Utilizing management zones for Rotylenchulus reniformis in Cotton: Effects on nematode levels, crop damage, and Pasteuria sp.

Authors: Davis, Richard; ARYAL, S - University Of Georgia; PERRY, C - University Of Georgia; SULLIVAN, D - Turf Scout,llc; Timper, Patricia - Patty; ORTIZ, B - Auburn University; STEVENSON, K - University Of Georgia; VELLIDIS, G - University Of Georgia; HAWKINS, G - University Of Georgia

Submitted to: Crop Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/10/2013
Publication Date: 5/10/2013
Citation: Davis, R.F., Aryal, S.K., Perry, C.D., Sullivan, D.G., Timper, P., Ortiz, B.V., Stevenson, K.L., Vellidis, G., Hawkins, G. 2013. Utilizing management zones for Rotylenchulus reniformis in cotton: Effects on nematode levels, crop damage, and Pasteuria sp. Crop Protection Journal. 50:53-60.

Interpretive Summary: The effect of soil texture on nematode levels is the primary basis for site-specific nematode management. Management zones (MZs) are sampled independently and decisions are based on those sample results. MZs based on soil electrical conductivity (EC, a proxy for soil texture) have not been tested for R. reniformis. We tested 1) whether reniform nematode levels and the amount of damage caused to cotton differed among MZs, 2) if the relative effectiveness of nematicides differed among MZs, and 3) whether the prevalence of Pasteuria sp. (a bacterial parasite of nematodes) on reniform nematodes differed among MZs and nematicide treatments. A field was divided into three MZs for a study conducted from 2008 to 2010. MZ3 had sandier soil than MZ1 or MZ2, which were similar to each other, and MZ2 had higher elevation than MZ1 or MZ3, which were similar to each other. The differences in soil texture in this study influenced reniform nematode population levels with greater nematode reproduction in finer-textured soil. Elevation also had an effect on reniform nematode levels with higher elevation having lower levels. The differences in elevation, which we believe led to differences in soil moisture, had a similar or greater effect on reniform nematode levels than did the differences in soil texture. Treatment effects on reniform nematode levels were the same in all MZs (no MZ × treatment interactions). The effects of texture and elevation on yield were similar to the effects on nematode levels. We observed endospores of Pasteuria sp. on reniform nematodes at the field site used for this study. Pasteuria sp. generally had greater spore attachment to juvenile reniform nematodes than to adults. There were no differences among MZs in percentage of reniform nematodes with endospores, but the number of spores per nematode was lower in MZ3, which had the greatest sand content. The nematicide aldicarb did not reduce the prevalence of Pasteuria sp., but 1,3-dichloropropene + aldicarb reduced both the percentage of nematodes with endospores and the number of attached endospores. Because the level of reniform nematode was above the action threshold in all MZs, a uniform rate of nematicide would have been recommended for this field and there would have been no cost savings from utilizing nematode MZs. However, we believe that utilizing MZ based largely on soil texture and elevation as a method of subdividing a large field into smaller units can be a useful contribution to nematode management and should be more widely utilized even though it will not provide cost savings in all fields.

Technical Abstract: The effect of soil texture on nematode levels is the primary basis for site-specific nematode management. Management zones (MZs) are sampled independently and decisions are based on those sample results. MZs based on soil electrical conductivity (EC, a proxy for soil texture) have not been tested for R. reniformis. We tested 1) whether R. reniformis levels and the amount of damage caused to cotton differed among MZs, 2) if the relative effectiveness of nematicides differed among MZs, and 3) whether the prevalence of Pasteuria sp. on R. reniformis differed among MZs and nematicide treatments. A field was divided into three MZs for a study conducted from 2008 to 2010. MZ3 had sandier soil than MZ1 or MZ2, which were similar to each other, and MZ2 had higher elevation than MZ1 or MZ3, which were similar to each other. The differences in soil texture in this study influenced R. reniformis population levels with greater nematode reproduction in finer-textured soil. Elevation also had an effect on R. reniformis levels with higher elevation having lower levels. The differences in elevation, which we believe led to differences in soil moisture, had a similar or greater effect on R. reniformis levels than did the differences in soil texture. Treatment effects on R. reniformis levels were the same in all MZs (no MZ × treatment interactions). The effects of texture and elevation on yield were similar to the effects on nematode levels. We observed endospores of Pasteuria sp., a bacterial parasite of nematodes, on R. reniformis at the field site used for this study. Pasteuria sp. generally had greater spore attachment to juvenile R. reniformis than to adults. There were no differences among MZs in percentage of R. reniformis with endospores, but the number of spores per nematode was lower in MZ3, which had the greatest sand content. Aldicarb did not reduce the prevalence of Pasteuria sp., but 1,3-dichloropropene + aldicarb reduced both the percentage of R. reniformis with endospores and the number of attached endospores. Because the level of R. reniformis was above the action threshold in all MZs, a uniform rate of nematicide would have been recommended for this field and there would have been no cost savings from utilizing nematode MZs. However, we believe that utilizing MZ based largely on soil texture and elevation as a method of subdividing a large field into smaller units can be a useful contribution to nematode management and should be more widely utilized even though it will not provide cost savings in all fields.