http://www.ag.ohio-state.edu/~corn/ |
|
In This Issue:
A) Gray Leaf Spot and Yield Losses on Corn
B) 1999 Ohio Wheat Performance Tests are Now Available
C) Assessing The Impact of Drought Damage on Corn Pollination
D) For More Information on Drought Damage in Corn
E) Field Crop Pest Activity
F) Postemergence Herbicides in Soybeans
G) Weed Control in Wheat Stubble
H) Pricing Standing Corn for Silage
Gray leaf spot has increased significantly over the past two weeks in continuous no-till corn fields in east central Ohio. The hot humid weather we have been experiencing has promoted disease spread. Probably the most significant environmental factor to watch is average daily humidity. Gray leaf spot develops to epidemic levels when we have an extended number of days in July and August with daily average relative humidity above 90%. So far this summer many locations in Ohio have reported relative humidity above 90% for at least 12 hours a day. Gray leaf spot does not need a lot of rain to develop. It does need free water on the leaf surfaces for about 13 hours, but this occurs in fields during the morning hours, especially those that routinely have fog. Gray leaf spot does need a dry period in the afternoon to spread spores that develop on infected tissues. We expect gray leaf spot to continue to develop as the season progresses, but the big questions is how much yield loss will be attributed to it.
A number of researchers have attempted to determine the amount of yield loss in several different hybrids due to the effects of gray leaf spot. Most have found that there is not a direct relationship between yield loss and the percentage of leaf area affected with the disease. This is because actual yield is dependent on a multitude of different factors. Yield losses from gray leaf spot results from reduced photosynthesis by the leaves which reduces grain fill and kernel size. A severe outbreak of gray leaf spot may lead to reduced stalk strength and standability, predisposing the crop to lodging.
The amount of yield loss is related to the time of infection in relation to the growth stage of the crop, weather conditions during grain fill, susceptibility of the hybrid, hybrid maturity, severity of lodging from stalk rot and yield potential of the hybrid. Thus, yield loss from this foliar disease is difficult to predict.
There probably is no way to accurately predict yield losses from gray leaf spot at this time. However, after working with this disease for many years we do have some guidelines. We know that the earlier the leaves above the ear leaf become infected the greater the yield loss. The greatest yield losses occur when over 90% of the leaf area of the plants are covered with disease by a week after tasseling and little yield loss occurs on plants when the upper leaves are not infected until 5-6 weeks after tasseling. Below are tentative guidelines for yield losses from gray leaf spot based on information from Kentucky, Indiana and Ohio; actual yield losses will vary.
Predicted Yield Loss Due to Gray Leaf Spot
| Percentage ear leaf area affected by early dent stage | Approximate yield loss expected |
| 5% or less | 0-2% loss |
| 6-25 % | 2-10% loss |
| 25% - 75% | 5-20% loss |
| 75%-dead leaf | 15-50% loss |
The Ohio Wheat Performance Tests is now available at your county OSU Extension offices and it will be posted on the Ohio State University Ohioline web page soon http://www.ag.ohio-state.edu/~perf. The publication reports the yield and performance characteristics of 52 varieties from 18 seed companies grown at five different locations in the state. Sites of the performance tests were: Northwest Branch (Hoytville), Bucyrus, Wooster, Greenville, and Circleville. Wheat yields were very good across all locations. The average yield for all varieties across locations was 79.6 bu/A. The location with the highest average yield was Bucyrus with 89.7 bu/A and the lowest was Wooster with 66.9 bu/A. There is a smorgasbord of other information available in the report including: heading dates, test weight, flour yield, flour softness rating, plant height, heading date, and powdery mildew severity. The varieties are listed in order of maturity, with the earliest varieties listed first.
