Submitted to: Nematology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/15/2003
Publication Date: 2/15/2004
Citation: Westphal, A., Robinson, A.F., Scott, A.W., Santini, J.B. 2004. Depth distribution of Rotylenchulus reniformis under crops of different host status and after fumigation. Nematology. 6(1):97-108.
Interpretive Summary: There are many kinds of microscopic worms called nematodes that feed on the roots of cotton and other crops, debilitating the plants and markedly decreasing yields. The direct losses to U.S. cotton farmers caused by nematodes each year are estimated by the National Cotton Council to exceed $300,000,000. The reniform nematode is one of the most important nematodes on cotton in the U.S. It also can damage and reproduce prolifically on roots of many types of soybean, allowing large numbers of nematodes to build up in the soil when soybean and cotton are planted in alternate years. Years ago, farmers in the Lower Rio Grande Valley of Texas tried growing soybeans in rotation with cotton and were dissatisfied with the crop yields they obtained. We considered the possibility, however, that this was because they planted types of soybean that were susceptible to the reniform nematode, which occurs in most of the areas there where cotton is grown. We found that susceptible soybean types did in fact suffer damage from the nematode and support high populations of the nematode in these soils. However, when a resistant soybean cultivar was planted, nematode populations in the soil decreased dramatically, and cotton planted the next year did not suffer much from nematode damage. Fumigation of soil at specific depths down to four feet showed that nematodes one to four feet deep in the soil were a key reason why growing resistant soybean was so beneficial and perhaps explained why the impact of nematode went unnoticed in the past, since most farmers and consultants only sample the top 6 inches or so of soil for nematodes. So, it looks like planting the right type of soybean and monitoring nematode populations deep in the soil to make sure they are kept under control, may be the key to success in growing soybean in rotation with cotton in these areas.
Technical Abstract: Population densities of Rotylenchulus reniformis were investigated in 15-cm sections in 0-120 cm depth under fallow, grain sorghum (cv. Asgrow 571), and soybean, susceptible (cv. DP6880RR) or resistant (cv. HY798) to R. reniformis. In 2000, population densities were monitored in non-fumigated plots and in plots that were preseason fumigated with 1,3-dichloropropene (1,3-D) at 38cm depth. Fallow, grain sorghum, and resistant soybean reduced incidence of R. reniformis down to 120-cm depth in comparison to susceptible soybean. In 2001, population densities were monitored under cotton in these plots and additional plots (soybean in 2000) that were preseason fumigated with 1,3-D at depths of 0-60, 60-120, or 0-120 cm. In 2000 non-fumigated plots, cotton fiber yields increased and average of 35% following fallow, grain sorghum or resistant soybean compared to following susceptible soybean. In the 2000 fumigated plots, cotton fiber yields were increased 38% following grain sorghum and resistant soybean over following susceptible soybean or fallow. Cropping the resistant soybean cv. Padre increased following cotton fiber yields over following the susceptible cv. Vernal by 34%. Fumigation of plots following susceptible cv. Vernal at 60-120 cm depth increased cotton fiber yields by 68% and the fumigation at 0-60 cm by 28% over the non-fumigated control. Population densities in 0-120 cm depth were a more accurate predictor for plant damage than population densities determined at 0-30 cm depth. The value of R. reniformis-resistant soybean cultivars for south Texas cotton sequences was confirmed and the importance of their effects on deep-occurring populations of R. reniformis demonstrated.