Stalkborer Damage on Yield and Quality of Sugarcane in Lower Rio Grande Valley of Texas

In the Lower Rio Grande Valley of Texas, the pyralid stalkborers Eoreuma loftini (Dyar) and Diatraea saccharalis (F.) damage ≈20% of sugarcane internodes annually. We quantified the relationships between stalkborer damage and sugar yield and quality to estimate the monetary loss incurred at these levels of damage. We also compared damage estimates and sugar quality between 2 important varieties in the region, ‘NCo 310’ and ‘CP 70–321’. NCo 310 showed greater mean percentages of bored internodes (19.4%) than CP 70–321 (10.9%). Sugar per ton also was greater in CP 70–321 (215.97 lb/t or 108 g/kg) than in NCo 310 (190.92 lb/t or 95.5 g/kg); as were juice purity and mean sucrose content. Other variables (sugar per acre, cane per acre, fiber, ash, and stalk weight) did not differ significantly between the 2 varieties. Sugar per acre, juice purity, stalk weight, cane per acre, sucrose per ton of sugarcane, and sucrose content all were inversely related to percentage of bored internodes. Ash content increased with damage, consistent with a plant displaying symptoms of stress. Regression slopes for CP 70–321 were steeper than for NCo 310, perhaps suggesting that although CP 70–321 usually displays less damage, yield and quality may be affected more severely in the event of borer damage because of its higher sugar content. In Texas, the share agreements between farmers and the sugar mill mandate that the mill retains 40% of proceeds as compensation for milling, with economic losses also shared in the same ratio. Assuming the value of raw sugar is $420/t (907.18 kg), 20% bored internodes results in a loss of $1,181.04/ha ($477.96/acre). For average Texas sugarcane acreage of 18,200 ha (45,000 acres), total losses would be $21.5 M ($12.9 M to the producers and $8.6 M to the mill). The ineffectiveness of insecticides and their abandonment by Texas sugarcane growers make it imperative that pest management alternatives, such as resistant varieties and biological control agents, be investigated to alleviate the losses.