Growers should use the report to help select varieties for growing this coming year by comparing varieties for different characteristics, not just yield. The tables listing two and three year performance summaries will be most helpful in determining varieties with proven performance in Ohio. There is a lot of information presented in this three page report. Spending half an hour looking over the data and comparing variety performance characteristics will help you choose the best varieties available to help insure those top yields. Make a list of the varieties that you are interested in and get additional information about these varieties from the seed company that sells seed of that variety. Ask the seed representative for information on straw strength (lodging), winter hardiness, and resistance to other diseases, like wheat yellow mosaic virus, Stagonospora blotch, leaf rust and head scab. Also ask about the seed treatment used on the seed. Raxil -Thiram or Dividend XL are two of the better seed treatments available today. Taking the time to review performance data now will help you select the right variety for your farm. The most expensive seed does not necessarily produce the most yield or profit. Consistent performance, high test weight, straw strength, disease resistance and grain quality are the factors that pay for themselves.
As July of 1999 ends as one of the driest and hottest on record, many corn growers may want to determine what impact drought stress had on corn pollination, the stage in corn development most senstive to such stress conditions.
There are two techniques commonly used to assess the success or failure of pollination. One involves simply waiting until the developing ovules (kernels) appear as watery blisters (the "blister" stage of kernel development). This usually occurs about 1 1/2 weeks after fertilization of the ovules. However, there is a more rapid means to determine pollination success.
Each potential kernel on the ear has a silk attached to it. Once a pollen grain "lands" on an individual silk, it quickly germinates and produces a pollen tube that grows the length of the silk to fertilize the ovule in 12 to 28 hours. Within 1 to 3 days after a silk is pollinated and fertilization of the ovule is successful, the silk will detach from the developing kernel. Unfertilized ovules will still have attached silks.
Silks turn brown and dry up after the fertilization process occurs. By carefully unwrapping the husk leaves from an ear and then gently shaking the ear, the silks from the fertilized ovules will readily drop off. Keep in mind that silks can remain receptive to pollen up to 10 days after emergence. The proportion of fertilized ovules (future kernels) on an ear can be deduced by the proportion of silks dropping off the ear. Sampling several ears at random throughout a field will provide an indication of the progress of pollination.
For those of you addressing questions concerning drought damage in corn, the following are some relevant articles from the National Corn Handbook (NCH) that may help (index of NCH publications available via the web at the following address - http://www.agcom.purdue.edu/AgCom/Pubs/NCH/)
I cited NCH-58 in a previous issue of C.O.R.N. as a source of information on salvaging drought damaged corn.
"Utilizing Drought-Damaged Corn" (NCH-58) - http://www.agcom.purdue.edu/AgCom/Pubs/NCH/NCH-58.html
"Weather Stress in the Corn Crop" (NCH-18) - http://www.agcom.purdue.edu/AgCom/Pubs/NCH/NCH-18.html
"Growing Season Characteristics and Requirements in the Corn Belt" (NCH-40) - http://www.agcom.purdue.edu/AgCom/Pubs/NCH/NCH-40.html
BEAN LEAF BEETLE ACTIVITY CONTINUES
The number one insect pest problem in Ohio at the present time is the bean leaf beetle (BLB), which is causing various levels of feeding injury throughout the State. Where a BLB population achieved a running start in early planted soybeans, 1st generation adult BLB abundance may be very high with significant defoliation. However, in most soybean fields, BLB numbers are averaging about 1 to 2 beetles per sweep which will cause about 4 to 6% defoliation (if you don't overestimate defoliation).
The questions has been raised about the need to treat soybeans at this point in time to prevent additional injury by the forthcoming 2nd generation. This question is often linked to the fact that many products available for BLB cannot be used later in the season due to pre-harvest limitation periods (e.g. Ambush & Pounce @ 60 days, Lorsban 4E @ 28 days, Warrior @ 45 days, etc.). However, it should be noted that various formulations of carbaryl (Sevin) can be applied late into the season.
If a soybean field is clearly exhibiting economic levels of BLB activity (i.e. 5 or more BLB per sweep plus defoliation levels exceeding 15%), then immediate action is warranted. However, it should be noted that the larvae of the forthcoming 2nd generation BLB are currently developing on the soybean root system and treatment applied at this point in time may or may not reduce the forthcoming generation.
