C.O.R.N. Newsletter 2006-30

Dates Covered: 
September 12, 2006 - September 18, 2006
Editor: 
Andy Kleinschmidt

Fall Herbicide Treatments

Authors: Mark Loux

Fall herbicide treatments have become a fairly common practice for some no-till producers, who recognize their value for managing certain tough winter weeds and providing a weedfree seedbed in the spring. Fall herbicide treatments should accomplish two major goals. First, the fall treatment has to control winter annual, biennial, and perennial weeds that emerge in late summer or fall or are already present at the end of the previous crop’s harvest. Weeds in this category include chickweed, annual bluegrass, purple deadnettle, marestail, wild carrot, and dandelion, among others. These weeds overwinter and regrow in the spring, interfering with crop establishment and early-season growth, and they need to be controlled by a fall or early-spring herbicide application. A secondary goal is to prevent seed production by these weeds, which reduces future weed infestations. Fall herbicide treatments are by far the most effective method for controlling dandelions, poison hemlock, and wild carrot, which are difficult to control in the spring.

We have conducted research on the effectiveness of fall herbicide treatments for a number of years. In previous falls’ C.O.R.N. articles on this subject, we have listed what we feel to be the most effective treatments based on our research. This list remains mostly unchanged between last fall and this fall. We have added a new herbicide, Autumn, an ALS inhibitor labeled for fall application prior to corn. We have somewhat limited research on the effectiveness of Autumn compared to the other herbicides listed here, but it appears to control many winter annuals and dandelion when mixed with either 2,4-D or glyphosate. Autumn does not provide residual control of weeds that emerge in the spring. Effective fall herbicide treatments include the following:

Any crop next spring-
Glyphosate + 2,4-D

Soybeans next spring-
Glyphosate + 2,4-D
Canopy EX + 2,4-D
Sencor + 2,4-D (excluding dandelions)

Corn next spring-
Glyphosate + 2,4-D
Simazine + 2,4-D
Basis + 2,4-D
Autumn + 2,4-D or glyphosate

For control of winter annual weeds, apply herbicides anytime after early October. For the most effective dandelion control, delay application until after a frost. We have applied as late as early December for control of winter annual weeds, but we generally recommend application when dandelions are still mostly green, or by mid-November if possible. Apply glyphosate-containing treatments with ammonium sulfate, and additional nonionic surfactant if specified by the product label. Treatments that do not contain glyphosate should generally be applied with crop oil concentrate for best results.

Other herbicides (Valor, Scepter, Python, Aim, etc) can be applied in the fall, but most of these will not effectively control winter weeds unless they are combined with one of the herbicide treatments listed above. Effective control in the fall can be obtained with treatments costing $6 to $12 (excluding application cost), and we question the value of treatments that cost more than about $12. One of the reasons for this is that the use of a fall treatment, even one with residual activity, does not guarantee that only one herbicide treatment will be required in Roundup Ready soybeans the following year. Excess money spent on fall treatments results in less money available for weed control in the crop, where it usually is greatly needed.

Our experience has been that the primary benefit of fall treatments is control of weeds that are present at the time of treatment, not residual control of weeds the following year. The primary exception to this is Canopy EX, which provides a longer period of residual control of a greater number of weed species than other residual herbicides that can be applied in the fall. An effective fall treatment usually results in a field that is mostly free of weeds until about late April, and this goes for treatments without residual as well as those with residual. In other words, in late April we cannot usually discern much difference between a fall treatment of glyphosate plus 2,4-D versus Canopy EX plus 2,4-D, even though the CanopyEX provides residual activity into the spring. However, the effect of the residual herbicide becomes much more apparent by the end of May, when its activity on summer annual weeds comes into play.

The issue here is not really control at the time of soybean planting, since any effective fall treatment results in a relatively weed-free field at the end of April. The issue is how well the residual herbicide controls weeds after planting, in order to build more flexibility into the postemergence application window. This flexibility can result in less risk of early-season yield loss from weed interference and result in a better chance of getting the postemergence herbicides applied to the right size weeds. We also look to the residual herbicide to help control several weeds that glyphosate can be somewhat variable on, such as giant ragweed and lambsquarters. It is our opinion that, if glyphosate is being managed properly, it is typically going to be extremely difficult to get by with one postemergence glyphosate application unless the residual herbicide applied in the fall provides substantial weed control into late May. Even when this occurs, a second postemergence application is often needed to obtain season-long control.

