cotton, corn, soybeans, sorghum€¦ · update 8 current situation on soybean loopers in louisiana...
TRANSCRIPT
In Louisiana, soybean varieties representing MG IV (indeterminate) and MG V and VI (determinate) are grown. Flowering of indeterminate soybean is initiated in the lower portion of the plant and proceeds upward; terminal buds continue growing several weeks after flowering. There can be considerable difference in seed maturity with bot-tom seed reaching maturity first. With the variation in seed maturation, indeterminate soybeans tend to retain leaf material and stems remain green later into the growing sea-son. In contrast, flowering of determinate soybean is initiated in the middle portion of the plant and proceeds towards the top and bottom; terminal bud growth ceases when flowering begins. While there may be some slight difference in seed maturity on the plant, most seed mature at the same time.
Paraquat was initially marketed as a harvest aid to desiccate weeds and improve har-vest efficiency. The Gramoxone Inteon/paraquat label states that application to indeter-minate soybean varieties should be made when at least 65% of the seed pods have reached a mature brown color or when seed moisture is 30% or less. For determinate varieties, paraquat should be applied when plants are mature, i.e., beans are fully de-veloped, half of the leaves have dropped, and remaining leaves are yellowing. The la-bel also states that soybean should not be harvested earlier than 15 days after applica-tion. Where morningglory vines are present 15 days may be needed to fully desiccate vines. Timing of application is critical and if harvest aid is applied too early and foliage is removed before all seed on the soybean plant have reached maximum dry weight, significant yield loss can occur.
Harvest Aid Research
Our research evaluated Gramoxone Inteon applied at 1 pint/A (maximum label rate) plus a non-ionic surfactant at 0.25% v/v in 15 gallons/A. Application was made to inde-terminate (Asgrow 4403RR) and determinate (Asgrow 5903RR) soybeans when mois-ture content of seed collected from pods at the four uppermost nodes of plants aver-aged 60, 50, 40, 30, and 20% (+ or – 2%). To determine seed moisture, pods were hand shelled and seed were weighed, oven-dried, and re-weighed to calculate average moisture percentage.
For indeterminate soybean, application at 60% average seed moisture reduced yield 10 Bu/A compared with the nontreated (See Figure 1) and yield reduction was accompa-nied by reduced seed weight. At this timing leaves had not begun to yellow and pods were green. At 50% average seed moisture soybean yield and seed weight were not negatively affected. Soybean was harvested 7 and 10 days after application depending on year and around 14 days before the nontreated. When application of Gramoxone Inteon was delayed until 40% average seed moisture yield was not affected and soy-bean was harvested around 9 d earlier than the nontreated.
For determinate soybean, application at 60% average seed moisture, reduced yield 13 Bu/A compared with the nontreated (See Figure 1) and yield reduction was accompa-nied by reduced seed weight. Application at 50% average seed moisture reduced yield
Volume 1 , Issue 8
Ins ide this issue:
When is it Safe to
Apply Gramoxone Har-vest Aid to
Soybeans?
1
Master Farmer
Program Field Days
5
Commodity Outlook 5
Grain Ban and Short-ages Create Opportu-nity for US Sorghum
7
Pest Profile:
Soybean Loopers in Louisiana Soybean
10
AgCenter Contacts 13
Cotton Insect Pest
Update
8
Current Situation on Soybean Loopers in Louisiana Soybean
11
Cotton Disease
Update
4
Where is All my Nitro-gen Going? Part Four: Nitrate Nitrogen
12
L OUISIANA CROPS NEWSLETTER
Cotton, Corn, Soybeans, Sorghum
Issue Contr ibutors
(a lphabet ica l l y)
Dr. James Griffin
Dr. Kurt Guidry
Dr. B. Rogers Leonard
Donna Morgan
Dr. Boyd Padgett
Shelee Padgett
Dr. J.A. Davis
S. Brown
Joseph Boudreaux
Dr. John Kruse
Josh Temple
When Is It Safe to Apply Gramoxone Harvest Aid to
Soybeans?
James L. Griffin, Joseph M. Boudreaux, and B. Roger Leonard, LSU AgCenter
Page 2 Volume 1 , Issue 8
9 Bu/A. At 40% average seed moisture soybean yield and seed weight were not negatively affected. Soybean was har-vested 12 and 14 days after application depending on year and around 7 day before the nontreated. The greater flexibil-ity in application with the indeterminate variety is because the most immature seed (seed that have not reached physio-logical maturity) are present in the top of the plant. For determinate soybean the most immature seed would be present in both the top and bottom of the plant.
It is not practical that growers determine application timing for a harvest aid by collecting and drying seed to quantify moisture. However, waiting until 50% leaf drop or until 65% of the pods have reached mature brown color would not be the best indicator for harvest aid application timing.
How to Determine When to Apply Harvest Aid to Soybeans
• Collect pods from the uppermost four nodes of plants at random across the field selecting both the most mature and most immature plants.
