Photo: Kochia, southwest Montana. © 2020 Delena Norris-Tull
Pesticide Drift
Summaries of the research and commentary by Dr. Delena Norris-Tull, Professor Emerita of Science Education, University of Montana Western, October 2020, updated November 2024.
Vieira, et al., 2020, report that, “Glyphosate, 2,4-D, and dicamba spray drift have been reported to cause severe injury on sensitive vegetation and crops….While the consequences of herbicide drift towards sensitive crops are extensively investigated in the literature, scarce information is available on the consequences of herbicide drift towards other plant communities surrounding agricultural landscapes… Herbicide drift exposure could be detrimental to long-term weed management as numerous weed species have evolved herbicide resistance following recurrent applications of low herbicide rates...In addition, herbicide resistance has been widely reported in weed populations inhabiting field margins and ditches surrounding agricultural landscapes…. Recombination and accumulation of minor resistance alleles can occur at a faster rate in cross-pollinated species, such as Palmer amaranth and waterhemp, during recurrent selection with low rates of herbicides.” They summarized results from previous studies that indicated that recurrent low level herbicide applications, such as occurs with herbicide drift, can cause population shifts that result in reduced sensitivity to various herbicides.
Vieira, et al., 2020, conducted a study in Nebraska of the response of Palmer amaranth and waterhemp to repeated herbicide applications of various doses of glyphosate, 2,4-D and dicamba. Using a low speed wind tunnel, they simulated the effects of wind drift. Calculating the biomass of the P2 offspring, Vieira, et al., 2020, found that glyphosate drift had “increased plant mortality on Palmer amaranth (81–95%...) compared to 2,4-D (16–36%...) and dicamba (23–45%...). 2,4-D drift resulted in higher plant mortality on waterhemp (37–61%...) compared to glyphosate (18–41%...) and dicamba (16–36%...). Both species had similar mortality when exposed to dicamba drift.”
Vieira, et al., 2020, found that, “The Palmer amaranth population from Perkins County evolved glyphosate resistance (54.7-fold…) [an unprecedented shift], after being recurrently exposed to glyphosate drift with the air inclusion nozzle. The Perkins population exposed to 2,4-D drift with the air inclusion nozzle had 2.5-fold shift… after two selection rounds, whereas the progeny exposed to 2,4-D drift with the flat fan nozzle had a 1.8-fold shift. On the other hand, the Palmer amaranth population from Chase County had no resistance shift after being recurrently selected with 2,4-D drift with both air inclusion and flat fan nozzles. Moreover, both Palmer amaranth populations had no sensitivity shift following dicamba drift selection with both air inclusion and flat fan and nozzles.”
“The waterhemp population from Stanton County showed no evidence of resistance shift when recurrently selected with glyphosate drift with the air inclusion nozzle, whereas plants exposed to glyphosate drift with the flat fan nozzle had a 2-fold glyphosate resistance shift. The Thayer population had a 2.4 and 3.3-fold glyphosate resistance shift after being recurrently exposed to glyphosate drift with the air inclusion and the flat fan nozzles, respectively. The Thayer population also had its 2,4-D sensitivity reduced after recurrent exposure to 2,4-D drift using the air inclusion (2.2-fold) and the flat fan nozzle (1.7-fold), whereas no shifts were observed for the Stanton population. Recurrent exposure to dicamba drift with the air inclusion and the flat fan nozzles resulted in dicamba sensitivity shifts in the Thayer population (1.5 and 2.2-fold shift, respectively). The Stanton population also had its sensitivity to dicamba increased, but only for progenies exposed to dicamba drift with the flat fan nozzle (2.4-fold).”
Vieira, et al., 2020, conclusions: “Herbicide sensitivity reduction in this study varied across weed species, weed population, spray drift potential (nozzle), and herbicide active ingredient. In this study, waterhemp was more prone to herbicide sensitivity shifts following herbicide drift selection compared to Palmer amaranth… Glyphosate sensitivity reduction was predominant over 2,4-D and dicamba… The results of this study confirm that herbicide drift towards field margins can rapidly select for biotypes with reduced herbicide sensitivity with minor and major herbicide resistance mechanisms. Preventing the establishment of resistance prone weeds on field margins and ditches in agricultural landscapes is an important management strategy.” This study also verified previous studies that showed that the air inclusion nozzle resulted in far less herbicide particle drift than the flat fan nozzle.
