I have been receiving reports of true armyworms and chinch bugs in corn. True armyworms will usually move into corn once grass hosts have been exhausted or a recent burndown application has been made removing their primary host source.
Corn planted in close proximity to wheat is also susceptible to damage by migrating armyworms. Infestations are typically found around field margins where armyworms have migrated from a wheat field or grassy area. True armyworm damage gives corn plants a tattered appearance with frass (insect feces) present on the leafs or in the whorl of the plant during active infestations.
Most transgenic corn varieties offer protection against armyworm damage. However, single gene varieties such as Yield Guard and Herculex 1 may be overwhelmed when large populations of armyworms are present. Adverse environmental conditions can influence the expression of Bt genes in corn, and larval size is also a contributing factor for control. Normally large larvae are more difficult to control than small larvae.
As long as the growing point has not been injured, young corn (up to V4) can withstand substantial amounts of defoliation and not see a significant drop in yield. Grass control around fields can help prevent outbreaks of armyworms.
Chinch bugs are small insects 1/5 to 1/6 inch in length, with a black body and white front wings creating a white X when viewed from above. Immature chinch bugs resemble the adults only smaller and lacking wings. Nymphs range in color from reddish brown to black in later instars.
Chinch bugs are typically active on grasses in and around fields and movement to seedling corn is common. Damage by both adults and nymphs causes corn to have a reddish appearance on the stem and leaves.
Continued feeding can cause plants to wilt and eventually die. Corn is most susceptible in the seedling stage when plant growth is slow and conditions are dry. Seed treatments and soil insecticides will typically give an 18 day window of protection after emergence. Once plants have surpassed the most susceptible stage, chinch bug damage becomes less of an issue.
If plant growth is slow and chinch bug numbers have reached 5 or more on 20% of plants 6 inches tall or less, a foliar rescue treatment should be applied to stop injury.
When using ground equipment, a high volume, high pressure sprayer delivering a minimum of 20 gpa should be used. Aerial applications should only be used if ground equipment cannot make it across a field.
If an application is deemed necessary, bifenthrin would be the product of choice for ground and air.
We have recently received reports of corn plants snapped off or crimped and laid over. The injury is most often associated with violent storms producing winds, but not always. “Brittle snap” or “Green snap” is much more widespread in the Midwest and High Plains where high winds can cause substantial damage, but occurs in Louisiana from time to time, particularly during periods of active weather. The damage usually occurs below the point on the stalk where the ear sets, is very visible, and generally results in total yield loss for that plant once the stalk has broken or severely crimped and fallen over. There are several factors that can contribute to brittle snap, including wind speed and direction, growing conditions, and hybrid type.
High wind speed, particularly when it hits perpendicular to the corn rows, is the main factor causing brittle snap. Injury may be more likely to occur during wind downbursts from a storm cloud, creating areas or pockets of damage in a field. If the winds hit during cooler periods of the day when transpiration is reduced and the plant is more turgid, the injury may be more widespread.
Growing conditions can be a factor as well. Warm weather, adequate soil moisture, and high soil nitrogen levels allow for rapid vertical stalk growth from roughly V5 to V18. Rapid cell elongation is occurring – thinning the cell walls – leaving the stalk vulnerable to snap. Inadequate potassium in relation to the amount of nitrogen available may exacerbate thin cell wall issues.
Corn seed producers recognize there are differences between hybrids as to their susceptibility to brittle snap. Some companies take the time to rate and report brittle stalk ratings, and it is worth taking these ratings into account when making seed buying decisions. Thin, rapidly growing stalks, high ear placement, and inherently thin cell wall structure in some hybrids make them more vulnerable to brittle snap than others. It may be that a few hybrids are susceptible enough that equipment (such as a boom) running through the field could knock over the plants, so producers should be aware if this is occurring and consider a different hybrid in the future.
Here are a few of the more prominent broadleaf weeds in the Cameron verification field.
The predominant grass is barnyardgrass. However,
the most troublesome grass is Creeping Rivergrass. I did not bother photographing the grasses this time. The variety planted is Cheniere so weed control is going to be a challenge. We will keep you informed of our progress.
