In This Issue:
- Corn Replant Decisions Update and Review - (Adapted from Singin’ From The Same Sheet of Replant Music, 5-22-2005)
- Weed Escapes in Corn and Postemergence Options
- Postemergence Control of Dandelion
- Assessing the Current Level Of Wheat Leaf Diseases In Ohio and Making Fungicide Applications
- Slugs Beginning to Feed
- Time to Scout for Cutworm
- Status of Soybean Rust
- Wheat Production Field Day June 21, 2005
- Forecasting Wheat Fusarium Head Blight or Head Scab in Ohio
Corn Replant Decisions Update and Review - (Adapted from Singin’ From The Same Sheet of Replant Music, 5-22-2005)
Authors: Patrick Lipps, Peter Thomison, Gregory Shaner, Bob Nielson
Germination and stand establishment for mid-April planted corn in parts of Indiana and Ohio have been stressed beyond their limits this year as a result of cold temperatures, imbibitional chilling injury, excessive rainfall, saturated soils, dense surface crusting, and seedling diseases during the first four weeks after planting. Stand establishment problems have been particularly common for corn planted 4 to 5 days prior to the onset of the cold snap and heavy rains of late April. Consequently, estimates of the number of replanted acres are higher than normal and perhaps greater than any year in recent history.
Typically, the greatest challenge in making a replant decision is assessing the health and survival of the original stand of corn. Unfortunately, as in most years, some percentage of replanted fields will not return an economic gain to the grower because the replant “trigger” was pulled on the basis of emotion, peer pressure, or misinformation. The following points are intended to make sure everyone is “singing from the same sheet of music” when it comes to assessing troublesome stands of corn.
Fields of otherwise healthy looking corn should not be replanted simply because of injury to the plants’ seminal (also called embryonic) root systems.
Having said this, it is true that assessing the true health of plants in some fields has been difficult at best. Growers have often been uncertain whether they are dealing with 20,000 healthy plants (and thus likely not economical to replant in mid-May) or 20,000 “wanna-be” “half-hearted” “weak-kneed” and otherwise less than vigorous plants that will never regain their potential glory to produce maximum sized ears. The adage “patience is a virtue” is very applicable to the need for growers to allow damaged stands time to demonstrate their ability to recover or not.
Every field needs to be judged on its own merits (or demerits).
It is particularly irresponsible this planting season to be handing out blanket recommendations on replanting based on observations (or hearsay) from other fields, perhaps with totally different scenarios. Fields that initially looked equally troublesome during emergence have often become polar opposites in terms of their eventual stand establishment.
The nutrient reserves in the kernel endosperm can completely sustain a young corn seedling from germination through about leaf stage V1 (one visible leaf collar) or V2 (Hochholdinger et al., 2004).
Consequently, prior to development of post-embryonic nodal roots from the crown area of the plant, good health of the kernel and mesocotyl is paramount for seedling survival and vigor.
A healthy kernel and mesocotyl can enable a seedling with damaged embryonic roots to survive until nodal roots begin developing from the crown area.
Significant disease development in the kernel and/or mesocotyl prior to nodal root development is usually considered to be the proverbial “kiss of death” for young seedlings.
The same prognosis holds true for severe insect injury (wireworms, seedcorn maggots, white grubs) or any other stress that damages the kernel or mesocotyl prior to nodal root development.
The importance of kernel and mesocotyl health to plant survival slowly diminishes as successive sets of nodal roots form from the crown of the plant (see below).
Health of the radicle and lateral seminal roots (aka embryonic roots) prior to nodal root development is desirable, but is not as critical for the survival of young seedlings as is the health of the kernel and mesocotyl.
Injury or death of embryonic roots due to fungal diseases is obviously not desirable, but does not impose a death penalty on the seedlings.
A return to cold and wet soil conditions, coupled with cloudy days not conducive for plant photosynthesis, would indeed favor the continued development of these seedling diseases and perhaps eventual seedling death or severe plant stunting.
Conversely, warmer and drier soils, coupled with plenty of sunshine for plant photosynthesis, would favor rapid corn root development plus would slow the progress of the disease organisms.
Loss of the radicle root, in and of itself, has no direct bearing on subsequent development or morphology of the corn plant.
Post-embryonic nodal roots begin to elongate from the first stalk node in the crown area of plants shortly after leaf stage V1 and are usually distinctly visible by V2.
