Daniel Fromme, Price, III, Paul P, Padgett, Guy B.
In this article:
|Using harvest aids in grain sorghum
|Soybean growth stages
|Cotton disease update
|LSU AgCenter Specialists
By Dan Fromme, LSU AgCenter grain sorghum specialist
Applying a harvest aid to grain sorghum has become a common practice in Louisiana. When properly applied, they permit faster and more efficient combining, with no reduction in grain weight. Grain moisture content will be more uniform across the field, which can result in fewer moisture discounts.
It is easy to determine the black layer stage of kernel development, which is when harvest aids should be applied. A black layer forms at the seed attachment point at physiological maturity when maximum seed weight is reached. At black layer, the vascular tissue, or phloem tubes, can no longer carry nutrients and water to the grain, and the seed can no longer increase in dry weight.
Grain sorghum producers may consider harvest aids to manage sorghum dry-down and harvest for several reasons, including:
Physiological maturity in grain sorghum is reached when a black layer appears on the sorghum kernels. This layer is visible at the base of the kernel following individual detachment from their outer glume. Mature seed will contain approximately 30% moisture. Sorghum seed change color and accumulate hard starch in a similar manner to maturing corn kernels. If you observe a considerable amount of green seed rather than red or brown mature seed, give the field more time to fully mature.
Seed at the top of the head will mature prior to those at the bottom of the head. Sorghum pollinates first at the top of the head and progresses steadily downward to the base of the panicle (or flower cluster) in six to nine days. On average, sorghum hybrids reach black layer at approximately 120 days after planting. Most sorghum hybrids reach 50% bloom about 75 days after planting, and another 45 days are required after pollination for the grain to reach physiological maturity.
In Figure 1, five kernels of sorghum have been removed from different locations on the seed head. Kernels 1, 2, 3, 4 and 5 were located in descending order down the seed head. The crop is considered mature when all the kernels look like kernels 1, 2 and 3. Kernels 1 and 2 have a fully developed black layer, and kernel 3 has a black layer that has formed. Kernels 4 and 5 show almost no formation of a black layer. Hard starch initially forms at the seed crown and progressively moves toward the base, where it develops a black layer similar to corn. Pinch a seed between your fingernails, and if you easily penetrate soft dough at the base of the seed, it is not mature.
Do not apply a harvest aid prematurely (before physiological maturity) because you will sacrifice yield and test weight by hastening seed fill. About 25% of seed weight is added during the last 14 days prior to physiological maturity. Therefore, it is extremely important to scout the entire sorghum field and properly determine physiological maturity before applying a harvest aid.
Three products are labeled for use as harvest aids: sodium chlorate, glyphosate and carfentrazone. Good spray coverage is essential for all three products.
Sodium chlorate: Provides leaf desiccation but does not kill the plant. Regrowth may occur. Apply 7 to 10 days prior to harvest. Rates are based on product formulation. If a 6 lb/gallon sodium chlorate is used, apply 1 gallon of product per acre and adjust rates accordingly for different formulations.
Use the lower rate when grain moisture is low and weather conditions are conducive to drying. Use the higher rate when conditions for desiccation are poor.
This product may be applied by aircraft (4 to 10 gallons per acre) or ground (10 to 20 gallons per acre). It is essential that the foliage be thoroughly covered. This product should not be mixed with insecticides or other organic materials unless specifically labelled because a fire or explosion may result. Apply as a medium or coarser spray. Desiccation is favored on clear, calm, sunny days with high temperatures and high humidity. If rain is anticipated within 24 hours, application should be delayed. Desiccation may be slowed when daytime temperatures are below 60 degrees Fahrenheit.
Glyphosate: Apply up to 44 fluid ounces per acre after sorghum has reached 30% moisture or less. Use a spray volume of 10 to 20 gallons of water per acre for ground application, or 3 to 10 gallons of water for aerial application. As with other herbicides that result in plant death, avoid preharvest application to plants infected with charcoal rot, as lodging may occur. Allow a minimum of seven days between application and harvest. Also, glyphosate is a late-season weed control option. Rainfastness can vary based on glyphosate formulation; however, six hours is sufficient time for absorption by the leaves.
Carfentrazone: The product label emphasizes to use it as a weed desiccant rather than for crop dry-down. It provides excellent control of morning glory. Apply at 1 ounce per acre and use a minimum of 10 gallons of finished product per acre for ground application and 5 gallons per acre for aerial application.
The time required between application and rainfast is one hour, and there is a preharvest interval of three days. Tank-mixing sodium chlorate with carfentrazone offers desiccation of grass weeds.
This information is provided as a guide only. Always consult the product label or manufacturer for complete information.
Healthy sorghum plants usually do not lodge after a harvest aid is applied and are capable of standing for up to three weeks after treatment. After 30 days, lodging can be significant. It is a good idea to apply harvest aids to only the fields that can be harvested within 14 days of application.
