C.O.R.N. Newsletter 2006-32

Dates Covered: 
September 26, 2006 - October 2, 2006
Editor: 
Andy Kleinschmidt

Western Corn Rootworm Recommendations for 2007

Authors: Bruce Eisley, Ron Hammond

With the summer fast coming to an end, growers are beginning to make plans for their 2007 planting season, including ordering corn and soybeans with or without seed treatments. Because of the unique situations that occurred (or not) in 2006, we have various recommendations in terms of pest management on these crops. Let’s look at corn first, which will be followed within a few weeks with an article concerning soybeans.

We saw higher levels of corn rootworm injury this past summer, much higher than we usually see, especially on corn following corn. This was followed by higher densities of adults feeding on silks in August. Suffice it to say that our rootworm populations, which we had normally thought of as low to moderate in Ohio, went into the high category. We saw injury ratings well over 1, at least one node missing, in many fields and in tests that were conducted. Thus, in considering management options for 2007, this past year should be taken into account.

If not in an area where the first year corn rootworm variant is thought to be a problem, rotation is still your first and best option. If growing corn following corn, there is still a chance that treatment will not be needed, but unless the field was scouted for rootworm adults in August, it is not possible to predict if rootworm will be a problem or not.

Also, we saw a different situation with the western corn rootworm variant than we had seen in recent years. In western Ohio where the rootworm variant is present, we saw areas where many of the soybean fields that were trapped with the yellow stick traps had adult rootworms over the established threshold of 5 adult beetles/trap/day. Obviously, these fields will need a preventive treatment next spring. If near one of these areas where the rootworm variant was higher in the trap collections, you might want to consider treating your first year corn. If trapped fields in your area were not at threshold (still the majority of fields), you should consider not treating. You can contact the extension educator for the situation in your area. We will have the entire trap data shortly when they are all collected.

If it is decided that a field needs to be treated for corn rootworm, there are a number of options that can be used for control. For rootworm control information visit:
http://entomology.osu.edu/ag/reports/06si.pdf

Granules – There are a number of granular insecticides that are labeled for rootworm control. All 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.

Liquids – Several liquid insecticides are labeled for corn rootworm larvae. They do a good job on low to moderate populations but do not do a good job against high populations as some of the other options. If in an area where the rootworm was a severe problem in 2006, we suggest NOT using them for rootworm management. 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 larval control. They do a good job against low to moderate populations but do not do a good job against high populations. If in an area where the rootworm was a severe problem in 2006, 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 the seed flows properly.

Bt-Rootworm hybrids – There are currently two Bt-rootworm proteins (YieldGard Rootworm or Plus, or Herculex RW or Extra) 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 are two things to remember if using a transgenic hybrid containing the Bt-rootworm toxin. First, and foremost, 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 newsletter article. When considering how you might treat that 20% refuge for rootworm control, you can use granules, liquids or seed treatments. But considering the higher levels of rootworm injury this year, we would probably recommend the use of a granular soil insecticide. But again, the 20% refuge is required!

The second item is to plan on leaving a strip in your corn without any protection from rootworm to determine if the first year rootworm variant is REALLY a problem in your field next year. Normally we recommend a strip to determine the efficacy of the product. For possible first year corn rootworm variant fields, leaving an untreated strip will be the only way to determine if the variant was actually present AND an economic problem. If using a Bt-rootworm hybrid, this strip would be best left in the refuge area. Corn in these untreated strips should have their roots dug and rated next July to determine the level of rootworm injury.

Corn Stalk Rot: A Disease Caused by Several Different Fungi

Authors: Pierce Paul, Peter Thomison, Dennis Mills

Corn stalk rot and lodging are the results of several different but interrelated problems. The actual disease, stalk rot, is caused by one or more of several fungi capable of colonizing and disintegrating of the inner tissues of the stalk. The most common members of the stalk rot complex are Gibberella zeae, Colletorichum graminicola, Stenocarpella maydis and members of the genus Fusarium.

The extent to which these fungi infect and cause stalk rot depends on the health of the plant. In general, severely stressed plants (due to foliar diseases, insects, or drought) are more greatly affected by stalk rot than stress-free plants. The stalk rot fungi typically survive in corn residue on the soil surface and invade the base of the corn stalk either directly or through wounds made by corn borers, hail, or mechanical injury. Occasionally, fungal invasion occurs at nodes above ground or behind the leaf sheath. The plant tissue is usually resistant to fungal colonization up to silking, after which the fungus spreads from the roots to the stalks. Following infection and colonization, leaves turn grayish-green in color, ears droop, the lower part of the stalk turns from dark green to light brown, and the pith inside the stalk becomes soft. When diseased stalks are split, the pith is usually discolored and shows signs of disintegration. As the pith disintegrates, it separates from the rind and the stalk becomes a hollow tube-like structure. Destruction of the internal stalk tissue by fungi predisposes the plant to lodging.