Individual “rings” of nodal roots will continue to develop from subsequent stalk nodes over time, approximately at the same pace as the emergence of leaf collars, up to the 7th or 8th stalk node.
By the time a plant reaches approximately V4 (four visible leaf collars), three “rings” of nodal roots should be visible at the crown of the plants. Such plants are essentially independent from any further sustenance that the kernel may yet be able to furnish.
While nodal root initiation usually does not occur beyond the 7th or 8th stalk nodes, lateral branching and dry matter accumulation of existing nodal roots continues throughout the growing season, although at an ever-decreasing rate once pollination occurs.
The primary (harvestable) ear in corn is not initiated until approximately V5 (five visible leaf collars). Consequently, stress prior to V5 has no direct effect on ear size determination unless its eventual outcome is a severely stunted plant. The main consequence of stress from planting through the early leaf stages is the potential loss in effective plant population, one of several components that determine final grain yield.
For more information refer to the following related sources.
Lipps, Patrick. 2005. Assessing Corn Seedling Emergence and Seedling Diseases. Crop Observation Reporting Network, Ohio State Univ. Available online at http://corn.osu.edu/story.php?setissueID=82&storyID=453[URL verified 5/19/05].
Lipps, Patrick and Peter Thomison. 2005. Corn Emergence Problems and Replant Decisions. Crop Observation Reporting Network, Ohio State Univ. Available online at http://corn.osu.edu/story.php?setissueID=83&storyID=461[URL verified 5/19/05].
Nielsen, R.L. (Bob). 2004a. Germination Events in Corn. Corny News Network. Purdue Univ. Available online at http://www.kingcorn.org/news/articles.04/Germination-0502.html[URL verified 5/19/05].
Nielsen, R.L. (Bob). 2005a. I’ve Got The Corny Stand Establishment Blues…. Corny News Network, Purdue Univ. Available online at http://www.kingcorn.org/news/articles.05/StandEstablishment-0503.html [URL verified 5/8/05].
Nielsen, R.L. (Bob). 2005b. Stress Continues for Corn Growing Under Refrigerated Conditions. Corny News Network, Purdue Univ. Available online at http://www.kingcorn.org/news/articles.05/RefrigCorn-0429.html[URL verified 5/3/05].
Authors: Mark Loux
Weed control is less than ideal in many corn fields, even where preemergence herbicides were previously applied. Some things to keep in mind as you assess weed control and make decisions on postemergence treatments:
- Although weeds may be escaping preemergence treatments, the weed population in these fields is going to be much lower than fields where no herbicides have been applied. So, the timing of postemergence application is probably less critical with regard to minimizing yield loss due to weed-crop competition. However, postemergence grass herbicides in corn are most effective when grasses are not more than 3 to 4 inches tall, and application timing should be based on the size of grasses in the field (unless grasses are absent from the weed population).
- Injury from postemergence corn herbicides is more likely when the health of the corn plants is less than ideal, as in a number of corn fields in Ohio where corn is currently struggling. We generally advise delaying postemergence applications until the crop resumes active growth, when it is better able to metabolize herbicides.
- The risk of injury from ALS-inhibiting herbicides is increased during periods of cool weather, such as we are experiencing this week. We have occasionally observed an increase in the frequency of stunting, yellowing, and internode shortening (stacking) when ALS inhibitors were applied to corn under cool conditions.
- We suggest avoiding postemergence applications to corn this week based on the following: 1) the health of the corn crop is less than ideal; 2) cool and cloudy conditions can increase the risk of herbicide injury; and 3) weed growth should be minimal under the weather conditions forecasted for the rest of this week.
- On a final note, corn development under this spring’s weather conditions may result in somewhat shorter plants for a given growth stage, compared to other years. In other words, a plant in the V5 stage might be only 13 inches tall this year, whereas in other years it might be 16 inches in height or taller. Staging corn properly is important to reduce the risk of injury from ALS-inhibiting herbicides (Accent, Option, Hornet, etc). Labels of products containing an ALS-inhibitor generally allow broadcast application through the V5 or V6 stage of corn development, and also specify a maximum corn height.
Authors: Mark Loux
Dandelion, which may have replaced Canada thistle as the state weed, is out of control in many corn and soybean fields. Burndown treatments provided less than adequate control in many fields, and others have yet to be treated. Dandelion can be extremely competitive with corn and soybeans, especially if moisture becomes limiting during the early stages of crop development. A common statement made by many producers several years ago in a season where early-season wet weather was followed by very dry weather: “where I had dandelions, I had no crop”. We strongly suggest the application of postemergence herbicides in fields where dandelions were not adequately controlled by tillage or prior herbicide application. An important aspect of dandelion biology that comes into play here – most seed produced earlier this spring will germinate within the next month. Therefore, the most effective postemergence treatments will control emerged dandelions and provide a period of residual control.
