Don’t ignore weeds between now and December

By Daniel Stephenson, LSU AgCenter weed scientist

It’s not hard to notice how green corn fields are following harvest, and we all know what that color means: weeds. Managing weeds post-harvest is not popular with farmers; however, weed seed production and subsequent seed deposition on the soil should be a great concern, especially if glyphosate-resistant Palmer amaranth and/or waterhemp are present. We know that it usually takes only one month for a newly emerged pigweed to produce viable seed this time of the year, so action needs to be taken monthly to stop seed production until the first killing frost. Even if glyphosate-resistant pigweeds are not present, preventing seed production of grass weeds like barnyardgrass or browntop millet will pay dividends next year.

Mowing, tilling and spraying herbicide are options to minimize or prevent weed seed production. I suggest mowing no sooner than two weeks after harvest, perform tillage that will destroy all plant material three to four weeks after mowing, then apply at least 0.75 lb ai/A of paraquat plus a residual herbicide three to four weeks after tillage. Residual herbicide options include Goal, Valor, LeadOff and Dual Magnum. If corn is harvested in mid-August, mowing would occur in late August and tillage in late September, followed by the herbicide application in late October. September tillage could be when producers are preparing fields for next year. Also, applying a residual herbicide in mid to late October will provide residual control of many winter annual weeds as well. If mowing and tillage are not options, then paraquat at 0.75 lb ai/A plus Valor is a good option to minimize pigweed seed production. Glyphosate is a good option for control of grass weeds.

Glyphosate-resistant Italian ryegrass has become a major issue in the past couple of years. Farmers in Mississippi have been dealing with this pest for almost 10 years. Mississippi State University weed scientists developed a program for glyphosate-resistant Italian ryegrass control. The program begins with management strategies implemented in the fall, such as a residual herbicide application like S-metolachlor, Zidua, Boundary and others. Double disking is also an option. Application of clethodim in the winter (January) is their second line of defense. Finally, if the producer waits until spring to target Italian ryegrass, the third line of defense is sequential applications of paraquat spaced two weeks apart with atrazine, metribuzin or diuron tank-mixed with the first paraquat application.

It is best to target Italian ryegrass in the fall. Unfortunately, Louisiana producers are tank-mixing clethodim with their burndown in the spring for Italian ryegrass. This strategy is proving to be ineffective for numerous reasons. Currently, the LSU AgCenter is investigating possible clethodim-resistant Italian ryegrass in Louisiana. Clethodim resistance has been documented in Mississippi. Therefore, Louisiana producers should use fall-applied residual herbicides and spring clethodim or paraquat applications to manage glyphosate-resistant Italian ryegrass and avoid clethodim-resistance.

Horseweed, which is also known as mare’s tail, was a tremendous problem for Louisiana corn, cotton and soybean producers this year. Horseweed predominately germinates in the fall, but little above-ground plant growth occurs until the spring. Spring emergence of horseweed has also been observed; however, most of the horseweed populations Louisiana producers face emerge in the fall. The best course of action is to scout for horseweed in the fall and apply 2,4-D or dicamba when found. If horseweed populations are targeted with spring burndown applications, 2,4-D, dicamba and Sharpen tank-mixed with glyphosate or Liberty are good options. Ensuring complete kill prior to planting the crop is crucial.

 

Entomology update

By Sebe Brown, LSU AgCenter entomologist

Cotton

With much of Louisiana’s cotton well beyond cutout, insect management decisions should be based on protecting those existing harvestable bolls and insects present in the field. 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 2.5 times, 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 is 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.

Soybeans

As Louisiana progresses into late summer, producers and consultants should be aware of late-season defoliators such as soybean looper, velvet bean caterpillar 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 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. Insecticides currently recommended for use against SBL in Louisiana include, Prevathon, Besiege, Intrepid Edge and Steward. 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 1/2 inch or longer 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.

Finally, when making insecticide application decisions for caterpillar pests in soybeans: insect species present, insect numbers present and defoliation percentage should be taken into consideration. After bloom, soybeans can tolerate 20% defoliation and not experience a significant yield loss.

