Previous research has shown that mechanical cultivation is the most effective and affordable method of weed control in organic peanut production. However, growers are in need of more information on specific integrated cultivation regimes for effective season-long weed control with minimal hand-weeding requirements. Therefore, field trials were conducted in 2010–2012 to evaluate the effects of various tine and sweep cultivation treatments combined with or without hand-weeding on season-long weed control, stand establishment, and yield and grade of an organically-managed peanut crop. Tine cultivation treatments consisted of no cultivation or weekly cultivations for 5 wks after planting (WAP). Sweep treatments consisted of no cultivation, weekly cultivations (for 5 WAP), cultivations at 2 and 5 WAP only, or cultivation at 5 WAP only. Hand-weeding treatments were no hand-weeding or hand-weeding of the entire plot. There were numerous significant interactions among tine and sweep treatments on weed control. Initial weed species composition greatly affected cultivation effects on overall weed control. Tine cultivation was most effective at controlling annual grass weeds. Sweep cultivation was effective at reducing weeds (
Weed control is one of the most limiting factors to organic crop production. Because direct control with synthetic herbicides is prohibited in certified organic systems (
Cultivation is a well-documented method of weed control, particularly in organic production systems (
Field trials were conducted at the University of Georgia (UGA) Lang-Rigdon, Ponder, and Horticulture Hill Farms near Tifton, GA in 2010, 2011, and 2012, respectively. The trials were conducted on a Tifton loamy sand (fine-loamy, Kaolinitic, thermic Plinthic Kandiudults) with pH between 6.0–6.5 and less than 1% organic matter. All plots were planted with non-treated Foundation seed of cv. Tifguard (
The experiment was arranged in a randomized complete block design, with a 2 × 4 × 2 factorial treatment arrangement of tine cultivation, sweep cultivation, and hand-weeding treatments. Tine cultivation treatments included 1) once per week for the first 5 wk after planting (WAP) or 2) no cultivations. Sweep cultivation treatments included 1) five total cultivations (once weekly for 5 WAP), 2) two total cultivations at 2 and 5 WAP only, 3) one single cultivation at 5 WAP only, and 4) no cultivation. Hand-weeding treatments were 1) fully weeded mid-season or 2) no hand-weeding. This design ensured the inclusion of a non-cultivated and non-weeded control for each variable. All treatments were replicated four times across each field location. Tine cultivations were conducted using a flex-tine cultivator (Aerostar, Einböck GmbH & CoKG, Austria) and were initiated 4 d after planting (DAP) (at ground-cracking immediately prior to seedling emergence) in 2010, 2011, and 2012 and continued every seven days until initiation of peanut blooming, or approximately 5 WAP. Sweep cultivations were conducted with a flat-sweep cultivator and the first treatments were initiated 6 DAP, 7 DAP, and 8 DAP in 2010, 2011, and 2012, respectively, and continued every seven days until approximately 5 WAP. Hand-weeding in selected plots was conducted on 6 July 2010, 25 July and 11 Aug. 2011, and 23 Aug. 2012, and the amount of time spent hand-weeding was recorded for each plot. Plant stand estimates were conducted on all plots using a 1.5-m length pole, on 21 June 2010, 5 July 2011, and 5 July 2012, following peanut emergence and stand establishment.
Weed control estimates were conducted each year on prevalent weed species at each location at the end of the season (prior to peanut inversion) to evaluate season-long effects of each weed control regime. This was done using a visual estimate of the percentage of the plot that had the weed present and subtracting from 100 for percent control (i.e. a plot with 5% coverage of the plot with a weed was determined to be 95% control for that weed). In 2010, visual estimates of percent control were conducted for southern crabgrass [
In 2012, however, the dominant weeds were a mixture of various pigweed species (
Due to intense weed pressure in the non-hand-weeded plots in 2011 and 2012, nearly all such plots were unreasonable to dig peanuts and salvage a yield estimate. Therefore, yield data were only collected from the hand-weeded plots those years and will be presented for 2010–2012. All plots that were able to be inverted were harvested 3 Nov. 2010, 22 Nov. 2011, and 21 Nov. 2012. Pod yields were adjusted to 7% moisture. Grade data were also collected from all harvested treatments and analyzed for % total sound mature kernels (
There were considerable differences in weed species and control among the three years of the experiment. Therefore, analyses were analyzed separately for each year. There were numerous significant two-way interactions involving tine and/or sweep cultivation treatments for many measured variables in each year. Weed control data will be presented for each individual year by discussing important interaction effects and their relevance to the interpretation of the data.
In 2010, when weekly tine cultivations occurred, there were no differences in southern crabgrass (88–92%) or Florida pusley (77–79%) control regardless of sweep treatments (data not shown). However, when tine cultivations were absent, the level of control decreased with decreasing frequency of sweep cultivations (
Effect of sweep cultivation on southern crabgrass and Florida pusley control when there was no supplemental tine cultivation, Tifton, GA – 2010a.
