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Corn Ear Tip Back
It appears corn ears have tipped back more than normal in a large number of fields and seed brands across a wide geography in the corn belt this year. What can we blame this on? Well, the list is long for possible causes of ear tip back from year to year. Drought, excessive post pollination heat, shortage of nutrients, hail, insects, disease, high planting populations, and genetics are just some of the many things that get blamed for this. Sometimes it’s a combination of more than one and sometimes it’s hard to pinpoint anything at all for why it happens. I would agree that in some instances loss of nitrogen can be to blame in those fields that were water logged early and often this year. But what about those fields showing excessive tip back that we know are not short of fertilizer, did not get flooded or hailed, have no real disease or insect pressure, experienced no drought, and are not planted at high populations? What about these that look absolutely beautiful and healthy but when you walk in and pull back ears, you see 3 inches of tip back? The answer isn’t always clear cut and may be fairly complex. One thing is certain. A stress or stresses at the time period following pollination triggered the corn plant to abort some of the kernels at the tip of the ear. Although there has been very little drought stress to our corn crop this year we have to remember drought stress and heat stress are not the same. A corn plant would rather go through its ear fill period at moderate temps than at temps much above 86 degrees. We did have a prolonged period of excessive temperatures during the post pollination period this year. Those nights where temps failed to dip below 70 degrees can be especially detrimental to grain fill and starch accumulation. This may have played a direct roll in some of this excessive ear tip back we are seeing in some fields this year. I would not try blaming it on any one hybrid either. Yes you will see some hybrids do it much worse than others at locations but I think it’s more about the way that specific hybrid responded to it’s environment at that location than the hybrid itself. The above picture shows two ears that I pulled from fields last week over 100 miles apart. The hybrids are both tipped back significantly and they share absolutely no genetic relation. In summary, the corn plant is a complex plant physiologically and reacts to the many different curve balls mother nature throws its way. As always, keep an open mind when trying to determine why things happen in a corn field. Often times there is no one absolute right or wrong answer.
Most cropping seasons see delayed emergence problems show up in corn and soybeans somewhere in the Cornbelt. I would like to help answer the question of what conditions cause emerging corn to be delayed. Agronomists commonly point to three major conditions for delayed emergence in corn: inadequate moisture, inadequate temperature, & poor seed-to-soil contact. Herbicide overdose, insect feeding, and diseases can also play a role in delayed emergence, but are considered secondary conditions.
Corn seed takes a certain amount of consistent moisture to emerge. Moisture levels can change within a small area or affect an entire field depending on the soil characteristics and the microclimatic conditions of the field, resulting in delayed emergence. In addition, a hard rain can create a crust barrier on the soil surface that will prohibit emergence to varying degrees depending on the characteristics of the crust matrix such as thickness.
Even though corn seed can begin emerging when soils are 50° F or higher, corn likes to emerge when the temperature is consistently above 55° F. where the seed is placed (seed zone). Some of the things that can reduce temperature and lead to delayed emergence are poor soil characteristics, dense surface residue, above normal moisture, and deep placement of the seed.
Corn seed does not sprout well when it is surrounded by air, water, or plant residue. Only soil structure that completely surrounds a seed provides the right environment for germination. Mostly to a lesser extent, herbicide injury, insect pressure and disease pressure can cause delayed seedling emergence. These categories should be suspect after the 3 main categories have been ruled out.
What are the effects on yield?
A corn seedling is considered late emerging if it is more than a week behind a neighboring plant. If the delay becomes severe enough, the late plant will not be competitive. This situation produces a barren plant, which is essentially a weed to the other corn plants. As a general rule, if more than 2 stages of vegetative growth exist between adjacent plants, the younger of the two will be barren. University studies estimate a yield loss of 5 to 20 percent can occur if the emergence of the late seedlings is 10 days or more.
What is Green Snap (sometimes called Brittle Snap)?
This is the condition where rapidly growing stalks are broken by strong, sudden winds, associated storms and similar related weather activity. During rapid growth, the cell walls are extremely fragile and stalk tissue may be at a greater risk of brittleness compared to other growth stages.
What Factors Affect Green Snap?