Felsot, et al., 2011, evaluated the effectiveness of various techniques to reduce pesticide spray drift. They point out that there is a lack of uniformity in how the magnitude of spray drift and its effects are measured across countries. There are no common procedures between countries, even within a single chemical company, for estimating chemical residues in water or on non-target organisms. “There is no universal consensus on how to assess mitigation.”
Felsot, et al., 2011, provide an overview of the history of concerns about spray drift, starting with the global use and impacts of the insecticide DDT and the herbicide 2,4-D. As the acutely toxic organophosphorus compounds began to replace DDT as insecticides, their use generated such a high level of concern that land managers paid less attention to the potential impacts of herbicide spray drifts. “But, with the development of more selective herbicides in the mid-1980s that were better–suited for post–emergence application, the potential of spray drift to damage susceptible plants became a more widespread problem. Indeed, the potential problems associated with spray drift have likely grown as widespread use of glyphosate has increased in conjunction with the planting of glyphosate-resistant soybean and corn.” There are growing worldwide concerns about water contamination from agrochemical residues, particularly in regards to effects on aquatic invertebrates and fish.
Felsot, et al., 2011, present an overview of the many variables that can affect spray drift. In the 1990s, the US agroindustries established the Spray Drift Task Force, to assess the impacts of spray drift. This task force developed the computer model, AgDRIFT, to predict spray drift. The US EPA has proposed (as of 2011) updated guidance for agrichemical drift labeling, for additional risk assessments related to human health, water resources, and wildlife. Felsot, et al., 2011, provide summaries of the risk assessment models used worldwide. And they provide an overview of the research on various techniques that have been shown to reduce spray drift. They provide data on the effectiveness of various spray drift agents and spray nozzles.
Felsot, et al., 2011, report that buffer zones have been found to help reduce the impact of spray drift, but the width of an effective buffer zone can vary, depending on the herbicide used, the herbicide drop sizes, the wind velocity, and the type of vegetation. In field experiments spray drift has been detected as far away as 150m. But a buffer zone of 3-6m has been shown to dramatically decrease the amount of spray in various settings. In a study of 17 chemicals, including 10 herbicides, “Creation of a 3 m buffer zone decreased drift deposition in a ditch by a minimum of 95 %. Adjacent to the buffer zone only 4 of the 17 agrochemicals investigated posed a (minor) risk to aquatic organisms. With a 6-m buffer zone no drift deposition in the ditch could be measured.” Larger buffer zones may be needed for diverse environmental settings. And much wider buffer zones are needed for aerial chemical applications, as spray drift is dramatically increased.
Surrounding farm fields with windbreaks (fences, walls, or trees), or placing windbreaks upwind of the fields or close to water bodies, has also been shown to be effective at reducing spray drift. Hedgerows of trees 7-8 m tall with good leaf density are very effective. Trees with needle-like leaves (e.g., evergreen conifers) have been shown to be more effective at capturing spray drift than broadleaf trees.
Felsot, et al., 2011, conclude with concerns about the lack of uniform, global, measures for spray drift risk assessment: “Regulatory agencies have generally not used empirical drift studies or modelling to estimate exposure to non-target plant or livestock and humans.”
As an example of one experimental study on spray drift, VanGessel, et al., 2005, evaluated three drift control agents (materials added to liquid herbicide mixtures) to determine whether they were effective in reducing herbicide drift and increasing herbicide efficacy. Unintended drift of herbicides, caused by wind or water, can result in significant injury to native plants, other crops, humans, animals, and water sources. Drift control agents are supposed to “result in a coarser spray with a higher percentage of larger droplets and lower percentage of droplets prone to drift.” VenGessel, at al., 2005, examined the effectiveness of these agents by “evaluating plant response of adjacent, susceptible [crop] plants.”
