C.O.R.N. Newsletter 2004-17

Dates Covered: 
June 8, 2004 - June 15, 2004
Editor: 
Greg La Barge

What Soybean Maturity Should I Plant in June?

Authors: Jim Beuerlein

Late planting reduces our cultural practice options for row spacing, seeding rate and variety maturity. The row spacing for June planting should be no greater than 7.5 inches. Appropriate seeding rates for the first half of June are about 200,000 to 225,000 seeds per acre. For the last half of June, 225,000 to 250,000 seeds per acre are recommended, and in early July drop 250,000 to 275,000 seeds per acre.

Soybeans are photo period sensitive. The date of physiological maturity is due to both day length and the stage of seed development in the uppermost pods on the plants. Relative maturity (RM) has little effect on yield for plantings made during the first three weeks of May but the effect can be large for late plantings. In May each 3-day delay in planting delays the physiological maturity date by about one day. During the first half of June, a 4-day delay in planting delays physiological maturity about one day. In the last half of June it takes a 5-day planting delay to delay physiological maturity a day. As planting is delayed, yield potential goes down and there is concern about whether late maturing varieties will mature before frost.

When planting late, the rule-of-thumb is to plant the latest possible maturing variety that will reach physiological maturity before the first killing frost. The reason for using late maturing varieties for late planting is to allow vegetative growth for as long as possible to produce nodes where pods can form before flowering and pod formation. More nodes equals more pods and more yield. So we need late maturing varieties that will mature before getting frosted but since we never know when first frost will occur, we use a narrow maturity range that will not be damaged by frost occurring at the normal time.

Assuming normal weather and frost dates, varieties with the following relative maturity should mature before frost and produce maximum possible yields when planted on the dates indicated. Varieties with an earlier relative maturity will mature earlier but will produce reduced yields.

OhioRegion
PlantingDate
SuitableRelative Maturity
YieldPotential
Northern
June 1-15
3.2-3.8
20-45

June 15-30
3.1-3.5
15-35

July 1-10
3.0-3.3
10-25
Central
June 1-15 3.4-4.0
25-48

June 15-30 3.3-3.7
20-40

July 1-10
3.2-3.5
15-33
Southern
June 1-15
3.6-4.2
30-50

June 15-30
3.5-3.9
25-45

July 1-10
3.4-3.7
20-40



Weed Control In Large Corn

Authors: Mark Loux

Weed control and herbicide use can be challenging in large corn, when a number of herbicides can no longer be used due to the risk of crop injury. Most herbicide products that contain ALS inhibitors should be applied broadcast before corn exceeds the V4 to V6 stage, depending upon the product. Several premix products that contain dicamba allow broadcast application to corn that is up to 24 inches tall, but application when corn is much smaller reduces the risk of injury. Broadleaf control tends to be easier to achieve in large corn, due to the restrictions on ALS inhibitors, but some grass herbicides can still be applied with drop nozzles as a directed spray to corn that is past the V6 stage. Some of the options for corn that is past the V6 stage or more than about 20 inches tall include the following (see also labels and Table 7 on page 75 http://ohioline.osu.edu/b789/pdf/table7.pdf of Ohio/Indiana Weed Control Guide):

Accent – directed spray up to 10 collars or 36-inch corn
Aim – broadcast or directed spray up to 8 collars
Basagran – no restrictions
Beacon – directed spray before tassel emergence
Bromoxynil – broadcast or directed spray before tassel emergence
Callisto – broadcast or directed spray up to 30-inch or 8-leaf corn
Dicamba – directed spray up to 36-inch corn
Equip – directed spray up to V8 stage or 36 inches
Exceed – directed spray up to 30 inches
Glyphosate (Roundup Ready 2 corn) – broadcast or directed spray up to 30 inches; directed up to 48 inches
Liberty (Liberty Link corn) – directed spray up to 36 inches
Lightning (Clearfield corn) – directed spray up to 45 days before harvest
NorthStar – directed spray up to 36 inches
Option – directed spray up to 36 inches
Permit – broadcast or directed spray prior to layby
Priority – broadcast or directed spray up to 8-collar stage
Resource – broadcast or directed spray up to 10-leaf stage
Yukon – broadcast or directed spray up to 36-inch corn

Some additional points to consider:

weeds that emerge 4 to 6 weeks or later after corn emergence are much less competitive than weeds emerging at the same time as the corn. Be sure that late-season weed infestations warrant herbicide treatment before making a decision to treat.

