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Sorghum issues need to be evaluated
By Charles Ikard and David Peterson
Pioneer Hi-Bred agronomists
Sorghum standability: Sorghum lodging is a continual threat to any producer under dryland conditions. When stressed during grain-fill, sorghum will mobilize crown and root starch reserves in order to meet increasing seed-development needs. When this happens, the roots and stalks are weakened, predisposing them to lodging. Immature sorghum that has its leaves frosted off also will mobilize root and crown starch reserves in a similar manner. Compounding this are two main pathogens (fungi) that can invade stressed plants and weaken stalks. These fungal stalk rots which cause sorghum standability problems are charcoal stalk rot and Fusarium stalk rot.
Ten suggestions for reducing sorghum lodging:
--Plant thinner stands. Sorghum possesses a tremendous ability to compensate for thin stands. Overplanting sorghum is more often a cause of reduced yields than underplanting. Overplanting results in increased plant stress and reduced stalk diameters thus increasing the chance of lodging.
--Plant disease-resistant varieties. Pioneer brand hybrids are rated five different ways for standability: 1) root strength, 2) stalk strength, 3) postfreeze lodging resistance, 4) charcoal stalk rot resistance, and 5) 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 postfreeze lodging rating becomes important.
--Plant varieties with strong stalk ratings. Hybrids differ in stalk and root strength. Note these characteristics ratings when choosing sorghum hybrids.
--Use no-till. A three-year study by researchers at 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.
--Fertilize properly. Any nutrient deficiency stresses the sorghum crop, leading to standability problems. Avoid potassium deficiency problems and excessive nitrogen rates to improve standability. Preliminary research in southeast Kansas has shown some standability improvements with the use of chloride fertilizer.
--Plant earlier. 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.
--Manage insect pressure. Chinch bug and greenbug pressure are highly associated with standability problems. Proper use of greenbug-resistant hybrids and insecticides that reduce insect pressure will result in improved standability. Fusarium stalk rot can enter plants through insect wounds.
--Manage weed pressure. Weed competition increases stress on sorghum. Effective use of acetanilide herbicides to manage grass pressure will reduce this stress and improve standability. Proper use of growth-regulator type herbicides to prevent brace-root damage will help improve standability.
--Rotate fields/crops. Disease pathogen levels can be reduced significantly with rotation to non-host crops such as wheat. In the case of Fusarium, which survives on plant residue, rotation can reduce stalk lodging by up to four times.
--Plant correctly. Often sorghum can have trouble rooting downward in the seedling stage, a phenomena known as "rootless milo 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 milo syndrome is made worse by loose-soil conditions that prevent good root-to-soil contact and by growth regulator-type herbicides. This syndrome is most common where plants have had soil washed or blown away from the crown region where roots are initiated.
Editor's note: Crop Talk is brought to you by agronomists serving your community to keep you informed about current growing conditions and important management issues. Charles Ikard, Dumas, Texas, and David Peterson, Ransom Canyon, Texas, are agronomists with Pioneer Hi-Bred International, Inc.
Date: 10/19/04
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