When is the Best Time to Harvest Sorghum Sudan Grass for Hay?

Sorghum Sudan Grass


Sorghum-Sudangrass, also known as “Sudex,” is a hybrid of forage sorghum and sudangrass. These warm-season, annual summer crops are highly productive and grow rapidly. While most grasses cultivated in Utah are cool-season crops, sorghum-sudangrass thrives in high temperatures. Apart from being a valuable source of forage, Sudex can also improve soil quality, control weeds, fight against nematodes, loosen compacted subsoils, and enhance drought tolerance. So, when is the best time to cut sorghum-sudan grass for hay? Let’s find out.

Site Selection

Sudex performs best in climates with temperatures regularly exceeding 90 °F during the growing season. It requires about 45 days for each harvest, so it’s essential to allow at least 90 frost-free days for the entire growing season when planning multiple cuttings. Sudex does not thrive in poorly drained soils, although it can grow in various soil types. Loam soils with a neutral pH are most suitable, but Sudex has also produced acceptable yields in soils with a pH range of 5.5-9.0.

Nutrient Management

Nitrogen is crucial for maximizing Sudex yields, similar to most grasses. Recommendations suggest around 50 pounds of nitrogen per acre, although the specific requirements may vary depending on location, year, and field history. Splitting fertilizer applications into two equal halves can improve yield and reduce the risk of forage nitrate poisoning. Other nutrients, such as phosphorus, potassium, sulfur, and micronutrients, should follow corn fertilizer guidelines for Sudex.

Variety Selection

Choosing Sudex varieties that are well-adapted to local growing conditions is crucial for achieving optimal results. In Utah, ‘Honeysuckle’ and ‘Super Sugar DM’ are commonly used varieties that prioritize high tonnage over digestibility. Other varieties, such as FS301BMR, FS6BMR, SX122 BMR, Nutri-King BMR6, offer better forage quality and digestibility. While variety trials for Sudex in Utah are limited, consulting seed dealers can provide valuable insights into suitable varieties.

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The ideal planting time for Sudex varies by region, but a general rule is to plant two weeks after the recommended planting dates for corn in your area. Sudex hybrids are susceptible to frost, so planting should occur after the last frost date. Soil temperatures above 65 °F are necessary for quick germination. Plant Sudex seeds at a depth of 1/2 inch in moist soil, ensuring a firm seed bed. Harrowing the field after broadcasting the seed can be helpful, and recommended seeding rates range from 20-30 pounds per acre drilled to 30-40 pounds per acre broadcast.


Sudex is known for its efficient water usage in hot summer months, making it a suitable crop for dry climates like Utah. It can thrive on less water compared to corn and alfalfa, making it an excellent choice for drought years or when water supplies are limited. Most irrigation systems, such as flood or overhead pivot irrigation, are compatible with Sudex. However, wheel lines may pose challenges due to the crop’s height. It’s crucial to avoid grazing or cutting Sudex during freezing temperatures or when frost is likely to prevent prussic acid poisoning.

Pest Management

Sudex hybrids can help suppress weeds due to their allelopathic properties. They release a compound called sorgoleone that inhibits weed growth. Sudex also competes with weeds for water and nutrients. To ensure effective weed suppression, prepare a clean and weed-free seedbed through tilling or herbicide application before seeding Sudex. Insects such as fall armyworms, corn earworms, and grasshoppers can cause damage but usually don’t significantly impact yield or require insecticide application.

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Sudex can be harvested as hay, haylage, green chop, silage, or grazed. The recommended cutting height for hay, haylage, and green chop is 6-8 inches above the ground to allow for regrowth and avoid killing plants. For silage, chop the plants in the mid to hard dough stage and ensile them at 65%-70% moisture. When grazing Sudex, start when the plants are between 18-40 inches tall and use an intensive rotational grazing system for efficient utilization. It’s crucial to monitor prussic acid levels and wait for five to six days after a frost before allowing livestock to graze on Sudex.


Testing the nitrate and prussic acid (HCN) levels in Sudex is essential for ensuring safe feeding. Nitrate testing is routine and relatively inexpensive, while prussic acid testing requires proper handling and freezing of samples. Cyanides and hydrocyanic acids (HCA) can be tested using cyantesmo paper as a rapid test. Symptoms of prussic acid poisoning in livestock include anxiety, weakness, labored breathing, increased respiration and pulse rates, and convulsions.

Yield and Quality

Yield and quality of Sudex are influenced by various factors, such as planting date, variety, soil conditions, irrigation, and nutrient availability. The highest yields are typically achieved with single-cut systems, although two-cut systems can still yield around 10 tons of dry matter per acre. Sudex generally has a higher percentage of crude protein but lower total digestible nutrients (TDN) compared to corn silage. Maturity at harvest also affects protein and energy contents. Protein and TDN decrease as Sudex matures.

In summary, Sudex is a valuable warm-season forage crop that can thrive in Utah’s dry climate. Choosing the right planting time, variety, and proper management practices can lead to successful Sudex cultivation. While considerations for prussic acid and nitrate poisoning are crucial, they can be mitigated through appropriate management techniques. So, if you’re considering growing Sudex for hay, ensure you follow the recommended guidelines and pay attention to the specific needs of your crop. For more information on agriculture and other topics, visit 5 WS.

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