Behind corn (105,218 ha), cotton (159,851 ha), and soybean (141,640 ha), peanuts (Arachis hypogaea L.), planted on 76,081 ha and valued at $564 million in 2024, are the fourth widely produced row crop in Alabama (USDA NASS, 2025). While peanuts are produced in 33 of 67 counties in Alabama, the bulk of the acreage is in counties adjacent to the Florida Panhandle. Due to extended periods of dry late summer and early fall weather in 2024, average yield for Alabama declined to 3363 kg / ha compared with 4200 and 4560 kg / ha for 2023 and 2022, respectively (USDA NASS, 2024). In addition, approximately 90% of peanut acreage in Alabama (USDA NASS, 2024) is rainfed compared with approximately 50% in Georgia (Porter, 2022).

Production practices that intensify diseases and nematode pests and potential yield loss include cropping patterns such as a peanut monoculture or one year out rotation with corn or cotton (Johnson et al., 1998; Rodríguez-Kábana et al., 1991), irrigation (Fulmer et al., 2019), cultivar selection (Woodward et al., 2008), planting date (Fulmer et al., 2019; Hagan et al., 2001; Jordan et al., 2019) and seeding rate (Hagan et al., 2015). Occurrence of tomato spotted wilt (TSW), which is caused by the thrips-transmitted tomato spotted wilt virus (TSWV), genus Orthotospovirus; family Bunyaviridae, has sharply intensified in Alabama in recent years (Hagan et al., 2023) and is best controlled with a combination of TSWV resistance, mid-May or later planting, twin row planting pattern, strip or no till, and recommended seeding rates (Brown et al., 2005; Hagan et al., 2015; Johnson et al., 2001; Monfort et al., 2004; Srinivasan et al., 2017). Following a century of peanut production in Alabama, Florida, and Georgia, stem rot (SR, Agroathelia rolfsii Redhead & S-T. Mullineux (anamorph Sclerotium rolfsii Sacc.)) and the peanut root-knot nematode (PRKN, Meloidogyne arenaria race 1 (Neal) Chitwood) are widely distributed and often damaging pests of peanuts (Bowen et al., 1996; Timper et al., 2018). Wet/dry and hot late summer weather patterns favor SR development (Bowen, 2003), while moist soil moisture conditions for an extended time period favor PRKN reproduction (Hagan et al., 2025). Cropping a non-host crop such as corn and/or cotton for a minimum of two years in between peanuts is a sustainable and cost-effective method for minimizing PRKN-incited yield loss, particularly when compared with nematicides (Bowen et al., 1996; Hagan et al., 2025; Rodríguez-Kábana and Touchton, 1984). Additionally, establishment of PRKN-resistant cultivars, with resistance introgressed from A. cardenasii (Starr et al. 2002), is an effective but often underutilized method of avoiding significant yield loss (Brenneman et al., 2017; Hagan et al., 2025). However, concerns about yield potential and grade compared with commercial standard cultivars, especially in fields where M. arenaria populations are low or absent, have limited the adoption of PRKN resistant cultivars (Grabau et al., 2020; Starr et al., 2002).

Winter cover crops are an integral component in Southern crop production systems, primarily for producers employing strip or no-till practices. Strip or no-till with a winter cover, accelerated with the introduction of USDA NRCS conservation farm plans, is designed to suppress soil and wind erosion (Johnson et al., 2006; Wallander et al., 2021), enhance soil quality and health by enhancing microbial flora and fauna diversity (Lehman et al., 2015), improve water infiltration and moisture retention (Hawkins et al., 2016), and nutrient recycling (Bender and van der Heijden, 2015) while reducing fuel and labor inputs and CO₂ emissions (Godsey et al., 2011; Sørensen and Nielsen, 2005). Additionally, enhanced carbon sequestration to increase percent (%) organic soil carbon is observed in strip and particularly no-till as compared with a conventional till production system (Veum et al., 2002). However, weed management issues have slowed the adoption of strip till practices for peanuts (Monfort and Tubbs, 2022). Presently, approximately 60% of the acreage cropped to peanuts in Alabama is strip or no-tilled (Balkcom, Personal Communication).

