Volume 11, Issue 3 - April 2021

David Moseley, Stephenson, Daniel O., Brown, Sebe, Padgett, Guy B., Foster, Matthew, Parvej, Md Rasel, Towles, Tyler, Deliberto, Michael, Tubana, Brenda S., Dodla, Syam

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Ryegrass control: We are not faring well

Daniel Stephenson, LSU AgCenter Extension Weed Scientist

The major issue I have discussed with Louisiana crop producers, LSU AgCenter parish agents, agricultural consultants, and agricultural industry this year is glyphosate-resistant Italian ryegrass. It is not a new problem for Louisiana producers as we have been dealing with it for five or six years and it is a problem in most parishes where row crops are produced.

In 2021, Italian ryegrass has caused significant issues. Even with the educational endeavors by the LSU AgCenter and others, Italian ryegrass is ‘stomping a mudhole in us’. This is not a new pest for the Mid-South. Mississippi has been dealing with glyphosate-resistant Italian ryegrass for many years. Mississippi State University weed scientists developed a great program to manage this pest and the LSU AgCenter has adopted that approach.

This program is divided into three options. The first option is a residual herbicide application or tillage in the fall. Second is a clethodim application in January. Third option is sequential applications of paraquat with the first application having either atrazine, diuron, or metribuzin tank-mixed. Implementation of the fall option is best, followed by the second and third options.

The first and best option, residual herbicide or tillage in the fall, is not popular in Louisiana. The primary complaint is bed erosion due to fall and winter rainfall. Use of a residual herbicide has the potential to control most winter annual weeds, thus no weeds are present to help prevent soil erosion. This is a very valid concern. However, Italian ryegrass emerges predominately in the fall, so by not implementing a management plan in the fall, we are effectively inviting an infestation. An option to consider is seeding a cover crop in the fall. LSU AgCenter research data has shown that a residual herbicide like S-metolachor or Zidua can be applied over the top two weeks after emergence of cereal rye, wheat, and many broadleaf cover crops without injury to the cover crop. Therefore, the cover crop will maintain bed integrity and physically compete with the Italian ryegrass slowing its growth. Plus, the addition of a residual herbicide will provide a barrier to help manage the ryegrass. Yes, this step requires money and effort that may be in short supply in the fall. However, compare that to what you have tried to do this spring to manage Italian ryegrass and it is easy to see that implementing a fall management program will pay dividends.

Honestly, the second and third options are failing Louisiana producers. Tank-mixing clethodim with other burndown herbicides (which is not part of Mississippi State’s plan) has consistently provided poor Italian ryegrass control because many burndown applications have had sublethal clethodim rates. Tank-mixing clethodim with 2,4-D or dicamba in a burndown treatment oftentimes leads to poor ryegrass control because 2,4-D and dicamba antagonizes clethodim which decreases clethodim efficacy. To overcome antagonism, at least 0.125 lb ai/A of clethodim must be applied. Another issue is the ryegrass is too big at clethodim application. For maximum clethodim efficacy, ryegrass should be less than 4-inches tall. Antagonism, low use rate, and large ryegrass at application has led to potential clethodim-resistant Italian ryegrass. The LSU AgCenter is investigating multiple population for resistance. Clethodim-resistant has been documented in Mississippi.

The lack of a fall program and the poor control provided by clethodim leads to the third option….paraquat plus atrazine/diuron/metribuzin followed by another paraquat application 10 to 14 days later. Many times, the first paraquat treatment may get applied, but the second application does not. Why? Because the corn has already emerged before the second application can be applied. This leads to a terrible situation in which no herbicide options are available. Dr. Jason Bond and others with Mississippi State, the team that developed the management program, applied almost all known herbicides to Italian ryegrass in the spring with little to no success. The lack of in-crop herbicides to manage ryegrass intensifies the need to implement a management program the fall.

