Step 1: Understanding boll worms.
Boll worms are a major pest for cotton plants, causing significant damage to the cotton crop by feeding on the plant's bolls.
Step 2: Analyzing the options.
(A) maize: This is incorrect, as boll worms do not primarily attack maize.
(B) rice: This is incorrect, as boll worms do not primarily attack rice crops.
(C) okra: This is incorrect, as boll worms do not primarily attack okra.
(D) cotton: Correct. Boll worms are known to attack cotton plants.
Step 3: Conclusion.
The correct answer is (D) cotton.