Stink bug issues in much of the soybean acreage around Louisiana have been minor this season. Brown stink bugs have been the predominant species found in northern Louisiana, with increasing reports of redbanded stink bugs occurring as the season progresses. Brown and redbanded stink bugs can be difficult to control with pyrethroids, and acephate plus pyrethroid or a neonicotinoid mix such as Leverage, Endigo or Belay plus bifenthrin would a better control option in fields where populations of these insects occur. The Louisiana threshold for brown stink bugs is 36 insects in 100 sweeps, and the redbanded threshold is 16 insects in 100 sweeps.

 

Winter cover crops: planning for success

By Josh Copes, James Hendrix, Lisa Fultz, Syam Dodla and Naveen Adusumilli

Corn harvest is in full swing across Louisiana, and soybean harvest has begun on a limited basis. As we move into the fall months, now is the time to begin planning your winter cover crop management strategy. Cover crops are used for several purposes, including protecting soil from erosion, improving soil structure, scavenging and cycling of soil nutrients, increasing organic matter, helping alleviate hardpans, etc.

Cover crop selection will depend on the goals a producer would like to accomplish by planting a winter cover crop. Having a clear objective for planting a cover crop will also aid in cover crop management. For example, if minimizing soil erosion is the main objective, a cereal cover crop would be a good choice. The fibrous root system of cereals will help prevent topsoil from leaving the field. Cereal winter covers are good nutrient scavengers as well. In contrast, a tap-rooted cover crop like forage or tillage radish (woolypod vetch, red clover, etc.) is better suited for deep nutrient scavenging and potentially aids in loosening a soil compaction layer or preventing one. Mixes of cereal and legume covers can reduce early-season N fixation issues in corn. Preliminary data collected by AgCenter scientists have shown that in soybeans, legume cover crops can supply N for early growth needs until nodules develop.

Other important considerations when selecting a winter cover crop include the cash crop to be grown following cover crop termination and winter cover crop termination. Be sure to plant only quality seed; this will help eliminate weed seed contamination issues. When planting legumes, make sure the rhizobium inoculant strain is correct for the legume species that will be planted, and always inoculate. If planting pre-inoculated legume seed, get pure live seed per pound and adjust seeding rates accordingly. Some pre-inoculated seed is larger and therefore has less pure live seed per pound. Seeding rates of cover crops will depend on the seeding method and date of sowing and whether the land is enrolled in a CSP or EQIP program. For cereals, avoid low seeding rates and establishment methods that could lead to spotty emergence. Spotty emergence could cause the cereal to “bunch” (a single plant with multiple tillers and large root system), which could lead to main crop establishment issues such as skips and variations with seed placement depth and seedling emergence.

Cover crops should be planted as soon as possible following the main crop harvest. When planted earlier in the fall, growth and biomass production will be maximized prior to cold weather, which will slow the growth and development of the cover crop. Planting your cover crop soon after harvest is especially important if corn will be planted. Early cover crop termination when planting corn combined with late planting of a cover crop (November) will reduce overall biomass production, therefore minimizing the benefits of the cover crop. Legumes are generally slow-growing if planted too late (November), and biomass production will be minimal prior to the onset of cold weather.

If fields are enrolled in an NRCS conservation program that requires cover crops, be sure to follow the NRCS’s cover crop guidelines. NRCS seeding rates and planting dates for common cover crops grown in Louisiana can be found at this link. The planting window for most winter cover crops is Oct. 1 to mid-November. Ranges for average first frost dates for Monroe, Shreveport, Alexandria and Baton Rouge are Nov. 15, 18, 19, and 29, respectively.

The AgCenter website has some useful tools that may aid in further refinement of accomplishing the intended goals for your farm, including potential scenarios and their implications for incentives payments and a Q&A on conservation policy and crop insurance. NRCS payments for cover crops change from year to year. Updated numbers are included in the decision tool located here in estimating overall costs of cover crops implementation.