We expected our verification field in Vermilion parish to test us because it has a history of Newpath resistant red rice and volunteer hybrid rice. It was fallow last year and was water seeded this year. The photo at right shows red rice seedlings that are already growing well in spite of having been worked in the water and water seeded.
An overview of the field is portrayed below. Rice was a day or so from emergence. We plan to fertilize and flood as soon as possible. The only other option would have been to try to apply glyphosate and start over.
Nearby rice, the late date, and poor results from trying that in the past eliminated that idea. I am afraid we will have an ugly field before it is over.
I know the field conditions are not the best for fertilizer application, especially nitrogen, but that is one of the limitations of pinpoint flood water management.
Last year I wrote the first edition of Rice Field Notes one month earlier than this year. In spite of the much warmer weather (hottest March since record keeping began in 1895), much of the crop is later than last year.
The photo below was taken in our verification field in Cameron parish and is a good example of why it is late.
The intention here was to drill seed. Each time it got almost dry enough to drill, it rained. In desperation we decided to vibrashank and broadcast seed. As you can see it had gotten pretty hairy with weeds in the interim. Nearby water seeded rice kept us from hitting it with glyphosate.
By the following Monday rice was up or coming up. A lot of emergence is occurring in 5 to 7 days when we normally expect 10 days to call it. By that time we could have drilled, but would have been a week behind. Based on the data generated by Dr. Steve Linscombe last year a week later could mean a significant drop in yield. We’ll just have to see how it goes.
By Dr. John S. Kruse, Cotton and Feedgrain Specialist
Several producers and consultants have contacted me this spring with photographs and reports of yellow-striped corn in the two to three leaf stage. ]
In many instances, these symptoms appear to be zinc deficiency, and what is so interesting is how widespread it was in the corn planting areas of Louisiana. Zinc is a trace element, meaning the corn plant does not require very much of it (compared to nitrogen or potassium), but it is very much needed in small amounts, and the lack of it can result in measurable yield reductions. Zinc is absorbed by the plant as a positively charged ion (cation: Zn2+), and is important in the synthesis of tryptophan – a building block of certain proteins that are needed for the production of auxins (growth hormones). Zinc is generally more available in acid soils and less available in neutral to alkaline soils.
Zinc can also react with phosphate to the point that it is bound up and less available to the plant. Many soils in the Red River Valley, with high pH and sometimes high phosphorus, often need supplemental applications of zinc to optimize yields.
However, apparent zinc deficiency has been observed on the Macon Ridge (generally acid soils) and in the Delta (generally slightly acidic soils) this year, as well. The causes can be varied, but certainly repeated corn production can result in less than ideal soil levels of zinc. Also, if a producer has historically planted cotton and/or soybeans for a number of years and has not had to pay close attention to zinc levels, a switch to corn may reveal the need for supplemental zinc. If soil test zinc is less than 1 ppm, supplemental zinc should be applied.
If soil test zinc is between 1 and 3 ppm, it may be needed, and if it is above 3 ppm it should not need to be applied under most circumstances. An ideal time to apply zinc is at planting in a band across the surface of the planting zone.
Recent research suggests between 2.5 to 5 pounds of actual zinc per acre is a good rate. If it is too late for a zinc application at planting, a second choice would be to include the zinc in the nitrogen sidedress application at 2.5 lbs per acre actual zinc. If a foliar application is desired, apply 0.1 to 0.25 pounds of actual zinc per acre in 20 gallons of solution.
The high volume of water is needed to prevent foliar burn. Repeat this application 10 to 14 days later, if possible. Mixing zinc with phosphorus fertilizer is not recommended due to the potential for nutrient binding. Chelated zinc, particularly EDTA-chelated zinc is a very good source of zinc. Zinc sulfate granules can also be dissolved in solution and applied as a spray.
Spreading granular zinc is not an ideal method due to the fact that such a small amount is spread over such a large area that many corn plants will not come into contact with it. Zinc oxides are relatively insoluble and slow to break down and become available, and are not recommended sources of zinc.
