Effects of oximecarbamate, organophosphate and benzimidazole nematicides on life cycle stages of root-knot nematodes, Meloidogyne spp.

A study was made of the effects of concentrations of 2 to 32 ppm of oximecarbamate, organophosphate and benzimidazole nematicides on the hatch, larval viability and migration of Meloidogyne javanica, M. incognita and M. hapla and on development of M. javanica in roots. Aldicarb at less than 8 ppm had little effect on hatch and methomyl markedly affected only the hatch of M. hapla. As little as 2 ppm of fenamiphos or thionazin markedly reduced hatch of all three species but less than 8 ppm ethoprophos significantly reduced only the hatch of M. incognita and phorate had little effect on hatch. Benomyl and thiabendazole had no significant effects on hatch. When egg masses of M. incognita were transferred from nematicides which suppressed hatch to water, hatching occurred, but aldicarb, fenamiphos, ethoprophos and thionazin significantly reduced total hatch. None of the nematicides killed larvae of the three species immersed in 16 and 32 ppm solutions of them for 3 days. Aldicarb at 2 ppm reduced migrations of all three species; the effects of methomyl, fenamiphos or thionazin on migration varied according to species, while phorate, ethoprophos, benomyl or thiabendazole had little or no effect on migration. Aldicarb or thionazin at 2 ppm stopped development of M. javanica in roots of tomato seedlings while methomyl, ethoprophos or fenamiphos at 4 ppm reduced development by 60% and at 8 ppm of ethoprophos or fenamiphos or 16 ppm of methomyl, development was stopped. Phorate had little effect on development and benomyl or thiabendazole had no effect. Nematicide concentrations which reduced development prevented the normal orientation of larvae in the roots and reduced or prevented giant cell formation.     

Changes in photosynthetic and transpiration rates of cotton leaves infested with the cotton aphid, Aphis gossypii: Unrestricted infestation

The influence of aphid, Aphis gossypii, feeding on photosynthesis and transpiration in cotton plants was investigated under greenhouse conditions. Four population densities of 0, 5, 10, and 25 aphids were used to infest individual cotton leaves. Gas exchange rates were determined for single attached cotton leaves after 9, 18, and 27 days of aphid infestation. Aphid feeding changed photosynthetic rates and transpiration rates. These changes were proportional to the number of aphids and the length of infestation period. Photosynthetic rates were significantly reduced in infested leaves with 25 aphids over 18 days, whereas significant reduction in photosynthetic rates was recorded within 27 days in infested leaves with 5, 10, and 25 aphids in comparison to their respective control. Initial population of 10 aphids increased significantly the transpiration rate of infested leaves over 9 and 27 days. Leaves of plants with 25 aphids had significantly greater transpiration rate than the control at all times.