In Roundup Ready soybeans, the most effective treatment is likely to be a mixture of glyphosate and chlorimuron. The addition of chlorimuron can improve control of existing plants, and it will provide some residual control. Classic and Synchrony XP contain chlorimuron, but Classic may be the better choice to minimize soybean injury and maximize residual control. Glyphosate rates of 1.1 to 1.5 lbs of acid equivalent should be used, the higher rate where dandelion pressure is more severe. In non-Roundup Ready soybeans, the highest labeled rate of Classic will be most effective.
In OSU research the past several years, the most effective postemergence treatments for control of dandelion in corn have included the following: Equip; Equip plus Callisto; Callisto plus atrazine; Steadfast/Steadfast ATZ plus dicamba; Steadfast/Steadfast ATZ plus Callisto. The treatments containing Callisto have more rapid activity on dandelion than the others. In our research, ratings of all of these treatments may be similar at 4 weeks after treatment, but ratings of the Callisto-containing treatments are considerably higher at 2 weeks after treatment.
Authors: Patrick Lipps
Wheat diseases have been quite low in Ohio this year probably due to the cooler temperatures experienced during late April and early May. Most of the wheat crop is developing normally with most of the wheat now heading or in late boot stage. By now we usually have seen several different wheat diseases in different parts of Ohio, but most fields in all areas of Ohio are quite clean of diseases. The only exception to this is a few fields planted to susceptible varieties that have moderate levels of powdery mildew. When scouting fields you need to assess level of disease before any fungicide should be applied. If you walk into a field and you have to hunt for the disease, then it does not need to be sprayed. Assess fields by pulling about 30 to 50 tillers randomly in the field and see how far up the plant the disease has moved. Spray only if the disease is moving onto the leaf below the flag leaf. Your objective is to keep the top two leaves clean and keep the head clean. Additionally, if the variety planted is resistant or moderately resistant to the disease, then a fungicide application will not improve yield or at least not pay for the fungicide. Fungicides provide economic return when applied to susceptible varieties and when disease is beginning to attack the upper leaves of the plants.
Decisions to use a fungicide need to be made fairly soon because of label restrictions. Quilt can not be applied after Feekes' growth stage 9, or pre boot stage. In Ohio, Tilt, PropiMax, Quadris and Stratego can be applied up to Feekes' growth stage 10.5 or through heading but not after the plants start to flower. If the majority of the heads in the field have anthers exposed, then it is too late to apply these fungicides. Headline is the only fungicide that is labeled to be applied through flowering (no later than the end of flowering or Feekes' growth stage 10.5.3). Each of these fungicides has activity against the major wheat leaf diseases but none of them do much for Fusarium head scab. We do not recommend applying a fungicide for head scab because research has indicated control is very inconsistent and usually not economical for this disease.
Authors: Ron Hammond, Bruce Eisley
Having experience egg hatch in most locations in the state, we are now getting reports of slug injury. Most slugs are still quite small, which suggests they are mostly juvenile gray garden slugs. However, in some fields, we are seeing numerous marsh slugs, the occasional small dusky or banded slugs, and even a few older adult gray garden slugs. In Fairfield County, we saw an early-planted corn field that had slug defoliation. In this field, juvenile slugs were getting large enough to cause leaf feeding. In Knox County, we saw significant feeding on soybean cotyledons, although the emerging unifoliate leaves were free of injury. Juvenile gray garden slugs were still relatively small, although numerous marsh slugs were also present. These observations suggest that most of this feeding was perhaps due to marsh slugs rather than the juvenile gray garden slugs. In Wayne County, injury to corn was just beginning.
Growers should expect feeding and defoliation to increase as the slugs grow in size over the next few weeks. Another factor to consider is the continuing cool and wet weather forecast for at least an additional week. Crops are growing very slow, and unless the weather turns warmer, crops will have difficulty outgrowing slug injury. If injury becomes severe and newer leaves are being defoliated, treatment may become warranted. The use of Deadline MPs or one of the newer molluscicide baits should be used at the recommended rate. At this time, the availability of the newer baits, Orcal Snail and Slug Bait and Metarex is not known. If these are not available, Deadline MPs is the choice of bait.