Tillage affects the occurrence of diseases and nematode pests of peanuts Johnson et al. (2001) and Monfort et al. (2004) observed a significant reduction in TSW incidence in strip and/or no-till systems compared with conventionally till peanuts. While greater SR has been recorded for strip than no- or conventionally till peanuts (Grichar, 1998), others have noted that tillage did not influence SR incidence (Godsey et al., 2011; Hartzog and Adams, 1989; Minton et al., 1991; and Sorensen et al., 2010). The impact of strip-till on PRKN juvenile population dynamics has not been assessed. Overall, most field trials addressing the influence of tillage practices on the occurrence of diseases and nematode pests have been conducted primarily on irrigated and not rainfed peanuts (Godsey et al., 2011; Grichar, 1998; Johnson et al., 1998; Johnson et al., 2001; Minton et al., 1991; Monfort et al., 2004; Sorensen et al., 2010).

In Alabama, rye and to a lesser extent wheat and oats are employed as a winter cover crop preceding peanuts, typically with limited supplemental fall and layby fertilization. However, most overwintering fields going into reduced till peanuts the following spring are not planted to a winter cereal but are maintained in a weed fallow. In Georgia, common winter weeds on fallowed fields after peanut or cotton, in no particular order, include wild radish (Raphanus raphanistrum L.), cutleaf evening primrose (Oenothera laciniata Hill), henbit (Lamium amplexicaule L.), Italian ryegrass (Lolium multiflorum Lam.), common and mouse-ear chickweed (Stellaria media L. and Cerastium fontanum Baumg., respectively), Carolina geranium (Geranium carolinianum L.), swinecress (Lepidum coronopus L.), and red sorrel (Rumex acetosella L.) (Prostko, Personal Communication).

Limited information is available concerning the impact of winter cover crops on diseases and, to a lesser extent, nematode pests in peanuts. In Alabama, Campbell et al. (2002) reported that the incidence of TSW and SR in peanuts did not significantly differ following wheat, rye, oats, ryegrass, or weed fallow. When weed fallow and rye were compared in Georgia, populations of PRKN and Belonolaimus longicaudatus Rau (sting nematode) on the following irrigated peanuts were similar, though a reduction in root and pod galling was noted in two of seven years in peanut after the former winter cover (Johnson et al., 1998). Similar populations of PRKN were also noted for peanut following weed fallow and rye (Rodríguez-Kábana and Ivey, 1986). Wang et al. (2004) also did not report any reductions in PRKN populations on irrigated peanuts cropped behind wheat, rye, oats, lupine (Lupus augustifolius L.), hairy vetch (Vicia villosa Roth), or crimson clover (Trifolium incarnatum L.).

The objective of the study was to compare the influence of selected cereals (oats, rye, and wheat) along with a weed fallow on the occurrence of TSW, SR, juvenile populations and damage associated with PRKN, along with yield and grade of the following peanut crop in a rainfed strip-till production system. In addition, the influence of planting date along with that of selected commercial PRKN-resistant and susceptible cultivars on the above variables was assessed.

The study site, which has a resident population of the peanut root-knot nematode (PRKN) and the causal fungus of stem rot [syn white mold], is located at the Wiregrass Research and Extension Center (WGREC; 31° 22" 34' N 85° 18" 54' W) in Headland, AL. In mid- to late-November, the winter cover crops Wrens Abruzzi rye (Secale cereale L.), Florida 501 oats (Avena sativa L.), and Jamestown wheat (Triticum aestivum L.) were sown with a no-till drill on 18 cm centers at 67 kg seed / ha following cotton (Gossypium hirsutum L.) in a Dothan fine sandy loam [fine-loamy, kaolintic, themic plinthic kandiudults; 0-2% slope; < 1% organic matter]. While rye, oats, and weed fallow were included in all studies conducted between 2014 and 2018, wheat was grown only in 2014, 2015, and 2016. A weed fallow treatment was included where the dominant weeds were henbit, common chickweed, Italian ryegrass, and wild radish, none of which are known hosts of M. arenaria (Rich et al., 2008). Individual cover crop plots, which were arranged in four complete blocks, were 14.6 m wide by 15.2 m long. In each year, adjustments in soil fertility and pH were according to the results of a soil fertility assay done by the Auburn University Soil, Forage & Water Testing Laboratory. No pre- or post-plant supplemental nitrogen or pesticide applications were made to the above winter covers. Winter covers and weeds were terminated with a mid-March application of glyphosate at 1.12 kg / ha (Roundup PowerMAX®, Bayer CropScience, St. Louis MO).

