David Moseley, Rezende, Josielle, Brown, Kimberly Pope, Parvej, Md Rasel, Watson, Tristan, Towles, Tyler, Stephenson, Daniel O., Brown, Sebe, Price, III, Paul P, Deliberto, Michael, Tubana, Brenda S., Wang, Jim Jian
In this article:
|Thoughts on Weed Management|
|Entomology Update August|
|Paraquat and Pre-certification Training|
|Harvest Moisture and Its Effect on Corn Price|
|Update on the Current Status of the Invasive Guava Root-knot Nematode in Louisiana|
|LSU AgCenter Variety Testing|
|Soil Sampling and Testing|
|Soil-test-based Fertilizer Recommendations and Fertilizer Application|
|Soil pH, Liming, and Liming Materials|
Daniel Stephenson, Extension weed specialist
Corn harvest is underway in Louisiana, and I have received questions about controlling morningglory that could decrease harvest efficiency. The best option for this situation is an application of Aim at 1 to 2 ounces/A, paraquat at 0.25 to 0.5 lb/A or 1 gallon/A of a 6 lb/gal sodium chlorate. Tank-mix crop oil concentrate at 1 % v/v with Aim or 0.25% v/v of nonionic surfactant with paraquat. Most likely, these herbicides will be applied with an airplane, but it must be understood that Aim, paraquat and sodium chlorate efficacy is highly influenced by coverage — so the higher the GPA, the better. Also note that corn must have reached black layer (physiological maturity) before any of these products can be applied. Regardless of herbicide used, allow at least seven to 10 days before harvest so that morningglory will become brittle.
Soybean harvest has begun in some areas of Louisiana too. Typically, paraquat is used to desiccate soybeans. Always follow the paraquat label and be sure you have earned your paraquat-certificated applicator license. Additional herbicide choices for desiccation are Aim, Sharpen and sodium chlorate. As with paraquat, read the Aim, Sharpen and sodium chlorate labels prior to use. It has been my experience that tank-mixing paraquat at 0.25 lb and 1 ounce/A of Aim or Sharpen plus nonionic surfactant or crop oil concentrate provides good soybean desiccation and weed control.
Finally, please remember to physically remove any glyphosate-resistant Palmer amaranth or waterhemp still present in your fields. They should be easy to spot because they are most likely 1 to 2 feet taller than cotton and soybean canopies. Practicing a little sanitation now will save you a big dose of heartburn in the future.
Please call or email with questions at 318-308-7225 or firstname.lastname@example.org.
Sebe Brown and Tyler Towles, LSU AgCenter entomologists
With much of Louisiana’s cotton approaching or beyond cutout, insect management decisions should be based on insects present in the field and protecting existing harvestable bolls. Once cutout (average of five nodes above white flower) is reached, growers and consultants can calculate the daily heat units (DD60s) from cutout and terminate insecticide applications accordingly. Fields that have accumulated 325 DD60s are safe from plant bugs while fields that have accumulated 350 DD60s are safe from first and second instar cotton bollworms. Fields accumulating 475 DD60s are protected from stink bugs.
Plant bugs have been persistent in many fields throughout the growing season, with insect numbers often reaching two to three times the threshold. Larger, more mature bolls are typically less susceptible to plant bug injury while smaller, less mature bolls may still be susceptible to adults and large nymphs. Overall, most of the harvestable bolls we now have should be safe from most plant bug injury, although adults and large immature plant bugs may still be a problem in later planted cotton. Therefore, plant bug treatment thresholds can be increased by 2.5, and small first and second instar nymphs can be omitted when determining insecticide applications.
Brown, green and southern green stink bug numbers will often increase as corn is harvested and the cotton crop matures. The Louisiana threshold for stink bugs in cotton is when one adult/nymph are found per 6 row feet, 5% adults/nymphs are in sweep nets or 15% to 20% of 12- to 16-day old bolls have internal injury. Late season applications of acephate plus pyrethroid, ULV malathion and Bidrin XPII give satisfactory control of stink bugs and plant bugs.
As Louisiana progresses into late summer, producers and consultants should look for late-season defoliators such as soybean loopers, velvet bean caterpillars and lingering populations of corn earworms.
