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April 14-21, 2003
C.O.R.N. 2003-9
In This Issue:
A) Common Lambsquarter - A Difficult to Control Weed in Soybeans
B) Use of 2,4-D Ester in No-Till Corn and Soybean Programs
C) Seedcorn Maggot in Field Crops
D) Warmer Weather and Alfalfa Weevil
E) Identifying Wheat Growth Stage 6 and Management Decisions
F) Nitrogen Issues for Wheat
G) What to do While Soil is Drying Out
H) Soybean Seed Treatment Primer
I) Calculating Seeding Rates for Corn
Common lambsquarters has always been difficult to control in soybeans, with postemergence herbicides. Common lambsquarters is a very diverse species, genetically, with many different biotypes present in fields, including some related species (believed to be limited). This complexity has caused problems with consistent and effective common lambsquarters control with postemergence herbicides, especially Raptor and Harmony GT (Pinnacle). Some people have also reported inadequate control of common lambsquarters with glyphosate in Roundup Ready soybeans.
Based upon recent greenhouse research, the presence of Harmony GT-resistant (ALS-resistant) common lambsquarters in Putnam County has been confirmed. Most likely, there are additional fields in Ohio with ALS-resistant common lambsquarters, based upon previously reported inadequate control of common lambsquarters in some fields. Current greenhouse research has also shown that common lambsquarters populations can vary in their sensitivity to glyphosate. This research also indicates that plants from more glyphosate-tolerant populations become even more difficult to control with increasing size.
The best way to control moderate to heavy infestations of common lambsquarters in soybeans, especially if postemergence herbicides have become inconsistent or ineffective, is to use preemergence herbicides. Many preemergence herbicides provide excellent control of common lambsquarters, especially when followed with Harmony GT ( as long as not resistant to ALS herbicides), glyphosate, or Raptor, postemergence. Preemergence soybean herbicides with good activity on common lambsquarters include any product containing the following active ingredients: chlorimuron (Canopy, Canopy XL), clomazone (Command), cloransulam (FirstRate), flumetsulam (Python), flumioxazin (Valor), imazethapyr (Pursuit), imazaquin (Scepter), linuron (Lorox), metribuzin (Sencor), pendimethalin (Prowl), and sulfentazone (Authority). Triazine-resistant common lambsquarters will not be controlled by metribuzin.
Control of common lambsquarters having increased glyphosate-tolerance or large plants at the time of the burndown application can be improved by the addition of 2,4-D to glyphosate.
Corn injury can occur when 2,4-D ester is applied at the time of corn planting,
especially when combined with acetamide grass herbicides (Harness, Dual, Outlook,
Define, etc). Injury is most likely to occur in coarse-textured soils with low
organic matter content, and when above-average rainfall and prolonged soil moisture
occur within a week after planting.
Seedcorn maggots are larvae of small flies, and are capable
of causing significant stand reductions in both corn and soybeans under the
appropriate conditions. Research over the past 20 years has shown that seedcorn
maggot populations are greatly enhanced when a green, living cover crop is plowed
or otherwise tilled into the soil. These covers might be old alfalfa stands,
stands of wheat or rye, or even an extremely heavy growth of weeds. There is
a possibility that a heavily manured field that is tilled might also result
in the problem. Stand losses might occur under these conditions. Although seedcorn
maggots are often found feeding on seeds in no-till situations, economic problems
are rarely seen. In our research, we have never seen increases in maggot populations
when no-tilling. In fields where a green cover is tilled into the soil in the
spring, growers should consider an insecticide seed treatment. If the seed is
not already treated when purchased, growers should check with their dealers
for available seed treatments.
As warmer temperatures begin to occur in Ohio, we will
need to begin scouting alfalfa for alfalfa weevil (AW). Although we have not
yet had any reports of weevils or damage from weevil, the time is approaching.
We would suggest that scouting begin when approximately 200 heat units at base
48 have accumulated. At this time, heat unit accumulations are below that for
all locations in Ohio. This will change over the next few 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 in-star larvae which cause most
of the foliar injury. Close inspection of the stem tips may be needed to detect
the early 1st and 2nd in-star 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
Fact-Sheet (http://ohioline.osu.edu/ent-fact/0032.html)
for more on alfalfa weevil scouting and thresholds.
Chemicals currently labeled for use on alfalfa for alfalfa weevil include:
Ambush* @ 6.4 to 12.8 fl oz/A
Baythroid* 2 @ 1.6 to 2.8 fl oz/A
Furadan* 4F @ ½ to 1 pint/A
Guthion* Solupak 50WP @ ¾ to 1 lb/A
Imidan 70-W @ 1 to 1.33 lb/A
Lannate* LV @ 3 pint/A
Lannate* SP @ 1 lb/A
Lorsban* 4E @ 1 to 2 pint/A
Malathion @ (check label for rate)
Mustang* @ 2.4 to 4.3 fl oz/A
Mustang MAX* 2.24 to 4.0 fl oz/A
Pounce* 3.2EC @ 4 to 8 fl oz/A
Sevin 80S @ 1-7/8 lb/A
Warrior* 1CS @ 2.56 to 3.84 fl oz/A
* Use is restricted to certified applicators.