I have no intention to be a fear monger. I have always tried to tell the truth. The truth is that we are losing the battle with glyphosate-resistant Italian ryegrass in Louisiana. Unless we implement a fall management program, Louisiana will continue to struggle with this pest.

Please feel free to contact your local parish agent or me. My email is dstephenson@agcenter.lsu.edu and my mobile number is 318-308-7225. Good luck.

Tips for a Healthy Cotton Stand

Matt Foster, LSU AgCenter Cotton Specialist

With cotton planting just around the corner, a couple key factors should be taken into consideration. Early planting is a key component of successful cotton production; however, if planted too early, yield potential can be reduced. Growing up, I often heard farmers say, “The day you plant cotton is the most important day for the crop.” Cotton seedlings are very sensitive to adverse conditions; therefore, it is important to consider factors such as soil temperature and heat units (DD60s) before deciding to plant.

Soil temperature is the main factor influencing seedling growth rate. Cool soils (below 50 degrees Fahrenheit) can cause chilling injury to germinating plants. Chilling injury can reduce vigor and increase the likelihood of seedling disease issues. Good germination and emergence can be expected once the soil temperature at a 4-inch depth is 65 degrees Fahrenheit or greater at 8 a.m. for at least three consecutive days with a good five-day forecast following planting. In Louisiana, cotton is generally planted in mid-April to mid-May but planting decisions should be based on soil temperature and not the calendar.

Once soil temperature is optimal, it is important to calculate the number of DD60s for the next five days to determine if conditions are optimal for planting. Emergence generally occurs after the accumulation of 50 to 80 DD60s after planting. If the five-day forecast after planting predicts the accumulation of less than 26 DD60s, planting should be postponed. Also, the low temperature for the next five days should remain above 50 degrees Fahrenheit. Basing planting decisions on soil temperature and the five-day forecast for DD60s can help ensure a healthy cotton stand.

The Economics of Replanting Soybeans

Michael Deliberto, LSU AgCenter economist

The economic impact on direct farm-level production costs from replanting soybeans can result in an increase in the number of bushels that will be required to offset the incurred production expenses associated with replanting field operations. The severity of this will depend on the type of soybean technology employed, as differences in the prices for seed, seed treatments, and seeding rate can influence the replanting costs and, hence, the number of additional bushels required at harvest to offset those costs.

The following economic analysis employs a general farm management approach to calculate the breakeven yield required to cover the increase in replanting costs across alternative soybean price levels. Under the assumption that the farm’s yield is expected to be 55 bushels per acre, estimated total variable production costs for Roundup Ready soybeans under irrigation are $377.51 per acre. The breakeven yield under these imposed conditions is calculated to be 34.32 bushels per acre, assuming a $11.00 per bushel price. The breakeven price is calculated to be $6.86 per bushel. This can be interpreted to the extent that a producer would need to receive in excess of $6.86 per bushel to cover the total variable production costs per acre.

Planting costs (e.g., machinery, fuel, and labor) are comprised of a planter, tractor, and seed. Planter costs are estimated to be $4.76 per acre in addition to the $42.00 seed cost to total $46.76 per acre. If a producer determines that a field must be replanted, the total variable costs for the growing season will increase from $377.51 to $424.27 per acre, reflective of the aforementioned replanting costs. Normal production conditions are assumed. The breakeven yield under these imposed conditions is calculated to be 38.57 bushels per acre, assuming a $11.00 per bushel price. This in an increase of approximately 5 bushels (4.25 bushels) per acre to offset the increase in production costs while the $11.00 price is held constant. The breakeven price is calculated to be $7.71 per bushel, an increase of $0.85 per bushel.

When the market price is varied from $13.00 to $9.00 per bushel (yield of 55 bushels per acre held constant), it is observed from Figure 1 that as price decline, more production is required to cover the increase cost of replanting.

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Figure 1. Soybean breakeven yield comparison.