Herbicides other than Canopy EX can provide residual control of certain weeds when applied in the fall, but they tend to control fewer weed species and/or be generally less effective than CanopyEX. For example, Valor provides residual control of lambsquarters into early June, but is less effective than Canopy EX and provides very little control of giant ragweed. Scepter provides very little control of lambsquarters or giant ragweed when applied in the fall, whereas it can provide substantial residual control of these weeds when applied in the spring. Gangster is labeled for fall application, and it may be fairly comparable to Canopy EX in its residual. Fall applications of Gangster would still require the addition of glyphosate plus 2,4-D, which would result in a high-priced treatment.

The bottom line on fall herbicide treatments – choose an effective treatment from the list above, and be cautious about adding residual herbicides that claim to improve control of weeds that emerge in the spring. The utility of most residual herbicides is maximized when applied in the spring prior to planting, not in the fall. A better alternative is use of a non-residual herbicide program in the fall, such as glyphosate plus 2,4-D, followed by spring application of residual herbicides. This approach provides for the greatest flexibility in the postemergence application window and the most effective control of weeds such as lambsquarters, marestail, and giant ragweed.

Troubleshooting Incomplete Ear Fill Problems in Corn

Authors: Peter Thomison

During the past two weeks, I have received questions about ears of corn with unfilled tips. In some cases, no kernels are evident on the last two or more inches of the ear tip. Several factors may cause this problem. The ovules at the tip of the ear are the last to be pollinated, and under certain conditions only a limited amount of pollen may be available to germinate late emerging silks. Pollen shed may be complete before the silks associated with the tip ovules emerge. As a result, no kernels form at the ear tip. Severe drought stress may result in slow growth of the silks that prevents them from emerging in time to receive pollen. Pollen feeding and silk clipping by corn rootworm beetles and Japanese beetles also contribute to pollination problems resulting in poorly filled tips and ears. I’ve observed this insect injury in late planted corn fields, especially field surrounded by early (late April/early May planted corn). In several fields, the damage has been extensive with many ears showing only a few scattered kernels.

Incomplete ear fill may also be related to kernel abortion. If plant nutrients (sugars and proteins) are limited during the early stages of kernel development, then kernels at the tip of the ear may abort. Kernels at the tip of the ear are the last to be pollinated and cannot compete as effectively for nutrients as kernels formed earlier. Stress conditions, such as heat and moisture stress, nitrogen deficiency, hail, and foliar disease damage, may cause a shortage of nutrients that lead to kernel abortion. Periods of cloudy weather following pollination, or the mutual shading from very high plant populations can also contribute to kernel abortion. Some agronomists characterize the kernel abortion that occurs at the end of the ear as “tip dieback”. Kernel abortion may be distinguished from poor pollination of tip kernels by color. Aborted kernels and ovules not fertilized will both appear dried up and shrunken; however aborted kernels often have a slight yellowish color.

Is the presence of barren tips a major cause for concern? Not always. In many cornfields this year, the favorable growing conditions may have resulted in a larger number of potential kernels per row than normal. So even if corn ear tips are not filled completely, due to poor pollination or kernel abortion, yield potential may not be affected significantly, if at all, because the numbers of kernels per row may still be above normal. The presence of ears consistently filled to the tip may actually indicate that a higher plant population is needed to optimize yields.

Potential for Stalk Rot and Lodging Problems in Corn

Authors: Peter Thomison, Pierce Paul

The dry weather that many areas of Ohio experienced in July and August is likely to increase the potential for lodging and stalk rot problems in corn. When stalk rot occurs late in the season as it often does, it may have little or no direct effect on yield. Nevertheless, stalk lodging, which results from stalk rot, can have such an impact on harvest losses that many plant pathologists consider stalk rots to be the most significant yield limiting disease of corn.

For a corn plant to remain healthy and free of stalk rot, the plant must produce enough carbohydrates by photosynthesis to keep root cells and pith cells in the stalk alive and enough to meet demands for grain fill. When corn is subjected to severe drought stress, photosynthetic activity is sharply reduced as leaves roll tightly and plant growth slows. As a result, the carbohydrate levels available for the developing ear are insufficient. The corn plant responds to this situation by removing carbohydrates from the leaves, stalk, and roots to the developing ear. While this "cannibalization" process ensures a supply of carbohydrates for the developing ear, the removal of carbohydrates results in premature death of pith cells in the stalk and root tissues, which predisposes plants to root and stalk infection by fungi. Even mild, early season water stress during the pretassel stage of development can significantly increase root infection by stalk rot fungi and result in greater stalk rot at maturity. As plants near maturity, this removal of nutrients from the stalk to the developing grain results in a rapid deterioration of the lower portion of corn plants in drought stressed fields, with lower leaves appearing to be nitrogen stressed, brown, and/or dead.

