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Ohio State University Extension


C.O.R.N. Newsletter 2012-19

Dates Covered: 
June 25, 2012 - July 3, 2012
Harold Watters

Dry weather continues

The trend continues with no relief expected. In fact, conditions are forecast to worsen.

The outlook the next two weeks is for much above normal temperatures and below normal rainfall. Normals highs are in the 80s and lows in the lower 60s. Rainfall averages just below 2".

Below normal temperatures will start this week but will be replaced with the hottest weather of this year by late in the week. By late this week, temperatures will soar through the 90s with a few places in the west nearing 100! Littlle or no rain is forecast as drought in the northwest spreads slowly southeast. 

Temperatures for the 4th of July week will remain above normal with highs mostly in the 80s and 90s. Limited rainfall is forecast. There is less than a 25 percent chance of 2" of rain the next two weeks so normal rainfall is not expected.

We had correctly forecast a warmer and drier than normal spring since January but thought normal rainfall would return by August. Confidence in this is now in question and we will monitor this closely. Expect warmer and drier weather through July at this point as soil moisture becomes depleted and a feedback loop develops where less rains causes drying soils which leads to less rains. It is a hard loop to break before August, based on historical data.

Tropical Storm Debby along the Gulf Coast will create sinking motion and drying conditions over our area, so Debby will impact us but in a dry way.

Hot, dry weather will impact pollination in corn

Hot, dry weather will impact pollination in corn

The combination of inadequate rainfall and above average temperatures is creating stress conditions in many corn fields across Ohio. According to the National Agricultural Statistics Service ( ), 75 percent of the state is currently estimated to have subsoil moisture content that is rated short to very short.

During the past week, tassels began appearing in corn fields planted in April. The pollination period, the flowering stage in corn, is the most critical period in the development of a corn plant from the standpoint of grain yield determination. Drought effects on yield potential are greatest during the reproductive stage.

Yield losses to moisture stress can be directly related to the number of days that the crop shows stress symptoms. According to Iowa research by Claassen and Shaw on effects of drought, four days of stress (i.e. corn wilted for four consecutive days) at the 12th-14th leaf stage has the potential of reducing yields by 5 to 10 percent. The potential for yield losses to soil moisture deficits increases dramatically when plants begin to flower. During tassel emergence, four days of moisture stress has the potential to reduce yields 10 to 25%. Silk emergence is the most critical period in terms of moisture use by the plant. During this stage, leaves and tassels are fully emerged and the cobs and silks are growing rapidly. Four days of moisture stress during silk emergence has the potential to reduce yields 40 to 50%. Keep in mind that the stress conditions we are alluding to over these “four day periods” are severe and involve extensive leaf rolling (characterized by plants with “pineapple” like leaves) throughout much of the day. Fields with scattered plants exhibiting some leaf rolling late in the afternoon are probably not experiencing severe stress.

 The following are key steps in the corn pollination process.

