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Agronomic Crops Network

Ohio State University Extension


C.O.R.N. Newsletter 2013-09

Dates Covered: 
April 16, 2013 - April 22, 2013
Glen Arnold
Scouting for Alfalfa WeevilAlfalfa weevil larvae

Scouting for Alfalfa Weevil

This is the time that growers in southern Ohio should begin scouting for alfalfa weevil, while those in central Ohio should start by the end of the week.  Enough heat units (200 HU) have accumulated in southern Ohio to warrant scouting.

The only part of the state not yet reaching sufficient heat units is the north, but we would expect that area to reach the required number next week.  Scouting is accomplished by collecting a series of three 10-stem samples randomly selected from various locations in a field. Place the stem tip down in a bucket. After 10 stems have been collected, the stems should be vigorously shaken in the bucket and the number of larvae in the bucket counted. The shaking will dislodge the late 3rd and 4th instar larvae which cause most of the foliar injury. Close inspection of the stem tips may be needed to detect the early 1st and 2nd instar larvae. The height of the alfalfa should also be recorded at this time.

Economic threshold is based on the number of larvae per stem, the size of the larvae and the height of the alfalfa. The detection of one or more large larvae per stem on alfalfa that is 12 inches or less in height indicates a need for rescue treatment. Where alfalfa is between 12 and 16 inches in height, the action threshold should be increased to 2 to 4 larvae per stem depending on the vigor of alfalfa growth. When alfalfa is 16 inches in height and there are more than 4 larvae per stem, early harvest is recommended.

For more information on the weevil, see the OSU Alfalfa Weevil Fact Sheet .

Mixing Corn Hybrids Within a Field to Increase YieldMixing Corn Hybrids Within a Field to Increase Yield

Mixing Corn Hybrids Within a Field to Increase Yield

In my CORN newsletter article last week, I cited planting a mix of hybrids with different maturities as one strategy to help reduce damage from diseases and environmental stress at different growth stages. Since then, I received questions as whether this practice was being proposed within a field or across the fields for an entire farming operation. I was thinking in terms of the latter.

However, planting a mix of hybrids within a field could have an advantage similar to those for mixing hybrids across fields. Mixing different hybrids within a field is sometimes promoted as a practice for increasing grain yield over that of hybrids planted separately, especially in environments where high temperatures and drought often occur during pollination.

Three advantages often cited to support mixing hybrids are:  1) planting mixtures of hybrids with different maturities (or flowering dates) in the same field lengthens the period of pollen availability thereby decreasing the risk of poor pollination resulting from moisture stress during flowering, 2) planting mixtures of hybrids reduces weather and soil related variation risks, and 3) planting mixtures promotes cross pollination resulting in larger kernels and higher grain protein.

Since the 1950’s, several studies have been conducted in the U.S. and Canada to evaluate the potential of within field hybrid mixing on yields (most of these have compared strips of two hybrids planted in pure and mixed stands (alternating rows of two hybrids). Most of these studies have shown little or no yield benefit from within field mixing of hybrids. However, researchers in South Dakota and Minnesota in the 1990’s concluded that mixtures of genetically diverse hybrids that flower at the same time can increase yields through cross pollination.

In 2005 - 2008, we conducted on-farm studies to investigate differences in grain yield and quality among corn hybrids planted in pure and mixed stands. The results indicated that mixed stands provided little yield advantage over pure stands. Effects of blending hybrids on grain composition were variable but relatively small. The protein content of grain from the mixed hybrid plantings was either similar to that of the hybrid with the higher protein content in pure plantings or intermediate that of the two hybrids in the pure plantings. Oil content of the grain from the mixed plantings was intermediate that of the grain for the two hybrids in the pure planting. Differences in the starch content of grain from the hybrid blends and the hybrids in pure plantings were negligible.

