Volume 13, Issue 6 - August 2023

David Moseley, Collins, Fred L., Monaghan, Tashia M, Waltman, William F., Burns, Dennis, Stephenson, Daniel O., Padgett, Guy B., Dufour, Justin, Harrison, Stephen A., Carriere, Mark, Miller, Donnie K., Villegas, James M.

August 2023 Louisiana Soybean Production Update: Extreme Heat and Drought Stress

David Moseley, LSU AgCenter Soybean Specialist

The Louisiana soybean crop has been severely affected by extreme heat and drought stress. Factors such as availability of irrigation, planting date, and soil type have all had a significant impact on the condition of plants.

Irrigation versus Dryland Production Systems

In some irrigated fields, plants that did not receive water matured early with little to no marketable seed. Figure 1 shows three irrigated fields in the central region. The left and middle pictures show fields with either a center pivot or furrow irrigation system. In both fields, the plants outside of the irrigation water matured early with small seeds (Figures 1, 2, and 3). The picture on the right also shows a field with furrow irrigation (Figure 1). The height of the beds did not allow the irrigation water to reach the middle soybean rows, which created droughty conditions.

Soybean plants growing in irrigated fields.

Figure 1. Soybean plants in irrigation production systems were showing signs of drought stress where the water did not reach.

One brown soybean plant and one green soybean plant.

Figure 2. Two soybean plants from the same field. The irrigation water did not reach the plant shown on the left.

One green soybean pod and seed and one dry soybean pod and seed.

Figure 3. Two pods from the same field. The pod on the right originated from a plant that did not receive irrigation water.

Heat Stress in Irrigated Production Systems

The extreme heat also caused stress in irrigated fields where some plants matured early with little to no marketable seed (Figure 4). The pictures show increased heat stress either between different sections of fields, between different rows of fields, or within the same row of a field.

Soybean plants in irrigated fields with different levels of heat stress.

Figure 4. Plants within irrigated fields in Richland Parish show various levels of heat stress and damage. (Left) All plants in the front had a greater effect from heat stress than plants in the back. (Middle) Some rows within a field had a greater effect from heat stress than other rows. (Right) Some plants within a row had a greater effect from heat stress than other plants within the same row.

Necrosis symptoms on soybean leaves.

Figure 5. The soybean plants from the irrigated fields shown in figure 4 expressed necrotic symptoms before maturing early. (Picture from Keith Collins)

Declining Conditions after August 1

On August 11, the USDA-NASS survey projected 1.09 million acres of the 1.12-million-acre soybean crop would be harvested, and the statewide yield would be 49 bushels per acre. This yield projection would be up two bushels from 2022. The survey report stated the projection was considering conditions as of August 1. With only approximately 25% of the crop at least coloring by July 30, the final yield of most of the soybean acres was still subject to heat and drought stress.

The USDA-NASS survey reported the soil moisture level began to decline rapidly after July 16. As of August 13, between 65-69% of the topsoil and subsoil moisture levels were rated as short to very short (Figure 6). The crop condition also declined after July 30. For the week ending on August 13, the USDA-NASS survey indicated 20% of the crop was rated as poor to very poor (Figure 6).

Soil moisture and soybean crop condition ratings.

Figure 6. The percentage of the Louisiana soil moisture level rated as very short and short; and the percentage of soybean acres rated as good to excellent and poor to very poor.

According to the Louisiana Agriclimatic Information System, operated by the LSU AgCenter, the daily average temperature at the Dean Lee Research Center from July 27 – August 14 was seven degrees Fahrenheit higher compared to the daily average temperature during 2020-2021. Furthermore, in 2023, the last recorded rainfall at the research station was on July 22. In 2020-2021, the average rainfall between July 23 – August 14 was 2.3 inches. (Figure 7)

Temperature and rainfall at the Dean Lee Research Station in 2023 and compared to 2020-2021.

Figure 7. The average temperature and total rainfall in 2020-2021 and in 2023 at the Dean Lee Research Station between March 2 and August 14. Note: Available data from the Louisiana Agriclimatic Information System for the Dean Lee Research Station was used to compare to 2023. Data from 2022 was excluded due to excessive rainfall in August.

For more information on drought and heat stress, read the article Soybean Drought and Heat Stress from the LSU AgCenter Louisiana Crops Newsletter Volume 12, Issue 6 – July 2022.

Post Harvest Weed Management in Corn and Soybean

Donnie Miller and Daniel Stephenson, LSU AgCenter Weed Scientists

Corn is historically planted early to mid-March in Louisiana. Summer annual weed emergence occurs in mid-April. Given this, what is the usual result of the following scenario:

  • corn planted on March 10th;
  • fertilizer applied on April 10th;
  • postemergence application of herbicide applied to 6- to 8-inch corn on April 14th;
  • summer annual weeds ½ to 2 inches tall.

