Over the last few weeks, the winter wheat crop has gone through the gamut of late winter/early spring conditions. During the week of February 10th, much of the state experienced bitterly cold temperatures as well as snow and ice. This was followed by nearly ideal conditions for the week of the 17th. This week saw producers out in the fields applying at least the first application of spring N, with many producers on the second application. This also resulted in tremendous growth and development for the winter wheat crop. Conditions changed again, however, in the beginning of the follow week (February 24th– 28th), with cooler, wet conditions which slowed growth and development (especially for the northern portions of the state) for much of the week. This last weekend presented great growing conditions, with adequate soil moisture and temperatures in the 70s and 80s for much of the state. Surprisingly, in the last week, the wheat crop has looked better than it has all year. This has resulted in much of the northern portion of the state showing anywhere from 1-3 nodes, while the southern fraction has progressed somewhat further.
Forecasters are calling for much colder conditions over the next several days. For the southern part of the state, this should be of very limited concern as temperature should be right around the freezing point and will not damage wheat. As for the northern part of the state, while there is some concern, limited damage is expected. It is forecast that temperatures in some areas could reach as low as the mid-20s. However, these temperatures are not expected to last for any sustained period of time. As can be seen from the table below (Kansas State University Extension Service), the wheat crop is still in its most resistant stages of development as it pertains to cold stress, with temperatures needing to be less than 24°F for over 2 hours. Overall, with the yield reduction of last season’s late-season freezes still fresh in our minds, it is justified to be concerned of these freezes as wheat begins to come out of dormancy. However, any damage from this week’s freezes should be mostly cosmetic. Additionally, if temperatures are colder or last longer than expected, only the oldest tillers that are the furthest along should be damaged.
For further questions or comments please contact:
Josh Lofton- Field crop agronomy, State wheat specialist, 318-498-1934
Dr. Daniel Stephenson, LSU AgCenter Dean Lee Research and Extension Center
Dr. Donnie Miller, LSU AgCenter Northeast Research Station
As the snow and ice melt, fields begin to dry, and the extended forecast predicts better conditions for weed management strategies, burndown applications will be going out. Research has shown that burndown applications need to be applied four to six weeks prior to planting to prevent physical competition between weeds and crop as well as reduce the chance of damage from insects such as cutworms. Louisiana corn producers historically have desired to plant corn in late February through early March, so the time is now.
Research has shown that corn yield was 15 to 25% greater when weeds were removed 4 weeks prior to planting compared to 2 weeks. Unfortunately, the cold weather over the last two or three weeks has prevented producers from applying burndown herbicides; therefore, it is likely that many producers will be planting corn in fields that have not been burned-down or were sprayed only one to two weeks prior. In addition to weed competition and possible insect infestation, plant-back restrictions to corn for many herbicides are very important. The standard burndown treatment for many Louisiana corn producers is glyphosate plus 2,4-D or dicamba. There are no labeled plant-back restrictions for glyphosate, 2,4-D, or dicamba, but the LSU AgCenter suggest not more than 0.5 lb ai/acre of 2,4-D be applied within 2 weeks of planting. Products such as Leadoff (generic formulations included), which is often times added by producers to their burndown tank-mix of glyphosate plus 2,4-D for residual control of weeds, does not have a plant-back restriction either. However, a burndown application containing glyphosate, 2,4-D, dicamba, or Leadoff requires at least two to four weeks for maximum activity, which may not prevent physical competition between weeds and corn or control the vegetation in a timely fashion to prevent insect damage if corn is planted within the two to four week window. Products such as Valor and Goal, when tank-mixed with glyphosate, offer some foliar activity on weeds, but they’re primarily utilized for residual control of winter annual weeds when applied as a burndown. However, Valor has a 30 day plant-back interval in conventional tillage corn and a 14 day plant-back interval in minimal tillage corn. If Goal is applied at least 30 days prior to corn planting and at least three rainfalls of 0.25-inches are received, then corn can be planted without worry. If applied within 30 days of planting, Goal needs to be incorporated into the soil to a depth of two or more inches prior to planting. Therefore, if a producer is within two to four weeks of corn planting, burndown applications containing glyphosate, 2,4-D, dicamba, Leadoff, Valor, or Goal are not optimal options based on the issues discussed earlier.