In each year, a factorial set of treatments were arranged in a split-split plot design with winter cover as the whole plot, planting date as the split plot, and peanut cultivar as the split-split plot. Individual subplots, which consisted of four 15.2 m rows on 0.9 m centers, were randomized in four complete blocks. Prior to planting, rows in the terminated winter cover were laid off with a KMC strip till implement with rolling baskets. A conventional tillage treatment for peanut was not included in the study design. In all years, the PRKN-susceptible cultivar, Georgia-09B [listed as GA09B in tables] (Branch, 2010), and the PRKN resistant cultivar, Tifguard (Holbrook et al., 2008), were sown at 13 seed / m row and were cropped behind one year of cotton. Both are obsolete runner, high-oleic market-type cultivars that display partial TSW resistance (Branch, 2010; Holbrook et al., 2008). Planting dates are listed in Table 1. Disease and weed control recommendations of the Alabama Cooperative Extension System were followed (Majumdar et al., 2025). Thrips control was obtained with an in-furrow application of 1.12 kg / ha phorate (Thimet 20G, AMVAC Chemical Corporation, Newport Beach, CA). Soil fertility and pH adjustments were according to the results of a soil fertility assay done by the Auburn University Soil, Forage & Water Testing Laboratory. The study area was not irrigated.

Rating dates for TSW are listed in Table 1. Loci counts for TSW (1 locus was defined as < 30.5 cm consecutive row of disease-damaged plants per row) were made on the two harvest rows in each plot (Branch et al., 2021; Culbreath et al., 2010; Hagan et al., 2023). Prior to plot inversion for each planting date (Table 1), soil samples consisting of ten subsamples of 2.5 cm diameter cores collected to a 10 cm depth, were randomly taken from the root zone of plants in the center two rows of each plot. Soil subsamples were stored in a cooler at 3°C until processed, then thoroughly mixed, and 100 cm³ of soil was processed using the centrifugal-flotation method for determining juvenile root-knot nematode densities (Jenkins, 1964). Nematode populations are presented as number of root-knot juveniles per 100 cm³ of soil (RKpop). Stem rot incidence (SR), presented as the number of loci (< 30.5 cm of consecutive symptomatic plants in row) in each of two center rows, was recorded immediately following plot inversion (Table 1). In addition, damage to the roots and pods attributed to the peanut root-knot nematode (RKDam), which was rated on a 1 to 5 scale where 1 = no visible damage to 5 = 75 to 100% of roots or pods damaged over the yield rows, was recorded immediately after plot inversion. Inversion dates listed in Table 1 were determined using the hull scrape method as described by Williams and Drexler (1981). Plots were mechanically harvested four to seven d following inversion. Heated forced air (35%) was employed to reduce kernel moisture to approximately 7-8% prior to collecting weights for yield. Farmer stock grade for a 500 g sample of the above in-shell peanuts from each plot was determined using USDA grading procedures (USDA, 2019).

Winter covers, primarily rye, are widely used as winter grazing for feeder calves, for minimizing soil erosion (Johnson et al., 2006; Wallander et al., 2021), enhancing soil moisture retention (Hawkins et al., 2016), and nutrient recycling (Bender and van der Heijden, 2015). Here, peanut cropped behind rye, which already is the preferred cereal winter cover for Alabama peanut producers, consistently produced greater yields over the five-year study period compared with wheat and oats. Surprisingly, peanut following the winter weed fallow produced comparable yields as peanut cropped behind rye, except in 2018. Previously, few direct comparisons of the yield response of peanut to winter cereals have been made. When comparing rye and weed fallow, Johnson et al. (1998) noted that following irrigated peanuts yielded significantly greater following the former than latter winter cover in only one year between 1988 and 1994. In the two years that yield differences were reported by Campbell et al. (2002), yield rankings for peanuts following the above cereal covers did not always match those recorded here. In contrast to the study herein, the yield of peanuts cropped behind wheat and rye were similar in both years as compared with only one year for oats and weed fallow. In addition, yields were greater for strip till peanuts cropped behind black oats than oats, rye, triticale, or wheat in one of two years (Sorensen et al., 2010).

Yield gains obtained following rye and weed fallow compared with wheat and oats are not closely linked to reductions in disease occurrence or PRKN suppression. While TSW has the potential to reduce peanut yield (Brown et al., 2005), the low disease pressure noted over the study period, which matched that noted in a concurrent trial at the same location (Hagan et al., 2023), was likely insufficient to cause a measurable decline in yield. As was noted here, Campbell et al. (2002) reported that winter covers, including a weed fallow, failed to influence TSW incidence in the following peanut crop. In contrast to TSW, SR indices and RKPop juvenile counts were sufficient to influence yield (Grichar, 1998; Hagan et al., 2024; Minton et al., 1991). For SR, however, similar loci counts were noted for peanuts cropped behind each of the winter covers, including the weed fallow, in all years. Previously in Alabama, oats, rye, and wheat, along with ryegrass and weed fallow failed to significantly impact SR incidence in the succeeding peanut crop (Campbell et al., 2002). Sorensen et al. (2010) noted that yield gains observed for peanut behind black oats compared with other cereal covers were not associated with any reduction in the incidence of SR. Finally, the yield advantage for peanuts cropped behind rye and weed fallow was not reflected in a decline in RKDam values or RKPop juvenile counts when compared with those for oats and wheat. While Wang et al. (2004) reported lower M. incognita juvenile counts for rye and oats in September 2001 and April 2002, reduced juvenile populations were not compared with the yield of any summer crops. Overall, variations in disease incidence and PRKN juvenile counts cannot account for the yield gains observed for peanut cropped behind rye and the weed fallow compared with wheat and oats.

