Tri-Parish Ag News - May 2023

May 2023 - Header Photo.

2023 Louisiana Soybean Production Update: An Early Start to Planting and a Freeze

d Moseley, LSU AgCenter Soybean Specialist

Article Highlights:

  • The Louisiana soybean planting season began early in 2023.
  • Depending on several possible factors, some soybean fields survived a freeze on March 20th, but others were completely lost.

The USDA-NASS survey reported that two percent of the Louisiana soybean crop was planted by March 19, 2023. The warm and dry weather during early March allowed producers to plant their corn crop early and then begin planting soybeans. Unfortunately, on March 20th, the temperature dropped to approximately 28 degrees Fahrenheit in Northeast Louisiana. Soybean tissue death can occur if the temperature falls to 28 degrees Fahrenheit for more than four hours, especially if the unifoliate leaves are exposed (Vann and Stokes, 2020).

On March 21st and over the following few weeks, the condition of three fields was documented. Two fields were at the LSU AgCenter Northeast Research Station and the other field was near Clayton, LA. The planting dates were March 1, 15, and 6, respectively. For the March 1st and 6th planting dates, with only 30 miles between the two fields, almost 100 percent of the soybean plants at the Northeast research station were killed, but approximately 50 percent of the soybean plants at the field near Clayton, LA survived. One explanation could be that the plants near Clayton, LA were less developed as they were planted five days later. At least 50 percent of the unifoliate leaves were likely still insulated by the cotyledons. The soybean in the field planted on March 15th at the Northeast Research Station was not emerged on March 20th and survived the freeze.

The producer near Clayton, LA planted 160,000 seeds per acre. With an approximate 50 percent survival rate, the final stand was approximately 80,000 plants per acre. According to data from the LSU AgCenter Dean Lee Research Station in 2020, a final stand of approximately 61,000 plants per acre may result in similar yield as a stand of over 100,000 plants per acre. Most University soybean agronomist would agree that 70,000 – 75,000 plants per acre that are healthy and uniformly distributed will allow approximately 95 percent of the full yield potential as compared to a more full stand.


Soybean Figure 1.jpg thumbnail

Figure 1. Soybean seedling damage on March 21, 2023. The seeds were planted on March 6th and were in the VE growth stage (the cotyledons had emerged past the soil surface, but the unifoliate leaves had not completely unrolled and in some cases the growing point was still protected by the cotyledons) when the freeze hit Louisiana on March 20th. The cotyledons had suffered damage from the freeze, and it was unknown if the growing point had been killed.

Soybean Figure 2.jpg thumbnail

Figure 2. On March 27, 2023, the original main stem on some plants had ceased from growing after the apical meristem was killed during the freeze. However, after the apical meristem was killed, two axillary branches had begun to develop trifoliolate leaves from the cotyledon node.

Soybean Figure 3.jpg thumbnail

Figure 3. By April 5, 2023, both axillary branches had developed two open trifoliolate leaves and had another trifoliolate leaf beginning to open on each branch. Both axillary branches can fully develop and replace the original main stem.

Soybean Figure 4.jpg thumbnail

Figure 4. It was observed on April 5, 2023, that the apical meristem was not damaged on most plants. The soybean plants were progressing normally and had reached the V2 growth stage (two open trifoliolate leaves). The plants had reached the V2 growth stage approximately 30 days after planting which is within the normal average duration between planting and V2.

Soybean Figure 5.jpg thumbnail

Figure 5. The soybean seed was planted on a 7.5 inch spacing with a seeding rate of 160,000 plants per acre. After the March 20, 2023, freeze, the final stand count on April 5 was estimated to be 80,000 plants per acre which can still support close to full yield potential of a field with a full stand.

Reference:

Vann, R., D. Stokes. 2020. Soybean Cold Damage. North Carolina State Extension.

Corn Disease Update

Trey Price and Boyd Padgett, LSU AgCenter Pathologists

Article Highlights:

  • Corn disease identification
  • Management considerations

Holcus spot/paraquat drift

Symptoms for Paraquat drift and Holcus spot are similar and are difficult to distinguish from each other. Symptoms appear as round to oval, light tan to white spots with or without yellow halos. Generally, if a drift pattern (gradient) is observed, if affected areas are large and more jagged than round, or if secondary fungi are within lesions, it is likely paraquat drift (Figure 1).If the distribution is random, the spots appear within 48 hours of a thunderstorm, and water-soaking is observed, it is likely holcus spot (Figure 2).Microscopic observation of holcus spot may reveal bacterial streaming, as the disease is caused by Pseudomonas syringae pv. syringae. Both issues are usually of minor concern.

Common rust

Common rust may be the first disease found in corn fields and usually occurs in the lower-to-mid-canopy. Pustules of common rust are brick red to dark orange, somewhat elongated, and will appear on both leaf surfaces (Figure 3). Common rust will progress during relatively cool, rainy, and cloudy weather; however, very rarely are fungicide applications warranted for common rust. Warmer temperatures will greatly slow common rust development.

Southern rust

Southern rust pustules are more orange than brick red, usually not as elongated, and usually appear on the upper surface of leaves (Figure 4). This disease develops in warmer temperatures than for common rust and can continue to develop throughout the growing season. Like common rust, the disease usually initiates in the lower-to-mid-canopy. The disease can reach the upper canopy during conditions favorable for development. Fungicides may be justified but should be made on a field-by-field basis. The genetic resistance of the hybrid and growth stage (post tassel) and current environmental conditions are factors to consider prior to applying a fungicide.

Northern corn leaf blight

Northern corn leaf blight (NCLB) is a disease usually seen every year in susceptible hybrids (Figure 5). This disease will first appear in susceptible hybrids in fields following corn with reduced tillage. The disease will progress slowly during dry weather, and more quickly during regular rainy periods. Most of the time fungicide applications are not needed for NCLB. However, severe disease may occur in susceptible hybrids following corn in reduced tillage situations. These are the fields that need to be watched closely.

Fungicide considerations

Fungicide application decisions should be carefully considered field by field based on: disease severity (Figure 6), crop stage (Table 1), hybrid susceptibility, fungicide efficacy, tillage regime, prevailing environmental conditions, previous experience, commodity price, and the probability of a return on the investment. If applications are warranted, apply at labeled rates using maximum (5 GPA by air, minimum) water volume is recommended.

Growth Stage

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Tassel

3

7

13

21

31

42

55

68

83

100

Silked

3

7

12

20

29

39

51

65

80

97

Silks Brown

2

6

11

18

27

36

47

60

74

90

Pre-Blister

2

5

10

16

24

32

43

54

66

81

Blister

2

5

10

16

22

30

39

50

60

73

Early Milk

2

4

8

14

20

28

36

45

55

66

Milk

1

3

7

12

18

24

32

41

49

59

Late Milk

1

3

6

10

15

21

28

35

42

50

Soft Dough

1

2

4

8

12

17

23

29

35

41

Early Dent

0

1

2

5

9

13

18

23

27

32

Dent

0

0

2

4

7

10

14

17

20

23

Late Dent

0

0

1

3

5

7

9

11

13

15

Nearly Mature

0

0

0

0

1

3

5

6

7

Table 1. Percent yield loss (in blue) because of defoliation by crop stage. The percentage of defoliation is shown on the top row of the table. For example…30% defoliation at dent stage results in a 2% yield loss.

Paraquat drift on cornFigure 1. Paraquat drift on corn.

Holcus spot of corn.Figure 2. Holcus spot of corn.