1/20/2008 Sunflower Insect Management The Painted Lady, Vanessa cardui (Lepidoptera: Nymphalidae) Larva of Vanessa cardui on sunflower leaf with frass and webbing (Photo credit: J.P. Michaud) Sunflowers defoliated by Vanessa cardui (Photo credit: J.P. Michaud) 1 1/20/2008 Adult painted lady butterfly Identification The painted lady, a close relative of the red admiral (Vanessa atalanta), is a very widely distributed butterfly with many host plants in the families Asteraceae and Malvaceae. The adult butterfly has a somewhat pointed forewing with a distinctive transverse white bar. The intensity of reddish coloration on the wings varies greatly, with some individuals brightly colored and others appearing quite drab. The eggs are green and barrel-shaped. The larvae can be quite variable in appearance and are often called the thistle caterpillar because of their prevalence on thistle plants. They are spiny, covered with bristles, and range in background coloration from mottled, pale green to dark, purplish hues. They feed singly, skeletonizing leaves and tying up silken nests that typically accumulate piles of larval frass. Life History and Behavior This butterfly can have two generations per year in Kansas, but it is migratory and overwinters only in the southern United States and Mexico. During summer, loosely- knit swarms migrate northward in search of suitable food plants. When large numbers of adults arrive in sunflower fields there is the potential for substantial defoliation to occur. Eggs are laid singly on the upper surfaces of leaves. Damage is normally confined to individual plants, but when many plants are affected, an effort to estimate percent defoliation in the field may be justified. Management Determining the need for a treatment to protect leaves requires an effort to estimate percentage defoliation. Drawings of sunflower leaves corresponding to various rates of defoliation can be found here: http://www.ag.ndsu.edu/pubs/plantsci/rowcrops/eb25-22.gif . To estimate the extent of an infestation, fields should be sampled by walking an ‘X’ pattern and examining 20 plants at each of five separate locations. Treatments against defoliators such as painted lady caterpillars are only considered justified if plants have sustained 25% defoliation and larvae are still less than 3.0 cm (1 ¼ inches) long. Larvae larger than this are approaching pupation and will have already caused 2 1/20/2008 most of their feeding damage. The localized nature of caterpillar infestations can sometimes afford growers the opportunity to selectively spot-treat affected areas to reduce control costs and leave untreated refuges for non-target insects. Author: J.P. Michaud Assistant Professor of Entomology Agricultural Research Center-Hays For insecticide management options refer to the latest edition of MF-814, Sunflower Insect Management at: http://www.oznet.ksu.edu/library/entml2/MF814.PDF Kansas State University Agricultural Experiment Station and Cooperative Extension Service K-State Research and Extension is an equal opportunity provider and employer. Issued in furtherance of Cooperative Extension Work, Acts of May 8 and June 30, 1914, as amended. Kansas Staten University, County Extension Councils, Extension Districts, and United States Department of Agriculture Cooperating, Fred A. Cholick, Director. 3.