Welcome to the United Sorghum Checkoff Program's Mid-South Production Handbook. We have integrated research from various sources to produce an easy-to-use guide that can help farmers manage their crop more efficiently. Sorghum has tremendous potential to return a profit to your farm and the work of the Sorghum Checkoff will only improve that potential over time. As you manage your sorghum, keep these tips in mind:
By following a few guidelines, you'll be amazed at what this crop can do for you. We strive to help you make sorghum more profitable for your operation. But remember, every situation is a bit different so contact your local county extension office, land-grant university or other area sorghum farmers to help you get the most out of this water-sipping crop.
Produced and edited by:
United Sorghum Checkoff Program
Dr. Angela McClure
Associate Professor, Univerity of Tennessee
Dr. Stephen Ebelhar
Agronomist, Univeristy of Illinois
Dr. Chad Lee
Associate Professor, University of Kentucky
Dr. Emerson Nafziger
Professor, University of Illinois
Mr. Terry Wyciskalla
Research Associate, Southern Illinois University
United Sorghum Checkoff Program
4201 N. Interstate 27,
Lubbock, TX 79403
It is important to understand the various developmental stages of sorghum since this understanding will assist in making irrigation and management decisions. The stages are based on key stages of sorghum growth that are used to describe sorghum from planting to maturity (Figure 1).
Another common scale that is used among sorghum researchers is a more simplified growth scale. GS1 would equate to stages 0-5 (vegetative stage) in this system. GS2 would represent from stages 5-10 (reproductive stage), and finally, GS3 would be from stage 10 to 11.5 (flowering stage).
Comprehensive grain sorghum growth and development guides are available, such as Kansas State How a Sorghum Plant Develops (currently being revised with your Sorghum Checkoff dollars) and Texas AgriLife How a Sorghum Plant Grows. Both of these guides provide pictures of different growth stages, graphs of cumulative nutrient uptake relative to growth stages (KSU), or approximate heat unit requirements (base temperature 50°F, maximum 100°F) for attaining a particular growth stage (Texas AgriLife). Cool or wet weather early in the season or an early planting date can significantly slow growth early in the season adding a week or even two weeks to the time to half bloom.
The criteria for selecting grain sorghum hybrids are similar to those for selecting corn hybrids. Yield, maturity, stalk strength (standability) and disease resistance are all important. Selecting sorghum hybrids suitable to the climatewith excellent yield potential and with tolerance or resistance to certain diseases is critical to high yields. Full season hybrids have yielded better in variety trials than early hybrids when planted in May. An earlier-maturing hybrid may be needed if planting after mid-June or as a double crop after wheat. Because of the limited acreage of grain sorghum in the eastern United States, most hybrids are developed and tested in the Great Plains and may not have been extensively tested under Mid-South conditions.
Commercial seed companies publish more detailed information about the agronomic characteristics and specific disease resistances of their hybrids. An ideal hybrid should have good seedling vigor, some resistance to anthracnose (primary cause of stalk rot), charcoal rot resistance and good stalk strength. Low lodging scores in local test plots are a good indication a hybrid has the potential to stand better when under stress.
Physical characteristics to be considered are head exsertion (the distance between the sorghum head and the upper most leaf) and head type (i.e. - compact, semi-compact, or open). The distance between the head and leaves can be from zero to eight inches and is of major importance when it comes time to harvest. The grain itself may be mature and ready for harvest but the plant material may still be green. The mature grain needs to be harvested with as little green material as possible because this green material, which can be sticky due to accumulated sugars, can cause problems with harvest and drying. Hybrids with greater head exsertion send less foliage into the combine at harvest. A harvest aid or desiccant may be needed to reduce the amount of green material in hybrids with low head exsertion.
The head type can affect the amount of pest damage to the seed and the quality of grain drying. Grain insects may be more difficult to scout and treat with the compact head types versus the open head types. The open and semi-compact hybrids will dry quicker in the field and are thought to be less susceptible to damage from head diseases.
Performance testing of commercial grain sorghum hybrids is not currently being done in Illinois or Kentucky, but hybrid test results are available from Tennessee and nearby states such as Missouri. Consult these and other tests to identify hybrids with excellent yield potential across multiple locations or environments. Hybrids are evaluated for yield and lodging in Tennessee in small plot replicated trials and in large strip plot county demonstration trials Tennessee Trials. Compared to corn, there are fewer commercial grain sorghum hybrids to choose from, so deciding what to plant is less challenging.
Site Selection Grainsorghum is adapted to a wide range of soils throughout the Mid-South region, but it is often placed on less-productive soils. If higher yields are desired, grain sorghum needs to be planted on soils that produce higher corn, cotton, or soybean yields. Even though grain sorghum is relatively drought resistant, it produces its best yields on deep, level soils rather than on drought-prone hillsides. It is common to see increased sorghum acreage in years following a drought as producers attempt to avoid two successive years of crop failure. Because chances of dry weather are not above normal the year after a drought year, it makes more sense to plant grain sorghum consistently on those fields with lower productivity for corn than to try to guess what the weather will be like in a given year.
Seedbed Preparation Seedbeds should have plenty of moisture, be suitable for good seed-to-soil contact and relatively weed free. These conditions can usually be obtained with light tillage or with no-tillage and burndown herbicides. Most planters used to plant grain sorghum are already set up to plant into no-till conditions.
