Grain Sorghum Fertilization and Pest Control
Fertilization
The first step in developing a fertilization program for grain sorghum is to take a good soil test. For information on the correct way to sample a field, see your county agent for a copy of Information Sheet 346, Soil Testing for the Farmer.A soil test will tell you the amount of lime, phosphate, and potash needed for that field. It is vital to keep the field limed to an adequate soil pH. Grain sorghum is intolerant of acid soils and prefers a soil pH above 5.6. If lime is needed and the soil test shows a deficiency of magnesium, use dolomitic limestone.
If lime is recommended, you will get best results by applying it in the fall and incorporating. If fall application is impossible, lime can still yield some results if applied in the spring, although this is not as effective as a fall application.
Apply phosphate and potash according to soil test. Both can be applied in the fall or spring on most soils. The exception is potash on very sandy soils. If the Cation Exchange Capacity (C.E.C.) of the soil is less than 6.0 (very sandy), potash can leach if applied in the fall. If the C.E.C. of the soil is greater than 8.0, potash can safely be applied in the fall without leaching. The C.E.C. rating is given on the soil test report.
The recommended rate of nitrogen for grain sorghum is 120-130 pounds nitrogen (N) per acre. Increase rates 10-15 percent on clay soils. This nitrogen rate is sufficient for 100 bushels of sorghum per acre. If irrigation is present and a realistic yield goal of more than 100 bushels of sorghum per acre is desired, apply an additional 1.5 pounds of nitrogen per extra bushel of yield goal. For example, if a yield goal of 125 bushels of sorghum is realistic, the nitrogen rate would be:
130 lb (first 100 bushels) + [25 (extra bushels) x 1.5 (lb N per bushel)] = 167 lb N per acre. Remember, keep your yield goal realistic.On medium-textured soils, all nitrogen can be applied preplant. On very sandy soils or on heavy clays, split the nitrogen application. For split applications, apply one-fourth to one-third of the nitrogen preplant. Apply the second part of the nitrogen before plants reach the 6-leaf stage. This is vital to insure maximum number of seed per head. If the plant undergoes nitrogen stress at the 6-8 leaf stage, heads will be small and yield potential reduced.
All sources of nitrogen are acceptable if used correctly. Base the decision for nitrogen source on price, availability, and ease of application.
Weed Control
Certain weeds are difficult or impossible to control in sorghum. Johnsongrass is a member of the sorghum family. Any herbicide that will control rhizome johnsongrass will damage or kill sorghum. You may get some seedling johnsongrass control with Dual or Lasso. Sorghum seed must be treated with Concep seed safener if you use Dual, or with Screen seed safener if you use Lasso.Bermudagrass is a problem. Sorghum is usually planted during the time when bermudagrass growth is flourishing. Sorghum will not provide a quick, early shade to reduce competition. Herbicides that will control bermudagrass must be applied well in advance of planting. Nutsedge presents similar problems; you must apply control measures well in advance of planting. In most instances you should not plant fields with heavy infestations of johnsongrass, bermudagrass, and nutsedge to grain sorghum.
For detailed weed control recommendations, see Extension Information Sheet 803 Grain and Forage Sorghum Weed Control.
Insect Control
Early planted grain sorghum usually has fewer insect problems than late planted sorghum. The most serious pest on early season small sorghum is probably chinch bug. This sucking insect can severely damage a stand of sorghum in the seedling or 4-leaf stage. Larger plants can also suffer damage, but as a rule, control after sorghum is 12 or more inches tall is not necessary.Sorghum planted in June or later may be attacked by the lesser corn stalk borer (LCSB) and armyworms. Look for LCSB outbreaks during periods of dry weather. Later planted sorghum may also have heavy infestations or budworms up to the heading stage. Budworms (either fall armyworm or bollworms) will feed on seed in the early- to mid-dough stage.
The sorghum midge may lay eggs in the flower as the heads bloom. As the eggs hatch, the larva feeds on the developing seed. Heavy midge infestations are more likely to occur in sorghum blooming in late July and August than in earlier blooming stands. Midge populations will build up on johnsongrass and can be quite heavy late in the season. Corn earworms and sorghum webworms can be problems in the maturing heads.
For recommendations of specific insecticides and rates see Extension Information Sheet 1160 Small Grains -- Oats and Wheat. Regular checks of fields throughout the growing season are necessary to monitor both insect and weed situations. Timely application of pesticides is necessary for effective control. Midge-resistant varieties are also available as an alternative control method.
Bird Damage
Since bird resistant varieties are not planted in many areas, other methods of dealing with birds must be used. Early planting keeps bird damage to a minimum because grain matures and can be harvested before migratory blackbirds arrive. Harvesting at 20 to 25 percent grain moisture and drying also reduces bird losses because grain does not stay in the field as long. The larger the field, the less grain lost to birds, because the majority of bird damage is along fence rows, power lines, and edges of wooded areas. Mechanical and chemical bird repellents have not been very successful.
By Dr. Eddie Funderburg and Dr. Lamar Kimbrough, Extension Agronomists and Dr. Jim Hamer, Extension Entomologist.
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Information Sheet
1225
Extension Service of Mississippi State University, cooperating with U.S.
Department of Agriculture. Published in furtherance of Acts of Congress,
May 8 and June 30, 1914. Ronald A. Brown, Director
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State University. All rights reserved.
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Extension Service.
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