Ask Mr. Smarty Plants

Lantana is so extensively hybridized that it is almost impossible to diagnose what plant will grow well where. We looked at the 5 species of Lantana that are native to North America: Lantana achyranthifolia (brushland shrubverbena), Lantana involucrata (buttonsage), Lantana urticoides (West Indian shrubverbena), Lantana velutina (velvet shrubverbena) and Lantana canescens (hammock shrubverbena). Of these, only Lantana urticoides (West Indian shrubverbena) is listed as being native to South Carolina; furthermore, none of the five has yellow blooms. It is more likely that what you have is Lantana camara, a tropical native to Mexico, Central and South America. At the Lady Bird Johnson Wildflower Center we are dedicated to the growth, protection and propagation of plants native not only to North America but also to the area in which they are growing. 

We looked at the  USDA Plant Profile for this plant, and found that it is growing in at least one coastal county of South Carolina, in the southeastern portion of the state. Just as an opinion, since we really don't know anything about the plant itself, the problems your plant is having could be a deficiency in the soil, possibly iron. A judicial addition of a soil amendment featuring iron is worth a try. Our second thought is that it may be the victim of a herbicide spraying, possibly not even on your property, but a drift from somewhere else in the neighborhood. Two other websites that we found that could give you some clues are  Floridata Lantana camara and  Dave's Garden forum Lantana camara. 

Pictures of Lantana camara from Google

Pictures of Lantana involucrata (buttonsage) from Google

From our Native Plant Image Gallery:

Lantana achyranthifolia

Lantana urticoides

Lantana velutina

Lantana canescens