CORN
Crop Observation and Recommendation Network

September 5 - 10, 2000
C.O.R.N. 2000-29

In This Issue:

A.) Wheat Planting Date: Do Not Plant Too Early!
B.) Tips for Evaluating Corn Hybrid Demonstration Plots
C.) Soybean Aphid Possibly Found in Ohio
D.) Slugs Damage Double-Cropped Soybeans
E.) Observations of Bean Leaf Beetles Activity in Central Ohio
F.) Fall Harvest Management of Forage Legumes
G.) Farm Science Review

A) Wheat Planting Date: Do Not Plant Too Early! - Pat Lipps CORN Questions

Over the past two growing seasons we have had considerable problems with barley yellow dwarf virus and several other diseases due to warm weather conditions favoring aphid movement in September. The best way to control many of these problems is to delay planting wheat until late September or early October. Choosing the correct time to plant wheat in Ohio is truly a balancing act. The goal is to plant late enough to avoid insect and disease problems that occur in September, but early enough so that the young wheat plants grow big enough in the fall to survive the winter. Ideally, plants should have developed two to three tillers, each with three leaves before winter dormancy for best over winter survival.

This year wheat growers need to pay attention to planting after the Hessian Fly Safe date for their location or county. This date ranges from September 22 for the most northern counties to October 5 for the most southern counties. This date is not an absolute date, it is more like a rule of thumb. In years with cold temperatures in September the actual date wheat could be planted could be a little earlier, but during years with warm fall temperatures the actual planting date may be later to avoid damage. However, this date is based on long term averages. The Hessian Fly Safe date is based on timing of when Hessian fly adults are no longer around to lay eggs on emerging wheat seedlings. If the adults find early planted wheat and lay eggs on the seedlings, Hessian Fly larvae overwinter on wheat plants and feed on developing plants in the spring causing severe lodging or premature stem death. Unfortunately we have seen low levels of infestations in some early planted fields in Ohio this last year.

Delayed planting of wheat also limits infections from several different diseases. Most important is Barley Yellow Dwarf. Barley Yellow Dwarf is caused by a virus carried by aphids. Aphids travel on wind currents from the South and land on early emerging wheat in Ohio. The aphid can transmit the virus to wheat plants within the first few hours after it lands on them. Infected plants turn yellow or have yellow leaves in the spring. In planting date field trials at Hoytville, Barley Yellow Dwarf reduced yield by 22% in plots planted 10 days before the Hessian Fly Safe date as compared to plots planted on Fly Safe Date. Additionally, foliar diseases like powdery mildew, Stagonospora leaf blotch and leaf rust can infect wheat if planted too early. Giving these fungal pathogens an early start in the fall can increase the potential for more severe problems in the spring if they overwinter on the wheat plants.

There has been considerable research on the effect of planting date on wheat yields in the past and only a few studies that are relatively recent. As most farmers understand, each year is different since seedling emergence depends on soil moisture and temperature. Thus, planting date recommendations are based on averages across years. In Ohio, under conventional tillage, yields are generally better when wheat is planted from 5 to 15 days after the Hessian Fly Safe date, but under no tillage, wheat yield is generally better if planted on the Hessian Fly Safe date to 10 days after this date.

B) Tips for Evaluating Corn Hybrid Demonstration Plots - Peter Thomison CORN Questions

Local corn hybrid demonstration plots can be useful in providing information on certain hybrid traits, especially those that are not usually reported in state corn performance summaries. There are a number of these plots established each year by various seed companies and county Extension personnel. An increasing number of growers are also conducting on-farm tests to evaluate hybrids.

The following are some hybrid characteristics to consider while checking out hybrid demo plots.

PLANT/EAR HEIGHT. Corn reaches it maximum plant height soon after tasseling occurs. Remember that although a big tall hybrid may have a lot of "eye appeal," it may also be more prone to stalk lodging in the fall. Unless your interest is primarily silage production, increasing plant height should not be a major concern. Generally later maturity hybrids are taller than earlier maturity hybrids. Big ears placed head high on a plant translate to a high center of gravity, predisposing a plant to potential lodging. The negative effects of stalk rot on stalk lodging in the fall may be worsened by high ear placement.