Soybean loopers (SBL) have the ability to build large populations quickly and are exaggerated by the use of broad-spectrum insecticides for three-cornered alfalfa hoppers and stink bugs. The threshold for SBL in Louisiana is 150 worms in 100 sweeps or eight worms that are 1/2 inch long or longer per row foot. Because SBL are foliage feeders, adequate insecticide coverage is essential to limiting defoliation and reducing population numbers. Soybean loopers often initiate feeding in the lower portion of the canopy, defoliating soybean plants from the inside out. This cryptic behavior allows SBL to stay protected from some predators and insecticide applications in the dense canopy of soybean plants. Thus, good insecticide coverage is essential for optimal control of SBL. Once soybeans reach R6.5, yield is set and protection from soybean looper defoliation is no longer critical.
Velvetbean (VBC) caterpillars, like soybean loopers, can build large populations quickly and defoliate large portions of soybeans in a limited amount of time. The Louisiana threshold for VBC is eight worms that are at least 1/2 inch long per row foot or 300 worms in 100 sweeps. Unlike loopers, VBC are easily controlled with pyrethroids and applications for insects such as stink bugs effectively control this pest.
When making insecticide application decisions for caterpillar pests in soybeans, the insect species and numbers present and defoliation percentage should be taken into consideration. After bloom, soybeans can tolerate no more than 20% defoliation and not experience a significant yield loss.
Lastly, green, southern green, brown and redbanded stinkbugs are currently infesting Louisiana soybean. Action thresholds for brown, green and southern green stinkbugs are 36 per 100 sweeps or one per 6 row feet. However, the action threshold for the redbanded stink bug is 16 per 100 sweeps or one per row foot. The lower action threshold for the redbanded stink bug is due to the increased damaging nature of the pest compared to the other previously mentioned species.
Kim Pope Brown, LSU AgCenter pesticide safety coordinator
It’s that time of year when producers are starting to desiccate soybeans to aid in harvesting. The product that many producers use is paraquat. As many of you should be aware, in the fall of 2019, paraquat received a new label requirement. Anyone who handles paraquat products must be a certified applicator and must successfully complete the new paraquat training course. Below are a few reminders for producers and applicators who are using or plan to use paraquat:
With the changes to some of our product labels, farm crew members that have previously been able to work under the direct supervision of a certified applicator can no longer do so, depending on label requirements. The LSU AgCenter Pesticide Safety Education Program has put together a few opportunities to assist in test prep or pre-certification training for applicators who need a little assistance prior to taking the exam. At this time, we are offering virtual pre-certification training. Please see the dates and times in Table 1.
Table 1. Virtual Pre-Certification training dates and times.
|Sept. 2 to 3, 2020||1 to 3 p.m. each day|
|Oct. 5 to 6, 2020||1 to 3 p.m. each day|
|Nov. 2 to 3, 2020||1 to 3 p.m. each day|
People who wish to participate must pre-register at the LSU AgCenter online store by 4 p.m. the business day prior to the selected event. Once you have registered, you will be provided a link via email that you will use to connect to the training event on both days of your selected event. This training will be in two parts to help ease the amount of time in front of a computer.
The training will take a total of four hours to complete. The cost of the training is $45. This is the link for registration.
If there is something more specific that you need in your area, please feel to contact Kim Brown or Bryan Gueltig with the LSU AgCenter Pesticide Safety Education Program for more information at email@example.com or firstname.lastname@example.org.
Michael A. Deliberto, LSU AgCenter economist
Two factors that can influence the price that a corn grower receives are the moisture content of the crop at harvest and the associated drying costs to reach a desired moisture content specified by the local elevator. Collectively, these factors can be considered harvest losses expressed as a portion of the price per bushel. Estimating these two factors against the projected price received are key determinants at to when a corn grower might begin their corn harvest operations.
The first factor associated with corn harvest losses relates to the removal of moisture from grain during the drying process that causes a reduction in grain quality, referred to as moisture shrink. For example, assume that the initial moisture content is 25% and the final desired moisture content is 15%. Using the aforementioned equation, moisture shrink (%) is calculated to be 11.76%. The second factor considers the cost of drying. Grain drying costs are based on either dry or wet grain and can be estimated with the following equations expressed as dollars per dry bushel.
