Efeitos do posicionamento tardio de glifosato em milho

Let's talk a little about the effects of late glyphosate application in corn. Symptomatology, why the damage occurs, and loss levels. Welcome to the channel that helps you stay updated and make more assertive decisions regarding the management of annual crops on your property. I am Paulo Adami, PhD in Agronomy, and today we will discuss the phytotoxicity of herbicides in corn, more specifically the problem of late glyphosate use in RR corn. In the 21/22 growing season, excessive rain and a sequence of cloudy days reduced the residual effect of atrazine and are favoring the occurrence of other weed emergence flushes, leading to situations where the producer intervenes late to control these weeds using glyphosate. What are the damage mechanisms? Glyphosate is mobile in the phloem and therefore tends to translocate and accumulate in sinks, i.e., in apical meristems and roots (Hetherington et al., 1999). Glyphosate is poorly metabolized by the plant, meaning that the herbicide remains in its active form and can damage developing tissues that show inadequate expression of the resistant form at the target site (Feng et al., 2010). Why are only some grains affected? Many glyphosate-resistant hybrids are not homozygous for the technology – one parent (usually the mother) is resistant and the other is not. The resulting F1 hybrid plants are all heterozygous for the trait, with one resistant allele and one susceptible allele. The resistant allele is dominant, so the F1 hybrid plants are all glyphosate-resistant. There may even be 3% segregation, which is a portion of plants that die after glyphosate application, but in general, hybrid plants are all glyphosate-resistant. The fertilized grains in the plant represent the F2 generation. Since the F2 embryos are the product of two heterozygous parents (F1), they will segregate into 25% homozygous resistant, 50% heterozygous resistant, and 25% homozygous susceptible. This means that approximately 25% of the developing grains in the ear are susceptible to damage if exposed to glyphosate after V7-V8. In the affected grains, the embryo will die while the endosperm remains alive. Initially, this results in the characteristic translucent – ​​“bubble” appearance. As ear development progresses, the damaged grains will appear hollow and eventually collapse. Adjacent grains expand to fill the gaps left by the damaged grains, resulting in an uneven ear. Factors influencing the risk of damage/phytotoxicity The main risk factor for damage or malformation of the corn ear due to glyphosate phytotoxicity occurs in late applications, including those outside the label recommendations. The risk of lesions also increases with increasing doses of glyphosate (up to 1300 g acid equivalent per hectare), and in areas with overlapping applications or application after V7. Yield impact As in most cases, 25% of the grains in the ear would be susceptible to glyphosate lesions, the theoretical yield loss could be up to 25%. The actual yield loss will likely be less than this, although it may still be significant. This is because the grains adjacent to those affected will expand into the gaps left in the ear, partially compensating for the lost grains. The greatest yield loss observed in a 3-year field study was 10% on average in five locations with an above-indicated rate of glyphosate applied at the V8-V10 stage. Nielsen, RL. 2013. Jumbled kernel symptom in corn & late glyphosate applications. Purdue Univ. http://www.ppdl.purdue.edu/PPDL/weekl... Feng, P.C.C., C.A. CaJacob, S.J. Martino-Catt, R.E. Cerny, G.A. Elmore, G.R. Heck, J. Huang, W.M. Kruger, M. Malven, J.A. Miklos, and S.R. Padgette. 2010. Glyphosate resistant crops: developing the next-generation products. In Nandula, V. K. (ed.) Glyphosate Resistance in Crops and Weeds. John Wiley and Sons, Inc., Hoboken, NJ. Hetherington, P.R., T.L. Reynolds, G. Marshall, and R. C. Kirkwood. 1999. The absorption, translocation and distribution of the herbicide glyphosate in maize expressing the CP-4 transgene. J. of Exp. Bot. 50:1567-1576