What type of crop injury symptoms does Atrazine cause?

Atrazine, a widely used herbicide primarily for controlling weeds in corn and other crops, is known to cause specific crop injury symptoms that help in identifying its effects. The correct choice reflects the characteristic symptoms of chlorosis, particularly beginning at the leaf tips and affecting older leaves first. This is because Atrazine interferes with photosynthesis in plants by inhibiting the process of photosynthetic electron transport, leading to a lack of chlorophyll production, and subsequently causing yellowing or chlorosis in the leaves.

Older leaves are often more affected by Atrazine because they have accumulated more of the herbicide over time due to the herbicide's systemic nature and its tendency to be absorbed by the roots and transported throughout the plant. This results in distinct chlorosis starting at the tips as the leaves lose their green coloration.

The other symptoms mentioned in alternative choices, such as blistered necrotic spots, yellowing at leaf veins, and speckling of leaves, are indicative of different types of plant stress or damage caused by other factors—like other herbicides or environmental stresses—rather than specifically by Atrazine. Thus, the presence of chlorosis beginning at the leaf tips with older leaves being affected is a clear indicator of Atrazine-related crop injury.