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For Week of May 4-10, 1998
C.O.R.N. 98-8
In This Issue:
A) Powdery Mildew in Wheat: Scout Susceptible Varieties!
B) Stagonospora Leaf Blotch Still on Lower Leaves
C) 24c Label for Tilt in Wheat
D) Efficacy of Tilt and Bayleton Fungicides
E) Wheat Spindle Streak Mosaic in Wheat
F) Barley Yellow Dwarf Virus in Wheat, Relationship to Planting
Date
G) Relationship Between Rootworm Insecticides and Corn Yields
H) Adapting Corn Planters to Small Seed Sizes
I) When is it Too Late to Plant Forages
J) Herbicide Burndown Concerns with Delayed Planting
K) Status of Preplant N
Stagonospora nodorum can be found on lower leaves in most wheat fields at this time. The incidence and severity is still quite low. The disease can be seen as small round to oval dark brown spots, sometimes with a yellow halo. These spots expand into oval light brown lesions with dark brown centers and yellow halos. As the temperatures begin to rise over the next few weeks we expect this disease to become much more important. Disease development is favored by 2-3 days of rain each week and temperatures in the 70 to 82 degrees F range. It takes from 14-18 days for lesions to develop after infection occurs. This disease usually starts off relatively slow in early May and develops rapidly near the end of the month, especially after head emergence. When rainy weather continues after head emergence, the fungus can cause lesions on the heads initiating the glume blotch phase.
Most varieties planted in Ohio are susceptible or moderately susceptible to Stagonospora leaf blotch. All the varieties in the Ohio Wheat Performance Trial were evaluated for reaction to this disease in 1997. You can review the results of these evaluations in the 1997 Ohio Wheat Performance Test, Hort and Crop Sci. Series 228. Under very favorable weather conditions for disease development nearly all varieties could benefit from a fungicide application if the upper two leaves are in danger of infection by flowering. The best time to scout for Stagonospora leaf blotch is boot stage (Feeke's 10) and heading (Feeke's 10.3- 10.5). Apply a fungicide when the first lesions can be detected on the second leaf (leaf below the flag leaf).
The Ohio Department of Agriculture has granted a Special Local Need (24c) registration for Tilt fungicide on wheat in Ohio. The original label limited applications of Tilt at or before flag leaf emergence (growth stage 8). In most years, diseases have developed at later growth stages, thus limiting the usefulness of Tilt to wheat growers in Ohio. The special registration was sought to extend the timing of Tilt application. The 24c registration permits applications of Tilt through full head emergence (Feeke's growth stage 10.5), but not within 40 days of harvest. Other restrictions include: 1) DO NOT apply more than 4 fl oz of Tilt per acre per season, 2) DO NOT graze or feed livestock treated wheat, straw, forage or hay, and 3)DO NOT cut the green chop for hay or silage. A copy of the label can be obtained from Ohio Department of Agriculture (614-728-6383).
Tilt and Bayleton are labeled for control of powdery mildew, Septoria (Stagonospora) leaf and glume blotch and leaf rust. Tilt is labeled for suppression of head scab. Bayleton (2-3 oz/A) is more efficacious for control of powdery mildew than Tilt (4 oz/A), but in terms of yield response to mildew control they are essentially equal. Tilt is the better material for control of Stagonospora (Septoria) nodorum leaf and glume blotch, especially when applied after boot growth stage. Bayleton (4.0 oz/A) or Bayleton (2 oz/A) combined with Benlate (4 oz/A) or a Mancozeb type product (2.0 lb/A) has been more effective than Tilt on Stagonospora only because of the early season (flag leaf emergence) restriction on the Tilt label. The 24c label for Tilt makes it the preferred material for Stagonospora control. Bayleton has always been weak on leaf rust control requiring 6.0 oz/A to restrict disease development to economic levels. Tilt at 4.0 oz/A will limit rust development if applied at or before 1% of the upper leaves become infected. Tilt is the only material available with a label (24c label) for suppression of head scab. Remember suppression does not mean control. You possibly could expect a 10 to 20% decrease in the level of scab in the field if Tilt was applied just prior to flowering. Tilt can be applied up to 40 days prior to harvest and Bayleton can be applied up to 35 days prior to harvest. Double crop soybeans can be planted after either Tilt or Bayleton applications.