In 2011, sweep cultivation had no effect on weed control for any species present. Interactive effects between tine cultivation and hand-weeding treatments were consistently observed for multiple weed species. The observed trends for these interactions were that hand-weeding improved weed control for all species whenever a difference occurred (only crowfootgrass was effectively controlled by tine cultivation without the need for hand-weeding), and tine-cultivation did not improve control for any species when hand-weeding was used (data not shown). When hand-weeding did not occur, tine cultivation greatly improved control of crowfootgrass and sorghum-sudangrass (
Effect of tine cultivation on crowfootgrass, smallflower morningglory, and sorghum-sudangrass control when no hand-weeding occurred, Tifton, GA – 2011a.
Despite no interactions, trends were still similar for goosegrass control (data not shown) where hand-weeding improved control regardless of cultivation (from 75 to 93%), and for redweed where hand-weeding improved control from 58 to 89%. There was also improved redweed control with weekly tine cultivation compared to lack of cultivation (from 70 to 77%;
Although a different evaluation method was used for pigweed in 2012 compared to the weed escapes in previous years, similar trends were still observed as the weed control estimates in 2010 and 2011 in several instances. The total number of pigweed present was zero or statistically equal to zero in all hand-weeded plots. Yet when hand-weeding was absent, the total number of pigweed across the entire row + middle span (92 cm) was reduced by nearly 40% with two sweep cultivations, and by over 52% with weekly sweep cultivations. However, the total number of pigweed was not reduced with a single sweep cultivation at 5 WAP compared to the non-treated control (
Effects of sweep cultivation on pigweed (
The total biomass of pigweed was also affected by interactions involving sweep cultivation. With no tine cultivation coupled with no sweep cultivation, pigweed biomass was largest, although not statistically greater than when sweeps were run weekly (
The amount of time spent hand-weeding exhibited a significant tine × sweeps treatment interaction in 2010 and 2012, thus were subsequently separated and analyzed for their interaction in each year. In both years, when tine cultivation occurred weekly, the amount of time needed for hand-weeding was not different for any sweep treatment. However, when tine cultivation was absent, there were large differences in labor among the various sweep treatments. In both years, the amount of hand-weeding was greatly reduced when sweeps were run at least twice, compared to only a single Week 5 cultivation or non-treated (
Effects of sweep cultivation on hand-weeding and pod yield, Tifton, GA – 2010–2012a.
There were no differences in plant stand or grade (% total sound mature kernels) in any year for any treatment effect. Although, plant stands were higher in 2010 (11.3 plants/m) than in 2011 or 2012 (6.6 and 6.7 plants/m, respectively). Similarly, there were no differences in yield for any treatment effect in 2010 or 2011 (average 2370 and 1320 kg/ha, respectively), while there were yield differences among sweep cultivation treatments in 2012 (
These data are significant in that there appeared to be a hierarchy of effectiveness for weed control in organic peanut production. Hand-weeding cannot be replaced by cultivation, whether tine or sweep or both, and is still the foundation of organic weed control systems. Peanut harvest could not even occur in plots where weeds were not removed by hand. However, by including various combinations of tine and sweep cultivation, there was enough overall weed control to warrant a significant reduction in total hand-weeding. This is notable because labor costs for hand-weeding represent one of the greatest expenditures by organic growers. Reducing the need for hand-weeding has great potential for increasing the economic viability of the system.
Tine cultivation had a more consistent effect on weed control than sweep cultivation, and should be considered an important supplement to hand-weeding. In addition, even though sweep cultivation did not give consistent supplemental weed control for any given weed when tine cultivation was present, the fact that there were reductions in some species of weeds by some levels of sweep cultivation when tine cultivation was not present is still relevant. Sometimes weather conditions or equipment malfunctions or breakdowns may prevent or delay the ability to run equipment through the field. Having sweep cultivation in combination with tine cultivation would allow for some level of weed control and reduction in hand-weeding requirements in the event a tine cultivator could not be used consistently. These data consistently showed improved results with weekly sweep cultivations, or at minimum two cultivations occurring 2 and 5 WAP to ensure improved weed control and/or reduction in hand labor in the event of tine-cultivation failure.
Successful weed control depends on initial species composition at a location (
The authors wish to express thanks to Chad Abbot, Paige Adams, Katie Davis, Justin Moss, Josh Ott, Jason Sarver, Corey Thompson, and Will Vance for outstanding technical assistance, all of whom were essential to the success of this research. Financial assistance from the National Peanut Board's Southeast Peanut Research Initiative was imperative to assist with labor expenses needed to conduct these experiments.