Excellent weed control. Combine that with rapid corn growth after fertilizer application and the potential for summer annual weeds to impact yield is greatly reduced. Results are similar for soybean planted in late March to early April, especially if MG III or early MG IV soybean are planted.

Controlling weeds in the crop is the goal of all producers; however, post-harvest control can be just as critical for long term weed management success. Weeds including annual grasses, pigweeds, and morningglories, among others, often emerge as these crops begin to dry down in mid to late summer due to sunlight reaching the soil surface and encouraging germination. In addition, early planting dates lead to late July through August harvest dates which can result in large weeds during the harvest.

The post-harvest environment in Louisiana is such that multiple generations of weeds can emerge and produce seed. In late summer through fall, as daylength decreases, many annual weeds require only 30 to 45 days from emergence to viable seed production. Although total seed production is not as great as during peak growing conditions in summer, even a small amount of viable seed can lead to yield limiting populations in the subsequent crop. Add in the possibility of seed being from herbicide resistant populations, the need to do something monthly to prevent seed production becomes more important.

Realizing that there is not a one size fits all approach for each producer, effective options include mowing, tillage, or a postemergence herbicide application. Unfortunately, to ensure little to no weed seed production, one of these should optimally be conducted monthly until first frost. Keep in mind that stubble covering rows after harvest can effectively reduce/delay weed germination by blocking light from reaching the soil. Although preventing seed production is the ultimate goal, previous research has shown that an application of glyphosate and other herbicides at initial seed set on weed species can effectively reduce seed viability.

Mowing, tillage, or postemergence herbicides (glyphosate, paraquat, Reviton etc.) can be used interchangeably. Paraquat co-applied with 2,4-D has effectively prevented or reduced seed production when applied after corn harvest. Additionally, Reviton has provided excellent control of broadleaf signalgrass and summer annual broadleaves in mid-summer application in previous research trials and observations from use on large scale farming operations after harvest in 2022 indicated potential for good control of select weeds post-harvest. If residual herbicides are applied in August or September, due to temperatures experienced and lack of adequate rainfall for incorporation, do not expect sufficient length of residual weed control to effectively impact winter annual weeds like Italian ryegrass, henbit, swinecress, and others (fall weed management will be covered in a subsequent article).These annual winter weeds often require only 7-10 days of temperatures below 90 degrees to germinate but lack of adequate moisture is often the limiting factor delaying germination to October or November. We suggest utilizing residual herbicides in October/November to provide residual control of winter annual weeds.

Pay attention to the herbicide labels to ensure they allow fallow application. Also, check the preplant interval for the crop you will plant in that field next spring as well as requirements for optimal activity. If you have any questions, please contact your local parish agent or Donnie Miller at 318-614-4044 or Daniel Stephenson at 318-308-7225.

Managing Stink Bugs in Louisiana Soybean Fields

James Villegas, LSU AgCenter Field Crops Entomologist

Different stink bug species.

Adult brown stink bug (left), adult southern green stink bug (center), and immature redbanded stink bug (right). Photos by J. Villegas

More stink bugs are starting to show up in soybean fields. The stink bug complex in Louisiana soybean includes several species such as the brown stink bug, green stink bug, southern green stink bug, and perhaps the most notorious, the redbanded stink bug. Each species is capable of causing damage. Stink bugs possess piercing-sucking mouthparts that enable them to feed on various parts of soybean plants (stems, pods, and seeds), potentially causing yield and quality losses. The redbanded stink bug stands out as the most economical insect pest due to its extended feeding behavior and ability to pierce deeper into pods.

To stay ahead of these insect pests, regular scouting using sweep nets is essential. Scouting not only helps determine the presence of stink bugs but also aids in deciding the appropriate control measures. For redbanded stink bugs, the threshold recommended by the LSU AgCenter is 4 bugs (nymphs and adults) per 25 sweeps, while for southern green, green, and brown stink bugs, the threshold is higher at 9 bugs (nymphs and adults) per 25 sweeps. When it comes to control, different species require different approaches. Please check the 2023 LSU AgCenter Insect Pest Management Guide for recommended insecticides.

Extend control measure for redbanded stink bug

While the standard recommendation for controlling southern green, green, and brown stink bugs is to cease insecticide applications once soybeans reach the R6.5 growth stage, the same cannot be said for redbanded stink bugs. Due to their extended feeding period and deeper pod penetration, soybeans must be protected from redbanded stinkbugs until at least the R7-R8 growth stages. Previous studies have documented an average seed weight reduction of 10% if redbanded stinkbugs are not controlled past R6.5.