STALK SIZE. Generally speaking, a thicker stalk is preferable to a thinner one in terms of overall stalk strength and resistance to stalk lodging. As you inspect a test plot, you will see distinct differences among hybrids for stalk diameter. However, also check that the hybrids are planted at similar populations. As population increases stalk diameter generally decreases.

LEAF DISEASES. During the grain fill period, leaf diseases can cause serious yield reductions and predispose corn to stalk rot and lodging problems at maturity. The onset of leaf death shortly after pollination can be devastating to potential yield, since maximum photosynthetic leaf surface is needed to optimize grain yield. Hybrids can vary tremendously for their ability to resist infection by these diseases. Pay close attention during the 6 to 8 weeks after pollination for development of leaf diseases among hybrids in a test plot. Demonstration plots provide an excellent opportunity to compare differences among hybrids to disease problems that have only occurred on a localized basis. While gray leaf spot has received considerable attention in recent years, check plots for Stewart's Bacterial Blight to identify hybrids with resistance. Stewart's Blight has been showing more frequently in recent years and some hybrids are much more susceptible than others. Another disease that's been seen more this year (due in part to cool weather conditions) is common corn rust. While there are significant differences among hybrids to common rust, it's not a common disease most years, and usually has little impact on hybrid yields.

STALK ROTS. Hybrids will likely differ widely when faced with strong stalk rot pressure. Begin checking plants in late August or about 6 weeks after pollination by pinching lower stalk internodes with your thumb and forefinger. Stalks that collapse easily are a sure indicator of stalk rot. Remember that hybrids with thicker stalks may be in plots having thin stands.

STALK LODGING/BREAKAGE. Perhaps as important as stalk rot resistance is the stalk strength characteristics of a hybrid. Sometimes, superior stalk strength will overcome the effects of stalk rot. If your variety plot is overcome with stalk rot in late August and early September, be certain to evaluate the stalk lodging resistance of the different hybrids. Demonstration plots also provide a good opportunity to evaluate another stalk related problem, green snap (a.k.a. brittle snap). Green snap damage in Ohio has usually been limited to localized areas where severe windstorms occur prior to pollination. Although green snap is not a major problem in Ohio, as it is in the western Corn Belt, there are differences in susceptibility among hybrids that growers may want to consider to avoid risks.

HUSK COVERAGE/EAR ANGLE. Hybrids will vary for completeness of husk coverage on the ear as well as tightness of the husk leaves around the ear. Ears that protrude from the husk leaves are susceptible to insect and bird feeding. Husks that remain tight around the ear delay field drydown of the grain. Hybrids with upright ears often associated with short shanks may be more prone to ear and kernel rots that those ears that point down after maturity. As a test plot nears harvest maturity, compare hybrids for these characteristics.

The following are some additional points to consider during your plot evaluations:

1. Field variability alone can easily account for differences of 10 to 50 bushels per acre. Be extremely wary of test plots that are not replicated, or only have "check" or "tester" hybrids every 5 to 10 hybrids. The best test plots are replicated (all hybrids repeated at least twice) or have a "check" hybrid repeated every other hybrid.

2. Don't put much stock in results from ONE LOCATION AND ONE YEAR, even if the trial is well run and reliable. Don't overemphasize results from ONE TYPE OF TRIAL. Use data and observations from university trials, local demonstration plots, and then your own on-farm trials to look for consistent trends.

3. Initial appearances can be deceiving, especially visual assessments! Use field days to make careful observations and ask questions, but reserve decisions concerning hybrid selection until you've seen performance results.

4.Walk into plots and check plant populations. Hybrids with large ears or two ears/plant may have thin stands.

5. Break ears in two to check relative kernel development of different hybrids. Use kernel milk line development to compare relative maturity of hybrids if hybrids have not yet reached black layer. Hybrids that look most healthy and green may be more immature than others. Don't confuse good late season plant health ("stay green") with late maturity.

