Growers have reported seeing salt marsh caterpillars (Estigmene acrea) feeding on garden mums. Univ. of Conn. extension horticulture and greenhouse IPM specialist Leanne Pundt said the caterpillars have a wide host range, including herbaceous perennials such as mallow, Joe-Pye weed (eupatorium), asters and yarrow (achillea), broad leaf weeds (especially pigweed), vegetable and field crops. The caterpillars are very hairy. The caterpillars may be found on the edges of outdoor mum fields especially near weedy areas, but they can move into the greenhouse.
Univ. of Md. Extension personnel said the dry weather in their state may cause the caterpillars to look for other host plants. They have received a report of the caterpillars on poinsettias.
Young larvae are yellowish white becoming more reddish brown as they grow. The larvae skeletonize the foliage and there may be large holes in the leaves. Also, look for caterpillar droppings (frass). Adults are fairly large white moths with many small black spots.
Larvae can be managed with either insecticides labelled for caterpillars or Bacillus thuringiensis when they are young and actively feeding.
Pictured: Mature saltmarsh caterpillars are very hairy.
Photo by John L. Capinera, Univ. of Fla.