There may also be various some management issues to consider when planting hybrid mixtures, e.g. selecting appropriate hybrids and mixing seed at planting; differences in grain moisture content at harvest between hybrids exhibiting varying field grain drying rates.  Nevertheless, with advances in precision agricultural technologies the concept of mixing hybrids within fields is receiving more attention. Some seed company agronomists propose varying hybrid plantings and seeding rates within a field in accordance with varying soil conditions and properties, e.g. differential planting of “defensive hybrids” and “high yield” hybrids at varying seeding rates depending on the differences in yield potential across a field.

Optimum Conditions for the “Cool” Pythium spp.

Rain and persistently cool soil temperatures are optimum for a large diverse group of pathogens, the water molds.  The cool soil temperatures reduce the rate of growth of both corn and soybean seedlings giving Pythium more time to infect and colonize these growing plants.

Soil temperatures from around the state are still on the cool side.  From the weather stations at the branches, these are the soil temperatures at 2.5 inches.


Research Branch

Temperature (F)








Muck Crops






North Central








Over the past ten years we have identified more than 25 different species of Pythium that can infect both corn and soybean in Ohio’s production fields.  These are the fields that require replanting, you know you put the right amount of seed in the planter, but the rows look thin and the yields are off by 10 to 15 bushels.

When seed is planted into these cool soils, and more rains come (this is Ohio after all), the ground becomes saturated for a short time.  These are perfect conditions for these water molds to develop the swimming spores, called zoospores.  What is very unique about this group of organisms is that these zoospores are attracted to seeds and seedlings through a process called chemotaxis.  In addition to identifying this diverse group of pathogens by several former students, we also identified differences in sensitivity to the key seed treatment fungicides:  metalaxyl and strobilurin compounds.  Some isolates were controlled by one compound and not the other, while a few species were not controlled by either.

Unfortunately, every field has a very diverse complement of these Pythium spp.  So the seed treatments will control some of what is in the field, but most likely not all.  Therefore, still use the seed treatment, but more importantly – plant in the most optimum conditions for the seed to germinate quickly and get established.  This is especially important for those fields that have poor drainage.

2013 Soybean Planting ConsiderationsFall compaction impacting spring emergence

2013 Soybean Planting Considerations

According to the U.S. drought monitor, most of Ohio has returned to normal soil moisture conditions with the exception northwest Ohio which still has lingering abnormally dry soil conditions (  Most of Ohio experienced drought conditions during the 2012 growing season.  The drought of 2012 may have impacted the seed lot for planting this spring, and many growers have asked “What do we need to consider going into the 2013 planting season?”

Consider soybean seed size:  On average, 2,500 individual soybean seeds make up one pound.  Dry conditions during seed fill can result in smaller than normal seeds (>2,500 seeds per pound).  However, dry conditions early in the growing season followed by August/September rains increased seed size in many areas.  I have heard/seen many reports of seed size being larger than normal.  One source reported seeds as large as 1,700 seeds per pound.  In the Ohio Soybean Performance Trial, soybean seed was close to normal at our Delaware County location.  However, there was a relationship between seed size and relative maturity.  Seed size increased with later maturing varieties.  (There was limited rainfall in August and above average rainfall in September at the Delaware County location.)  Check soybean seed size before planting this year and contact your equipment dealer/operator’s manual to adjust for seed size if planting abnormally large (or small) seed.

Consider soybean seed quality:  Drought can have a negative effect on seed quality.  Federal law requires seed bags to show results of a standard warm germination test, so be sure to check germination results of your seed.  Germination is considered good if it is approximately 95%.  If germination is less than 90%, consider increasing seeding rate.  I talked to a few seed companies this winter and most will not sell seed with poor germination (unless there is a shortage of seed).  To adjust seeding rate because of low reported germination test results, divide 0.9 by the germination rating on the seed tag.  Then, multiple this number by the normal seeding rate.  For example, my seed germination is 80% (0.8) and my normal seeding rate is 160,000 seeds per acre.  First, I divide 0.9 by 0.8.  This gives me 1.125.  Then, I multiply 1.125 by my normal seeding rate of 160,000.  This gives a new seeding rate of 180,000 seeds per acre.

