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Soybean Variety Response to Taproot Decline (TRD)

Soybean Variety Response to Taproot Decline (TRD) published on No Comments on Soybean Variety Response to Taproot Decline (TRD)

Trey Price, Associate Professor, & Myra Purvis, Research Associate, Agronomic Crop Pathology, Macon Ridge Research Station

Boyd Padgett, Professor, Agronomic Crop Pathology, Dean Lee Research Station

Taproot decline (TRD) of soybean, caused by Xylaria sp., usually is not noticed until pod fill when interveinal chlorosis and necrosis (Figure 1) become evident from the turn row.  However, the disease may cause seed rot, seedling disease (Figure 2), and plant death (Figure 3) at any point the growing season.  Infected seedlings and vegetative stage plants usually go unnoticed because they are quickly covered by rapidly growing neighboring plants.  Infected plants will break at the soil line when pulled.  Roots will appear black when excavated (Figure 4), and are usually in contact with blackened debris from the previous season.  Reproductive structures of the pathogen known as “dead man’s fingers” may appear at the base of affected plants or on other debris during periods of high humidity producing spores that resemble powdered sugar (Figure 5).  Disease distribution within the row usually will have a focal point of dead plants, surrounded by those with foliar symptoms, and neighboring healthy plants.  These areas may overlap creating a clustered and streaky distribution within a given field.  Fields in soybean for two years or more are at risk to taproot decline, and yield losses can be significant.  For more information concerning taproot decline, please read the first report at the following link: https://doi.org/10.1094/PHP-01-17-0004-RS.

Figure 1. Interveinal chlorosis and necrosis.
Figure 2. Taproot decline of seedling.
Figure 3. Plant death caused by taproot decline.
Figure 4. Blackened root diagnostic of taproot decline adjacent to infested debris.
Figure 5. “Dead man’s fingers” produced by Xylaria sp., causal agent of taproot decline.

Many requests for a list of susceptible/resistant varieties have been received prompting the release of preliminary data.  During the past two off-seasons in the greenhouse, we have challenged varieties from the 2016 Official Variety Trials against the pathogen, Xylaria sp.  The process is briefly described hereafter.  We used sterilized millet infested with the pathogen to infest growing medium.  Inoculum was standardized using inoculum concentration experiments (data not shown).  A total of 145 varieties were screened.  During each “run”, 4 replications of 40 varieties (4 seed/4” pot, planted in a linear furrow) were either inoculated at planting or left non-inoculated then removed to flood-irrigated greenhouse tables for three weeks.  Plant roots were harvested, dried to final moisture, and weighed.  The experiment was repeated once, and paired t-tests (α=0.05) were used to compare inoculated (n=8) vs. non-inoculated (n=8) root weights for each variety.  For simplicity, we present the results here as the percentage of root weight reduction.

Paired t-tests indicated that significant root weight reduction occurred at 48% and higher.  Based on percent root weight reduction, varieties were divided into four categories: susceptible (>48%), moderately susceptible (36-48%), tolerant (24-36%), and resistant (<24%).  Out of 145, 97 varieties were deemed susceptible with percent root weight reduction ranging from 48 to 85%.  There were 25 moderately susceptible, 16 moderately resistant, and 7 resistant varieties.  For brevity, we will not present the susceptible varieties in this report.  A list of all varieties included in the screening can be found here.  Resistant, tolerant, and moderately susceptible varieties with corresponding percent root weight reduction are in Tables 1, 2, & 3, respectively.  Field confirmation of these results is ongoing.  Preliminary data from inoculated field trials indicates that varieties deemed resistant in the greenhouse show no significant response.  Varieties deemed susceptible in the greenhouse show significant responses to inoculum in the field.

Table 1.  List of TRD-resistant varieties as determined by inoculation and response.

Variety % Root Weight Reduction
OSAGE 8.391702
CZ 4818LL 18.879462
5N490R2 19.263012
S42RY77 20.944016
5N433R2 22.215409
5067 LL 22.559704
R07-6614RR 22.970824

Table 2.  List of varieties moderately resistant to TRD as determined by inoculation and response.

Variety % Root Weight Reduction
Armor 55-R68 25.253945
RJS47016R 25.793535
CZ 5375RY 26.205598
HBKLL4953 27.339808
4880 RR 27.926596
P5752RY 28.094408
CZ 5225LL 28.605468
ARX4906 29.805397
Go Soy IREANE 30.762175
4995 RR 30.883269
AG 48X7 31.611326
P4788RY 32.46393
AG 46X6 34.502577
S47RY13 35.157094
5625 RR2 35.190462
S49XT07 35.483918

Table 3.  List of varieties moderately susceptible to TRD as determined by inoculation and response.