Seed Treatments When selecting sorghum herbicides, consult the label or contact your seed or herbicide retailer to see if a seed safener, such as Concep® or Screen® might be needed. Using such herbicides without the safer seed treatment can result in severe crop injury. Insecticide seed treatments should be considered in areas where local university data supports such use.
Planting Date The optimum planting period for grain sorghum varies some by region. Planting grain sorghum from May 1 to June 1 results in highest yields in Kentucky and Tennessee, while in Illinois, the best date to start planting ranges from mid-May in southern Illinois to late May in northern Illinois. Grain sorghum is a warm season plant and emergence is best when soils are at least 60° to 65°F in the upper two inches of soil and warm weather is expected to continue. Grain sorghum prefers soil conditions similar to soybean, and germinates rapidly when soil temperatures are near 70°F. Soils in the Mid-South will often reach these temperatures prior to May 1.
Early planted sorghum usually has less damage from sorghum midge and worm pests. May planted sorghum will receive adequate rainfall in the spring for vegetative growth and will bloom during July when rainfall amounts are lower, thus reducing occurrence of head diseases.
Later planting results in lower yields and higher moisture grain at harvest. Grain sorghum can be planted after wheat harvest, but soil moisture supply should be adequate to achieve good stands, and double-cropping sorghum will be more successful on soil with better water-holding capacity. Hybrids used in late planting situations should be early maturing in order to reach maturity before frost.
Planting Depth Sorghum seed is smaller than corn seed and tends to emerge less vigorously. It should be planted shallow enough for easy emergence but deep enough to assure good contact with moist soil. Adequate seed coverage makes plant emergence more uniform in a field. Sorghum should be planted one inch deep under most situations. Seeds should be placed to moisture, but no deeper than about one inch in heavy soils and about two inches in sandy soils. Planting into a moist, warm seedbed allows for quick germination and uniform stands. Planter units should be set to firm the soil around the seed to expedite germination and emergence.
Because sorghum seedlings are slow to emerge, care is needed when using reduced- or no-till planting methods. Surface residue usually keeps the soil cooler and may harbor insects that can attack the crop, causing serious stand losses, especially when the crop is planted early in the season. No-till sorghum may have to be planted slightly deeper to ensure adequate seed coverage. Be sure that the planting slot closes well.
Row Spacing Since grain sorghum is planted on fewer acres than corn or soybean by most producers in the Mid-South, row width is generally that which is used for corn and soybean. Rowspacing experiments in Missouri have shown that narrow rows produce more than wide rows (Table 1), but recent University of Illinois experiments produced mixed results. In two of eight site-years, both in 2004, yields were significantly higher for the 30-inch row spacing (Table 2). Grain sorghum in 30-inch rows facilitates inter-row cultivation, which can help with weed control.
Narrow rows can make the crop more competitive with weeds, and they work well if weeds can be controlled without cultivation. Narrow rows are suggested for late planted sorghum if the equipment is available. Grain sorghum in 15- or 7.5-inch rows will usually have less lodging. Using a split-row planter to plant 15-inch rows may be a good option in fields where weeds can be controlled.
Table 1. Yield of Grain Sorghum as Affected by Row Spacing in a Missouri Trial (Conley et al. 2005) Data is in 2-year averages
|Row Spacing (inches)||Yield (bu/Acre)|
Plant Population Grain sorghum seeding rates depend upon soil type, soil fertility, soil moisture and seasonal rainfall. The number of grain sorghum seeds per pound can vary from 10,000 to 20,000. Years ago, seeding rate recommendations were expressed as pounds of seed per acre, which caused overplanting with small-seeded hybrids. Too-high plant populations can cause lodging problems and yield loss. Targeting a specific plant population and adjusting seed drop rate for the row width used is a much more accurate way to plant sorghum. Most grain sorghum hybrids have about 16,000 seeds per pound.
Seeding rates of 60,000 to 100,000 viable seeds per acre are sufficient for maximum yields regardless of row spacing. Some nearby states are evaluating twin-row sorghum at seeding rates of 100,000 plants per acre or above, but little data is available at this time. If planting into soils where drought is expected, use the lower population. In irrigated fields, a final population of 75,000 plants per acre is adequate based on University of Arkansas information.
University of Illinois seeding rate experiments conducted from 2003 through 2005 (Table 3) showed no significant yield increases across the different seeding rates within locations. When averaging the entire study across years and locations, therewas only one bushel per acre difference between the 60,000 and 120,000 seeds per acre planting rate. This shows that grain sorghum has an excellent ability to compensate for low plant populations. There is clearly no need to plant more seeds "just to be safe" in full season conventional tillage sorghum.
Divide the desired plant stand by the germination given on the seed tag to determine the actual seeding rate. For example, if a seed tag says 85 percent germination and you want to establish 90,000 plants per acre, 90,000÷0.85 = 105,882 planted seedsper acre. If there is reason to believe that emergence percentage may be less than the germination, then divide by expected establishment percentage instead of germination. When planting into no-till, especially as a double crop, it is best to assume that only 65 to 75 percent of what is planted will become a viable plant so divide by that percentage.