Avoid field operations when soil condition is inadequate.  The fall of 2011 was really wet, which made harvest difficult for many growers.  In some areas of Ohio, harvesting when soil conditions were too wet caused compaction from tire tracks.  Compaction can be decreased during winter freeze/thaw cycles, but during winter 2011/2012, there really weren’t many freeze/thaw cycles.  Soybean germination and emergence were negatively affected by compaction areas from the 2011 harvest (see picture).  So, if possible, avoid field operations when soil conditions are inadequate because you may see uneven soybean emergence as a result. 

Weed Identification – Intro and Basics

We frequently receive questions about how to identify weeds and what the best resources are for help with identification.  There are many resources available for plant identification, but these are some of the ones we use the most.

1. There’s an App for that? Yes.

“ID Weeds” from the University of Missouri Extension. A little technical; however, a solid weed list with a good vocabulary to get you heading in the right direction.

Weed ID” by BASF. This one has a “take a picture” option that can be very helpful. It also has general ID pictures instead of just terms when choosing characteristics.

2. The Internet. You have questions it has answers.

Many solid weed ID websites are available, and the best one is really a matter of personal preference.  Weed science programs at Virginia Tech, and the Universities of Illinois and Wisconsin, all have good ID sites.  A favorite for just looking at photos of weeds is .  The “images” tool in Google is very helpful for confirming an ID.

3. Books. Yes they still make books and they are usually our favorite for weed identification.

We have shelves of ID books and all of them serve a purpose. They are full of amazing descriptions, sketches, and pictures. Our top picks, in no particular order, are Weeds Of the Midwestern United States and Central Canada, Weeds of the North Central States, and Weeds of the Northeast.

The first and normally easiest step in identification is determining if the weed is a monocot (grass) of dicot (broadleaf). If you go with grass the main characteristics to look at are the leaf shape, presence or absence of hair, auricle, ligule, flower shape, and overall plant structure. If you go with broadleaf the main characteristics are cotyledons (if still present), hair (present or absent), leaf arrangement, leaf type, leaf shape, leaf margin, petioles, ochrea, and flower shape/color.  With all of these characteristics a lot of variation occurs, and not just between species but within as well.  Feel free to email us for help with weed identification.  We can often identify a weed with a few good digital photos.

Weather OutlookWeather Outlook

Weather Outlook

As discussed a few weeks ago, we expected a change to above normal temperatures. This has happened and will continue this week. A weather system will stall and produce heavy rainfall from Missouri through Illinois and eastern Iowa into northern Indiana and Michigan this week. As the storm finally moves east rain will sweep across Ohio. The best chances are Tuesday and again later Thursday into Friday. Much of the corn and soybean belt from Iowa and Southern Wisconsin to Ohio should receive at least their normal rainfall of about an inch this week. Within that area, 2-4 inches of rain is likely from parts of the northern half of Indiana into Illinois and southern Wisconsin and eastern Iowa. Some totals could reach 5 or more inches especially in parts of Illinois.

Our next issue as we also discussed several weeks back was an increased chance for late spring freezes this year. It appears we will see temperatures at or below freezing in many places this weekend. Our weather models indicate there may be another freeze potential by the end of the month or beginning of May. We will monitor this issue.

For the rest of April...temperatures will go from above normal this week to slightly below normal normal for the rest of the month. Rainfall is forecast to average normal to slightly above normal at 1.5 to 3 inches with normal near 2 inches. The greatest totals will be in the north and west.

Week of April 15...temperatures 5 degrees above normal...rainfall slightly above normal at 0.75 to 2 iinches with higher totals.

Week of April 22...temperatures 5 degrees below normal...rainfall at or below normal at 0.5 to 1 inch.

Early May outlook...

After a cold start to May it will turn warmer than average again. Really...these swings going on are very typical of spring and all these changes are within what I would label as typical for spring in Ohio after the very cold March. After a dry start to May it should return to normal.

This spring outside of the cold March is behaving very close to what the National Weather Serivce Ohio River Forecast Center called for last fall and early winter for this spring.




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Crop Observation and Recommendation Network

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.