Variety % Root Weight Reduction
P4814LLS 36.6288
CZ 4105LL 36.631044
GS48R216 37.120729
REV 57R21 37.152585
CZ 4222LL 37.789292
S49LL34 39.360691
P54T94R 39.928806
S12-2418 40.28502
S52RY77 40.607899
REV 51A56 40.734935
P41T33R 41.997581
S11-17025 43.578124
4967 LL 43.925284
S47-K5 43.984519
Armor 46-D08 44.015611
Armor 48-D24 44.107678
Go Soy 5115LL 44.470801
Armor 48-D80 45.47956
REV 56R63 45.566353
REV 49R94 45.659963
Rev 49L49 45.896947
S43RY95 46.122564
5N480R2 46.84488
5N406R2 47.288423
P4588RY 47.58291

In addition to variety selection, data from research trials, numerous observations, and other anecdotal accounts indicate that tillage and/or rotation will reduce TRD incidence and mortality.  To date, there are no recommended seed treatments for taproot decline.  Ongoing research indicates that a few fungicides applied in-furrow at planting may be effective on the pathogen.  Taproot decline is soil/debris borne; therefore, avoiding spread via equipment is recommended.  More research is needed to develop and further refine management strategies for taproot decline.

For more information on these topics or others, please contact your local extension agent, specialist, nearest research station, or visit www.lsuagcenter.com or www.louisianacrops.com.

Louisiana Rice – Tips And Recommended Varieties For 2016

Louisiana Rice – Tips And Recommended Varieties For 2016 published on No Comments on Louisiana Rice – Tips And Recommended Varieties For 2016

lsu-cover-20160127The 2016 version of the Rice Varieties and Management Tips publication is now available online (click here for PDF version). The publication contains the official LSU AgCenter recommendations for all phases of rice production including variety selection, agronomy, fertility, diseases, insects, and weed management.

Hard copies of the publication should arrive at your local county extension office any day now. If you are like me, I like to keep a hard copy of the publication in my truck so I can have it handy when I am in the field and not worry if it gets wet. So, be sure to pick up your copy at your local extension office soon.

Recommended Rice Varieties for 2016 In Louisiana

One of the first decisions that a producer must make every year is determining which varieties to plant. In the Rice Varieties and Management Tips publication, we have a breakdown of every recommended variety to help you make your variety decisions. In addition to the recommended varieties, we also have general information on other commonly grown rice varieties in Louisiana.

Table 1 below shows the recommended varieties and hybrids for production in Louisiana in 2016. More detailed information can be found in the 2016 Rice Varieties and Management Tips publication.

Long Grain Medium Grain Clearfield Special Purpose
Catahoula Caffey CL111 (L) Jazzman
Cheniere Jupiter CL151 (L) Jazzman-2
Cocodrie CL152 (L)
Mermentau CL271 (M)
Roy J CLXL729 (L)
XL753 CLXL745 (L)

2015 Soybean Variety Yields and Production Practices

2015 Soybean Variety Yields and Production Practices published on No Comments on 2015 Soybean Variety Yields and Production Practices

By:

Dr. Ronnie Levy: LSU AgCenter Soybean Specialist

2015 Soybean Variety Yields and Production Practices


For more information please contact Dr. Ronnie Levy at rlevy@agcenter.lsu.edu

Wheat cultural management in Louisiana

Wheat cultural management in Louisiana published on No Comments on Wheat cultural management in Louisiana

by:

Josh Lofton and Steve Harrison, LSU AgCenter


 

As much of the state is just gearing up for harvest of corn, soybeans and grain sorghum, it is time to start preparing for the state’s wheat crop. While wheat planting is still months away, it is this early season management that begins to determine the yield potential for the upcoming season.

Variety selection:

Choosing varieties for the upcoming season is potentially your most important decision prior to planting. Most producers agree that grain yield is the most important criterion for variety selection. However, there are many aspects of grain yield that need to be evaluated when selecting varieties. Two-year average yields give some indication of stability. This not only demonstrates the performance of varieties across various growing environments but also attempts to minimize environmental influence on variety performance (i.e. current year was better for early- or late-maturing varieties). Additionally, test weight is important because varieties with low test weight may result in the producer being docked at the mill.  Therefore, when evaluating variety yield performance, it is essential to use as many parameters as possible.

Heading day, plant height, lodging and disease susceptibility are also important selection criteria. Heading day allows producers to gauge relative maturity of the individual variety. Early-heading and maturing varieties permit earlier harvest and timelier planting in a double-cropping system, while later-heading varieties guard against damage from a late spring freeze and can be planted a little earlier. Early-heading varieties should be planted in the second half of the recommended planting window to avoid the likelihood of spring freeze damage. Lodging resistance helps in some years. Intense storms can occur during late grain fill and cause severe lodging, which results in lower test weight, decreased yields and lower harvest efficiency. Disease susceptibility is very important in terms of yield and profitability. It should be noted that varieties less susceptible to disease may not always produce the highest yields, especially if disease pressure is not present. However, in high disease pressure situations, the resistance may result in higher yields as well as enhanced profitability by saving the costs of fungicide applications. Therefore, managers and producers must weigh the benefits of disease susceptibility with potential yields.

