High Rootworm Pressure? Try These Alternate Forage Options

• Corn is increasingly the preferred forage crop for dairy production because of its high yield potential and energy content.
• Continuous production of corn for grain or silage in the same field can lead to corn rootworm problems.
• Forage programs that combine a winter cover crop followed by an alternative spring-seeded forage crop can come close to replacing the value of a corn crop, particularly if corn rootworm damage is limiting corn yields.
• Use this article as a starting point for introducing rotation into a feed production operation using some of the easier-to-manage forage alternatives to corn.

Corn is king in much of dairy country and is displacing alfalfa acres in the rotation because it supplies high forage quantity and quality. However, planting corn in the same fields year after year may lead to challenges in managing corn rootworm. Continuous corn fields can favor higher corn rootworm populations, even when using Bt corn products (Pilcher et al., 2018). Relying on a single corn rootworm management tactic can result in reduced efficacy over time.

Rotating fields with historically high levels of corn rootworm pressure out of corn can greatly aid in reducing corn rootworm populations and maintaining the efficacy of corn rootworm control options. There is no single crop that can completely replace the tonnage and feed value of corn silage.

Corn rootworm larvae feeding on corn roots and lodging caused by root damage.

However, by leveraging multiple crops in the growing season, a producer can come close to replacing the value of a corn crop. This is particularly true if corn rootworm damage is limiting corn yields. Table 1 summarizes the comparative values for various forage crops. Combining a winter cereal with a summer forage crop results in similar feed value to corn silage when corn yields are challenged.

Rotating out of corn into an alternative forage crop can help reduce corn rootworm populations. (Silage harvest photo courtesy of Deere and Co.)

Developing an alternative forage cropping plan that uses multiple crop species can help meet the feed needs of a dairy or livestock operation while also effectively managing corn rootworm. An effective plan involves two key steps:

Step 1 – Start with a small grain cover crop planted shortly after corn silage harvest.

Step 2 – In the spring, follow the small grain cover crop with an alternate forage crop. Common spring-planted options discussed in this article include:

• Forage sorghum
• Sorghum-sudangrass

Many fall cover crop options are available, but winter rye or winter triticale are currently the most common. They are widely available, adaptable to establish stands and overwinter in cold conditions, and have relatively low seed cost. Small grain forages are widely used by many dairy operations and growers who have integrated cover crops into their management systems.

How to Manage Small Grain Cover Crops

Planting

• Plant winter rye (or winter triticale) in the fall after corn silage harvest.
• Target a seeding rate of around 100 lbs/acre. Seeding rate should be higher under challenging seeding conditions or when broadcasting and can be lower (75-80 lbs/acre) when planting conditions are favorable.
• Planting is best accomplished using a drill with a seeding depth of ¾ to 1 inch.
• Plant as soon as possible after corn silage harvest. If applying manure prior to planting, a tillage pass may be necessary to incorporate the manure and prepare the field for planting.
• Consider broadcast seeding in late August (corn dent stage) if harvest will occur after early October.

Management

• Weed control is not typically needed for a fall seeded crop with adequate stands, but watch for winter annuals, such as chickweed and henbit. Yield can be reduced if weeds are not adequately controlled.
• Apply 50-75 lbs/acre of nitrogen at green-up in the spring to encourage tillering and increase forage yields. Higher rates of nitrogen can improve crude protein levels in the harvested forage, and a summer annual crop can use any remaining nitrogen.

Harvest

• Harvest small grain crops in the late-boot to early-heading stage to optimize forage quality and energy content.
• Apply Pioneer^® inoculant 11G22 when harvesting for silage to reduce DM losses during fermentation and feed out.

Newly-emerged fall-seeded cereal rye cover crop.

Option 1: Forage Sorghum

Hybrid forage sorghum types grow 8-10 feet tall and have thick stems. Like corn grown for silage, they are designed to be harvested a single time during the grain maturation stage for forage.

Hybrid Selection

• Pioneer^® hybrid 845F is a 68 RM forage sorghum widely adapted across the U.S.
• Pioneer^® hybrid 849F is a slightly fuller season choice with increased plant height.

Planting

• Plant at a rate of 7-8 lbs/acre (90,000-100,000 seeds/acre) in 30-inch rows to optimize forage harvest for silage. If planting with a drill or broadcasting, increase seeding rate to 10-15 lbs/acre.
• Forage sorghum should be planted after the over-wintering cover crop is harvested and when soil temperature has reached 65 °F.
• Sorghum is sensitive to cool soils; adequate soil temperatures at planting are necessary to ensure rapid emergence.

By leveraging multiple crops in the growing season, a producer can come close to replacing the value of a corn crop.

