard error. Similar trends were observed in other trials.