I am terribly weak on this sector of Zimbabwe society. But a superb PhD (at London School of Health/Hygiene) was written by Rene Loewensen during the late 1980s about plantation agriculture in Zimbabwe (Rene has been the lead progressive technocrat in the Zimbabwe Congress of Trade Unions for more than a decade). Zed published the thesis.
Actually, that book is sitting in a little house--writing cabin, really--on a tiny plot that my Zimbabwe family and I use on the country's eastern border (with Mozambique), in the Bvumba mountains. I haven't been there in the past couple of months because of the petrol crisis. The scenic area around includes a few major banana, tea, coffee and tobacco plantations, which are staffed predominantly by Mozambican migrant farmworkers. As far as I can tell, Mozambicans are paid less than US$0.33 per day on these farms and similar plantations along the 1,000 km border. Many cross the border to work, and indeed to go to school or for shopping, over fairly treacherous terrain, including a series of mine fields (still active). Migrant Malawians also are found in some of the largescale commercial farms in the North of the country.
There are very few reliable stats, unfortunately. The 1999 Human Development Report for Zimbabwe (written by a fabulous Harare-based marxist social scientist and former Ugandan cabinet minister, Yash Tandon) suggests there are today just 120,000 formal permanent wage workers on these large farms, down from 600,000 at independence in 1980. Volume and value output grew substantially, as have large farm profits. Workers are taking the hit, and migrancy has increased; those things are clear even without reliable stats.