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Common Name: Mexican Rice Borer Scientific name: Eoreuma loftini (Dyar)
The Mexican rice borer is a devastating pest of sugarcane and a serious pest of rice. Mexican rice borer moths are light tan with delta-shaped wings. Adult moths lay spherical, cream-colored eggs in groups of five to 100. Young larvae feed on the tissue inside the leaf sheath and bore into the rice stem after about one week of feeding. Larvae are whitish in color with a light-colored head capsule and two pair of dark purple stripes running the length of the body. Pupation takes place inside the rice stem after mature larvae have constructed an emergence window covered by one or two layers of plant tissue. Emergence holes are smaller than those made by the sugarcane borer.
Damage caused by larva: Injury to rice results from stem borer larvae feeding on plant tissue as they tunnel inside the stem. Injury is often first noticed when the youngest partially unfurled leaf of the plant begins to wither and die, resulting in a condition called deadheart. Later in the growing season, these rice stems are weakened and may lodge before harvest. Stem feeding that occurs during panicle development causes partial or complete sterility and results in the whitehead condition. The white, empty panicles are light in weight and stand upright.
Facts: Mexican rice borers overwinter as larvae in the stem of rice and other weedy plants. These larvae pupate in the spring, and adults attack rice when stem diameter is large enough to support larval feeding. Early infestations are noticed when the youngest partially unfurled leaf of the rice plant withers and dies, resulting in a condition called deadheart. Stem feeding during panicle development causes whiteheads. Severe infestations cause stalk breakage and plant lodging. Once larvae enter the stalk pesticides are not effective. Larvae pack tunnels with frass, which prevents the entry of predators and parasitoids.
What should you look for: Similar to the sugarcane borer, begin scouting for Mexican rice borers at green ring and intensify at early boot stage. Look for orange lesions caused by the larva that feeds underneath the leaf sheath before it bores into stems. Peel off the leaf sheath to expose the feeding larva or to detect the presence of frass to ensure it is the borer and not sheath blight damage. Unfortunately, by the time signs of field infestations (deadhearts, whiteheads) are noted, it is usually too late to apply foliar insecticides effectively. Pheromone traps can assist in monitoring for Mexican rice borer adults.
How you can manage Mexican rice borer: Destroy crop residues after harvest to reduce overwintering borer population. Plant early, especially in areas with a history of borer infestations. Early planting allows the crops to mature before the beginning of moth migration from other crops and non-crop hosts. Apply insecticides to coincide with larval emergence so larvae are killed before they enter the rice stems. Once larvae enter the stems, foliar insecticides are not effective. Use pheromone trap to monitor for Mexican rice borer infestation. Seed treatments are available in some regions. No resistant cultivars are available.