While some labels allow broadcast application to large corn, applying as a directed spray with drop nozzles may more effectively place herbicide below the crop canopy and toward the base of the corn plant. This will improve control of weeds that are much smaller than the corn and minimize the risk of crop injury.

Where weeds and corn are close to the same size, it may be impossible to use crop nozzles without reducing effectiveness (these will be large and difficult weeds anyway). In this situation, be sure to apply herbicide(s) that are labeled for broadcast application to large corn. Position the nozzles far enough above the corn to allow for proper spray pattern and minimize excess delivery of herbicide into the corn whorl.

Slugs

Authors: Bruce Eisley, Ron Hammond

We received reports of significant slug injury in corn and soybean fields from Fulton County in northwest Ohio last week, a part of the state that has never had much in the way of slug problems. Reports were received from fields having been in continuous no-till now for the past few years. No-till growers throughout the state who are experiencing defoliation or other unexplained injury to corn or soybeans should at least consider the possibility of slugs, especially if they have been in continuous no-till for a number of years. If injury is severe and new crop growth has significant feeding injury, molluscicide bait should be applied. The most common bait is use is Deadline MPs at a recommended rate of 10 lbs per acre.

Soybean Aphid

Authors: Bruce Eisley, Ron Hammond

Although still too soon to begin sampling for soybean aphids, growers should begin thinking about the potential for problems in the coming months. As mentioned in a previous C.O.R.N. report, we are not yet sure whether soybean aphids will become a major problem this year. So far, reports from others states suggest the possibility of lower populations. However, we are recommending growers continue to monitor the situation by reading the C.O.R.N. newsletter on a weekly basis because the situation might change at any time!

Recently, a 16 page bulletin that updates growers on the latest aphid research and information, including current thresholds, has been published. This bulletin is a compilation of information gathered from workers in all Midwestern states. The bulletin was written through cooperation with the North Central Soybean Research Program (NCSRP) which is a twelve-state coalition that invests checkoff dollars to research programs having a regional impact. The Ohio Soybean Council, a part of this regional effort, is a joint sponsor through its checkoff dollars. This soybean aphid bulletin is available in the spring issue of Ohio Soybean Review magazine, on the NCSRP Web site at http://www.ncsrp.com, or soon-to-be at your local extension office.

With All The Rain Do I Need Additional Sidedress N?

Authors: Robert Mullen, Edwin Lentz

With all the spring rain that has fallen the past few weeks, many producers are considering sidedressing N to replace what may have been lost. If extensive denitrification (clay soils) or leaching (sandy soils) has occurred, sidedressing can make a large economic impact on the operation. Determining how much N was lost and what the sidedress rate should be is complex and difficult. Soil temperature, nitrogen form, length of saturation, and organic matter all play critical roles in determining microbial activity and resultant denitrification. As an aid to help make sidedressing decisions, University of Minnesota scientists have developed a simple question and answer point system. We have adapted that point system to Ohio and propose its use for this year’s corn crop (see below).

1) What N source was utilized?
1 point - Anhydrous ammonia with nitrification inhibitor
2 points - Anhydrous ammonia
3 points - Other fertilizer banded
4 points - Other fertilizer broadcast

2) When was the N applied?
2 points - After April 20
5 points - Before April 20

3) How much N has been applied?
1 point - >200 lbs/A
2 points - 150-200 lbs/A
3 points - 100-150 lbs/A
4 points - <150 lbs/A

4) What has been the predominant soil moisture status in the field this spring?
1 point - Normal
2 points - Wet
4 points - Excessively wet (saturated – standing water)

5) What is crop’s condition?
1 point - Green plants > 12” tall
2 points - Green plants < 12” tall
3 points - Chlorotic plants < 12” tall
5 points - Chlorotic plants > 12” tall

