Information is limited concerning the impact of delaying applications of pesticides after solution preparation on efficacy. Experiments were conducted to determine weed control when diclosulam, dimethenamid-
Unforeseen circumstances such as high wind speed, excessive rain, and equipment failure may prevent timely application of spray solutions. Spray water quality has been shown to reduce efficacy of glyphosate and other herbicides applied postemergence [
Efficacy may be affected when pesticides remain in spray solutions for extended periods of time. Permethrin left in municipality ultra-low volume spray tanks for 4 months averaged 55.5% degradation of the product when analyzed by gas chromatography [
Stewart et al. [
When postemergence herbicide applications are delayed, rapid weed growth may occur when environmental conditions are conducive for growth. Weed size has been shown to influence postemergence herbicide efficacy [
Understanding the potential loss in herbicide efficacy when applications are delayed is important to prevent weed control failures. Therefore, experiments were conducted to determine the influence of delayed applications on efficacy of seven residual soil-applied herbicide spray solutions prepared up to 9 days prior to application. Experiments were also conducted to determine the impact of increased weed size due to delayed application on herbicide efficacy compared with efficacy when application of spray solutions was delayed.
Field experiments were conducted during 2009 and 2010 in North Carolina at the Central Crops Research Station near Clayton, the Peanut Belt Research Station near Lewiston-Woodville, the Upper Coastal Plain Research Station near Rocky Mount, and an on-farm site near Falcon. Soils at Clayton, Rocky Mount, Lewiston-Woodville, and Falcon were a Johns sandy loam (fine-loamy over sandy, siliceous, semiactive, thermic
Herbicide solutions were prepared in plastic bottles (3 L volume), sealed, and stored in the dark at room temperature. The water solution was from a municipal source in Wake County, NC with pH 6.7; hardness of 31 mg kg−1; and concentrations of boron, calcium, magnesium, and zinc of 0.04, 7.3, 0, and 0.06 mg kg−1, respectively. Herbicides were applied using a CO2-pressurized backpack sprayer calibrated to deliver 140 L ha−1 at 207 kPa with tapered flat-fan nozzles (TeeJet TP11002 flat-fan spray nozzles, Spraying Systems Co., Wheaton, IL 60189, USA). Spray solutions were thoroughly agitated each time a new solution was prepared and immediately prior to application to bring herbicides into solution.
Three trials were conducted during 2009 in two separate fields at the Upper Coastal Plain Research Station near Rocky Mount and in one field at the Central Crops Research Station near Clayton and during 2010 in two separate fields at Rocky Mount. Experiments were conducted in tilled fallow areas with uniform populations of weeds. Plot size was 2 by 6 m. Broadleaf signalgrass (
Treatments included four mixing intervals (0, 3, 6, and 9 days prior to application) and seven preemergence herbicides. A nontreated control was included. Herbicides included diclosulam (Strongarm herbicide, Dow AgroSciences, Indianapolis, IN, USA) at 30 g ai ha−1, dimethenamid-
Visible estimates of percent control of broadleaf signalgrass, common lambsquarters, entireleaf morningglory, and Palmer amaranth were recorded 6 weeks after treatment using a scale of 0 to 100, where 0 equals no control and 100 equals complete control [
The experimental design was a randomized complete block with treatments replicated four times. Data for percent control of each species were subjected to ANOVA for a seven (herbicide) by four (interval of delayed application) factorial treatment arrangement using the PROC GLM procedure in SAS (SAS v9.1, SAS Institute Inc., Cary, NC, USA). Means of significant main effects and interactions were separated using Fisher’s Protected LSD test at
Field experiments were conducted during 2009 and 2010 in North Carolina at the Central Crops Research Station near Clayton, the Peanut Belt Research Station near Lewiston-Woodville, the Upper Coastal Plain Research Station near Rocky Mount, and an on-farm site near Falcon. Experiments were conducted in areas with uniform populations of weeds. Plot size was 2 by 4 m.
