Estimating hop parameters prior to calculating economic thresholds of intervention against Phorodon humuli (Hemiptera: Aphididae)

SummaryEconomic thresholds of intervention against the hop aphid, Phorodon humuli, can be expressed using different parameters. Some of these parameters are calculated using measurements which are not easy to record directly, but which can be obtained from simpler measurements. In this paper, the functions relating two simple measurements to two more complex ones were obtained from two hop plots in Leon, Spain, in 2002 and 2004. The function relating the area of the hop leaf (y) to its length (x) is obtained by y = 1.13 (± 0.10) x2 – 3.55 (± 1.91) x + 3.64 (± 8.25). The functions relating the number of leaves (y) in the canopy volume formed by the area (x) of the bine section of the hop plant (which normally had two strings per rootstock and three bines trained per string) as a base and a height of 20 cm, to this area (x) are y = 0.020 (± 0.002) x + 5.291 (± 2.278), at heights of 2 m and 3.25 m from ground level, and y = 0.034 (±0.004) x – 0.419 (± 4.310), at a height of 6 m above ground level.