Total the score and use the following guidelines:

Less than 13 - Additional fertilizer not recommended
13-16 - Evaluate again in 4-7 days
17 or greater - Add an additional 40-70 lbs N/A


Some producers may consider the use of the presidedress soil nitrate test (PSNT) to determine if additional N fertilizer is warranted. To attain a representative soil sample, collect 15, 1-ft deep random cores from a field and mix them thoroughly. Submit a grab sample from the composite to a reputable lab (a list of labs is available at the following web address: http://www.ag.ohio-state.edu:8000/%7Ecorn/library/testlabs.pdf). You may want to contact the lab and find out the turn-around time (some may be able to complete analysis in a couple of days). If the nitrate level in the soil is between 25-30 ppm then additional N is probably not warranted. Nitrate levels lower than 25 ppm have an increased likelihood of response, but the rates should not be greater than 70 lbs N/A. Work out of Illinois reveals that application of only 50 lbs N/A results in maximum yield over a wide variety of growing conditions.

Update On Wheat Head Scab Development

Authors: Dennis Mills, Patrick Lipps

We have received many reports of growers finding some head scab in fields now that the crop is several weeks past flowering. In southern Ohio the wheat is now beginning to turn due to natural maturing and scab symptoms will become more difficult to assess as time goes on. In northern Ohio scab symptoms will be developing over the next week if it will be present. The bleached out florets on the heads are easy to detect at the late watery ripe to late milk stage of development.

Because of the contrast between bleached out florets on affected heads and the dark green coloration of healthy heads there is a tendency to overestimate the severity of scab in the field. An easy way to estimate the incidence of the disease is to take a handful of tillers together in the field and count the number of healthy heads and diseased heads. Most people can grab a handful of about 20 to 25 heads, so making several counts across the field will give a reasonable estimate of the level of disease. Although the incidence of diseased heads is not a good predictor of actual impact on yield, it is good to have a relative idea of the amount of disease in the field. Genereally, the higher the disease level the greater the yield loss. The Scab Risk Prediction models that we have been using consider 10% field severity as being an ‘epidemic’ and at the point which will significantly impact yield. Examples of 10% field severity include when one head is completely killed out of 10 heads examined or when 1 to 2 spikelets on each of 10 heads is diseased. Obviously, there can be a great variation in the way the disease may affect individual heads.

Wheat fields with significant amount of head scab should be concerned with the accumulation of deoxynivalenol (commonly called DON or vomitoxin) in the grain. The severity of the disease in the field is not a real good predictor of the amount of DON in the grain at harvest except when disease levels are very high. The amount of DON in the grain is influenced by many factors including the severity of scab in the field, how much rain occurs between symptom development and harvest, and the variety of wheat affected. Grain buyers and wheat millers usually do not want to buy grain with DON levels over 2 ppm (parts per million), so a dockage is usually associated with higher levels of contamination. In preparation for harvest, those fields with higher levels of scab should be harvested as soon as possible. Turn up the air as much as possible to remove as many small and shriveled kernels as possible in an attempt to improve the test weight.

The extent of head scab in Ohio will likely be known over the next week to 10 days. We will provide additional information on the intensity of disease as data comes in. Although head scab can be detected in most fields, the level reported appears to be low to moderate. We are still waiting for symptoms to develop fully in wheat in north central Ohio where the disease risk was the greatest.

Archive Issue Contributors: 

State Specialists: Pat Lipps & Anne Dorrance, Dennis Mills (Plant Pathology), Peter Thomison (Corn Production), Jim Beuerlein (Soybeans & Small Grain), Mark Loux (Weed Science), Jeff Stachler (Weed Science), Bruce Eisley (IPM) and Ron Hammond (Entomology); Extension Agents: Woody Joslin (Shelby), Barry Ward (Champaign), Steve Foster (Darke), Gary Wilson (Hancock), Greg La Barge (Fulton), Glen Arnold (Putnam) Mark Keonig (Sandusky), Harold Watters (Miami), Dusty Sonneberg (Henry) and Steve Prochaska (Crawford).

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.