Many factors affect green snap severity. The timing and velocity of the wind are the most obvious, coupled with the hybrid involved. Heavy winds during cool morning hours will cause more green snap than if the wind occurred during the heat of the day when plants are more flexible. Strong-rooted hybrids with less give at the base will have more green snap than a shallow-rooted variety. Conditions that favor rapid growth will increase the incidence of green snap; some of these conditions include adequate nitrogen, high temperatures, good soil moisture and the use of growth stimulator herbicides such as 2,4-D, dicamba, and clopyralid. Field geography, soil type and crop management practices also influence green snap severity.
When is a Corn Plant Most Susceptible to Green Snap?
During a corn plants vegetative growth phase, rapidly elongating internodes are often brittle and susceptible to breakage. The two most common periods for green snap are the V5 to V8 stage, or when the growing point is just emerging from the soil line, and the V12 to R1 stage, which is about the two weeks prior to tasselling, until just after silking.
The V5 to V8 Stage?
When the growing point is just emerging above the soil line, the corn plant is entering a period of rapid change. The nodal root system is beginning to expand rapidly so the plants ability to take up water and nutrients is increased dramatically which enhances faster leaf and stalk growth in the plant. Fast growth means the cell walls become thinner or are more fragile. Also at this stage of growth, the many nodes and internodes are arranged together in a small area. This concentration may make the plant less flexible and more susceptible to breakage. Green snap at this stage usually occurs below the growing point so snapped plants usually do not recover.
V12 to Tasselling?
At this time the corn plant is going through its most rapid stage of growth. This is the 21 to 28 day time period when the corn plant increases in size from about 3 feet to its mature
Most universities base Nitrogen (N) fertility recommendations on a target yield. The assumption is that the target yield is accurate and that the crop is removing what was supplied. Excess N can leave corn vulnerable to rapid growth, poor stalk quality and increased lodging, and delayed maturity. Whatever formula you use to determine N needs, your N levels after removing the crop should be low and levels from year to year should not be increasing.
Ammonium works best in the fall for 2 main reasons. First, it is usually the cheapest source of N available, and second, if applied when soils are cool (soil temp at 2-4" depth is <50°F), the N stays in ammonium from instead of converting to nitrate which is susceptible to leaching. If in doubt about keeping the ammonium from nitrifying, use N-Serve* to stabilize the ammonium in the soil over the winter. Some areas have no choice about using a nitrogen stabilizer like NServe because of lighter soils. Furthermore, some areas are too sandy to do any fall fertilizing and must have broadcast in-season N applied to be at the lowest leaching risk.
--Advantages to Fall Application
Fall application redirects resources from spring to fall to when you have time available. Fall application is good insurance against getting fertilizer in late due to bad weather in the spring. In some years, it also protect against rising fertilizer prices. Soil sampling is usually much easier in the spring when the weather pattern is warm and dry.
--Disadvantages to Fall Application
The time period from when fertilizer is put down to when the next crop needs it leaves the fertilizer vulnerable to the environment. Nitrification of ammonium to nitrate is possible, which then leaves the N in a vulnerable from which can be leached away from where the crop can use it.
When temperature and moisture conditions favor normal plant development, tassels emerge and begin to shed pollen one to three days before silking. Pollen shedding generally occurs early to mid-morning, after the dew has dried off the tassel. Since pollen is light, it may be carried by the wind one-half to one mile, but most will fall within 50 feet of the tassel. Pollen shed occurs for about one week; peak production is usually on the third day. It is estimated that one tassel can produce between 2 and 5 million pollen grains. Pollen shed is not a continuous process. It stops when the tassel is too wet or too dry, and begins again when temperature and moisture conditions are favorable. On a typical midsummer day, the peak pollen shed occurs between 9 and 11 a.m. Under favorable conditions, released pollen will remain alive for 24 hours. For pollination to occur, silks must be receptive during the time that pollen is shed. The first silks to emerge are those from the base of the ear progressing to the tip. Pollination occurs when a pollen grain lands on a receptive silk. After pollination, the future kernel will start to develop in approximately 30 hours. Adequate moisture is extremely critical for successful pollination. When moisture is short, silks may grow very little, if at all, during the day. Most often, poor pollination results when the silks were not receptive the same time as pollen was available (often described as a poor nick in fields). Very high plant populations will delay silking more than pollen shed, especially under moisture stress. Silks also dry rapidly under hot, dry conditions and may not have enough moisture to support pollen germination and subsequent fertilization of the ovule. Failure of ears to set kernels during pollination can be attributed to:
In most cases during hot weather, poor pollination is a result of tassels shedding pollen before silk emerges.