Reproduction of Pratylenchus hexincisus and P. scribneri in Corn Inbreds.

Population development of lesion nematodes was measured in 17 inbred lines of South Dakota and A619Ht dent corn. In two greenhouse groundbed tests, lines SD 101, SD 102, and SD 103 supported fewer than 1,000 Pratylenchus hexincisus per gram of dry root after 12 weeks. In an irrigated field test, inbred SD101 supported fewer than 1,000 P. scribneri per gram of dry root on each of two sampling dates, whereas line A619Ht supplied high populations of P. scribnerni on both dates. Inbreds SD45, 84742, and 84763 supported high populations of both P. hexincisus and P. scribneri.

Relationship of Yields and Pratylenchus spp. Population Densities in Dryland and Irrigated Corn.

Analyses of covariance were used to relate corn yields to population densities of Pratylenchus hexincisus in South Dakota dryland corn or P. scribneri in irrigated corn. The relationship for P. hexincisus was Y = 5,825 - 0.14X - 0.03X' where Y = yield (kg/ha), X = number of P. hexincisus per gram of dry root at midseason and X' = number at harvest. The relationship for P. scribneri was best described by Y = 7,400 - 0.06X' for nematode populations measured at harvest. Yield loss estimates indicated P. hexincisus was more damaging to dryland corn than was P. scribneri to irrigated corn.

Effect of Tylenchorhynchus robustoides on Growth of Buffalo Grass and Western Wheatgrass.

Tylenchorhynchus robustoides reduced (P = 0.05) growth of Agropyron smithii (western wheatgrass) at soil temperatures of 20, 25, 30, and 35 C. Growth reduction increased with increasing soil temperatures. Highest populations of T. robustoides were recovered at 25 and 30 C. Clipping weights of Buchloe dactyloides (buffalo grass) were reduced at 25 and 30 C; however, root/crown weights were reduced at 15, 20, 30, and 35 C in nematode infested vs. noninfested soil. Reproduction of T. robustoides was greater at 25, 30, and 35 C than at 20 C on B. dactyloides. In a greenhouse study, T. robustoides reduced clipping and root/crown weights of both grasses 24-64%.

Effect of Tylenchorhynchus nudus on Growth of Kentucky Bluegrass.

The effect of Tylenchorhynchus nudus on growth of Kentucky bluegrass was investigated under controlled environmental conditions in both a phytotron and a greenhouse. The nematode significantly reduced weights of clippings, crowns and roots. Pathogenicity was greater in sandy loam soil than in loam and was enhanced by submitting plants to nutrient and/or moisture stresses; soil nutrient level was most critical. The results suggest that T. nudus contributes significantly to summer decline of bluegrass lawns in South Dakota.