A plausible explanation for the differential yield response of peanut following oats, rye, wheat, and weed fallow is allelopathy, which occurs when leachates from straw of cereal or broadleaf covers influence germination, seedling emergence, and eventually yield of the following summer crop (Martinez-Feria et al., 2016). Such phenomenon, which is usually suppressive but may be stimulatory, occurs in no-till when debris is near the target crops (Patrick et al. 1963). Overall, rye (Yenish et al., 1996), oats (Guenzi et al., 1967), and wheat (Wu et al., 2001) residues have allelopathic activity with the former capable of providing significant weed suppression in the following peanut crop (Aulakh et al., 2015). However, the potential suppressive and/or stimulatory activity of oats, rye, and wheat on seed germination, seedling growth, and yield of peanuts has not been established nor has the host status of oats, rye, and wheat to PRKN. Strip till peanuts, which often produces greater yield (Dowler et al., 1999) or dollar value (Grichar and Boswell, 1987) compared with no-till, suggests that winter cover-related allelopathy may cause yield suppression. Here, greater yield for peanut following rye and weed fallow than oats and wheat suggests the former either maintains or enhances yield response or the latter two winter covers may suppress yield.

Yield gains for peanuts obtained with weed cover compared with oats and wheat are difficult to explain. As was noted for rye compared with oats or wheat, no reductions in SR indices or RKPop juvenile counts were associated with greater yields for peanut following the weed fallow. Henbit, which was the primary species in the weed fallow, along with chickweed and wild radish are hosts for M. incognita but not M. arenaria (Rich et al., 2008). Among the plants identified in the weed fallow, only chickweed, which constituted only a small percentage (<1%) of total weed population, is a host for A. rolfsii (Hollowell and Shew, 2007). Given that winter soil temperatures were well below the optimum for SR (Punja, 1985) and PRKN (Dickson and Melouk, 1995) development along with the absence of a high susceptible host population, the weed fallow likely did not contribute to SR or PRKN development on the subsequent peanut crop. Of the common winter weeds, wild radish, henbit, and chickweed but not Italian ryegrass are hosts for TSWV (Parrella et al. 2003). Given the low TSW incidence during the study period, the former weed species likely had little if any effect on the occurrence of this disease in peanuts. Overall, the weeds in the fallowed plots likely did not increase inoculum density of virus, fungal, or nematode pests on peanuts, which may account for the similar yields for peanuts behind the weed fallow and rye. Overall, similarly higher yield for peanuts cropped behind winter weed fallow and rye compared with those for oats and wheat indicate that latter cover crops have a detrimental allelopathic effect on the yield of the following peanut crop.

Winter cover influenced peanut grades for 2017 and 2018 but not for the 2014 to 2016 study. While peanuts behind rye and weed fallow had similarly high grades both years, those following oats had higher grades in 2018 than 2017. Greater yields obtained for peanut cropped behind rye and the weed fallow are not reflected in enhanced grades. Previously, Sorensen et al. (2010) reported that winter cover crops, including oats, rye, and wheat, did not have a significant effect on peanut grade.