  • Past studies indicate that pollen shed may begin up to three days prior to silk emergence and continue for five to eight days with peak shed on the third day (However, silks may actually emerge before tassels fully emerge and pollen shed starts in certain hybrids under favorable conditions). Under very dry conditions, silk emergence may be delayed, and such “asynchronization” of pollen shed and silking may result in poor kernel set and reduced grain yields. When such delays in silking are lengthy, varying degrees of barrenness will result. This year it's very likely that silk emergence will be delayed in severely drought-stressed corn fields unless we receive some timely rain.
  • On a typical midsummer day, peak pollen shed usually occurs in the morning between 9:00 and 11:00 a.m. followed by a second round of pollen shed late in the afternoon. This pattern reduces pollen exposure to the highest temperatures of the day.  Pollen may be shed before the tassel fully emerges (“stretches out"). Pollen shed usually begins in the middle of the central spike of the tassel and spreads out later over the whole tassel with the lower branches last to shed pollen. 
  • Pollen grains are borne in anthers, each of which contains a large number of pollen grains. The anthers open and the pollen grains pour out in early to mid morning after dew has dried off the tassels. Pollen is light and is often carried considerable distances by the wind.
  • Pollen shed is not a continuous process. It stops when the tassel is too wet or too dry and begins again when temperature conditions are favorable. Pollen stands little chance of being washed off the silks during a rainstorm as little to none is shed when the tassel is wet. Also, silks are covered with fine, sticky hairs, which serve to catch and anchor pollen grains.
  • Under favorable conditions, pollen grain remains viable for only 18 to 24 hours. However, the pollen grain starts growth of the pollen tube down the silk channel within minutes of coming in contact with a silk and the pollen tube grows the length of the silk and enters the female flower (ovule) in 12 to 28 hours.
  • A well-developed ear shoot should have 750 to 1,000 ovules (potential kernels) each producing a silk. The silks from near the base of the ear emerge first and those from the tip appear last. Under good conditions, all silks will emerge and be ready for pollination within 3 to 5 days and this usually provides adequate time for all silks to be pollinated before pollen shed ceases.
  • Pollen of a given plant rarely fertilizes all the silks of the same plant. Under field conditions 97% or more of the kernels produced by each plant may be pollinated by other plants in the field. The amount of pollen is rarely a cause of poor kernel set. Each tassel contains from 2 to 5 million pollen grains, which translates to 2,000 to 5,000 pollen grains produced for each silk of the ear shoot. Shortages of pollen are usually only a problem under conditions of extreme heat and drought. As noted above, poor kernel set is more often associated with poor timing of pollen shed with silk emergence – with silks emerging after pollen shed (poor “nick”). However, hybrids seldom exhibit this problem unless they experience extreme drought stress.


Nielsen, RL (Bob). 2010a. Silk Development and Emergence in Corn. Corny News Network, Purdue Univ. [URL verified June 2012]

Nielsen, RL (Bob). 2012b. Next Big Hurdle: Pollen Shed and Silking. Corny News Network, Purdue Univ. [URL verified June 2012]


Alfalfa Management Considerations in a Drought

An established alfalfa plant has a deep taproot that enables the plant to extract moisture from the soil and continue growing even under drought conditions.  In addition the alfalfa plant has the ability to go into a prolonged dormancy under severe moisture stress and then recover once rainfall begins again.  Many areas across the state of Ohio are facing drought conditions and the short term forecast is not encouraging.  There are reports of alfalfa regrowth beginning to bloom at 4 to 6 inches of height in some fields and growers have questions about alfalfa management under these conditions.  

Dry matter accumulation in alfalfa is most rapid when the plant is in vegetative and early reproductive growth stages.  Once the plant begins to flower dry matter accumulation slows down.  By the time the plant is at full flower or 100% bloom, no further dry matter accumulation will occur. So, in our example of alfalfa beginning to bloom at 4 to 6 inches of height, there will be very little additional tonnage added by delaying harvest. 

Here are some things we know about alfalfa growth under drought conditions.

  • ·      The number of basal buds and the number of shoots or stems/plant is reduced when the alfalfa plant experiences moisture stress in the first 14 days after a harvest.
  • ·      The stem internode length is reduced under moisture stress; thus the blooming that is being seen at 4 to 6 inches of height.
  • ·      Leaf area/leaf size and leaf growth rate is reduced under moisture stress, although to a lesser degree than stem growth.  The result is that the leaf to stem ratio is higher under drought stress.  A higher leaf to stem ratio equals higher forage quality.

If a decision is made to cut the alfalfa stand under drought conditions, alfalfa should be mowed at the normal cutting height.  There is no advantage to raising the cutting height.  Alfalfa can regrow from either axillary buds higher up on the stubble or from buds on the crown, but stems produced from axillary buds are smaller and produce lower yield than stems growing from the crown buds. So cutting at a high stubble height will not result in increased regrowth and may even result in lower tonnage of the regrowth. Besides, if nonstructural carbohydrate reserves are adequate in the plant, most of the regrowth will occur from the crown even if a higher stubble is left on the plant. So you might as well harvest alfalfa at normal height and gain all the yield that is there to be had.

