Jimsonweed has been shown to be a problematic weed in North Carolina and Virginia; however, its effects of interference in peanut have not been evaluated. Therefore, the objectives of this study were to determine peanut yield and growth reductions caused by jimsonweed interference. Experiments were conducted in 2004 at the Upper Coastal Plain Research Station located near Rocky Mount, North Carolina and the Cherry Research Farm near Goldsboro, North Carolina. With the exception of jimsonweed, the experimental area was kept weed-free utilizing herbicides and hand hoeing. Jimsonweed seedlings at the cotyledon to 2-leaf stage were transplanted into plots immediately after peanut planting at the following densities: 0, 1, 2, 4, 8, 16, or 32 plants per 6 m of row. Peanut diameter, measured as canopy row width at four random locations, increased over time at the lower jimsonweed densities. At the two highest jimsonweed densities, peanut diameters never exceeded 25 cm (70 cm less than weed-free peanut). Thus, peanut diameter does not appear to be a reliable predictor of peanut productivity or jimsonweed interference. Jimsonweed plant and seed pod weights decreased logarithmically as jimsonweed density increased. When jimsonweed was grown at lower densities, seed production amounted to nearly 30,000 per plant, which was reduced to 10,000 per plant when densities increased to 32 plants per 6.1 m of row. However, overall seed production increased from 60,000 seed per plot at the lowest jimsonweed density to 640,000/plot at the highest density. Peanut height increased from 44 to 57 cm as jimsonweed density increased from 0 to 5.25 plants/m of row. Similarly, jimsonweed heights increased from 97 to 139 cm as jimsonweed density increased from 0 to 5.25 plants/m of row. A rectangular hyperbola equation described the effect of density on percent yield loss with
Jimsonweed possesses many characteristics that make it a competitive summer annual broadleaf weed. It is capable of very high growth rates, prodigious seed production, and rapid seed germination (
Jimsonweed interference has been evaluated in cotton (
Currently registered postemergence herbicides allow growers to successfully manage jimsonweed in peanut; however, questions exist concerning treatment threshold levels. Additionally, weed seed production has been cited as a concern of growers and other agricultural personnel (
Not only do weeds cause yield loss in peanut but also peanut inversion can be affected, thus causing reduced harvesting efficiency (
Experiments were conducted in 2004 at the Upper Coastal Plain Research Station located near Rocky Mount, NC and the Cherry Research Farm near Goldsboro, NC. The soil types were Norfolk loamy sand (fine-loamy siliceous thermic Typic Paleudults) with 2.1% organic matter and pH 6.1 and Wickham loamy sand (fine-loamy, mixed, thermic Typic Hapludults) with 2.1% organic matter and pH 5.8, respectively. The soil was disked and seedbeds were conventionally prepared (
The experimental design was a randomized complete block with 3 replications. Individual plots consisted of four rows spaced 91 cm apart that were 6.1 m long. Fertilization, insect, and disease management practices were standard for peanut production in North Carolina (
Greenhouse-grown jimsonweed seedlings at the cotyledon to 2-leaf stage were planted into plots immediately after peanut planting at the following densities: 0, 1, 2, 4, 8, 16, or 32 plants per 6.1 m of row or 0, 0.16, 0.33, 0.66, 1.31, 2.62, or 5.25 plants per m of row. Jimsonweed seedlings were planted into the center two rows of each plot with the two outer rows left as weed-free borders. The transplanting method allowed the establishment of plants with uniform size and distribution along the row. Although jimsonweed seedlings were transplanted at peanut planting, an acclimation period of 1 to 2 wk was required before the jimsonweed plants resumed growth (data not shown). Peanut emerged within 1 wk of planting and had nearly equaled jimsonweed height at the first measuring interval 2 wk after planting. Herbicide applications of clethodim at 0.28 g ai/ha over the top and a hooded application of acifluorfen at 0.14 kg ai/ha plus bentazon at 0.28 g ai/ha (to keep the herbicide treatments off of the jimsonweed) were made six weeks after planting to control weeds other than jimsonweed. Clethodim does not control or injure jimsonweed (
Height measurements were recorded for up to four jimsonweed plants (one treatment contained only two jimsonweed plants in a plot) and four peanut plants and peanut canopy diameter measurements were taken bi-weekly during the season. At the end of the growing season, up to four jimsonweed plants were harvested in each plot, and the remaining plants were cut at ground level to facilitate peanut inversion and harvest. At jimsonweed harvest, seed pods were hand-removed from plants, kept separate, and seed production was quantified. Plants and pods were dried and dry weights were taken for each sample. Peanut yield was determined by inverting the middle two rows of each plot and allowing the peanuts to air-dry in the field for approximately 1 wk. Finally, peanuts were harvested with a combine modified for small-plot research and weighed.
Data were tested for homogeneity of variance prior to statistical analysis by plotting residuals. Analysis of variance (ANOVA) was performed on peanut yield loss, jimsonweed dry biomass, jimsonweed seed weight and number, and jimsonweed pod weight. Linear, quadratic, and higher-order effects were tested by partitioning sums of squares (
Plant height was measured at different time intervals after planting each location. Therefore, the Gompertz equation (Equation 1,
The relationship between jimsonweed density per meter of row and percent peanut yield loss was fitted to the rectangular hyperbola (Equation 2) (Cousens, 1998).
Coefficients of determination (
Peanut diameter, measured as canopy row width at four random locations, increased over time in plots with low jimsonweed density. However, in the two highest density jimsonweed plots, peanut diameters were less than 25 cm. Average peanut diameter at the lower jimsonweed densities was near 85 cm (93% of row width) at harvest. Thus, peanut diameter does not seem a reliable predictor of peanut productivity or jimsonweed interference.
Analysis of variance on estimated parameters of the Gompertz equation (Equation 1) (
There was no location effect for jimsonweed plant and seedpod weights; therefore, data were combined over locations. Jimsonweed plant and seedpod weights were significantly influenced by jimsonweed density (
There was no location effect for jimsonweed seed production; therefore, data were combined over locations. Number of seed produced per plant decreased with increasing jimsonweed density (
Relationship between jimsonweed density per meter of crop row and jimsonweed seed production, averaged over location.
A hyperbolic function (
Analysis of variance on estimated parameters of the rectangular hyperbola equation (Equation 2) (
Relationship between jimsonweed density and peanut yield loss, averaged over location.
A hyperbolic yield loss function (
Predicted peanut yield loss from season-long interference of one jimsonweed plant per meter of crop row was 40% (
Peanut diameter did not accurately predict peanut productivity or jimsonweed interference. Weed biomass response to plant density indicated that intra-specific weed interference occurred at higher weed densities. Weed biomass was also inversely related to peanut yield. The high growth rate of jimsonweed coupled with the height of the jimsonweed observed in this study makes jimsonweed one of the most competitive weeds in peanut. When jimsonweed is present and emerges at or before peanut emergence, treatment should be eminent as population densities of jimsonweed rarely occur below economic thresholds. Future studies need to focus on yield loss caused by infestations emerging during the growing season.
We thank Scott Clewis, Caitlyn Wilcut, and Jared Wilcut for technical support and Cavell Brownie for reviewing statistical analyses. Appreciation is also extended to the North Carolina Peanut Growers Association for partial funding of this research.
Plant Physiol., National Soil Dynamics Laboratory, Agriculture Research Service, United States Department of Agriculture, 411 South Donahue Drive, Auburn, AL 36832. Email address of corresponding author:
Grad. Res. Assist., Grad. Res. Assist., Assist. Prof., Grad. Res. Assist. and Prof., Crop Science Department, Box 7620, North Carolina State University, Raleigh, NC 27695-7620.