CORN
Crop Observation and Recommendation Network

June 16-22, 2003
C.O.R.N. 2003-18

In This Issue:

A) Yield Expectations for Late Corn Plantings
B) Weather Stress and Corn Yield Potential
C) Seeding Rates for Late Planted Soybeans in 2003
D) Herbicide Performance Issues
E) Harvest Aids For Wheat
F) Wheat Head Scab Update
G) Slug Activity Continues
H) Soybean Aphid
I) OSU Weed Science Field Day

A) Yield Expectations for Late Corn Plantings - Thomison CORN Questions

Most farmers who are still planting corn have switched to early maturing hybrids (95-103 day relative maturity). Based on past OSU research, such corn planted in mid-June will likely yield about half the expected yield of a full season crop planted May 1. Good rainfall during the remainder of the growing season and a mild fall (late killing frosts) could reduce such losses. However, as we saw in 2002 drought during July and August could destroy a late planted crop. Late planted corn is typically associated with higher grain moisture at harvest, lower test weights, and greater potential for stalk lodging problems.

We compared planting date effects on hybrids representing a range of maturities several years ago in a study conducted at Hoytville in northern Ohio. Although adapted hybrids (106-115 days) produced significantly greater yields than a short season 97-day hybrid planted before mid-late May, the 97-day hybrid produced yields similar to the fuller season hybrids for the mid -June planting dates. Moreover, the 97-day hybrid reached harvest moisture (25% moisture) 12 days before the earliest adapted hybrid. Results of this study suggest that acceptable yields can be obtained with corn planted as late as mid-June when growing conditions are favorable, but they don't indicate the potential yield reduction that might occur under heat and drought stress.

B) Weather Stress and Corn Yield Potential - Thomison CORN Questions

I've received several questions as to what impact this year's weather conditions will have on the yield potential of the corn crop (i.e. Has yield potential been significantly reduced by the cloudy, cool, wet conditions we've experienced since early May?) There are a number of factors to consider in making such an assessment. However the impact of this year's early season weather stresses will be determined largely by weather conditions in July and August. If growing conditions are favorable during pollination and grain fill, yield losses from early season stresses should be minimal. However, if weather turns hot and dry (as in 2002), the adverse effects of these late season stresses will be much greater than they would have been if conditions during crop establishment had been drier and warmer. Several corn specialists in neighboring states have also addressed this issue in the articles shown below.

Bob Nielsen "Blue Skies Smiling On Me..." Available on-line at http://www.agry.purdue.edu/ext/corn/news/articles.03/BlueSkies-0606.html

Emerson Nafziger "Thinking About Crop Stress". Illinois Pest & Crop Bulletin (6 June) Available on-line at http://www.ag.uiuc.edu/cespubs/pest/articles/200311i.html

C) Seeding Rates for Late Planted Soybeans in 2003 - Beuerlein CORN Questions

Plant size at the end of the growing season is the determinate of the most efficient seeding rate for soybeans. The larger the plants the fewer needed for maximum yield and vis versa. When planted in late June, soybean plants don't get very big so more plants are needed for both sunlight interception and to supply more nodes where pods can form. For late June planting, we need to drop 3 seeds per foot of row in 7.5" rows (209,000 seeds per acre). In the first week if July we need to drop 3.2 to 3.5 seeds per foot in 7.5" rows (224,000 to 244,000). In areas of the field with dark colored soil where the plants will get larger, the seeding rate can be reduces 15,000 to 25,000 seeds per acre. If germination percent is less than 90, then adjust the seeding rate up to account for that difference. Rows wider than 7.5" will reduce yield. Be sure the seed is treated with appropriate fungicides to aid in stand establishment and maintenance.

D) Herbicide Performance Issues - Stachler CORN Questions

If marestail (horseweed) and common lambsquarters are not being completely controlled by glyphosate please let Mark or I know about this. We need to know where the glyphosate-resistant marestail is spreading to in this state. If you have other weed species that are not being controlled by herbicides feel free to contact us as well. Understanding the presence of herbicide-resistant weeds is very important for future management decisions. Jeff Stachler can be reached at 614-292-1393.

