During the last decade, the production of off-season maize has increased in several regions of Brazil. Growing maize during this season, with sowing from January through April, imposes several climatic risks that can impact crop yield. This is mainly caused by the high variability of precipitation and the probability of frost during the reproduction phases. High production risks are also partially due to the use of cultivars that are not adapted to the local environmental conditions. The goal of this study was to evaluate crop growth and development and associated yield, yield components and water use efficiency (WUE) for maize hybrids with different maturity ratings grown offseason in a subtropical environment under both rainfed and irrigated conditions. Three experiments were conducted in 2001 and 2002 in Piracicaba, state of Sa˜o Paulo, Brazil with four hybrids of different maturity duration, AG9010 (very short season), DAS CO32 and Exceler (short season) and DKB 333B (normal season). Leaf area index (LAI), plant height and dry matter were measured approximately every 18 days. Under rainfed conditions, the soil water content in the deeper layers was reduced, suggesting that the extension of the roots into these layers was a response to soil water limitations. On average, WUE varied from 1.45 kg m )3 under rainfed conditions to 1.69 kg m )3 under irrigated conditions during 2001. The average yield varied from 4209 kg ha )1 for the hybrids grown under rainfed conditions to 5594 kg ha )1 under irrigated conditions during 2001. Yield reductions under rainfed conditions were affected by the genotype. For the hybrid DKB 333B with a normal maturity, yield was reduced by 25.6 % while the short maturity hybrid Exceler was the least impacted by soil water limitations with a yield reduction of only 8.4 %. To decrease the risk of yield loss, the application of supplemental irrigation should be considered by local farmers, provided that this practice is not restricted by either economic considerations or the availability of sufficient water resources.

RESUMO -Um levantamento de plantas daninhas foi realizado em 20 lavouras de milho safrinha em 1997 e 40 em 1998 e 1999, depois da soja, na região do Médio Paranapanema-SP. O levantamento abrangeu os municípios de Assis, Campos Novos, Cândido Mota, Cruzália, Florínea, Maracaí, Palmital, Pedrinhas Paulista e Platina. No estádio de enchimento de grãos, as lavouras foram percorridas em ziguezague, a partir de quatro pontos de entrada, de maneira a representar a área total. As lavouras foram subdivididas de acordo com as condições de manejo das culturas: semea dura direta, semeadura convencional em solo preparado com grade e semeadura de milho safrinha na palha de soja cultivada no sistema convencional. Em cada lavoura fora m cadastrados o nível de infestação e as espécies daninhas. Foram coletadas informações quanto ao manejo das plantas daninhas adotado nas lavouras, assim como sobre os herbicidas empregados. As espécies de plantas daninhas mais importantes foram Cenchrus echinatus, Bidens pilosa, Euphorbia heterophylla, Raphanus sativus, Digitaria horizontalis, Commelina benghalensis, Amaranthus sp., Achyrocline satureioides, Sinapis arvensis , Sida sp., Glycine max, Avena strigosa, Eleusina indica e Sorghum halepense. Houve acentuado aumento na infestação da espécie C. echinatus nas lavouras, a qual passou a constituir-se na principal espécie infestante. R. sativus também se tornou importante e apresentou grande incremento de 1997 a 1999. Na semeadura convencional houve predomínio de alta infestação, evidenciando desempenho inferior desse sistema em relação aos demais no controle de plantas daninhas. O controle químico mais utilizado foi a mistura atrazine + óleo vegetal + 2,4-D, seguido por atrazine + óleo e atrazine isolado. De modo geral, não se efetuou o controle das plantas daninhas em 22% das lavouras, as quais apresentaram as maiores porcentagens de infestação. O nível de infestação em função do tipo de controle foi variável de acordo com o ano agrícola. Palavras-chave:Zea mays, manejo do solo, herbicidas, infestação, plantas daninhas. ABSTRACT -A weed infestation survey was performed in 20 second corn crop areas in 1997 and in 40 areas in 1998 and 1999 after soybean planting in the Médio

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The Middle Paranapanema region concentrates a large part of the second corn production in São Paulo State. Weed surveys in commercial areas are important for monitoring and directing their management. In 2006, 2007, and 2008, weed surveys were carried out on 27, 25, and 24 corn crops, respectively, in ten counties of this region. At the grain filling stage, crops were zigzag sampled with 20 points of 1 m2 per area. In addition, information on weed management, soil cover, and history of the summer crop were collected. The phytosociological parameters frequency, density, abundance, and importance value index were determined. The results evidenced Cenchrus echinathus as the most important species in 2006 and 2007, in addition to high importance values in 2008, which reflected the need to improve its management. Bidens pilosa, Digitaria horizontalis, and Euphorbia heterophylla were important species for the crop. Although under a low frequency, outbreaks of Leonurus sibiricus and Gnaphalium spicatum were observed in the areas, increasing their importance in 2007 and 2008. Atrazine was the most used herbicide over the agricultural years, with a low use of other products. Soil cover presented a high variation, but a high number of fields presented a low soil cover. Despite the increase of transgenic soybean in this region, no consistent evidence of changes in weed community resulted from this transition.

This work is the first one after the consolidation of the introduction of the RR technology in maize and soybean crops, following weed surveys previously carried out in the region of the Middle Paranapanema, São Paulo state. The objective was to carry out a phytosociological survey of weeds in off-season maize crops no-tillage, in the same properties where the studies had been previously carried out, in the described region, taking into account the management of the weed community adopted by farmers, and the percentage of plant coveron the soil. The surveys were carried out in 19 farms conducted under no-tillage systems, with off-season maize cultivated in soybean succession, both RR crops, in nine municipalities of the São Paulo region of the Middle Paranapanema, in 2016. The main weeds were Bidens pilosa, Cenchrus Echinatus, Commelina benghalensis, Digitaria horizontalis, Gnaphalium spicatum, Leonotis nepetifolia, Raphanus sativus and Sonchus oleraceus. The predominant management of weeds was the chemical method, and in the vast majority of properties, control was based on the use of glyphosate and atrazine. The other used herbicides are nicosulfuron, chlorimuron-ethyl, clethodim, haloxyfop, tembotrione and 2,4-D, almost always associated with the EPSPs inhibitor. The soil cover with straw, found at the time of the evaluation, had no correlation with the presence or absence of the weeds.