Seeding rates are independent of row width. Table 4 illustrates seed number per foot of row that is needed to achieve a desired population of sorghum for a specific row width. Pounds of seed per acre based on seed size are indicated for desired populations (example: if you desire to plant 80,000 seeds per acre and a hybrid has 15,000 seeds per pound, this is equivalent to 5.3 pounds of seed/acre).
The philosophy of fertilizer recommendations differ by state but there are several similarities. Consult state fertilizer guides for specific guidelines.
Soil Test Although grain sorghum is not an extremely heavy user of nutrients, it does require proper fertilization for optimum production. Be sure to include regular soil testing to aid in determining lime, phosphorus and potassium requirements. Soil tests are recommended every two to four years and each soil sample should represent no more than 20 acres (5 acres in Illinois).
Lime Lime rates are generally tied to the soil test pH values. In Tennessee, lime is recommended when water pH is below 6.0. If lime is needed, it can be applied any time before planting. In Kentucky, agricultural lime applications are triggered when water pH is 6.2 or less.
Phosphorus and Potassium While potassium is required in relatively smaller amounts than phosphorus, potassium is the primary nutrient that helps regulate stomatal control in leaf tissue and promotes stalk strength. The regulation of stomata helps the plant take in CO2 and release O2 in reducing lodging losses at harvest. Specific recommendations for P and K fertilizers follow.
Illinois: Farmers are encouraged to build soil test P levels to between 40 and 50 pounds per acre depending upon the supplying power of the soil, and to build soil test K levels to between 260 and 300 pounds per acre. Once these levels are reached, they are maintained by applying crop removal rates of nutrients. Grain sorghum yields of 80, 100 and 120 bushels per acre would remove 34, 42 and 50 pounds P2O5 per acre and 17, 21, and 25 pounds K2O per acre, respectively.
Kentucky: Fertilizer phosphorus is recommended when soil test levels drop below 60 pounds of P2O5 per acre (30 ppm using a 6" soil test, 20 ppm using a 10" soil test) and fertilizer potassium is recommended when soil test levels drop below 300 pounds of K2O per acre (150 ppm using a 6" soil test, 20 ppm using a 10" soil test). Rates are tied to soil test results.
Tennessee: Recommended amounts of K20 and P205 range from 30 pounds per acre for both nutrients on medium testing soils to 60 pounds per acre for low testing soils and are usually applied immediately before or at planting time. For soils testing high in phosphate and potassium, no additional fertilizer is recommended. Fertilizer may be effectively applied in the fall if fields are not subject to severe erosion or flooding.
In general, sorghum production needs application of 1.0 pound of nitrogen per bushel of expected yield. This amount needs to be adjusted for soil test results as well as nitrogen credit from legumes. If beginning a no-till program, an additional 20 to 30 pounds of nitrogen needs to be applied to account for nitrogen immobilization due to the increased residue with no-till. This immobilization effect should disappear by the third year into the no-till program.
Illinois: The response to nitrogen is somewhat erratic, due largely to the extensive root system's efficiency in taking up soil nutrients. For this reason, and because of the lower yield potential, in the past the maximum rate of total nitrogen suggested was about 125 pounds per acre. For sorghum following a legume such as soybean or clover, the nitrogen rate may be reduced by 20 to 40 pounds per acre. More recent research data conducted by the University of Illinois from 2003-2005 at Brownstown, Dixon Springs, and Belleville (8 site-years) suggests an economic approach using the price of nitrogen per pound and the price per bushel of grain sorghum (Tables 5 and 6).
Kentucky: About 100 to 125 pounds of N per acre are recommended for sorghum in most crop rotation systems. The higher rate would be used on soils that are poorly drained. When grain sorghum follows a field that has been in pasture for four years or less, the nitrogen rate can be reduced to 75 to 100 lbs. N per acre and if sorghum follows a field that has been in pasture for five years or more, then nitrogen rates can be dropped to 50 to 75 lbs. of N per acre.
Tennessee: Sixty to 90 (60-90) pounds of nitrogen per acre should be applied to grain sorghum immediately before planting, at planting or side-dressed within four weeks after planting. Response to the higher rate would most likely occur when grain sorghum follows a nonlegume, is grown no-till, or is grown on soils with restricted drainage or which have textures with more clay than silty clay loam. Nitrogen sources containing urea are more susceptible to losses when surface applied to moist soils followed by three or more days of rapidly drying conditions without rainfall.
Adequate nitrogen, potassium and phosphorus are needed for excellent sorghum yields. However, grain sorghum typically does not respond to the addition of nutrients other than N, P and K.
Table 5. Recommended N application rates (lb/acre) for grain sorghum based on grain sorghum price and N fertilizer price following soybeans. An extra 20-40 pounds of N may be warranted when sorghum follows corn or a grass crop.
Weeds should not be allowed to compete with grain sorghum. Normally, all weeds should be controlled with tillage and/or herbicides prior to planting grain sorghum. Most herbicides used in grain sorghum are selective, meaning that they kill certain weed species and do not harm the crop or certain other weed species. In addition, many herbicides require applications on small weeds. Grain sorghum producers need to pay close attention to weeds that emerge in a sorghum field and to try to control them before they get too large.
Do not plant grain sorghum into fields heavily infested with Johnsongrass (Sorghum halapense). Johnsongrass is a very close relative to grain sorghum (Sorghum bicolor) making chemical control of Johnsongrass in grain sorghum extremely difficult. In addition, Johnsongrass is extremely competitive and it harbors several diseases and insects that attack grain sorghum.
