Daniel Fromme, Brown, Sebe | 6/27/2019 3:01:03 PM
In this article:
|Count your kernels before you get bent out of shape|
|Estimating corn yield potential|
|Progression of the corn milk line to blacklayer|
|Identifying adult and immature plant bugs in Louisiana cotton|
|LSU AgCenter Specialists|
By Dan Fromme
Many fields exhibit some degree of pollination failure or minor kernel abortion near the tip of the ears. Often you will find 1 to 2 inches of barren cob. The good news is you will find the normal 30 to 35 kernels per row even though 1 or 2 inches of the ear tip are barren (Figure 1). So count your kernels before you get all bent out of shape with the poor tip fill in your fields.
However, tip issues in other fields may exist to varying degree and frequency where only find 15 to 20 kernels per row are found. This year, warm nights and days or limited photosynthate supply cannot be the culprit. Temperatures have been moderate, and we have had adequate sunshine. Also, we probably can rule out leaf diseases, hail, too much rainfall during pollination and, in most instances, severe nitrogen deficiencies. Approximately 70% of the corn acres in Louisiana are irrigated; therefore, soil moisture should be adequate.
In some of the fields that I have walked, emergence was uneven due to cold or wet planting conditions and excessive rainfall after planting. Normal and delayed plants side by side typically exhibit ears that are night-and-day different in the success of pollination. Therefore, the best guesses for the pollination issues this year could be uneven emergence and possibly weak or shallow root systems from excessive rainfall received prior to the V6 stage. These weak root systems could limit water uptake, which in turn could cause moisture stress during the critical pollination stage.
Figure 1. Normal 30 to 35 kernels per row even though one or two inches of the ear tip are barren. LSU AgCenter photo
By Dan Fromme
Every year as we enter the month of June, we begin to wonder how good the corn crop is going to be. This especially holds true in years that corn yields are looking really good.
There are several yield prediction methods. The most popular is the yield component method, which can be used well ahead of harvest. The method can be used beginning at the roasting ear, or milk or R3, stage of kernel development. Estimates made earlier than the R3 stage could overestimate yield if stress occurs and causes kernel abortion.
Find more information on Estimating Yield Potential of Corn.
LSU AgCenter photo.
By Dan Fromme
Staging kernels within R5 (dent) stage is possible by identifying the milk line on the non-embryo side of the kernel or by slicing the kernel longitudinally and looking internally. The starchy solid interior portion moves from the top of the kernel toward the cob as the kernel matures. Kernels within R5 are specifically designated by the progression of the milk line: 1/4, 1/2 and 3/4. Progression of the milk line and time required between each quarter varies based on temperature, available moisture and hybrid maturity. The time needed in each R5 stage is not the same for each of the quarter milk line positions (Table 1).
In Louisiana, you will need about 3.8 inches of water in the time period from R5 to R6. At half milk line, only 90% of total dry matter has been accumulated. Running out of water at this time would result in a 10% yield reduction.
Following the progression of the milk line during R5 is a good way to estimate when a field will reach physiological maturity, or blacklayer. After reaching this stage, any type of stress has little effect on grain yield.
Table 1. Progression of milk line during R5 with approximate percent moisture, dry matter, growing degree days (GDD) and days for each substage.
|Dry matter (percent of total dry weight)||GDD1||Days2||Water use to maturity (inches)|
|5.25 (1/4 milk line)||52||65||120||4||2.85|
|5.5 (1/2 milk line)||40||90||175||6||1.9|
|5.75 (3/4 milk line)||37||97||205||7||.95|
|6.0 physiological maturity)||35||100||0.0|
1Growing degree days. Number of growing degrees days per substage based on corn growth and development publication, Iowa State University, PMR 1009, March 2011.
2Average number of days for each substage based on Louisiana growing conditions and temperatures.
Figure 1. R5 or dent stage. LSU AgCenter photo
Figure 2. R5.5 or half milk line stage. LSU AgCenter photo
Figure 3. At the R6 or blacklayer stage, corn has reached physiological maturity. LSU AgCenter photo
By Sebe Brown
Tarnished plant bugs (TPB) are 1/4-inch-long insects that vary in color from yellowish brown to green with black markings and a conspicuous triangle located on the dorsal (back) side. Nymphs resemble the adults in general body shape and color but do not have wings. Tarnished plant bugs damage cotton from pinhead square to final boll set. Larger square damage affecting anthers, stigma and styles can cause fertilization problems and fruit shed. The Louisiana threshold for bloom to harvest is two to three TPB per 5 feet of black drop cloth, 10 TPB per 100 weeps or 10% dirty squares. Pre-bloom threshold levels are 10 to 25 TPB per 100 sweeps.