Other plant stresses which increase the likelihood of stalk rot problems include: loss of leaf tissue due to foliar diseases (such as gray leaf spot or northern corn leaf blight), insects, or hail; injury to the root system by insects or chemicals; high levels of nitrogen in relation to potassium; compacted or saturated soils restricting root growth; and high plant populations.

Most hybrids do not begin to show stalk rot symptoms until shortly before physiological maturity. It is difficult to distinguish between stalk rots caused by different fungi because two or more fungi may be involved. Similarly, certain insects such as European corn borer often act in concert with fungal pathogens to cause stalk rot. Although a number of different fungal pathogens cause stalk rots, the three most important in Ohio are Gibberella, Collectotrichum (anthracnose), and Fusarium. For more information on stalk rot in corn, consult the OSU Plant Pathology web site "Ohio Field Crop Diseases" (http://www.oardc.ohio-state.edu/ohiofieldcropdisease/) for more details and pictures of the disease symptoms associated with these pathogens.

The presence of stalk rots in corn may not always result in stalk lodging, especially if the affected crop is harvest promptly. It’s not uncommon to walk corn fields where nearly every plant is upright yet nearly every plant is also showing stalk rot symptoms! Many hybrids have excellent rind strength, which contributes to plant standability even when the internal plant tissue has rotted or started to rot. However, strong rinds will not prevent lodging if harvest is delayed and the crop is subjected to adverse weather conditions, e.g. strong winds and heavy rains.

A symptom common to all stalk rots is the deterioration of the inner stalk tissues so that one or more of the inner nodes can easily be compressed when squeezing the stalk between thumb and finger. It is possible by using the "squeeze test" to assess potential lodging if harvesting is not done promptly. The "push" test is another way to predict lodging. Push the stalks at the ear level, 6 to 8 inches from the vertical. If the stalk breaks between the ear and the lowest node, stalk rot is usually present. To minimize stalk rot damage, harvest promptly after physiological maturity (about 30% grain moisture). Harvest delays will increase the risk of stalk lodging and grain yield losses, and slow the harvest operation.

Frogeye Leaf Spot

Authors: Anne Dorrance

Very few fields in the state have very high levels of frogeye leafspot this year. This will be the first time that we will be recording some significant yield losses due to frogeye this year. Now is the time to check to see what level of disease you had in your fields. Some of these fields – every plant is covered with spots and where fogs lay, stem lesions and pod lesions are also forming. To manage these fields – harvest these as soon as possible. This will prevent late infections of seed – similar to what can occur with Phomopsis. The next thing is to manage the residue. The fungus that causes frogeye leaf spot overwinters on residue. There are some options till- bury the residue and/or rotate to wheat or corn. If the field is a no-till field – this must be rotated out. Two years would be best. If you can till, then the fall is the better time. This will give more time over the winter to begin to degrade that residue. This fungus is not supposed to overwinter up in Ohio, this is a very common disease in the southern part of the US, however, it does appear that it did overwinter during 2005-2006 winter. We did walk one of the performance trials this past week and many of the lines have good resistance to frogeye leaf spot. I expect that these susceptible lines will disappear quite quickly.

Western Bean Cutworm

Authors: Ron Hammond, Bruce Eisley

There is a new corn insect pest that is working its way towards Ohio that growers should keep an eye out for, the western bean cutworm (WBCW). This insect has been a sporadic dry-land bean and corn pest in Colorado and Nebraska. In the early 2000’s, damage from the WBCW was reported in western Iowa. Since that time, the insect and damage has progressively moved eastward. In 2005, Illinois found numbers that were higher than thought, including a few moths that were captured in eastern Illinois. This past summer, numerous Midwestern states including Ohio placed out pheromone traps to determine its current spread. Surprisingly, three moths were collected from western Ohio. You can see the 2006 collections via the Western Bean Cutworm Monitoring Network, at http://www.ent.iastate.edu/trap/westernbeancutworm/, including where the sites were in Ohio. This site also contains pictures of the adult moth and larva.

