CORN
Crop Observation and Recommendation Network

For April 1-9, 1999
C.O.R.N. 99-4

In This Issue:

A) Questions on Soybean Cyst Nematode in Ohio
B) Early Preplant Treatments in No-Tillage Soybean or Corn
C) Weed Control in Wheat
D) On-Farm Seed Treatment Options
E) Will Roundup Ready Corn Hybrids Perform as Well as Their Non-Tolerant Isolines?
F) Planter Inspection - A Key Step for Improving Stand Uniformity in Corn
G) U.S. Corn Exports to Europe Threatened

A) Questions on Soybean Cyst Nematode in Ohio - Anne Dorrance and Mac Riedel CORN Questions

During the Regional Agronomy Presentations throughout the state in December and January, producers had numerous questions concerning soybean cyst nematode, below is a sampling of the questions and the answers from Mac Riedel, nematologist at Ohio State.

Q. How many races of SCN have been found in Ohio?
A. We have found races 1, 2, 3 (the most common race in the survey), 4, 5, 6 and 14. However, field populations of SCN likely consist of more than one race. Remember this is a biological organism and it does have a considerable amount of variability.

Q. How are SCN races determined?
A. The race concept has been used to develop SCN resistant beans but in this system SCN races aren't as sharply defined as with most fungal pathogens. In determining if a variety is resistant to SCN, reproduction rates of SCN females are compared to reproduction on a known susceptible. If SCN reproduction is less than 10% of the control, it is considered resistant. So there can be some reproduction even on "resistant varieties". Another factor in SCN resistance may be the size of the cyst that develops.

Q. How does SCN resistance work?
A. Resistance can work in several different ways depending on the source of resistance used. The resistance action can be any of the following. Reduce the number of feeding sites established by the females. Lengthen the time before egg production begins, which results in fewer eggs developed per cyst. Decrease the success of the nematode in establishing feeding sites, or once a feeding site is established - the plant cells at the feeding site die which starves the nematode.

Q. What is the best way to use resistant varieties?
A. The best way to use resistant varieties is to first get field populations of SCN below 2000 eggs/200cc of soil if possible and certainly below 5000 with rotation. Then use resistant varieties with varying sources of resistance until the population is low enough to reintroduce a crop of susceptible beans and then to rotate to nonhosts and back to resistant varieties. Including a susceptible variety in the rotation will be important to prevent isolation of biotypes that will reproduce on resistant varieties.

Q. Where can I find a listing of resistant varieties?
A. We have compiled a list of resistant varieties from soybean seed companies and based on their results have indicated if a variety is resistant or not. This listing can be found on the web at: http://www.ag.ohio-state.edu/~perf/scn99/index.html

Q. What about "alternative" controls that are currently being promoted by various companies - what works?
A. For chemical control, Counter hasn't been effective on soybean cyst nematodes. The only chemical that has been economically successful (most of this data comes from Illinois) is Temik. Due to ground water concerns and our soil types this may not be feasible for Ohio producers. At this time we are not recommending any soil additives. Ohio State University researchers are examining the effects of certain soil amendments on SCN populations. We also maintaining contact with other researchers who are examining bacteria for biological control as well as other potential management option for Ohio farmers. Nothing at this time is ready for farmer trials.

The most economical means to manage soybean cyst nematode is through crop rotation and the use of resistant varieties.

B) Early Preplant Treatments in No-Tillage Soybean or Corn - Jeff Stachler CORN Questions

The current warm temperatures are allowing winter annual weeds to grow fairly rapidly and causing weeds such as giant ragweed and Atriplex to begin emergence in some fields. Those individuals looking to plant soybeans or corn soon using a herbicide program of a preemergence plus burndown herbicides follow by a postemergence herbicides (two pass system) need to apply the burndown plus preemergence herbicides part of the program now. First, scout the fields to determine the appropriate burndown herbicide. Where no perennial grasses are present, the most appropriate burndown herbicides would be 2,4-D ester or Gramoxone Extra. If perennial grasses are present then Roundup Ultra or Touchdown should be used, however now is not the best time to control those perennial grasses. In soybeans, herbicides like Canopy, Canopy XL, Authority, Python, Sencor, Steel or Scepter have potential to control certain winter and summer annual weeds present in fields at this time. Canopy and Canopy XL have the broadest spectrum of burndown control. At this time of the season, tank-mixing 2,4-D ester with any of these soybean herbicides will provide effective burndown weed control, as long as no perennial grasses are present. 2,4-D ester must be applied 7 days before planting.

