C.O.R.N. Newsletter 2008-34

Dates Covered: 
October 6, 2008 - October 14, 2008
Editor: 
Curtis E. Young

Volunteer Corn Issues: Planning for Next Year

Authors: Mark Loux

One likely result of the current corn stalk breakage and harvest problems is an increase in volunteer corn populations next year. Planting soybeans in fields that are likely to have a major volunteer corn problem is by far the best option. Volunteer corn is easily managed in Roundup Ready or non-GMO soybeans through the use of post-emergence grass herbicides - Assure II/Targa, Fusion, and clethodim products (Select Max is the only clethodim product that should be applied in a mixture with glyphosate, however).

Management of volunteer corn in continuous cornfields can be easy or difficult, depending upon the type of hybrids that were planted in the 2008 season. The best-case scenario is that a non-GMO hybrid was planted in 2008 or a hybrid with a single herbicide resistance trait, either Liberty Link or glyphosate-resistant. In this case, it should be possible to plant a hybrid next year that allows the use of either glufosinate (Ignite) or glyphosate for control of the volunteer corn. Examples: 1) where non-GMO corn was planted in 2008, glyphosate-resistant or Liberty Link corn can be planted in 2009; 2) where Liberty Link corn was planted in 2008, glyphosate-resistant corn can be planted in 2009; or 3) where glyphosate-resistant corn was planted in 2008, Liberty Link corn can be planted in 2009. Glufosinate can be somewhat variable for control of volunteer corn, but has the potential to at least suppress it to the point of being non-competitive. All of this is stated with the assumption that well-performing hybrids with the desired herbicide resistance are available, along with corresponding non-BT hybrids to satisfy refuge requirements.

The major problem occurs where the hybrid planted in 2008 has resistance to both glufosinate and glyphosate, because this means there are no chemical control options for volunteer corn where corn is planted in the same field next year. In fields with this type of hybrid that appear to have the potential for substantial volunteer corn problems, we suggest reconsidering the decision to plant corn again. Consider switching these fields to soybeans instead, and plant corn in other fields with fewer stalk breakage problems. We have been asked whether tillage can be altered to minimize volunteer corn infestations. Volunteer corn most often develops from partially buried ears or parts of ears. We can generalize therefore that the severity of volunteer corn infestations could be reduced by either not tilling at all or using a combination of fall and spring tillage that shatters ears and buries them fairly deep. Minimum tillage that partially buries fairly intact ears may be the worst case. Another non-chemical option would be to cultivate between rows next spring after emergence of the crop and volunteer corn. This is really the only viable method of volunteer corn control in fields planted continuously to hybrids with resistance to both glyphosate and glufosinate.

Sampling Fields for Soybean Cyst Nematode

Authors: Dennis Mills, Anne Dorrance

Soybean cyst nematode (SCN) continues to be a pest in many of Ohio's production fields. Light infestations of SCN in fields will have no above ground symptoms, which is part of the challenge, but yields will be anywhere from 5-10 bushels off. Higher infestations on susceptible soybean cultivars will have more severe symptoms, such as: soybeans will be irregular in height, mixtures of tall and short soybeans; early yellowing; and very low yields. This pest is best managed with crop rotation, which reduces the SCN population levels and planting resistant cultivars. However, SCN readily adapts to ALL sources of resistance so it is important to manage the type of resistance that is planted in a field. The correct management plan starts with knowing what level of infestation is present.

The best time to sample fields for soybean cyst nematode is in the fall after the soybeans are harvested. Soybean cyst nematode populations can increase as much as 10-30 fold per growing season. Soybean cyst nematodes will not be distributed evenly throughout a field. Techniques for sampling soil for SCN by the Soybean Cyst Nematode Coalition are as follows:

1. Use a one inch diameter soil probe to collect samples (6-8" in depth).
2. Following a "zig zag" pattern, collect 10-20 soil cores per 10-20 acres.
3. Collect cores from areas of similar soil type and crop history.
4. Dump cores from each 10-20 acre area into a bucket or tub and mix thoroughly.
5. Place 1 pint (2 cups) of mixed soil in a plastic zippered bag and label with a permanent marker.
6. Store sample in cool, dark place until shipped to the lab doing SCN analysis.