In general, grain sorghum should be planted in fields with relatively low weed pressure. The lower weed pressure can be achieved with aggressive weed management in the preceding crops (i.e. soybean). Grasses are typically more challenging than broadleaves to control with herbicides in grain sorghum.
Prior to planting Weeds can be removed prior to planting grain sorghum either by tillage or with herbicides. A field cultivator or chisel plow are probably the best options for tillage. Table 7 shows several available herbicides with sorghum applications approved on the label.
In no-till situations, herbicide programs involving glyphosate or paraquat plus 2,4-D and atrazine are usually very good options. Expert® (S-metolachlor + atrazine + glyphosate) and Sequence® (S-metolachlor + glyphosate) are premixes containing glyphosate and are suitable for killing vegetation before planting in no-till fields.
At planting Several herbicides can be applied at planting for grain sorghum. Dual II Magnum® (S-metolachlor), Micro-Tech® (alachlor) and Outlook® 6E (dimethenamid-P) or premixes of these herbicides with atrazine, all can be applied at planting, as long as seed is treated with either Concep® or Screen® safener. Atrazine alone (up to 1.2 pounds active ingredient per acre) can be applied at planting without a safener. Milo-Pro® 4L (propazine) can be applied without a safener.
Postemergence or Foliar Herbicides that can be applied after grain sorghum has emerged include Aim® (carfentrazone), Basagran® (bentazon), Buctril®(bromoxinyl), 2,4-D Amine, Rage D-Tech® (carfentrazone + 2,4-D), dicamba, Weedmaster® (dicamba + 2,4-D), Starane® (fluroxypyr), Permit® (halosulfuron), Yukon® (halosulfuron + dicamba) and Prowl® (pendimethalin). Prowl® should not make contact with brace roots and drop nozzles are suggested on larger plants. Paraquat can be applied postemerged if directed with drop nozzles. Most of the foliar herbicides have crop height limitations. Some allow the use of directed spray for later applications.
Interrow cultivation can be conducted in relatively flat soils where grain sorghum is grown in rows wide enough to accommodate the equipment. If interrow cultivation is used, set the shovels only as deep as necessary to remove the weeds.
For more specific information on herbicide options, timings and use rates, consult the local state extension weed controlpublication.
|Product||Active Ingredients||Required Seed Treatment||Timing||Products with Same Active Ingredient|
|2,4-D Amine||2,4-D amine||POST|
|Banvel||dicamba||POST||Clarity, Oracle, Sterling|
|Bicep II Magnum||S-metolachlor + atrazine||CONCEP or SCREEN||PP,PPI,PRE||Cinch ATZ|
|Bullet 4WDL||alachlor + atrazine||SCREEN||PP,PPI,PRE||Lariat|
|Duall II Magnum||S-metolachlor||CONCEP||PP,PPI,PRE||Cinch|
|Expert 4.88L||S-metolachlor + atrazine + glyphosate||SCREEN|
|Outlook 6E||dimethenamid-P||CONCEP or SCREEN||PP,PPI,PRE|
|Roundup Power Max||glyphosate||PP,PRE,DES||Roundup, Gly-Star, Mad Dog, Many Others|
|Sequence 5.25L||S-metolachlor + glyphosate||CONCEP or SCREEN||PP,PRE|
|Sodium Chlorate||sodium chlorate||DES||Defol 6|
|Touchdown||glyphosate||PP,PRE,DES||Roundup, Gly-star, Mad Dog, many others|
|Weedmaster||dicamba + 2,4-D||POST|
|Yukon 67.5 WDG||halosulfuron + dicamba||POST|
Grain sorghum does not dry to safe levels normally in the field. In addition, mature grain sorghum is prone to harvest losses from lodging, birds, insects, molds and poor weather. A chemical desiccant or a killing frost will hasten field drying, and artificial drying is normally required before marketing or storing grain sorghum.
Harvest aids help kill both green weeds and the sorghum plant, thus providing some reduction in moisture from plant matter. Glyphosate (Roundup PowerMax®, Touchdown® others) used as a harvest aid should be applied after grain moisture has reached 30 percent or less. Glyphosate products are slow acting and may not reduce grain moisture. Desiccants are intended to hasten the drydown of weed and sorghum foliage, and may cause small decreases in grain moisture. Sodium chlorate (Defol 6®, others) is a chemical desiccant and should be applied seven to 10 days prior to anticipated harvest date.
A number of insects can attack sorghum during the growing season in the Mid-South. The most common insects found at planting are cutworm, wireworm and grubs. Mid- and late-season insects commonly found include greenbugs and other aphids, sorghum midge, flea beetles, grasshoppers, fall armyworm, corn earworm, sorghum webworm and spider mites. The extent of damage by insects in grain sorghum is often related to the planting date. The greenbug is more common in early planted sorghum, while the sorghum midge, corn earworm, fall armyworm and sorghum webworm are more severe in lateplanted sorghum.
Seed insecticide treatments such as clothianidin (Poncho®), thiamethoxam (Cruiser®) and imidicloprid (Gaucho®) are fairly new for use in sorghum and have good efficacy on many below ground soil pests and early seedling pests of sorghum such as flea beetle, chinch bug or stink bug. Many granular insecticide products for control of rootworm in corn can be used in grain sorghum. A number of foliar insecticides provide excellent control of sorghum leaf and grain pests.