If you have any questions or concerns, please feel free to contact your parish AgCenter agent or one of us.

Josh Copes
Cell: 318-334-0401
Office: 318-766-4607
jcopes@agcenter.lsu.edu

James Hendrix
Cell: 318-235-7198
Office: 318-766-4607
jhendrix@agcenter.lsu.edu

Lisa Fultz
Cell: 225-366-8863
Office: 225-578-1344
lfultz@agcenter.lsu.edu

Syam Dodla
Cell: 225-505-7064
Office: 318-741-7430
sdodla@agcenter.lsu.edu

Naveen Adusumilli
Cell: 318-884-0514
Office: 225-578-2727
nadusumilli@agcenter.lsu.edu

 

Managing cotton regrowth

By Dan Fromme, LSU AgCenter cotton specialist

One of the main considerations in the selection of harvest aids is regrowth control and, to be more specific, the activity of the defoliation product on juvenile growth and regrowth prevention.

Regrowth vegetation is difficult to defoliate because the juvenile tissue does not form abscission zones. Basal regrowth is the first to form and hardest to control, but generally is less troublesome to a harvest operation. The new leaves subsequent to defoliation can appear as terminal regrowth and often are a source of green staining, fine leaf trash and excessive moisture in seed cotton. Excessive regrowth vegetation must be desiccated before harvest, requiring additional harvest aid chemicals. Additional chemical treatments often are insufficient to prevent staining during harvest and storage.

Factors that contribute to regrowth include:

• Warm temperatures. Favorable temperatures can lead to increased regrowth.
• Soil moisture. Abundant soil moisture increases regrowth.
• Light penetration. Once the crop is defoliated, sunlight is able to reach the axillary buds at the base of each branch which induces regrowth.
• Fertility. If soil nitrogen is not depleted by the time of harvest aid application and moisture is available, plants will continue to produce healthy, vigorous growth. This late-season vigorous growth not having reached the state of senescence required for rapid abscission is very undesirable.
• Ethephon. High rates of ethephon in your defoliation application may cause increased regrowth.
• Low yields. When maturing bolls are not present to act as carbohydrate sinks, undesirable regrowth may increase if temperatures remain warm and water and nitrogen are available in the soil.
• Reduction of thidiazuron. Lowering the rate or omitting thidiazuron from your initial harvest aid application can increase the incidence of regrowth, especially with favorable environmental conditions.
• Varieties. In the past decade, varieties have become more robust and later in maturing in their growth and development. The good news is this has coincided with the trend in yield increases in the mid-south and Louisiana.

In summary, harvest aid applications that include thidiazuron can help suppress cotton regrowth. Thidiazuron rates vary based on weather, regrowth potential and presence of juvenile tissue at defoliation. Conditions that favor juvenile or regrowth will require a higher application rate (3 to 4 oz/acre). Also, a pre-mix of thidiazuron and diuron may be used in most situations (Table 1). Last but not least, defoliate only what can be harvested 10 to 14 days after application.

Table 1. Use pattern of thidiazuron and thidiazuron plus diuron for defoliation and regrowth suppression.

Harvest aid	Labeled broadcast rate	Maximum use per season	Estimated rain-free period (hours)	Pre-harvest interval (days)	Estimated minimum temperature
Thidiazuron SC	1.6 to 6.4 oz	9.6 oz	24	5	65°F
Thidiazuron + diuron	6.4 to 16 oz	16 oz	12	5	60°F

 

Fusarium head blight of wheat (scab) in Louisiana

Steve Harrison, Professor, Department of Soil, Plant and Environmental Sciences

Trey Price, Associate Professor, Macon Ridge Research Station

Boyd Padgett, Professor, Dean Lee Research, Extension, and Education Center

Introduction

Fusarium head blight (FHB, commonly referred to as scab) is primarily caused by Fusarium graminearum. The fungus causes shriveled and poorly filled seed that result in reduced yield and test weight. The pathogen also produces the mycotoxin, deoxynivalenol (DON), which is toxic to animals and humans and can cause grain rejection at the elevator. Scab has been a major problem in Louisiana wheat over the past several years and is one of the reasons that Louisiana wheat acreage has declined. Management of FHB is difficult because there are no highly effective single management practices (varieties or fungicides) and an integrated approach is required.

