A farmer in Butler County KY observed a corn field that seedlings were being severely damaged and there was a heavy reduction in the number of stands (Figure 1). Inspection of plants showed entrance holes in the stalk just below ground level, tunnels going to plant crowns, suckers (Figure 2), stunting and center leaves were desiccated (deadheart) (Figure 3).
The farmer or consultant did not see any wireworm larvae, which might be suspected as the most likely cause of some of these injuries. They commented that they had not seen this type of damage before. This reaction is entirely possible in view of the fact that the insect responsible for these symptoms has only been reported sporadically affecting corn in many areas of the southern USA.
After a visit to the farm during the last week of May, sugarcane beetles (Euetheola humilis rugiceps, Coleoptera: Scarabaeidae) were identified as the insect causing these injures. The adult beetles (Figure 4) chew large, ragged holes in the main stem just belowground.
Seedling corn may be killed entirely, but if plants survive, they are stunted and suckers are produced excessively. All of these symptoms were observed in this field. Injury to corn has been observed from emergence (VE) through mid-whorl stage (V10), but typically is observed from V3 to V5 growth stages in the southern United States.
Sugarcane beetles can feed on seedling plants up to plants 1.2 m (4 feet) in height.
Description and Biology
The sugarcane beetle is a black beetle approximately 1.5 cm long (half inch) and sporadically can affect corn as seedlings or during late whorl stage (Figure 4). These beetles are in the same family as the Japanese or June bugs. They can affect sugarcane, rice, tobacco, greenhouse roses, strawberry, sweetpotato, and turfgrasses.
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It has been reported that these beetles feed and survive on Bermudagrass. Dr. D. Johnson reported this insect feeding on corn in Kentucky in 2003.
The sugarcane beetle overwinters as an adult and is univoltine (one generation per year). Adults become active as temperatures begin to increase in late April or early May.
To complete development from egg to adult, sugarcane beetle requires between 81 to116 d whereas the developmental time for larvae ranges from 50 to 60 d, undergoing three larval instars. Larvae are white grubs with red headshields.
Since sugarcane beetles are sporadic pests, most universities do not recommend insecticide applications for curative management of active sugarcane beetle infestations in corn. However, in Tennessee, it is recommended that a pyrethroid can be applied post-emergence and directed at the base of the plant when stand loss is 5 to 10%.
In Mississippi, Dr. Catchot recommended that seed treatments with clothianidin (Poncho) at the higher use rates of 500 or 1250 are effective, compared with rates less than 500. Catchot also mentioned that in-furrow pyrethroid sprays may be used as a preventive.
However, he pointed out that pyrethroid insecticides are not systemic, and they will stay only where you apply them; they also have short duration.