Nebraska is one of the top five corn-growing states in the United States, with the planting of corn on 3.5 to 4 million hectares annually. Harvest loss of corn results in volunteer corn interference in the crop grown in rotation. Estimating the extent of harvest loss and expected volunteer corn density is a key to planning an integrated volunteer corn management program. This study aimed to evaluate the harvest loss of corn and estimate the potential for volunteerism. Harvest loss samples were collected after corn harvest from a total of 47 fields in six counties, including 26 corn fields in 2020, and 21 fields in 2021, in south-central and southeastern Nebraska. An individual cornfield size was 16 to 64 ha. A total of 16 samples were collected from each field after corn harvest in 2020 and 2021. Harvest loss of corn was 1.5% and 0.7% of the average yield of 15,300 kg ha−1 in 2020 and 2021, respectively. Corn harvest loss was 191 and 80 kg ha−1 from dryland fields, and 206 and 114 kg ha−1 from irrigated fields in 2020 and 2021, respectively. An average kernel loss of 68 and 33 m−2 occurred in 2020 and 2021, respectively. The germination percentage of corn kernels collected from harvest loss was 51%, which implies that volunteer corn plants of 35 and 17 m−2 from 2020 and 2021, respectively, could be expected in successive years. A volunteer corn management plan is required, because if it is not controlled, this level of volunteer corn density can cause yield reduction depending on the crop grown in rotation.

Herbicide options for management of volunteer corn in soybean include a variety of acetyl CoA carboxylase-inhibiting herbicides, yet often, applications of acetyl CoA carboxylase herbicides are delayed until the weed is visible above the soybean canopy. Volunteer corn growing above the soybean canopy is a highly competitive weed, and herbicides applied at this point can kill the weed, yet soybean yield loss is still a concern. Our objective was to compare the effect of controlling various densities of volunteer corn growing in soybean EARLY (≤ 30 cm) versus LATE (≈ 90 cm) on percent control and soybean yield. Seven volunteer corn densities (0, 0.5, 2, 4, 8, 12, and 16 plants m−2) were hand planted into 19-cm row soybean. Clethodim 79 g ai ha−1 was tank-mixed with glyphosate at 840 g ae ha−1 and applied to the volunteer corn EARLY and LATE. The EARLY application provided higher and less variable control of volunteer corn 14 d after treatment (DAT) compared to LATE applications at all volunteer corn densities. There was no difference in control at 28 DAT for both the EARLY and LATE applications. Soybean yield was not affected by either application timing. Although no yield reduction was seen with the LATE treatments, later-season applications of clethodim to control volunteer corn may offer more variable control and could allow for additional Bt selection pressure on targeted insect pests.

Initial corn (IC) in a replant situation, which is surviving corn from the initial planting, as well as volunteer corn from the previous season, is a competitive weed, but little is known regarding the effect of IC density on grain yield of desirable replant corn (RC). Field trials were established in central and northeast Missouri during 2008 to 2010 to determine the impact of IC on the leaf chlorophyll, stalk diameter, and grain yield of RC. Glyphosate-resistant RC was planted in 76-cm rows, with hybrid glyphosate-resistant IC established for season-long competition between rows at densities of 0 to 8 plants m−2. At vegetative growth stages with six and eight leaf collars and at tasseling (V6, V8, VT), RC leaf nitrogen levels were reduced by 5 to 30% in the presence of IC at densities of one to eight plants m−2 compared with control plants lacking competition. Stalk diameters of RC at the VT growth stage were reduced from 8 to 30% by IC as densities increased from 0.5 to 8 plants m−2. Grain yield of row corn was reduced by IC, with yield losses ranging from 7 to 81%. Growth rate and biomass accumulation of hybrid and volunteer corn from V2 to VT were compared in the greenhouse to determine if competitive potential was similar. The second filial generation (F2) of corn from hybrid (DKC ‘63-42′) corn was collected from a field in central Missouri and southeastern Nebraska. There were no statistical differences found in growth rate or biomass accumulation between hybrid and F2 corn up to VT, although F2 plant biomass was numerically (up to 41%) lower at numerous growth stages. Hybrid corn is likely to be equally or more competitive with RC than volunteer corn. This research documents that in areas where IC remains among replanted corn, the IC has a negative impact at all densities evaluated.