Basic identification and threshold information are included below for some of the most troublesome insect pests in grain sorghum. Refer to the extensionpublication in your state for specific treatment recommendations for these insects as control options may vary by state. In Kentucky refer to ENT-24: Insecticide recommendations for grain sorghum (milo) and IPM-5: Kentucky IPM manual for grain sorghum. In Tennessee, use PB1768 2009 Insect Control Recommendationsfor Field Crops. In Illinois, refer to IAPM09 2009 Illinois Agricultural Pest Management Handbook.
Greenbug The greenbug is a small, light green aphid with a dark stripe down its back, usually found on the underside of leaves. Early plantedsorghum is more likely to be infested by this pest. Reproductive potential is very high compared to other aphids. The greenbug injects a toxic substance in its saliva that causes red spots on leaves where it feeds. Treatment for greenbug is suggested once there are one or two greenbugs on the majority of the plants in the seedling stage and when leaves show damage or when one or more leaves are dying on larger sorghum plants.
Corn leaf aphid The corn leaf aphid has a bluish-green body about 1/16th inch long with black cornicles (tailpipes at the end of the abdomen), legs and antennae. Corn leaf aphids are usually found in sorghum whorls. Corn leaf aphids can transmit viral diseases from weeds like Johnsongrass, but sorghum can tolerate large numbers of these aphids. Treatment is not usually necessary for the corn leaf aphid. Corn leaf aphid populations early in the year can help attract beneficial insects to combat other pest later in the growing season.
Yellow sugarcane aphid Adults and nymphs are bright yellow to light green in color with two double rows of darker spots down the top of the abdomen. Feeding causes reddening of sorghum leaves and may transmit viral diseases. This aphid feeds on the underside of sorghum leaves in mid- to late-season, and can reach numbers large enough to require treatment. Treat when one or two aphids are found on most seedling plants and damage is visible or when one or more leaves show severe damage on larger plants.
Corn earworm The corn earworm larva has alternating light and dark strips down its body. The color varies from green to pink. The head capsule is a creamy-yellow. Larvae feed on whorl tissue of young sorghum plants and on developing grain in maturing plants. Full-grown larvae are about 1.5 inches long and feed on grain heads. Treatments should be applied when two or more small larvae or one large (greaterthan 1/2 inch) larva is found per head.
Fall armyworm Fall armyworm larvae have a dark head capsule and a prominent inverted Y on the front of the head. Body color is greenish to brownish with brownish to black strips on the sides of the body. Check whorls of young, late-planted sorghum and inside grain heads of more mature plants. Treat when an average of two or more small larvae or one large (greater than 1/2 inch) larva is found per head.
Sorghum webworm These are small, greenish, hairy caterpillars with four reddish brown stripes down the back. Full-grown larvae are about 1/2 inch long and are usually associated with sticky webbing in the area of their feeding. Check inside grain heads for worms and on leaves under grain heads forwhite fecal droppings. Treat when an average of three to four or more larvae are found per grain head.
Sorghum midge The sorghum midge is one of the most damaging insects to sorghum. The adult sorghum midge is a small, fragile-looking, orange-red fly with a yellow head, brown antennae and legs and gray, membranous wings.
During a single day of adult life, each female lays about 50 yellowish-white eggs in flowering spikelets of sorghum. Eggs hatch in two to three days. Larvae are colorless at first, but when fully grown, are dark orange. Larvae complete development in nine to 11 days and pupate between the spikelet glumes. Shortly before adult emergence, the pupa works its way toward the upper tip of the spikelet. After the adult emerges, the clear or white pupal skin remains at the tip of the spikelet.
A generation is completed in 14 to 16 days under favorable conditions. Sorghum midge numbers increase rapidly because of multiple generations forming during a season. Midge numbers also increase when sorghum flowering times are extended by a range of planting dates or sorghum maturities. Sorghum midges overwinter as larvae in cocoons in spikelets of sorghum or Johnsongrass. Johnsongrass spikelets containing diapausing larvae fall to the ground and become coveredwith litter. When sorghum is shredded, spikelets containing larvae fall to the ground and are disked into the soil. Sorghum midges emerging in spring do so before flowering sorghum is available, and these adults infest Johnsongrass. Sorghum midges developing in Johnsongrass disperse to fields of sorghum when it flowers. Early-season infestations in sorghum are usually below damaging levels. As the season progresses, sorghum midge abundance increases, especially whenflowering sorghum is available in the area. Numbers often drop late in the season.
A sorghum midge damages sorghum when the larva feeds on a newly fertilized ovary, preventing normal kernel development. Grain loss can be extremely high. Glumes of a sorghum midgeinfested spikelet fit tightly together because no kernel develops. Typically, a sorghum grain head infested by sorghum midges has various proportions of normal kernels scattered among non-kernel-bearing spikelets, depending on the degree of damage.