• Open pods and look for separation of beans from the white membrane inside the pod. If separation has occurred beans should be easy to shell from the pods. If this is observed for all pods collected, then seed have reached maxi-mum dry weight (R6.5 growth stage) and are beginning to lose moisture. Leaves can now be safely removed with-out affecting seed weight. At this time some leaves on plants may have started to yellow and some leaves may also have dropped but this can vary greatly depending on variety and environmental conditions. Also, some of the pods on the lower portion of plants have begun to turn yellow. If after opening the pods not all beans easily separate from the pod wall, application of harvest aid will result in some yield loss because of lower seed weight and the effect will be greater for determinate than for indeterminate varieties.
Another sure-fire way to know that it is safe to apply a harvest aid is when one normal pod on a main stem has reached mature color (R7 growth stage). At this time many of the pods in the lower canopy should have turned light green to yel-low. Because leaf drop is variety and environment dependent, level of defoliation at R7 can vary. Therefore, use of leaf drop as a basis for harvest aid application should not be the primary criterion for application timing.
Louis iana Crops Newsle t ter Page 3
52b60a 61a 60a
63a62a
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10
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Soybea
n y
ield
(B
u/A
)
60 50 40 30 20 Nontreated
Average seed moisture (%)
AsGrow 4403 Indeterminate MG IV
Green Plant Malady Research
In recent years in the mid-South, there has been an increased incidence of the soybean “green plant malady” where leaf retention and presence of green stems and pods can delay harvest. Our research over two years shows that where fun-gicide was applied at R3 and insecticide was applied as needed to keep stinkbug population below action threshold, at harvest leaf retention was 8%, green stem was 33%, and green pod was 4%. When fungicide was not applied and stink-bug was not controlled (nontreated control), green stem and green pod percentage was around 1.7 times greater. Appli-cation of Gramoxone Inteon decreased green leaf retention, green stems, and green pods. Where fungicide plus insec-ticide was applied and followed by harvest aid compared with the nontreated control, yield was 14% greater and seed moisture, foreign material, and seed damage were reduced.
46c50b
59a 61a 61a 59a
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Soybea
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60 50 40 30 20 Nontreated
Average seed moisture (%)
AsGrow 5903RR Determinate MG V
Figure 1. Yield of indeterminate and determinate soybeans as affected by Gramoxone Inteon applied as a harvest aid
based on average seed moisture. Data averaged over two years and means for each variety followed by the same
letter are not significantly different (P≤ 0.05).
Page 4 Volume 1 , Issue 8
Over the past several weeks I have received numerous calls concerning leaf spots on cotton foliage and bolls. There are several leaf spotting fungi that affect foliage and bolls. The two most common are Alternaria leaf spot and Cercospora leaf spot. This is NOT the same Cercospora that infects soybean. These leaf spots are usually found when cotton is stressed (fertility or drought stress). Other less frequently seen leaf spotters are Ascochyta blight and bacterial blight.
Alternaria Leaf Spot
Alternaria Leaf Spot (Image 1) is favored by ambient temperatures of 68 to 86o F and high relative humidity. In-fection can occur early season on the cotyledons, but typi-cally symptoms are usually evident late season. Spots be-gin as pale green spots on the leaves and other plant tis-sue (stems, petioles, and bolls). Mature spots consist of concentric rings that are irregularly circular with straw or reddish brown centers. Under humid conditions the centers may appear sooty (these are the spores of the fungus). In some cases the centers may deteriorate and fall out giving the leaf a shot-hole appearance. The fungus overwinters in infected plant debris from the previous season. Other sources of inoculum are adjacent cotton and weeds.
Image 1. Alternaria Leaf Spot
Cercospora Leaf Spot
Cercospora Leaf Spot (Image 2 and 3) is favored by the same conditions that are needed for Alternaria leaf spot. Symptoms are similar to those caused by Alternaria. The
initial symptoms are usually present late season, and occur as small red lesions on the leaves. As the lesions mature the centers are tan with a red margin and concentric rings can be present. The fungus will overwinter in infected plant debris.
In most cases Alternaria and Cercospora leaf spots are present on cotton growing in poor areas of the field. Cotton growing in areas in the field that are deficient in potassium or drought-stressed is at risk to these leaf spots. Yield losses are thought to be minimal because they typically occur in areas of low production.
Cotton Disease Update
Boyd Padgett, LSU AgCenter
Image 2. Initial Cercospora Leaf Spot
Image 3. Cercospora Leaf Spot
Louis iana Crops Newsle t ter Page 5
For much of the May, June, and July period, many of our agricultural commodities markets were trading in a side-ways to downward pattern. Unlike in most years when commodity prices generally trend higher due to uncertainty about acreage and crop development, price movement dur-ing this three month period in 2010 was limited as the out-look for growing supplies and the potential for higher stocks levels helped to limit price movement. In addition, spill over impacts from struggling financial and energy markets and fluctuations in the strength of the US dollar helped keep prices from making any sustained improvement. However, that all changed when concerns over supplies began to surface and enticed renewed interest from specu-lative funds.
