SAMPLING PLANT BUGS, LYGUS SPP. (HETEROPTERA: MIRIDAE), IN CANOLA TO MAKE CONTROL DECISIONS

Abstract

The Canadian Entomologist 130: 825 -836 (1998) Plant bugs in the genus Lygus infest canola (Brassica napus L. and Brassica rapa L.) when the crop is producing buds, flowers, and pods. Field studies in cages and open plots show that plant bugs can reduce yield by 20% or more, but have little effect on seed size. A single application of a foliar insecticide when the crop has finished flowering and is beginning to produce pods will prevent most or all of the yield loss. The yield loss of canola that can be prevented by control is 0.007 t/ha per plant bug per 10 sweeps sampled at the end of flowering or the beginning of pod formation. The yield loss that can be prevented by a later application drops to 0.005 t/ha. When precipitation is greater than 100 mm from the onset of bud formation to the end of flowering, the crop may partially compensate for plant bug damage. The economic threshold for control of plant bugs in canola at the end of flowering or at the beginning of pod formation is 15 plant bugs per 10 sweeps, based on crop prices and control costs from 1989 to 1992. If plant bugs are present but control is not warranted when most flowenng is complete, plant bug densities should be assessed again 5-7 days later as pods develop, but at this stage the threshold is 20 plant bugs per 10 sweeps. The use of economic thresholds for chemical control of plant bugs will maximize seed yield and minimize unnecessary or ineffectively timed insecticide applications. Wise, I.L., et R.J. Lamb. 1998. Seuil Cconomique des punaises des plantes Lygus spp. (Heteroptera : Miridae) sur le colza. The Canadian Entomologist 130 : 825-836.

ECONOMIC THRESHOLD FOR PLANT BUGS, LYGUS SPP. (HETEROPTERA: MIRIDAE), IN CANOLA

“…Plant bug counts per square metre were converted to number per 10 sweeps to allow comparison with field plot data, based on studies of the sampling efficiency of sweep netting in canola (conversion factor of 0.526, Wise and Lamb 1998). In the cages where 10 plant bugs were introduced, densities at the end of the season were equivalent to about 78 per 10 sweeps, close to the highest density observed in the field (see below).…”

“…This timing was also recommended by Butts and Lamb (1991b) for canola in Alberta. An efficient method for sweep sampling plant bugs in canola and a sequential sampling scheme are described separately (Wise and Lamb 1998).…”

Sampling Methods for Forest Understory Vegetation

“…For example, speed of net motion has an impact on catch size, with a greater speed collecting more insects (Balogh & Loska 1956), and experienced samplers may capture more insects because they sweep more vigorously and more deeply into the crop (Wise & Lamb 1998). Vegetation density and crop phenology are also significant (Byerley et al 1978, Wilson & Gutierrez 1980, Ellington et al 1984.…”

“…Wise and Lamb (1998) found that there was stability and repeatability in the relationship between variance and mean, allowing sweep nets to be used to detect whether pest populations were above or below level of control. However, there can be biases, for example towards adults and large nymphs of Lygus species (probably due to their location in the upper parts of the plant) (Wise & Lamb 1998). Linders (1995) found the sweep net to be effective for sampling the weevil Trichosirocalus troglodytes on Plantago lanceolata spikes, but the catches were influenced by diurnal and seasonal activity.…”

Comparing four simple, inexpensive methods for sampling forest arthropod communities

“…Studds and Marra () modified sweep nets to sample higher above ground, but were still limited to a height of ~ 5 m, below that of most forest canopies. In addition, potential human sampling effects (speed, strength, and experience; Wise and Lamb , Cooper et al. ) and weather conditions (Ozanne ) can introduce bias in sweep‐net samples.…”