Charcoal rot can cause premature lodging; therefore, it is a good idea to inspect fields before an application is made. Infected plants die prematurely before grain fill is completed (Figure 2). Visual inspection of plants before applying a harvest aid requires splitting the stalk lengthwise. Infected stalks will be soft, spongy or disintegrated at the crown with charcoal-colored specks, which are fungal reproductive structures. If the stalk is unhealthy, plants will generally fall regardless of treatment. Figure 3 provides the visual symptomology when charcoal rot is present.
Figure 1. Sorghum kernels in various stages of maturity harvested from the same panicle from the most mature (1) to the least mature (5). The black layer is first visible in kernel 3 and becomes more distinguishable as the seed loses moisture. LSU AgCenter photo by Dan Fromme
Figure 2. Infected plants die prematurely before all grain can be filled. Upon closer inspection, many sorghum heads will appear dull and lackluster, and the spikelets may droop, giving the panicle a ragged appearance. Panicles will contain shriveled grain, with the worst being found at the base of the sorghum head, which would have been the last grain to mature. Texas A&M University photo by Tom Isakeit
Figure 3. By the time sorghum begins to lodge, it may be too late to apply glyphosate. When sliced open, the lower 5 to 6 inches of the stalk will be soft, spongy or disintegrated with charcoal-colored specks, which are reproductive structures of the pathogen. As prematurely killed plants continue to lose moisture, the plants will fall rapidly under the weight of their own grain. Texas A&M University photo Isakeit
Every year, soybean producers, consultants, extension agents and specialists make herbicide, insecticide, fungicide and defoliant applications based on a specific growth stage. Pesticide labels may recommend when or when not to apply a pesticide. Therefore, it is important that individuals make an accurate assessment of the growth stage prior to application of a pesticide to optimize efficacy and possibly prevent crop injury. It would be nice if all plants matured uniformly across the field, but this is not the case. To further complicate the issue, it is common to find flowers and pods of varying sizes on a single plant.
The vegetative growth stages are very straightforward. However, when assessing the reproductive growth stage of a crop, individuals should base this on what is occurring in the uppermost four nodes (except R1). Listed below are the descriptions and figures of selected growth stages of soybeans.
Table 1 provides the estimated time of development for each stage.
Figure 1. VE = emergence. LSU AgCenter photo
Figure 2. VC = cotyledon. Unifoliate leaves are fully expanded. LSU AgCenter photo
Figure 3. V1 = one fully expanded trifoliate. LSU AgCenter photo
Figure 4. V2 = two fully expanded trifoliates. Vx = x corresponds to the number of fully expanded trifoliates (ex. V5 = five fully expanded trifoliates). LSU AgCenter photo
Figure 5. R1 = beginning bloom. LSU AgCenter photo
Figure 6. R2 = full bloom. One flower on the uppermost two main stem nodes. LSU AgCenter photo
Figure 7. R3 = pod initiation. There is a 3/16-inch pod at one of the four uppermost nodes on the main stem. LSU AgCenter photo
Figure 8. R3 = pod initiation. There is a 3/16-inch pod at one of the four uppermost nodes on the main stem. LSU AgCenter photo
Figure 9. R4 = full pod. There is a 3/4-inch pod at one of the four uppermost nodes on the main stem. LSU AgCenter photo
Figure 10. R5 = seed is 1/8-inch long in a pod at one of the four uppermost nodes on the main stem. LSU AgCenter photo
Figure 11. R6 = full seed. A pod containing a green seed that fills the pod capacity is located at one of the four uppermost main stem nodes. A photo showing the R7, or beginning maturity, stage can be found on the website listed above. In R7, one pod on the plant has reached maturity color. LSU AgCenter photo
Figure 12. R8 = fully mature. 95% of pods have reached mature color. LSU AgCenter photo
Table 1. Number of days between stages. From Fehr and Caviness.
|Average number of days
|Range in number of days
|Planting to VE
|5 to 15
|VE to VC
|3 to 10
|VC to V1
|3 to 10
|V1 to V2
|3 to 10
|V2 to V3
|3 to 10
|V3 to V4
|3 to 8
|V4 to V5
|3 to 8
|2 to 5
|R1 to R2
|0 to 7
|R2 to R3
|5 to 15
|R3 to R4
|5 to 15
|R4 to R5
|4 to 26
|R5 to R6
|11 to 20
|R6 to R7
|9 to 30
|R7 to R8
|7 to 18
In the past week, target spot has been found in central and northeastern Louisiana. Overall incidence and severity seem to be very low at this point.
