C.O.R.N. Newsletter 2007-08

Dates Covered: 
April 10, 2007 - April 16, 2007
Steve Prochaska

Burndown Herbicide Activity - Can We Kill Anything When It’s This Cold?

Authors: Mark Loux

The effectiveness of burndown herbicides can be reduced in cold weather, and we expect to observe sub-optimum performance from herbicides applied late last week or early this week due to the cold conditions. At the same time, soil conditions in many fields are suitable to allow traffic, and rain is forecast for later in the week, so it’s reasonable to expect that herbicides will be applied before the return of warmer weather. We can try to provide some guidance to maximize herbicide activity, but activity can be fairly unpredictable during periods of adverse weather. It is therefore difficult for us to be certain that any of these suggestions will ensure effective control where applicators choose to spray this week.

1. The best strategy is to delay herbicide applications until the return of warmer weather. Even waiting until the end of this week may allow for an improvement in herbicide activity. Our general suggestion is to avoid applying herbicides when nighttime temperatures are below 40 degrees. Allowing for several days of warmer weather prior to application may result in more effective control than applying on the first warm day. By “warm”, we mean daytime temperatures in the high 50’s to low 60’s, and nighttime temps above 40. Weed scientists from North Dakota (a relatively cold place) suggest that when night temperatures fall below 40 degrees, herbicides should not be applied unless temperatures during the day are above 60.

2. The effect of cold on herbicide activity is likely to vary by weed species and size. We expect that burndown treatments may retain much of their effectiveness on small summer annual weeds that have emerged within the past several weeks. Conversely, activity can be greatly reduced on overwintered winter annuals, biennials, and perennials. For some weeds, such as chickweed and purple deadnettle, burndown treatments may eventually work, but activity may be extremely slow. The problem with slow activity is that there can still be a green mat of weeds at the time of planting, which can interfere with crop establishment and harbor insects. We expect that control of tough no-till weeds such as wild carrot, dandelion, dock, and large marestail will generally decrease. In a study we conducted several years ago at OARDC Northwest Ag Station near Custar, control of dandelion with glyphosate/2,4-D decreased to near zero when herbicides were applied during a period of cold weather at the end of April. For the tougher no-till weeds, failure of an initial herbicide application to control a weed can result in a situation where the weeds become hardened off and even less susceptible to subsequent herbicide applications (i.e. they get “ticked off”).

3. Now for the hard part – specific suggestions for herbicide treatments applied this week. Probably the best advice we can give to maximize activity of burndown treatments is to combine several herbicides that work well together, and increase herbicide rates. Whether following this advice will result in effective control during cold weather is debatable, and waiting for the return of warmer weather is likely to be a more successful strategy. Single ingredient applications, such as glyphosate or 2,4-D ester applied alone, may be affected more by weather compared with application of mixtures of glyphosate and 2,4-D ester. Apply a mimimum of 0.75 lb ae/A of glyphosate and 1.0 lb ai/A of 2,4-D ester where there is adequate time between application and soybean planting, and use a glyphosate rate of 1.1 to 1.5 lb ae/A where the 2,4-D is applied at rates lower than 1.0 lb.

4. Control in soybeans may be improved by applying glyphosate plus 2,4-D ester plus one of the following: Canopy EX, Canopy DF, Synchrony XP, Valor XLT, Sonic, Authority First, or Gangster. While the Valor component of Valor XLT and Gangster may improve the speed of burndown in these types of mixtures, our research shows that Valor can antagonize the activity of glyphosate/2,4-D on dandelion unless chlorimuron or cloransulam is included in the mix. This antagonism may be exacerbated under cold conditions. We would be cautious about full rates of metribuzin (Sencor, etc) with glyphosate/2,4-D this week for the same reason. Conversely, Gramoxone is most effective when applied with 2,4-D ester plus metribuzin or Canopy DF. This might be a week where Gramoxone is a better choice than glyphosate in some fields as long as we get some sun and some daytime temps in the 50’s (the theory here being that because Gramoxone’s activity does not rely on translocation in the plant, cold night temperatures have less effect on it than on glyphosate). We suspect, however, that Gramoxone treatments in soybeans may not be any better than glyphosate/2,4-D treatments on truly tough no-till weeds under cold conditions

5. Due to the synergism between Gramoxone and atrazine, the combination of these herbicides may be more effective than systemic herbicides in no-till corn under cold conditions. Combinations of atrazine plus Gramoxone (plus 2,4-D for certain weeds) are even more effective than combinations of Gramoxone plus Sencor. A list of the most effective corn burndown programs in OSU research for control of a variety of common broadleaf weeds includes the following: Lexar/Lumax; glyphosate + atrazine; Basis/Resolve + atrazine; dicamba + atrazine; Gramoxone + 2,4-D + atrazine; and Radius/Balance + atrazine + glyphosate. We assume that, under cold conditions, we would be more likely to observe antagonism between glyphosate and atrazine on the more tolerant and larger weeds. Lexar and Lumax have been among the more consistent burndown treatments in OSU research, but we assume their activity could also be reduced under cold conditions. We observed more effective dandelion control with a combination of Lumax plus 2,4-D ester compared with Lumax alone in one study in northwest Ohio, so the addition of 2,4-D ester may help maintain control under cold conditions.