Severe drought in Russia and parts of Eastern Europe caused significant reductions in the expectations for grain production in those areas. Despite much of the impact af-fecting the wheat industry, this shock certainly created sig-nificant movement in most feed grain and oilseed markets. This news seemed to spark the purchasing interest of the speculative funds which helped push prices higher. As
prices began to move higher, technical signals began to be reached which only reinforced the interest of the specula-tive funds. The ending result has been a significant in-crease in prices, not only for wheat, but for most feed grain and oilseed commodities.
While this current movement in prices was initiated by drought impacted production and has been helped along by highly variable projections for yields in the United States, there are many that believe the largest component of this price increase has been a result of the increased specula-tive activity in the market and strong technical buy signals. The issue with this type of increase is that it has likely pushed prices higher then what the supply and demand balance sheets for these commodities would suggest. So, as long as the speculative funds continue to aggressively purchase commodity contracts, prices should continue to trend higher. However, when they begin to offset positions and the market is forced to rely on supply and demand fac-tors to support prices, then we could see prices begin to fall. Unfortunately, with the continued struggles in the economy and the variability that we have seen in the finan-
Commodity Outlook
Kurt M. Guidry, LSU AgCenter
Image 4. Alternaria and Cercospora Varying Degrees of Infection
The risk of these fungi can be reduced by plowing under infected plant debris before planting, maintaining adequate fertility, provide adequate moisture (irrigation), and any practices that maintain plant vigor. Fungicides have been used to reduce these diseases, but they are usually cost-prohibitive.
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Dr. Ronnie Levy
Page 6 Volume 1 , Issue 8
cial and energy markets, it is very difficult to predict if and when we see a downturn in the activity of these speculative funds.
The reality of the situation is, however, that prices are markedly higher (See Table 1). Corn futures prices are currently 30 percent higher then they were at this time last year while soybean prices are roughly 2 percent higher. With a very positive ending stocks outlook, cotton prices are nearly 50 percent higher than last year. As mentioned, how long this current trend in prices will last is really difficult to project. What is more easy to say is that the current out-look for supply and demand conditions of many of the com-modities does do not necessarily suggest these type of prices, particularly when the full weight of harvest is on the market.
For corn and grain sorghum, expectations for strong de-mand and lower-then-expected acres help to create a gen-erally favorable supply and demand picture. In the USDA’s August supply and demand report, ending stocks for corn were decreased to 1.31 billion bushels, the lowest since the 2006/07 marketing year. Much stronger prospects for ex-port demand help to provide more optimism for this market despite the potential for record or near record yields. While the variability in reports on yield potential have helped sup-port prices, it seems safe to say that the 2010 corn crop will be large. While it may not be record crop, history would suggest that, even with just a large crop, prices would be pressured as harvest gets into full swing. The current view of ending stocks will likely, however, be positive enough to reduce the potential of a significant price fall. USDA’s latest projections for prices place corn prices in the mid to upper
$3.00 to low $4.00 range and grain sorghum prices in the low to upper $3.00 range.
The major challenge facing the soybean market is the pro-jection for ending stocks increasing by over 100 percent in the 2010/11 marketing year from the previous year. Slightly higher-then-expected acreage along with yields projected to reach last year’s record level has pushed total supplies to significantly higher levels. Despite very strong export demand, ending stocks are projected to increase to 360 million bushels, up from 160 million bushels the year before. With the USDA currently is projecting a season av-erage price from $8.50 to $10.00 per bushel and with cur-rent futures prices at the $10.00 level, there would seem to be some downside risk from current price levels, particu-larly if harvest results in record yield levels. .
Finally, for cotton, a much improved supply and demand situation continues to place prices at significantly higher levels than has been experienced in recent years. Cotton acres were increased in 2010 and anytime that you have higher acres and the potential for higher production, there is some risk that prices could come under some pressure. Looking at the USDA’s current productions for prices in the $0.61 to $0.75 per pound range certainly shows a signifi-cant discount to current futures prices. While this certainly points to some downside risk in this market, there seems to be enough uncertainty about yields and enough optimism about potential demand to suggest that prices would cer-tainly be on the upper end of USDA’s projection and could potentially surpass this projection.
