The Influence of Environmental Factors on Anthracnose ofXanthium spinosum

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Abstract
Anthracnose on Xanthium spinosum (Bathurst burr, spiny clotburr, or spiny cockleburr) is caused by the fungus Colletotrichum orbiculare. The optimum dew period temperature for anthracnose development was between 20 and 25 C. The optimum post dew period temperature for disease development was 30 C. Anthracnose development increased with the duration of dew period. Maximum disease development resulted from a 48-hr dew period. Maximum disease development resulted from a 48-hr dew period at 25 C. Long dew periods (48 hr) at low temperatures increased disease development compared with short dew periods, while significant anthracnose development resulted from an 8-hr period at a high temperature (35 C). Disease development was increased by two consecutive dew periods of at least 12-hr duration. Exposure to light for up to 8 hr at the beginning of a 24-hr dew periods did not reduce disease development. A dark period of at least 10 hr during the dew period significantly increased disease development. All experiments were undertaken in controlled environments. The results are discussed in terms of possible use of C. orbiculare as a mycoherbicide against X. spinosum.