A damage index for estimating yield loss in sunflowers caused by sunflower midge

Mechanisms of Hybrid Sunflower Resistance to the Sunflower Midge (Diptera: Cecidomyiidae)

“…In cases where the damage was clearly intermediate between two whole ratings, half-values were assigned. A similar rating scale was used by Bracken (1991) and found to correspond closely with yield.…”

Screening Sunflower for Tolerance to Sunflower Midge Using the Synthetic Auxin 2,4-Dichlorophenoxyacetic Acid

“…Plants of each hybrid were planted on the same date and were treated as they reached the proper growth stage. A damage rating scale developed by Bracken (1991) was used in this and subsequent tests: 0, no distortion; 1, creases in surface of the head; 2, curling of bracts inward and slight cupping toward center of the head; 3, pronounced cupping to center of the head; 4, severe cupping to center of the head; and 5, head closed, no seeds present.…”

Within-Field Distribution of the Sunflower Midge (Diptera: Cecidomyiidae)

“…Larvae develop through three instars, drop to the ground, and enter the soil in early to mid-August (Glogoza et al 1997). A second generation is possible, but in general, only the Þrst generation causes economic damage (Bracken 1990, Glogoza et al 1997.…”

“…Plant damage is variable depending on the density of larvae within the sunßower head and time of year (Bracken 1990). Estimating larval populations and sunßower head damage is difÞcult because eggs and larvae can both be present over a 2-to 3-wk period (Hodgson et al 2000.…”

“…Heavy sunßower midge populations can produce complete seed loss and severe deformities. A damage rating scale (Bracken 1990) is currently used to rate sunßower heads for seed loss and head abnormalities.…”