Simulated Hail Research in Sunflower: Defoliation¹

Abstract

Accurate loss procedure and compensation due to hail losses are a major concern to both the producer and the insurance company. Field experiments simulating leaf loss such as that which would occur as a result of a hail storm were conducted on hybrid sunflower (Helianthus annuus L.) at Carrington and Fargo, ND. The objective of this study was to investigate the agronomic response of sunflower to various levels of defoliation applied at different stages of plant development. Defoliation treatments (0, 25, 50, 75, and 100% of the leaves randomly removed with a knife) were applied at nine stages of plant development from V4 through R7. Fifty, 75, and 100% defoliation averaged across all developmental stages decreased seed yield significantly compared to the check. Seventy-five and 100% defoliation decreased seed yield significantly compared to the check when treatments were applied at the R1 through R6 stages. Plant death often resulted when treatments of 100% defoliation were applied at stages R3 and R4. Oil percentage decreased significantly with 100% defoliation at the R4 through R7 stages. One-hundredpercent defoliation averaged over all stages of plant development decreased oil percentage an average of 11.9%. One-hundred-percent defoliation averaged across all stages of plant development decreased head diameter, plant height, percent stem breakage; days to R5.5, and achene weight. Complete removal of leaves at the reproductive (R) stages of plant development affected the variables measured to the greatest degree. As defoliation percentage decreased, values of variables measured were affected to a lesser degree.

Dwarf sunflower response to row spacing, stand reduction, and defoliation at different growth stages

“…At GS R6, full leaf display has occurred and removal of leaves is complete without the possibility for development of small uncounted leaves as is the case at GS R1 where even at 100% defoliation perhaps 10 or more small leaves could develop after treatment. Schneiter et al (1987) showed 48 and 82% yield reductions from 100% defoliation at GS R1 and R6, respectively, for Hybrid 894. They observed the greatest yield reduction when defoliation was applied at GS R3 and R4 where the majority of plants died at 100% defoliation.…”

“…Yield was also reduced by the 50 and 75% defoliation levels at the 15 leaf to flowering stages. Schneiter et al (1987) studied sunflower response to defoliation by utilizing a conventional height hybrid where treatments were applied at defined maturity stages. Schneiter reported a significant growth stage by defoliation interaction where yield reductions increased with increasing defoliation and maturity until stage R4.…”

Escala diagramática de quantificação de dano causado por granizo em folhas de girassol

“…Os poucos trabalhos sobre simulação de danos foliares por granizo, ou mesmo por insetos, para culturas, como para o próprio girassol (BUTIGNOL, 1983;KARADOGAN;AKGÜN, 2009;MORIONDO;ORLANDINI;VILLALOBOS, 2003;MURO et al, 2001;NEZAMI et al, 2008;SCHNEITER;JONES;HAMMOND, 1987), utilizam a desfolha artificial de folhas inteiras como metodologia, o que não reflete o dano físico em área proporcional de todas as folhas, com suas consequências no transporte de assimilados, água e demais nutrientes e estresse fisiológico (TAIZ;ZEIGER, 2004). Trabalhos que relacionam a injúria foliar e a estimativa de perdas de área fotossintetizante na forma de escala para quantificação dos danos foliares por granizo não foram relatados na literatura.…”

“…Dessa forma, pode-se inferir que a metodologia de desfolha artificial utilizada para a avaliação e estimativa de dano foliar por granizo (KARADOGAN; AKGÜN, 2009;MORIONDO;ORLANDINI;VILLALOBOS, 2003;MURO et al, 2001;SCHNEITER;JONES;HAMMOND, 1987) pode não ser a mais adequada.…”

The effect of defoliation on the yield of leek (Allium porrum L.)

“…Three different types of responses to plant defoliation have been described (McNaughton, 1983): (1) detrimental effect, which consists of a decrease of growth rate and fitness of attacked plants; (2) no effect, when attacked plants show similar growth rates and fitness to control plants unless a certain damage threshold is reached above which a negative effect occurs; (3) beneficial effect, when, after moderate level of damage, a recovery in plant growth and fitness is observed (Prins et al, 1989). On the other hand, Schneiter et al (1987) and Schneiter and Johnson (1994) pointed out that (a) defoliation affects yield and (b) its occurrence in different developmental stages results in significant differences in final yield.…”