Table 1. Closing Futures Prices on August 26, 2010 - Selected Commodities
Contract Closing Price Previous Previous Previous
Commodity Unit Month July 27,2010 Week Month Year
Corn Bushel Sept 10 $4.17 $4.14 $3.64 $3.21
Corn Bushel Dec 10 $4.33 $4.29 $3.78 $3.26
Soybeans Bushel Nov 10 $10.14 $10.12 $9.66 $9.96
Cotton Pound Dec 10 $0.8620 $0.8414 $0.7649 $0.5747
Louis iana Crops Newsle t ter Page 7
Recently Israel purchased 1.6 million bushels of U.S. sor-
ghum as a direct result of an agricultural export ban in Rus-
sia and the short grain supply in Ukraine. Israel has the
intention to purchase 2.4 to 3.1 million bushels in the near
future, increasing their imports of U.S. sorghum by about
65 percent. This will bring the U.S. market share of sor-
ghum to Israel to about 85 percent this calendar year.
Identifying and developing new drought tolerant sor-ghum germplasm....project update at USDA-ARS, Lub-bock, TX
Post-flowering drought tolerance (the “stay-green” trait) is an essential trait for increasing the production of sorghum in increasingly variable climates. Previously, methodologies for identifying the nonsenescent (stay-green) trait required the right intensity of drought stress at the right developmen-tal stage to visually evaluate lines in the field. Field-based evaluations of drought tolerance are notoriously difficult to manage, and often require growing lines in multiple loca-
tions across several years in order to acquire a meaningful assessment of the stay-green trait. Now, because of a new technique developed in the USDA-ARS laboratory, funded by the Sorghum Checkoff, researchers can readily identify stay-green lines by means of a 30-minute high temperature challenge to leaf tissue from pre-flowering well-watered sorghum and 30-minute room temperature recovery. This technology will greatly reduce the selection time needed to identify drought tolerant sorghum. The research will con-tinue to use this new technology in a two pronged research approach to identify germplasm with improved drought tol-erance. Both research avenues are providing new sources of drought tolerance that can be used to improve sorghum hybrids.
Shelee Padgett
United Sorghum Checkoff Program
765.586.7373
wwww.sorghumcheckoff.com
Grain Ban and Shortages Create Opportunity for US Sorghum
KEY POINTS:
► Spider mites “Bug” pests and caterpillars remain prob-lems in cotton.
► Co-applications of insecticides are necessary to manage most pest complexes.
► Control of pests is necessary at least until mainstem NAWF < 5 + 350 HU’S.
Several cotton insect pests remain at problem levels in Louisiana cotton fields. The most common pests include spider mites, tarnished plant bugs, brown stink bugs, and bollworms. Most of the spider mite problems are not se-vere, but in dry weather populations can explode in a few days. Most of the insecticides used for “Bug” control could flare populations. A good rule of thumb with late-season spider mites is that unless the crop is mature and ready for harvest aid application, this pest should not be allowed to defoliate the upper plant canopy. Immature bolls still need subtending leaves to complete their development. In addi-tion, spider mite infestations are usually much larger in area than just the local spots where discolored red leaves are found. The actual areas of infestation may be twice as large and this is one reason that it appears that the area of damaged plants increases so rapidly. Much of the cotton crop is close to maturity and the most cost-effective treat-
ments for spider mites will be those that are the least ex-pensive. The cost of the most effective residual products may not be justified. Tarnished plant bugs remain a per-sistent problem and will feed on small bolls in the absence of squares. As square retention declines, this becomes the preferred fruiting structure for feeding. In contrast, stink bugs are seed feeders and prefer quarter-sized or larger bolls. Both pests are common in late-maturing fields across the state. At this time, the treatments for control will be similar and will likely include Bidrin, Acephate, or co-applications of pyrethroids with these and other products. ULV applications of the Malathion + pyrethroid treatment are effective against these pests. Bollworm moths are common in all crops. I have been finding eggs and small larvae scattered throughout the upper 1/3 of the plant can-opy for the last 10 days. The injury levels from large larvae do not appear to be as high as that observed during July. Bollworm will only be able to damage soft bolls at this time. For those later-maturing crops, it will be important to treat these infestations to protect any bolls that producers intend to harvest. However, remember that the value of bolls set during late August is usually much lower than that of ma-ture bolls lower on the plant. Therefore, we can adjust our action thresholds upward and not as concerned about sig-nificant yield losses
Cotton Insect Pest Update
B. R. Leonard
LSU AgCenter Macon Ridge Station, Winnsboro, LA
Page 8 Volume 1 , Issue 8
Louisiana soybeans can be attacked by a host of late season caterpillars that are capable of causing severe defoliation. The primary species in this pest complex include the velvetbean caterpillar, green cloverworm, and soybean looper. All are perennial pests of soybeans in Louisiana, but the soybean looper (Plate 1) has been the most difficult to manage in
recent years.
Historically, outbreaks of soybean looper are somewhat sporadic, but significant yield losses can occur from high infesta-tions that are not managed with timely applications of insecticides. Leaf defoliation levels can be quite se-vere if soybean looper populations exceed action thresholds (150 per 100 sweeps) (Plate 2). Late-season infestations of this pest are often the result of insecticide treatments that have been applied for other pests, resulting in loss of natural enemies. Sprays that are applied for pests such as stink bug, bean leaf beetle, or three-cornered alfalfa hopper in soybean fields during the mid-to-late growing season can induce outbreaks of soybean looper. However, considerable problems with stink bugs (primarily the redbanded stink bug) in the last five years have in-creased numbers of late-season insecticide applica-tions, which in turn have increased the occurrence and intensity of soybean looper problems.
