Pseudaletia unipuncta

Isas, Marcos, L., María, Pérez, P., Salvatore, Analia, Gastaminza, Gerardo, Willink, Eduardo & White, William, 2016, Impacts of crop residue on damage by sugarcane pests during the tillering phase in Argentina, Florida Entomologist 99 (1), pp. 1-5 : 4

Pseudaletia unipuncta

The crop residue undoubtedly provides the appropriate temperature and humidity conditions for larval development as well as protection against large predators (e.g., birds) and protection from dehydration. These assumptions are consistent with Carnegie & Dick (1972), Ganeshan & Rajabalee (1996), and Salas et al. (1998), who observed that attacks of the sugarcane armyworms (mainly Mythimna species; Lepidoptera : Noctuidae ) were restricted almost entirely to areas where crop residue retention rather than burning has been practiced. However, Ridge et al. (1979) found evidence of armyworm activity in fields where a pre-harvest burning of sugarcane was performed, suggesting that the residue burning afer harvest may have a greater adverse effect on P. unipuncta than pre-harvest burning.

Both Species

The high frequency (100%) of damage caused by P. unipuncta and E. lignosellus observed in “residue retained” and “residue burned” plots, respectively, allows us to predict the likelihood of damage by these pests. Clearly, the ecological conditions present in the burned plots seem to be unfavorable for P. unipuncta , because the damage was observed exclusively where the crop residue was allowed to remain. This exclusivity indicates a strong dependence of this insect pest on crop residue for its development, and/or protection from adverse ecological conditions. Conversely, damage by E. lignosellus was strongly associated with burning, as has been observed by many authors. Nevertheless, E. lignosellus showed a degree of adaptability to varying conditions, as damage also was detected in several plots with residue retained.

Both burning and retention of crop residue are linked with the presence of insect-inflicted injury in the tillering phase of sugarcane. However, when comparing the pest status of two such pests, E. lignosellus attacks seem to be more consistently deleterious to sugarcane yield ( Sandhu et al. 2013) than P. unipuncta attacks ( Chandler & Benson 1991). Moreover, chemical control of lesser cornstalk borer is not effective (Lapointe & Ferrufino 1991), whereas this control strategy is effective for armyworm ( Salas et al. 1998). Therefore, taking into account the potential for yield losses by E. lignosellus and the difficulty to control this species, leaving the crop residue without burning seems to be the most appropriate management approach. Nevertheless, surveys should be performed during the spring in fields where the crop residue has been retained in order to implement control of P. unipuncta , should it be necessary. Although these insects create concern among growers, their impact on yield loss has not been established definitively. We therefore consider it a high priority to elucidate their bioeconomics in Tucumán, Argentina.