6. Differences in standability will not show up until later in the season and/or until after a wind storm. Pinch or split the lower stalk to see whether the stalk pith is beginning to rot.

7. Visual observations of kernel set, ear-tip fill ("tip dieback"), ear length, number of kernel rows and kernel depth, etc. may provide some approximate basis for comparisons among hybrids but may not indicate much about actual yield potential.

C) Soybean Aphid Possibly Found in Ohio - Ron Hammond & Hal Willson CORN Questions

Last week, a number of soybean fields in Fulton, Lucas and Wayne Counties were found to be infested with very low populations of an aphid. Since aphids do not commonly colonize soybeans, it may be assumed that the aphids found may be the soybean aphid, Aphis glycines, which has recently been detected in Wisconsin, Michigan, Illinois, Minnesota and Iowa. The aphid specimens collected have been submitted for taxonomic identification and confirmation. None of the soybean fields in which the aphids were found were showing symptoms of aphid feeding or was honeydew secretion which have been reported for heavy infestations detected in other states.

Assuming aphids observed in Fulton, Lucas and Wayne counties may be the new soybean aphid described in the CORN newsletter 2 weeks ago, it is important that the distribution of this new aphid pest be determined. County agents and field personnel are requested to inspect soybean fields, collect specimens of any unusual aphid infestations, and submit specimens for confirmation. The following observations were associated with the detection of aphid activity in soybean fields. In each case, aphids were located on the edge of the field. Thus, fields being sampled can be chosen based on the ability to easily park and reach the field. Development of infested soybeans ranged from pre-discoloration to early yellowing. No special field symptoms were associated with fields found to have low level infestations. The aphids were generally found on the underside of the leaves within 1 or 2 steps from the edge of the field The aphids collected were small and yellow, about the size of small, early instar potato leafhopper nymph. However, unlike leafhopper nymphs that are quite active, the aphids were relative sedentary. A good hand lens, or better yet, a small magnifier similar to those available at Radio Shack, will enable identification as aphids. The coloration of the aphids against the foliage facilitated detection. In a number of cases, a single, wingless adult was surrounded by many young aphid nymphs. Where aphids were present in low numbers, most leaves will not have them, so one may need to examine many leaves. However, where aphids were present, detection was generally achieved after a few minutes searching of one or two locations in Fulton and Lucas Counties.

If aphids are detected on soybeans, a sample of the infested foliage should be submitted to the nearest Extension office for identification and confirmation. Samples submitted to a local Extension office should be forwarded to the OSU Extension Entomology office or the OSU Plant and Pest Diagnostic Lab for identification. Infested foliage may be placed in a small plastic bag and kept cool to maintain freshness of sample. Relevant information should be included with any sample submitted (e.g. name of farm and field, township, nearest crossroads, addresses and phone numbers of parties to be contacted).

D) Slugs Damage Double-Cropped Soybeans - Ron Hammond CORN Questions

While looking for the soybean aphid, I happened upon a double-cropped soybean field that followed wheat in Lucas County with an extremely poor stand. More than 2/3 of the field had no soybeans. Upon examination, it became evident that slugs had taken out this field. Patches of plants that were present, especially near the edges, were about 8-10 inches in height and were flowering. Slime trails were evident on most plants along with some defoliation. Between these patches and areas without any plants, numerous small, completely defoliated plants were observed that were heavily covered with slug slime. Upon searching underneath the residue, numerous adult gray garden slugs were found. This area has had large amounts of rain, and the soil underneath the wheat residue was very moist. Damage at this time of early to double-cropped soybeans is very unusually. It is the first instance of a double-cropped soybean field I have ever seen having any slug damage, let only having such a stand loss. If growers are experiencing stand loss in their double-cropped soybean fields at this time, field visits should be done to examine remaining plants. Slug injury and presence will be confirmed by extensive defoliation and damage and presence of large amounts of slime. It is doubtful if there are any remedies possible at this time. The damage is probably already done and replanting is not possible. However, these fields might be prime candidates for problems next spring, and thus, should be identified. Visits to fields with known slug populations were also visited, and slug activity was evident from the amount of slug trails that were observed. All this suggests that other fall planted crops being no-tilled should be monitored in the coming months, included plantings of wheat and alfalfa.