In Corn, Atrazine, Atrazine containing premixes, Balance, Bladex, and Hornet can control certain winter and summer annual weeds currently in fields. The addition of 2,4-D ester will enhance the broadleaf weed control. As in soybeans it is best to apply 2,4-D ester at least 7 days before planting corn, to reduce the risk of corn injury. Crop oil concentrate and/or 28% nitrogen added to 2,4-D ester and the above mentioned preemergence herbicides will increase the weed control.

C)  Weed Control in Wheat - Jeff Stachler and Mark Loux  CORN Questions

Wheat as a rule is very competitive with weeds and some wheat fields do not require herbicide treatment. However, other fields can benefit greatly from herbicide application and failure to scout fields and take the appropriate measure can result in yield loss and harvesting problems. The weeds that appear above the wheat canopy late in the season, such as ragweeds and Canada thistle, can often be easily controlled with a spring herbicide treatment. Many wheat herbicides have some activity on Canada thistle and can suppress it enough to prevent harvest problems. Effectiveness often depends upon the size of the thistle at the time of application. Best products for thistle control, ranked, are Stinger, Curtail, and Express. The mild fall weather allowed many winter annual weeds, such as chickweed and field pennycress, to get established in many fields and they are now growing rapidly. These weeds can interfere with the early spring development of wheat. Winter annuals are more easily controlled when still in the rosette stage, before the stem has bolted. Best products for wild garlic, ranked, are Harmony Extra, Peak, and 2,4D.

Before the jointing stage, any labeled herbicide can be safely applied. As wheat growth stage advances past jointing and then past boot stage, the herbicide choices become much more limited. Most herbicides can be applied in nitrogen fertilizer solution when the wheat is topdressed. This may increase injury somewhat, and some labels recommend adjusting surfactant rates to minimize injury. Some key herbicide limitations are listed below these are also shown in a figure on page 100 of the 1999 OSU Weed Control Guide and in the text on pages 9399 (for World Wide Web users, go to the small grain section of the Guide for this information).

2,4D: all 2,4D products are labeled for application before jointing. A few are labeled up to early boot stage. 2,4D is generally safe up to early boot, but the risk of injury increases after jointing. To minimize the risk of injury after jointing, use water as the carrier and do not apply more than ½ pint of ester or 1 pint of amine. 2,4D will not control chickweed or henbit, and can be weak on smartweed. MCPA products have characteristics and labeling similar to 2,4D products.

Banvel: Apply before jointing! Not as effective as 2,4D on mustard species, but more effective on smartweed. Weak on chickweed, henbit, and wild garlic. Can be tank mixed with 2,4D.

Buctril/Moxy: Apply before the boot stage. Applying in fertilizer solution increases leaf burn. Weak on most winter annuals, dandelion, and wild garlic. For best results apply to weeds before 4-leaf stage or are 2 inches tall.

Curtail: premix of 2,4D plus Stinger. Apply until jointing. Weak on chickweed, henbit, and wild garlic. Do not plant double crop soybeans in fields treated with Curtail.

Harmony Extra: Apply before flag leaf is visible and when weeds are less than 4 inches tall or across (rosette). Apply with nonionic surfactant. Best choice for wild garlic. Weak on ragweeds.

Express: Apply before the flag leaf is visible when weeds are less than 4 inches tall or across (rosette). Not as broad spectrum as Harmony Extra, but more effective on Canada thistle. Apply with nonionic surfactant.

Peak: Apply before 2nd node is detectable in wheat stem elongation, and when weeds are 1 to 3 inches tall. Do not plant double crop soybeans in fields treated with Peak. Apply with crop oil concentrate or nonionic surfactant.

Stinger: Best suited for spot treatment due to high cost. Effective for Canada thistle and ragweeds, primarily. Apply up to early boot.

D)  On-Farm Seed Treatment Options - Anne Dorrance and Pat Lipps  CORN Questions

 The new Seed Treatment for Agronomic Crops (Bulletin 639) and Efficacy of Seed Treatment Fungicides for Agronomic Crops in Ohio (Bulletin 639A) for Commercial Seed Treaters are now available from County Extension Offices and Ohioline. Commercial seed treaters have access to a broader range of seed treatment materials than those available for on-farm treatment. Several seed treatment products contain a fungicide that is a skin irritant, so proper handling and personal protective clothing is essential. In addition, many of the fungicides are applied at very reduced rates requiring precise application to seed. Commercial application equipment for seed treatment is more suited for low rate applications than traditional hopper box treatments.

