Kenaf (Hibiscus cannabinus L.), a nonwood fiber crop, was recently reported to be susceptible to Phymatotrichum omnivorum, a soil-borne fungal pathogen of the southwestern United States. Field plot studies were conducted in 1991-1993 at Weslaco, TX in an area naturally infested with P. omnivorum. Six kenaf cultivars were evaluated for disease incidence at four weeks after initial symptoms and crop maturity, for plant height at maturity, and for total stalk yield. No significant (P less than or equal to 0.05) cultivar x year interaction occurred for any measurement. Across the three-year study, the six cultivars did not differ for disease incidence at four weeks after initial symptoms or at maturity, nor for plant height or stalk yield, indicating that there was no significant genetic resistance or host tolerance to II omnivorum present. Disease incidence increased from 43.9% in 1991 to 55.4% in 1992. In 1993, disease symptoms on 10 June were 60.9% compared to the final disease incidence of 41.8% at crop maturity. This behavior resulted from rainfall occurring in the early stages of pathogen infection and the inherent ability of kenaf to produce and survive with new lateral roots. Although several plants were able to recover from pathogen attack in 1993, severe reductions in plant height and stalk yield were observed. Disease incidence four weeks after initial symptoms was increased and plant height and stalk yields were greatly reduced with each successive year, indicating that continuous kenaf culture should be avoided on soils highly infested with P. omnivorum.