A consultant recently asked if grain sorghum needs supplemental zinc. It turns out little research has been done in this area, but several University-authored sorghum production manuals did not emphasize sensitivity to zinc as a major issue. Texas producers are cautioned to maintain optimal levels of iron (Fe) in grain sorghum due to the nature of their soils.
Figure 1. Apparent zinc deficiency in young corn. Note interveinal striping. As the condition worsens, striping may appear white and become broader.
by J Stevens, Associate Professor and Extension Soils Specialist
As of recent, I have become aware that there are some fertilizer dealers who might be unaware of some of the differences in the fertilizers they are handling and selling to producers. Let’s take Sulfur and look at it first.
The use of sulfur in soil fertility programs has become more routine. The most common chemical forms of sulfur used in fertilizers are sulfate-sulfur and elemental sulfur. However, these two forms of sulfur react quite differently in the soil. It’s very important to understand the differences between sulfate-sulfur and elemental sulfur in order to use these two forms in the most effective manner possible.
Plants can only absorb sulfur through their root system in the sulfate form. Thus all soil sulfur must be converted to a sulfate in order to be utilized by plants. For the most part, sulfates move freely with soil moisture, especially in the upper part of the soil profile. This is very much like nitrate-nitrogen in soils. As a result, sulfate levels frequently increase with increasing depth in the soil profile. Like nitrates, sulfates can leach in sandy-textured and silt loam soils.
Elemental sulfur is totally unavailable to plants. Plant roots cannot absorb elemental sulfur. Elemental sulfur is inert and is water insoluble. When elemental sulfur is added to a soil, it has to be converted to the plant-available sulfate form through the activity of soil bacteria. The rate at which this conversion takes place is the determining factor regarding the effectiveness of elemental sulfur as a fertilizer source of sulfur. This transformation of elemental sulfur to the plant-available sulfate form is a slow process often taking months to be accomplished. Thus, for most crops in the initial sulfur fertilization, a sulfate fertilizer like Ammonium sulfate is recommended and elemental sulfur is not.
Now, let’s look at Zinc, specifically zinc sulfate and zinc oxysulfate. Most of the formulations of these two products contain 35.5 – 36% zinc. Among the inorganic zinc sources on the market, the most common sources are sulfates, oxides, and oxysulfates. Zinc sulfate is essentially 100% water soluble, while the Zinc oxides are essentially insoluble in a single crop year, thus unavailable to the crop to be planted. Many agronomists consider the oxides to be ineffective as a fertilizer source. Oxysulfates are a mixture of sulfates and oxides, with varying proportions of sulfates and oxides. The solubilities of the oxysulfates vary considerably, from 0.7 to 98.3%. The effectiveness of these can be highly variable. Low solubility materials may have some value in a long-term build up program, however, when immediate results are the goal, highly soluble fertilizers are the best choice. It is suggested that in order to be effective, a Zinc fertilizer should be at least 50% water soluble.
I’ll leave you with a few questions to ponder; Are you using sulfur and/or zinc in your soil fertility program? Are you soil testing to determine if your crops could benefit from adding one or both of these nutrients? If you are applying sulfur and/or zinc, have you ever considered which form is being field-applied? The answers to these questions could lead you toward a better soil fertility program and enable your crops to improve their yields as they come closer to reaching their genetic potential.
If you have any questions on this article or would like to discuss your soil fertility program, please feel free to contact me by email JStevens@agcenter.lsu.edu , telephone, 318-308-0754 cell, or text.
By Sebe Brown, Dr. David Kerns, Dr. Rogers Leonard – LSU AgCenter Entomologists
Thrips are annual pests of cotton in Louisiana. Damage by these insects cause stunted growth, delayed plant maturity and plant death under heavy infestations. Cotton is most susceptible to thrips from emergence to the 4 true leaf stage. Once cotton has reached the 4 true leaf stage, root differentiation has increased, terminal bud growth is accelerated and plants become less susceptible to injury.
