The period for cassava planting is very wide in São Paulo State, Brazil, covering the whole dry season (May to October). There are large differences in the plant growth and its interference with the weed community when the planting time is early or late in the dry season. Aiming to study the weed interference on cassava growth and productivity, four field assays were carried out under different planting times (06/28/1989, 06/30/1989, 10/30/1989, and 07/23/1990) in a randomized complete blocks experimental design with three or four replications. The treatments were divided in two groups: in the first one (group 1), the crop was maintained weedy from the planting date to 30, 60, 90, 120, 150, 180, 210, 240, 270 and 360 days. In the second group (group 2), the crop was kept weed free from the planting date to 30, 60, 90, 120, 150, 180, 210, 240, 270, and 360 days. The weed interference reduced drastically the dry matter accumulation by the cassava plants and the root production losses reached up to 90%. The increase in the rate of dry matter accumulation in the cassava roots in the presence of weed could not be analyzed in two assays. In the group 2, all the data were properly analyzed in the four assays. The Boltzman Sigmoidal Equation suited well the data on cassava root dry matter accumulation and provides good prediction models. The best dry matter production was obtained for 360 day old roots.
Manihot esculenta; growing; weed interference; planting date
