Tara P. Smith, B. Rogers Leonard, Abner M. Hammond and Rhett Gable
The sugarcane beetle is a sporadic pest of several crops including field corn, sugarcane and sweet potatoes across many southern states. Only the adult stage of these beetles is reported to cause crop injury. Although the sugarcane beetle has been documented as a pest in field corn for several decades, it has become a more common problem during recent years, severely reducing seedling plant stands. The beetles attack corn seedlings below the soil surface by feeding on the roots or the growing point of the plant. This feeding often causes the plants to wilt and die. Individual beetles are capable of damaging multiple plants in a row and severe infestations may require that the crop be replanted.
Granular organophosphate insecticides such as Lorsban 15G and Counter 15G applied in the seed furrow or banded across the row can reduce sugarcane beetle infestations in field corn. Seedling injury has also been reduced in field plots treated with a variety of different insecticides as rescue treatments including Capture 2EC, Lorsban 4EC and Baythroid 2EC. In spite of these treatments, however, significant plant injury and ultimate yield losses still occur. Treated Seed
A study conducted in 2004 at the LSU AgCenter’s Macon Ridge Research Station
in Winnsboro, La., examined the efficacy of selected seed treatments against sugarcane beetles in field corn. The neonicotinoid insecticides are widely used against many agricultural and urban pests because of their specificity to insects and safety to humans, livestock and pets. Seed treatments are also environmentally safe and do not require calibration of equipment. In addition, many of the neonicotinoids are systemic – they are translocated throughout the plant – which provides protection to seedlings. Insecticide treatments on field corn seed are the current standard integrated pest management practice in Louisiana to manage seed and seedling pests on field corn.
In small-plot field studies, corn seeds were treated with the neonicotinoid insecticides clothianidin (Poncho) at 0.25 and 0.45 milligrams active ingredient per seed, imidacloprid (Gaucho) at 0.60 milligrams active ingredient per seed and thiomethoxam (Cruiser) at 0.25 milligrams active ingredient per seed. Control seeds were treated with water only. Treatments were replicated five times in a randomized block design, where each treatment is randomly distributed within several similar subdivisions or blocks in the field to account for any field variation that may exist.
Polyvinylchloride pipe tubes 2 inches in diameter and 15 inches tall were placed 3 inches into the soil around emerged corn seedlings in “microplots.” Sugarcane beetles were collected at blacklights during the evening hours and were maintained on sweet potato roots until needed for infestations. The insects were starved 48 hours before infestation on corn seedlings. Sugarcane beetle adults were individually placed on 10 plants in each plot. Corn seedlings were infested at the growth stage when the collar of the second leaf was visible through the growth stage when the sixth-leaf collar was visible. Infested corn seedlings were then covered with a mesh screen cap secured by a rubber band. Feeding injury to corn plants and insect mortality were evaluated seven days after treatments began. Plant Injury Reduced
All treatments significantly reduced seedling injury when compared to the nontreated controls. After seven days, plant injury ranged from 44 percent (Poncho at 0.45 milligrams active ingredient per seed) to 92 percent in the nontreated controls (Figure 1). However, only Poncho at 0.45 milligrams per seed had significantly fewer injured plants when compared with the nontreated control plants. In addition, sugarcane beetle adult mortality was not significantly influenced by any insecticide treatment in the study.
The neonicotinoid insecticides used in the study are effective against other early-season pests of field corn including chinch bugs, wireworms and fire ants. At the rates tested, none of these treatments will eliminate sugarcane beetle damage to field corn seedlings. However, Poncho did significantly reduce seedling injury, and overall plant stands may be improved where seed treatments are integrated into a multidisciplinary pest management program.
LSU AgCenter scientists will be evaluating other rates of these products in future studies to define pesticide dose and pest response relationships. These neonicotinoid seed treatments are alternatives to traditional soil-incorporated insecticides for many pests and have improved the efficacy and efficiency of integrated pest management programs in field corn. However, sporadic pests such as the sugarcane beetle will continue to exploit weaknesses of specific pest management strategies, and producers should be aware that no IPM strategy is failsafe. (This article was published in the fall 2006 issue of Louisiana Agriculture.)