Pest Profile: Soybean Loopers in Louisiana Soybean
J. Temple, S. Brown, J. A. Davis, and B. R. Leonard
LSU AgCenter Department of Entomology, Baton Rouge LA
Sprayed Non-Sprayed
Plate 1. Soybean looper. (J. A. Davis 2010)
Plate 2. Soybean looper infestations above action thresholds that remain non-treated can cause severe defoliation. (B. R. Leonard, 2010)
Page 9 Louis iana Crops Newsle t ter
In addition, soybean looper infestations are typically more common in farmscapes that have soybean and cotton fields in close proximity. Soybean looper moths which feed on cotton flower nectaries have much higher egg production than moths feeding only in soybean flowers. Therefore, this is one factor contributing to higher numbers of soybean looper larvae in soybean fields adjacent to cotton. Two or three generations of soybean looper can occur in Louisiana per growing season. The intensity of problems increases during the season with the highest populations occurring during August and September.
Soybean looper larvae damage soybean plants by feeding on the foliage. The adults (moths) deposit their eggs on leaves in the mid-to-lower canopy. The caterpillars usually initiate their feeding in the lower soybean canopy and migrate upward moving toward the plant terminal as they grow older. Small larvae do not cause much injury, and may create a “window-paning” effect on leaves by not feeding entirely through the leaf. Most of the significant defoliation is caused by larger caterpillars in the fourth to sixth instar stages of larval development. Greater than 90% of the total leaf consump-tion takes place during these larval stages. This observation is the reason that most action thresholds used to initiate insecticide applications suggest only counting caterpillars that are greater than ½ inch in length.
Soybean plants can tolerate a significant amount of defoliation without negatively affecting yield. These plants do not need to retain 100% of their foliage at any time during their development to reach maximum yield potential. Prior to flow-ering, plants can tolerate up to 35% defoliation without yield loss. However, during flowering, pod set, and seed develop-ment, foliage loss greater than 20% will decrease yield. As the plant matures and seed have fully developed in pods, defoliation levels have much less of an impact on yield.
Fortunately, several insecticides are recommended for soybean looper control in Louisiana. This list is much shorter today because soybean looper has developed resistance to numerous insecticides in the organophosphate, carbamate, and pyrethroid classes. The most effective products that are currently recommended in Louisiana (Table 1) include In-trepid (methoxyfenozide), Larvin (thiodicarb), Steward (indoxacarb), and Tracer (spinosad). There are several other products that list soybean looper as a target pest, but they either have performed inconsistently or field populations have
demonstrated resistance levels. Intrepid has been the standard insecticide for soybean looper across Louisiana as a result of its efficacy, long residual activity, and availability. Although the current label recommends rates as low as 4 oz/acre, Intrepid is recommended at higher rates of 6 to 8 oz/acre in Louisiana, because the lower 4 oz rate has given in-consistent control. Since 2008, less than adequate control has been reported in Louisiana with these lower rates of In-trepid. Factors that could have contributed to this unsatisfactory control include unusually heavy pest pressure, non-labeled rates, application problems, and poor timing of application. Mr. Sebe Brown (graduate student in the LSU Dept. of Entomology working under Dr. J. A. Davis) has measured significant variability in susceptibility to Intrepid among Lou-isiana soybean looper populations during 2009 (Figure 1). All field collections required more insecticide than the labora-tory colony (LSU1) to achieve an estimated 95% mortality level. In spite of these laboratory results, Intrepid has contin-
Table 1. Insecticides for Soybean Looper Control in Louisiana Soybean1
Insecticide (Form.)
IRAC Mode of
Action Class Amount
(Form.) / Acre Lb AI / Acre Acres/Gal Intrepid (4F) 18 6 – 8 oz 0.09 – 0.125 16 – 21.3
Larvin (3.2F) 1A 18 – 30 oz 0.45 – 0.75 4.3 – 7.1
Steward (1.25SC) 22A 5.7 – 11.3 oz 0.055 – 0.11 11.3 – 22.6
Tracer (4F) 5 2.0 oz 0.062 64
Belt (4SC) 28 2.0 - 3.0 oz 0.062-0.094 42.6-64
1Note: Action threshold is 8 loopers (≥1/2 in) per row foot or 150 worms per 100 sweeps.