Figure 2 illustrates the required increase in breakeven yields from replanting a 55 bushel per acre potential field across multiple price levels. As the soybean market price declines the required increase in breakeven yield also increases from 3.60 ($13.00 price) to 5.20 bushels per acre ($9.00 price).

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Figure 2. Required increase in breakeven yields from replanting soybean.

In some situations, input suppliers may offer a rebate on the purchase of soybean seed for replanting. For example, if a supplier offered a 50% rebate on the cost of seed, the addition seed cost would total $21.00 per acre (plus the $4.76 planting cost). Therefore, the total variable costs for the growing season will increase from $377.51 to $403.27 per acre. The breakeven cost of production (via the seed rebate option) increases $0.47 from $6.86 to $7.33 per bushel. This in an increase of approximately 3 bushels (2.34 bushels) per acre to offset the increase in production costs at an $11.00 price per bushel. Following the concept illustrated in Figure 2, under this rebated seed offer, the required increase in breakeven yield ranges from 1.98 ($13.00 price) to 2.86 bushels per acre ($9.00 price).

For more information on soybean enterprise budgets, please visit the LSU AgCenter Website.

Considerations for Planting and Replanting Soybean

David Moseley, Daniel Stephenson, Boyd Padgett, Sebe Brown, Michael Deliberto, AgCenter Scientist

Although mid-April to mid-May is the current recommended planting dates for soybean in Louisiana, late March and early April soybean plantings are possible and may lead to higher yield potential. However, cool and wet conditions common during late March and early April may lead to poor emergence and vigor. If a poor stand and/or plant health is a concern, it is important to get an accurate estimate of the final plant stand and correctly identify the cause of poor plant health.

To accurately assess the final stand across a field, random plants from at least ten areas of a field should be counted. Plants from a specific length of row should be counted for different row spacings. The number of plants counted with in a specific length of row should be multiplied by 1,000 to get the average final plant stand (Table 1).

Maintenance inputs such as flumioxazin can cause cotyledon and leaf damage (Figure 1). Seedlings injured from flumioxazin will likely grow out of the damage (Figure 2) with no yield loss.

The current soybean seeding rate recommendation for soybean is approximately 130,000 plants per acre with a final stand count of 104,000 to 113,000 plants per acre. Higher seeding rates should be considered when planting in unfavorable conditions and outside the optimum planting window. In addition, higher planting rates should be considered for some varieties based on population trials.

Soybean varieties that have good branching ability can compensate for low final plant stands by filling in gaps. In 2020, a population trial planted on May 6 and on June 1 at the Dean Lee Research Station consisted of three varieties and six populations from 50,000 to 175,000 seeds per acre in 25,000 seed per acre increments. The percent of final stand was low: 61% and 54% for the May 6 and June 1 planting dates, respectively. (Figures 3 and 4) show the average yield for each final plant stand. For the May 6 and June 1 planting dates there was a yield reduction when the final plant stand fell below 61,000 and 67,500 plants per acre, respectively.

The yield data for the June 1 planting date suggest a slightly higher final plant stand is required to maximize yield potential for planting outside optimum planting dates. Increasing the planting rate has also been suggested in areas of low productivity.

When considering if a replant is economical, it is important to weigh the potential yield increase from a higher plant population against the potential yield loss from a late planting date. Please read “The Economics of Replanting Soybeans” from the LA Crops Newsletter (Volume 11, Issue 3 – April 2021).

In some cases, it is possible to fill in large gaps by planting into the existing stand (Figure 5). This method can help If the replant is soon enough to not cause competition between the plants from the two planting dates, and if the soybean from the replant matures in time to not cause harvest delays.

It is also important to consider possible increase in pest pressure for soybean planted late. Soybean plants sown later in the growing season will likely have decreased vegetative growth resulting in a possible increase in weed pressure. Soybean planted late can also be subjected to higher insect and disease pressure.

Table 1. To determine final stand, count plants in the length of row corresponding with each row spacing.

