The response of an effector is
to maintain homeostasis
to decrease the external stimulus
to transmit a negative feedback impulse
to provide a counter stimulus to neurons

To maintain homeostasis

Explanation:

Effectors are organs, cells or tissues that provides the required output after receiving a feedback from the control center. Nerve impulse instructs the effector to bring things into balance and required range. They then influence the magnitude of stimulus and maintain homeostasis.

wild parsnip is a perennial plant which reproduces rapidly in areas which have no sign of agricultural activity such roadside or at no tillage open areas. it's considered invasive because it can inhibit the growth of another plant  and its reproduction is fast. there are several harmful effects of this invasive plant although its taproot is edible since it is a member of the carrot family. wild parsnips can cause skin blistering when in contact because of the chemicals it contains, second it inhibits the growth of other plants, it will restrict the growth of animals when eaten and lastly, it drives away natural pollinators like bees.