Their first study, in 1999 and 2000, evaluated the effect of drift control agents on herbicide efficacy. The three brands tested were Breeze Ease, Windbrake, and Border EG. They compared the efficacy of the agents and the effects of two different spray nozzles, flat-fen and flood. The herbicide used in the sprayers was RoundUp Ultra (glyphosate). The control was water. The crops were glyphosate-resistant soybeans, planted in 76 cm wide rows, and the non-target sensitive crop was sorghum, planted in 18-cm wide rows, parallel to the soybean rows. The rows were separated by 1.5 meters. The two crops were planted at the same time. The sorghum received soil-applied metolachlor plus atrazine.
“Treatments were applied 6 weeks after planting. The plots were sprayed using a C02-pressurized backpack sprayer and a handheld boom, held in the stream of air generated from the canon-style sprayer... As soybean were sprayed, drift was measured with two water-sensitive (WS) cards placed at various heights above the ground. These cards change color (from yellow to blue) when water comes in contact with the card. The WS cards were evaluated for spray coverage on a scale of 0 = no coverage (all yellow) to 100 = total coverage (all blue).”
“The soybean plots were rated for weed control, and sorghum was rated for visual injury 2 weeks after treatment.” The following year, the experiments were repeated, and the crops were evaluated 4 weeks after treatment. “Visual estimates were based on 100% equals complete plant death and 0% equals no weed control or crop injury. Percent spray coverage of the WS cards was evaluated visually. Grain sorghum was harvested both years from the four rows adjacent to soybean, and in 2000, the remaining 12 rows were harvested separately. In 2000, weeds in the 1.5-m area between the soybean and sorghum were harvested for fresh weights. In both years there were four replications.”
“A second study [also in 1999 and 2000] determined the effect of the drift control agents on herbicide performance. This study was designed as a two-factor factorial, drift control agents and herbicide type (contact vs. translocated herbicides). A nontreated control was included for comparison. The [same] three drift control agents… were used at the same rates and were included in treatments of acifluorfen or glyphosate. Acifluorfen is a contact herbicide that does not translocate in the plant, whereas glyphosate needs to translocate from leaves to the meristematic regions of the plant for effective control. Treatments were applied with flat-fan nozzles…, and herbicides were applied at reduced rates of 0.4 kg ae/ha glyphosate and 0.2 kg ai/ha acifluorfen. Acifluorfen treatments included a nonionic surfactant at 0.25% v/v.”
“In 1999, clethodim (0.2 kg ai/ha) was applied to plots treated with acifluorfen to control large crabgrass …infestations 3 wk after treatments were applied. In 2000, clethodim was included with the acifluorfen treatments. There were three replications for each year… No-tillage, double-cropped soybean (glyphosate-resistant…) was planted in seven 38-cm-wide rows... Treatments were applied 3 wk after planting. Visual estimates of weed control were made 2 wk after treatment... Plots were mechanically harvested to determine soybean yield.”
VanGessel, et al., 2005, results of the first study: “The drift control agents did not reduce spray drift compared with a spray mixture without a drift control agent for either the flood or flat-fan type nozzles… In general, more drift was recorded on the higher WS card (placed 36 cm above the ground) than the lower cards (placed 13 cm above the ground). Percent coverage values were higher in 1999 than 2000. However, sorghum injury was greater in 2000 than 1999.”
“Drift control agents did not reduce the injury observed on grain sorghum…Number of sorghum rows injured, severity of injury to sorghum row closest to the spray boom, and an overall plot injury rating did not differ among the drift control agents or the spray mixture without a drift control agent, regardless of the nozzle type used. Overall, sorghum injury was greater in 2000 than 1999… In 2000, treatments were applied with a wind of 8 to 13 km/h, with gusts up to 24 km/h. The wind direction was the same as the direction of the canon-style sprayer. In 1999, there was no wind at the time of application. The increased injury in 2000 is postulated to be the result of the additional wind.”