The most common thrips found in Louisiana cotton are tobacco thrips, eastern flower thrips, onion thrips and western flower thrips. These insects overwinter on a variety of weed hosts. Planting seasons with windy conditions can have considerable influence on the severity of thrips populations in early cotton. Thrips are typically weak flyers and wind helps to distribute infestations across fields.
Cotton seedlings that experience cool, wet soils develop very slowly and remain susceptible to thrips injury much longer than cotton planted in a warmer, more optimum, environment. This year has been very warm and wet with considerable alternate hosts around cotton fields to produce sources of thrips infestations. With the loss of Temik for the 2012 growing season, insecticide seed treatments (ISTs) and over-sprays will be critically important for controlling thrips on seedling cotton.
Cotton seed comes with a variety of seed treatment options that may either be purchased through a seed company or applied by a dealer downstream. Outlined below are a few of my thoughts with regards to insecticide seed treatment packages on cotton seed.
Dow’s Phytogen seed comes with a base package of thiamethoxam (Cruiser), with Avicta Complete Cotton available upon request. Avicta Complete Cotton includes Cruiser for the IST, multiple fungicides and abamectin for nematode control. Information on Phytogen seed treatment options can be found here.
Monsanto’s Deltapine cotton seed comes with a combination of products that fall within the Acceleron treatment umbrella. The base package in cotton includes imidacloprid (Gaucho) and several fungicides. However there are several options within the Accereleron brand. Be sure that your seed is treated with what was ordered. These options are upgrades to Avicta Duo Cotton with Cruiser for insect control, several fungicides for disease control and abamectin for nematodes. Beware: the Acceleron seed treatment label in other crops may contain other products. More information on Acceleron seed treatment options can be found here.
Bayer’s Stoneville/Fibermax cotton seed comes with a base package that includes Gaucho for insect control and thiodicarb for nematodes that falls under the Aeris treatment umbrella. Producers also have the option to upgrade to Poncho/Votivo with clothianidin (Poncho) for insects and Bacillus firmus (Votivo) for nematodes. More information on Aeris seed treatment options can be found here.
Another option is to buy the minimum insecticide treatment available, and have a dealer apply additional insecticides downstream after the seed is purchased.
IST’s offer limited early season protection from thrips. Effective residual efficacy usually offers 10-14 days of control after plants emerge. Unsatisfactory residual control can occur with these treatments and cotton should be frequently scouted for thrips until the four leaf stage and when cotton plants are actively growing.
During 2011, western flower thrips were a problem in many Louisiana cotton fields. Western flower thrips can be difficult to control with standard applications of acephate, dimethoate, bidrin, etc. Producers also risk flaring spider mites and cotton aphids with repeated applications of broad-spectrum insecticides. Recent research conducted by the LSU AgCenter demonstrated satisfactory control of a complex of species including western flower thrips with Tracer and Radiant at 2 and 7 days after treatment.
The use of a nonionic surfactant with these insecticides can help increase efficacy against thrips. Rescue applications of foliar insecticides should be applied early in cotton development with applications at the 1-2 true leaf stage yielding significantly greater lint per acre than treatments applied at the 3-4 true leaf stage. Do not wait for thrips treatment in an attempt to time an overtop herbicide application.
Insecticide seed treatment options get producers off to a good start when it comes to insect pest management in cotton. However, these treatments should not be relied upon for sole control of all early season pests. IST’s are one of the best management practices (BMP’s) recommended by the LSU AgCenter for cotton IPM.
For more information concerning insect pest management, contact your local LSU AgCenter parish agent, LSU AgCenter specialist, or Louisiana independent agricultural consultant.
Louisiana is projected to plant a little over one million acres of soybeans in 2012. Strong exports and demand for soybeans continue and soybean acres may increase throughout the planting season. The acres planted will probably be limited by weather. If the weather is favorable, we could see up to 1.1 million acres of soybeans planted. Each year seems to present different problems for production, hopefully this will be the year without one.
