Which of the following is NOT a technique to study a plant problem for pests?

Relying on word of mouth is not a scientific or systematic technique for studying plant problems related to pests. This method lacks the rigor and objectivity required for effective pest identification and management. Word of mouth can often lead to misinformation or generalizations that may not accurately reflect the specific issues present in a particular plant or landscape.

In contrast, using a hand lens allows for close observation of pests and plant symptoms, enabling the identification of specific organisms and signs of damage. Carrying an index card can help document findings and organize information systematically, which is important for tracking the issues over time. Keeping records is another vital technique as it allows for an analysis of trends and patterns, informing better pest management strategies. Therefore, these methods are crucial tools for an accurate assessment of plant problems, while relying on word of mouth does not provide the necessary depth or clarity required in pest management practices.