One generation of western bean cutworm occurs each year. Moth emergence usually begins in early July. After mating, females lay eggs on available host plants such as field corn, sweet corn, popcorn, or dry beans. Corn fields attractive to western bean cutworms for oviposition are fields in which plants are tasseling or near tasseling and fields that have hybrids with upright leaf characteristics. Larvae feed on pollen, silks, and kernels. Since the larvae are not cannibalistic like corn earworm, several cutworms can be observed on one ear. This insect can be distinguished from the corn earworm by dark stripes immediately behind the head, and the absence of small dark spines or stripes on the side of the body. There is only generation per year and larvae drop to the ground to spend the winter. It is unlikely that any western bean cutworms can still be found in the ears in mid-September, but their damage will be evident until harvest.

We are bringing this pest up now at the end of the season because 1) it is of importance to note a new insect pest species in the state, but letting growers know that 2) having found only three moths, it is not a reason to panic (at least yet). Collections in Iowa and Illinois are in the hundreds if not thousands per site compared with the total of three found in Ohio. If and when WBCW starts becoming more numerous in our state, we will then begin discussing identification, scouting procedures, economic thresholds, insecticide spray timing, Bt corn hybrid options, etc. Suffice it to say that there are ways to manage this pest, including timely insecticide applications and the use transgenic corn. Currently, of the available transgenic corn hybrids, only those that contain the Cry 1F toxin (Herculex I and Herculex XTRA Insect Protection) are labeled for control of the western bean cutworm.

At this time, there is no reason for Ohio growers to plant hybrids specifically for this pest, nor plan on having to develop a scouting program. Growers in Ohio hopefully will not worry about this until future years. However, it will be good to stay on top of any developments.

Getting That Last Cutting of Alfalfa

Authors: Mark Sulc

Early September is ideal for taking that last yearly cutting of alfalfa. The timing of this cutting can be very important to the long-term health of the stand. It is best for alfalfa to not be cut during the 5 to 6 week period before a killing frost. During this critical period, cold resistance and energy reserves for winter survival are built up.

A killing frost for alfalfa occurs when temperatures drop to 25F or less for several hours. So the period from mid-September through October is the critical fall rest period in our region. Harvesting during this period disrupts accumulation of energy reserves and development of cold hardiness.

Producers often harvest alfalfa during the critical fall period despite the increased risk of winter injury. Research shows that often the tonnage gained by cutting during the critical fall period is lost in the first cutting the following year. Plus there is the increased risk of winter injury and ultimately shorter stand life by stressing alfalfa in this way.

The tonnage expected from a cutting and the need for the forage should be high before considering a cutting during the critical fall period.

When harvesting alfalfa during the critical fall period, several factors can help reduce the risk of winter injury:

1. Young, healthy stands are less susceptible to winter injury from fall harvesting than older stands. On the other hand, more future production potential is lost if a younger stand is injured from fall cutting.

2. Forages in well-drained soils will be at lower risk of injury than those with marginal drainage. Fall cutting should not be attempted on soils prone to heaving! Removal of the topgrowth cover increases the potential for heaving injury.

3. Length of harvest interval during the growing season is often more important than the actual date of fall cutting. Making a 3rd cutting during the fall is less risky than making a 4th cutting in the fall, because a 3-cut schedule allows longer intervals for plant recovery between cuttings compared with a 4-cut schedule. Likewise, a growth interval of 45 days BEFORE a fall harvest will reduce the risk of injury compared with a pre-harvest growth interval of 30 days. The longer growth period allows more energy buildup before the fall harvest, lessening the amount of energy reserves needing to be built up after harvest.

4. Fields with optimal soil fertility levels (pH, P, K) are at less risk than where fertility levels are lower.

5. Disease resistant and winter hardy varieties lessen the risk of injury from fall cutting.

6. Alfalfa that was not under stress during the summer will be at lower risk. Any stress (wet soils, potato leafhopper injury, etc) that weakened the crop during the year can increase the risk of damage from fall cutting.

7. Cutting AFTER a killing frost (25 F for several hours) in late October or early November can be an option for well-drained soils only. Leave a 6-inch stubble after late fall cutting. Cutting this late in the year prevents regrowth that burns up energy and protein reserves; however late removal of plant cover increases the risk of frost heaving! Fall cutting should not be practiced on soils prone to heaving.

Cancellation of Carbofuran (Furadan)

Authors: Ron Hammond, Bruce Eisley

EPA has just announced the cancellation of most uses of carbofuran, Furadan, on crops, including all field crops that would be grown in Ohio (corn, soybeans, wheat, and alfalfa). This action was taken based on “high ecological and worker risks and low economic benefits for growers”. Thus, Ohio growers that have used Furadan in the past will need to consider alternative insecticides.