Note: This disease has been confused with Stagnospora leaf blotch--not all spots are caused by fungi! Stagnospora nodorum at this time in Ohio is still confined to the lower leaves. Fungicide applications will have no effect on Wheat Spindle Streak Mosaic. Selecting a resistant variety is the best control method for Wheat Spindle Streak Mosaic Virus, especially since the fungus that carries it can survive for many years in the soil. For more information refer to OSU Extension Factsheet AC-3-96 on Ohioline.
We have observed relatively high levels of Barley Yellow Dwarf Virus in research trials at South Charleston and Custer where wheat was planted before the Hessian Fly Free Date. In the same trials there was no Barley Yellow Dwarf in plots planted on or after the Fly Free Date. Barley Yellow Dwarf is a viral disease that is transmitted by aphids. Aphids from the southern wheat growing regions carry the virus northward and transmit the virus in early to mid September. Since little to no northward migration occurs in late September-October, we can reduce barley yellow-dwarf infection by planting after the fly-free date.
Barley Yellow Dwarf can be recognized as stunted plants with yellow and red leaf tips. The disease will become more evident as flag leaves emerge and turn yellow. Essentially all wheat varieties are susceptible. There is nothing you can do at this time to prevent yield losses. Planting after the fly-free date is the best control option.
We are currently entering our tenth year of conducting soil insecticide trials on corn at either the OARDC Western Branch or Northwestern Branch stations. Most of our field research is conducted at the Western Branch station, but we periodically attempt to duplicate trials at the Northwestern Branch. To date, we have accumulated stand count, root rating and yield data from 18 trials. All of these trials have included Counter, Force and Lorsban, which I will refer to as the CFL standard when comparing treated to untreated plots. Every year our trials include new products such as Aztec, Fortress and Regent, but the CFL standard provides us with long term information.
In regard to benefits over time in the 18 trials, the average yield of the CFL standard treatments was 11 bu/acre higher than that of untreated continuous corn. On a site basis, the yield gain was 12.9 bu per acre in 13 trials at the Western Branch and 6.2 bu/acre in 5 trials at the Northwestern Branch. The yield gain of 13 bu at the Western Branch was associated with an average root rating of 3.3 in the untreated plots and a 5.2% stand increase in treated plots. In contrast, the 6 bu/acre yield gain at the Northwestern Branch was associated with an average root rating of 2.6 in the untreated plots and a stand increase of less than 1% in the treated plots.
It is worth noting that the yield gains over time have been fairly significant despite the relatively low level of rootworm injury. Our root ratings in untreated plots have ranged from a high of 5.4 to a low of 2.0. Although, we often precede our continuous corn trials with a late planted trap crop, average rootworm pressure rarely exceeds a 4.0 rating.
The average yield gain of 13 bu/acre at the Western Branch from soil insecticide use has been substantial as a result of stand protection and less root injury. In contrast, the benefit of 6 bu/acre from soil insecticide treatment at the Northwestern Branch has been limited because of low levels of rootworm injury and minimal stand losses caused by cutworms. These results illustrate how soil insecticides may not have the same benefits for each location.
The following is an adaptation of an article written by Dr. Bob Nielsen which appeared in the April 24, 1998 issue of the Purdue Pest Management and Crop Production Newsletter.
Seed lots of some corn hybrids being delivered this spring are uncommonly small. The smallest I have seen is a 100,000 kernel bag that weighs 32 lbs. (equivalent to a 25-lb. 80,000 kernel bag). This translates to about 3100 seeds per lb. or almost twice as small as what many farmers would prefer to plant. Seed size in and of itself should not be of concern relative to the potential yield of a given seed lot of hybrid corn. But, seed as small as mentioned above deserves some additional comments relative to planter adjustments and operation.
Finger-Pickup Style Seed Metering Units: Several options exist for adjusting a finger-pickup style metering unit for small seed sizes. First of all, replace the brushes that help remove double seed pickups. Secondly, the tension of the finger assemblies can be increased, but is best performed by planter service technicians. If you have the time, take a sample of the small seed plus your metering units to your dealer and ask them to fine tune the units to your seed. Be aware, however, that increasing the finger tension will also cause the whole planter drive system to operate a little harder and increase the odds for slippage of the drive tires. Double check the planter tire pressures and keep the starter fertilizer tanks full to ensure maximum ballast to prevent tire slippage.
Another option to deter double drops with excessively small seed is to decrease the planting speed to allow the metering unit more time to eliminate doubles and triples. Planting speed should be no greater than five miles per hour.
Vacuum or Air Seed Metering Units: Most planters that utilize this type of pneumatic metering technology can be adjusted to accurately meter extreme seed sizes through prudent choice of both seed disc size (size of holes) and the system's air pressure. Case planters utilize a pneumatic metering technology, but with a single metering unit (drum) that delivers seed to all the rows of the unit. Adjustment for seed size with this planter is primarily by choice of drum size and secondarily by modification of air pressure to the system.