When applying final treatments, particularly when tank-mixing pyrethroids with acephate or neonicotinoids, two critical factors should be kept in mind: the pre-harvest interval (PHI) and the maximum active ingredient (a.i.) allowed per acre per growing season. Adhering to these guidelines ensures both effective pest control and compliance with safety regulations.

LSU AgCenter 2022-23 Wheat Variety On-farm Demonstrations

Boyd Padgett, Steve Harrison, Fred Collins, Tashia Monaghan, Dennis Burns, Justin Dufour, Mark Carriere, and Bill Waltman

Listed below are the yields and test weights from the LSU AgCenter wheat variety on-farm demonstrations conducted during 2022-23.

Wheat Demos for 2023_AugNewsletterpdf

2023 Wheat On-Farm Demonstration Pointe Coupee

Variety

Yield

bu/A

AGS 3022

48.0

AgriMaxx 492

58.9

Delta Grow 1800

41.5

Delta Grow 3500

41.0

Go Wheat 6000

45.3

2023 Wheat On-Farm Demonstration Avoyelles 1

Variety

Test

Weight

Yield

bu/A

AgriMaxx 492

62.9

66.7

AgriMaxx 514

57.6

62.3

Delta Grow 1200

58.0

48.8

Delta Grow 1800

64.2

56.5

Delta Grow 3500

61.3

68.0

Dyna-Gro Plantation

62.6

64.3

Dyna-Gro Riverland

63.3

32.0

Go Wheat 6000

61.4

27.3

Progeny Bingo

58.2

54.1

Progeny Chad

61.2

68.9

2023 Wheat On-Farm Demonstration Avoyelles 2

Variety

Test

Weight

Yield

bu/A

AgriMaxx 492

62.1

59.7

AgriMaxx 514

56.0

49.4

Delta Grow 1200

57.2

38.7

Delta Grow 1800

63.2

46.2

Delta Grow 3500

61.7

51.5

Progeny Bingo

55.0

37.2

Progeny Chad

57.0

69.5

2023 Wheat Demonstration Northeast Research Station

Variety

Test

Weight

Yield

bu/A

AgriMax 492

54.4

52.5

AgriMax 514

34.8

35.0

AGS 3022

52.0

40.6

Delta Grow 1800

52.7

36.1

Dyna-Gro Riverland

50.2

35.4

Dyna-Gro Plantation

53.7

32.0

GO Wheat 6000

58.8

32.4

Progeny Bingo

51.5

37.2

Progeny Chad

52.2

52.9

2023 Wheat Demonstration Red River Research Station

Variety

Test

Weight

Yield

bu/A

AgriMaxx 492

52.5

79.3

AgriMaxx 514

46.3

42.0

AGS 3022

56.5

71.0

Delta Grow 1200

49.7

33.0

Delta Grow 1800

53.9

79.4

Delta Grow 3500

51.7

51.2

Dyna-Gro Plantation

54.3

69.0

Dyna-Gro Riverland

50.6

64.2

Go Wheat 6000

50.2

52.6

Progeny Chad

50.9

78.4

2023 Wheat On-Farm Demonstrations Yields (bu/A)

Variety

Red River

Res. Sta.

Avoyelles

1

Avoyelles

2

Pointe Coupee

Northeast

Res. Sta.

AgriMaxx 492

79.3

66.7

59.7

58.9

52.5

AgriMaxx 514

42.0

62.3

49.4

-

35.0

AGS 3022

71.0

-

-

48.0

40.6

Delta Grow 1200

33.0

48.8

38.7

-

-

Delta Grow 1800

79.4

56.5

46.2

41.5

36.1

Delta Grow 3500

51.2

68.0

51.5

41.5

-

Dyna-Gro Plantation

69.0

64.3

-

-

32.0

Dyna-Gro Riverland

64.2

32.0

-

-

35.4

Go Wheat 6000

52.6

27.3

-

45.3

32.4

Progeny Bingo

-

54.1

37.2

-

37.2

Progeny Chad

78.4

68.9

69.5

-

LSU AgCenter Specialist

Specialty Crop Responsibilities Name Phone
Corn, cotton, grain sorghum Agronomic Trey Price
318-235-9805
Soybeans Agronomic David Moseley 318-473-6520
Wheat Agronomic Boyd Padgett 318-614-4354
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 James Villegas
225-266-3805
Weed science Corn, cotton, grain sorghum, soybeans Daniel Stephenson 318-308-7225
Nematodes Agronomic Tristan Watson 225-578-1464
Irrigation Corn, cotton, grain sorghum, soybeans Stacia Davis Conger 904-891-1103
Ag economics Cotton, feed grains, soybeans Kurt Guidry 225-578-3282
Precision ag Agronomic Luciano Shiratsuchi 225-578-2110
Soil fertility
Corn, cotton, grain sorghum, soybeans Rasel Parvej 318-435-2908

8/19/2023 1:20:12 AM
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