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For Month of March 23-29, 1998
C.O.R.N. 98-3
In This Issue:
A) Wheat Condition Good
B) Possible Disease in Wheat
C) More on Soybean Seed Treatments
D) Weed Control in Wheat
E) Does Seed Corn Size Affect Hybrid Performance
F) First Year Corn Rootworm Survey in Ohio for 1998
The mild winter conditions have been favorable for winter survival of the wheat crop and for several of the fungi causing leaf diseases. We have found powdery mildew and Stagonospora (Septoria) leaf blotch in some fields already. The recent cold weather has held disease development in check. Powdery mildew will begin to spread as soon as the temperatures get into the 60-70 F range. We can not predict if these diseases will be important this year because the weather that occurs in April and early May determines the fate of disease development. However, the early occurrence of disease in fields means that the probability of having a problem is greater than normal. We suggest that as fields are top-dressed with N or as herbicides are applied, the fields should be examined for disease on the lower leaves. Fields with powdery mildew should be checked again prior to flag leaf emergence for possible application of a fungicide. We will be watching fields also, and we will provide additional information on disease development as the season progresses. Monitor fields from now through April, but do not apply fungicides until later when they provide the most economic return (around flag leaf emergence).
We continue to get questions on the use of soybean seed treatments. We feel the use of the modern seed treatmentss have provided very effective control of a number of seed and seedling diseases. You only see a response to seed treatments when a disease is present in the field. We hope you do not have the conditions for disease development, but it is highly likely if you plant early into cold soils, are planting using no-till or have poorly drained soil. In Ohio, it is likely that everyone will have some fields like this. This is why we recommend that all soybean seed be treated to control diseases and that growers use seed treatments specific for the conditions they predict they will face at planting. Last month we provided some information on specific fungicide chemicals that are effective against certain diseases. We have been questions about the fungicides in certain brand name products. The products of choice should be those that control the diseases you expect to face at planting and for the first week or so after planting. The premier products on the market for disease control are Agrosol FL (Captan and TBZ), Rival (Captan, PCNB, and TBZ) and Apron (Metalaxyl). These are the premier products because the better seed treatment products are usually made up of several different fungicides that act against more than one disease. Captan and TBZ are effective in increasing germination of seed affected by Phomopsis. Rhizoctonia seed and stem rot is difficult to control even with the best seed treatment fungicides and PCNB is the best we have available. Metalaxyl is the only fungicide effective against Phytophthora and it is more effective than Captan against Pythium. Apron can be combined with Captan, Agrosol FL or Rival to improve control of Pythium and provide control of Phytophthora.
We have been questioned about rates of Apron for control of Phytophthora and Pythium. There are two formulations of Apron on the market, Apron FL and Apron XL. They both contain Metalaxyl. Basically Apron XL contains twice the amount of active ingredient as does Apron FL, thus they have different application rates. Secondly, it takes less metalaxyl to control Pythium as it does Phytophthora. The level of control of Phytophthora is very rate dependent, thus the more amount of active ingredient applied to the seed the better the disease control. Research results have shown over many years that the best yield occurs when Apron is used on varieties with single gene resistance (Rps genes) and those with partial resistance (tolerance) to Phytophthora. Apron will not effectively or economically protect completely susceptible varieties. It will increase the yield of susceptible varieties, but not to the level of the more resistant varieties. The rates recommended for control of Pythium seed rot and damping off are 0.2 oz./cwt for Apron FL and 0.16 fl. oz./cwt of Apron XL. For Phytophthora use 1.5 fl. oz/cwt of Apron FL or 0.64 fl. oz./cwt of Apron XL. The lower rate of Apron may provide some control of Phytophthora under some condition, but with sufficient rain causing saturation of the soil after planting, the low rate may result in failure to control Phytophthora damping off in the field.
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 winter weather may have allowed winter annual weeds to thrive in some fields (we have already received calls about chickweed), and these 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 2,4-D.
When wheat has not yet reached the jointing stage, any herbicide labeled 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 top-dressed. 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 96 of the 1998 OSU Weed Control Guide and in the text on pages 89-95 (for World Wide Web users, go to the small grains section of the Guide for this information).
2,4-D: all 2,-4-D products are labeled for application before jointing. A few are labeled up to early boot stage. 2,4-D 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 1/2 pint of ester or 1 pint of amine. 2,4-D will not control chickweed or henbit, and can be weak on smartweed. MCPA products have characteristics and labeling similar to 2,4-D products.
Banvel: Apply before jointing. Not as effective as 2,4-D on mustard species, but more effective on smartweed. Weak on chickweed, henbit, and wild garlic. Can be tank mixed with 2,4-D.
Buctril: Apply before jointing. Applying in fertilizer solution increases leaf burn. Weak on most winter annuals, dandelion, and wild garlic.
Curtail: premix of 2,4-D 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.
Corn seed size and shape is controlled by the genetics of the parent plant. Seed of three- or four-way crosses is generally larger than seed of single-cross hybrids. Seed size is also influenced by environmental conditions during plant development and grain fill. Stresses such as high temperatures, low soil moisture, or low fertility can reduce seed size.
Placement of the seed on the ear also affects both seed size and shape. The sequential development of the corn ear from the base to the tip causes a range in seed maturity and filling period, and affects the seed's ability to compete for available photosynthate and space on the cob. The result is that seed from a single ear could fall into many size/shape classes. Large-round classes usually come from the base of the ear, flats from the center, and small-round seed from the tip.