What does a Louisiana corn producer do for burndown if they desire to plant as soon as it dries up? Products that contain paraquat (Gramoxone SL and other generics) or Sharpen should be considered. Both products offer rapid desiccation of weed vegetation and no plant-back restrictions to corn. The positives and negatives of paraquat are well understood by producers and should be utilized properly. Sharpen at 1 oz/A plus 1% v/v methylated seed oil (MSO) is good for burning vegetation down, but increasing the rate to 2 to 3 oz/A will provide residual control of many broadleaf weeds in addition to controlling existing vegetation. Research has shown that tank-mixing Sharpen with glyphosate will control a broader spectrum of weeds and if Sharpen is mixed with a brand name glyphosate (i.e. Roundup PowerMax), then the addition of MSO is not needed for winter annual control. However, if Sharpen is applied alone, addition of MSO is critical to achieve expected weed management. It should be noted that activity of paraquat and Sharpen can be influenced by sunlight, temperature, and coverage; therefore, sunny days and warm temperatures at application with good sprayer output (higher the better) will increase the chances of good weed control. Another thing to consider is an application of a product that contains atrazine at planting following the first burndown application. Atrazine at planting is not a substitute for a burndown application discussed earlier. However, if a producer is forced to apply a burndown application within two weeks of planting, applying atrazine (or a product containing atrazine) will provide good control of weeds that were not completely controlled by the first burndown application.
Ultimately, it is best to burn down winter vegetation four to six weeks before planting, but a producer may not have that option. Therefore, use good judgment when selecting herbicides for burndown. Don’t just assume that glyphosate plus 2,4-D will work if applied within two weeks of planting. It is crucial that weeds be removed so they don’t negatively influence yield. If you have specific questions, please call your local LSU AgCenter county agent or weed scientist.
Dan Fromme1, Beatrix Haggard2, Josh Lofton2, and Rick Mascagni3
Alexandria1, Winnsboro2, and St. Joseph3, respectively
Planting the 2014 corn crop is just around the corner and everyone is asking when we should plant. The goals to a successful corn establishment are a rapid and uniform stand emergence. To achieve this goal, make sure that soil temperatures are adequate. Consequences of planting too early are a delayed and non-uniform stand of corn. The time from planting to emergence varies widely with environmental conditions and to a lesser degree, with planting depth. During this stage, development is affected directly by soil temperature and indirectly by air temperatures.
Importance of Uniform Seedling Emergence
Uneven seedling emergence can cause grain yield losses. When 25% or more of a stand is made up of plants that emerged 7-10 days late, yield losses will approach seven percent. When 25 to 50% of a stand is made up of plants that emerged 21 days late, yield losses will approach 10 percent. When more than 50% of stand is made up of plants that emerged 21 days late, yield losses will approach 20 percent. Yield losses from delayed emergences are related to several factors. First, delayed emerging plants are at a disadvantage for light, water, and nutrients when surrounded by older, larger plants. Plants that emerge early reach the grand growth phase (about V5 or V6) sooner than delayed emerging plants. By the time the delayed emerging plants begin their rapid growth phase, the early emerging plants have leaped ahead of them in terms of overall plant growth. The critical differences in growth stages between early and delayed emerging plants are about two leaves (e.g., V4 versus V2). When the differences in growth stages are more than two, the delayed emerging plants become barren plants (i.e., no ears). Therefore, when delayed emerging plants compose a large percentage of a stand, yield loss is simply equivalent to that associated with late planting. Secondly, delayed emerging plants often silk and pollinate significantly later than the rest of the field. A small number of late tasseling plants scattered throughout the field may not provide adequate amounts of pollen for successful fertilization of the silks.
Three Requirements for Uniform Germination and Emergence in Corn
There are three requirements for a rapid and uniform germination and emergence in corn. First, an adequate and uniform soil temperature is needed. An adequate soil temperature for corn is simply defined as being greater than 50oF at the 2-inch depth. Corn will not germinate or emerge quickly and uniformly when soil temperatures are less than 50oF. Uneven or non-uniform soil temperatures can be caused by different soil types in the field, uneven residue cover in reduced tillage systems and uneven seeding depth control.
Second, adequate and uniform soil moisture is needed at the seed zone. Adequate moisture is when the soil is not too wet or dry. Uneven soil moisture in the seed zone can be caused by different soil types, tillage patterns, and uneven seeding depth control.
