Is the plant biostimulant application ameliorative for herbicide-damaged sunflower hybrids?

Sunflower (Helianthus annuus L.) is one of the most economically important field crops grown in Bulgaria. In some cases sunflowers from different systems (IMI-SUN or ExpressSUN) are sprayed by mistake with the unappropriated herbicidal product for the growing system - IMI- or Express SUN and reverse. Then, acute or chronic phytotoxic effects (even death of the plants) may occur. In some situations, the plants mistakenly treated with the wrong herbicidal product may recover completely, or to different extents after ameliorative treatment with plant biostimulants. For this reason, two field trials in three consecutive growing seasons in 2017, 2018, and 2019 were conducted. The experiments were performed in the experimental field of the Department of Agriculture and Herbology at the Agricultural University of Plovdiv, Bulgaria. The experiments aimed to evaluate the ameliorative effect of the plant biostimulant Amino Expert (R) Impuls after imitation of "mistaken" herbicide application. In the first experiment the ExpressSUN sunflower hybrid "P 64 LE 25 '' was treated with imazamox, and in the second, the IMI-SUN sunflower hybrid "Bacardi" CLP (Clearfield Plus) was sprayed with tribenuronmethyl. The treatments included untreated control plots, application of imazamox (Pulsar Plus - 2.00 l ha-1), or tribenuron-methyl (Express 50 WG (water-soluble granules) - 0.04 kg ha-1 + Trend 90-0.1%) alone and variants with the ameliorative supplication of plant biostimulant four days after the herbicidal intervention. After the application of the plant biostimulant Amino Expert Impuls for ameliorative treatment, the plants from both cropping systems overcome the herbicide stress to different extents. The Chlorophylls (a and b) and carotenoids as well as net photosynthetic rate were higher for the untreated plants from both technologies. For the treatments where plant biostimulant application was used, an increase of the parameters sunflower head diameter, plant height, seed yield, absolute seed mass, as well as seed oil content were recorded. The obtained results showed that the significant results are in favor of ExpressSun technology. In the event of errors in the application of herbicides in these two cropping systems, the consequences are much more corrective in cases where tribenuronmethyl-tolerant sunflower is treated with Pulsar Plus than if IMI-SUN sunflower is treated with the herbicide Express 50 WG + Trend 90.