E) Harvest Aids for Wheat - Loux CORN Questions

Several herbicides are approved for application to mature wheat to prevent weeds from interfering with harvest. Ragweeds, thistle, and lambsquarters are some of the weeds most likely to be a problem at the time of harvest, especially where wheat stands were not of uniform density. Take precautions to reduce spray drift when applying harvest aids, since sensitive crops and other desirable plants are likely to be growing in adjacent areas. Some specifics on the application of harvest aids follow (consult labels for more information).

- Various 2,4-D products are labeled as harvest aids at rates of 1 to 3 pints/A depending upon the product. 2,4-D can be applied with ground or aerial equipment after wheat has reached the hard dough stage. Some labels advise that crop injury can occur, and spot treatments should be used to minimize the extent of injury. Do not feed wheat straw to livestock where 2,4-D is applied as a harvest aid. Amine formulations have less potential than ester formulations to volatilize and move off-target, but spray particle drift is possible with either.

- Many glyphosate products can be applied as a preharvest treatment in wheat for control of annual and perennial weeds. Application rate is 22 oz for WeatherMax and 32 oz for most other glyphosate products. Apply at least 7 days prior to harvest, and after the hard dough stage when grain moisture is 30% or less. Glyphosate can be applied with ground or aerial equipment, and some glyphosate products can be mixed with 2,4-D. Wheat grown for seed should not be treated with glyphosate preharvest.

- Weedmaster is a premix of 2,4-D amine plus dicamba that can be applied at least 7 days before harvest when wheat is in the hard dough stage, and after all green color has disappeared from the nodes of the wheat stem. This product can be mixed with glyphosate. Do not use treated wheat for seed unless a germination test is performed on the seed prior to planting.

F) Wheat Head Scab Update - Lipps and Mills CORN Questions

We are in the third year of testing our head scab predictive models. The models were quite accurate the first two years. Each year has been a bit different and this year has been no exception. This year the models have indicated that head scab should be at relatively low levels in most of the state. The exception to this will likely be in the early flowering wheat in the southern part of the state. Our models indicated that wheat in flower from around May 11 to May 17 had a higher risk of scab than those fields that flowered later. Reports from Butler Co. indicate scab incidence ranging from 0 to 6% and in Jackson Co. scab incidence has been a bit higher, ranging from 10 to 19%.

Additionally, we visited some fields in Pickaway Co. last week and evaluated various varieties in the Ohio State Wheat Variety Performance trial. Scab severity ranged from 0 to about 15%. Of the nearly 70 varieties in the trial only 4 varieties had severities above 10%. The rest had severities ranging from 0 to about 7%. It was obvious that the earlier flowering varieties had more scab than the later maturing varieties. Thus, maturity group had a definite influence on the scab level. Scab generally has a impact on yield when severity reaches about 10%, thus scab will likely impact some fields in southern Ohio. If scab will be important in other locations in Ohio this year, symptoms will likely start showing up in central Ohio this week and in northern Ohio later this week and next week. We certainly hope our forecast for low severity will hold true. This is the first year our scab models have been tested during a season with such persistent rain showers during and after flowering. The temperatures during the critical flowering time were generally too cool for severe infection, and that is the reason for the low predictions. By next week we will have evidence if the models were correct or not.

G) Slug Activity Continues - Hammond and Eisley CORN Questions

Concern with slugs persists, especially on crops planted the past few weeks and on those crops remaining to be planted. Growers should continue to monitor their fields. Questions have come up the past week on the efficacy of Deadline MPs. Most reports being received suggest that the material is working as expected. When judging whether a treatment has worked, growers should examine the new corn leaves emerging from the corn whorl or on soybeans, the top-most leaves that are opening. If these newer leaves are free of slug feeding, one can usually assume that the majority of slugs have been controlled and the treatment worked. If feeding continues to be heavy on these upper most leaves, re-treatment might be warranted. However, growers should only treat those areas of the field where slug feeding is continuing. Usually, the majority of the field will not need re-treatment. Looking for dead slugs following treatment will not be worthwhile as none will be found, nor is looking for the continued presence of Deadline MP pellets. A heavy population of slugs will often consume most of the bait. Counting slugs at dusk will also indicate whether many slugs are left and the relative efficacy of the bait, but the slug counts should be random across the field, not just in areas where feeding is continuing. Also, these counts are only valid if you knew how many slugs were present prior to treatment.

