Effects of simulated seedling defoliation on growth and yield of cotton in southern New South Wales

Abstract

Early-season leaf loss due to damage by thrips (Thysanoptera: Thripidae) is considered an important issue by Australian cotton growers. To understand the potential impact of early-season leaf loss in the southern region of New South Wales, we investigated the effects of artificial defoliation on cotton growth, maturity timing and lint yield over four seasons (2013–14 to 2016–17) in commercial cotton crops in the Riverina district. Four defoliation scenarios were investigated: (i) complete defoliation, 100% removal of all true leaves from all plants; (ii) partial defoliation by plant, 100% removal of all true leaves from 75% of plants; (iii) partial defoliation by leaf, removal of 75% of leaf area from all individual true leaves on all plants; and (iv) no defoliation. Defoliation was done by hand at the onset of the 2-, 4-, and 6-node growth stages. Defoliated plants were initially shorter than undefoliated (control) plants, but by ~100-days post seedling emergence, height differences were no longer statistically significant in two of the four seasons. Defoliation did not affect the total number of bolls shortly before harvest. However, complete defoliation delayed crop maturity by up to 18 days and partial defoliation by plant delayed crop maturity by up to 8 days. Because of the delays, fully defoliated plants often had fewer open bolls shortly before harvest and yielded significantly less than undefoliated plants in three of the four seasons. A laboratory experiment with caged cotton seedlings showed that weekly introductions of up to10 thrips per seedling (predominantly onion thrips (Thrips tabaci), the most abundant species on cotton in the region) caused significant clubbing in true leaves, but the total leaf area was not significantly reduced at the 6-node stage. Implications of the results for southern cotton integrated pest management are discussed.

Impacto da Desfolha Artificial no Desenvolvimento, Produtividade e Qualidade de Fibra do Algodoeiro (Gossypium hirsutum L.) Convencional e Adensado

“…A desfolha artificial provocou atraso na frutificação da cultura, em ambos sistemas de cultivos. Segundo Mo et al (2018) altos níveis de desfolhamento podem atrasar o ciclo da cultura, podendo atrasar a maturidade da cultura em até 18 dias, enquanto que a desfolha parcial pode atrasar até em 8 dias a maturação da planta. E consequentemente pode gerar menos capulhos abertos antes da colheita e, dessa forma, redução na produtividade, a depender das condições meteorológicas subsequentes.…”

A new method of gall mite management: application of artificial defoliation to control Aceria pallida

“…Artificial defoliation is widely applied to cotton to facilitate mechanical harvesting and often used to simulate defoliation by herbivory to study plant responses (Kulman, 1971; Lee & Morton, 2003; Quentin et al, 2010). Many studies have been published about the effects of artificial defoliation on plant physiology, yield and quality (Reichenbacker, Schultz & Hart, 1996; Faircloth et al, 2004; Eyles et al, 2013; Mo et al, 2018). Additionally, artificial defoliation has been shown to be effective in preventing leaf disease caused by Colletotrichum gloeosporioides Penz.…”