Effective control of sorghum midge requires the integration of several practices that reduce sorghum midge abundance and their potential to cause crop damage. The most effective cultural management method for avoiding damage is early, uniform planting of sorghum in an area so flowering occurs before sorghum midges reach damaging levels. Planting hybrids of uniform maturity early enough to avoid late flowering of grain heads is extremely important. This practice allows sorghum to complete flowering before sorghum midges increase to damaging levels. Cultural practices that promote uniform heading and flowering in a field are also important in deciding on treatment and in achieving acceptable levels of insecticidal control. To reduce sorghum midge abundance, use cultivation and/ or herbicides to eliminate Johnsongrass inside and outside the field. Where practical, disk and deep plow the previous year's sorghum crop to destroy overwintering sorghum midges.
Multiple insecticide applications are used to kill adults before they lay eggs. Sorghum planted and flowering late is especially vulnerable to sorghum midge. To determine whether insecticides are needed, evaluate crop development, yield potential and sorghum midge abundance daily during sorghum flowering. Because sorghum midges lay eggs in flowering sorghum grain heads (yellow anthers exposed on individual spikelets), they can cause damage until the entire grainhead or field of sorghum has flowered. The period of susceptibility to sorghum midge may last from seven to nine days (individual grain head) to two to three weeks (individual field), depending on the uniformity of flowering.
To determine if adult sorghum midges are in a sorghum field, check at mid-morning when the temperature warms to approximately 85° F. Sorghum midge adults are most abundant then on flowering sorghum grain heads. Because adult sorghum midges live less than one day, each day a new brood of adults emerges. Sampling must be done almost daily during the time sorghum grain heads are flowering. Sorghum midge adults can be seen crawling on or flying about flowering sorghum grain heads.
The simplest and most efficient way to detect and count sorghum midges is to inspect carefully and at close range all sides of randomly selected flowering grain heads. Handle grain heads carefully during inspection to avoid disturbing adult sorghum midges. Other sampling methods can be used, such as placing a clear plastic bag or jar over the sorghum grain head to trap adults.
Because they are relatively weak fliers and rely on wind currents to aid their dispersal, adult sorghum midges usually are most abundant along edges of sorghum fields. For this reason, inspect plants along field borders first, particularly those downwind of earlier flowering sorghum or Johnsongrass. If no orfew sorghum midges are found on sorghum grain heads along field edges, there should be little need to sample the entire field. However, if you find more than one sorghum midge per flowering grain head in border areas of a sorghum field, inspect the rest of the field. Sample at least 20 flowering grain heads for every 20 acres in a field. For fields smaller than 20 acres, sample 40 flowering grain heads. Flowering heads are those with yellow blooms. Avoid plants within 150 feet of field borders. Record the number of sorghum midges for each flowering head sampled and then calculate the average number of midges per flowering head. Almost all of the sorghum midges seen on flowering sorghum heads are female.
Next, calculate the number of flowering heads (yellow blooms present) per acre. Record the number of flowering heads along a length of row equal to 1/1000 of an acre. As an example, for a row spacing of 40 inches, 13.1 row feet is equal to 1/1000 of an acre. Make counts in at least four areas of the field. If flowering (plant maturity) is highly variable across the field, additional sites should be sampled. Average all counts and multiply by 1000 to estimate thenumber of flowering heads per acre. If there is only one head per plant, then the number of flowering heads per acre is equal to the percent heads in bloom multiplied by the number of plants per acre.
Sorghum midge density per acre is then calculated as the mean number of midges per flowering head times the number of flowering heads per acre. For example, if there are 30,000 flowering heads per acre and scouting records show an average of 0.5 sorghum midge per flowering head, then there are an estimated 15,000 sorghum midges per acre (0.5 sorghum midge per head x 30,000 flowering heads per acre). The percentage of flowering heads changes rapidly during bloom and should be determined each time the field is sampled. Studies have shown that the larvae from a single female sorghum midge will destroy an average of 45 grain sorghum kernels. The seed weight of sorghum hybrids averages 15,000 seeds per pound (range of 12,000 to 18,000, depending on the hybrid). A loss of 45 kernels per midge, therefore, represents 0.0030 pounds (1.364 grams) of grain.
|Number of sorghum midges per flowering head||=||(Cost of control as $ per acre) x 33,256 |
(Value of grain as $ per cwt) x (Number of flowering heads)
|$5 x 33,256|
$4 x 18,000
|=||2.3 sorghum midges per flowering head|
In this example, the field density of 1.1 sorghum midges per flowering head is below the injury level and treatment would not be justified. If the field is scouted two days later and the sorghum midge density is again 1.1 midges per flowering head, but now the number of flowering heads has increased to 45,000 per acre (50 percent of the plants now have a flowering grain head in a plant density of 90,000 per acre and one head perplant), the injury level is now:
|$5 x 33,256|
$4 x 45,000
|=||0.9 sorghum midges per flowering head|
In this example, the field density of 1.1 sorghum midges is now above the economic injury level of 0.9 per flowering head and treatment would be justified. This shows the importance of considering the number of flowering heads (grain susceptible to midge damage) in estimating the economic injury level. Economic injury levels, as determined from the above equation, are shown in Table 8 for a range of typical treatment costs per acre, market values per 100 pounds of grain and numbers of flowering heads per acre. Use the equation for estimating injury levels for your actual control costs, crop value and number of flowering heads per acre.Table 8 Estimated economic injury levels for sorghum midge for a range of factors. (This table is only a guide. Use the equation in the text to estimate injury level in your field.)