Based on our observations and reports coming in from across the state, stalk rot and lodging seem to be the main causes for concern as growers prepare for harvest. Although the level of stalk rot generally varies from location to location, the problem seems to be more widespread this year; with huge sections of some fields having almost every plant showing stalk rot symptoms. This is largely because many areas of the state experienced an extended period of dry weather during the grain fill period (July and August). Please refer to a recent C.O.R.N Newsletter article by Thomison and Paul for more on drought-related stresses and stalk rots (“Potential for Stalk Rot and Lodging Problems in Corn”) available at:
http://corn.osu.edu/story.php?setissueID=153&storyID=919

Nothing can be done about stalk rots at this stage; however, growers can minimize yield losses associated with lodging by harvesting fields with stalk rot problems early. Scout fields early for visual symptoms of stalk rot and test stalk integrity by squeezing the lower internodes between the thumb and forefinger. Stalks that are likely to lodge are easily compressed between the fingers. Since the level of stalk rot varies from field to field (being more severe when corn follows corn) and hybrids vary in their stalk strength and susceptibility to stalk rot, each field should be scouted separately. For more information on the different type of stalk rot and stalk rot management please refer to the OSU Plant Pathology web site "Ohio Field Crop Diseases" at:
http://www.oardc.ohio-state.edu/ohiofieldcropdisease/

Back-to-Back Wheat or Late-Planted Wheat After Soybeans?

Authors: Pierce Paul, Jim Beuerlein, Dennis Mills

The development and maturation of the soybean crop is lagging behind in some locations because of unfavorable weather conditions (cool temperatures). This may lead to late soybean harvest, and consequently, later-than-normal wheat planting. The recommended planting date for no-till wheat in Ohio is within the first 10 days after the Hessian fly-safe date which is between September 22 (for the northern counties) and October 5 (southern counties). We generally like to see most of the wheat planted by mid October. However, based on the fact that most soybean fields have not been harvested and may not be harvested within the next two weeks or so, Ohio growers (especially in northern counties) may be forced to plant wheat well after the recommended period.

Late planting may result in poor stand establishment (fewer tiller per foot of row) and increase winter kill. Some growers who had to deal with these problems last year and are facing a similar situation again this year may be considering planting wheat into the wheat fields they just harvested. While this will ensure that wheat is planted at the recommended time for adequate tiller development before winter dormancy, it increases the potential for disease and insect (Hessian fly) problems.

Planting back-to-back wheat is not recommended. Growers who plant wheat after wheat usually have more problems with diseases such as Cephalosporium stripe and Take-all root rot. Plants severely infected in the fall and winter will become weak and discolored in the spring and often die prematurely without producing grain. In addition, foliar diseases such as Stagonospora leaf blotch, Septoria leaf blotch and tan spot, and Fusarium head blight (head scab) become more problematic when wheat follows wheat. These diseases are all caused by fungi that survive in wheat residue left in the field, and as such, can readily attack the new crop and spread shortly after germination or early in the spring. When diseases become established early, growers are more likely to suffer higher yield and quality losses.

Given the problems associated with planting wheat after wheat, growers would be better off sticking to the recommended practice of planting wheat after soybeans, even if it means planting wheat a little later than normal. To compensate for fewer tiller development in late-planted wheat (during the third and fourth week after the fly-safe date), growers are recommended to plant at a higher seeding rate than the regularly recommended rate of 1.2 to 1.6 million seeds per acre for 7.5-inch rows (that is about 18 to 24 seeds per foot of row with normal sized seed). Plant at a rate of 1.6 to 2.0 million seed per acre instead. The number of seeds per pound and germination rate are important for determining the correct seeding rate and drill calibration. There are fewer seeds per pound of large seeds than per pound of small seeds. The number of seeds per pound can be found on the seed bag. To determine the amount of seed needed to plant 1.6 to 2.0 million seeds per acre use the above information along with the table provided in the C.O.R.N newsletter “Correct Wheat Seeding Rates Can Increase Profit” by Jim Beuerlein, 2005-29: September 6, 2005, available at:
http://corn.osu.edu/story.php?setissueID=102&storyID=605

Since late planting also affects the ability of wheat to compete with weeds (poor stand establishment and winter injury - fewer tiller per foot of row), for dandelion control in no-till wheat, growers are recommended to apply glyphosate before the wheat emerges.