Crop management:

Planting dates for Louisiana wheat depend on location and variety. For southern and central Louisiana optimum planting dates range from November 1 through November 30. The optimum planting for northern Louisiana is slightly earlier, ranging from October 15 through November 15. Early-heading varieties should generally be planted after the mid-date, while late-heading varieties can be pushed a little on the early side of the planting window. The weather in north Louisiana is cooler in the fall and early winter, which slows growth and prevents excess winter growth. It is important that the wheat crop be well-established and fully tillered before going dormant in the coldest part of the winter. Additionally, because of the cooler conditions, the threat for fall pests (Hessian fly, army worms and rust) are decreased earlier in the fall compared to south and central Louisiana. While these dates are the optimum planting window averaged over years, the timing will vary in some years depending on weather patterns. Additionally, if wheat cannot be planted within these optimum windows, planting later than the optimum window would be preferred. Early planting can result in greater insect and fall rust establishment and also makes plants more prone to spring freeze injury due to excessive fall growth and development. Planting too late (more than 14 days after the optimum window) can result in significant stand loss due to slow emergence and seed rotting and can decrease yield potential due to poor tillering and decreased canopy density.

Wheat can be planted by broadcasting seed and incorporating; however, it is preferred that the seed be drilled. Drilling the seed increases the uniformity of depth and stand. If drill seeding, wheat should be planted at a rate of 60 to 90 pounds per acre of high quality seed into a good seedbed with adequate moisture. If the seed is broadcast, seeding rates should be increased to 90 to 120 pounds of high quality seed to account for decreased germination and emergence. This higher seeding rate should be adapted for conditions in which high germination or emergence is not expected, as with late-planted wheat or heavy, wet soils. Late-planted seed should be planted at a higher seeding rate using a drill to ensure rapid, adequate and uniform emergence.

Nitrogen fertilization of wheat can be a challenging aspect of production. Total N application should normally range from 90 to 120 pounds per acre, but this will vary depending on soil type and rainfall after applications. Timing of N application depends on several factors. The wheat crop needs adequate N in the fall and early winter to establish ground cover and properly tiller; however, excessive levels of fall N can result in rank growth and increased  lodging potential, as well as a higher probability of spring freeze damage from early heading. If the wheat crop is following soybeans, soil residual or mineralizable N should be adequate for fall growth, and no pre-plant N is needed. However, if the wheat crop follows corn, sorghum, rice or cotton, the application of 15 to 20 pounds of N per acre would typically be beneficial. Where the wheat crop is planted later than optimum, additional N may be necessary to ensure adequate fall growth prior to winter conditions. If the wheat crop did not receive a fall application and appears to be suffering from N deficiency in January, the initial topdress N application can be made early to promote additional tillering. Early spring is when the majority of N for the wheat crop should be applied. There is no universal rule on how early spring N should be applied. Each field should be evaluated based on tillering, stage of development, environmental conditions and crop color. A crop that has good growth and good color should not need N fertilization prior to erect leaf sheath (Feekes 5), usually sometime in February. However, first spring fertilizer application should be applied prior to first node (Feekes 6) in order to ensure optimum head development, tiller retention and head size. Crop N stress around jointing (Feekes 6) will result in yield losses. Any additional N applied following flag leaf typically contributes very little to crop yield. Splitting topdress N into two or three applications is common in Louisiana production systems due to the increased risk of N losses often associated with heavy rainfall and our long growing season. Splitting N typically occurs by applying fertilizer N at or just prior to jointing with a second application occurring 14 to 28 days later. About 50 percent of the topdress N is normally applied with the first split, but this may be decreased if the first split is put out early and plants are not well enough developed to take up that much N.

Phosphorus, K, and micronutrients should be applied in the fall based on soil test reports. All fertilizers applied as well as lime should be incorporated into the soil prior to planting. Required lime should be applied as soon as possible because it takes time for the lime to begin to neutralize the acidity of most soils. The application of sulfur is a growing concern in Louisiana production systems, with increasing deficiencies appearing every year. Oftentimes, early spring S deficiencies are mistaken for N deficiencies and additional S is not applied. Because sulfur is mobile, similar to N, the application solely in the fall will not be adequate. Supplemental applications of S with spring N applications are often warranted.

 

For further questions or comments contact:

Josh Lofton, Wheat Extension Specialist, jlofton@agcenter.lsu.edu

Steve Harrison, Small Grain Breeder, sharrison@agcenter.lsu.edu