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 lo ftini (Dyar) and Diatraea saccharalis (F.) damage approximate to 20% Of sug arcane internodes annually. We quantified the relationships between stalkbo rer damage and sugar yield and quality to estimate the monetary loss incurr ed at these levels of damage. We also compared damage estimates and sugar q uality 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 pu rity and mean sucrose content. Other variables (sugar per acre, cane per ac re, fiber, ash, and stalk weight) did not differ significantly between the 2 varieties. Sugar per acre, juice purity, stalk weight, cane per acre, suc rose per ton of sugarcane, and sucrose content all were inversely related t o percentage of bored internodes. Ash content increased with damage, consis tent with a plant displaying symptoms of stress. Regression slopes for CP 7 0-321 were steeper than for NCo 310, perhaps suggesting that although CP 70 -321 usually displays less damage, yield and quality may be affected more s everely in the event of borer damage because of its higher sugar content. I n Texas, the share agreements between farmers and the sugar mill mandate th at the mill retains 40% of proceeds as compensation for milling, with econo mic losses also shared in the same ratio. Assuming the value of raw sugar i s $420/t (907.18 kg), 20% bored internodes results in a loss of $1,181.04/h a ($477.96/acre). For avenge Texas sugarcane acreage of 18,200 ha (45,000 a cres), total losses would be $21.5 M ($12.9 M to the producers and $8.6 hi to the mill). The ineffectiveness of insecticides and their abandonment by Texas sugarcane growers make it imperative that pest management alternative s, such as resistant varieties and biological control agents, be investigat ed to alleviate the losses.