Page 10 Volume 1 , Issue 8
ued to perform very well in most soybean fields. Reduced susceptibility to Intrepid has not yet become fixed in Louisiana populations because soybean loopers do not overwinter here. They migrate each year from areas in lower Florida, Texas, Central America, and the Caribbean basin. Therefore, Intrepid susceptibility of the soybean looper populations that fly into Louisiana will likely be variable and unpredictable. The other insecticides, Larvin, Steward, and Tracer, are alternatives to Intrepid and have performed very well in annual field screening trials. As a statement of caution for Lar-vin, producers should be aware that this product is very water soluble and exhibits poor rain-fastness. All of these prod-ucts exhibit a relatively narrow spectrum against Louisiana soybean insects, especially non-caterpillar pests such as stink bugs. For effective control of stink bugs and soybean looper, co-application of products expressing efficacy against both species is necessary.
The agrochemical industry is currently developing a new insecticide, Coragen (chlorantraniliprole) for use against soy-bean caterpillars. Another insecticide in that class, Belt (flubendiamide) from Bayer has become recently registered. Both express novel modes of action and have demonstrated excellent initial and residual efficacy against soybean looper in Louisiana field trials during 2008-2010. Federal and state label approval for Belt is anticipated during 2010, but neither product is currently labeled in soybean.
Figure 1. Intrepid susceptibility (LC95 values) among 2009 populations of Louisiana soybean loopers.
(J.A. Davis and S. Brown, LSU AgCenter Department of Entomology)
Page 11 Louis iana Crops Newsle t ter
KEY POINTS:
► Soybean loopers are above action thresholds (150 lar-vae/100 sweeps) and remain a
persistent problem across Louisiana.
► Intrepid, Steward, Belt, Larvin, and Tracer are effective chemical control strategies.
► Re-treating may be needed 10-14 d after application; when possible, rotate products.
► None of these treatments provide effective control of stink bugs.
Many fields in North and Central Louisiana are under heavy pressure with soybean looper. I have received several calls from farmers, consultants, and dealers during the last two weeks on the performance of Intrepid. At this time, I have not seen any field control problems that I would call an out-right failure when the correct rate and timing of Intrepid was used. Based upon conversations with several folks work-ing in soybean IPM across Louisiana and surrounding states, it appears that Intrepid is working ok. However, there may be some other application problems that I am not aware of which also may have affected efficacy.
It is important to note that Dr. Jeff Davis’s laboratory (LSU AgCenter Dept. of Entomology) has confirmed consider-able variability in Louisiana soybean looper responses to Intrepid, but fortunately the 2010 field control issues have not been correlated to insecticide-resistant popula-tions. This may change as the season continues and addi-tional applications of Intrepid are used. I have not heard of any significant problems with Belt, Steward and Larvin (except for one each with a wash-off possibility) or Tracer.
All of the products, other than Intrepid, kill soybean loopers relatively quickly and significant efficacy should be ob-served within 2 days after application. More insects will continue to die for about a week after application. Intrepid requires much more time after application before it can be evaluated in the field. Most of the confusion with post-treatment evaluation is associated with the fact that this compound is an insect growth regulator (IGR) and requires at least 4 – 5 days to really show a reduction in field num-bers. Treating small larvae (<1/2 inch) with Intrepid does not increase the speed of kill as it does for other prod-ucts. Larvae have to ingest (eat) the product and begin the moulting process for toxicity to occur. This intoxication ap-pears to occur most readily at about 5 – 6 days after appli-cation. With very close field observations, you can usu-ally tell that Intrepid was used when a sweep net sample
shows a high proportion of the larvae are in the same growth stage. This is the point where many larvae have attempted to moult and cannot feed. Larval mortality oc-curs from starvation and usually the population is nearly destroyed within 24 - 48 h after that effect is observed. Per-formance in field trials for the past several years has pro-vided confidence in this product because of its rain fast-ness and residual. The other insecticides work very well, and certainly are options, but have not always demon-strated the same rain fastness and residual efficacy. Belt is a new product recently registered by the US-EPA in soy-bean and LSU AgCenter scientists are trying to character-ize its activity.
This persistent pressure in many late-maturing soybean fields during this season may require another application to control this pest. The most logical selection of products should include a rotation among all the insecticides that are recommended. See the LSU AgCenter’s website for prod-ucts and rates (www.lsuagcenter.com). This will increase the probability of successful control and reduce selection pressure for resistance to a single product. In addition, products other than Intrepid will provide more rapid mortal-ity and hopefully further reduce defoliation. When re-treating fields, use the same action thresholds. Do not get in a hurry and treat too early in an effort to target small lar-vae. Small larvae cause little defoliation and by waiting until more larvae hatch from eggs, the initial and residual efficacy of products will be more cost effective.
One pertinent question during the end of the season is “How long do we need leaves?” Dr. Jim Griffin’s (LSU Ag-Center) data show that harvest aid application between soybean growth stages R6.5 and R7 is sufficient to prevent any significant yield loss. (Refer to another article in this newsletter for additional information). Other work by Dr. Angus Catchot (Mississippi State University) with insect-simulated defoliation also has shown that some leaves are required until soybean reach the mid-R6 stages. In these MSU trials, only 100% leaf removal loss on soybean plants beyond the R6 stages caused a significant yield loss. That loss was in the range of 2-3 bu/acre. He and his team are repeating those studies this year. These results suggest that as long as soybean plants retain a small portion of ac-tive leaf tissue until the mid-R6 stages or until the plants are safe for harvest aids, final yield should not be compro-mised.
