Damage Loss Assessment and Control of the Cereal Leaf Beetle (Coleoptera: Chrysomelidae) in Winter Wheat

Abstract

Cereal leaf beetle, Oulema melanopus (L.), invaded northern Alabama and Georgia more than a decade ago and since has become an economic pest of winter wheat and other cereal crops in the southeastern United States. A series of trials was conducted beginning in 1995 to determine optimal rate and timing of applications of selected foliar insecticides for managing cereal leaf beetle in soft red winter wheat. These trials, cage studies with larvae, and a manual defoliation experiment were used to provide information on cereal leafbeetle yield loss relationships and to develop economic decision rules for cereal leaf beetle in soft red winter wheat. Malathion, methomyl, carbaryl, and spinosad effectively controlled larval infestations when treatments were applied after most eggs had hatched. Encapsulated endotoxin of Bacillus thuringiensis, methyl parathion, and disulfoton applied at the lowest labeled rates were not effective treatments. Organophosphate insecticides generally were not effective when applied before most eggs had hatched. The most effective treatments were the low rates of lambda cyhalothrin when applied early while adults were still laying eggs and before or near 50% egg hatch. These early applications applied at or before spike emergence virtually eliminated cereal leaf beetle injury. The manual defoliation study demonstrated that defoliation before spike emergence has greater impact on grain yield and yield components than defoliation after spike emergence. Furthermore, flag leaf defoliation causes more damage than injury to lower leaves. Grain test weight and kernel weight were not affected by larval injury in most trials. Regression of larval numbers and yield losses calculated a yield loss of 12.65% or 459 kg/ha per larva per stem, which at current application costs suggested an economic threshold of 0.4 larvae per stem during the spike emergence to anthesis stages.

Barley yield losses due to defoliation of upper three leaves either healthy or infected at boot stage by Pyrenophora teres f. teres

“…Grain yield losses due to flag leaf removal were 25% and 21% for main stems and totality of tillers, respectively. This result supports the importance of the flag leaf as an important organ contributing to cereal grain yield and that any damage to its green leaf area would generate significant yield losses (Sharma et al 2003;Buntin et al 2004;Jebbouj and El Yousfi 2006). Removing upper leaves and consequently measuring losses in grain yield, scientists logically attribute the magnitude of losses to the contribution to grain yield by these defoliated leaves.…”

“…Consequently, this reduction mainly arises from a decreasing number of fertile spikelets affected by the disease (Buntin et al 2004). This study also demonstrated that removing all leaves, followed by flag leaf removal, had the greatest impact on wheat yield components during the flag leaf and spike emergence stages.…”

“…According to Buntin et al (2004) grain yield was greatly affected by manual defoliation before spike emergence than at spike emergence or grain filling stages. This explains in our study the difference between losses obtained in the greenhouse and in the field.…”

“…Most studies dealing with the contribution of upper leaves to grain yield were carried out on wheat using different approaches such as defoliation, shading or inoculation of functional leaf area (Seck et al 1991;Buntin et al 2004). Unfortunately, few reports have investigated leaf removal effects on the grain yield of barley.…”

Cereal crop volatile organic compound induction after mechanical injury, beetle herbivory (Oulema spp.), or fungal infection (Fusarium spp.)

“…A cereal leaf beetle (Oulema melanopus L.) represents the most important wheat pest in many European countries (Dimitrijevic et al, 1999), and has become an economic pest of winter wheat and other cereal crops in the United States (Ihrig et al, 2001;Buntin et al, 2004). Also, fungal growth can substantially damage food and animal feeds; these forms of food damage can be manifested as general spoilage, reduced nutritional quality, mycotoxin formation, and production of (potentially allergenic) spores (Schnurer et al, 1999).…”