Special Needs Vehicles at Farm Science Review

Authors: Matthew Sullivan, Chuck Gamble

We hope that you join us at Farm Science Review September 19-21, 2006. As the Farm Science is a pedestrian show, it is important to limit the use of golf cars, ATVs or similar vehicles to those individuals who require these types of vehicles to use at the show. An expressed need for the use of a special need vehicle should be apparent, whether the vehicle is rented or brought by the individual. It is also the policy of the Farm Science Review to limit all vehicular traffic inside the exhibit area to a minimum and to maintain the area as a primary pedestrian facility.

The use of a motorized vehicle is a privilege provided to the user. The abuse of this privilege will result in the revoking of the issued Special Needs Vehicle Permit and the removal from the grounds of the Molly Caren Ag Center of the vehicle and the individual(s) to whom the Permit was issued. In such cases, no refunds of any collected fees shall be granted.

The following are the Rules and Regulations for permitting Special Needs Vehicles during the Farm Science Review.

1) The vehicle may not exceed a speed of 5 mph.

2) The vehicle may not be used to enter an exhibit space housed inside a building or a tent with the exception of motorized wheelchairs/handicapped vehicles.

3) The vehicle may not enter an outdoor exhibit space but shall remain in the street without obstructing the access to the exhibit space, with the exception of motorized wheelchairs/handicapped vehicles.

4) The operator must remove the key from the vehicle at such time that the vehicle is vacated.

5) The operator may not transport more individuals than that for which the vehicle has seats.

6) No pull-behind attachments to vehicles are permitted.

7) ***New for 2006...The vehicle must stay between the white lines (drive lane) while traveling down the roadways. The vehicle may leave the drive lane to visit an exhibitor or vendor and then return to the drive lane. Motorized wheelchairs/handicapped vehicles are exempt from the drive lane.

8) Vehicles must have a minimum of four wheels; three wheel golf cars are exempted. If the vehicle is a riding lawnmower type, the mowing deck must be removed.

9) Operators must be a minimum of 25 years of age.

10) Operators shall operate the vehicle in a safe and prudent manner.

11) In those situations where questions arise relative to any aspect of these rules and regulations, the Farm Science Review Management shall be responsible for all final decisions.

12) If a FSR visitor operator brings his/her own golf car/ATV/transportation mode, he/she must pay a $10.00 fee prior to the issuance of a disabled permit.

Individuals that bring these modes of transportation need to register the vehicle at the FSR Headquarters located at the west end of the exhibit area or at the special need vehicle registration area on the east end of the exhibit area inside Gate C. Vehicle registration is $10.00 for the 2006 show. A current copy of the rules and regulations will be issued for each Permit.

For golf cart and mobility scooter rental please contact:

The Golf Car Company
8899 Memorial Drive
Plain City, OH 43064
800-589-8833
614/873-1055
Fax: 614/873-3526

Rental prices and additional details are available online at http://fsr.osu.edu/golfcar.html. The Farm Science Review office does not accept golf cart rental agreements

Archive Issue Contributors: 

State Specialists: Ann Dorrance and Pierce Paul (Plant Pathology), Peter Thomison (Corn Production), Mark Loux and Jeff Stachler (Weed Science), Ron Hammond and Bruce Eisley (Entomology) and Mark Sulc (Forages). Extension Agents: Harold Watters (Champaign), Steve Prochaska (Crawford), Glen Arnold (Putnam), Roger Bender (Shelby), Harold Watters (Champaign), Steve Foster (Darke), Howard Siegrist (Licking), Steve Bartels (Butler), Mark Koenig (Sandusky), Greg LaBarge (Fulton), Wesley Haun (Logan), Ed Lentz (Seneca), Bruce Clevenger (Defiance), Alan Sundermeier (Wood), Mike Gastier (Huron), Greg La Barge (Fulton), and Keith Diedrick (Wayne).

About the C.O.R.N. Newsletter

C.O.R.N. Newsletter is a summary of crop observations, related information, and appropriate recommendations for Ohio crop producers and industry. C.O.R.N. Newsletter is produced by the Ohio State University Extension Agronomy Team, state specialists at The Ohio State University and the Ohio Agricultural Research and Development Center (OARDC). C.O.R.N. Newsletter questions are directed to Extension and OARDC state specialists and associates at Ohio State.