Please click the picture below to view the effects of weathering on grain sorghum by Dr. Dan Fromme.
The 9th installment of Louisiana Rice Field Notes is now available. This is the second flood edition this week. This edition covers recommendations on how to proceed with harvest with all of the flood damaged rice, a very important proposed changed to the crop insurance “practical to replant” definition and the final planting dates (FPD) for rice, corn, sorghum, cotton and soybeans, and an important flood recovery meeting in Crowley tomorrow.
The 8th installment of Louisiana Rice Field Notes is now available. This edition covers potential damage to rice caused by the flood, an estimate of the economic impact of the flood to the unharvested rice crop, effects on the ratoon rice crop, comments and pictures from rice producers and consultants.
Assessment of Weed Control Programs and Post-harvest Weed Control in Problem Fields.
Josh Copes, Donnie Miller, and Daniel Stephenson
Assessment of weed control programs.
With corn harvest underway and soybean and cotton fields approaching maturity, this is a great time to evaluate this year’s weed control programs. Things to consider include: what herbicides were applied, when they were applied in respect to crop and weed growth stages, what were weather conditions like before and after application, and what weed species are present after final weed control efforts. In addition, knowing which fields contain glyphosate-resistant weeds and other difficult to control species that escaped control can help us better plan and budget for more effective herbicide programs. These factors will help critically evaluate weed control programs and may offer insights into becoming more effective at herbicide selection, improving application timing, and how environmental conditions may dictate the need for more aggressive weed control tactics in certain fields.
Post-harvest weed control.
The time period from corn harvest and the first killing frost can range from 1 to 4 months. The average first frost date in North and Central Louisiana is November 15 and 25, respectively. A lot of money and effort is spent in controlling weeds during the growing season to negate yield loss. With the extended window from harvest to first frost, weeds will continue to emerge and produce seed. Timely weed control practices following harvest (post-harvest weed control) can reduce weed seed return to the soil, thus ensuring fewer weeds to fight in future cropping seasons. Post-harvest weed control is especially important in fields containing herbicide resistant weeds. A good example to illustrate the importance of post-harvest weed management is the ability of glyphosate-resistant Palmer amaranth to produce mature seed in as little as 30 days after emergence during late summer and early fall. Many other grass and broadleaf weeds are capable of setting viable seed in a similar time frame.
For weeds that are present in the field at harvest time, mowing and/or tillage should be conducted as soon as possible upon harvest to ensure viable seed set is eliminated or reduced. Rainfall will influence subsequent germination of weed seed and therefore the need for additional weed control. Furthermore, rainfall following cultivation could increase weed seed germination, however, if the weeds are controlled the soil seedbank would be reduced.
Other methods of weed control include the use of herbicides. Herbicide applications should be targeted from late-September through October when the time period from application to first killing frost is shortened. Multiple herbicide applications for post-harvest control of summer annual weeds should be avoided. Residual herbicides such as S-metolachlor, pyroxasulfone, linuron, and diuron, among others, can be applied in the fall following harvest. However, rotation interval restrictions must be followed and length of residual control will be influenced by soil temperature and saturation. Glyphosate plus 2,4-D and/or dicamba or paraquat plus diuron and/or linuron are some choices for late-fall post-harvest applications. Diuron and linuron will offer soil residual; however, if soil temperatures are warm and rainfall frequent, do not expect long residual from these products. Likewise the lack of rainfall to properly activate residual herbicides to minimize weed germination can negatively impact treatment effectiveness. Maximize water volume to ensure good weed coverage as this is critical for good weed control, especially for paraquat plus diuron and/or linuron.
To reiterate, weeds are capable of setting viable seed within 30 days after emergence during late summer and early fall. Post-harvest weed control is especially important when combatting glyphosate-resistant weeds such as Palmer amaranth, waterhemp, or johnsongrass. Problem fields should be identified and receive top priority for preventing seed return. Once harvested these problem fields should be mowed or tilled shortly after harvest to prevent and/or reduce seed set. Fields should then be regularly scouted for emerging weeds and additional control tactics applied prior to seed set. This will require close inspection of weed species to determine when they are flowering. Once a weed species is observed flowering a weed control operation should be implemented. Depending on weather conditions following harvest, weed control tactics may need to be implemented approximately every 3 to 4 weeks until a killing frost has occurred. If glyphosate-resistant Palmer amaranth or waterhemp is an issue, a management tactic (i.e. mowing, tillage, herbicide application) should be done every 3 to 4 weeks.
If you have any questions please contact us.