Wheat growth appears to have been a bit slower this spring than during the past few years, but growth has been about average based on the past ten years. Cold temperatures in late March and early April have prevented early and rapid growth of the crop. This is primarily due to the soil temperatures remaining below 45 F for most of this time. However, the good news is that plants in most areas are producing additional tillers in addition to vigorous new crown roots. Wheat producers throughout the state have been applying top-dress nitrogen as fields become dry enough to handle application equipment. Plants are now ready for rapid growth as soon as consistent warmer weather occurs. Wheat producers should be checking fields for tillers in the stem elongation or jointing growth state (Feekes' growth stage 6). Jointing growth stage can be identified by examining the larger tillers in the fields. Pull tillers and strip down the lower leaves and leaf sheaths on the stem to check for the presence of the first node at the base of the stem. Jointing is a critical stage for management reasons. Growth stage 6 signals the end of tillering and the beginning stem elongation. All top dressed nitrogen should be applied by this time in order to maximize yield. This is also the growth stage when some herbicides can no longer be applied.
Some earlier planted fields in southern Ohio are reported to be in growth stage
6, but in the more northern counties of the state plants are beginning regrowth
or are becoming erect. Warmer weather and a shift to longer day lengths will
cause the wheat crop to advance through the tillering growth stage by late April.
Wheat growers in Southern and Central Ohio should check fields for growth stage
before herbicides are applied. Growers in Northern Ohio still have time to apply
nitrogen before wheat reaches growth stage 6. Assuming the weather will be near
normal, we would predict that wheat in the more northern counties would reach
growth stage 6 by the last week of April.
Many parts of the state have been unable to spring topdress nitrogen on wheat. Fortunately drying conditions should allow many areas to finish topdressing this coming week. Part of my research at the OARDC Northwestern Branch has shown that this delayed application should not affect yield, and in years of nitrogen loss, a later application may have larger yields than a single application at initial greenup. In this study, yields for initial greenup applications have been 94.2, 87.9, 70.6 bu/A for 2000, 2001, and 2002, respectively. For single applications at early stem elongation (Feekes growth stage 6), yields were 97.3, 86.4, 83.8 bu/A for the same years, respectively. As the data shows, yields did not drop with the later application. Wheat does not rapidly assimilate nitrogen until early stem elongation and that fall applied nitrogen along with small amounts of mineralized nitrogen will adequately meet the crop needs until Feekes GS 6. Yields in this study did drop significantly for applications after Feekes growth stage 7 in two of the three years (2001 and 2002).
Most N sources would be satisfactory at this time, but price and availability may limit some products. Most retailers have urea, urea-ammonium nitrate solutions (UAN), and/or ammonium sulfate. The research from the same study discussed earlier had similar yields among these three sources except in years of N loss. Urea-ammonium nitrate solutions have the greatest potential for loss, then urea, and ammonium sulfate the least. Even though physical damage from UAN applications after early stem elongation were not observed in our research, producers in this state and researchers from other states have observed significant burn from late applications of UAN.
For producers who had planned on a split spring application program, if the
first top-dress has not been applied, there is probably not an advantage with
two applications this late in the growing season. Yields will probably be similar
for the split or a single application at this time.
Planting is about to begin in full force over the next few weeks, but while you are watching the soil temperatures and testing the soil to see if it is ready - there is one more thing to do. Write down what the resistance package is in your varieties. A variety is comprised of, what we hope, is the best genetics a company has to offer. How well that variety performs is based on the environment that occurs during 2003 growing season, but also how well that variety performs against the challenges of disease in your fields. For soybeans, if Phytophthora is the problem, how well does the resistance gene work against your population and was there any partial resistance or field resistance behind it. If corn leaf blights are a problem, was there any resistance to these pathogens in the hybrid? For wheat - is there sufficient resistance for powdery mildew of Stagnospora blotch in this variety? The county agents in the NW district developed a sheet that can be downloaded from this website to help in this endeavor: http://www.oardc.ohio-state.edu/ohiofieldcropdisease/
Through the C.O.R.N. newsletter, we tell you if certain field crop diseases
are present in the state. From this information, you can scout fields to tell
if your variety performed under the disease pressure that year. This is critical
information for making future variety selections. Let's face it, not knowing
what your resistance package in your variety is similar to not knowing if your
truck is a Ford or a Chevy.
We've received some last minute questions regarding fungicide seed treatment rates. The following is a brief summary.
Products for Pythium and Phytophthora: Allegiance and ApronXL: For those areas of Ohio where Phytophthora has been a problem - the highest rates on the label are required to manage Phytophthora. The low rates are only effective against Pythium. Some products are sold as fungicide combinations which have a low rate of Allegiance or ApronXL in them (ApronMaxx and SoyGard). These products need an extra "hit" of Allegiance or Apron XL to bring them up to the high rate of the Allegiance and ApronXL to get the best control of Phytophthora.
