EFFECTS OF ALFALFA BLOTCH LEAFMINER ON CHEMICAL COMPONENTS OF ALFALFA

Abstract

Some effects of the alfalfa blotch leafminer (Agromyza frontella (Rond.)) on chemical components of alfalfa (Medicago sativa L.) were determined. At an early stage of infestation by adults, little or no change in the chemical components measured was found in leaves with 50 pinhole punctures/cm² or less in a greenhouse experiment. In leaves with more advanced degrees of infestation, the concentrations of chlorophyll, N and K decreased. A leaching of nitrogen compounds and K occurred from these infested leaves. In a field experiment a combination of cypermethrin application and three different cutting systems resulted in various degrees of infestation. The effect of these control measures on the concentrations of N, P and K in alfalfa leaves and stems was insignificant. The concentration of water-soluble carbohydrates, however, tended to be lower in the infested plants than the non-infested plants. Leafminer-infested alfalfa did not seem to lose dry matter or nutrients more than the non-infested plants during harvesting and haymaking operations. These results suggest that although the alfalfa blotch leafminer may not cause a great loss in forage yield or N, P and K of alfalfa, it may reduce the content of water-soluble carbohydrates.