Another key factor in BLB management is the relationship of soybean development to BLB activity. Early soybeans filling pods at this point in time may be susceptible to pod injury by the 1st generation BLB currently in the field. However, it should be noted that pod feeding by BLB is generally most intense at a point when pods are more succulent than foliage that is beginning to discolor. Thus, some plantings may be more susceptible than others depending on the occurrence of peak BLB activity in relation to pod development. Finally, it should be emphasized that pod feeding injury by BLB only results in significant yield losses if an infection period occurs causing the development of moldy seeds. In 1994, BLB activity was above normal and significant levels of pod injury were observed, but the impact on yield was minimal due to a dry late summer season and an absence of mold development in the damaged pods.
CORN ROOTWORM ACTIVITY
We are currently into the third week of the adult corn rootworm survey. Observations of adult rootworm catch in many central and south-western Ohio soybean fields during the first bi-weekly trap period continues to demonstrate that first year corn rootworm is not likely a problem in most regions of the State. Parallel observations on first year corn at various sites also indicate that adult rootworm activity is exhibiting normal patterns of activity. Trap data from the northwest region of the State has not been reported at the time of this release.
Visual counts conducted in corn fields during the past week indicate that adult rootworm activity in corn is decreasing as many fields reach the brown silk stage. Thus, movement of adult rootworm beetles to attractive sites such as late planted corn fields should be in progress. If a first year corn rootworm population exists in an area, movement of the rootworm beetles into soybeans should be evident at this time.
POTATO LEAFHOPPER ON ALFALFA
As we enter the month of August, potato leafhopper (PLH) populations continue to be very activity and should be monitored to determine whether treatment of the third cutting is warranted or not. In general, PLH activity tends to decline at this time of the year as the development of the immature nymphs tends to taper off. However, above normal temperatures combined with dry weather continues to maintain PLH activity this year. Sweep-net collections in our plots last week were averaging 4 to 5 PLH adults per sweep (plus some nymphs) on 10 inch high alfalfa. Such a level of PLH activity is about five fold the economic threshold, and symptoms of hopper burn were becoming evident.
Herbicides should no longer be applied in soybeans, unless they are double crop soybeans and/or Roundup Ready soybeans. The shortest time frame from herbicide application until harvest is 14 days for Roundup Ultra. The next interval is 30 days for Basagran and 45 days for Cobra. Flexstar and Reflex certainly should not be used any more as crop rotation to corn or wheat is 10 and 4 months respectively. Fields with weeds two feet above the soybean canopy have already reduced most of the soybean yield for the season and any field with weeds just coming out of the soybean canopy should not reduce yield too much as the soybeans have out competed the weeds for most of the season. Only if the soybeans are small and delayed in maturity will the weeds just coming out of the soybean canopy significantly reduce soybean yield.
Double crop soybeans should be sprayed as soon as possible to allow for maximum time of recovery from herbicide injury, allow enough time between application until harvest and allow the proper interval for crop rotation. When spraying double crop soybeans try to reduce the amount of soybean injury as much as possible. Basagran, FirstRate, Roundup Ultra, Select, Poast Plus, Fusion, and Assure II will be the safest products to apply to double crop soybeans. Select has the shortest interval from herbicide application to harvest of 60 days with all others being greater than 75 days, except Fusion that says to apply prior to the bloom stage. Flexstar and Reflex should not be applied to double crop soybeans, unless rotating to soybeans next year. The earlier the herbicide application in double crop soybeans the sooner the soybean recovery from any possible weed competition to maximize yield.
If annual weeds are the dominate species in the field then mow the field as soon as possible and probably another time so as to not allow the weeds to go to seed. The other option is to apply Roundup Ultra or Touchdown at 1.0 to 1.5 pt/A or 0.8 to 1.2 pt/A, respectively as soon as possible. Not allowing the annual weeds to go to seed in the wheat stubble can make weed control substantially easier in years to come.