Products for soil fungi (Rhizoctonia, Fusarium) and seedborne fungid (Phomopsis and Sclerotinia) are Agrosol, AgrosolT, Maxim, Rival, SoyGard. Some of these products list a range of rates. For example, in our studies, Maxim at 0.08 fl/oz/cwt has given excellent control of Rhizoctonia seed rot and seedling damping-off. So in these cases the lowest rates listed on the label should provide adequate control.
Application: As you read these labels, not that very low rates of application are needed because the level of activity of some of these products is quite high. It is critical that the seed treatment equipment be calibrated. Seed that is treated is also required to have a colorant added to it. Either a blue or more typically pink color. Look at your seed, if the colorant on the seed is spotty and not even on the seed, then most likely the seed treatment is also spotty and not even on the seed.
For more information on seed treatment in general refer to: http://ohioline.osu.edu/b639/index.html.
For information on efficacy of specific products to specific soybean diseases
refer to http://www.oardc.ohio-state.edu/ohiofieldcropdisease/
If the recommended plant population for a corn hybrid is 28,000 plants/acre based on various factors including site yield and potential hybrid characteristics, what should the seeding rate be? Remember a recommended plant population refers to final plant stand or the number of plants/A at harvest not seeding rate.
The number of plants/acre at harvest is always less than the number of seeds planted (unless you have a lot of volunteer corn!) Planting date, tillage practices, pest problems, chemical injury, planter performance, and seed quality can affect final corn populations obtained in the field. To compensate for these losses, a corn grower needs to plant more seed than the desired population at harvest.
To determine an appropriate seeding rate, use the following formula:
Seeding rate = Plant population per acre at harvest/(Seed germination x Expected
survival)
Seed germination is the percent germination shown on the seed tag. Most seed
corn has a germination rate of 95% or higher. Expected survival is the percentage
of plants that you expect to survive to become harvestable plants in the fall.
Keep in mind that survival rates for corn are often in the range of 85 to 95%
but can vary considerably depending on planting conditions and other environmental
factors. When early planting is likely to create stressful conditions for corn
during emergence (e.g. no-till in early to mid April), consider seeding rates
10 to15% higher than the desired harvest population.
EXAMPLE: A grower wants to achieve a final stand of 28,000 plants/acre. The seed tag indicates a germination rate of 95% and the grower expects that 90% of the germinable seed will survive until harvest. Based on the formula above, divide the desired plant population at harvest, 28,000 plants/acre, by 0.95 x 0.90 (0.855) to obtain a seeding rate of 32,749 seeds/A. (Note that % germination and % survival are converted to decimal form for use in the formula.) If only 85% of the germinable seed were expected to survive (due to stressful environmental conditions during emergence), then dividing 28,000 by 0.95 x 0.85 (.8075) would give a higher seeding rate of 34,675 seeds/A.
Readers can subscribe electronically to this newsletter by sending an e-mail message to: corn-out-on@postoffice.ag.ohio-state.edu. A successful subscription message will receive by an automatic reply from the listserv. Contact your local Ohio State University Extension Office or e-mail labarge.1@osu.edu if you have problems subscribing.
Past versions of C.O.R.N. can be found on the World Wide Web at: http:/www.ag.ohio-state.edu/~corn/archive/
C.O.R.N. is a summary of crop observations, related information, and appropriate recommendations for Ohio Crop Producers and Industry. C.O.R.N. is produced by the Ohio State University Extension Agronomy Team, State Specialists at The Ohio State University and Ohio Agricultural Research and Development Center. C.O.R.N. Questions are directed to State Specialists, Extension Associates, and Agents associated with Ohio State University Extension and the Ohio Agricultural Research and Development Center at The Ohio State University.
State Specialists: Pat Lipps, Anne Dorrance & Dennis Mills (Plant Pathology), Mark Loux and Jeff Stachler (Weed Science), Bruce Eisley (IPM) , Peter Thomison (Corn Production , and Ron Hammond (Entomology); District Specialists: Ed Lentz (Agronomy); Extension Agents: Allen Sundermeier (Wood), Bruce Clevenger (Defiance), Roger Bender (Shelby), Glenn Arnold (Putnam), Clark Hudson (Seneca), Barry Ward (Champaign), Steve Foster (Darke), Howard Siegrist (Licking), Jim Lopshire (Paulding), Mark Koenig (Sandusky), Greg La Barge (Fulton), Todd Mangen (Mercer), Harold Watters (Miami) and Steve Prochaska (Crawford).Editor: Steve Prochaska Web Editor: Nathan Watermeier
Information presented above and where trade names are used, they are supplied with the understanding that no discrimination is intended and no endorsement by Ohio State University Extension is implied. Although every attempt is made to produce information that is complete, timely, and accurate, the pesticide user bears responsibility of consulting the pesticide label and adhering to those directions.
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