Grain elevators often charge corn growers a per bushel fee to dry grain based on the moisture level and their costs of running and maintaining drying equipment at the facility.
Figure 1 shows a chart of the shrinkage and drying costs based on the corn moisture at harvest and the costs of propane and electricity for corn priced at $4.00 per bushel. Assuming that an elevator prefers to accept corn at 15% moisture, a grower can infer from the figure that harvesting corn at higher moisture content can negatively affect the price received. Meaning that a moisture levels of 23%, the price risk is $0.83 cents ($0.38 from shrink and $0.46 for drying charges) from the original $4.00 corn price (net price of $3.17). As the moisture content of the corn is reduced, the grower price increases.
Figure 1. The shrinkage and drying costs based on the corn moisture at harvest and the costs of propane and electricity for corn priced at $4.00 per bushel.
A decision tool was developed by the LSU AgCenter through which a producer — by inputting their initial expected price of corn at harvest, estimated harvest and target moisture levels, price per gallon for liquified petroleum gas and price per KWH for electricity — can calculate their risks or potential losses associated with moisture, shrinkage and price risk. The user-specified decision tool also contains a worksheet that allows a corn grower to enter their initial moisture content and the final desired moisture content so that the total cost per bushel can be calculated on a per bushel basis. Cells containing blue font in both worksheets can be changed by the grower. The grower can also enter their gas and electricity costs to estimate the drying costs. To access a detailed report and accompanying decision tool, please visit the LSU AgCenter corn production webpage.
Appreciation is extended to the Louisiana Soybean and Feed Grain Research and Promotion Board for their support of this applied farm management research.
This graph shows the effect that higher moisture content has on the corn price a grower received. At higher moisture levels, greater that 15%, the corn price is reduced, assuming the desired level is 15%.
The effect that higher moisture content has on corn price. At higher moisture levels, greater than 15%, the corn price is reduced, assuming the desired level is 15%.
Tristan Watson, LSU AgCenter nematologist, and Josielle Rezende, LSU AgCenter plant pathologist
Plant-parasitic nematodes are semi-microscopic roundworms that feed on plants, often resulting in yield loss on economically important crops. There are a range of plant-parasitic nematode species that are fairly common in Louisiana production fields, including southern root-knot nematode (Meloidogyne incognita) and reniform nematode (Rotylenchulus reniformis). Recently, a new nematode, known commonly as guava root-knot nematode (Meloidogyne enterolobii), has been introduced into Louisiana on contaminated sweetpotato planting material from North Carolina. Guava root-knot nematode is potentially a serious problem for Louisiana growers due to the wide host range of this pest, the devastating crop damage it can cause, and the ability of this pest to overcome nematode resistance in commercially available crop varieties. On many crops, feeding by guava root-knot nematode results in the formation of large, spherical growths (i.e. root knots) on the root system. Unlike the more common southern root-knot nematode, infestation by the invasive guava root-knot nematode can cause total crop loss in a production field.
The guava root-knot nematode was introduced into Morehouse Parish, Louisiana, in 2018 via contaminated storage roots imported from North Carolina. In 2020, the guava root-knot nematode was detected in Franklin Parish, Louisiana, in a shipment of certified pest-free sweet potato planting material. Although this nematode has been introduced twice, our 2019 soil survey results indicated that this nematode has not yet established in Louisiana soils. The guava root-knot nematode soil survey will continue during the 2020 growing season. We encourage any growers experiencing nematode symptoms characteristic of root-knot nematode (i.e. knots in root tissue; Figure 1) to submit soil and root samples collected from symptomatic fields (Figure 2) to the LSU AgCenter Nematode Advisory Service for free diagnosis. Included here is a link to the LSU AgCenter Nematode Advisory Service root-knot nematode survey form and a guide on how to sample fields for nematodes.
