Effects of defoliation and reduction of stand on yield of sugar beets in southern Alberta

Abstract

In southern Alberta insect pests often cause serious damage to roots or Eol iage of sugar beets. Prior to til inning, fiea beetles, Phyllotreta spp., may cause serious defoliation. After beets are thinned the sugar beet webworm, Loxostege sticliealis (L.), the beet leaf miner, P egomya iJetae Curtis, and the spinach carrion beetle, Silpha bitu berosa Lee., may cause extensive damage to the leaves. The sugar beet root maggot, Tetanol)s myopaeformis (Roder), the red-backed cutworm, Eux oa ochrogaster (Cuen.) , and the three wireworms Limoni'lls californicu.s (Mann.), Cten­ icera destructor (Brown), and HY!Jolithlls bieolor Esch. attack the root and may kill young bee ts . There is little information con­ cerning the amount of damage the plants can withstand or the level of protection required, and therefore the value of treating with insecticides cannot be adequately estimated beforehand. In England, Jones et al. (5) 3 found that 50, 75, and 100% defoliation of sugar beets in the 4- and 8-l eaf stages reduced yields by 5, 10, and 270;0) respectively. In Montana, Morris (6) found that complete defoliation of sugar beets in late June or early July reduced yi eld by Yl and 50% defoliation reduced yield by 1/ 6. Afanasiev et aZ. (I), work­ ing in the same area, reported that up to 75% defoliation reduced yield of roots by amounts not exceeding 6% and yield of tops by amounts not exceeding 20%. Complete defoliation resulted in reductions in foliage weight of up to 80% and a 23 to 270;0 reduction in beet yield. The greatest loss of: top weight occurred when plants 'were injured late in. the season. The following experiments were conducted to determine the effects of defoliation and of reduction of stand on the yields of sugar beets grown in southern Alberta so that the economic sig­ nificance of damage caused by sugar beet insects could be assessed. Materials and MethodsIn 1960 and 1961 experiments were carried ol!t on irrigated land near Lethbridge. The soil was a sil ty clay loam with a pH of 7.7. Plots had been summer fallowed the previous year and each had received an application of ammonium phosphate (11­ 48-0) at 100 pounds per acre prior to seeding. The sugar beets 1 Contribution from the Entomology Section, Canada Agriculture Resea rch Station.