Epidemiology and Symptoms

Scab management begins with an understanding of the conditions favoring infection and disease development. The fungus infects corn and wheat grown in or near fields planted to corn the previous year, and these fields are at higher risk of developing scab than fields planted after soybean. Infected corn debris (also wheat straw and other hosts) can harbor the pathogen and serve as initial inoculum. Fungal spores produced on this debris are dispersed by rain splash or wind to nearby wheat plants. Other inoculum can be introduced into the field as windblown spores. Other hosts include 14 genera of Poaceae, two genera of Fabaceae, and one genus of Curcurbitaceae. Once an epidemic is initiated, plant to plant spread is likely to occur. Infection normally occurs during flowering but can occur from head emergence though early grain fill. Prolonged periods of rainfall during flowering and temperatures from 75-85^oF are conducive to infection and spread of Fusarium head blight. Symptoms usually appear 10 to 14 days after flowering as bleached sections of heads, which will be evident from the turn row or head row (Photo 1). This symptom is often mistaken with the appearance of maturing wheat. Upon closer inspection, affected fields will usually have infected heads showing the characteristic bleached appearance of sections (florets)

with pinkish/salmon/light orange coloration along the glumes (Photo 2, 3). This coloration is caused by millions of microscopic spores (reproductive structures) of the pathogen. There are usually healthy kernels along with the diseased kernels on the same head (Photo 3). In extreme cases, however, the entire head may be infected. At harvest, infected seed will be shriveled, off color, much lighter than healthy kernels, and are referred to as “tombstones” (Photo 4) or Fusarium Damaged Kernels (FDK).

Photo 1. FHB infected field showing bleaching of heads.

Photo 2. Discoloration caused by FHB

Photo 3. Wheat head showing infected and healthy sections.

DON

The advisory levels for DON are as follows¹:

1. 1 ppm DON on finished wheat products, e.g. flour, bran, and germ, that may potentially be consumed by humans. FDA is not stating an advisory level for wheat intended for milling because normal manufacturing practices and additional technology available to millers can substantially reduce DON levels in the finished wheat product from those found in the original raw wheat. Because there is significant variability in manufacturing processes, an advisory level for raw wheat is not practical.
   Photo above shows Scabby kernels with shriveling and discoloration vs healthy kernels.
   Photo 4. Scabby kernels showing shriveling and discoloration vs healthy kernels.
2. 10 ppm DON on grains and grain by-products (on an 88% dry matter basis) and 30 ppm in distillers grains, brewers grains, and gluten feeds and gluten meals derived from grains (on an 88% dry matter basis) destined for ruminating beef and feedlot cattle older than 4 months and ruminating dairy cattle older than 4 months, with the added recommendations that the total ration² for ruminating beef and feedlot cattle older than 4 months not exceed 10 ppm DON, and the total ration for ruminating dairy cattle older than 4 months not exceed 5 ppm DON. For chickens, 10 ppm DON on grains and grain by-products with the added recommendation that these ingredients not exceed 50% of the diet of chickens.
3. 5 ppm DON on grains and grain by-products destined for swine with the added recommendation that these ingredients not exceed 20% of their diet.
4. 5 ppm DON on grains and grain by-products destined for all other animals with the added recommendation that these ingredients not exceed 40% of their diet.

---

1. This guidance has been prepared by the Division of Plant and Dairy Food Safety in the Center for Food Safety and Applied Nutrition and the Office of Surveillance and Compliance in the Center for Veterinary Medicine at the Food and Drug Administration (FDA).

2. The total ration includes grains, all grain by-products including distillers and brewers grains, hay, silage, and roughage.