There have been several requests for information concerning on-farm seed treatments. Seed should be of high quality and have a high percent germination. For producers who wish to use bin-run seed, a germination test can be done at home. Place two paper towels in the bottom of a dish or tray, one on top of the other; wet the towels thoroughly and tilt the tray up on one end so that excess water runs off the tray. Select a random sample of 100 seeds from the seed lot and place them in between the moist paper towels. Put the tray in a plastic bag and tie the end shut to prevent the towels from drying out. Place the tray in a location of diffuse, not direct light, such as north window. The location should be warm enough (75 to 85 oF) for good plant growth. After five to seven days open the plastic bag and count the number of germinated seeds with an intact tap root and shoot. Do not count moldy seed or diseased seedlings. Testing 400 seeds this way will give a good indication of the germination percentage.

There are several products available to producers to treat their seed on-farm either as a hopper box treatment or with systems designed for an auger conveyance system. For all of these seed treatments it is very important that producers read and follow the label directions. Be sure to wear the protective clothing that is listed on the label in that some of these products are skin irritants. Be sure that the seed and seed treatment compounds are thoroughly mixed to ensure even distribution of the material on the seed. Even coverage of the seed is necessary for maximum protection of the seed and seedling. 

E= excellent, N= no control, G= good, F=fair, Phyto.=Phytophthora, Rhizoc.=Rhizoctonia
** EPA revoked 24C use permit on April 22, 1999. This material is no longer available for the 1999 production season.

E)  Will Roundup Ready Corn Hybrids Perform as Well as Their Non-Tolerant Isolines? - Thomison, Jordan, Geyer, and Minyo CORN Questions

The introduction of corn hybrids with tolerance to Roundup herbicide (Roundup Ready corn) has given corn growers another option to consider for weed control. There are reports that Roundup Ready corn was planted on almost 1 million acres in its inaugural season. More Roundup Ready hybrids with a wider range of maturity are available in 1999, which should meet the needs of different production environments and farmer operations. DeKalb was the only company marketing Roundup Ready corn in 1998, this year other companies including Asgrow and Land of Lakes are introducing Roundup Ready hybrids.

Roundup Ready corn hybrids were developed to grow normally in the presence of Roundup with no effect on grain yield. Like Roundup Ready soybeans now grown on over a third of soybean acres, Roundup Ready corn is a transgenic crop. In the past, conversion of normal (herbicide non-tolerant) hybrids to herbicide tolerant hybrids was not always "clean". Sometimes undesirable agronomic characteristics are strongly linked to the tolerance gene and this linkage decreases hybrid performance. Moreover, conversion of normal (non-tolerant) hybrids to herbicide tolerant hybrids requires numerous cycles of backcrossing.

The time required to complete the backcross process can result in the introduction of the tolerant hybrid lagging a few years behind that of its normal parent hybrid. Sometimes, this results in an automatic yield disadvantage when tolerant hybrids are compared to newer, more elite hybrids.

The potential for such yield loss in herbicide tolerant corn is a major concern of corn growers. Since seed costs of Roundup Ready hybrids are higher - $18 more per 80,000 kernel unit, there is considerable interest in whether Roundup Ready hybrids yields are significantly different from their normal counterparts (non-tolerant isolines). Aside from seed and chemical company data there is limited university information comparing the performance of Roundup Ready hybrids with their non- tolerant isolines.

In 1998 we conducted evaluations of Roundup Ready corn at six Ohio sites, Hoytville, South Charleston, Wooster, Van Wert, and two separate field sites at Mt. Gilead, to determine effects of the Roundup tolerance trait on yield potential. The experimental design was a randomized complete block in a split-plot arrangement with four replications. Main plots were four corn hybrids and split plots were hybrid isoline pairs with either Roundup tolerance or non-tolerance. In these tests, both the Roundup Ready and non-tolerant isolines were grown using conventional herbicide programs. This comparison allowed us to evaluate effects of the Roundup tolerance gene insertion without confounding effects (different herbicide programs).

The relative maturities and growing degree day (GDD) maturity ratings of the four DeKalb Roundup Ready (RR) corn hybrids evaluated were as follow: DK493RR - 99 days (2470 GDD); DK512 - 101 days (2520 GDD); DK566 - 106 days (2660 GDD); and DK580 - 108 days (2710 GDD).

