Impact of Banks Grass Mite1Damage to Yield and Quality of Maize Silage

Banks grass mite, Oligonychus pratensis (Banks), is a major pest of maize, Zea mays L., causing significant economic loss of yield of maize grown for grain. However, damage and economic loss to maize grown for silage are not well documented. This study evaluated damage associated with infestation by different numbers of mites (noninfested check, low, medium, and large) and subsequent effects on yield and quality of maize harvested for silage. Mite densities in each of the designated infested treatments steadily increased weekly, but at different level, until after Aug 10. Weekly changes in damage rating level corresponded to the increases of mite densities that occurred in each of the infested treatments. The population decline of mites after this date was associated with increasing predator densities. No significant differences in silage yields were detected between noninfested (80.21 Mt/ha), low (82.38 MT/ha), and medium (78.87 MT/ha) infestations, but significant differences occurred with the high-infested (70.43 MT/ha) treatment. Regression analysis between mite damage and yield by plot showed losses occurred after the cumulative damage was >20. Economic loss from maize infested with large numbers of mites ranged for -$97.80 to -489.00 when silage prices ranged from $10.00 to 50.00 per ha. Damage to maize by any of the mite-infested levels did not detrimentally affect the nutritional quality of maize cut for silage. The data indicated a threshold could be developed for making management decisions. Impact of predators in managing spider mites also is discussed.