Managing Black Cutworms with Fall Herbicide Applications

Authors: Ron Hammond, Bruce Eisley

Two weeks ago in the CORN newsletter, Mark Loux wrote an article on the benefits on fall herbicide treatments and providing a weed free seedbed in the spring (CORN Newsletter 2006-30, September 12-18, 2006). The article discussed the various goals in using fall herbicide treatments, the various weeds that can be controlled, and what herbicide regimes are appropriate. The article is available at:
http://corn.osu.edu/story.php?setissueID=153&storyID=917

Another outcome that comes from providing a weed free seedbed in the spring relates to an insect pest that can cause significant damage to field crops, black cutworms. Having seen increased cutworm problems this past spring, growers should be reminded how various cultural practices, fall herbicide applications in this case, that 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. Much of this insect movement occurs when the weeds are killed in the spring with a spring herbicide application.

A management practice known for years is providing a weed free situation in the spring; without the weeds, the likelihood of cutworm problems are greatly diminished. An easy way to accomplishment this is with a fall herbicide application that not only rids the field of the weeds, but removes the oviposition sites for this insect. Thus, when considering the benefits to a fall herbicide application, do not forget the added benefit of black cutworm management.

Using Flat Buildings for Dry Grain Storage

Authors: Alan Sundermeier

Here are some things to consider when deciding whether a given building would be a good choice for grain storage, according to Dr. Bill Wilcke, Ag Engineer, University of Minnesota.

Sanitation – Can you get the building clean enough for grain storage? Do not contaminate grain with manure, ag chemicals, or petroleum. Also, can birds and rodents be kept away from the grain.

Wall Strength – Dry grain exerts high pressure on walls, and unless the building was specifically designed to withstand the pressure of grain it will need to be reinforced. Bulk heads inside the building would keep grain away from the walls. Also placing metal grain bin rings inside the building would be an option.

Capacity – To estimate capacity, calculate the volume of the planned grain pile in cubic feet and then multiply by 0.8 bushels per cubic foot.

Water-tightness – For buildings with earthen floors, consider piling the grain on plastic. Older concrete floors without a vapor barrier will also need plastic lining to prevent moisture migration. Check the roof for leaks and make sure the grade around the building allows water to flow away.

Filling and unloading – A portable grain auger is needed to fill flat storage. Openings in the roof may be needed if the ceiling is too low to fill from inside. Unloading with a portable auger and front end loader or pneumatic grain conveyor can be used.

Grain moisture – Because it is difficult to achieve uniform air movement in flat storage, it is even more difficult to dry grain adequately in these buildings. Corn needs to be no more than 15% moisture to be stored until spring.

Grain aeration – Even if grain is dry when it is moved into flat storage, it should still be aerated to reduce mold and insect activity and to prevent moisture migration. Perforated ducts placed on the floor can work well for flat buildings. If the pile is level, duct spacing should be about equal to the pile depth. Duck lengths less than 100 feet are needed to reduce problems with non-uniform air distribution. Air blowing into ducts and out of the top of the pile work best for flat storage. To prevent condensation problems under the roof, provide plenty of air exhaust and movement over the pile while fans are running.

For more information on grain storage and sizing fan motors , refer to the University of Minnesota web site at:
http://www.bae.umn.edu/extens/postharvest/

Soybean Aphid Update

Authors: Ron Hammond, Bruce Eisley

This past week we sampled buckthorn for the presence of soybean aphids beginning their cycle of overwintering. This is the approximate time that winged, adult females fly to buckthorn and lay more females prior to males arriving which is then followed by mating. Much to our surprise, we immediately found a few small colonies of what appeared to be soybean aphids on buckthorn in Wayne County in northeast Ohio. Of greater surprise was then finding large populations of aphids on buckthorn on the OSU campus in Columbus. This latter location is an area that we have monitored overwintering aphids for the past 3-4 years. There were large numbers of winged aphids as well as unwinged individuals. The significance of these finds are that the soybean aphid is still following the sequence that will in all likelihood lead to larger densities and economic problems next year. We still need to see what fall collections in suction traps do over the next month, but so far, it all seems to be progressing as expected.

Archive Issue Contributors: 

State Specialists: Ann Dorrance, Pierce Paul and Dennis Mills (Plant Pathology), Peter Thomison (Corn Production), Jim Beuerlein (Small Grains), Ron Hammond and Bruce Eisley (Entomology). Extension Educators: Glen Arnold (Putnam), Roger Bender (Shelby), Todd Mangen (Mercer), Howard Siegrist (Licking), Mark Koenig (Sandusky), Steve Foster (Darke), Bruce Clevenger (Defiance), Wesley Haun (Logan), Greg LaBarge (Fulton), Alan Sundermeier (Wood), Mike Gastier (Huron), Gary Wilson (Hancock), and Keith Diedrick (Wayne).