Crop yields and nematode population densities in triticale-cotton and triticale-soybean rotations

Triticale cv. Beagle 82, cotton cv. McNair 235, and soybean cv. Twiggs were arranged in three cropping sequences to determine the effects of fenamipho s and cropping sequence on nematode population densities and crop yields un der conservation tillage for 4 years. The cropping sequences were triticale (T)-cotton (C)-T-C, T-soybean (S)-T-S, and T-GT-S. Numbers of Meloidogyne incognita second-stage juveniles declined on triticale but increased on cot ton and soybean each year. Root-gall indices of cotton and soybean ranged f rom 1.00 to 1.08 (1 to 5 scale: 1 = 0%, 2 = 1% to 25%, 3 = 26% to 50%, 4 = 51% to 75%, and 5 = 76% to 100% of roots galled) each year and were not aff ected by fenamiphos treatment or cropping sequence. Numbers of Pratylenchus brachyurus were maintained on triticale and generally increased more on so ybean than on cotton. Population densities of Helicotylenchus dihystera wer e near or below detection levels in all plots during the first year and inc reased thereafter in untreated plots in the T-CT-C and T-STS sequences. Gen erally, yields of triticale in all cropping sequences declined over the yea rs. Yields of cotton and soybean were not affected by fenamiphos at 6.7 kg a.i./ha. Cotton and soybean were grown successfully with little or no suppr ession in yields caused by nematodes in conservation tillage following trit icale harvested for grain.