Planting date often influences the occurrence of diseases in peanuts. While previous irrigated studies in Alabama, Florida, Georgia, and Texas, have shown that mid- to late April compared with later May plantings are prone to greater TSW and subsequent yield loss (Culbreath et al., 2010; Hagan et al., 2015; Mitchell et al., 1991; Tillman et al., 2007), which is likely linked with elevated thrips vector populations (Brown et al., 2005; Srinivasan et al., 2017; Todd et al., 1995). Here, planting date, largely due to low disease pressure, had no impact on the occurrence of TSW in either cultivar. While the dryland production system may contribute to the reduced TSW pressure, disease activity in a concurrent irrigated nematicide study at the same location was also negligible (Hagan et al., 2025). Incidence of SR differed by planting date only in 2015 with greater disease noted for the April than May planting, which matches the response previously reported by Bowen (2003) and Hagan et al. (2001). Otherwise, planting date, in the remaining four study years, failed to influence development of this disease, which was previously noted by Branch et al. (2021) and Hagan et al. (2015). Limited information is available concerning the impact of planting date on PRKN galling on roots and pods along with juvenile populations. Here, the effect of planting date on the level of PRKN galling to the roots, pegs, and pods differed by year and cultivar with greater damage noted for the April than May planting of Georgia-09B in 2015 and Tifguard in 2016. In a prior Alabama study, Hagan et al. (2001) noted that planting date generally did not significantly impact the level of pod and root damage on PRKN-susceptible cultivars. Planting date had little influence on final PRKN juvenile populations on both the susceptible Georgia-09B and resistant Tifguard. No prior studies have addressed the impact of planting date on PRKN population dynamics on a susceptible or resistant peanut cultivar.

Under minimal TSW pressure, the influence of planting date on yield here along with previous studies was mixed. In 2016, May compared with April plantings had greater mean yield, while superior mean yield for both cultivars was recorded for April than May plantings for the 2017 and 2018 study. In addition, yield did not significantly differ by planting date and cultivar in either the first or second study period. To reduce the risk of sizable yield losses due to intense TSW pressure, recommended planting dates were shifted from late April to mid- to late May (Brown et al., 2005). Under light to moderate TSW pressure, McKinney and Tillman (2017) recorded similar yields for Florida-07 and Georgia Green along with two breeding lines at mid-April to mid-May planting dates. Concurrently, Hagan et al. (2015) noted a yield response to planting date in only one of three years with greater yield recorded for April than May plantings of Georgia Green, Georgia-06G, and Florida-07.

Due in large measure to superior resistance to SR and PRKN, Tifguard, which is a product of the COAN (Starr et al., 2002) PKRN resistance lineage along with TifNV-High O/L (Holbrook et al., 2017), TifNV-HG (Holbrook et al., 2023), Georgia-14N (Branch and Brenneman, 2015), and Georgia-22MPR (Branch and Brenneman, 2023) consistently produced significantly greater yield than Georgia-09B in a dryland production system. Concurrently, Hagan et al. (2025) recorded similar reductions in SR incidence, but similar yields for Tifguard compared with previous industry standard, Georgia-06G, with the PRKN-resistant TifNV-High O/L producing superior yields compared with the latter cultivar. In the absence of damaging PRKN populations but similar TSW and Total Disease (TSW + SR) indices, Branch et al. (2021) reported that Georgia-09B produced significantly greater yield than Tifguard in 30 irrigated and rainfed field trials conducted over a 3-yr period. Overall, this and the concurrent study (Hagan et al., 2025) illustrate the value in terms of reduced SR and PRKN damage and resulting superior yields often associated with the use of resistant cultivars on irrigated and rainfed sites with potentially damaging resident A. rolfsii and M. arenaria Race 1 populations.

Similarly low yields to those noted in 2014 were also seen after the dry summer of 2018. As previously reported by Hagan et al. (2025), dry weather patterns in 2018 likely contributed to greatly reduced PRKN juvenile populations, particularly on the root-knot susceptible Georgia-09B, along with elevated SR indices (Bowen, 2003). Unlike the above study (Hagan et al., 2025), yield gains associated with reduced PRKN juvenile populations did not occur due to the dry weather patterns in 2018, which likely suppressed nematode reproduction and their influence on yield (Wilcox-Lee and Loria 1987). In contrast, the elevated PRKN juvenile counts noted in 2014 were likely associated with the high rainfall, which was uniform across the production season as indicated by a high Shannon's Diversity Index value.

Despite having limited impact on diseases and nematodes, superior yields were noted in the following peanuts cropped after a rye compared to oats or wheat winter covers; weed fallow often giving greater yields than the latter cereal winter covers. While the response of disease and nematode activity along with yield over five years was muted in part due to the rainfed production system, the PRKN-resistant Tifguard, which also suffered less SR damage, greatly out yielded the PRKN-susceptible Georgia-09B in a one-year out rotation with cotton on a rainfed site with established M. arenaria Race 1 and A. rolfsii populations, a common situation across Alabama, Florida, and Georgia. Overall, the yield response of Tifguard was significantly better here, and in a concurrent study (Hagan et al., 2025) than has been recorded in irrigated trials when PRKN and SR pressure was negligible (Branch 2021; Grabau et al., 2020; Hagan et al., 2023).