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.

Transgenic volunteer corn is a competitive weed in soybean that decreases soybean yield at densities as low as 0.5 plants m−2, yet the competitive effects of volunteer corn in corn have yet to be quantified in the peer-reviewed literature. In order to quantify competition between volunteer corn and hybrid corn, seed was harvested from transgenic hybrid corn. The seed was then hand-planted at two locations (Lafayette, IN and Wanatah, IN) into 3 by 9 m plots of hybrid corn at five densities: 0 (control), 0.5, 2, 4, and 8 plants m−2. Volunteer corn competition reduced leaf area and biomass of hybrid corn plants. Hybrid corn grain yield at Lafayette, IN, was reduced by 23 and 22% due to competition with volunteer corn growing in densities of 8 plants m−2 in 2010 and 2011, respectively, but when volunteer corn grain yield was combined with the hybrid corn grain yield, there was no reduction in total grain yield. This study demonstrates that the competitive effects on the grain yield of the hybrid corn will be offset by the grain yield of the volunteer plants. However, because the unpredictable locations and densities of volunteer corn plants present challenges to machine harvesting, future studies should examine what proportion of the volunteer crop is actually harvestable.

Glyphosate-resistant (GR) volunteer corn has emerged as a problematic weed in corn:soybean rotational systems, partly because of the rapid increase in adoption of corn hybrids that contain traits for both glyphosate and insect resistance. Volunteer GR corn can decrease soybean yields. The objectives of this study were to quantify the impact of volunteer corn on soybean growth and yield and determine how volunteer corn densities affect western corn rootworm (WCR) emergence. Volunteer corn seed was hand-planted at targeted densities of 0.5, 2, 4, 8, 12, and 16 seeds m−2 at soybean planting and 21 d after planting to evaluate both early- and late-emerging cohorts. WCR emergence was assessed with the use of field emergence traps placed over individual corn plants in the 0.5- and 16-plants-m−2 plots in 2008 and 2009. In 2010, WCR emergence traps were also placed over individual and clumped volunteer corn plants at densities of two and eight plants m−2. Soybean yield reductions ranged from 10 to 41% where early-emerging volunteer corn densities ranged from 0.5 to 16 plants m−2. No soybean yield loss occurred with the late-emerging cohort of volunteer corn. Twice as many adult WCRs emerged from a single volunteer corn plant growing at densities of 8 and 16 plants m−2, compared with plots containing 0.5 and 2 plants m−2. These results demonstrate that controlling volunteer corn will not only prevent soybean yield loss, but also may reduce the risk of WCR larval survival after exposure to Bt (Bacillus thuringiensis Berliner derived) corn.

The rapid adoption of genetically engineered (GE) crops by U.S. farmers suggests that these technologies have been perceived to improve farm financial performance. This study develops and applies an econometric model to data from corn and soybean producers in order to evaluate the financial impacts of the adoption of GE crops. Results indicate that the adoption of GE crops has had a limited impact on financial performance that varies by crop, type of technology, type of farm, and region of the nation. Factors other than the financial impacts appear to be important reasons for the rapid adoption of GE crops.

This article examines the impact of Bt corn adoption in the Philippines using an econometric approach that addresses simultaneity, selection, and censoring problems. Although previous literature emphasizes the importance of simultaneity and selection problems, this is the first study that addresses the issue of censoring in estimating the effects of Bt corn adoption at the farm in a developing country context. We show that Bt corn adoption provides modest but statistically significant increases in farm yields and profits. Furthermore, our results provide some evidence of inference errors that can potentially arise when censoring in the pesticide application variable is ignored in the estimation procedures.

The cultivation of genetically modified (GM) Bt maize (Zea mays L.) events MON810 and Bt11 is permitted in Uruguay. Local regulations specify that 10% of the crop should be a non-GM cultivar as refuge area for biodiversity, and the distance from other non-GM maize crops should be more than 250 m in order to avoid cross-pollination. However, the degree of cross-fertilization between maize crops in Uruguay is unknown. The level of adventitious presence of GM material in non-GM crops is a relevant issue for organic farming, in situ conservation of genetic resources and seed production. In the research reported here, the occurrence and frequency of cross-fertilization between commercial GM and non-GM maize crops in Uruguay was assessed. The methodology comprised field sampling and detection using DAS-ELISA and PCR. Five field-pair cases where GM maize crops were grown near non-GM maize crops were identified. These cases had the potential to cross-fertilize considering the distance between crops and the similarity of the sowing dates. Adventitious presence of GM material in the offspring of non-GM crops was found in three of the five cases. Adventitious presence of event MON810 or Bt11 in non-GM maize, which were distinguished using specific primers, matched the events in the putative sources of transgenic pollen. Percentages of transgenic seedlings in the offspring of the non-GM crops were estimated as 0.56%, 0.83% and 0.13% for three sampling sites with distances of respectively 40, 100 and 330 m from the GM crops. This is a first indication that adventitious presence of transgenes in non-GM maize crops will occur in Uruguay if isolation by distance and/or time is not provided. These findings contribute to the evaluation of the applicability of the “regulated coexistence policy” in Uruguay.

Release of transgenic insect-resistant crops creates the potential not only for the insect pest to evolve resistance but for the escape of transgenes that may confer novel or enhanced fitness-related traits through hybridization with their wild relatives. The differential response of diamondback moth (Plutella xylostella) populations in eastern and western Canada to Bt-producing (GT) Brassica napus and the potential for enhanced fitness of GT B. napus and weedy GT Brassica rapa × B. napus hybrid populations (F1, BC1, BC2) were studied. Comparative bioassays using neonates and 4th instars showed that GT B. napus and GT B. rapa × B. napus hybrids are lethal to larvae from both populations. No measurable plant fitness advantage (reproductive dry weight) was observed for GT B. napus (crop) and GT B. rapa × B. napus hybrid populations at low insect pressure (1 larva per leaf). At high insect densities (>10 larvae per leaf), vegetative plant weight was not significantly different for GT B. napusand non-GT B. napus, whereas reproductive plant weight and proportion of reproductive material were significantly higher in GT B. napus. Establishment of the Bt trait in wild B. rapa populations may also increase its competitive advantage under high insect pressure.