Does continuous cropping of maize contribute to infestation with Johnsongrass (Sorghum halepense (L.) Pers.)?

Abstract

Johnsongrass (Sorghum halepense (L.) Pers.) is a very common weed in maize fields in Serbia. Dense Johnsongrass infestations severely limit maize production, especially under continuous maize cropping. The key tool to manage this weed is to implement multiple control strategies when Johnsongrass is first observed and not to wait until it is firmly established. Experiments were conducted in the Maize Research Institute (MRI), Zemun Polje, Belgrade, in order to examine how economically driven continuous cropping of maize influences weed infestation, especially the distribution and abundance of Jonhsongrass, as well as maize productivity. The maize hybrid ZP 606 was grown in continuous cropping from 2009 to 2018 at a density of 59,500 plants ha-1. The experimental field was split into a part treated with the pre-emergence herbicide isoxaflutole + metolachlor (750 + 960 g a.i.) and untreated control. The level of complete weed infestation was evaluated 4-5 weeks after herbicide application by determining the number of weed individuals per species (NI), total fresh biomass (TB) and total dry weight (TDW) of all weeds and Johnsongrass fresh biomass (JB) and dry weight (JDW). Maize harvest index (HI) and grain yield (GY) were determined at the end of each growing period. All measured weed parameters were highly dependent on agro-meteorological conditions of the year, herbicide application and their interaction. On average, TDW was 760.7 g m-2 in the control plot, and 142.2 g m-2 in the treated plot, while Johnsongrass participated with 34.8% and 48.7%, respectively. Herbicide application reduced JDW by 77.6% on average, even though its biomass increased over the years. A regression analysis revealed that GY was negatively influenced by JDW (R2= - 0.094) in untreated control, while GY was higher with a lower JDW under herbicide treatment (R2=-0.4439). Continuous cropping of maize should be replaced with crop rotation in order to prevent Johnsongrass prevalence and to obtain higher crop productivity.

Divlji siriak (Sorghum halepense (L.) Pers.) je vrlo čest korov na poljima u Srbiji. Intenzivna zakorovljenost divljim sirkom ozbiljno ograničava proizvodnju kukuruza, naročito kada se on gaji u monokulturi. Suština borbe protiv ovog korova je pravovremena primena više mera suzbijanja čim se divlji sirak uoči i pre nego što razvije veliku masu rizoma i dobro se ukoreni. Poljski ogled je izveden u Institutu za kukuruz Zemun Polje, sa ciljem da se utvrdi kako profitom dirigovano gajenje kukuruza u monokulturi utiče na zakorovljenost, naročito na rasprostranjenost i brojnost divljeg sirka, kao i na produktivnost kukuruza. Hibrid ZP 606 je gajen u monokulturi u periodu 2009-2018. godine u gustini od 59.500 biljaka ha-1. Polje pod kukuruzom u monokulturi je podeljeno na deo na kome je primenjivan herbicid pre nicanja useva (isoksaflutol + metolahlor (750 + 960 g am) i deo koji nije bio tretiran - kontrola. Intenzitet zakorovljenosti je određen 4-5 nedelja nakon primene herbicida merenjem broja jedinki vrsta (NI), ukupne sveže biomase (TB) i ukupne suve mase (TDW) svih korova i sveže biomase divljeg sirka (SB) i njegove suve mase (JDW). Žetveni indeks (HI) i prinos zrna (GY) određeni su na kraju vegetacionog perioda kukuruza. Svi parametri korova u velikoj meri su zavisili od agro-meteorološkoh uslova godine, primene herbicida i njihove interakcije. U proseku, TDW je iznosila 760,7 g m-2 u kontroli i 142,2 g m-2 na tretiranoj parceli, od čega je udeo suve mase divljeg sirka bio 34,8% u kontroli i 48.7% na tretiranoj parceli. Primena herbicida smanjila je suvu masu divljeg sirka prosečno za 77.6%, iako se ona sa godinima povećavala. Prema regresionoj analizi, JDW je negativno uticala na GY (R2= - 0,094) u kontroli, dok se GY povećavao sa smanjenjem JDW u varijanti sa primenjenim herbicidom (R2=-0,4439). Monokulturu kukuruza bi trebalo zameniti plodoredom da bi se sprečilo zakorovljavanje divljim sirkom i postigla veća produktivnost useva.