This level of sampling is necessary to obtain relatively accurate counts of the nematode population (egg and cyst) and to make meaningful recommendations for management. Charges this year at the C. Wayne Ellett Plant & Pest Diagnostic Clinic are $15.00 for each soil sample. Forms to accompany samples can found at the county extension offices or at the following web page:
http://www.ag.ohio-state.edu/~plantdoc/cweppdc/scnform.html

Mail samples to:
C. Wayne Ellett Plant & Pest Diagnostic Clinic, Room 110, Kottman Hall, 2021 Coffey Road, The Ohio State University, Columbus, OH 43210

Additional Ohio SCN testing labs:
Brookside Laboratory Inc., 308 S Main St., New Knoxville, OH 45871, Phone: (419) 753-2448, Fax: (419) 753-2949, E-mail: mflock@blinc.com, Cost: $13.00 per sample, Results reported: egg and cyst counts per 100cc of soil

Geophyta Inc., 2685 CR 254, Vickery, OH 43464, Phone: (419) 547-8538, Fax: (419) 547-8538,
E-mail: nathan@geophyta.com, Cost: $15.00 per sample, Results reported: cyst counts per 100cc of soil

On-farm SCN demonstration and research plots were established at two locations in Ohio in 2008 along with 10 other Midwest states as part of a 3 year study to improve management and awareness of SCN and to demonstrate the effects of SCN resistance sources on field populations in a single cropping season. The trial in Ohio contains 5 varieties: one SCN susceptible and four with sources of resistance from PI88788, Peking and CystX. This project will directly benefit all soybean producers by increasing awareness of the problem and defining the proper management.

Aphids and Barley Yellow Dwarf

Authors: Bruce Eisley, Andy Michel, Pierce Paul, Ron Hammond

With wheat currently being planted, we thought we would discuss the various reasons and options for aphid management during the coming weeks. Aphid infestations in wheat great enough to cause economic damage are rare in Ohio. However, aphids can, under certain conditions, build in numbers and damage wheat by feeding on the plant during seedling stages. The treatment threshold for aphid management in wheat is 50 aphids per linear foot of row.

The most concern over the next two months deals with virus transmission. Most of the insecticide applied in the fall is used to control aphids in hopes of lowering the incidence of barley yellow dwarf virus (BYDV) in the following spring. For aphids to successfully transmit the virus, they normally need between 12 and 30 hours feeding to acquire the virus, and then 4 or more hours of feeding to transmit it. However, aphids are capable of acquiring the virus after feeding on infected plants for only 30 minutes and once they acquire the virus, they can transmit it to healthy plants for the rest of their life.

High incidences of BYDV had been reported some years in parts of Ohio. The typical symptoms of this disease are erect leaves with yellowish to reddish-purple tips. Yield reduction due to BYDV is generally greater when infections occur in the fall than in the spring. BYDV tends to be most severe in fields planted before the fly-free date in which aphid populations can reach high levels. However, some fields planted after the fly-free date can have high levels of BYDV, most likely because of warm temperatures that keep aphids active for a longer time period. Recommended management tactics for BYDV are as follows: 1) plant varieties less susceptible to BYDV; 2) delay planting until after the Hessian fly safe date to avoid early fall infections; 3) balanced fertility; and 4) controlling volunteer wheat, barley, and oats (for more on BYDV, visit the field crops disease website at http://www.oardc.ohio-state.edu/ohiofieldcropdisease/wheat/byd.htm).

Spraying insecticide to control aphids in an attempt to manage BYDV is open to discussion, and usually not a recommended tactic. During active feeding, a few aphids will be enough to transmit the virus from one plant to another. Any aphids present prior to spraying may have already transmitted BYDV, while other aphids may continue to arrive in the field after the spraying. When spraying insecticides to control aphids early, growers should know that the residual effect of the insecticide may not last long enough to protect against later aphid population buildup nor virus transmission. Though insecticides applied after infection will reduce the aphid population, it will not prevent the disease from developing once the plants have been infected. Once infections occur, there is very little that can be done.

There are situations where it is acceptable to spray for aphids, and where insecticide application might pay. These include: 1) wheat under drought stress with aphids present; 2) growing a variety known to be susceptible to BYDV with aphids present; 3) wheat being grown for seed; 4) wheat that is intensively managed with a 100+ bu/A potential yield; and 5) wheat planted before the fly-free date. However, for most growers, cost-effective control of BYDV may not be possible by aphid spraying. If a decision is made to spray an insecticide, see the following web site (http://bugs.osu.edu/ag/545/sgiap.pdf) for a list of labeled materials.

Another "Good" Year for Marestail

Authors: Mark Loux

The spring weather and its effect on crop establishment wreaked havoc with marestail control programs, and stimulated much additional late-spring marestail emergence. Even the most effective herbicide programs can fail to completely control herbicide-resistant marestail under these conditions. However, some of the problems with marestail are due to a failure to plan and implement effective control measures. Much of the marestail that infests Roundup Ready soybean fields is glyphosate-resistant, and resistant populations can by now occur anywhere in Ohio. Some of these populations have multiple resistances, to both glyphosate and ALS inhibitors, which eliminates the possibility of post-emergence control in soybeans, and also limits soybean herbicide options for residual control.