Table 1 shows grain yields of the Roundup Ready hybrids and their non-tolerant isolines at each of the six test sites in 1998. Averaged across hybrids at each location, yields were highest at Van Wert and lowest at the Mt. Gilead/low productivity site. Preliminary results of the 1998 trials indicated significant differences in grain yield among the four genotypes, with the early 99-day DK493 yielding less than the later maturing hybrids. However differences in yield between the Roundup Ready hybrids and their non-tolerant counterparts were not significant. These results suggest that Roundup Ready hybrids produce yields comparable to normal corn when conventional herbicide programs are used. Two of the genotypes tested in 1998 are not widely used in Ohio because of their early maturity. In 1999 we plan to compare additional Roundup Ready hybrids including hybrids with maturities better adapted to Ohio growing conditions.

Table 1. Yield data in bushels per acre from the 1998 Roundup ready corn hybrid evaluations at Van Wert (VW), Hoytville (HV), Mt. Gilead (MG), Wooster (WO) and South Charleston (SC).

F)  Planter Inspection - A Key Step for Improving Stand Uniformity in Corn – Peter Thomison  CORN Questions

Uneven stands of corn are a common problem some years - often associated with fields where corn has been planted using reduced tillage. Fields that exhibit stand uniformity problems are characterized by tall and short corn, large within-row gaps, and groups of crowded plants. Lack of stand uniformity is a problem involving uneven seedling emergence and within-row spacing of plants.

Variable seedbed soil moisture associated with uneven crop residue distribution and weather conditions is a major factor causing uneven corn emergence, whereas high planting speeds (in excess of 6 mph) and poor planter maintenance/adjustment are primarily responsible for uneven within-row plant spacing.

Uneven plant stands characterized by large within-row gaps of 4 to 6 feet can reduce grain yields up to 5%. About 1/4 pound of potential yield can be lost for every ear in a tight grouping of two or more plants. Uneven emergence can also have a major impact on potential yield even if within-row spacing is relatively uniform. If 1/2 or more of a stand is delayed two weeks in emerging, yield losses of 5 to 8% can be expected. If 1/2 or more of a stand is delayed in emerging three weeks or later, yield losses of 20% or more can occur.

Corn sometimes emerges unevenly because of environmental conditions beyond the control of growers. However, timely planter servicing and adjustment, as well as appropriate management practices, can help prevent many stand uniformity problems. The following are some tips for improving the uniformity of seed placement during planting.

1. Avoid excessive tillage trips and tilling wet soils.
2. Check seed depth and seed soil contact periodically during planting.
3. Distribute residues over row areas evenly.
4. Plant at speeds between 4 1/2 to 5 1/2 mph.
5. With plate-type planters, match the seed grade with the correct planter plate.
6. Planters with finger pick-ups should be checked for wear on the back plate and brush, use a feeler gauge to check tension on the fingers, then tighten them correctly.
7. Check for wear on double-disc openers and seed tubes.
8. Make sure the sprocket settings on the planter transmission are correct.
9. Check for worn chains, stiff chain links, and improper tire pressure.
10. Lubricate all chains and grease fittings.
11. Make sure seed drop tubes are clean and clear of any obstructions.
12. Clean seed tube sensors if you have a planter monitor.
13. Make sure coulters and disc openers are aligned properly.
14. With air planters, match the air pressure to the weight of the seed being planted.
15. Make sure press wheels are adjusted to close the seed slot.

G)  U.S. Corn Exports to Europe Threatened (March 22/99, Reuters)

SAN FRANCISCO - USDA undersecretary Gus Schumacher was cited as telling the National Grain and Feed Association Monday that U.S. corn exports will likely suffer again this year due to a huge lag in the European Union's approval of genetically modified crops grown in the United States, adding, "We believe the EU approval process simply has broken down for largely political reasons, threatening U.S. corn exports for the second consecutive year." Schumacher added that U.S. exporters lost about $200 million in sales last year due to a backup in varieties waiting for approval.

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.

Contributors to C.O.R.N. this week include: STATE SPECIALISTS: Pat Lipps (Extension Specialist, Plant Pathology), Anne Dorrance (Extension Specialist, Plant Pathology), (Jeff Stachler (Extension Associate, Weed Science), and Peter Thomison (Extension Specialist, Corn Production); EXTENSION AGENTS: Larry Lotz (Fayette), Roger Bender (Shelby), Greg LaBarge (Fulton), Steve Bartels (Butler), Clark Hutson (Seneca) and Barry Ward (Champaign).

Editor: Greg LaBarge        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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