6. Use the appropriate spray adjuvants. We suggest using true ammonium sulfate (AMS) with glyphosate-containing treatments under the current weather conditions, especially where the effectiveness of an AMS substitute product is unknown (see article that follows). While the labels for many “loaded” glyphosate products allow the use of additional nonionic surfactant, we doubt that this will overcome the effect of cold weather of glyphosate activity. However, it can still be a good practice to add nonionic surfactant to certain glyphosate products that contain less surfactant. The addition of crop oil concentrate or 28% to glyphosate-containing mixtures may reduce the effectiveness of glyphosate. Burndown mixtures that do not contain glyphosate should generally be applied with crop oil concentrate, and the addition of some 28% may also improve control. In no-till corn, mixtures of Gramoxone plus atrazine are most effective when the spray solution contains a high concentration of 28%, or 28% is used as the spray carrier.

Water Conditioners for Glyphosate Applications

Authors: Mark Loux

The following article was written by Bob Hartzler, extension weed management specialist at Iowa State University, and was posted on the ISU Weed Science webpage http://www.weeds.iastate.edu on January 22, 2007.

AMS (ammonium sulfate) is widely used with glyphosate to enhance its performance. AMS is different than other spray additives (surfactants, crop oil concentrates, etc.) in
that AMS is primarily active in the spray tank (negating the effect of antagonistic salts) rather than at the leaf surface. While AMS is a cost-effective means of counteracting the negative effects of antagonistic salts in water, many applicators desire alternatives due to the inconvenience of handling and dissolving AMS in the spray tank. A variety of products, often referred to as water conditioners, have been introduced as AMS substitutes in order to avoid the problems associated with handling AMS. Water conditioners typically contain a number of ingredients, including AMS, surfactants, anti-foaming agents, etc. University research has shown that not all water conditioners are as effective as AMS at protecting glyphosate performance when hard water is used as the carrier. Differences in performance among conditioners probably are related to how much AMS is found in the product. Spray additives are not regulated, thus manufacturers are not required to provide specific information regarding quantities of AMS or other active ingredients found in the product. Because of this, it is difficult, or impossible, to know exactly how much AMS the water conditioner provides.

The influence of AMS and several water conditioners on the efficacy of glyphosate against velvetleaf was evaluated by the University of Nebraska, using either distilled water (no cation) or water with 160 ppm Fe added. In the absence of antagonistic cations, all additives provided velvetleaf control equivalent to or better than glyphosate alone. However, when hard water was used as the carrier (Fe added), several of the products were less effective than AMS at eliminating the effect of the antagonistic salts, and two products actually resulted in poorer control than glyphosate alone.

The reason for water conditioners failing to perform as well as AMS in hard water is probably due to them containing an insufficient quantity of AMS. The solubility of water in AMS is 5.9 lb/gal at 32 F, but since water conditioners contain other
ingredients they always contain less AMS than 5.9 lb/gal. Typical use rates of water conditioners are 0.25 to 1% v/v. Thus, if a conditioner contained 4 lb AMS/gal and was applied at a rate of 1% v/v, it would apply the equivalent of 4 lbs/100 gal. Most
glyphosate products recommend 8.5 to 17 lbs/100 gal, thus water conditioners provide much lower rates of AMS than recommended on glyphosate labels.

So, what's the bottom line on conditioners? In situations where hard water is used as a carrier, many water conditioners may not be as effective as AMS at eliminating the antagonistic effect of Fe, Ca, Mg and other salts. However, most water sources in
Iowa contain relatively soft water and the full rate of AMS is not required to counteract antagonistic cations. Thus, water conditioners may sufficiently counteract negative effects of the carrier due to low levels of antagonistic cations. The only way to
determine whether a water conditioner is appropriate is to determine the hardness of the water used as a carrier and the amount of AMS in the specific product.

Acknowledgement: Much of the information and data in this article was adapted from an article prepared by Mark Bernards, Extension Weed Specialist at University of Nebraska.
Mark L. Bernards. 2007. AMS - What is it doing in my tank? Proceedings 2007 Crop Protection Clinics. University of Nebraska-Lincoln.

What Will Cold Temperatures Do To Our Wheat?

