Which of the following is NOT a type of cordon system?

The correct choice is based on the understanding of cordon training systems used in viticulture. Cordon systems are specific ways to train grapevines to optimize growth and fruit production.

Bilateral, unilateral horizontal, and vertical cordon systems are recognized methods in vineyard practices. The bilateral cordon system involves training the vine along two horizontal arms extending from the main trunk. The unilateral horizontal cordon has a similar concept but focuses the training on a single arm, while the vertical cordon system involves training the fruiting canes upward along a single trunk, supporting vertical growth.

In contrast, the diagonal cordon is not recognized as an established training method within viticulture. It does not have the defined structure or the recognized benefits associated with the other three systems. Therefore, identifying the diagonal cordon accurately as not being a type of cordon system correctly highlights its absence in standard grapevine training techniques. Understanding these distinctions is crucial for effective vineyard management and maximizing grape quality.