“In 2000, plant biomass was collected in the 1.5- m area separating the soybean and grain sorghum... The amount of weed biomass was similar for all treatments containing glyphosate, regardless of whether a drift control agent was added. In all cases, the spray drift reduced the plant biomass compared with the nontreated areas.”
“Similar to grain sorghum injury, sorghum yield was reduced for all treatments containing glyphosate in 1999, regardless of drift control agent... In 2000, sorghum yield was lower with glyphosate application with flood nozzles, regardless of drift control agent... Overall yield was not reduced for the flat-fan nozzles. However, yield of the four rows closest to the soybean was reduced by glyphosate….The canon-style sprayer generated wind speeds higher than speeds used in wind tunnel studies... The higher wind speed may not have allowed the larger droplets, created by the drift control agents, to settle out over the short distance used in this study…However, herbicides are often applied with wind speeds as high as or higher than those recorded in this study….The addition of the drift control agents did not adversely affect glyphosate performance for control of summer annual weeds…[But, possibly due to low rainfall] none of the treatments provided commercially acceptable weed control in 1999.”
VanGessel, et al., 2005, results of the second study: “Drift control agents did not affect the efficacy of glyphosate or acifluorfen, a translocated and contact herbicide, respectively. Weed control was as good with no drift control agents as with the drift control agents included.” The two herbicides performed somewhat differently for different weed species. Overall, glyphosate provided better weed control.
VanGessel, et al., 2005, conclusions: “Spray drift over a short distance was not reduced with the three drift control agents evaluated, and these drift control agents did not alter weed control.”
References:
Links to other impacts of herbicides and other pesticides:
Pesticide Drift
Summaries of the research and commentary by Dr. Delena Norris-Tull, Professor Emerita of Science Education, University of Montana Western, October 2020, updated November 2024.
Vieira, et al., 2020, report that, “Glyphosate, 2,4-D, and dicamba spray drift have been reported to cause severe injury on sensitive vegetation and crops….While the consequences of herbicide drift towards sensitive crops are extensively investigated in the literature, scarce information is available on the consequences of herbicide drift towards other plant communities surrounding agricultural landscapes… Herbicide drift exposure could be detrimental to long-term weed management as numerous weed species have evolved herbicide resistance following recurrent applications of low herbicide rates...In addition, herbicide resistance has been widely reported in weed populations inhabiting field margins and ditches surrounding agricultural landscapes…. Recombination and accumulation of minor resistance alleles can occur at a faster rate in cross-pollinated species, such as Palmer amaranth and waterhemp, during recurrent selection with low rates of herbicides.” They summarized results from previous studies that indicated that recurrent low level herbicide applications, such as occurs with herbicide drift, can cause population shifts that result in reduced sensitivity to various herbicides.
Vieira, et al., 2020, conducted a study in Nebraska of the response of Palmer amaranth and waterhemp to repeated herbicide applications of various doses of glyphosate, 2,4-D and dicamba. Using a low speed wind tunnel, they simulated the effects of wind drift. Calculating the biomass of the P2 offspring, Vieira, et al., 2020, found that glyphosate drift had “increased plant mortality on Palmer amaranth (81–95%...) compared to 2,4-D (16–36%...) and dicamba (23–45%...). 2,4-D drift resulted in higher plant mortality on waterhemp (37–61%...) compared to glyphosate (18–41%...) and dicamba (16–36%...). Both species had similar mortality when exposed to dicamba drift.”
Vieira, et al., 2020, found that, “The Palmer amaranth population from Perkins County evolved glyphosate resistance (54.7-fold…) [an unprecedented shift], after being recurrently exposed to glyphosate drift with the air inclusion nozzle. The Perkins population exposed to 2,4-D drift with the air inclusion nozzle had 2.5-fold shift… after two selection rounds, whereas the progeny exposed to 2,4-D drift with the flat fan nozzle had a 1.8-fold shift. On the other hand, the Palmer amaranth population from Chase County had no resistance shift after being recurrently selected with 2,4-D drift with both air inclusion and flat fan nozzles. Moreover, both Palmer amaranth populations had no sensitivity shift following dicamba drift selection with both air inclusion and flat fan and nozzles.”