Authors: Pierce Paul, Jim Beuerlein, Dennis Mills

Over the last few days, average temperatures have dropped considerably, with lows between 20 and 29F and highs between 34 and 40F. The wheat in now greening up across most of the state, but in some southern counties, early planted wheat is already jointing. Growers, especially in southern Ohio, are concerned that the cold temperatures may have damaged their crop. Whether or not the crop is damaged by cold spring temperatures and the extent of the damage depend on three main conditions: 1) how cold it gets, 2) the length of time the crop is exposed to the cold temperatures and 3) the growth stage of the crop at the time of exposure. Freezing temperatures are most damaging when the crop is at more advanced stages of development. Once it warms up in the spring and the wheat starts to grow, it looses its cold-temperature hardiness, making it more prone to injury from freezes. Such injuries are most severe when freezing temperatures occur during boot and heading growth stages.

We have certainly had extended periods of temperatures below freezing over the past 5 days or so, however, at our current growth stage (tillering to jointing), freeze injuries will likely be less than they would have been if we were at boot or heading. Based on information coming out of a Kansas State University publication http://wheat.colostate.edu/freeze.pdf temperatures below 12 F are injurious during tillering, where as, during jointing 2 hours of exposure to 24 F may be injurious. At these growth stages, injuries tend to be greatest if the wheat is lush and actively growing (especially after spring nitrogen application) and are more common in low areas of the field.

Frost injury during tillering appear as light green to yellow discoloration (burning) of the tips of the leaves (early symptoms may be confused with those caused by some viruses and nutrient deficiency). Although these injuries may reduce tiller numbers, at this early growth stage, the wheat crop still has time to recover and produce new leaves and tillers once it warms up. In addition, since the growing points are still close to the soil line, they are protecting from cold temperatures injury.

Once the wheat starts to joint, which may be the case in some southern counties, the growing point is no longer protected by the soil, but is somewhat protected by the vegetation and its nearness to the soil surface. Also wheat is a cool season crop and can tolerate temperatures well below freezing. In addition to discolored leaf tips, the growing point of injured plants will become brownish, with a water soaked appearance. To assess the extent of the injury, remove the leaves, split the stem longitudinally (lengthwise), and examine the growing point, which is located above the uppermost node. Examine both main and secondary tillers from different areas of the field and determine the average number of healthy and injured tillers per foot of row. A healthy growing point is usually white to yellowish-green in color as opposed to off-white or brown. When the growing point is severely damaged, growth of the affected stem stops, even on healthy-looking plants. In extreme cases, the leaves in the whorl die and the affected tiller may not produce a head, however, secondary tillers may remain unaffected and should develop normally and produce grain.

Alfalfa Weevil Present?

Authors: Ron Hammond, Bruce Eisley

With warmer temperatures now occurring, alfalfa growers plan on scouting for alfalfa weevil in the coming weeks. The need for scouting is especially true in southern counties where heat unit accumulation has reached the 300 HU last week needed for egg hatch and beginning feeding. Although central and northern Ohio is behind this accumulation of heat units, growers in those areas should begin their scouting over the next 1-2 weeks. Remember that fields that have a south facing slope tend to warm up sooner and need to be checked for weevil earlier.

Alfalfa weevil scouting is accomplished by collecting a series of three 10-stem samples randomly selected from various locations in a field. Place the stem tip down in a bucket. After 10 stems have been collected, the stems should be vigorously shaken in the bucket and the number of larvae in the bucket counted. The shaking will dislodge the late 3rd and 4th instar larvae which cause most of the foliar injury. Close inspection of the stem tips may be needed to detect the early 1st and 2nd instar larvae. The height of the alfalfa should also be recorded at this time. Economic threshold is based on the number of larvae per stem, the size of the larvae and the height of the alfalfa. The detection of one or more large larvae per stem on alfalfa that is 12 inches or less in height indicates a need for rescue treatment. Where alfalfa is between 12 and 16 inches in height, the action threshold should be increased to 2 to 4 larvae per stem depending on the vigor of alfalfa growth. See the OSU Alfalfa Weevil FactSheet http://ohioline.osu.edu/ent-fact/0032.html for more on alfalfa weevil scouting and thresholds. For insecticides that are labeled for alfalfa weevil, see http://entomology.osu.edu/ag/545/aiaw.pdf . Remember that it is still too early to scout for potato leafhopper since they do not move into Ohio until May.

Monitoring for Corn Insects

Authors: Ron Hammond, Bruce Eisley

We have begun trapping for some of the agronomic insects that can cause problems in Ohio. At the present time we have pheromone traps in the field for black cutworm and common armyworm. Other traps will be added later in the season for European corn borer and western bean cutworm. Pheromone traps will not tell us if a particular insect is going to be a problem or in which field(s) the problem is going to occur, but the traps can be used to track insect emergence, movements and when peak populations occur. Information from the traps will be reported in future newsletters and on the web at: http://entomology.osu.edu/ag/07traps.htm

Avail – Can It Improve Phosphorus Fertilizer Efficiency?