In separate experiments, control by atrazine (AAtrex herbicide, Syngenta Crop Protection, Inc., Greensboro, NC, USA) at 1,100 g ai ha−1, clethodim (Select Max herbicide, Valent U.S.A Corporation, Walnut Creek, CA, USA) at 1,100 g ai ha−1, the dimethylamine salt of dicamba (Clarity herbicide, BASF Corporation, Research Triangle Park, NC, USA) at (280 g ae ha−1), glufosinate (Ignite 280 herbicide, Bayer CropScience, Research Triangle Park, NC, USA) at 500 g ai ha−1, the potassium salt of glyphosate (Roundup WEATHERMAX herbicide, Monsanto Company, St. Louis, MO, USA) at 840 g ae ha−1, the ammonia salt of imazethapyr (Pursuit herbicide, BASF Corporation, Research Triangle Park, NC, USA) at 70 g ae ha−1, lactofen (Cobra herbicide, Valent U.S.A. Corporation, Walnut Creek, CA, USA) at 220 g ha−1, and paraquat (Gramoxone Inteon herbicide, Syngenta Crop Protection, Inc. Greensboro, NC, USA) at 560 g ai ha−1 was compared. Atrazine and clethodim were applied with crop oil concentrate (Agri-Dex crop oil concentrate, Helena Chemical Company, Collierville, TN, USA) at 1.0% (v/v). Imazethapyr, lactofen, and paraquat were applied with nonionic surfactant (Induce adjuvant, Helena Chemical Company, Collierville, TN, USA) at 0.25% (v/v). Dicamba, glufosinate, and glyphosate were applied without adjuvant. Herbicides were applied when weeds were 8 to 12 cm in height corresponding to the desired timing for optimal control based on the manufacturer’s recommendations. Herbicides were also applied 4 or 8 days after optimum weed size using solutions prepared the day of application or 4 or 8 days prior to application. Weed size increased as application was delayed by approximately 10 cm for each 4-day interval. Broadleaf signalgrass control by clethodim; entireleaf morningglory control by lactofen; common ragweed control by glufosinate, glyphosate, and lactofen; Italian ryegrass (
Visible estimates of percent weed control were recorded as described previously 4 weeks after each herbicide treatment irrespective of timing of application. In addition to visible estimates of control, above-ground fresh weight of three broadleaf signalgrass, common ragweed, and Palmer amaranth plants representative of plants in each plot was determined 4 weeks after optimum timing of herbicide application.
The experimental design was a randomized complete block with treatments replicated four times. Data for visible estimates of percent weed control and percent reduction in fresh weight were subjected to ANOVA appropriate for the treatment structure using the PROC GLM procedure in SAS (SAS v9.1, SAS Institute Inc., Cary, NC, USA). Means were separated using Fisher’s Protected LSD test at
Broadleaf signalgrass, common lambsquarters, and Palmer amaranth control was not affected by the main effect of mixing interval or the interaction of experiment by mixing interval. In general, weed control reflected known performance of these herbicides on weeds present in these experiments [
Broadleaf signalgrass control by clethodim was influenced by the interaction of experiment and combination of time of solution preparation and weed size at time of application. Efficacy of clethodim was not affected when spray solution was prepared 4 or 8 days prior to application when comparing within each timing of solution preparation (Table
Visible estimates of broadleaf signalgrass, entireleaf morningglory, and common ragweed control by clethodim, lactofen, and glyphosate 4 weeks after application at the manufacturer’s suggested weed size and 4 and 8 days after this weed size using spray solutions mixed the day of application or 4 or 8 days prior to applicationa.