“The waterhemp population from Stanton County showed no evidence of resistance shift when recurrently selected with glyphosate drift with the air inclusion nozzle, whereas plants exposed to glyphosate drift with the flat fan nozzle had a 2-fold glyphosate resistance shift. The Thayer population had a 2.4 and 3.3-fold glyphosate resistance shift after being recurrently exposed to glyphosate drift with the air inclusion and the flat fan nozzles, respectively. The Thayer population also had its 2,4-D sensitivity reduced after recurrent exposure to 2,4-D drift using the air inclusion (2.2-fold) and the flat fan nozzle (1.7-fold), whereas no shifts were observed for the Stanton population. Recurrent exposure to dicamba drift with the air inclusion and the flat fan nozzles resulted in dicamba sensitivity shifts in the Thayer population (1.5 and 2.2-fold shift, respectively). The Stanton population also had its sensitivity to dicamba increased, but only for progenies exposed to dicamba drift with the flat fan nozzle (2.4-fold).”
Vieira, et al., 2020, conclusions: “Herbicide sensitivity reduction in this study varied across weed species, weed population, spray drift potential (nozzle), and herbicide active ingredient. In this study, waterhemp was more prone to herbicide sensitivity shifts following herbicide drift selection compared to Palmer amaranth… Glyphosate sensitivity reduction was predominant over 2,4-D and dicamba… The results of this study confirm that herbicide drift towards field margins can rapidly select for biotypes with reduced herbicide sensitivity with minor and major herbicide resistance mechanisms. Preventing the establishment of resistance prone weeds on field margins and ditches in agricultural landscapes is an important management strategy.” This study also verified previous studies that showed that the air inclusion nozzle resulted in far less herbicide particle drift than the flat fan nozzle.
Felsot, et al., 2011, evaluated the effectiveness of various techniques to reduce pesticide spray drift. They point out that there is a lack of uniformity in how the magnitude of spray drift and its effects are measured across countries. There are no common procedures between countries, even within a single chemical company, for estimating chemical residues in water or on non-target organisms. “There is no universal consensus on how to assess mitigation.”
Felsot, et al., 2011, provide an overview of the history of concerns about spray drift, starting with the global use and impacts of the insecticide DDT and the herbicide 2,4-D. As the acutely toxic organophosphorus compounds began to replace DDT as insecticides, their use generated such a high level of concern that land managers paid less attention to the potential impacts of herbicide spray drifts. “But, with the development of more selective herbicides in the mid-1980s that were better–suited for post–emergence application, the potential of spray drift to damage susceptible plants became a more widespread problem. Indeed, the potential problems associated with spray drift have likely grown as widespread use of glyphosate has increased in conjunction with the planting of glyphosate-resistant soybean and corn.” There are growing worldwide concerns about water contamination from agrochemical residues, particularly in regards to effects on aquatic invertebrates and fish.
Felsot, et al., 2011, present an overview of the many variables that can affect spray drift. In the 1990s, the US agroindustries established the Spray Drift Task Force, to assess the impacts of spray drift. This task force developed the computer model, AgDRIFT, to predict spray drift. The US EPA has proposed (as of 2011) updated guidance for agrichemical drift labeling, for additional risk assessments related to human health, water resources, and wildlife. Felsot, et al., 2011, provide summaries of the risk assessment models used worldwide. And they provide an overview of the research on various techniques that have been shown to reduce spray drift. They provide data on the effectiveness of various spray drift agents and spray nozzles.
