The Q&A Archives: Sulfowers Wilting And Dying

Question: I have two sunflower gardens; one has newley planted flowers and the other has grown flowers. The sunflowers have been wilting and now are dying. There are small holes around the dirt at the root of each flower and when we pulled the plant up there were masses of hard shelled black bugs;not worms; that were eating the roots of the flowers. What type of bug is this and what can I do to kill them and prevent them?

Answer: I'd guess the pest is Zygogramma exclamationis (Fabricius), commonly called sunflower beetle. The sunflower beetle is associated exclusively with sunflower. Adults closely resemble adult Colorado potato beetles and may be confused with potato beetles except that sunflower beetles are smaller and do not feed on potatoes and Colorado potato beetles do not feed on sunflower.

The head of the sunflower beetle is reddish-brown and the thorax (area between head and abdomen) is pale cream with a reddish-brown patch at the base. Each front elytron (wing cover) has three dark stripes that extend the length of the back. A shorter, lateral stripe ends at the middle of the wing in a small dot that resembles an exclamation point. The beetle is 0.25 to 0.5 inch long and 0.16 to 0.19 inch wide. The larvae are yellowish-green, humped-back and about 0.35 inch at maturity.

The sunflower beetle has one generation per year. The adults overwinter in the soil, emerging in late May or early June. Adult sunflower beetles damage plants soon after they emerge from hibernation. Most feeding occurs at
night and if populations are large, they may completely defoliate a plant.

Natural enemies include general predators such as ladybird beetles, lacewings, nabids and anthocorids destroy both eggs and larvae of the sunflower beetle. Application of rotonone or sabadilla should control the pests.

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