An effective marestail management program ensures that the field is free of marestail at the time of soybean planting, and includes herbicides with residual activity to prevent marestail emergence for a month or so after crop emergence. It also helps to plan for the worst - assume that the population has multiple resistances and will be impossible to control after soybean emergence. The question is, can a fall herbicide treatment consistently accomplish all of this, and allow the use of post-emergence herbicides exclusively in next year's soybeans without sacrificing marestail control? The short answer is - No.

In OSU research, the most effective control of marestail has occurred from a combination of 2,4-D ester, residual herbicides and either glyphosate or paraquat applied in April, when the marestail is still in the rosette stage or has only an inch or two of stem elongation. The residual herbicide component can consist of primarily ALS inhibitors, but this will be less consistently effective than a combination of ALS inhibitor plus an effective rate of Valor, Authority or metribuzin. So, products such as Valor XLT, Envive, Gangster or Authority First/Sonic often provide more effective residual control than Canopy, unless the Canopy is supplemented with additional metribuzin. Even when applied in spring, the most effective residual herbicides can fail to completely prevent emergence of marestail after soybean emergence. Applying residual herbicides in fall results in an even greater risk of late-spring marestail emergence problems, since much of the herbicide dissipates over the winter. This is consistent with our results on most summer annual weeds. The bottom line - applying herbicides in fall does not ensure that marestail will be controlled until the crop is well developed enough to suppress the late-emergers. The only way to accomplish this is to follow the fall application with a preplant spring application of residual herbicide (plus a low rate of 2,4-D to control any small emerged marestail). Deviations from this approach are likely to result in the presence of marestail at the time of post-emergence application, and a major marestail problem for the rest of the season.

As we move into the fall herbicide application season, consider the following to maximize marestail control in next year's soybeans:

* In fields where winter annual and dandelion weed populations are low, skip the fall herbicide application. Apply preplant herbicides in spring instead, by about the 3rd week of April, using the approach outlined above. The exception to this would be fields that have no potential to be treated with herbicide in spring, either due to soil conditions or grower stubbornness. In that case, make a fall application of a high rate of the most effective residual possible and hope that post-emergence herbicides will have some effectiveness (but know that this approach may not work)

* In fields that require a fall herbicide application for winter annual or dandelions, apply a combination of glyphosate and 2,4-D ester in the fall, and follow with a preplant application of residual herbicide. An alternative to this would be to apply a low rate of Canopy EX plus 2,4-D in the fall (which could be less expensive than glyphosate), followed by residual herbicide in the spring. In either case, make sure the spring treatment includes 2,4-D and a residual product that contains a full rate of Valor, metribuzin or Authority/Spartan to account for any ALS resistance.

Black Cutworm and Fall Applications of Herbicides

Authors: Ron Hammond, Andy Michel, Bruce Eisley

Fall herbicide application is a great way to get a jump on weed management. One outcome is providing a weed-free seedbed in the spring that can reduce the likelihood of an insect pest that can cause significant damage to corn, the black cutworm. Growers should be reminded how various cultural practices, fall herbicide applications in this case, can help reduce the level of this insect pest.

The adult black cutworm moth migrates from more southern locations each spring, laying their eggs on numerous perennial weeds in the spring followed by movement to corn, with chickweed being a specific weed to which cutworm moths are highly attracted. Much of the insect movement occurs when the weeds are killed in the spring with a spring herbicide application and larvae search for other hosts. By providing a weed free situation in the spring, the likelihood of cutworm problems is greatly diminished. A fall herbicide application not only rids the field of the weeds, but also removes the oviposition sites for this insect. When considering the benefits of a fall herbicide application, do not forget the added benefit of black cutworm management. Eliminating weeds in the fall is an excellent preventive tactic to begin your corn insect management for 2009!

Should Fall Herbicide Treatments Be Delayed?

Authors: Mark Loux

Dry weather in late summer and fall has resulted in relatively sparse populations of winter annuals in many fields at this time, and regrowth of dandelions is limited. This could lead to the conclusion that delaying fall herbicide treatments for another month could be beneficial. The delay could allow for some rain and winter annual emergence, and additional growth of dandelion to the point that it is more readily controlled by herbicides. Dandelion is more effectively controlled after a frost anyway.