In Louisiana approximately 60% of the acres are planted to maturity group IV’s and 35% of the acres to maturity group V’s. The remaining 5% is planted to maturity group III’s and VI’s. Then trend has been toward maturity group IV’s.
Soybean planting got started early this year with a few acres being planted in late March. As planting continues to progress, the question always arises – What is the optimum plant population?
Too dense a plant population reduces yields, encourages diseases and lodging and increases seed cost. When calibrating planters, use seed per foot as your guide rather than pounds of seed per acre. In the following table, the estimated pounds per acre should be used only to calculate how much seed to buy. Because of varietal difference in seed size, as well as seasonal variation within lots of the same variety, planting rates can be misleading if expressed in pounds per acre. The following rates are recommended:
When planting is delayed until June 15 or later, the amount of vegetative growth that the plant produces becomes more critical. It is important to choose varieties that grow rapidly in a short time. When blooming starts, most vegetative growth ceases in determinate varieties. When planting late, seeding rates should be increased to compensate for reduced vegetative growth.
All, I have been seeing more instances of true armyworms infesting wheat in the North Louisiana. These include wheat plots at St. Joe and Winnsboro at various stages of growth. Our threshold for armyworms is 5 worms per square foot with foliage loss occurring. If armyworms reach the flag leaf and the wheat has not headed an application should be made. I have also encountered varying levels of stink bugs (primarily rice stink bug) in wheat. Populations of stink bugs have to be high for damage to occur and our threshold is 10% infested wheat heads in the milk stage and 25% infested heads in the soft dough stage. Stink bug numbers will usually be higher around the edges of a field with numbers falling off as you walk further toward the middle. This means you may reach threshold around the edges of a field, but may also be well below threshold 100 feet in. Applications of pyrethroids can control both of these pests.
Rice stink bug photo courtesy of Gus Lorenz
Armyworm larvae on wheat heads photo courtesy of Robert Bellm, University of Illinois Extension
Recently I was talking to a producer who wanted to learn about making variable rate applications of nitrogen. The first question he asked was: “How much was am I going to save by making the application variable rate?” My response was not what he expected. I said “Don’t look at it as saving money, but as making money.” By matching the optimum nitrogen rate to the corresponding soil/production zone, crop use efficiency is highest and the potential profit from the nitrogen application is maximized.
To make a variable rate nitrogen application, a producer has to define the application zones. This can be based on soil types, Veris Ec soil zones, yield maps, producer knowledge or a combination. The producer’s knowledge of the field along with a yield goal helps determine the nitrogen rate assigned to each zone. The total amount applied to a field with a variable rate application may not be much different than if a producer had gone with a single rate, but by putting the correct rate in the right area the field doesn’t have areas with over or under applications of nutrients.
Soil Sampling is an essential part of variable rate applications, whether it is grid sampling or zone sampling. Each method would benefit from the addition of yield map data to the analysis. Yield maps over several crops and several years can help define the potential yield and profitability of a field. It can also assist with the definition of productivity zones for a field. This is especially obvious when a cropping history is developed over several years.
Variable rate applications of lime, P, K, and other essential nutrients need to be applied in areas defined by the sampling pattern (grid or zone). Variable rate applications of other nutrients is the most cost effective and efficient method for supplying crop needs. Variable rate also allows a producer to match fertility needs to the current crop’s needs. Supplying/maintaining fertility levels enhances the nitrogen efficiency and use by the crop.
The most useful piece of precision ag equipment a producer can own is a yield monitor. A yield monitor gathers the information from the field with which a producer can evaluate how well fertilizers, varieties, etc. performed. Verification strips of a nutrient, nitrogen rate, or another input can be used as a comparison for the rest of the field. Analyzing the results as whole strips and soil/production zones allows a producer to determine the most productive/economical practices to use on their farm.
Precision agriculture, its use, the results, and the incorporation of the practices into a farming operation is a long term process which can enhance the productivity of a farm. For more information or assistance with precision ag applications or yield data on your farm, contact Dennis Burns at 318-267-6709 or R.L. Frazier at 318-267-6714.