Third, an adequate and uniform seed to soil contact is critical. Soil must be firmed around the seed in order for it to imbibe water. When planting conditions are not optimum is when have seed to air contact, seed to clod contact, or seed to trash contact. Seed to air contact occurs when planting into wet soils which results into an open planter furrow. Kernels lying in this open environment are dependent on rainfall for germination and emergence to occur. Seed to clod contact results from planting into cloddy fields created by working the soil too wet. Seed to trash contact results from surface trash falling into the seed furrow during no till planting when soil and or trash are too wet for adequate coulter cutting action.
Influence of Soil Types and Tillage Systems
One management aspect that is often overlooked for planting date determination is tillage systems. It has been well documented in the literature that high residue tillage systems typically warm slower in the spring than those with the soil surface exposed. In addition to these production practices, soil color will also affect the speed at which the soil warms. Darker soils will typically warm faster if they have similar amount of moisture as a lighter colored soil.
Determining When to Plant for a Rapid and Uniform Plant Stand
Rapid and uniform corn emergence helps ensure a strong and vigorous stand establishment. Adequate soil temperature is most simply defined as being greater than 50F at the 2-inch depth. However, when soil temperatures warm to the mid-50’s or greater, emergence will occur in 7-10 days which will give you a better chance of having a rapid and uniform stand. Keep in mind, when average daily soil temperatures are less than or fluctuating about 50oF, corn emergence will occur much more slowly and less uniformly making the seedlings more susceptible to soil borne insects, pathogens, and herbicide injury.
Remember, we have had a cooler than normal winter, make sure soil temperatures are adequate for achieving a rapid and uniform stand. Consequences of planting too early are a delayed and non-uniform stand of corn.
For further questions or comments, please contact:
Dan Fromme, Corn and Cotton Specialist, 318-473-6522 or email@example.com
Josh Lofton, Field crop agronomist, 318-498-1934 or firstname.lastname@example.org
Cold artic air has invaded the southern US, with temperatures projected to reach about 20 F in south Louisiana on the morning of January 7 and into the mid-teens in north Louisiana. This is the coldest in a recent string of cold nights and follows a pattern of cool weather that has predominated since mid-December. From an agricultural perspective this is probably a good thing because it helps control insect problems but it can damage many wheat and oat production fields as well as pastures.
The cold weather has caused some concern among wheat producers in the region. With the major question, how will the low temperatures impact wheat? Generally the answer to this question would depend on the growth and development of the wheat crop. The positive news is wheat that is well-developed, fully tillered but not jointed, and hardened off can withstand temperatures in the low teens with minimal damage. At this stage, the growing point is still below ground level and it would take temperature around 0 F to kill the plants. Additionally, the cold weather of the past month has hardened off the tissue such that it withstands cold temperatures. The positive news is the majority of our wheat is fully tillered and has not jointed. Therefore, it can be expected that the majority of the wheat crop will not sustain any yield loss and probably on fairly minor leaf tissue damage from this cold snap.
Any wheat that has jointed (has nodes above the ground) will be damaged by temperatures that remain below 25 F for several hours. The stems will freeze at growing points below the node and the stem will be effectively girdled and killed. It is not expected that a large amount of wheat has reached these advanced stages and therefore this damage should be minimal. However, if this occurs the stems will be discolored (split with a knife) and the tillers will bleach out and die over the next 10-14 days with warmer weather. The good news is, as long a majority of the tillers have not jointed, it is still quite early in the growing season the yield loss may still be relatively minor even if primary tillers are lost.
Oats are more susceptible to freeze damage than wheat and there is a wide range in the level of cold tolerance among oat varieties. Temperatures approaching 10 F can severely damage most oat varieties. While the amount of leaf tissue burn with oats will be more intense, it is expected that a majority of the oats will only incur minimal if any loss to yields.
This has been a very good start for the wheat growing season. The majority of the region should have certainly met our cold requirement for most of our wheat varieties. The cool weather has prevented excessive growth and the crop is in excellent shape. Growers concerned about freeze damage probably want to wait 7-10 days for leaf damage symptoms to show as dried, bleached tissue. Keep in mind that leaf tissue damage is superficial and should not impact yield.
Glyphosate-resistant (GR) Italian ryegrass has been documented in Mississippi and growers have been forced to adopt practices to manage it. GR Italian ryegrass has been shown to significantly reduce corn yield and is troublesome in cotton and soybean if not controlled. LSU AgCenter weed scientists currently have samples from multiple locations in Louisiana where glyphosate did not control the Italian ryegrass populations this past spring. Preliminary data indicates that GR Italian ryegrass is present in Louisiana. As a consequence, Louisiana crop producers need to begin mitigation/management programs.
