Maximizing Forage Production with Summer Annuals

June 21, 2024 2:48 PM
Blog Post

Summer annuals are valuable to forage production systems due to their heat and drought tolerance. These high-yielding crops are typically ready for grazing within 40-45 days under optimal conditions, making them ideal for double cropping systems. They provide excellent options for silage, baleage, hay, and grazing. If you need more forage this summer, want to alleviate the summer slump, or have delayed planting due to a wet spring, summer annuals are a great opportunity to get quick high-yield forage that can be planted anytime now to approximately mid-July.  Here are some summer annual forage options (Table 1):


Table 1. Forage uses, seeding rates, plant by date, estimated yields, and potential toxicities.

Sudangrass is a multiple-cut, summer annual; used for greenchop forage, pasture (rotation grazing is recommended), or silage; difficult to dry thoroughly for hay; varieties vary in height and leafiness. Plant through early July. The first growth is usable in about 30 to 40 days. Leave a 6-inch stubble height to maximize regrowth. Prussic acid poisoning risk is minimal, but avoid pasturing severely drought-stressed or very short (<18 inches) growth/tiller regrowth and use caution if grazing soon after frost. Will terminate with fall frost.

Sorghum × Sudangrass can be used as a multiple-cut or single-cut summer annual; used for green chop, pasture (rotational grazing is recommended), or silage; varieties vary greatly in height, leafiness, grain yield depending on the parent lines making up the hybrid. Plant through early July. The first growth is usable in as little as 30 days in the right environment, and regrowth is from tillers. Leave a 6 to 8-inch stubble height to maximize regrowth. There is prussic acid poisoning risk if plants or tillers are grazed or greenchop at short height (<24 inches) or during severe drought and do not graze following a frost for at least one week, or until that plant is killed.


Figure 1: Multiple sorghum species: sorghum x sudangrass, sudangrass, and sorghum x sudangrass, pictured left to right.

Forage Sorghum is a single-cut, summer annual; used for green chop, and silage. Varieties can vary greatly depending on their parent lines. It can be planted till early/mid-July. Useable in 40 to 50 days but will take approximately 15 to 25 days longer to reach soft dough (ideal timeframe for silage harvest).  Will terminate with a fall frost. 

Sudangrass, sorghum × sudangrass, and forage sorghum hybrids are better adapted than most species to drought, high temperature and low soil pH but will yield less in seasons with cool August and September temperatures. Sudangrass and sorghum × sudangrass hybrids should be harvested at 2 to 3 feet of height (two to three cuttings per season). Harvesting at later maturity may increase yield but will result in lower forage quality. Will terminate with fall frost.

Foxtail Millet, also called German, Siberian or hay millet, is a summer annual grass; used as harvested or grazed forage. Plant through mid-July. Useable in about 50 days. One summer growth (vegetative 1-2 ft, with seed head 2-3 ft); best of the 'millets' for an emergency hay crop; can become a weedy grass if allowed to produce mature seed. Will terminate with fall frost.

Japanese Millet is a summer annual grass; relatively coarse (stemmy) forage; used as fresh cut forage, hay, silage or pasture. Plant through mid-July. Useable in about 50 days. Very little regrowth if first growth is allowed to reach maturity; if cut at vegetative growth stage, regrowth yields are more likely. Leave a 5 to 6-inch stubble height to maximize regrowth. Closely related to the grassy weed barnyard grass, so avoid allowing seed formation. Will terminate with fall frost.

Hybrid Pearl Millet is a multiple-cut, warm-season annual; green chop, pasture (rotational grazing is recommended), or silage; resembles sorghum × sudangrass hybrids in plant structure. Usable in about 30 to 45 days. Leave a 6-inch stubble height to maximize regrowth. Somewhat slower regrowth than sorghum × sudangrass hybrids; poor production in cool summer seasons; no risk of Prussic acid poisoning. Will terminate with fall frost.

Incorporating summer annuals into your forage production system can provide a reliable source of high-quality forage during the challenging summer months. By selecting the appropriate species and managing them effectively, you can optimize forage yield and quality while mitigating risks associated with drought and heat stress. Evaluate your specific needs and conditions to determine the best options for your operation, ensuring a successful and productive season.

Two resources with additional information on warm season annual forages are the ISU publication ICB 0136 “Alternative Annual Forages” and the UNL publication G2183 “Summer Annual Forage Grasses”.

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Rebecca Vittetoe Field Agronomist in EC Iowa

Rebecca Vittetoe is an extension field agronomist in east central Iowa. Educational programs are available for farmers, agribusiness, pesticide applicators, and certified crop advisors.

Areas of expertise include agronomy, field crop production and management of corn, soybeans, and...