Management

• Forage sorghum requirements for nitrogen, phosphorus, and potassium are like those of corn silage. Use a yield target of 80-90% of a typical corn silage crop for the area.
• When applying manure, incorporate it prior to planting and credit the available manure nutrients when calculating fertility needs.
• Metolachlor or s-metolachlor products (contained in the herbicide brands Bicep^® and Dual^®) can be used for grass weed control when safened seed is used. Pioneer^® brand forage sorghum hybrids are available with Concep^® III seed safener to help protect against phytotoxic effects of s-metolachlor herbicides.
• Atrazine, dicamba and 2,4-D can be used for broadleaf weed control in sorghum crops.
• Check state labels for herbicide products and consult local advisors for all potential herbicide options including pre-harvest intervals for use as forage.

Harvest

• Harvest at mid-dough to mature grain color stage to optimize tonnage and quality.
• Maturity can change quickly, so close monitoring of grain maturity and whole plant forage moisture is necessary for proper fermentation and to optimize feed quality. Starting early is preferable to delayed harvest for best quality and can help avoid lodging.
• Using a BMR forage sorghum hybrid improves fiber digestibility of the forage, though there may be reduced dry matter yields and agronomic concerns like standability.
• Apply Pioneer^® inoculant 11G22 when harvesting as silage to reduce fermentation and feed out losses.

Field of sorghum-sudangrass.

Option 2: Sorghum-Sudangrass

Sorghum-sudangrass hybrids have high yield potential provided adequate rainfall or irrigation. They are designed for multiple harvests and can be stored as silage or hay when properly wilted or dried down.

Hybrid Selection

• Pioneer^® hybrid 877F sorghum-sudangrass is widely adapted and suitable for planting across the U.S.

Planting

• Plant at a rate of 8-12 lbs/acre (100,000 seeds/acre) in rows or at 15-20 lbs/acre when seeding with a drill or broadcasting.
• Sorghum-sudangrass should be planted after the overwintering small grain crop is harvested and when soil temperature has reached 60 °F.
• Sorghum-sudangrass is sensitive to cool soils; adequate soil temperatures at planting are necessary to ensure rapid emergence.

Management

• Forage sorghum requirements for nitrogen, phosphorus, and potassium are similar to those of a corn silage crop.
• Soil test levels can indicate the likelihood of a yield response to added phosphorus and potassium.
• Nitrogen response is similar to that of corn. Yield target with sorghum-sudangrass should be 60-70% of a good corn silage crop.
• Metolachlor and alachlor products (contained in the herbicide brands Dual^® and Lasso^®) can be used for grass weed control when safened seed is used. Pioneer^® brand sorghum-sudangrass hybrids are available with Concep^® III seed safener to help protect against phytotoxic effects of s-metolachlor herbicides.
• Atrazine, dicamba and 2,4-D can be used for broadleaf weed control in sorghum crops.
• Check state labels for herbicide products and consult local advisors for all potential herbicide options.

Harvest

• Two cuttings are often achievable in a 75- to 90-day growth period. Take the first cutting at boot stage to optimize tonnage and quality. Leave 4-7 inches of stubble when harvesting to encourage rapid regrowth.
• A second cut is typically ready 30-35 days after the first cut. Ensure that the crop is at least 26 inches tall before cutting.
• Apply Pioneer^® inoculant 11G22 when harvesting as silage to reduce fermentation and feed out losses.

• Butzen, S. 2007. Managing Forage Sorghum and Sorghum-Sudan. Pioneer Field Facts Vol. 7 No. 5. Corteva Agriscience.
• Mahanna, W. (Ed.) 2019. Pioneer Silage Zone Manual (3rd Edition). Johnston, IA: Corteva Agriscience.
• O’Reilly, C. 2020. Forage Options to Replace Silage Corn. Field Crop News. Ontario Ministry of Agriculture, Food, and Rural Affairs.
• Paulson, J. 2015. Growing and Feeding BMR Sorghum. Midwest Forage Association.
• Pilcher, C., M. Price, and S. Endicott. 2018. Informing Future Management Decisions for Corn Rootworm. Pioneer Agronomy Research Update Vol. 8 No. 19. Corteva Agriscience.
• Pryor, R., B. Anderson, and P. Hay. 2013. Tips for Growing Forage Sorghum. University of Nebraska-Lincoln. CropWatch.
• Ramsey, W. 2013. Feeding Forage Sorghum. Inside the Zone Newsletter. Corteva Agriscience.
• Roth, G. and J.K. Harper. 1995. Forage Sorghum. Agronomy Facts 48. Penn State Extension.