This issue contains information on the South American rice miner, the new Provisia rice system, grain spotting and pecky rice, Field Day highlights, north east Louisiana research in 2016, and rice sustainability.Click to open
Southern Corn Rust Confirmed in Louisiana
Trey Price, Extension/Research Plant Pathologist, Macon Ridge Research Station
Based on a tip from an industry representative, southern rust, Puccinia polysora, was suspected along the Atchafalaya River in milk to early dough stage corn. Yesterday afternoon samples were collected from two locations (Woodside and Lettsworth) and confirmed to be southern rust this morning via microscopic examination. Since then, other similar reports have come in from Rapides and Bordelonville. Incidence in these fields is very low (<1%). Given the stage of the crop and low incidence, I would not recommend treating these fields. Current conditions (warm/humid) are favorable for disease development and producers, agents, and consultants should monitor for disease development in their corn fields. It is noteworthy that we have detected southern rust about one month earlier in 2016 than in 2015.
Scouting is key to managing southern rust. First, identify the disease correctly. Southern rust pustules will appear reddish orange and will almost always occur on the upper side of the leaf (Figure 1). In severe cases pustules may appear on leaf sheaths and husks (Figure 2). Common rust, which has been very common this year, will appear more brick red, and pustules will occur on both sides of the leaf (Figure 3). Most common rust has ceased to develop because of the warm temperatures, and pustules have turned brown. There are differences in susceptibility to southern rust among hybrids; therefore, it is important to define disease incidence/severity prior to making management decisions.
If southern rust is not present, fungicide applications are not necessary. If southern rust occurs near tasseling, a fungicide application will likely be needed for management and provide economic benefit (See Table 1 for products and efficacy) as this disease can be very aggressive under optimal conditions. As the crop matures from tasseling stage, a return on fungicide investment becomes increasingly less likely (See Table 2). Application decisions must be considered on a field by field basis taking into account disease incidence/severity, crop stage, prevailing environmental conditions, and likelihood of economic return. If a fungicide application is deemed necessary, using recommended rates and maximum water volumes will increase efficacy. Ideally, fungicides should be applied prior to disease onset, but realistically, fungicides are usually applied at or just after onset. Therefore, individuals should make efforts to detect and treat diseases as early as possible to prevent losses to yield and quality. Later planted corn is at higher risk for developing southern rust that requires management.
Table 1. Fungicide efficacy for control of corn diseases.
The Corn Disease Working Group (CDWG), which includes many members from the mid-South including several pathologists from Louisiana, has developed the following information on fungicide efficacy for control of major corn diseases in the United States. Efficacy ratings for each fungicide listed in the table were determined by field testing the materials over multiple years and locations by the members of the committee. Efficacy ratings are based upon level of disease control achieved by product, and are not necessarily reflective of yield increases obtained from product application. Efficacy depends upon proper application timing, rate, and application method to achieve optimum effectiveness of the fungicide as determined by labeled instructions and overall level of disease in the field at the time of application. Differences in efficacy among fungicide products were determined by direct comparisons among products in field tests and are based on a single application of the labeled rate as listed in the table. Table includes systemic fungicides available that have been tested over multiple years and locations. The table is not intended to be a list of all labeled products1. Efficacy categories: NR=Not Recommended; P=Poor; F=Fair; G=Good; VG=Very Good; E=Excellent; NL = Not Labeled for use against this disease; U = Unknown efficacy or insufficient data to rank product
1Additional fungicides are labeled for disease on corn, including contact fungicides such as chlorothalonil. Certain fungicides may be available for diseases not listed in the table, including Gibberella and Fusarium ear rot. Applications of Proline 480 SC for use on ear rots requires a FIFRA Section 2(ee) and is only approved for use in Illinois, Indiana, Iowa, Louisiana, Maryland, Michigan, Mississippi, North Dakota, Ohio, Pennsylvania, and Virginia.
2Harvest restrictions are listed for field corn harvested for grain. Restrictions may vary for other types of corn (sweet, seed or popcorn, etc.), and corn for other uses such as forage or fodder.
Many products have specific use restrictions about the amount of active ingredient that can be applied within a period of time or the amount of sequential applications that can occur. Please read and follow all specific use restrictions prior to fungicide use. This information is provided only as a guide. It is the responsibility of the pesticide applicator by law to read and follow all current label directions. Reference to products in this publication is not intended to be an endorsement to the exclusion of others that may be similar. Persons using such products assume responsibility for their use in accordance with current directions of the manufacturer. Members or participants in the CDWG assume no liability resulting from the use of these products.
Table 2. Estimated % corn grain yield loss due to defoliation at various growth stages.
Adapted from the National Crop Insurance Service’s Corn Loss Instruction to represent the leaf collar growth staging method. Included in the Mississippi State University, Grain Crops Update June 4, 2010, Erick Larson.
If you require additional information, please do not hesitate to contact your nearest county agent, research station, or specialist.
The EPA has granted a section 18 request for the use of Transform (sulfoxaflor) for 2016 Louisiana cotton production season. Please see the link below for information on conditions and restrictions outlined by the section 18 label.