|Control costs, $/acre||Crop value, $100 lbs||Flowering heads = 18,000/acre||Flowering heads = 455,000/acre||Flowering heads = 67,500/acre|
Insecticide residues should effectively suppress sorghum midge egg laying one to two days after treatment. However, if adults still are present three to five days after the first application of insecticide, immediately apply a second insecticide treatment. Several insecticide applications at three-day intervals may be justified if yield potential is high and sorghum midges exceed the economic injury level (Table 9).
|Chlorpyrifos (Lorsban® 4E)||8 oz||30||30|
|Cyfluthrin (Baythroid® 2E)||1.0-1.3 oz||14, see remarks|
|Esfenvalerate (Asana®XL)||2.95-5.8 fl oz||21|
|Malathion (Fyanon® ULV)||8-12 oz||7||7|
|Methomyl (Lannate®)2.4LV, 90WSP||12-24 oz|
|Zeta-cypermethrin Mustang Max®||1.28-4.0 fl oz||14||45|
|Cause:||Macrophomina phaseolina (Charcoal Rot), Colletotrichum graminicola(Stalk Red Rot/Anthracnose)|
|Symptoms:||Stalk is spongy, and internal tissue (pith) shredded and often discolored. Plants sometimes turn grayish-green after jointing.|
|Key Features:||Fungi survive on crop residue. High plant population, high nitrogen and low potash can aggravate the diseases. Charcoal Rot is prevalent in hot, dry weather. Stalk Red Rot is prevalent during warm weather with alternating wet and dry periods.|
|Management:||Use hybrids resistant to Stalk Red Rotand tolerant to Charcoal Rot. Avoid excessive plant populations. Maintain proper soil fertility. Rotate away from sorghum for two or more years following a severe outbreak of eitherdisease. Avoid soybeans and corn for two or more years following severeoutbreaks of Charcoal Rot. Azoxys trobin is labeled for management of C. graminicola and Charcoal Rot.|
|Cause:||Sporisorium reilianum (syns. Sphac elotheca reiliana)|
|Symptoms:||At heading, large galls occur in place of the head. Head turns into mass of dark brown, powdery spores.|
|Key Features:||Infection occurs in seedlings from spores in the soil.|
|Management:||Use resistant hybrids.|
|Disease:||Leaf spots and blights|
|Cause:||Setosphaeria, Collectotrichum, Cerco spora, Gleocercospera, Ascophyta|
|Symptoms:||Older leaves are infected first with round, oval, or rectangular leaf spots. Spots are tan, yellow, reddish or purple and sometimes have a darker margin.|
|Key Features:||These fungi survive in crop residue and spores are spread by air currents or by splashing rain. Normally, thesediseases do not hurt yields. If the upper leaves become infected, then severe yield losses can occur.|
|Management:||Use resistant hybrids, especially forno-tillage. Rotate away from sorghum or corn for 1 to 2 years. Control weeds that may be a source of the inoculum. Azoxystrobin is labeled as a foliar spray for Cercospora (Gray leaf spot)control in sorghum.|
|Disease:||Maize Dwarf Mosaic|
|Cause:||Maize Dwarf Mosaic Virus|
|Symptoms:||Irregular, light and dark green mosaic patterns on the leaves, especially the younger leaves. Tan stripes with red borders between the veins ("red-leaf ") occurs under cool conditions.|
|Key Features:||The virus lives in Johnsongrass rhizomes and other perennial grasses. The virus is transmitted by certain aphids.Late-planted sorghum is at greater risk.|
|Management:||Use tolerant hybrids and eradicate John songrass and other perennial grassy weeds.|
|Cause:||Periconia, Pythium, Rhizoctonia,Fusarium|
|Symptoms:||Stunting, sometimes leaf yellowing and/or wilting. Rotted roots are pink, reddish brown, or black.|
|Key Features:||Common fungi in soil, but not damaging unless plant is stressed. Common stresses include cool soils, poor drain age, or inadequate fertility. Vigorously growing plants are able to replacedamaged roots with new roots.|
|Management:||Use adapted hybrids. Plant in warm (above 65°F) moist soils at the proper depth and seeding rate. Place herbicide, fertilizer, insecticide and seed properly to avoid stress or injury to seedling. Azoxystrobin is labeled for in-furrow use for Rhizoctonia and Pythium diseases.|
|Cause:||Burkholderia andropogonis (syns.Pseudomonas andropogonis)|
|Symptoms:||Long, narrow brick-red to purplish red stripes, becoming tan when dry. Lesions are bound by secondary veins.|
|Key Features:||Bacteria survive in infected seed and in undecomposed sorghum residue. Warm, humid weather favors infec tion. Generally does little damage.|
|Management:||Use clean seed. Rotate away from grainsorghum for two years. Control weeds, especially shattercane (Sorghum bicolor). Use resistant hybrids, espe cially for reduced tillage and no-tillage fields.|
|Disease:||Fusarium head blight|
|Symptoms:||The head becomes infected first while stalk tissue at and immediately below the head become infected later. Cream to pink fungal growth can occur ongrain.|
|Key Features:||The fungus can occur in seed or crop residue. Spores are spread by air. Warm moist conditions provide a favorableenvironment for disease development.|
|Management:||Timely harvest of grain at propermoisture. Hybrids with pigmented seed coats are more tolerant grain mold. Hybrid with dense, compact heads could be more damaged.|
|Disease:||Sorghum Downy Mildew|
|Symptoms:||Yellow-green stripes in leaves. "Downy" growth from fungal spores may occur on underside of leaf. Leavesbecome shredded as season progresses. Heads are partially or completely sterile.|
|Key Features||The fungus survives in the soil for many years. Spores germinate and infect roots, and colonize plants inter nally. Infected plants produce spores carried by the air to other plants. Alsoinfects corn and shattercane.|
|Management:||Use resistant hybrids. Use seed treatedwith metalaxyl. Control shattercane to reduce inoculum. Long-term rotation to soybeans, wheat or forages reduces inoculum in the soil. Avoid cornsorghum rotation where the diseaseoccurs.|
Grain quality at harvest is influenced by grain variety, weather and combine adjustment. Minimizing grain damage to maintain quality requires good handling, drying and cooling equipment and conscientious stored-grain management.