Additionally, many fields that have not yet emerged or that will be planted over the coming few weeks will be very vulnerable to slug injury. Slugs will be even greater problems if the seeds are planted in less than ideal conditions, resulting in seed furrows that do not close well. Slugs will crawl up and down the seed furrows eating to their heart's content. Growers who have had stand problems caused by slugs in the past should check their fields carefully. If a large number of slugs are present in a field with a history of stand problems, growers might consider an at-planting time molluscicide application.
Authors: Bruce Eisley, Ron Hammond
We have not seen any cutworm damage nor have we had any reports about cutworm damage but this is about the time that we would expect to begin seeing cutworm injury. Even though adult flights were down this year, there still could be some fields with injury. As always, our suggestion is to scout fields for cutworm injury and larvae and make treatments as needed. Treatments for cutworm are usually recommended when 3% or more of the plants are cut and worms are small, 1inch or less. Corn that was planted into fields with a lot of winter annuals, especially chickweed, should be scouted as the corn emerges beginning this week. Fields that have a history of cutworm injury should also be checked.
Authors: Anne Dorrance
No further positive finds were posted last week on the USDA website (www.sbrusa.net). In addition, the first finding in Georgia, which occurred on volunteer soybeans, was destroyed. This reduces the inoculum load to only those locations in Florida. In conversations with some of my colleagues in the south, Louisiana is dry and they have stopped planting for the time being. We will continue to monitor the situation as the season continues to develop. Most of Ohio’s 46 sentinel plots have emerged and are between the cotyledon and V1 (first true leaf growth stage. One sentinel plot, Pickaway county, reported light feeding by bean leaf beetle. No other diseases or insect problems were reported.
Authors: Patrick Lipps
The Ohio Agricultural Research and Development Center will be holding a Wheat Production Field Day form 9:00 am to noon on Tuesday, June 21, 2005 at the Northwest Agricultural Research Station near Hoytville, OH. The station is located one mile east of SR235 between Hammansburg and Oil Center roads in Wood County. All wheat growers and persons involved in wheat production are invited to attend. Presentations will be given on wheat disease identification, scouting and fungicide usage; wheat variety and row spacing interaction effect on yield; managing nitrogen and sulfur in wheat; and an update on wheat breeding at OARDC and new variety releases. In addition, representatives from the Ohio Wheat Growers Association will present an update of their recent activities to help wheat production in Ohio. Please come and take this opportunity to speak with the researchers and ask questions relative to your wheat production problems.
Authors: Patrick Lipps, Pierce Paul, Dennis Mills
The wheat crop is now entering the heading and flowering stage in the southern part of the state and much of the wheat will be in flower during the latter part of this week and over Memorial Day weekend. The wheat in the more northern counties is still in boot stage and they will likely go into flower next week sometime. The weather that has occurred last week and this week has not been favorable for the Fusarium fungus and although we are getting some precipitation this week, the temperatures have been quite low. We have looked at the most recent forecasts for head scab on the Fusarium Head Blight Prediction Center ( website can be found at : http://www.wheatscab.psu.edu/) which have indicated that for those growers that have planted wheat after soybeans the risk of scab is quite low for those fields in southern Ohio that were in flower over the past several days. The risk of head scab is moderate for those growers that have planted wheat into corn residue. Corn residue is where the Fusarium fungus survives the winter so the more corn residue in the field the higher the level of spores there is to infect the wheat crop. We recommend that growers check the scab forecast web site daily as the wheat crops begins to flower in their part of the state. When you visit the web site you will note that there has been a problem with getting a risk prediction from specific weather station locations (blue dots on the forecast state map). There has been some problem with accessing this information. However, the overall predictions presented on the state map are functioning well.
State Specialists: Peter Thomison (Crop Science-Corn), Pat Lipps, Anne Dorrance and Dennis Mills (Plant Pathology), Mark Loux and Jeff Stachler (Weed Science), and Bruce Eisley and Ron Hammond (Entomology). Extension Educators: Roger Bender (Shelby), Steve Foster (Darke), Gary Wilson (Hancock), Dusty Sonnenberg (Henry), Harold Watters (Champaign), Tammy Dobbels (Logan), Glenn Arnold (Putnam), Mark Koenig (Sandusky), Todd Mangen (Mercer), Steve Bartels (Hamilton), Bruce Clevenger (Defiance), and Steve Prochaska (Crawford)