Timing of application after optimum weed size | Timing of solution preparation prior to application | Visible control | |||||
---|---|---|---|---|---|---|---|
Broadleaf signalgrass | Entireleaf morningglory | Common ragweed | |||||
Clethodim | Lactofen | Glyphosate | |||||
Rocky Mount | Rocky Mount | Lewiston-Woodville | |||||
Field 1 | Field 2 | Field 1 | Field 2 | Field 1 | Field 2 | ||
Days | Days | % | |||||
| |||||||
0 | 0 | 96a | 94a | 90a | 93a | 97ab | 89c |
4 | 0 | 93ab | 88ab | 84a | 86c | 96ab | 95ab |
4 | 4 | 94ab | 86b | 85a | 88bc | 98a | 99a |
8 | 0 | 90bc | 75c | 58b | 93ab | 86b | 88c |
8 | 8 | 88c | 79c | 56b | 98a | 93ab | 91bc |
Entireleaf morningglory control by lactofen using spray solution prepared 4 or 8 days prior to application was similar to control by spray solution prepared the day of application (Table
Common ragweed control by lactofen was influenced by timing of solution preparation prior to application (Table
Visible estimates of common ragweed control by lactofen and Palmer amaranth control by atrazine, imazethapyr, and 2,4-D 4 weeks after application at the manufacturer’s suggested weed size and 4 and 8 days after this weed size using spray solutions mixed the day of application or 4 or 8 days prior to applicationa.
Timing of application after optimum weed size | Timing of solution preparation prior to application | Visible control | |||
---|---|---|---|---|---|
Common ragweed | Palmer amaranth | ||||
Lactofen | Atrazine | Imazethapyr | 2,4-D | ||
Days | Days | % | |||
| |||||
0 | 0 | 97a | 85a | 87a | 92a |
4 | 0 | 93b | 79ab | 85a | 89a |
4 | 4 | 95ab | 87a | 83ab | 88a |
8 | 0 | 97a | 68b | 77b | 77b |
8 | 8 | 97a | 68b | 74b | 75b |
The letters (a, b, c, ab, and bc) following the means in the table are used to differentiate between the numbers in terms of statistical differences. Numbers may be different numerically, but if they have the same letter, they are not statistically different because of variation in the biological system.
The combined effect of mixing interval and Palmer amaranth size was not affected by experiment but did affect Palmer amaranth control by atrazine, imazethapyr, and 2,4-D (Table
Palmer amaranth control by dicamba, glufosinate, and lactofen was influenced by the combination of mixing interval, weed size, and experiment. Efficacy of dicamba and glufosinate was not reduced when left in spray solution for up to 8 days when comparing within application timings (Table
Visible estimates of Palmer amaranth control by glyphosate, dicamba, glufosinate, and lactofen 4 weeks after application at the manufacturer’s suggested weed size and 4 and 8 days after this weed size using spray solutions mixed the day of application or 4 or 8 days prior to applicationa.
Timing of application after optimum weed size | Timing of solution preparation prior to application | Palmer amaranth control | |||||
---|---|---|---|---|---|---|---|
Dicamba | |||||||
Rocky Mount | Glufosinate | Lactofen | |||||
Field 1 | Field 2 | Rocky Mount | Falcon | Rocky Mount | Falcon | ||
Days | Days | % | |||||
| |||||||
0 | 0 | 88a | 89a | 86a | 70b | 93a | 67a |
4 | 0 | 80ab | 93a | 86a | 75ab | 88a | 67a |
4 | 4 | 78bc | 91a | 85a | 75ab | 89a | 57b |
8 | 0 | 70cd | 84b | 73b | 78ab | 58d | 68a |
8 | 8 | 68d | 84b | 71b | 80a | 68c | 57b |
Italian ryegrass control by glyphosate was influenced by the combination of weed size and timing of solution preparation. Control did not differ when comparing within application timings but was generally lower when application was delayed (Table
Visible estimates of Italian ryegrass control by glyphosate and paraquat 4 weeks after application at the manufacturer’s suggested weed size and 4 and 8 days after this weed size using spray solutions mixed the day of application or 4 or 8 days prior to applicationa.
