Which scenario represents a situation where weather has little effect on a pesticide application?

The scenario where weather has little effect on a pesticide application is when controlling cockroaches in a restaurant. This indoor application is typically not influenced by outside weather conditions, as it takes place in a controlled environment. Factors such as temperature, humidity, and precipitation outside will not directly impact the effectiveness of the pesticide or the behavior of the pests within the confines of the restaurant.

In contrast, scenarios involving outdoor applications—like controlling weeds along a highway, managing light blight in a potato field, or addressing mosquito populations in a marsh—are significantly affected by weather conditions. For instance, rain could wash away pesticides before they fully bond to their target, while wind can disperse pesticides away from the intended area, leading to reduced effectiveness and potential harm to non-target organisms. Thus, the indoor setting surrounding the control of cockroaches allows for a more stable and predictable application environment, making it the most unaffected by weather conditions among the given options.