Drs. Jason Bond and Tom Eubank, weed scientists with Mississippi State University, have published excellent programs to control GR Italian ryegrass in corn, cotton, soybean, and rice. The programs can be found at http://msucares.com/pubs/infosheets_research/i1355.pdf. Their research has shown that fall applications of Dual Magnum at 1.33-1.67 pints/acre (corn, cotton, soybean), trifluralin at 3 pt/A (cotton, soybean), Boundary at 2 pints/acre (soybean), or Command at 2 pints/acre (rice) provide excellent control of GR Italian ryegrass. Boundary has received a 24c label for fall application in Louisiana.
All afore mentioned fall-applied herbicides should be tank-mixed with paraquat at 0.5-0.75 lbs. a.i./acre to kill any emerged Italian ryegrass. Their research also showed that double-disking in the fall is another option. In mid-January to mid-February, either 12-16 oz./acre of Select Max or the equivalent rate of a 2 lb/gallon clethodim is needed if Italian ryegrass begins to emerge, but a 30 day preplant interval is required if corn or rice will be planted. In the spring, if glyphosate applied as a burndown is not effective for control of Italian ryegrass, their research indicates that two applications of paraquat at 0.75-1.0 lb a.i./acre spaced 14 days apart will be required for control. Adding either atrazine (corn) at 1 quart/acre, metribuzin (soybean) at 4 oz./acre, or diuron (cotton) at 1.5 pints/acre with the first paraquat application will increase efficacy of paraquat against GR Italian ryegrass.
Steps should be taken to mitigate and/or manage GR Italian ryegrass. If you have questions, please call your local LSU AgCenter county agent or Dr. Daniel Stephenson (318-308-7225) or Dr. Donnie Miller (318-614-4044).
BY: Dr. Daniel Stephenson, Weed Scientist, LSU AgCenter
The recent cool, wet weather can influence herbicide application decisions for weed management in corn. Numerous acres of corn in Louisiana were damaged by frost this past weekend and a majority of that corn ranges V3 to V5 (3 to 5 visible collars). The damage is seen as leaves that are necrotic. Add this to the corn that has been sand-blasted, wind-blown, and/or had its growth hampered by cool temperatures and wet soils, corn in Louisiana does not look as normally expected for late April. The current condition of the Louisiana corn crop has to be considered when appling a postemergence herbicide application.
One issue is plants that were damaged by a frost often appear less developed than they really are. Many herbicide labels contain application restrictions based upon corn development stages (growth stages) or plant height. In a normal year, Louisiana corn producers apply their herbicides well before any restriction specified by a label. Imagine you want to apply a herbicide whose label specifies application prior to V5 (five visible collars). However, two leaves were lost due to frost damage earlier in the season, so the corn is actually at V7. If applied, the application would be off-label. Care should be taken to count corn collars to ensure the herbicide application follows the label.
Another issue to consider is the potential for herbicide injury to the frost-damaged corn. In many of the phone calls I have had, the leaf in the whorl is relatively healthy (green and intact). Therefore, proper growth can be expected if the environment cooperates. However, I suggested that producers delay their herbicide application until new growth is observed (i.e. the new leaf has unfurled out of the whorl). Secondly, the addition of adjuvants that contain oil-based additives to the tank should be avoided to minimize phytotoxicity. With the past environmental conditions already hampering the growth of the crop, avoid further injure the corn crop with a herbicide application.
The cool environmental conditions that are affecting the corn crop may also have an effect on the weeds. Frost does not play favorites, so it may injure a weed as well. Frost damaged leaf tissue will not absorb and translocate a herbicide properly, which may lead to less than expected control. Like corn, ensure the weeds are actively growing prior to a herbicide application. Please understand that I am not advocating waiting until the weeds are bigger to make the application. It is always easier to kill a small weed versus a large weed.
Preliminary Yield Data: The LSU AgCenter Cotton Extension Program conducted a total of fifteen trials throughout the cotton growing areas of the state in 2012. Yields were determined by weighing cotton in a boll buggy equipped with weigh scales. Samples of each variety were retained and ginned in a 20-saw gin at the Northeast Research Station for turnout.