Hairy Fleabane as a Source of Major Insect Pests of Soybean

Abstract

-Weeds compete with crops for essential inputs, but they are also important hosts for pests, both during the crop and between crops. Hairy fleabane (Conyza bonariensis) is an important weed growing in both summer and winter crops. The aim of this study was to evaluate the occurrence and population fluctuations of soybean pests using hairy fleabane as an alternative host. Samples of hairy fleabane plants were collected fortnightly over twelve months at two sites (Boa Vista do Incra and São Vicente do Sul) in Rio Grande do Sul state, Brazil. The results showed that hairy fleabane plants provided shelter to important soybean pests, including the pentatomid stink bugs Edessa meditabunda, Piezodorus guildinii, Dichelop sp. and Euschistus heros, especially after soybean maturation, and also served as an alternative food source. This weedy species was also an important alternative host for caterpillars such as Anticarsia gemmatalis, Chrysodeixis includens, Spodoptera spp. and Helicoverpa gelotopoeon.Keywords: soybean pests, integrated pest management, weeds, Conyza bonariensis. RESUMO -As plantas daninhas competem com as culturas por elementos essenciais, mas também são importantes hospedeiros para pragas, tanto durante quanto entre os cultivos. A buva (Conyza bonariensis) é uma importante planta daninha que cresce tanto em cultivos de verão quanto nos de inverno. O objetivo deste estudo foi avaliar a ocorrência e flutuação populacional de pragas da soja utilizando a buva como hospedeiro alternativo. Amostras de plantas de buva foram coletadas quinzenalmente durante 12 meses em duas localidades (Boa Vista do Incra e São Vicente do Sul), no

Survival and Development of Fall Armyworm (Lepidoptera: Noctuidae) in Weeds During the Off-Season

“…The no-tillage system and herbicide-resistant transgenic plants have favored the increase of herbicide use to control weeds, which has generated great selection pressure on these herbicide-resistant weeds, and as a result has increased the reported cases of resistant weeds (Christoffoleti & Lopez-Ovejero 2008;Carvalho et al 2011;Cerdeira et al 2011;Heap & Duke 2018). This fact is alarming, because it may cause an increase in the seed bank of an area, and consequently the increase of weeds during the off-season, which then serves as a green-bridge for insect pests and diseases (Dalazen et al 2016).…”

Leaf Consumption and Preference to Conyza sp., Conventional and Bt Soybean by Helicoverpa armigera

“…Research on insect pests in Conyza sp. plants demonstrated peak A. gemmatalis, S. frugiperda and Helicoverpa gelotopoeon occurrence during the V0-V2 stages of soybean, indicating the role of the weed as a food source for early generations of lepidopteran species (Dalazen et al, 2016). Following crop maturity and harvesting, the authors observed another peak in the presence of the pests on Conyza sp.…”

“…Following crop maturity and harvesting, the authors observed another peak in the presence of the pests on Conyza sp. plants, indicating that the caterpillars migrated from soybean plants to the weeds after senescence (Dalazen et al, 2016).…”

“…Weeds must be eliminated during this period to prevent this species from serving as a green bridge and providing caterpillars with a continuous food source. Weed management in crops is important not only to reduce competition for resources, but also because weed species can serve as hosts for insects (Dalazen et al, 2016) and nematodes (Kaspary et al, 2017).…”

“…Studies conducted in soybean growing areas found several other insect pests on Conyza sp. plants, including Anticarsia gemmatalis, Chrysodeixis includens, Spodoptera frugiperda, Edessa meditabunda, Piezodorus guildinii and Euschistus heros (Dalazen et al, 2016). Additionally, the trichomes present on stem surface of Conyza sp.…”