Row Spacing (in)

Length of Row to Count Plants (1/1000th of an acre)

7.5

69' 8"

10

52' 3"

15

34' 10"

20

26' 2"

30

17' 5"

36

14' 6"

38

13' 9"

40

13' 1"


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Figure 1. Soybean cotyledon damage from flumioxazin preemergence herbicide.

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Figure 2. Soybean plants at the VC growth stage that have recovered from flumioxazin preemergence herbicide.

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Figure 3. May 6, 2020 population trial at Dean Lee Research Station.

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Figure 4. June 1, 2020 population trial at Dean Lee Research Station

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Figure 5. Planting soybean into thin stands

Early Season Insect Considerations in Cotton

Sebe Brown and Tyler Towles: LSU AgCenter Entomologists

Cotton

In Louisiana and the cotton belt, thrips are considered the number one early season pest of seedling cotton. Tobacco thrips compose the primary species infesting Louisiana cotton while western flower thrips are often present at lower numbers. With the absence of Aldicarb (although we now have a commercially available Aldicarb replacement named AgLogic) insecticide seed treatments now dominate the early season cotton insect pest management landscape. As of 2021, there are only two seed treatment options: acephate and neonicotinoids. Imidacloprid and thiamethoxam are the two most commonly used neonicotinoids and these treatments are offered alone or in combination with nematicides. Based on bioassay data generated over the last decade, the LSU AgCenter does not recommend thiamethoxam alone as a seed treatment for cotton; this is due to the development of resistance by tobacco thrips. However, imidacloprid is still somewhat effective and when used in conjunction with the insecticide/nematicide thiodicarb (Aeris), provides very good control of thrips. If Aeris is not an option, imidacloprid overtreated with acephate (6.4 oz/cwt) is another viable option. Acephate alone will control thrips; however, acephate has a significantly shorter residual than imidacloprid and the probability of returning with a foliar application is high. Also, if you elect to overtreat cotton seed with acephate, the seed cannot be returned.

In-furrow applications of imidacloprid are also an option for controlling thrips. Four-pound imidacloprid at 9.2 oz/acre or 2 lb material at 19.0 oz/acre provide satisfactory control of thrips. AgLogic has demonstrated excellent control of thrips at the 3.3 and 4 lb/acre rate.

Lastly, foliar rescue treatments are also an option. Foliar treatments should be made when immature thrips are present and/or when large numbers of adults are present and damage is occurring. Seedling cotton will typically always have a few adult thrips but the treatment trigger is the presence of immatures. The presence of immature thrips often signifies that the insecticide seed treatment has lost its efficacy and reproduction is occurring. Avoid spraying solely based on plant injury since the damage has already occurred. Beware, residual herbicides and sand blasting injury can mirror thrips injury.

Below are some considerations when deciding what foliar insecticide to use.

Dimethoate:

Positives: Relatively inexpensive, good efficacy at high rates, less likely to flare spider mites and aphids than acephate

Negatives: Less effective on Western Flower Thrips, less effective than acephate or bidrin when applied at lower rates

Acephate

Positives: Relatively inexpensive, effective towards Western Flower and Tobacco Thrips

Negatives: May flare spider mites and aphids if present

Bidrin

Positives: Effective, less likely to flare spider mites and aphids than acephate

Negatives: More expensive, less flexibility with applications early season

Radiant

Positives: Effective, least likely to flare spider mites and aphids

Negatives:More expensive, requires adjuvant, more effective on Westerns than Tobacco Thrips

Intrepid Edge

Positives: Effective, unlikely to flare spider mites and aphids. Intrepid edge is a mix of Radiant (spinetoram) and Intrepid (methoxyfenozide). Activity is similar to Radiant

Negatives: Requires the application of two modes of action but only gets the benefit of one.

