Weeds are a major problem in potato production in Florida and can reduce yields through direct competition for light, moisture, and nutrients, or by harboring insects and diseases that attack potatoes. Weeds can have a detrimental impact on tuber yield when compared to potatoes grown in weed-free conditions (Love et al. 1995; Nelson and Thoreson 1981). For example, Love et al. (1995) found a reduction in vine biomass, tuber biomass, and total yield in both 'Frontier Russet' and 'Russet Burbank' in weedy plots compared to weed-free plots. Weedy conditions also resulted in a greater number of small tubers and fewer US No. 1 grade tubers compared to weed-free conditions (Love et al. 1995). Nelson and Thoreson (1981) found that competition with weeds reduces both the average tuber size and the number of tubers. However, in both studies, there was little effect of weed competition on specific gravity (Love et al. 1995; Nelson and Thoreson 1981). Aside from impacts on the physiological formation of yield during the season, weeds present at harvest can be detrimental to yield by increasing mechanical damage to the tubers and reducing harvesting efficiency by slowing the harvesting operation, leaving un-dug tubers in the ground, and/or carrying them over the conveying chain.
Early season competition with weeds is extremely critical; therefore, weed control measures should be emphasized during this period. Potatoes may be planted during a seven-month period in Florida. During this period, variable climatic conditions influence the diversity and severity of weed species present. Growers should plan a total weed control program that integrates chemical, mechanical, and cultural methods to fit their weed species and production practices.
One cultural method that may have an impact on weed control is row spacing. Love et al. (1995) compared the effect of two row spacings (28" and 37.8") on weed competition and found no difference in either weed and vine biomass or tuber yield. This may be related to their findings that row spacing did not greatly affect the time to canopy closure, which impacts the establishments of weeds. They also compared three within-row seed piece spacings (5.9", 9.8", and 13.8") and found a small numerical decrease in weed biomass with decreasing within-row spacing, likely because of more rapid vine elongation and a greater impact on canopy closure (Love et al. 1995).
Beyond row and plant spacing, researchers have studied other management practices for weed control, such as cover crops. Boydston and Hang (1995) studied the impact of a rapeseed crop preceding potatoes on the presence of weeds. Rapeseed contains a compound called glucosinolate that has been found to have negative effects on seed germination (Evenari 1949). In a two-year study comparing rapeseed and sudangrass covers, rapeseed produced more biomass and had a greater reduction in midseason and final weed density in the following potato crop than sudangrass (Boydston and Hang 1995). Potatoes following rapeseed (with or without herbicide) yielded higher than comparative plots following sudangrass, while the specific gravity of tubers was not affected by either cover (Boydston and Hang 1995).
Cultivation is another effective way to manage weeds early in the season, a time when weed presence is most detrimental to potato growth and yield (Connell, Binning, and Schmitt 1999; Nelson and Thoreson 1981). Weeds that emerge before potatoes have been shown to be the most competitive with the crop (Love et al. 1995). Connell, Binning, and Schmitt (1999) determined that the canopy of the potato crop would continue to shade out weeds emerging after initial cultivation and herbicide applications at 7–8 weeks after crop emergence. This timeline may vary by cultivar because of variable canopy structures. In addition, if the canopy is damaged, additional herbicide applications may be necessary until the canopy recovers (Connell, Binning, and Schmitt 1999). During hilling operations, rolling cultivators behind the hilling blades can uproot many annual weeds that may have survived preplant herbicides. Cultivation and hilling, while useful, also disrupt the efficacy of several soil-applied herbicides. For cultivars that require several hilling operations during the season, additional herbicides may be necessary during or directly following hilling and cultivation operations. This combination of practices can greatly enhance and extend weed control during the season.
Herbicide performance depends upon weather, irrigation, soil properties, proper selection for weed species to be controlled, and accurate herbicide application and timing. Obtain consistent results by reading the herbicide label and other information concerning the proper application and timing of each herbicide. To avoid confusion between commercial formulations, the suggested rates listed in Table 1 are stated in pounds of active ingredient per acre (lb. a.i./A). On marl and sandy soils with low organic matter, the lower rates should be applied. All herbicides listed below have been tested in research trials in Florida with successful results.
When applying an herbicide for the first time in a new area, use in a small trial area first. Before applying an herbicide, carefully read and follow the label.
Boydston, R. A., and A. Hang. 1995. "Rapeseed (Brassica napus) Green Manure Crop Suppresses Weeds in Potato (Solanum tuberosum)." Weed Technology 9 (4): 669–675.
Connell, T. R., L. K. Binning, and W. G. Schmitt. 1999. "A Canopy Development Model for Potatoes." American Journal of Potato Research 76 (3): 153–159.
Evenari, M. 1949. "Germination Inhibitors." The Botanical Review 15 (3): 153–194.
Love, S. L., C. V. Eberlein, J. C. Stark, and W. H. Bohl. 1995. "Cultivar and Seedpiece Spacing Effects on Potato Competitiveness with Weeds." American Journal of Potato Research 72 (4): 197–213.
Nelson, D. C., and M. C. Thoreson. 1981. "Competition Between Potatoes (Solanum tuberosum) and Weeds." Weed Science 29 (6): 672–677.
Preemergence chemical weed control in potato.
Postemergence chemical weed control in potato