Sorghum can tolerate short-term drought and is often planted towards mid-summer (in June). A late-summer sorghum may follow an early-season corn. Because sorghum is grown during a short season, weed control is essential to achieve high yields and efficient harvest. However, it is often difficult to achieve good weed control in sorghum production. This publication provides information on weed control options to the growers, pesticide applicators, and Extension personnel who must select appropriate weed control options in sorghum.
Sorghum is a small-seeded grass and is relatively slow growing in the first few weeks after emergence. In addition, sorghum is susceptible to many of the herbicides that can be effectively used on corn. Slow seedling growth combined with a limited number of labeled herbicides and low use rates create a challenge for weed control. Another problem is that many of the herbicides normally used on sorghum in other states either cannot be used or must be used at low rates due to the coarse texture of many Florida soils.
For these reasons, it is essential that practices such as choice of hybrid, soil fertility, soil pH, moisture, and row spacing be optimized to give sorghum the best possible growing conditions in order to compete with weeds. Sorghum seeds are often treated with safener that enables the use of a specific herbicide product. Therefore, producers need to be aware of the types of safener and the herbicide product that can be applied without injuring the crop.
The most important consideration is control of grass weeds during sorghum emergence and seedling development. If grasses are not controlled at this stage and are as large as the sorghum, then cultivation will not control the grasses without killing the sorghum. Sorghum should not be planted in fields that are heavily infested with johnsongrass. If grasses can be controlled until the sorghum gets taller than the grasses, then cultivation can be effective. If sorghum is taller than the grass weeds, post-directed herbicide sprays may be applied to provide effective weed control. Broadleaf weeds are a less serious problem because several herbicides can be effectively used for their control.
Use Table 1 to determine which herbicides are most effective for anticipated weeds. Use Table 2 to determine rates and application recommendations. Proper sprayer equipment calibration and application (https://edis.ifas.ufl.edu/publication/wg013) are essential because low rates will result in poor control and high rates may result in crop injury.
Table 1. Estimated effectiveness of herbicides on common weeds in Florida sorghum.1