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10 Steps to Improved Sorghum Standability

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By John Mick

Introduction

Stalk lodging is a continual threat when growing grain sorghum under dryland conditions. When sorghum is stressed during grain-fill, the plant will mobilize crown and root starch reserves in order to meet increasing seed development needs. When this happens, the roots and stalk are weakened, predisposing plants to lodging. Immature sorghum that loses leaf tissue to frost will also mobilize root and crown starch reserves in a similar manner. Lodging problems are increased by two primary pathogens (fungi) that weaken stalks and invade stressed plants. The primary fungal stalk rots which cause sorghum standability problems are charcoal stalk rot and Fusarium stalk rot.

Charcoal stalk rot, caused by the fungus Macrophomina phaseolina, can survive in soil for up to three years (Frederiksen, 1986). This fungus is more prevalent in continuous sorghum rotations. High temperatures and water stress predispose sorghum to charcoal stalk rot and the fungus enters plants through the roots. The definitive charcoal rot symptom is shredded, black stalk pith tissue on lodged plants.

Fusarium stalk rot is caused by the fungus, Fusarium moniliforme, that survives on crop residue (Frederiksen, 1986). This fungus also enters the plant through roots. Cool, wet conditions following a period of stress, such as grain-fill, favor Fusarium stalk rot. Fusarium stalk rot symptoms include premature death, reddish discoloration of the stalk tissue, shriveled grain, and lodging.

10 Suggestions for Reducing Sorghum Lodging

  1. Reduce seeding rate. Sorghum possesses a tremendous ability to compensate for thin stands. Over planting sorghum more often causes reduced yields than under-planting. Over planting results in increased plant stress and reduced stalk diameter, thus increasing the probability of lodging.
  2. Plant disease resistant varieties. Pioneer® brand hybrids are rated five different ways for standability:
    • Root strength
    • Stalk strength
    • Post-freeze lodging resistance
    • Charcoal stalk rot resistance
    • Fusarium stalk rot resistance

    For continuous sorghum production under stressful conditions, resistance to charcoal and Fusarium stalk rots is important to consider. With late plantings, the post-freeze lodging rating becomes important.

  3. Plant strong-stalk varieties. Hybrids differ in stalk and root strength. Note individual characteristic ratings when choosing sorghum hybrids.
  4. Use no-till techniques. A three-year study by the University of Nebraska reported a 28 percent reduction in stalk lodging in no-till versus conventional tillage systems. No-till results in less water stress and improved plant health during grain-fill.
  5. Implement a balanced fertility program. Any nutrient deficiency stresses the sorghum crop, leading to standability concerns. Avoid potassium deficiencies and excessive nitrogen rates to improve standability. Preliminary research in southeast Kansas has shown some standability improvements with the use of chloride fertilizers.
  6. Plant sorghum earlier in Kansas. For growers in the central Great Plains region, Kansas State University research has shown improved standability with an early May planting date versus a mid-May planting date.
  7. Manage insect pressure. Chinch bug and greenbug pressure are highly correlated with standability problems. Proper use of insecticide seed treatments such as Cruiser1, which reduce insect pressure, will result in improved standability. Fusarium stalk rot can enter plants through insect wounds.
  8. Manage weed pressure. Weed competition produces increased stress on sorghum. Effective use of chloroacetamide herbicides in conjunction with Concep1 treated seed to manage grass pressure will reduce weed competition stress and improve standability. Proper use of growth regulator herbicides, such as 2,4-D and dicamba, to prevent brace root damage, will help improve standability.
  9. Rotate fields and crops. Disease pathogen levels can be reduced significantly with rotation to non-host crops such as wheat. In the case of Fusarium stalk rot, which survives on plant residue, rotation can reduce stalk lodging by up to four times (Frederiksen, 1986).
  10. Use best management practices for planting. Sorghum can have trouble rooting downward in the seedling stage. This is a phenomenon known as “rootless sorghum syndrome.” When a sorghum plant tries to establish a crown and brace roots in hot soil, the high soil surface temperature can actually restrict growth. Rootless sorghum syndrome is exacerbated by loose soil conditions, which prevent good root to soil contact. Growth regulator herbicides also contribute to rootless sorghum syndrome, when used improperly. Rootless sorghum syndrome is most common where soil has been washed or blown away from the plant crown, where roots are initiated.

References

Frederiksen, R.A. 1986. Compendium of Sorghum Diseases. The Amer. Phytopathological Soc. Home, C.W., and R.W. Berry. Sorghum Diseases Atlas. Texas Agric. Ext. Service Pub. Jardine, D.J. Stalk Rots of Corn and Sorghum. Kansas State Univ. Coop. Ext. Service Pub. L741

John Mick holds a Bachelor of Science degree in agronomy, with a science option, from Kansas State University. He currently serves as District Sales Manager northwest Kansas and previously worked as a Field Sales Agronomist. He is an expert in grain sorghum production and has been with Pioneer Hi-Bred since 1993.


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