Grower Practices for Blackbird Control in Wild Rice in California

We surveyed 29 wild rice growers, representing 96% of the California acreage grown in 1993, to determine current practices for blackbird damage control. Twenty-seven growers (93%) had blackbird damage. The period of greatest damage and most intensive control was July through September. Red-winged blackbirds (Agelaius phoeniceus) most frequently caused damage, but three other species of blackbirds and the European starling (Sturnis vulgaris) were also identified. Most growers (72%) reported 1 to 10% yield loss. Average loss ranged from $121 to $309/ha, and from $14,530 to $32,061/grower. Most growers (97%) attempted to control blackbirds for an average of 3.5 months during the growing season, relying primarily on shotguns, propane cannons, shellcrackers or bird bombs, and patrols. Growers in northeastern California tended to rate these techniques as more effective than growers in the Sacramento Valley, possibly due to the larger field sizes in the Valley. Average effectiveness ratings for all techniques indicated little better than slight control for the techniques used, suggesting grower dissatisfaction with the available techniques. Average cost for control averaged $86.21/ha, which was among the highest costs for any single aspect of wild rice production. Proc. 16th Vertebr. PestConf. (W.S. Halverson& A.C. Crabb, Eds.) Published at Univ. of Calif., Davis. 1994. INTRODUCTION Wild rice (Zizania palustris) is an emergent-aquatic grass native to North America. In the wild it grows along the edges of slow-moving streams and shallow lakes in the Upper Mississippi-Great Lakes region of the United States and Canada (Archibold et al. 1985). Within the past 25 years wild rice has become a crop of commercial importance with three distinct production systems: natural stands, managed natural stands, and cultivated paddies (Hayes et al. 1989). The major production areas for wild rice are Canada, California, and Minnesota, with paddygrown wild rice from the latter two states accounting for the majority of production (e.g., more than 95% of the 1985 world production of 15,200 metric tons of unprocessed grain). Wild rice is not native to California. It was introduced in 1972 using seeds from Minnesota. Commercial acreage of wild rice increased rapidly from 970 ha in 1982 to a peak of about 7300 ha in 1986. California has been the leading producer of wild rice since 1986 with yields that range from about 1120 to over 2240 kg/ha (1000 to 2000 lb/ac). There are three separate production areas in California differentiated by geographic or climatic factors: the Sacramento Valley, northeastern California, and the Clear Lake region in the northern Coast Range (hereafter referred to as SV, NC, and CL, respectively). An eight-county region (including Butte, Colusa, Placer, Sacramento, San Joaquin, Sutter, Tehama, and Yuba counties) centered in the SV produces the majority of wild rice in California. The NC production region includes parts of Shasta, Modoc, and Lassen counties. The CL production area occurs in Lake County. In 1993, 41 growers harvested about 6800 metric tons (15 million lb) of wild rice from 3920 ha (9685 ac) in California (M. Androus, Calif. Wild Rice Program, Personal Communication). From the early days of paddy cultivation, wild rice growers have been plagued by bird damage. Waterbirds such as ducks, coots, and swans forage on sprouting wild rice early in the growing season. Blackbirds (family Icteridae), however, due to their numbers and extended presence during the growing season are considered by growers to be the primary vertebrate pests of wild rice. Blackbirds, such as the red-winged blackbird (Agelaius phoeniceus) or the yellow-headed blackbird (Xanthocephalus xanthocephalus), are highly adapted to wetland habitats, such as cattail (Typha spp.) and bulrush (Scirpus spp.) marshes (Orians 1980). Wild rice grown in flooded paddies and reaching heights of 1.5 to 2.4 m (5 to 8 ft) provides the same resources to blackbirds as their natural habitats. Blackbirds use wild rice for loafing and escape cover, as nighttime roosts, and for nest sites. Wild rice paddies provide the same emergent insects important in the diet of blackbirds on natural wetlands and also one additional resource, namely the wild rice grain. Wild rice seed is consumed by blackbirds during the milk, dough, and mature stages of growth. Wild rice in the mature stages also easily shatters or falls off the seed head as a result of bird movements within the crop, resulting in additional crop loss. Wild rice growers have not been able to control blackbirds to their satisfaction and are seeking improved control techniques. The purpose of this study is to provide baseline information on current control practices and costs, ratings of effectiveness, and loss estimates suffered by wild rice growers in California prior to initiating research and development of new control techniques and strategies.