Timing of application after optimum weed size | Timing of solution preparation prior to application | Italian ryegrass control | |
---|---|---|---|
Glyphosate | Paraquat | ||
Days | Days | % | |
| |||
0 | 0 | 87a | 95a |
4 | 0 | 80bc | 93a |
4 | 4 | 85ab | 94a |
8 | 0 | 73d | 91a |
8 | 8 | 77cd | 93a |
Percent reduction in common ragweed fresh weight by glufosinate, glyphosate, and lactofen was not influenced by the interaction of experiment and combination of weed size and timing of solution preparation. However, percent reduction in broadleaf signalgrass fresh weight was affected by the combination of mixing interval and weed size. Broadleaf signalgrass fresh weight reduction was 86% to 89% when clethodim was applied at the optimum timing or 4 days past the optimum weed size (Table
Percent reduction in fresh weight of common ragweed following glufosinate, glyphosate, and lactofen and percent reduction in fresh weight of broadleaf signalgrass following clethodim 4 weeks after application at the manufacturer’s suggested weed size and 4 and 8 days after this weed size using spray solutions mixed the day of application or 4 or 8 days prior to applicationa.
Timing of application after optimum weed size | Timing of solution preparation prior to application | Percent reduction in fresh weight | |||
---|---|---|---|---|---|
Common ragweed | Broadleaf signalgrass | ||||
Glufosinate | Glyphosate | Lactofen | Clethodim | ||
Days | Days | % | |||
| |||||
0 | 0 | 96a | 85a | 93a | 89a |
4 | 0 | 98a | 79a | 86a | 86a |
4 | 4 | 81a | 85a | 88a | 88a |
8 | 0 | 97a | 74a | 88a | 62b |
8 | 8 | 100a | 81a | 92a | 73b |
Palmer amaranth fresh weight reduction by 2,4-D, atrazine, dicamba, glufosinate, glyphosate, imazethapyr, lactofen, and paraquat 4 weeks after the manufacturer’s suggested weed size and 4 and 8 days after this weed size using spray solutions mixed the day of application or 4 or 8 days prior to applicationa.
Timing of application after optimum weed size | Timing of solution preparation prior to application | Palmer amaranth fresh weight reduction | |||||||
---|---|---|---|---|---|---|---|---|---|
2,4-D | Atrazine | Dicamba | Glufosinate | Glyphosate | Imazethapyr | Lactofen | Paraquat | ||
Days | Days | % | |||||||
| |||||||||
0 | 0 | 55a | 72a | 97a | 96a | 85a | 27a | 93a | 62a |
4 | 0 | 55a | 72a | 55a | 98a | 79a | 40a | 86a | 73a |
4 | 4 | 50a | 63a | 34a | 81a | 85a | 14a | 88a | 82a |
8 | 0 | 59a | 60a | 72a | 97a | 74a | 8a | 88a | 56a |
8 | 8 | 50a | 47a | 37a | 100a | 81a | 19a | 92a | 78a |
Although delaying applications of herbicide solution may not decrease weed control, these data suggest sporadic changes in herbicide efficacy can occur when spray solutions remain in the tank for extended periods of time. A complete weed control failure across all experiments and all weed species did not occur when herbicide remained in spray solution for an extended period of time. Stewart et al. [
Delayed application of postemergence herbicides will lead to increased growth and size of weeds, often making them more difficult to control. In postemergence herbicide experiments, a delay in application of 4 days did not result in a reduction in weed control even though weeds were on average 10 cm taller when herbicides were applied compared with application timing based on manufacturer recommendations. However, a delay of 8 days resulted in a general increase in weed height of approximately 20 cm over the time interval beginning at optimum application timing and resulted in less weed control in many instances. Other research [
None of the authors has a conflict of interests in terms of the products mentioned in the paper.
The North Carolina Peanut Growers Association, Philip Morris USA, and the Monsanto Co. provided partial financial support for this research. Appreciation is expressed to the staff at the Central Crops Research Station, Peanut Belt Research Station, and Upper Coastal Plain Research Station for technical assistance.