In the spring of 2007, a widespread freeze occurred that led to the replanting of about 81,000 hectares of corn in Tennessee. Limited research was available on effective herbicide options to control failed stands of glyphosate-tolerant corn where replanting to corn was desired. Therefore, in 2007 on three failed freeze-damaged corn stands (27,000 plants/ha) and in 2008 on two non–freeze-damaged corn stands (81,000 plants/ha), studies were initiated to determine how to control the failed stand while not harming subsequent replant corn. The results from this research clearly show that producers have several effective options to manage undesirable glyphosate-tolerant corn before replanting to corn. Clethodim at 0.14 kg/ha, paraquat at 0.84 kg/ha, or paraquat at 0.70 kg/ha plus a photosystem II (PSII) inhibitor provided very good control of the original corn stand without affecting the yield of the replanted corn. Moreover, the addition of a PSII inhibitor could provide residual weed control in the replanted corn. Paraquat should be applied at rates of 0.70 kg/ha or greater to obtain consistent control of an undesirable corn stand.

Volunteer Enlist corn with the AAD-1 (aryloxyalkanoate dioxygenase-1) transgene can become a problem when glyphosate-resistant (GR) soybean follows Enlist corn in the rotation. Field trials were conducted at Ridgetown, Ontario in 2013 and 2014 to evaluate the control of volunteer Enlist corn in GR soybean. Glyphosate plus clethodim at 30 g ai ha−1 provided 75 to 92% control of volunteer Enlist corn at 1, 2, 4, and 8 weeks after treatment application (WAT) and reduced volunteer Enlist corn density and dry weight 95 to 97%. Glyphosate plus clethodim at 60 g ai ha−1 provided 84 to 98% control of volunteer Enlist corn at 1, 2, 4, and 8 WAT and reduced volunteer Enlist corn density and dry weight 97 to 99%. Glyphosate plus sethoxydim at 150 g ai ha−1 provided 66 to 86% control of volunteer Enlist corn at 1, 2, 4, and 8 WAT and reduced volunteer Enlist corn density and dry weight 91 to 97%. Glyphosate plus sethoxydim at 300 g ha−1 provided 84 to 96% control of volunteer Enlist corn at 1, 2, 4, and 8 WAT and reduced volunteer Enlist corn density and dry weight 96 to 98%. Glyphosate plus fenoxaprop-p-ethyl, fluazifop-p-butyl, and quizalofop-p-ethyl applied POST provided 0 to 9% control of volunteer Enlist corn at 1, 2, 4, and 8 WAT and reduced volunteer Enlist corn density and dry weight 18 to 44%. Soybean yields closely reflected the level of volunteer Enlist corn control. Based on these results, the cyclohexanedione herbicides, clethodim and sethoxydim, provide adequate control of volunteer Enlist corn in GR soybean. In contrast, the aryloxyphenoxypropionate herbicides, fenoxaprop-p-ethyl, fluazifop-p-butyl and quizalofop-p-ethyl do not provide control of volunteer Enlist corn in GR soybean.

Volunteer corn is often overlooked as a weed in soybean. To aid in management decisions, this study determined soybean yield loss attributed to volunteer corn and efficacy of various herbicides at several rates and timings. A hyperbolic equation estimated (R2 = 0.88) incremental yield loss (I) of 39.7% at low density when maximum yield loss (A) was constrained to 71%, the highest yield loss observed in these trials, revealing a more competitive plant than many common midwestern weedy species. Clethodim applied at 51 g ai ha−1 at V4 soybean resulted in > 90% volunteer corn control with < 5% soybean yield loss, whereas if applied at 12.7 g ai ha−1 volunteer corn control was 15%, but soybean yield was 50% greater than the nontreated control. On the basis of these data, the partial volunteer corn control improved soybean yield. Timing of glufosinate application influenced volunteer corn control. Glufosinate applied to 15-cm-tall corn resulted in 33% control, whereas applications to 36- to 91-cm corn resulted in > 70% control. Glufosinate combined with grass herbicides improved control to > 85%, with concomitant yield increases. Results demonstrated that volunteer corn substantially reduced soybean yield at low densities and yield increased when volunteer corn was controlled with various herbicides. On the basis of these results, and current soybean grain and herbicide prices, soybean yield gains from volunteer corn control could increase net return by > $150 ha−1.