Grain sorghum is harvested with a combine with a grain table with a rigid header, a flex header in the rigid position, and a row crop header. Guards that help pick up heads are recommended if heads are drooping or stalks are lodged. Sorghum stalks are generally much wetter than corn stalks at harvest, and they may be sticky from sugars. Stalk material pulled into the harvester is more likely to clump in the combine, thus increasing harvest losses, and residue can also collect in the hopper with grain. Stalk material mixed in with grain can cause problems with drying and storing. To avoid problems with green stalks, harvest as little of the stems and leaves as possible.
Handling. Grain sorghum may need to be cleaned before storing in a grain bin, depending on the amount of trash that accompanies the grain. The trash can be reduced by harvesting after a killing frost or after using a desiccant. Excessive trash in the bin can accumulate and become hot spots during drying or can even catch on fire.
Drying. Harvest grain sorghum at 18 to 22 percent moisture if a suitable heated-air system is available for drying the crop. Harvesting above 22 percent will result in more trash material in the grain.
Producers should be extremely cautious in holding high-moisture grain sorghum prior to drying. High-moisture grain sorghum packs much tighter than high-moisture corn. This inhibits air circulation within the grain and can result in heating, molding and sprouting problems. Never hold wet sorghum longer than two to four hours unless aeration is provided.
Grain sorghum is much harder to dry than corn because the seed is small and round and it is harder to force air through it. Actual drying capacity will be about two-thirds to three-fourths as fast as corn for the same grain depth and air temperature.
Continuous flow or batch dryers are the preferred methods for drying grain sorghum. If it must be dried in a bin, the bin should be used as a batch-in bin dryer, limiting the drying depth of each batch to four feet. After drying, cool the grain and move it to another storage bin before the next day's harvest. A three-foot depth of sorghum is equivalent in resistance to four-foot depth of corn at an airflow rate of 10 cubic feet per minute. An individual seed of grain sorghum will dry faster than an individual seed of corn, but greater flow resistance from a bin of sorghum will reduce the airflow. As a result, drying time for grain sorghum is longer than for corn. Cooling time is also longer.
Optimum drying temperature depends on the type of dryer, airflow rate, end use (feed, market, seed) and initial and final moisture contents Maximum temperature for drying grain sorghum for use as seed should not exceed 110°F. Dry for milling below 140°F in high airflow batch and continuous flow dryers and 120°F in bin dryers. If used for feed, drying temperatures can be up to 180°F. Always cool grain to within five to 10 degrees of the average outside airtemperature after drying. Natural, unheated air may be used when the relative humidity is 55 percent or less and the grain moisture is 15 percent or less.
Natural, unheated air drying can be used to dry grain sorghum if the moisture content is 16 percent or below and the drying depth is less than 10 feet. Drying fans must be capable of delivering at least one to two cfm/bushel. Because the drying process is slow, it is important to start the fans immediately after the floor is covered.
Storage Moisture Content. The final storage moisture for grain sorghum depends on the expected length of the storage period and whether the grain sorghum is to be fed out to the bin continuously or is allowed to remain undisturbed in the bin until it is sold.
Storing Grain Sorghum. Aeration is one of the most important management tools available to producers for maintaining grain quality in storage. Aeration extends the storage life of grain by removing odors, preventing moisture accumulation and controlling conditions favorable to mold growth and insect activity.
Grain should be aerated after it is dried and in the fall, winter and spring. Begin aeration when the average outdoor temperature is 10 to 15°F lower than the grain temperature. Average outside temperature can be taken as the average of the high and low temperatures over a three to five day period. Check graintemperatures at various locations in the bin with a probe and thermometer.
Inspect all grain in storage at least once a week. Check for indications of moisture such as crusting or condensation on the bin roof. Check and record the temperature at several points in the stored grain. Any increase in temperature indicates a problem unless outside temperatures are warmer than the grain. Probe the grain to check for insects or other problems. If problems are noticed, run the aeration fans.
Grain Quality. Sorghum grain is placed into U.S. Grade Numbers 1, 2, 3, 4 or Sample Grade, with U.S. No. 1 being the highest quality (Table 11). Value of grain sorghum follows this grading system. Proper harvesting, drying and storing are important to achieving the higher grades.
For more information on harvesting, drying and storing in specific states, consult Kentucky's AEN-17: Harvesting, drying and storing grain sorghum, and AE-82-W: Harvesting, drying and storing grain sorghum.