Figure 1. Root damage caused by root-knot nematode (Meloidogyne spp.) on (A) cotton, (B) soybean, (C) cucumber and (D) sweet potato. Notice the presence of numerous large, spherical knots or bumps on root tissue characteristic of nematode parasitism.
Figure 2. Crop
damage caused by root-knot nematode (
Meloidogyne spp.) on (A) cotton and
(B) soybeans. Notice the circular patch of stunted plant growth characteristic
of a field infested with this nematode.
David Moseley, LSU AgCenter soybean specialist, and Trey Price, LSU AgCenter plant pathologist
Selecting a soybean variety is one of the most important decisions a producer can make to have a successful season. To help Louisiana soybean producers select the most suitable variety, the LSU AgCenter conducts an Official Variety Trial (OVT) and Core-block Demonstration Plots.
The 2020 OVT consist of 158 varieties entered by 16 seed companies and three university soybean breeding programs. The varieties consist of several different herbicide technologies, and the maturity groups range from 3.7 to 6.0. The trial is replicated at seven research stations across the state in different soil types including fine sandy loam, silt loam, silty clay and clay. At each location, the varieties are replicated four times (Figure 1). Because of varying disease pressure across the state, the trial is over-treated with fungicides at some locations while at others, it is not.
Figure 1. The 2020 official variety trial at the Dean Lee Research Station showing growth differences between varieties.
In addition to the OVT, the LSU AgCenter collaborates with soybean producers to evaluate soybean varieties directly on farms. For these core-block demonstration plots, LSU AgCenter parish agents cooperate with the producers to plant, maintain and harvest strip trials submitted by seed companies and university soybean breeding programs. These demonstrations provide valuable yield data from local growing conditions and agronomic practices. In some cases, observations from these large plots can result in identification of varieties that are resistant to a number of soilborne maladies.In 2020, 11 seed companies and two university soybean breeding programs submitted varieties to be evaluated in the core-block demonstrations. Eighteen demonstrations were planted across 11 parishes (Figure 2). The demonstrations were divided by maturity group (MG). A demonstration consisted of varieties with a MG of 3.7 to 4.4; 4.5 to 4.9; or 5.0 to 5.6. The number of varieties submitted for each MG were seven (MG 3.7 to 4.4), 20 (MG 4.5 to 4.9) and 16 (MG 5.0 to 5.6).
Figure 2. Eighteen core-block demonstrations across 11 parishes.
The yield data from the OVT and core-block demonstrations will be published by the LSU AgCenter in the annual soybean variety testing summary. Maturity date, height, lodging and disease reaction information from the OVT also will be included. The 2020 OVT results will be published following harvest to assist with 2021 variety selections and planting decisions. The variety publication for the 2020 growing season can be found at 2020 Soybean Variety Yields and Production Practices.
When choosing a variety, it is important to consider performance and stability. A producer should evaluate varieties that perform the best in an environment similar to their own and varieties that perform well over multiple environments. When possible, variety performance over multiple environments and multiple years should be considered.
When time and resources allow, specialists may plant specialized variety trials aimed at solving one specific problem. Such a trial was planted this year at the Macon Ridge Research Station in Winnsboro. Essentially, a scaled-down (two-row plots) copy of the official variety trial was inoculated with Xylaria sp. in an effort to identify commercial sources of resistance to taproot decline (Figure 3). Row 1 was inoculated at planting, while Row 2 was subjected to natural infestation (Figure 4). The location has not been tilled and has been in soybean monoculture for many years. The trial has been rated multiple times, and results will be provided to stakeholders in a timely manner this fall and winter.
Figure 3. Soybean plants showing interveinal chlorosis caused by taproot decline at the R2 growth stage after inoculation at planting.
Figure 4. A soybean plot (R5.5) from the 2020 Specialized Variety Trial (taproot decline) at the Macon Ridge Research Station. Non-inoculated (left) vs. inoculated (right).
Rasel Parvej, Brenda Tubana, and Jim Wang, LSU AgCenter soil scientists
Rasel Parvej, Brenda Tubana, and Jim Wang, LSU AgCenter soil scientists
Rasel Parvej, Brenda Tubana, and Jim Wang, LSU AgCenter soil scientists