Abstract
Volunteer corn resistant to glyphosate is constant as weed in soybeans planted in succession. This work aimed to identify the emergence flows of volunteer corn plants in the period of time from the harvest of corn planted following soybean (autumn corn) to the plenty establishment of the canopy of the following soybean crop (summer soybean), as a function of different types of propagules generated by preceding corn harvest losses. Four field experiments were carried out in 2013 and 2014, at a Cerrado location (Sinop, MT) and a subtropical location (Londrina, PR), Brazil. Treatments included the distribution of corn crop residues (factor “A”) either on soil surface or incorporated into superficial soil layers. Four types of propagules (factor “B”) were characterized as ears with whole husk; ears with half husk; broken ears, no husk; and loose grains. The density of emerged plants was recorded fortnightly between August and December. When partially incorporated into soil, propagules generate an increased density of emerged plants as compared to the surface deposition treatments. The main sources of volunteer plants, in descending order of importance, were: (1) loose grains, (2) broken ears, (3) ears with damaged husk, and (4) ears with intact husk. Ears emerged later compared to loose grains or broken ears. Climatic conditions influence the emergence pattern. For the climate of (Savannah-like) Cerrado, the beginning of the rainy season is preponderant for the start of corn emergence. Under subtropical climatic conditions, mild low temperatures, associated or not to rainfall, determine the emergence peaks.
Highlights
The most important crop rotation in grain-producing areas of Brazil is the cultivation of soybeans in spring/summer, immediately followed by corn planted in summer/fall
Where there is no control of volunteer corn plants, soybean yield losses of approximately 25% is expected with volunteer corn densities of 1 plant m-2 (Alms et al, 2016)
The first experiment was conducted at Embrapa Agrossilvipastoril, Sinop, Mato Grosso (MT) (Lat.: 11°51′37′′ S; 55°36′19′′ W), and the second at Embrapa Soja, Londrina, Paraná (PR), (Lat.: 23°11′30′′ S; 51°10′58′′ W), Brazil
Summary
The most important crop rotation in grain-producing areas of Brazil is the cultivation of soybeans in spring/summer, immediately followed by corn planted in summer/fall. Soybean resistant to glyphosate (GR) was officially approved in Brazil to be planted in 2006, and the GR corn in 2010. After the approval of the GR corn it became itself one of the main weeds to be controlled into GR soybean fields. Volunteer plants come from grains lost during corn harvest in fall/winter, and start to emerge with the first rain events at or right after soybean sowing, in the planting season. Marquardt et al (2012) reported that 0.5-16 corn plants m-2 caused 10-40% of reduction in soybean grain yield. The soybean yield was not affected when corn, at these densities, emerged later compared to soybean. In addition to competing for environmental resources, volunteer corn can serve as a host, or green bridge, for pests and diseases, causing even more losses to soybeans. Pests which affect several crops as armyworm (Spodoptera frugiperda), may migrate from volunteer corn to soybean and impact its plant stand and productivity
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