Insecticide choice depends on a number of factors such as cost, impact on secondary pests and spectrum of thrips species present. If a foliar thrips treatment is justified, do not wait for a herbicide application and only spray when necessary to avoid flaring spider mites and aphids.

Fertilizer Recommendations for Soybean Production in Louisiana

Rasel Parvej, Brenda Tubana, Syam Dodla, and David Moseley, LSU AgCenter scientist

Soybean is a very nutrient-intensive crop. One bushel soybean requires about 5 lbs nitrogen (N), 1 lb di-phosphorus penta-oxide (P2O5), and 3.8 lbs di-potassium oxide (K2O) per acre. Since soybean can meet its own N requirement by fixing atmospheric N, the crop is mainly fertilized with phosphorus (P) and potassium (K) and sometimes sulfur (S), zinc (Zn), and molybdenum (Mo). Soybean fertilization in Louisiana mainly depends on Mehlich-3 soil-test nutrient concentrations of soil samples collected from 0- to 6-inch depth except for Mo which depends on soil pH.

Phosphorous

Phosphorus deficient soybean does not usually display any striking visual symptom, but stunted growth is the most common characteristics of P deficiency. The soil-test-based P recommendations for soybean production in Louisiana is shown in Table 1. The medium soil-test P level (21 – 35 ppm or 42 – 70 lbs/acre; 1 ppm = 2 lbs/acre) is considered as the critical soil P concentration. Soybean yield response to P fertilization is often expected in soils with below critical P level (< 21 ppm), seldom expected in soils with critical P level (21 – 35 ppm), and not expected in soils with above critical P level (> 35 ppm). Therefore, soybean must be fertilized with P for soils with less than 21 ppm P and P fertilization is not recommended for soils with more than 35 ppm P. For P fertilization, use granular triple super phosphate (TSP; 0-46-0) and apply either in the Fall or in the Spring at or before planting. The information about the effect of P application timing on soybean yield can be found at “Phosphorus and potassium fertilizers application in spring vs. fall”.

Potassium

Severe K deficient soybean produces irregular yellowing along the leaf margin and yields significantly lower than its potential. The soil-test-based K recommendations for soybean production in Louisiana is shown in Table 2. The critical soil-test K concentrations (i.e., medium soil K level) for soybean production depend on soil types. For example, the critical soil-test K concentration ranges from 107 to 141 ppm (214 to 282 lbs/acre) for soybean production in alluvial silt loam or loam soils but 177 to 264 ppm in alluvial silty clay loam or clay loam soils (Table 2). The critical soil-test K concentration also depends on the type of sediment deposition such as alluvial vs. upland soils. Therefore, care should be taken in interpreting soil-test K concentration and K fertilizer recommendations for soybean production in a particular field in Louisiana.

Soybean is somewhat more responsive to K than P fertilization. Soybean yield response to K fertilization is almost certain in soils with below critical K level. However, like P, soybean yield response to K fertilization is seldom expected in soils with critical K level and not expected in soils with above critical K level. Therefore, soybean must be fertilized with K for soils with less than critical/medium K level (i.e., very low and low level) and K fertilization is not recommended for soils with more than critical/medium K level (i.e., high and very high level). For K fertilization, use granular muriate of potash (MoP; 0-0-60) and apply either in the Fall or in the Spring at or before planting. The information about the effect of K application timing on soybean yield can be found at “Phosphorus and potassium fertilizers application in spring vs. fall”.

Sulfur

Sulfur is often recommended when Mehlich-3 soil-test S concentration falls below 12 ppm (24 lbs/acre). In this case, about 20 lbs S, as sulfate, is recommended per acre. Sulfur can be applied at or after planting. There are many S products available in the market. Gypsum (16% S) is a very good source of S for soybean production. Ammonium sulfate (21-0-0-24S) is another readily available S source, but not recommended for soybean production since it contains 21 percent N. This small amount of N may negatively affect soybean nodulation and possibly reduce yield. There are some soil-applied liquid S sources available in the market such as potassium thiosulfate, magnesium thiosulfate, etc. and these products are as good as dry S fertilizers when applied as sidedress.