Current Situation on Soybean Loopers in Louisiana Soybean
B. R. Leonard and J. A. Davis
LSU AgCenter Department of Entomology, Baton Rouge LA
Page 12 Volume 1 , Issue 8
Almost all soils in Louisiana have a net negative charge that comes from soil organic matter and clay. When ni-trogen mineralizes into the ammonium (NH4
+) form, it has a net positive charge that can ‘stick’ (adsorb) to the negatively charged sites in the soil. This provides a ready reserve of nitrogen in a form that plants can use, and at the same time not leach out of the soil. However, nature rarely stands still and this is especially true in soils used for crop production. Vast populations of microbes (mostly beneficial bacteria) exist in the soil and they convert NH4
+ into nitrate (NO3-) over a
period of days to weeks, depending on the soil temperature, moisture content, pH and nitrogen supply. These microbes are very specialized and one species – Nitrosomonas – converts ammonium into nitrite (NO2
-), and another species – Nitrobacter – converts NO2
- into NO3-. This reaction is called an oxidation-reduction or ‘redox’ reaction, and it has two
major effects in the soil. The first is that it converts a positively charged form of nitrogen into a negatively charged form of N, and the second is that for every unit of ammonium converted, the process generates two units of hydrogen, creating soil acidity. (Don’t forget to check your soil pH this fall!)
Step 1: Ammonium (NH4+) + 1 ½ Oxygen (O2) Nitrite (NO2
-) + 2 Hydrogen (H)
Step 2: Nitrite (NO2
-) + ½ Oxygen (O2) Nitrate (NO3-)
The good news is that nitrate is a form of nitrogen that plants readily utilize. Since NO3- has a negative charge
just like the soil surrounding it, nitrate moves freely in the soil water. As rain or irrigation causes water to move deeper into the soil profile, nitrate moves with it, providing nutrients further into the soil for deeper root growth. The bad news is that when there is more NO3
- in the soil than the crop can utilize, leaching can take place as the nitrogen moves past the root zone. Once it has passed crop roots, it is effectively ‘wasted’ nitrogen. Further problems can occur as this nitrate nitrogen moves into the water table, contaminating water supplies, or drifts into the surrounding streams and rivers. Ex-cess nitrogen that makes its way down river can contribute to algae blooms and hypoxic zones - areas of low oxygen where aquatic life struggle to survive. On the other hand, excess nitrate that is still within the upper plant root zone can rapidly convert to nitrous oxide gas (N2O) or nitrogen gas (N2) when the soil becomes saturated, vaporizing into the at-mosphere in a process called denitrification. Either way, the grower loses the value of the nitrogen fertilizer applied, and the environment must cope with the added stress.
Effective nitrogen management can substantially reduce the amount of nitrogen lost from the cropping system,
while ensuring optimal yields. Many growers in Louisiana are already practicing the beneficial technique of splitting their
nitrogen applications, especially in corn. Most Louisiana corn varieties have maturity lengths of 110 to greater than 120
days, which is a very long time for nitrogen to remain in the root zone in this hot and rainfall-prone state. By splitting the
nitrogen load a grower can provide sufficient nitrogen to optimize yields without leaving more nutrient in the field than the
crop can use. Interestingly, University research has not demonstrated a yield benefit for cotton by splitting the N load. It
is important to remember, though, that cotton is a perennial plant that we treat like an annual, and it does not require the
same level of N to optimize yield as compared to corn. The nitrification inhibitor di-cyandiamide or DCD has been proven
effective in University trials to slow the conversion of ammonium into nitrate, thus holding the nitrogen in the positively
charged form longer and reducing the potential for leaching or denitrification. Polymer coated urea has demonstrated
less leaching and denitrification than standard urea in many University corn trials in the Midwest and irrigated West, and
is currently being tested in Louisiana. Overall, the single best technique a grower can use to maximize a nitrogen fertil-
izer investment is to calibrate the nitrogen rate to the expected yields. If the grower has a yield monitor, he could apply
his historical nitrogen rate in several strips across the field, and alternate it with strips of nitrogen that are 15 to 30
pounds less per acre. Then track yield at the end of year on these strips. By running these ‘calibration strips’ for at least
two years in a row, a grower can begin to get a firmer grip on the amount of N actually needed to optimize a crop without
wasting fertilizer dollars.
