Which condition indicates a nursery may require chemical treatment of its soil?

The indication that a nursery may require chemical treatment of its soil is the existence of A, B, or Q rated pests. These classifications reflect the severity and potential impact of pest infestation on plant health and, by extension, on the overall operation of the nursery. A-rated pests are known to cause significant harm, while B-rated pests are of concern but may have a lesser impact, and Q-rated pests are quarantine pests that must be controlled to prevent their spread. The presence of such pests necessitates an immediate response, which could include chemical treatment, to protect the plants and ensure the nursery's viability.

The other conditions, such as the presence of common weeds, soil moisture levels, and the use of non-native plants, do not directly indicate a critical need for chemical treatment in the same urgent manner as the presence of harmful pests. Weeds can often be managed through cultural or physical methods rather than chemical treatments. Soil moisture levels are more related to irrigation practices and overall plant health, while non-native plants may affect biodiversity but do not directly call for soil chemical treatments.