Additional information on DON can be found at: https://www.fda.gov/regulatory-information/search-fda-guidance-documents/guidance-industry-and-fda-advisory-levels-deoxynivalenol-don-finished-wheat-products-human

Management

While there is no single effective management practice, combining a moderately resistant variety with a timely fungicide application for suppression can significantly reduce damage from this disease. It important to have a management plan in place before planting. Over the past several years, LSU AgCenter scientists have evaluated scab severity in variety trials, and in inoculated, misted nurseries at several locations.

These ratings can be found at: http://www.lsuagcenter.com/topics/crops/wheatoats/variety_trials_recommendations or at http://www.wheat.lsu.edu/data.shtml. This information can be used to help a grower choose varieties with moderate levels of FHB resistance along with good yield and agronomic characteristics. Keep in mind that scab is greatly influenced by rainfall and temperature during heading. When comparing FHB, FDK, and DON of varieties in these trials, it is important to compare varieties that head within a few days of each other. Very early or late-heading varieties may escape disease by virtue of flowering at a time when weather was not conducive for infection. The use of misted and inoculated nurseries helps to avoid confounding of genetic resistance with heading date. Determination of genetic resistance should be based on several locations and years when scab was present. LSU AgCenter scientists also collaborate with other scientists across the nation as a part of the U.S. Wheat and Barley Scab Initiative (https://scabusa.org/), and this is an excellent source of information on scab. Efforts from this multi-state initiative are directed toward developing and identifying varieties and management practices that minimize this disease. In addition, new and existing fungicides are evaluated for their ability to reduce infection and spread of scab.

Other practices that may aid in management include: crop rotation with non-host crop, tillage, mowing/shredding, or staggered planting/varietal maturity. At harvest, combine fan speed may be increased to blow out infected seed, which is lighter than healthy seed. This practice can lower FDK, DON, and prevent a reduction in test weight of harvested grain. Additionally, seed cleaning equipment may help remove affected seed but may not be cost effective. These cultural practices alone will not completely manage FHB. An integrated approach is required to lessen the impact of FHB.

• If possible plant moderately resistant, locally adapted varieties.
• Plant high quality seed (Cleaning seed or treating with fungicides are not effective management options for FHB).
• Apply a suppressive fungicide in a timely manner. Triazole fungicides are suppressive on FHB, and some are more effective than others (Figure 1). Generally, applications of Prosaro, Proline, or Caramba at flowering will reduce scab severity and DON while preserving yield.
• More recently, an SDHI/triazole premix marketed as Miravis Ace, has been shown to be competitive with the best triazoles (Figure 2).
• Do not apply a QoI (strobilurin) fungicide after flag leaf emergence. These fungicides can increase DON.

Timing is critical. There is a very short window during flowering to make an effective fungicide application for FHB. The biggest problem is that ideal conditions (wet weather) for FHB infection are not conducive to making fungicide applications by ground. Head coverage also is critical. Sprayers should be calibrated to deliver maximum water volume (minimum 15 GPA by ground, 5 GPA by air) and optimal droplet size (300 to 350 microns). For ground sprayers, nozzles angled at 30° to the horizontal will maximize head coverage. Some research has shown that dual nozzles angled in opposite directions will also increase head coverage. Please refer to the fungicide efficacy table below for more information.

It is common to see 2-3 years of scab epidemics followed by years with little to no disease. In Louisiana, scab epidemics have occurred in 4 of the last 5 seasons. There are disease forecasting tools that predict the likelihood of a scab epidemic based on weather pattern, variety susceptibility, and crop growth stage. The ScabSmart (www.wheatscab.psu.edu) risk assessment tool that is based on temperature and relative humidity is available online, and has regional commentary that will help you to determine scab risk at your given location. This is the only practical way to determine the need to spray since scab symptoms may not show up for a week or more after infection occurs.