Felsot, et al., 2011, report that buffer zones have been found to help reduce the impact of spray drift, but the width of an effective buffer zone can vary, depending on the herbicide used, the herbicide drop sizes, the wind velocity, and the type of vegetation. In field experiments spray drift has been detected as far away as 150m. But a buffer zone of 3-6m has been shown to dramatically decrease the amount of spray in various settings. In a study of 17 chemicals, including 10 herbicides, “Creation of a 3 m buffer zone decreased drift deposition in a ditch by a minimum of 95 %. Adjacent to the buffer zone only 4 of the 17 agrochemicals investigated posed a (minor) risk to aquatic organisms. With a 6-m buffer zone no drift deposition in the ditch could be measured.” Larger buffer zones may be needed for diverse environmental settings. And much wider buffer zones are needed for aerial chemical applications, as spray drift is dramatically increased.
Surrounding farm fields with windbreaks (fences, walls, or trees), or placing windbreaks upwind of the fields or close to water bodies, has also been shown to be effective at reducing spray drift. Hedgerows of trees 7-8 m tall with good leaf density are very effective. Trees with needle-like leaves (e.g., evergreen conifers) have been shown to be more effective at capturing spray drift than broadleaf trees.
Felsot, et al., 2011, conclude with concerns about the lack of uniform, global, measures for spray drift risk assessment: “Regulatory agencies have generally not used empirical drift studies or modelling to estimate exposure to non-target plant or livestock and humans.”
As an example of one experimental study on spray drift, VanGessel, et al., 2005, evaluated three drift control agents (materials added to liquid herbicide mixtures) to determine whether they were effective in reducing herbicide drift and increasing herbicide efficacy. Unintended drift of herbicides, caused by wind or water, can result in significant injury to native plants, other crops, humans, animals, and water sources. Drift control agents are supposed to “result in a coarser spray with a higher percentage of larger droplets and lower percentage of droplets prone to drift.” VenGessel, at al., 2005, examined the effectiveness of these agents by “evaluating plant response of adjacent, susceptible [crop] plants.”
Their first study, in 1999 and 2000, evaluated the effect of drift control agents on herbicide efficacy. The three brands tested were Breeze Ease, Windbrake, and Border EG. They compared the efficacy of the agents and the effects of two different spray nozzles, flat-fen and flood. The herbicide used in the sprayers was RoundUp Ultra (glyphosate). The control was water. The crops were glyphosate-resistant soybeans, planted in 76 cm wide rows, and the non-target sensitive crop was sorghum, planted in 18-cm wide rows, parallel to the soybean rows. The rows were separated by 1.5 meters. The two crops were planted at the same time. The sorghum received soil-applied metolachlor plus atrazine.
“Treatments were applied 6 weeks after planting. The plots were sprayed using a C02-pressurized backpack sprayer and a handheld boom, held in the stream of air generated from the canon-style sprayer... As soybean were sprayed, drift was measured with two water-sensitive (WS) cards placed at various heights above the ground. These cards change color (from yellow to blue) when water comes in contact with the card. The WS cards were evaluated for spray coverage on a scale of 0 = no coverage (all yellow) to 100 = total coverage (all blue).”
“The soybean plots were rated for weed control, and sorghum was rated for visual injury 2 weeks after treatment.” The following year, the experiments were repeated, and the crops were evaluated 4 weeks after treatment. “Visual estimates were based on 100% equals complete plant death and 0% equals no weed control or crop injury. Percent spray coverage of the WS cards was evaluated visually. Grain sorghum was harvested both years from the four rows adjacent to soybean, and in 2000, the remaining 12 rows were harvested separately. In 2000, weeds in the 1.5-m area between the soybean and sorghum were harvested for fresh weights. In both years there were four replications.”
“A second study [also in 1999 and 2000] determined the effect of the drift control agents on herbicide performance. This study was designed as a two-factor factorial, drift control agents and herbicide type (contact vs. translocated herbicides). A nontreated control was included for comparison. The [same] three drift control agents… were used at the same rates and were included in treatments of acifluorfen or glyphosate. Acifluorfen is a contact herbicide that does not translocate in the plant, whereas glyphosate needs to translocate from leaves to the meristematic regions of the plant for effective control. Treatments were applied with flat-fan nozzles…, and herbicides were applied at reduced rates of 0.4 kg ae/ha glyphosate and 0.2 kg ai/ha acifluorfen. Acifluorfen treatments included a nonionic surfactant at 0.25% v/v.”