Zinc

Zinc is one of the important micronutrients that often limits yield if deficient in soils. Zinc is not usually recommended for soybean. However, for high yielding soybean fields, it is advised to apply 10 lbs of Zn/acre if the Mehlich-3 soil-test Zn concentration falls below 1 ppm, 5 lbs of Zn/acre for soil-test Zn concentration of 1 to 2.25 ppm, and no Zn for soil-test Zn concentration more than 2.25 ppm. Zinc sulfate or zinc chelate is the most common Zn source and can be applied at or after planting as broadcast (dry formulation) or sidedress (liquid formulation).

Molybdenum

Molybdenum is a vital component of the nitrogenase enzyme that helps Rhizobium bacterial to fix atmospheric N for soybean plants. Molybdenum is not typically recommended for soybean production in Louisiana since most of Louisiana soils have enough Mo for optimal soybean growth. However, Mo availability is drastically decreased if the soil pH falls below 6.0. Therefore, Mo should be applied as seed treatment at planting for soils with less than 6.2 pH if lime is not applied in the Fall. If Rhizobium inoculum is used as seed treatment, Mo should not be used unless seeds are planted immediately after treating. Otherwise, Mo salt will reduce the viability of inoculum, resulting in poor nodulation. Since nutrient availability is maximum between soil pH 6.5 and 7.0, it is better to raise soil pH to near neutral (7.0) rather than applying Mo.

Table 1. Soil-test-based phosphorus recommendations for soybean production in Louisiana.

Soil-test LevelMehlich-3 soil-test P concentration in parts per millionRecommended P2O5 in pounds per acre
Very low≤ 1080
Low11 - 2060
Medium21 - 3530
High36 - 600
Very high> 600


Table 2. Soil-test-based potassium recommendations for soybean production in Louisiana. The Mehlich-3 Soil-test potassium concentrations in parts per million are shown for alluvial and upland soils. The fertilizer recommendations are shown as K2O in pounds per acre

Soil TypeSoil - test levelAlluvial SoilsUpland SoilsRecommended K2O in pounds per acre
Loam Sand or sandy loamVery low≤ 35≤ 3580
Loam Sand or sandy loamLow36 – 53 36 – 53 60
Loam Sand or sandy loamMedium54 – 79 54 – 88 30
Loam Sand or sandy loamHigh80 – 123 89 – 106 0
Loam Sand or sandy loamVery high> 123 > 106 0
Very fine or fine sandy loamVery low≤ 53≤ 4480
Very fine or fine sandy loamLow54 – 88
45 – 70 60
Very fine or fine sandy loamMedium89 – 123 71 – 106 30
Very fine or fine sandy loamhigh124 – 141 107 – 123 0
Very fine or fine sandy loamVery high> 141> 1230
Loam, silt loamVery low≤ 70≤ 6280
Loam, silt loamLow71 – 106 63 – 97 60
Loam, silt loamMedium107 – 141 98 – 141 30
Loam, silt loamHigh 142 – 158 142 – 158 0
Loam, silt loamVery high> 158> 1580
Clay loam or silty clay loamVery low≤ 123≤ 8880
Clay loam or silty clay loamLow124 – 176 89 – 141 60
Clay loam or silty clay loamMedium177 – 264 142 – 176 30
Clay loam or silty clay loamHigh265 – 282 177 – 194 0
Clay loam or silty clay loamVery high> 282> 1940
Silty clay or clayVery low≤ 141≤ 8880
Silty clay or clayLow142 – 211 89 – 141 60
Silty clay or clayMedium212 – 317 142 – 176 30
Silty clay or clayHigh318 – 334 177 – 194 0
Silty clay or clayVery high> 334> 1940

4/8/2021 1:07:55 AM
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