| Summary: | <i>Diatraea saccharalis</i> (F.) and <i>Eoreuma loftini</i> (Dyar) are stem boring pests of sugarcane (<i>Saccharum</i> spp.) and rice (<i>Oryza sativa</i> L.) crops in the Gulf Coast region. Studies were conducted to determine the role of agroecological factors, including predator disruptions, alternate hosts, and crop phenological conditions, on stem borer populations.<br>
The year after Hurricane Rita storm surge flooded sugarcane in Louisiana, a 71% reduction in the predaceous <i>Solenopsis invicta</i> Buren was recorded. Even with a 2.4-fold increase in the number of insecticide applications used for <i>D. saccharalis</i> management in flooded fields, growers still incurred higher injury.<br>
In two field experiments, October sampling showed that sugarcane planted in early August harbored 4.7 to 19.0-fold greater <i>D. saccharalis</i> infestations than September plantings. Although there is a potential for increased <i>D. saccharalis</i> overwintering populations in early plantings, differences in infestations were not recorded during the spring.<br>
Sentinel plant experiments confirmed that a number of non-crop grasses are stem borer hosts. Subsequently, sampling along transects every 6-8 wk compared stem borer infestations in non-crop grasses adjacent to rice fields. While <i>D. saccharalis</i> densities were relatively low, <i>E. loftini</i> average densities were 0.3 to 5.7 immatures/m2 throughout a 2-yr period. A greenhouse study showed that rice is more preferred for <i>E. loftini</i> oviposition than the primary non-crop hosts johnsongrass [<i>Sorghum halepense</i> (L.) Pers.] and Vaseys grass (<i>Paspalum urvillei</i> Steud.). In addition, <i>E. loftini</i> larval development duration in degree-days above a threshold temperature is 1.7-fold greater on johnsongrass and Vaseys grass than on rice.<br>
A 2-yr rice study showed that a lower than traditional harvest cutting height (20 vs. 40 cm) reduced <i>E. loftini</i> infestations by 70 to 81% whereas <i>D. saccharalis</i> infestations were not changed. Furthermore, rice stubble under favorable conditions represents an overwintering habitat in addition to non-crop hosts.<br>
This research showed that predator disruptions, sugarcane planting dates, non-crop hosts, and rice stubble management impact stem borer populations when they are traditionally left unmanaged. Thus, the evaluation of a stem borer management strategy that targets infestations in late season sugarcane and rice, but also in non-crop hosts, is warranted.
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