For more information, please see the following resources:

www.scabsmart.org

www.scabusa.org

Fungicide Efficacy for Control of Fusarium head scab

Fungicide(s)
Class	Active ingredient	Product	Rate/A (fl. oz)	Head scab1	Harvest Restriction
Strobilurin	Picoxystrobin 22.5%	Aproach SC	6.0 – 12.0	NL	Feekes 10.5
	Pyraclostrobin 23.6%	Headline SC	6.0 - 9.0	NL	Feekes 10.5
Triazole	Metconazole 8.6%	Caramba 0.75 SL	10.0 - 17.0	G	30 days
	Tebuconazole 38.7%	Folicur 3.6 F5	4.0	F	30 days
	Prothioconazole 41%	Proline 480 SC	5.0 - 5.7	G	30 days
	Prothioconazole19% Tebuconazole 19%	Prosaro 421 SC	6.5 - 8.2	G	30 days
	Propiconazole 41.8%	Tilt 3.6 EC2	4.0	P	Feekes 10.5.4
Mixed modes of action	Tebuconazole 22.6% Trifloxystrobin 22.6%	Absolute Maxx SC	5.0	NL	35 days
	Cyproconazole 7.17% Picoxystrobin 17.94%	Aproach Prima SC	3.4 - 6.8	NR	45 days
	Prothioconazole 16.0% Trifloxystrobin 13.7%	Delaro 325 SC	8.0	NL	Feekes 10.5 35 days
	Pydiflumentofen 13.7% Propiconazole 11.4%	Miravis Ace SE	13.7	G3	Feekes 10.5.4
	Fluapyroxad 2.8% Pyraclostrobin 18.7% Propiconazole 11.7%	Nexicor EC	7.0 - 13.0	NL	Feekes 10.5
	Fluoxastrobin 14.8% Flutriafol 19.3%	Preemptor SC	4.0 - 6.0	NL	Feekes 10.5 and 40 days
	Fluxapyroxad 14.3% Pyraclostrobin 28.6%	Priaxor	4.0 - 8.0	NL	Feekes 10.5
	Propiconazole 11.7% Azoxystrobin 13.5%	Quilt Xcel 2.2 SE2	10.5 - 14.0	NL	Feekes 10.5.4
	Prothioconazole 10.8% Trifloxystrobin 32.3%	Stratego YLD	4.0	NL	Feekes 10.5 35 days
	Benzovindiflupyr 2.9% Propiconazole 11.9% Azoxystrobin 10.5%	Trivapro SE	9.4 - 13.7	NL	Feekes 10.5.4 14 days

¹Application of products containing strobilurin fungicides may result in elevated levels of the mycotoxin Deoxynivalenol (DON) in grain damaged by head scab.

²Multiple generic products containing the same active ingredients also may be labeled in some states.

³Based on application timing at the beginning of anthesis (Feekes 10.5.1).

Varietal Resistance to Fusarium Head Blight Disease. Over the past 10 years a very high priority has been placed on development of FHB resistant varieties by all wheat breeding programs, particularly the LSU AgCenter wheat breeding program. Our goal is to develop high-yielding FHB-resistant wheat varieties adapted to the unique environment of the Gulf Coast region and to provide information necessary to help growers deal effectively with FHB. To accomplish this, a misted nursery inoculated with scabby corn kernels is grown at Baton Rouge, Winnsboro, and Alexandria or Crowley in order to characterize FHB reaction of LSU breeding lines and entries in the state variety trials and regional nursery entries. Molecular markers and genomic selection methods are also used to enable ‘stacking’ of several FHB resistance genes in the same variety. This is important because there are no single genes that provide a high level of resistance, but genes can be stacked in a variety to provide a higher level of resistance.

Tables 1 and 2 present the Fusarium head blight data collected in these misted nurseries over the past three years. Keep in mind that this data is from a misted and inoculated nursery and that disease pressure is intense in order to separate varieties. Normal yield plots and grower fields are very unlikely to have disease levels this high.

