CDFA Pest Prevention Plant Regulation Practice Exam

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Which type of environmental condition is conducive to the spread of Dutch elm disease?

  1. A. Dry conditions

  2. B. Humid conditions

  3. C. Cold conditions

  4. D. Windy conditions

The correct answer is: B. Humid conditions

Dutch elm disease, caused by the fungal pathogen Ophiostoma ulmi, is primarily spread by bark beetles, which thrive in environments that support their lifecycle. Humid conditions facilitate the survival and reproduction of these beetles, allowing them to effectively spread the disease as they move from infected to healthy elm trees. In humid environments, the moisture supports the growth of the fungus and enhances the beetles' ability to transmit it when they feed on the bark of the trees. This combination of high humidity and the presence of the vector (bark beetles) exemplifies how conducive such conditions are to the spread of this particular disease. Other environmental conditions such as dry, cold, or windy conditions do not support the same level of fungal growth or beetle activity, thereby reducing the likelihood of disease spread. Therefore, humid conditions stand out as the optimal setting for the transmission of Dutch elm disease due to the synergy between moisture, fungal growth, and beetle behavior.