Figure 1. Tarnished plant bug adult. LSU AgCenter photo
Figure 2. Tarnished plant bugs nymph. LSU AgCenter photo
Fleahoppers are small, 1/8-inch insects that have an oval-shaped, elongated body. These insects are yellow to green and resemble other Hemipteran true bugs. They essentially look like a very small green TPB. However, unlike TPB nymphs, fleahopper nymphs have dark spots on the hind legs.
Cotton should be scouted for fleahoppers during the first three weeks of squaring. Detection can be difficult due to the flighty nature of these insects. Simply casting a shadow over the pest often will make them take flight. Louisiana pre-bloom thresholds for fleahoppers are 10 to 25 insects per 100 sweeps, with adjusted pre-bloom treatment levels to maintain between 70% and 85% first-position square retention.
However, scouting small cotton with a sweep net is difficult and produces questionable results. Additionally, detecting small fleahopper nymphs in a sweep net is difficult. A better technique is to simply examine the terminal of plants, watching for adults taking flight and then examining the terminal very closely for small nymphs. Morning is the best time to scout for fleahoppers, and if the wind is blowing, they take shelter in the plant canopy.
Figure 3. Cotton fleahopper adult. LSU AgCenter photo
Figure 4. Cotton fleahopper nymph. LSU AgCenter photo
Clouded plant bugs (CPB) are 3/8-inch-long insects characterized by a thickened first antennal segment and hind legs that are noticeably larger than the first two pairs. Adult CPB are generally brown with mottled patches of black, yellow or white. Nymphs are often greenish yellow with red and white horizontally striped antennae. Larger nymphs also can be identified by a dark spot on the dorsal side of the abdomen. Clouded plant bugs are an occasional pest in Louisiana cotton with pre-bloom and bloom threshold levels being the same for tarnished plant bug, but each CPB should be counted as 1.5 TPB.
Injury by CPB is similar to TPB with square abscission, bloom injury and boll feeding (cat-facing) occurring mid to late season. As with other plant bugs, monitoring square retention and sweep net sampling prior to bloom should be used to determine levels of CPB infestations. Sampling for plant bugs from bloom until harvest is aided by the use of a drop cloth because this technique is more suitable for detecting nymphs.
Figure 5. Clouded plant bug adult. University of Tennessee photo
Figure 6. Clouded plant bug nymph. University of Tennessee photo
Rapid plant bugs (RPB) are 3/10-inch-long insects that occasionally infest cotton in Louisiana. Adults are often orange-black to yellow-black in color and are larger than other species of plant bugs encountered while sampling. Nymphs are often green with a red or yellow tint and have a dark band across the abdomen. The thorax and abdomen of immature RPBs lack dark spots that are typically found on TPB nymphs.
Injury by the RPB is often sporadic and may be confused with other plant bugs. However, due to this pest’s larger size, injury levels can be significanlty greater than other species of plant bugs encountered in cotton. Therefore, pre-bloom and bloom RPB threshold levels should be the same for tarnished plant bug, but each RPB should counted as an equivalent to two TPB.
Figure 7. Rapid plant bug adult. LSU AgCenter photo
Figure 8. Rapid plant bug nymph. LSU AgCenter photo
|Corn, cotton, grain sorghum||Agronomic||Dan Fromme||318-880-8079|
|Grain sorghum||Agronomic||Dan Fromme||318-880-8079|
|Pathology||Cotton, grain sorghum, soybeans||Boyd Padgett||318-614-4354|
|Pathology||Corn, cotton, grain sorghum, soybeans, wheat||Trey Price||318-235-9805|
|Entomology||Corn, cotton, grain sorghum, soybeans, wheat||Sebe Brown||318-498-1283|
|Weed science||Corn, cotton, grain sorghum, soybeans||Daniel Stephenson||318-308-7225|
|Irrigation||Corn, cotton, grain sorghum, soybeans||Stacia Davis Conger||904-891-1103|
|Ag economics||Cotton, feed grains, soybeans||Kurt Guidry||225-578-3282|
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