Submitted to: Small Ruminant Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/15/2005
Publication Date: 12/1/2007
Citation: Hatfield, P.G., Blodgett, S.L., Spezzano, T.M., Goosey, H.B., Lenssen, A.W., Kott, R.W. 2007. Incorporating sheep into dryland grain production systems: I. Impact on over-wintering larva populations of wheat stem sawfly, Cephus cinctus Norton, (Hymenoptera: Cephidae). Small Ruminant Research. 67:209-215. Interpretive Summary: Wheat stem sawfly is the most injurious pest of wheat in Montana. Many methods of control of wheat stem sawfly have been tried, but none are effective, reliable and inexpensive to producers. We conducted grazing trials with sheep on Montana wheat fields infested with wheat stem sawfly and found that sheep grazing caused up to 70% mortality of over-wintering larvae, substantially greater than for tillage, burning, or untreated controls.
Technical Abstract: Wheat stem sawfly (WSS), Cephus cinctus Norton, (Hymenoptera: Cephidae) is the most damaging insect pest to Montana's $1 billion dollar per year grain industry. Current WSS control methods are either cost prohibitive, reduce wheat yields, or are not consistently effective. Our objective was to compare burning, grazing, tilling, trampling and clipping wheat stubble fields on over-wintering WSS larval populations. Treatments were evaluated in a series of three experiments using a completely randomized block design and four replications at each site. Eight, six, and two sites were used for Experiments 1, 2, and 3, respectively. Contrast statements were used to make pre-planned comparisons among treatments. For Experiment 1, treatments were fall tilled (GT), fall grazed (GF), spring grazed (GS), fall and spring combined grazed (GFS), and an untreated control (GC). Five mature ewes were confined with electric fence for 24 h for fall and spring graze treatments resulting in a stocking rate of 400 sheep d/ha. For GFS, the stocking rate was 800 sheep d/ha. For Experiment 2, treatments were fall grazed (BF), fall burned (BB), fall tilled (BT), and an untreated control (BC). Tillage and burning treatments were imposed within one week of fall grazing in both Experiments 1 and 2. In Experiment 3, treatments were fall trampling by sheep (TF), spring trampling by sheep (TS), fall and spring combined trampling by sheep (TFS), hand clipping to a stubble height of 4.5 cm (TCP), and an untreated control (TC). Trampling treatments were done at the same stocking rates as grazing treatments but sheep were muzzled to prevent intake. Wheat stem sawfly larval numbers were collected in the fall and spring, prior pre- and post treatment, respectively, by collecting all plant material from three, 0.46 m lengths of row and counting the number of live larvae present. In Experiment 1, WSS mortality was greater (P<0.01) for the mean of all grazing treatments (68.4%) than either GC (43.4%) or GT (46.6%). Mortality did not differ (P=0.75) between GF (67.2%) and GS (64.0%) but was greater (P=0.02) for GFS (73.9%). In Experiment 2, post treatment WSS larva numbers and mortality did not differ (P>0.60) between BB and BC or BB and BT. Post treatment larval numbers were lower (P<0.01) and mortality greater (P<0.01) for BF (6.9 and 63.1%) than BB (9.3 and 51.9%). In Experiment 3, WSS mortality was greater (P<0.01) for the mean of all trampling treatments (57.3%) than either TC (32.8%) or TCP (32.3%). Mortality did not differ (P>0.25) between TF (54.3%) and TS (46.9%) but was greater (P = 0.01) for TFS (70.6%). No differences (P>0.25) were detected for WSS mortality when grazing was compared to trampling. These results indicate the potential for using grazing sheep to control wheat stem sawfly infestations in cereal grain production systems.