With the introduction of plateless planters corn growers are better able to plant seed of any size/shape combination without obtaining plates for specific sizes. Nevertheless, medium- flats or large-flats still remain the choice of many farmers despite greater cost than other seed size/shape combinations or mixtures. This preference is due to concerns that small and/or round size/shape combinations may not have the same performance of other seed classes. Are these concerns justified?
Seed size has been shown to be a valid indicator of vigor for certain crop species - with small seed exhibiting reduced seedling growth rates. However, for corn, studies have evaluated the relative performance of size/shape combinations and have found few differences in emergence, growth or grain yield. Small corn seed has been associated with slight delays in tasseling and/or silking but this has seldom translated into yield losses.
Some growers favoring big kernels contend a large seed provides a greater "food supply" than a small seed when emergence and development are slowed during cold springs. A recent Wisconsin study involving two corn hybrids did find evidence that emergence was reduced 5 to 15% in small-round seed compared to small-flat and large-rounds under such stressful conditions as early planting, no-till, and soil crusting. However, under other environmental conditions, such as water stress, small seed have shown an advantage in emergence over large seed.
Although seed size may influence various stages of corn development, as well as emergence under certain conditions, it has little, if any, effect on a hybrid's potential performance. Corn producers should focus on genetic potential, seed quality (e.g. high germination), and seed price rather than a specific seed size/shape combination when selecting a hybrid.
The "plantability" of small sized seed, as well as mixed seed sizes can also be a potential problem. A poor job of placing unusual seed sizes in the furrow can result in plant populations greater than desired or between plant spacings more variable than desired, both of which can seriously reduce grain yield.
Take the following steps to ensure that small or unusual seed sizes will be dropped uniformly and at the desired seeding rate.
1) Make sure the planter is properly adjusted and checked out for worn parts.
2) Adjust the planter for the specific seed size being used, and
3) Check the accuracy of seed drop periodically during the planting operations.
Western corn rootworm (WCR), Diabrotica virgifera virgifera LeConte, is one of the most significant corn pests in Ohio. Over the years, adopted rotation practices between corn and other crops, particularly soybeans, has drastically reduced soil insecticide use. Recent emergence of a new WCR biotype adapted to corn after soybean rotation may cause growers to treat substantial portions of first year corn with a soil insecticide. Nearly two million acres of first year corn (1996 Agricultural Statistics) in Ohio may be exposed to this insect under current rotational practices. This will lead to a significant increase in soil insecticide use and higher input costs at the farm level.
In 1996 and 1997, a detection survey was undertaken to identify counties in western tiers of Ohio for evidence of the first year western corn rootworm (FYCRW) which has been spreading across the corn belt in the past decade. Over the past 2 years in Ohio, nineteen counties have been surveyed using various methods to assess the presence and abundance of this pest in soybean fields or corn fields rotated after soybeans. Techniques used to identify suspect or positive FYCRW fields included: digging first year corn root systems and inspecting them for larval feeding; burying emergence cages to capture adults in corn fields rotated after soybeans; sweeping soybean fields for adult rootworm beetles; and deployment of Scentry Multigard sticky traps in both first year corn and soybean fields. Fields suspected to contain this pest showed elevated two week sticky trap catch averages in both corn and soybean compared to historical pre-invasion records. Likewise, sweepnet samples taken in soybean fields could be used to separate infested and non-infested fields based on rootworm beetle abundance.
In 1998, Ohio State University Extension personnel will be continuing and expanding the detection efforts conducted during the past two growing seasons throughout Ohio to determine the extent of infestation by the FYCRW. Integrated Pest Management personnel from Columbus, the SW District Office and the NW District Office, and OSU Extension County Agriculture and Natural Recourse Agents will be involved in the survey. Again, detection methods to be employed include: digging corn root systems from first year corn fields following soybeans to detect rootworm root injury during July; sweeping soybean fields with sweepnets to detect the presence and numbers of adult corn rootworms from mid-July through early September; and placing Scentry Multigard yellow sticky traps in soybean and first year corn fields from mid-July through early September. Other independent groups will be conducting similar activities throughout Ohio.
Research to be conducted by OSU Extension IPM personnel in regards to first year corn rootworm problems includes: first year corn rootworm soil insecticide trials; comparisons of effectiveness of two yellow sticky trap types, Scentry Multigard and Pheracon AM, to trap corn rootworm adults; and development of economic thresholds using yellow sticky traps for the monitoring tool. Results from research and survey efforts conducted in 1998 will be presented at OSU Extension field days and winter meetings and published in annual reports and newsletters as they become available. These reports and newsletter can be obtained at your local OSU County Extension Office.
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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: Pat Lipps (Extension Specialist, Plant Pathology), Ann Dorrance (Extension Specialist, Plant Pathology), Peter Thomison (Extension Specialist, Corn Production), Mark Loux (Extension Specialist, Weed Science), Jeff Stachler (Extension Associate, Weed Science), Curtis Young (Extension Associate, Integrated Pest Management), Mike Estadt (Pickaway Co.), Dennis Baker (Darke Co.), Larry Lotz (Fayette Co.), Barry Ward (Marion Co.), Ray Wells (Ross Co.), Roger Bender (Shelby Co.), Tom Krill (Van Wert), Clark Hutson (Seneca Co.) and Steve Prochaska (Crawford Co.).
Information presented above and where tradenames are used, they are supplied with the understanding that nodiscrimination 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.
All educational programs conducted by Ohio State University Extension are available to clientele on a nondiscriminatory basis without regard to race, color, creed, religion, sexual orientation, national origin, gender, age, disability or Vietnam-era veteran status.
Issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture, Keith L. Smith, Director, Ohio State University Extension.
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