FHB rating is a measure of scab that occurs on the heads in the field, on a scale of 0 = no infection to 9 = very severe infection. FDK is the percent of kernels that show symptoms of scab (bleaching, pink, and shriveled) in a sample harvested by hand from the nursery and threshed with little air flow so that scabby kernels are captured for rating. DON is concentration (ppm) of the mycotoxin measured in the grain samples. DON analysis is performed by the University of Minnesota DON Testing Lab with financial support from the US Wheat and Barley Scab Initiative, which also helps funds LSU AgCenter breeding efforts.

Photo 5. Misted and inoculated nursery used to evaluate FHB reaction of wheat varieties.

Each table contains data on FHB, FDK, and DON for 1, 2 and 3 years that is available. Varieties are classified as Resistant (R), Moderately Resistant (MR), Moderately Susceptible (MS), or Susceptible (S) based on FDK and DON data for at least two years. There are big differences in FHB reaction of the varieties. If possible, growers should choose a MR or R variety that has good grain yield and agronomic characteristics.

Tables 3 and 4 present the yield data for the LSU AgCenter statewide trials for two years across north Louisiana. Complete data for all locations can be found at: http://www.lsuagcenter.com/topics/crops/wheatoats/variety_trials_recommendations

or at http://www.wheat.lsu.edu/data.shtml .

These tables contain the two-year FHB data, highlighted in the grayed columns on the right side of the yield table. Note that FHB and FDK from the yield plots (non-inoculated and natural infection) are also presented in these tables. FHB and FDK in the yield trials, as would be expected, is much lower than in the misted nursery.

Figure 1. Effect of triazole fungicides applied at flowering on scab.
*Denotes statistically significant difference (P=0.10) compared to the non-treated control.

Figure 2. Effect of triazole and SDHI fungicides applied at flowering on scab.
*Denotes statistically significant difference (P=0.10) compared to the non-treated control.

---

Table 1 (xlsx)

Table 1. Fusarium Headblight Data for LSU Agricultural Center Wheat Variety Trial-Normal Maturity.

---

Table 2 (xlsx)

Table 2. Fusarium Headblight Data for LSU Agricultural Center Wheat Variety Trials-Early Maturity.

---

Table 3 (xlsx)

Table 3. Normal maturity wheat performance trial across North Louisiana for two years, 2018 and 2019.

---

Table 4 (xlsx)

Table 4. Early maturity wheat performance trial across North Louisiana for two years, 2018 and 2019.

---

Acknowledgements:

The authors appreciate and acknowledge support for this research provided by the Louisiana Soybean and Grain Research and Promotion Board.

DON analysis was conducted by the USDA Mycotoxin Diagnostic Laboratory in the Department of Plant Pathology Department at the University of Minnesota under the direction of Dr. Yanhong Dong.

This research is also supported by the U.S. Department of Agriculture, under Agreement

No. 59-0790-4-027. This is a cooperative project with the U.S. Wheat & Barley Scab Initiative.

 

LSU AgCenter Specialists

Specialty	Crop Responsibilities	Name	Phone
Corn, cotton, grain sorghum	Agronomic	Dan Fromme	318-880-8079
Cotton	Agronomic	Dan Fromme	318-880-8079
Grain sorghum	Agronomic	Dan Fromme	318-880-8079
Soybeans	Agronomic	Boyd Padgett	318-614-4354
Wheat	Agronomic	Boyd Padgett	318-614-4354
Pathology	Cotton, grain sorghum, soybeans	Boyd Padgett	318-614-4354
Pathology	Corn, cotton, grain sorghum, soybeans, wheat	Trey Price	318-235-9805
Entomology	Corn, cotton, grain sorghum, soybeans, wheat	Sebe Brown	318-498-1283
Weed science	Corn, cotton, grain sorghum, soybeans	Daniel Stephenson	318-308-7225
Nematodes	Agronomic	Edward McGawley	225-342-5812
Irrigation	Corn, cotton, grain sorghum, soybeans	Stacia Davis Conger	904-891-1103
Ag economics	Cotton, feed grains, soybeans	Kurt Guidry	225-578-3282