H) Soybean Aphid - Hammond and Eisley CORN Questions

Although we have not yet observed the soybean aphid in Ohio, reports from neighboring states indicate that the aphid is starting to occur in soybeans. Sampling for the soybean aphid should begin over the next few weeks, and definitely be on-going by the R1 to early R2 (flowering) growth stages. When the soybean aphid begins to occur in larger numbers, most people will have no problem making the correct identification. It will be the only aphid colonizing soybeans. However, at the early stage of infestation when only a few aphids might be on the plant, care needs to be taken that they are correctly identified. This might take examining the aphid underneath a microscope or magnifier to ensure it is truly an aphid. Remember that soybean aphids are similar in size to small potato leafhopper nymphs, although the leafhoppers are usually more active. You should also not confuse the aphids with other small critters such as thrips, and the other small invertebrates that might be on the leaf. This is the reason for using a microscope or good hand lens.

When aphids become common, sample the upper leaves from 4-5 plants from 20 locations in the field, and get an estimate of the number of aphids per plant. Current recommendations suggest that if plants average approximately 250 or more aphids per plant, treatment will be required. This level will be approximately 100-150 aphids per leaf, or 30-50 aphids per leaflet. If the rating scale below is used, treatment is recommended when the average rating is 3 or above.

0 = none
1 = 1-10 per single leaflet
2 = 10-30 per single leaflet
3 = 30-100 per single leaflet
4 = 100-300 per single leaflet
5 = >300 per single leaflet

Timing of the insecticide application will be very important in achieving good control. The current thought is that the late vegetative stages prior to flowering will be too early to spray. Other states have seen a rebound in aphid densities when an insecticide is applied this early because of the reproductive capabilities of the remaining aphids. However, detecting an early infestation in late June will alert growers to potential problems.

Most insecticide applications should occur in early to mid July during flowering or immediately thereafter. Observations suggest that the greatest benefit from an insecticide application will come during this time period. The later in the summer an insecticide application is made, the less the benefit from that spray. Spraying late in the season after pods have filled or following dispersal of winged aphids in mid-to-late summer will be too late to prevent economic yield loss.

Good coverage is essential and will be best achieved by spraying with higher pressures and higher gallons per acre. The following insecticides are labeled for soybean aphid control:

Care should be taken during flowering if bees are actively working a soybean field. Although bees are not usually associated with soybeans, they do forage in soybeans and problems could occur if hives are nearby. Label directions pertaining to most of the insecticides and state regulations state that the insecticide should NOT be applied to blooming or flowering crops if bees are actively working in the target area. Thus, most materials for soybean aphid control should be applied in early morning or late day when bees would not be active in fields. Ohio regulations state in 901:5-11-04 of the Ohio Administrative Code "No pesticide which is required to carry a special warning on its label indicating that it is especially toxic to honey bees, shall be dispensed over an area of one-half acre or more in which the crop plant is in flower unless the owner or caretaker of any registered apiary located within one-half mile of the treatment site shall be notified by the person who applies for himself or engages a pesticide applicator no less than twenty-four hours in advance of such intended treatment; provided, however, that these locations are registered and identified as required by section 909.02 of the Revised Code of Ohio, and that such apiary locations have been posted with the name and telephone number of the owner or a responsible caretaker". The names and addresses of registered apiaries are available at the Ohio Department of Agriculture at 1-800-282-1955. Growers should be advised to follow all label directions and state regulations; it is the soybean grower's responsibility!

I) OSU Weed Science Field Day - Loux CORN Questions

The OSU Weed Science field day is scheduled for, Wednesday, July 9 at the OARDC Western Branch in South Charleston, OH. The field day starts at 9 am, and is the usual self-directed tour of our research plots. Drinks and plot maps will be available free of charge. Directions to Western Branch: From I-70, take SR 41 south approximately 4 miles. The branch is on the right side of the road. After coming in the main driveway, follow the road around to the right of the large white barn and park near the pine trees.

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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: Nathan Watermeier

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.

All educational programs conducted by Ohio State University Extension are available to clientele on a nondiscriminatory basis without regard to race, color, creed, religion, sexual orientation, national origin, gender, age, disability or Vietnam-era veteran status.

Issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture, Keith L. Smith, Director, Ohio State University Extension.

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