We have most often applied fall herbicide treatments in November in our research, much of the time under relatively warm conditions. There is really no risk of less effective control by delaying treatment until that time, and dandelion control should be more consistently effective. This has to be weighed against the possibility that it will turn wet later this month, rendering fields unsuitable for traffic. Waiting until early November could also allow for a more informed decision on whether fall treatment is actually necessary. One possibility is that winter weed populations will be low this year, and scouting fields in November would provide better information on this, compared with what is known now. The major benefit of a fall herbicide treatment is control of weeds that have emerged by the time of application. Where scouting in early November fails to turn up many winter weeds, the better decision may be to delay application until spring, which makes better use of residual herbicides (see marestail article in this issue of C.O.R.N.).

Corn Rootworm Control in 2009

Authors: Ron Hammond, Andy Michel, Bruce Eisley

With growers making plans for their 2009 planting season including ordering corn hybrids that are perhaps transgenic, and with or without seed treatments, we thought a review of management recommendations for rootworms is in order.

As in previous years, we continue to see rootworm root feeding injury ratings well over 1, at least one node missing, in both corn following corn and first year corn throughout much of the state. If you have read this CORN newsletter throughout the summer, you know that the variant has continued its march eastward into central Ohio. Thus, there are many management decisions that need to be considered.

If not in an area where the first year corn rootworm variant is considered a problem, and this includes much of eastern and southern Ohio, rotation is still your first and best option. Rotation will break the rootworm cycle and prevent injury because the field will be in a non-host crop. If in areas where the rootworm variant has been identified, you might want to consider treating your first year corn. If it is decided that a field needs to be treated for corn rootworm, there are a number of management options that can be used for control.

Granular Insecticides - There are a number of granular insecticides that are labeled for rootworm control. They continue to do a good job against low to moderate populations (the typical level in Ohio) of rootworm and some do a good job against higher levels. The most important thing about using granules is to make sure the granular equipment is properly calibrated and the granules are applied properly at planting.

Liquid Insecticides - Several liquid insecticides are labeled for corn rootworm larvae. They do as good a job against rootworm larvae as some of the other options on the market. As with the granules, it is important the liquid application equipments be properly calibrated and the material delivered properly at planting.

Seed Treatments - Currently there are two seed treatments, Cruiser and Poncho, labeled at 1.25 mg ai/seed for rootworm larval control. They do a good job against low to moderate populations but may not do a good job against high populations. They will probably do a good job against most of the rootworm populations we encounter in Ohio but if in an area where the rootworm is considered severe, we suggest NOT using them for rootworm management. If one of the seed treatments is used, it is important to follow company directions concerning hopper box additives to make sure that seed flows properly.

Bt-Rootworm hybrids - There are three Bt-rootworm proteins (YieldGard Rootworm, Plus, VT, VT Triple; Herculex RW or Extra; and Agrisure RW, CB/RW, or 3000GT) that can be used to control the rootworm. Hybrids with the Bt-rootworm proteins do a good job of controlling rootworm against all levels, even high ones. There is an important thing to remember if using a transgenic hybrid containing the Bt-rootworm toxin. You MUST plant a 20% refuge within or adjacent to your Bt-hybrid corn. This is not an option. Your seed dealer should provide you with detailed information on this refuge requirement; we will discuss some of these requirements in a later CORN newsletter. When considering how you treat that 20% refuge for rootworm control, you can use granules, liquids or seed treatments. Also be aware that these hybrids will come treated with the low rate of an insecticide seed treatment to control secondary soil insect pests.

Weather Update

Authors: Jim Noel

It looks like the dry pattern may finally let up for much of the state. The operative term here is it MIGHT, but there are signs of some wetness in the next week or two. It may not break the dry pattern long term, but we are likely to see some shorter term wetness.

Temperatures will be warmer than average over the next week with some rain about Wednesday. There could be a few more showers during the weekend as well, but not of much significance. Next week we will see near normal temperatures and above normal rainfall. Best chance of rain will come about Tuesday and Wednesday next week with some locally heavy rain, especially in the north and west sections of the state.

After that we will with be normal for temperatures and precipitation or go back to normal for temperatures and below normal for rainfall.

Archive Issue Contributors: 

ontributors: State Specialists: Ann Dorrance, Pierce Paul, and Dennis Mills (Plant Pathology), Ron Hammond, Andy Michel, and Bruce Eisley (Entomology), Mark Loux (Weed Science) and James Noel (NOAA/NWS/OHRFC). Extension Associates and Agents: Roger Bender (Shelby), Harold Watters (Champaign), Glen Arnold (Putman), Greg LaBarge (Fulton), Howard Siegrist (Licking), Jonah T. Johnson (Clark), Mark Koenig (Sandusky/Ottawa), Todd Mangen (Mercer), Les Ober (Geauga), Wesley Haun (Logan), Steve Foster (Darke), and Curtis E. Young (Allen).

About the C.O.R.N. Newsletter

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.