The bottom line is that drought induced moisture stress can cause plants to move through maturity stages quicker, and plants bloom sooner on fewer and shorter stems.  While quality may be improved, quantity is reduced.  Since quality is not declining as rapidly with advancing maturity as is the case under normal growing conditions, it may be a good idea to let the plants approach 100% bloom before harvest.  This will allow the plant to build nonstructural carbohydrate reserves.  In some cases there may not be enough quantity to make a machine harvest cost effective. 

One option that might be considered if livestock are available is to salvage a low tonnage yield by grazing the alfalfa.  Take precautions to prevent livestock bloat if alfalfa is grazed.  Those precautions include, do not turn livestock into alfalfa hungry, do not graze alfalfa when the dew is on it, make sure stocking density is high enough to prevent animals from selectively grazing only the tops of plants, and, consider the use of a bloat preventative.


Brush up on your Sweet Corn Pest Management

Brush up on your Sweet Corn Pest Management

Information supplied by Jim Jasinski, OSU IPM - Veg Team.

In 2008, the Great Lakes Vegetable Working Group produced the “Sweet Corn Pest Identification and Management Pocket Guide” to help growers better manage this crop.  The pocket guide is a quick, colorful, and handy reference for sweet corn growers, Extension educators, crop consultants, and industry field representatives who work in the North Central Region. 

The information presented in this guide covers almost every aspect of pest management a fresh market or processing sweet corn grower is likely to encounter.  The 103 page spiral bound guide is printed on weatherproof synthetic paper with full color pictures of weeds, herbicide injury, diseases, pest and beneficial insects, and vertebrates, including their damage.   There is also thorough information about general horticulture, nutrient deficiencies, and fertility recommendations surrounding production of this crop.

The pocket guide can be ordered directly from Purdue University for $10 a copy at

The PDF version of the pocket guide can also be downloaded for free at

OSU Weed Science Field Day – July 11


The OSU Weed Science field day will be held on Wednesday July 11, at the OARDC Western Agricultural Research Station.  The field day will start at 9 am and include a wagon tour during which OSU weed scientists will discuss current weed control issues, herbicide evaluation plots, new herbicide demonstration plots, and a herbicide mode of action plot.  The cost of the tour will be $20, which includes a tour book and lunch.  Those planning to stay for lunch should RSVP to Bruce Ackley  for an accurate lunch count.  The research farm is at 7721 S. Charleston Pike, South Charleston, OH 45368, about 5 miles south of I-70 on SR 41.


Spray Tank Water Quality

Water often comprises ninety-five percent (or more) of the spray solution. What affect might it have on product performance? Research clearly shows that the quality of water used for spraying can affect how pesticides perform.  There are two main water characteristics that can negatively impact the effectiveness of a pesticide application; water hardness and pH.  Pesticides includes: insecticide, herbicides, fungicides, etc.  If the pest is properly identified, the correct product is selected, equipment calibrated, but yet the water quality in the spray tank is poor, the application can be less effective.

Ultimately, the pesticide label is the first place to start to find warnings about spray tank water quality.  For example, the 5 Lb. Dimethoate systemic insecticide (Helena Chemical Co.) label warns: “DO NOT ADD DIMETHOATE TO WATER WITH PH VALUES BELOW 4.0 OR ABOVE 7.0.”  Another example, “The additional of dry ammonium sulfate (AMS)…may increase the performance of this product particularly under hard water conditions.  When using AMS, apply this product at rates directed…lower rates will result in reduced performance.”

Numerous water-testing kits are commercially available for both spontaneous and scheduled testing. The kits are readily available, reasonably priced, easy to use and interpret, and reliable. The majority of the test kits use color-changing, sensitive paper to document water hardness, pH, and iron levels.  The pesticide label may be very specific as to the water conditioner and application rate to be used.

In an era of resistant pests to some pesticides, the quality of the spray water needs to be managed to maximize the effectiveness of the product.  It is unknown how often poor pesticide performance is blamed on poor water quality. By testing water sources used for pesticide application for hardness and pH, water quality can be eliminated or considered as a reason for poor pesticide performance.

The Impact of Water Quality on Pesticide Performance – Purdue Extension



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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.