If perennial weeds are the dominate species in the field or thick patches of perennials are in the field, then mow the field as soon as possible, as long as there is substantial moisture to allow for regrowth. For those areas of the state that have been dry and are still dry, do not mow the fields as there will not be enough regrowth to control the perennials. The reason for mowing the field is to reduce seed production of the annual weeds in the field and make the perennial weeds regrow to a uniform height for application. Allow weeds to regrow until end of September or early October before making an herbicide application. Waiting until then will allow for maximum movement of Roundup Ultra or Touchdown to the roots or rhizomes of the weeds.
In the dry areas of the state, apply the Roundup Ultra or Touchdown now when the perennials are not stressed or wait until October to spray. It is hard to say when is a good time to spray to get maximum control of the roots or rhizomes in the dry spots of the state. If plants are stressed now then not enough herbicide will translocate to the roots or rhizomes for effective control, but if it stays dry then the plants may stop growing altogether for the rest of the season and no herbicide will translocate. Apply at least 1.0 qt/A of Roundup Ultra or 1.6 pt/A of Touchdown for control of several perennial species, but higher rates will be needed for species such as bindweeds, common milkweed, honeyvine milkweed, Canada bluegrass, horsenettle, and smooth groundcherry.
The following approaches can be used to price standing corn purchased from a neighbor. The first two equations establish a negotiation range by determining the price needed by the grain farmer and feeding value to the livestock producer. Other equations are provided to estimate yield per acre.
1) Grain value (Value of potential grain production to the grain farmer)
Value, $/ton = (grain, $/bu - drying and storage, $/bu)* (grain yield, bu/acre) -
harvesting costs, $/acre) / silage yield, ton/acre
Feed value (nutritional value based on prices for corn, SBM, and alfalfa hay)
Value, $/ton = (grain, $/bu * 6.89) + (44% CP SBM, $/ton * - 0.085)+(17% CP alfalfa hay,
$/ton * 0.326) - silage harvesting cost, $/ton
(This formula assumes 35% DM; adjust value based on actual %DM)
Feed value will be higher than grain value, but this approach allows you to establish a NEGOTIATING RANGE. The common approach of establishing value of corn silage at 7 * grain, $/bu will usually result in a value between grain and feed value and is not as responsive (grain price is the only variable) as the equations listed above.
To use the equations above, grain and silage yield must be estimated.
2) Silage yield: If 30 inch rows, measure off 17.5 feet (1/1000 of an acre) and cut all plants at the height that will be used by the chopper. Weigh and average for 4 to 6 areas in the field.
yield (tons/acre of wet silage) = (avg lbs per 17.5 ft * 1000) /2000
3) Grain yield: Take the same plants from step #1, count total number of ears. Remove every 5th ear in each row, and on each of the selected ears, count the number of kernel rows per ear and the number of kernels per row (ignore kernels on butt and tip of ear that are less than half the size of normal size kernels).
Grain yield, bu/acre = (avg number of ears per 17.5 ft * avg number of rows per ear * avg number of kernels per row) / 90.
Drought stressed corn example:
24 plants per 17.5 ft of row
12 kernel rows on each year
18 kernels per row
grain yield = (24 * 12 * 18)/90 = 57.6 bu/acre
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
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), Hal Willson (Entomology), Peter Thomison (Corn Production), and Jeff Stachler (Weed Science); District Specialists: Jim Jasinski (IPM), and Ron Hammond (IPM); Extension Agents: Dave Jones (Allen), Steve Prochaska (Crawford), Larry Lotz (Fayette), Greg La Barge (Fulton), Roger Bender (Shelby), and Gary Wilson (Hancock).
Editor: David A. Jones Web Editor: Nathan WatermeierInformation 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.
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.
TDD # 1 (800) 589-8292 (Ohio only) or (614) 292-1868
| C.O.R.N. | Newsletter | Archive | Search | Questions? | Ohioline | Publications |