If weeds are allowed to grow in sorghum plots unchecked, they will reduce the plants' yield and make harvesting difficult. Sorghum can actually protect itself from weed growth to a degree by releasing toxins into the soil that impede the growth of other nearby plants. But for the plot to remain entirely weed-free, farmers must intervene. The best way to keep sorghum completely weed-free is to combine chemical, mechanical and cultural control methods.
Once the land is cleared and tilled, apply a pre-emergent herbicide listed as safe for use around crops to the area. Spread the weed killer over the sorghum plot at the rate dictated by the manufacturer, then water the area (some herbicides require watering before application). This initial herbicide application will keep the weeds out during the crucial first 45 days when sorghum most needs to be weed-free.
Plant the sorghum closely to crowd out weed growth. Sorghum can be planted immediately after the application of a plant-safe pre-emergent herbicide. To control weeds, limit the space between rows of sorghum to 18 inches, and the space between plants to 5 inches.
Spread 2 to 3 inches of straw mulch between each row of sorghum. This will smother any new weed growth and help the soil retain moisture.
Rotate the location of your sorghum crop. Growing sorghum in the same location year after year leaches important nutrients from the soil and actually encourages weed growth.
Hand-weed the few weeds that may manage to crop up in spite of your efforts.