“In 1999, clethodim (0.2 kg ai/ha) was applied to plots treated with acifluorfen to control large crabgrass …infestations 3 wk after treatments were applied. In 2000, clethodim was included with the acifluorfen treatments. There were three replications for each year… No-tillage, double-cropped soybean (glyphosate-resistant…) was planted in seven 38-cm-wide rows... Treatments were applied 3 wk after planting. Visual estimates of weed control were made 2 wk after treatment... Plots were mechanically harvested to determine soybean yield.”
VanGessel, et al., 2005, results of the first study: “The drift control agents did not reduce spray drift compared with a spray mixture without a drift control agent for either the flood or flat-fan type nozzles… In general, more drift was recorded on the higher WS card (placed 36 cm above the ground) than the lower cards (placed 13 cm above the ground). Percent coverage values were higher in 1999 than 2000. However, sorghum injury was greater in 2000 than 1999.”
“Drift control agents did not reduce the injury observed on grain sorghum…Number of sorghum rows injured, severity of injury to sorghum row closest to the spray boom, and an overall plot injury rating did not differ among the drift control agents or the spray mixture without a drift control agent, regardless of the nozzle type used. Overall, sorghum injury was greater in 2000 than 1999… In 2000, treatments were applied with a wind of 8 to 13 km/h, with gusts up to 24 km/h. The wind direction was the same as the direction of the canon-style sprayer. In 1999, there was no wind at the time of application. The increased injury in 2000 is postulated to be the result of the additional wind.”
“In 2000, plant biomass was collected in the 1.5- m area separating the soybean and grain sorghum... The amount of weed biomass was similar for all treatments containing glyphosate, regardless of whether a drift control agent was added. In all cases, the spray drift reduced the plant biomass compared with the nontreated areas.”
“Similar to grain sorghum injury, sorghum yield was reduced for all treatments containing glyphosate in 1999, regardless of drift control agent... In 2000, sorghum yield was lower with glyphosate application with flood nozzles, regardless of drift control agent... Overall yield was not reduced for the flat-fan nozzles. However, yield of the four rows closest to the soybean was reduced by glyphosate….The canon-style sprayer generated wind speeds higher than speeds used in wind tunnel studies... The higher wind speed may not have allowed the larger droplets, created by the drift control agents, to settle out over the short distance used in this study…However, herbicides are often applied with wind speeds as high as or higher than those recorded in this study….The addition of the drift control agents did not adversely affect glyphosate performance for control of summer annual weeds…[But, possibly due to low rainfall] none of the treatments provided commercially acceptable weed control in 1999.”
VanGessel, et al., 2005, results of the second study: “Drift control agents did not affect the efficacy of glyphosate or acifluorfen, a translocated and contact herbicide, respectively. Weed control was as good with no drift control agents as with the drift control agents included.” The two herbicides performed somewhat differently for different weed species. Overall, glyphosate provided better weed control.
VanGessel, et al., 2005, conclusions: “Spray drift over a short distance was not reduced with the three drift control agents evaluated, and these drift control agents did not alter weed control.”
References:
- Felsot, A.S., Unsworth, J.B., Linders, J.B.H.J, Roberts, G., Rautman, D., Harris, C., & Carazo. E. (Jan., 2011). Agrochemical spray drift; assessment and mitigation-A review. Journal of Environmental Sciences & Health Part B, 46: 1-23.
- VanGessel, M.J., & Johnson, Q.R. (Jan.-March, 2005). Evaluating drift control agents to reduce short distance movement and effect on herbicide performance. Weed Technology, 19(1):78-85.
- Vieira, B.C., Luck, J.D., Amundsen, K.L., Werle, R., Gaines, T.A., & Kruger, G.R. (Feb. 7, 2020). Herbicide drift exposure leads to reduced herbicide sensitivity in Amaranthus spp. Scientific Reports,10:2146.
Links to other impacts of herbicides and other pesticides: