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2010 Plant Management Network. This article is in the public domain.
Accepted for publication 9 November 2010. Published 27 December 2010.


Effects of Varying Planting Dates and Tillage Systems on Reniform Nematode and Browntop Millet Populations in Cotton


Salliana R. Stetina, Research Plant Pathologist, USDA-ARS Crop Genetics Research Unit, P.O. Box 345, Stoneville, MS 38776; and William T. Molin, Research Plant Physiologist, and William T. Pettigrew, Research Plant Physiologist, USDA-ARS Crop Production Systems Research Unit, PO Box 350, Stoneville, MS, 38776


Corresponding author: Salliana R. Stetina. Sally.Stetina@ars.usda.gov


Stetina, S. R., Molin, W. T., and Pettigrew, W. T. 2010. Effects of varying planting dates and tillage systems on reniform nematode and browntop millet populations in cotton. Online. Plant Health Progress doi:10.1094/PHP-2010-1227-01-RS.


Abstract

Cropping practices that reduce damage from reniform nematode (Rotylenchulus reniformis) and browntop millet (Urochlora ramosa) are needed for improved cotton (Gossypium hirsutum) management. The impacts of early planting dates and reduced tillage systems on these pests were investigated from 2005 to 2007. Planting dates (April 1 or May 1) and tillage systems (conventional or minimum-tillage) were evaluated on four commercial cotton cultivars in a field study at Stoneville, MS. Despite some variability in early-season root infection, reniform nematode soil populations were not affected by any of the treatments. Thus, it appears that neither the tillage practices nor the planting dates examined in this study should be recommended for inclusion in a reniform nematode management program at this time. Mid- and late-season browntop millet pressure was greater in minimum-till plots and in plots planted early. More effective season-long suppression of browntop millet was associated with the traditional planting date and conventional tillage system, so these production practices could benefit producers who need to manage this weed.


Introduction

Cotton (Gossypium hirsutum) producers must reduce losses to pests and utilize production practices that maximize yields. Recent research indicates that Mississippi cotton yields may increase as much as 22% if cotton is planted earlier in the spring (7). Because of their potential for adoption in Mid-South cotton production, the impact of early planting dates and reduced tillage systems on populations of reniform nematode (Rotylenchulus reniformis) and browntop millet (Urochlora ramosa) were examined.

In the Mid-South, losses to reniform nematode in cotton have been increasing (12). Traditionally, producers suppress reniform nematode populations using soil fumigants or nematicides, but concerns over costs, efficacy, and safety have encouraged researchers to explore other options for nematode control (12,13). As no resistant cultivars are available (12), other crop production practices must be evaluated to determine if they can help reduce losses to reniform nematode.

Browntop millet, a summer annual pasture grass used for hay and forage, has become a problematic late season weed in row crops because it germinates and grows beneath the crop canopy. Culms grow up through the canopy and form entanglements with cotton, interfering with harvest of the lower bolls and reducing quality by introducing fiber into lint (3,4). Herbicide application provides acceptable levels of early-season control, but mid- to late-season resurgence in the weed population has been observed after herbicides dissipate (3,4). There are no published reports describing the effects of later-developing browntop millet populations on cotton yield.

No differences among reniform nematode populations were detected when conventional, ridge-till, and no-till plots were compared (16). More reniform nematodes were associated with reduced tillage systems than with conventional tillage in irrigated trials; in dryland trials, the populations were not affected by any of the tillage treatments (1). One report comparing conventional tillage, no-tillage, and stale seedbed soybean production systems indicated that tillage did not affect early-season populations of browntop millet (9). In cotton, larger late-season populations of browntop millet were associated with no-till plots than with tilled plots (4).

In this study, planting dates and tillage practices were evaluated to describe their impact on reniform nematode and browntop millet populations.


Field Experiment

Field studies examined early (April 1) or normal (May 1) planting dates and conventional or minimum-tillage cotton production. Treatment effects were evaluated on four cotton cultivars (DeltaPine 444 BGRR, DeltaPine 555 BGRR, FiberMax 960 BGRR, and Stoneville 4892 BGRR) in a randomized complete block design with a split plot treatment arrangement (main plot is planting date × tillage, subplot is cultivar) and four replications. The design included a repeated measures component for soil nematode populations examined at planting and harvest.

Experiments were conducted from 2005 through 2007 in a field near Stoneville, MS, that had been in continuous cotton production prior to initiation of the study and was naturally infested with both pests. Standard crop management practices for Mississippi were followed, except that disulfoton was used instead of aldicarb in-furrow for early season thrips control. Plots of each cultivar were 4 rows wide (1-m row spacing) and 12.2 m long and were established on a Dundee silty clay loam soil (fine-silty, mixed, active, thermos Typic Endoaqualfs). Once treatments were assigned to plots, they remained in the same place for the duration of the study. Results from each year were analyzed separately.

Cotton growth parameters and yield were measured as previously described (7). Light interception by the crop canopy was determined by taking measurements above (LI 190SB point quantum sensor; LI-COR, Lincoln, NE) and below (1-m long LI 191SB line quantum sensor placed on the ground perpendicular to and centered on the row) the canopy. Two measurements taken per plot on 13 June and 12 July 2005, 14 June and 11 July 2006, and 14 June and 19 July 2007 were used to calculate the percent of available light passing through the canopy.

Minimum and maximum soil temperatures (Table 1) were obtained from the National Weather Service Cooperative Observing Station in Stoneville, MS, and summarized for April and May of each year using the weather data comparison tool available online from the website of the Mississippi Agricultural and Forestry Experiment Station Delta Research and Extension Center, Stoneville (8). April soil temperatures were 5°C cooler than May soil temperatures in 2005, and 4°C cooler in 2006. 2007 saw the widest temperature range, with minimum and maximum April soil temperatures 6°C and 7°C cooler than in May, respectively.


Table 1. Average soil temperatures (10 cm deep) in April and May as reported by the National Weather Service Cooperative Observing Station, Stoneville, MS.

Month Minimum temperature (°C) Maximum temperature (°C)
2005 2006 2007 2005 2006 2007
April 17 19 17 25 27 24
May 22 23 23 30 31 31

Analysis of variance (SAS PROC MIXED, SAS Institute Inc., Cary, NC) and differences of least squares means at P ≤ 0.05 identified differences between treatments. Nematode counts were transformed using log10(x+1) prior to analysis to normalize the data. Interactions between treatments were described only if they were statistically significant in more than one year.


Response of Reniform Nematode Populations

The reniform nematode population was quantified from a composite soil sample collected from the two center rows of each plot as described by Stetina et al. (14). Plants collected from an outer row of each plot were assessed for early-season root infection in 2005 and 2006; dry soil conditions in 2007 caused extensive damage to roots during collection and compromised sample integrity. Female reniform nematodes attached to four roots collected from each plot 3 to 5 weeks after planting were stained (15) and counted. Roots were blotted on paper towels before fresh weights were measured. Root infection data were expressed as nematodes per gram of root tissue.

Neither tillage nor planting date affected soil reniform nematode populations in any year of the study (Table 2). In 2005 and 2007, ‘FiberMax 960 BGRR’ supported larger populations than ‘DeltaPine 444 BGRR.’ In 2006 and 2007, the population increased during the growing season as expected, but not in 2005.

A significant tillage × season interaction was noted in 2005 and 2007 (Table 2), with the reniform nematode population increasing from planting to harvest only in conventionally tilled plots (Fig. 1). Nematode populations at planting in minimum-till plots were comparable to those at harvest, suggesting better winter survival in plots with reduced tillage.


 

Fig. 1. Seasonal reniform nematode soil population changes as affected by tillage system. Within each year, values designated with the same letter are not significantly different from each other based on differences of least squares means (P ≤ 0.05).

 

In 2006, conventional plots had higher levels of early-season root infection than minimum-till plots (Table 2). No consistent trends were noted with respect to planting date, and no differences among cultivars were noted.

Despite some variability in early-season root infection, neither planting dates nor tillage practices consistently reduced reniform nematode populations. It was anticipated that cooler soil temperatures typically associated with earlier planting dates would limit infection. The observed May temperatures closely approached the reported optimum temperature range of 27°C to 32°C for rapid completion of the reniform nematode life cycle (12). Though temperatures slightly cooler than the optimum occurred in April, they were not associated with suppressed reniform nematode populations. The population was maintained at or above Mississippi’s damage threshold of 1000 nematodes per 473 cm³ soil at planting (6) under both tillage systems. Thus, it appears that neither the tillage practices nor the planting dates examined in this study should be recommended for inclusion in a reniform nematode management program at this time.


Response of Browntop Millet Populations

Midseason (July 30) browntop millet population estimates were determined by counting the number of browntop millet per 1 m² measured at the geometric center between the two middle rows of the subplot. Fewer weeds were present in conventionally tilled plots than in minimum-till plots in 2005 and 2006, but planting date did not affect the number of weeds present in any year (Table 3). Differences among cotton cultivars occurred only in 2005, when plots planted to ‘FiberMax 960 BGRR’ had more weeds than plots planted to either of the DeltaPine cultivars; ‘Stoneville 4892 BGRR’ was intermediate.

Late-season percent weed cover, an average of two independent visual estimates of weed cover made from each end of the plot, was higher in minimum-till plots than in conventionally tilled plots in all years (Table 3). This observation was consistent with previous work reporting larger browntop millet populations in no-till plots compared to tilled plots (4). In 2006 and 2007, plots planted early had greater weed coverage than plots planted at the normal time, but this was not observed in 2005. Differences among cotton cultivars occurred only during 2006 and 2007, with ‘FiberMax 960 BGRR’ plots having greater weed coverage than ‘DeltaPine 555 BGRR’ and ‘Stoneville 4892 BGRR’ plots. These results suggest that certain cultivars may be better than others at keeping browntop millet populations in check, though the mechanisms contributing to this effect were not determined.

Browntop millet pressure was greater in minimally tilled plots and in plots planted one month early. More effective season-long suppression of browntop millet is associated with the traditional planting date and conventional tillage system.


Relationships Between Nematodes, Weeds, and Crop Growth, and Cotton Yield

Associations between reniform nematode (soil populations, root infection), browntop millet (percent cover, weed counts), crop growth (light infiltration, plant height, dry weight, leaf area, number of nodes), and cotton yield (lint percent, lint yield) were examined using correlation analysis (SAS PROC CORR) at P ≤ 0.05.

Percent weed cover was positively correlated with percent light infiltration on 12 July 2005 (ρ = 0.55) and 19 July 2007 (ρ = 0.45) and negatively correlated with plant height on 11 July 2006 (ρ = -0.36) and 12 July 2007 (ρ = -0.38). Light infiltration on 11 July 2006 was negatively correlated with plant height on 11 July 2006 (ρ = -0.39). These results suggest that taller plants provided more shade below the canopy, resulting in reduced weed coverage. Percent weed cover was negatively correlated with cotton lint yield in 2005 (ρ = -0.37) and 2006 (ρ = -0.39). This association was not surprising, as worldwide cotton losses to weeds were recently reported to be 9% (5). A yield loss of 13% previously reported in minimum-till plots (7) may be due, at least in part, to pressure from larger browntop millet populations. No other significant correlations were detected involving weed parameters. Although numerous plant species have been demonstrated to support at least some reniform nematode reproduction (11,12), the host status of browntop millet has not been reported. Browntop millet roots collected late in the season from fields infested with reniform nematode showed no evidence of infection by the nematode (data not shown). No positive correlations were found between weed and nematode populations, suggesting that browntop millet was not a good host for reniform nematode in this study. Though reniform nematode has been reported to adversely affect crop growth and yield (2,10,12), no significant correlations were evident in this study.


Implications for Cotton Production

Neither the tillage systems nor planting dates evaluated in this study affected reniform nematode populations. While these practices did not inhibit nematode population development, neither did they allow significant population increases. Therefore, adoption of alternative planting dates or tillage systems should be based on factors other than reniform nematode management.

The browntop millet population was larger in the minimal-till production system, even though herbicides were applied on a regular basis for weed control in all plots. Our observations suggest that improved control can be achieved with a combination of cultural and chemical production practices, as conventional tillage systems and normal planting dates were associated with less mid- to late-season browntop millet pressure.


Disclaimer and Acknowledgements

The mention of trade names or commercial products is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the United States Department of Agriculture.

The authors thank D. Boykin for help with data analysis and K. Jordan, M. Gafford, W. Reese, T. Miller, and C. Brown for technical assistance. This research was funded by the United States Department of Agriculture, Agricultural Research Service, project number 6402-22000-005-00D.


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