Southern root-knot nematode affects common cocklebur (Xanthium strumarium) interference with cotton

Authors: Webster, Theodore; Davis, Richard

Submitted to: Weed Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/4/2006
Publication Date: 3/1/2007
Citation: Webster, T.M., Davis, R.F. 2007. Southern root-knot nematode affects common cocklebur (Xanthium strumarium) interference with cotton. Weed Science. 55:143-146.

Interpretive Summary: Common cocklebur, among the 10 most common cotton weeds in the southern US, is a very competitive weed with agronomic crops. Nematodes are the most damaging pathogens of cotton, costing an estimated $6.7 billion in the US in 1994, with southern root-knot nematode causing the most damage. Interactions between weeds and nematodes and their effect on cotton yield have not been evaluated. Maximum yield loss from common cocklebur in the absence of nematodes exceeded 80%. The presence of nematodes at each common cocklebur density increased cotton yield loss 15 to 35%. Common cocklebur plant biomass was 25% greater in nematode treatments, likely due to the reduced competitiveness of the cotton plants in these plots. This study demonstrates that multiple pests can interact to cause an additive reduction in crop yield. With limited nematicide options, non-host-crop rotation is a critical component of a nematode management plan. The presence of nematode-susceptible weeds will have negative consequences, in terms of nematode populations, during the non-host-crop portion of the rotation. However, weed-nematode interactions in cropping systems may go beyond simply weeds serving as an alternate nematode host. The current research supports this contention, as common cocklebur and southern root-knot nematode caused an additive reduction in cotton yield that was greater than the cotton yield loss from either pest in isolation. Greater understanding of these interactions will improve the efficiency of IPM.

Technical Abstract: Southern root-knot nematode and common cocklebur will both interfere with cotton growth and yield. A greater understanding of the interaction of these pests on cotton growth and yield is needed for effective IPM (integrated pest management). An additive design was used in outdoor micro-plots with five common cocklebur densities (0, 1, 2, 4 and 8 plants per plot) growing in competition with cotton, with and without the presence of southern root-knot nematode. Differences in cotton height could not be detected among common cocklebur densities or nematode presence at 3 WAT, however differences in crop height were observed at 5 WAT between nematode treatments. In the absence of nematodes, the relationship between cotton yield loss and common cocklebur density was described by a rectangular hyperbole regression model (P<0.0001). Maximum yield loss from common cocklebur in the absence of nematodes exceeded 80%. In the presence of nematodes, there was a linear relationship between cotton yield loss and common cocklebur density (P=0.0506). The presence of nematodes at each common cocklebur density increased cotton yield loss 15 to 35%. Common cocklebur plant biomass was 25% greater in nematode treatments, likely due to the reduced competitiveness of the cotton plants in these plots. This study demonstrates that multiple pests can interact to cause an additive reduction in crop yield.