Determining purple nutsedge sensitivity to foliar and soil applied residues


University of Florida

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Southeast (GA, FL, AL)

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Experiments were conducted using imazapic and sulfentrazone applied to the soil to determine if soil-borne microbe populations were influencing imazapic activity. Unfortunately, the results of this experiment were highly variable. Pre-germinated tubers (roots extending from the tuber) to ensure that healty, live tubers were used in the experiment to minimize variation between pots. Although pre-germinated tubers were used, they would often not develop sprouts, even in the untreated pots. Because of the high variability in planted material, data from this experiment will not be shown. 
Foliar Bioassay 
The standard field use rate of imazapic is 0.063 lb ai/ A. From the results in Table 1, the Citra population (suspected resistant) required an almost 2X rate to reduce growth by 50%. This is significant considering that the Tifton population (known susceptible) only required 0.027 lb ai/A (less than a ½X rate) for a 50% reduction in biomass. This essentially translates to a 1 OX difference in imazapic rate to elicit the same response from the susceptible and suspected resistant populations. Furthermore, the comparison of these 
two populations to glyphosate revealed statistically similar EC50 values of 1.34 and 1.01 lb ai/A. This indicates that there is likely a physiological mechanism within the plant that is conferring the tolerance/resistance to imazapic alone. 
Though not included in the original proposal, the Citra tubers were shared with a collaborator at USDA. He tested this population in outside mesocosms and sprayed with 
dose-rates of imazapic. At this location, the EC5o value for the Citra population was 0.012 lb ai/ A (Figure 1 ). These data suggest that the Citra population IS NOT demonstrating increased tolerance to imazapic. 
The reason for the great difference between the two test sites is unknown. It is possible that the Citra population is a mixture ofresistant and susceptible and that the USDA location received a disproportionate number of susceptible tubers. Other reasons for this vast difference between locations are unknown. Additional research will need to be conducted to confirm or deny these results. 

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