Target spot, caused by Corynespora cassiicola, starts on the lowest leaves in the canopy, and “fresh” lesions appear as pencil eraser- to dime-sized, water soaked, green to gray, circular lesions (Figure 1). Centers of lesions later become tan to brown and may have a distinct bullseye appearance as the disease progresses upward (Figure 2). Lesions in the lowest part of the canopy usually will not have reddish margins; however, as the disease progresses to the mid to upper canopy, reddish margins may develop that resemble the cotton leaf spot complex.
Target spot can significantly defoliate cotton over a short period of time under optimal environmental conditions (warm, long dew periods, rainy). Disease intensity increases with the frequency of rainfall events, while hot and dry weather will usually keep target spot in check. Any cotton variety that develops rank growth is susceptible to target spot, which makes canopy management a factor in managing the disease. Excessive N application may increase the risk to target spot by increasing the risk of rank growth.
Small-plot research trials since 2014 at the Northeast, Macon Ridge and Dean Lee research stations indicate that fungicide applications during the first month of blooming may significantly reduce defoliation due to target spot. Priaxor (4 oz/A) applied by ground with at least 10 GPA total water volume has consistently delayed defoliation due to target spot compared with other available materials. However, statistically significant (90% confidence level) yield preservation has not been observed in any of the trials to date. Trends towards yield preservation have been observed under severe disease pressure (more than 50% defoliation). The highest defoliation that has been observed to this point is less than 1%, which is encouraging. If the weather changes and fungicide applications are warranted in later-planted cotton, applying by air will likely not result in the desired coverage. Application by ground using flat fan or hollow cone tips at a minimum of 10 GPA are preferred to achieve the necessary coverage. Applications after significant defoliation has occurred are unlikely to provide economic benefit.
Refer to the Plant Disease Management Guide (here) for more information on available fungicides.
The cotton leaf spot complex (CLSC), which does not include target spot, is caused by several different species of fungi. This disease complex has become commonplace in Louisiana cotton. Most often, CLSC is associated with K deficiency and/or drought stress (Figure 3). Also, any type of crop injury (herbicide, fertilizer, etc.) may exacerbate CLSC. Fungicide applications are effective on CLSC; however, they are not recommended, as economic benefit is unlikely. It is best to solve the underlying issue, which is usually K deficiency. Soil test and apply nutrients as appropriate. Very limited data exists on in season, foliar applications of potassium and the effect on CLSC.
Reports of bacterial leaf blight (BLB) have been common this year in Louisiana cotton, which is likely due to planting of susceptible varieties and a favorable environment for disease development. Initial infection through wounds and/or natural openings in leaves produces dark green, angular water-soaked spots; however, most of the time, BLB is not noticed until lesions are reddish brown, which may or may not have yellow halos (Figure 4). The bacterium infects all cotton plant parts but is most commonly observed on leaves. Infection of leaf veins may occur creating a characteristic appearance (Figure 5). When bacterial blight is severe, infection will be observed on bolls causing rot and significant losses. Sometimes BLB may be confused with target spot. It is possible that a secondary fungal pathogen may invade after initial infection by the bacterium. Notice the dark, angular center in the lesion in Figure 6. This may be confused with target spot.
The bacterium that causes BLB may be seedborne or overwinter in cotton debris. Ensuring that sanitary measures have been taken by the seed company prior to purchasing seed is recommended. Tillage may reduce inoculum the following spring if you are following cotton with cotton. Rotation to a field where cotton was not the previous crop will reduce the chances of BLB occurring. Overhead irrigation or excessive rainfall may increase disease incidence and severity. Varieties that are resistant to BLB are commercially available and are the best management option. For more information on bacterial blight, please refer to the online publication here.
Scientists at Auburn University reported CLRDV last year. This virus and other similar viruses have been commonly referred to as cotton blue disease. Symptoms associated with the virus cover a wide range and can mimic many other things that we see annually in cotton fields. We are still trying to figure out exactly what we need to look for and are sending suspect samples to Auburn for confirmation. We will continue to release more information pertaining to Louisiana as it becomes available. To date, CLRDV has not been officially reported in Louisiana. For more information, please click here.
Figure 1. Early symptoms of target spot. LSU AgCenter photo
Figure 2. Characteristic target-like lesions of target spot. LSU AgCenter photo
Figure 3. K deficiency and cotton leaf spot complex. LSU AgCenter photo
Figure 4. Angular lesions of bacterial leaf blight. LSU AgCenter photo
Figure 5. Vein infections characteristic of bacterial leaf blight. LSU AgCenter photo
Figure 6. Yellow halos surrounding bacterial leaf blight lesions that mimic target spot. LSU AgCenter photo
|Corn, cotton, grain sorghum
|Cotton, grain sorghum, soybeans
|Corn, cotton, grain sorghum, soybeans, wheat
|Corn, cotton, grain sorghum, soybeans, wheat
|Corn, cotton, grain sorghum, soybeans
|Corn, cotton, grain sorghum, soybeans
|Stacia Davis Conger
|Cotton, feed grains, soybeans
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