Authors: Robert Mullen

A new additive to phosphorus fertilizer is currently being marketed in Ohio called Avail. Unfortunately, at this point limited research data is available from land-grant universities to validate its efficacy, but some data out of Kansas on corn is intriguing. Avail is a polymer that can be used as a coating for dry phosphorus or as an additive to liquid phosphorus fertilizers. The polymer has an extremely high cation exchange capacity (reportedly 1800 meq/100 g) that binds soil cations calcium, magnesium, and aluminum decreasing their ability to interact with phosphorus in solution. The primary mechanisms affecting phosphorus plant availability are interactions with positively charged species (calcium, magnesium, aluminum, iron, etc.) in soil solution. Theoretically, application of this material with a phosphorus fertilizer source should improve phosphorus availability at least in the short term.

Data collected at Kansas State University in 2001-2003 showed that Avail coated monoammonium phosphate (MAP) applied at planting increased corn yields in two of the three years compared to uncoated MAP http://www.oznet.ksu.edu/library/crpsl2/srp957.pdf (page 34). The soil test P level was 23 ppm using Bray-Kurtz P1 extractant and not considered deficient.

The greatest concern regarding Avail is that very little information is available at this point, so widespread use of this product may not be warranted. The other issue to be considered is how does high soil P fertility affect response. High P soils are unlikely to benefit from application of this material, but research information is not available at this time.

Managing Pollen Contamination of Non-GMO Corn

Authors: Peter Thomison

Transgenic (GMO) corn acreage is likely to soar in 2007 with greater planting of Roundup Ready and Bt corn hybrids. Pollen from corn containing transgenic traits may contaminate (by cross-pollination) nearby non-GMO corn. Ohio growers of identity preserved (IP) non-GMO corn should become more familiar with planting practices that limit pollen drift from nearby GMO corn fields. Several methods, including isolation and border rows, planting dates, and hybrid maturity, are effective in limiting exposure of non-GMO corn fields from pollen of GMO fields. For more details concerning these methods, consult Extension Fact Sheet AGF-135, Managing "Pollen Drift" to Minimize Contamination of Non-GMO Corn; it’s available online at http://ohioline.osu.edu/agf-fact/0153.html .

Yield and April Nitrogen Applications to Wheat

Authors: Edwin Lentz, Robert Mullen, Jim Beuerlein

Producers still have time to apply their spring top-dress of nitrogen. Ohio State University research has shown that yields are not affected by delayed nitrogen until after early stem elongation. Studies over the last five years have shown that yields were the same or slightly better when a single application occurred at Feekes 6 (first node visible of early stem elongation) compared to initial green-up. Yields dropped 10 – 15% when a single application was delayed to early boot stage. We would recommend that producers not wait until early jointing but apply as soon as field conditions allow application equipment. At this time of year, any nitrogen source would be appropriate, so selection should be based on cost and availability. These studies were completed at the Northwest and Western OARDC Research Stations, Hoytville and South Charleston, respectively. In addition to the nitrogen research, we investigated the affects of adding sulfur in the top-dress. We did not observe any yield increase from supplemental sulfur. These results would suggest minimal benefit from adding sulfur to wheat on medium to fine-textured mineral soils that contain adequate organic matter. We would recommend sulfur for sandy or gravelly soils or soils with low organic matter.

Archive Issue Contributors: 

Peter Thomison (Corn Production), Jim J. Beuerlein (Soybean and Wheat Production), Anne Dorrance, Pierce Paul and Dennis Mills (Plant Pathology), Ron Hammond and Bruce Eisley (Entomology), Robert Mullen (Agronomy) and Mark Loux (Weed Science). Extension Educators and Program Agents: Woody Joslin (Shelby), Howard Siegrist (Licking), Glen Arnold (Putnam), Keith Diedrick (Wayne), Todd Mangen (Mercer), Bruce Clevenger (Defiance), Greg LaBarge (Fulton), Mark Koenig (Sandusky), Gary Wilson (Hancock), Ed Lentz (Seneca), Harold Watters (Champaign), Steve Bartels (Butler), Wes Hahn ( Logan), Jonah Johnson (Clark), Jim Lopshire (Paulding), Allen Sundermeier (Wood) and Steve Prochaska (Crawford).

About the C.O.R.N. Newsletter

C.O.R.N. Newsletter is a summary of crop observations, related information, and appropriate recommendations for Ohio crop producers and industry. C.O.R.N. Newsletter is produced by the Ohio State University Extension Agronomy Team, state specialists at The Ohio State University and the Ohio Agricultural Research and Development Center (OARDC). C.O.R.N. Newsletter questions are directed to Extension and OARDC state specialists and associates at Ohio State.