E) Observations of Bean Leaf Beetles Activity in Central Ohio - Hal Willson CORN Questions

Soybean fields sweep net sampled for bean leaf beetle (BLB) in Madison and Clark counties during the past week exhibited relatively low levels of adult BLB activity. Average collection of BLB adults ranged from 0.1 to 0.5 beetles per sweep which was similar to BLB activity observed in mid-August. A slight increase in beetle catch in a couple fields suggested that 2nd generation BLB activity may be appearing at this time in central Ohio. Most fields are starting to turn color and some are rapidly dropping foliage, thus potential for additional pod injury is low given the low numbers of beetle collection and the fact that beetles will very likely disperse from fields where leaf drop is underway. Fresh pod injury due to BLB feeding was minimal in fields sampled. However, it should be noted that fields may differ significantly in BLB activity and soybeans should be monitored at this point in time for possible pod injury problems associated with increasing activity of 2nd generation BLB where economic levels of activity occur.

F) Fall Harvest Management of Forage Legumes - Mark Sulc CORN Questions

The optimal time of the last harvest of forage legumes is upon us. Forage legumes should be cut by Sept. 7 in northern Ohio and by Sept 15 in southern Ohio. They should not be cut during the 5 to 6 week period before a killing frost. For our region, this means the period from mid-September through October is the critical fall rest period. Harvesting during this period disrupts accumulation of energy reserves and development of cold hardiness.

Late September and early October cutting can be especially stressful, but the injury suffered depends on the winter conditions which no one can predict. The damage can be severe, mild, or non-existent. Despite the known risk, each year growers harvest forages during the fall. This year rainy weather has delayed cutting schedules throughout the growing season for many producers, pushing back the time when the crop will be ready for a last harvest. Growers should carefully weigh the need for additional forage against the increased risk of stand injury from fall cutting. The tonnage expected from a fall cutting and the need for the forage should be high before considering a cutting during the critical fall period.

When harvesting alfalfa in the fall, research has shown that several factors can moderate the risk of winter injury. These can be used to assess the risk associated with cutting specific alfalfa fields this fall:

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

- 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 cover increases the potential for heaving injury.

- Length of harvest interval during the growing season is often more important than the date of fall cutting in determining alfalfa stand survival. For example, a 3rd cutting during the fall is less risky than a 4th cutting taken during the fall, because a 3

-cut schedule allows longer intervals and better 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 35 days or less. The longer growth period allows more energy buildup before the fall harvest, and lessens the need for energy buildup after harvest.

- Maintaining optimal soil fertility levels (pH, P, K) is extremely important in keeping the stand healthy and reducing risks from added stresses like fall harvesting. - Disease resistant and winter hardy varieties will lessen the risk of injury from fall harvesting.

- Alfalfa that was protected from potato leafhopper injury during the summer will be at lower risk than if leafhoppers caused severe injury. Any stress (like wet soils) that weakened the crop during the year can increase the risk of damage from fall cutting.

- Cutting AFTER a killing frost (25 F for several hours) in late October or early November can be an option for WELL-DRAINED SOILS! Leave a 6-inch stubble after late fall cutting. Cutting this late in the year prevents regrowth that burns up energy reserves; however late removal of plant cover increases the risk of frost heaving!!! Fall cutting SHOULD NOT BE PRACTICED ON SOILS PRONE TO HEAVING (did I say that before?!).

- Do not harvest late summer seedings this fall.

G. Farm Science Review

This years Farm Science Review will be held on September 19-21, 2000 at Ohio State's 2,100-acre Molly Caren Agricultural Center is located two miles north of London on U.S. Route 40 and S.R. 38. Admission is $4 in advance or $6 at the gate, children 5 and under admitted free. Advance tickets are available from all county Extension offices. Additional information and a map of the sight can be found at: http://www.ag.ohio-state.edu/~ofsr/welcome.html.

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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.

Editor: Clark Hutson         Web Editor: Tom Rosati

Information 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.

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