What impact do root-feeding aphids have on plants?

Root-feeding aphids adversely affect plants primarily by weakening the root system. These aphids feed on the sap from the roots, which can lead to several detrimental effects. The extraction of nutrients and water from the roots can impair the plant's ability to uptake essential resources, ultimately weakening its overall health.

When the root system is compromised, plants are more susceptible to stress from drought and other environmental factors. Additionally, a weakened root system can result in decreased stability and may lead to increased vulnerability to diseases. In contrast to the other choices, which suggest positive impacts on plant growth and health, the weakening of the root system is a clear and direct consequence of the feeding behavior of root-feeding aphids.