Nitrosomonas
Nitrobacter
Where is all my nitrogen going? Part 4: Nitrate nitrogen
John Kruse, LSU AgCenter
Parish County Agent Phone Email Acadia Barrett Courville 337-788-8821 [email protected]
Allen Randall Bellon 337-639-4376 [email protected]
Avoyelles Rob Ferguson 318-308-4191 [email protected]
Beauregard Keith Hawkins 337-463-7006 [email protected]
Bossier
Caddo John Levasseur 318-226-6505 [email protected]
Calcasieu Tommy Shields 337-475-8812 [email protected]
Caldwell Jim McCann 318-649-2663 [email protected]
Cameron Tommy Shields 337-905-1318 [email protected]
Catahoula Glenn Daniels 318-336-5315 [email protected]
Concordia Glenn Daniels 318-336-5315 [email protected]
Desoto
East Carroll Donna Lee 318-282-1292 [email protected]
Evangeline Keith Fontenot 337-363-5646 [email protected]
Franklin Carol Pinnell-Alison 318-267-6713 [email protected]
Grant Matt Martin 318-627-3675 [email protected]
Iberia Blair Hebert 337-369-4441 [email protected]
Iberville Kellee Lassiter 225-687-5155 [email protected]
Jeff Davis Allen Hogan 337-824-1773 [email protected]
Lafayette Stan Dutile 337-291-7090 [email protected]
LaSalle
Madison R.L. Frasier 318-267-6714 [email protected]
Morehouse Terry Erwin 318-282-3615 [email protected]
Natchitoches
Ouachita Richard Letlow 318-282-2181 [email protected]
Pointe Coupee Miles Brashier 225-281-9469 [email protected]
Rapides Matt Martin 318-473-6605 [email protected]
Red River Joshua Salley 318-932-4342 [email protected]
Richland Keith Collins 318-355-0703 [email protected]
St. Charles Rene’ Schmit 985-785-4473 [email protected]
St. Landry Vincent Deshotel 337-831-1635 [email protected]
St. Martin Alfred Guidry 337-332-2181 [email protected]
St. Mary Jimmy Flanagan 337-828-4100 [email protected]
Tensas Dennis Burns 318-267-6709 [email protected]
Vermilion Stuart Gauthier 337-898-4335 [email protected]
Washington Henry Harrison 985-839-7855 [email protected]
West Baton Rouge Louis Lirette 225-336-2416 [email protected]
West Carroll Myrl Sistrunk 318-267-6712 [email protected]
West Feliciana James Devillier 225-635-3614 [email protected]
Newsletter Ti t le Page 13
P A R I S H C O N TA C T S I N F O R M AT I O N
Louis iana Crops Newsle t ter
Louisiana Crops Newsletter created and distributed By:
Dr. Ronnie Levy
Dr. John Kruse
Brandi Woolam
Dean lee Research Station
8105 Tom Bowman Drive
Alexandria, LA 71302
Phone: 318-473-6520
Fax:318-473-6503
We’re on the Web.
http://www.lsuagcenter.com/en/communications/publications/newsletters/Louisiana-Crops-/Louisiana-Crops-Newsletter.htm
Specialists
Soybean Ron Levy 318-473-6523
318-290-8747(cell)
Cotton and Feed Grains John Kruse 318-473-6522
318-229-8180(cell)
Weeds Bill Williams 318-334-36309(cell) [email protected]
Weeds Daniel Stephenson 318-308-7225(cell) [email protected]
Entomology Rogers Leonard 318-435-2157
318-334-0147(cell)
Nematodes Charlie Overstreet 225-578-2186 [email protected]
Pathology Boyd Padgett 318-435-2157
318-308-9391(cell)
Pathology Clayton Hollier 225-578-1464 [email protected]
Economics Kurt Guidry
Ken Paxton
225-578-3282
225-578-2763
Ag Economics and
Agribusiness
Kurt Guidry 225-578-3282 [email protected]
Fertility J Stevens 318-427-4408
318-308-0754(cell)
Soybeans
Cotton, Corn, Sorghum
Corn, Grain Sorghum, Cotton. Soybeans
Corn, Grain Sorghum, Cotton weed control. Soy-beans
Cotton, Corn, Soybean, Grain Sorghum
All agronomic crops
Soybean, Corn, grain Sor-ghum
Soybean, Corn, grain Sor-ghum
Cotton
Soybean and Feed Grain
marketing
All agronomic crops
Specialty Responsibilities Name Phone Email
Entomology Soybean, Corn, Grain Sorghum
Jack Baldwin 225-578-1634 [email protected]
Louisiana State University Center Agricultural Center, William B Richardson, Chancellor
Louisiana Agricultural Experiment Station, David J. Boethel, Vice-Chancellor and Director
Louisiana Cooperative Extension Service, Paul D Coreil, Vice Chancellor and Director
Issued in furtherance of the Cooperative Extension work, Acts of Congress of May 8 and June 30, 1914, in cooperation with the United States Department of Agriculture.
The Louisiana Cooperative Extension Service provides equal opportunities in programs and employment