Final Comments: No matter what style of seed metering unit your planter uses, take the time to 1) calibrate the planter to the seed size prior to planting and 2)check the seed placement during the planting operation. Both activities are recommended every year, but may be especially important when faced with unusually small seed corn.
Thanks to Bruce Reynolds (Orville Redenbacher Popcorn) and Larry Cline (John Deere) for their suggestions regarding finger-pickup metering units.
How late can forage crops be planted? In the Ohio Agronomy Guide, I recommend that forages be planted by April 20 in southern Ohio, and May 1 in northern Ohio. These are the ideal dates. Forages can be planted later than these dates, but as planting is delayed, the risks increase. It all depends on the weather conditions six to eight weeks after planting. Delayed planting results in young seedlings being subject to the stresses that can develop during the normally drier and hotter summer months, and the likelihood of insect damage (potato leafhopper on pure legume stands). Weed competition will become greater as planting is delayed, so be prepared to use herbicides for good seedling establishment.
As Ohio continues to be soggy and the weeds continue to grow, some more reminders on burndown herbicides:
Don't use rates that are too low for the size of the weeds present. While we can often use 1 or 1 1/2 pints of Roundup (or the corresponding rate of Touchdown) with a pint of 2,4-D ester in April, weeds may be too large for these rates now. If necessary, use 1 quart or more of Roundup (or 1 1/2 pints or more of Touchdown) to achieve complete control of emerged weeds. If 2,4-D ester is omitted to provide maximum flexibility in the soybean planting schedule, it will be even more important to use the higher rates of Roundup or Touchdown. The addition of ammonium sulfate may improve control of large weeds. Rates of Gramoxone should be increased also with increased weed size, but keep in mind that systemic herbicides will probably be more effective than Gramoxone on large annual weeds and perennials.
As perennial weeds and sods get larger, there will be an opportunity to get better control of the entire plant, rather than just the suppression of top growth that often occurs with early spring applications. Ideally, perennials should be in the bud to flower or boot to seedhead stage for most complete control with Roundup/Touchdown, but control should improve with increasing size even before these stages are reached. Control of perennials generally requires at least 1 quart of Roundup or Touchdown.
When perennial weeds or large annual weeds are the target, mixing other herbicides with Roundup/Touchdown can reduce their activity (herbicides with contact activity). Herbicides in this category include any product containing atrazine, cyanazine, metribuzin, or simazine. Increasing Roundup/Touchown rates or adding ammonium sulfate can reduce this antagonism, but we suggest separate applications when going for maximum burndown herbicide activity. Using fluid fertilizer as the spray carrier is also not recommended when perennials or large annual weeds are the target.
As planting is delayed, the burndown program becomes a more significant part of the overall herbicide program. The delay allows more summer annual weeds to emerge, which are controlled by the burndown herbicides. This will allow for more effective implementation of total postemergence systems, possibly reducing postemergence herbicide use. So, as we stated above, do not make the mistake of using lower than required rates of burndown herbicides. You may get "burnt" by doing so.
Over the past 4 weeks many areas of Ohio have had 10-12 days of rain. I would anticipate little N loss from Spring applied anhydrous ammonia with N-Serve (5-10% loss), even on wet soils. Small amounts of N may have been lost in soils where drainage has allowed the surface to dry between rains. In these well drained soils one could expect around a 10-20% N loss from anhydrous ammonia applications and a 20-30% loss from UAN or urea applications. In poorly drained fields, losses of N may be higher than normal. A loss between 20 and 50% may have occurred in those fields with anhydrous ammonia applications and losses between 30 and 60% may have occurred with UAN or urea applications. Wet spots in fields will have the greatest susceptibility to N losses from denitrification.
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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: State Specialists: Pat Lipps and Anne Dorrance (Plant Pathology), Mark Loux (Weed Science), Hal Willson (Entomolgy), Peter Thomison (Corn Production), Jay Johnson (Fertility); District Specialists: Ed Lentz (Agronomy); Extension Agents: Larry Lotz (Fayette), Roger Bender (Shelby), Greg LaBarge (Fulton), Dennis Baker (Darke), Max Mohler (Lima Branch), Gary Wilson (Hancock), Barry Ward (Marion), Mike Estadt (Pickaway), Ray Wells (Ross) and Steve Prochaska (Crawford).
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.
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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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