Corn Growth & Development – R2 Blister

Today managing your corn crop requires knowledge of the different growth stages of the corn plant.  Growth stage identification is critical for scouting and proper timing of fertilizer and pesticide applications.

R2 – Blister

The R2 (blister) stage occurs about 10 – 12 days after silking.  At this stage the kernel is visible and resembles a blister.  The kernel is filled with clear fluid, the embryo is barely visible and it is at about 85% moisture.

Kernels are in a rapid period of grain-fill.  Rapid and steady grain-fill will continue through R6.  If severe stress occurs now or during R3, kernel abortion will occur from the tip of the ear downward.  Kernel abortion will continue until the plant has has enough carbohydrates for the remaining kernels.

Silks outside the husk leaves are drying and changing in color from tan to light brown.  The silks will naturally detach from their kernels following fertilization.

Kernel Set Scuttlebutt

Source: Dr. Bob Nielsen, Purdue

The post-pollination scuttlebutt overheard in coffee shops throughout Indiana during late summer often revolves around the potential for severe stress that might reduce kernel set or kernel size in neighborhood cornfields. Growers’ interest in this topic obviously lies with the fact that the number of kernels per ear is a rather important component of total grain yield per acre for corn.

Poor kernel set, meaning an unacceptably low kernel number per ear, is not surprising in fields that are obviously severely stressed by drought, but can also occur in fields that otherwise appear to be in good shape. Good or poor kernel set is determined from pollination through the early stages of kernel development; typically 2 to 3 weeks after pollination is complete.

Problems with kernel set stem from ineffective pollination, ineffective fertilization of the ovaries, kernel abortion, or all three. Distinguishing the symptoms is easy. Determining the exact cause of the problem is sometimes difficult.

Potential Yield Loss

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Soybean Vegetative Growth Stages- VC vs V1

By: Laura Lindsay, OSU

Across the state, soybean growth and development is variable, ranging from early vegetative stages to flowering. However, there has been some confusion regarding the identification of the VC and V1 growth stages. This confusion is mostly due to two definitions of V1…that actually mean the same thing. The Fehr and Caviness Method (1977) is based on the number of nodes that have a fully developed leaf, whereas Pederson (2009) focuses more on leaf unrolling so that the leaf edges are no longer touching. The VC definition for both methods is the same, but the differences start to appear between the methods at V1. Fehr and Caviness define V1 as “fully developed leaves at unifoliolate nodes,” which also means that there is “one set of unfolded trifoliolate leaves unrolled sufficiently, so the leaf edges are not touching.” This second definition is common in extension publications (Pedersen, 2009).

Soybean growth stages are described in the OSU Corn, Soybean, Wheat, and Forages Field Guide (available for purchase here: https://extensionpubs.osu.edu/corn-soybean-wheat-and-forages-field-guide-pdf/). A visual guide to soybean staging is available as a pdf from Dr. Shawn Conley at the University of Wisconsin-Madison (https://coolbean.info/library/documents/2017_Soybean_GrowthDev_Guide_FINAL.pdf).

Recommendations for Soybeans Planted in June

Source: Laura Lindsey, The Ohio State University

While progress is way ahead of last year, soybean planting is spilling into June. (According to USDA NASS, 53% of soybean acreage was planted by May 24, 2020. Last year, at the same time, only 11% of soybean acreage was planted.) As planting continues into June, farmers may want to consider adjusting their cultural practices:

Row spacing. Soybean planted in narrow rows (7.5 or 15-inch row width) generally yields higher than soybean planted in wide rows (30-inch). The row spacing for June-planted soybeans should be 7.5 to 15 inches, if possible. Row width should be narrow enough for the soybean canopy to completely cover the interrow space by the time the soybean plants begin to flower. The later in the growing season soybeans are planted, the higher the yield increase due to narrow rows.

Seeding rate. Higher seeding rates are recommended for June planting dates. The final (harvest) population for soybean planted in June should be 130,000 to 150,000 plants/acre. (For May planting dates, a final stand of 100,000 to 120,000 plants/acre is generally adequate.)

Relative maturity. Plant the latest maturity variety that will reach physiological maturity before the first killing frost. This is to allow the plants to grow vegetatively as long as possible to produce nodes where pods can form before vegetative growth is slowed due to flowering and pod formation. The recommended relative maturity ranges are shown in the table below.

 

Cold Weather Impact on Corn and Soybean

Alexander Lindsey, Laura Lindsey – The Ohio State University

In Ohio, between May 9 and 10, temperatures were as low as 26°F with some areas even receiving snow. The effect on corn and soybean depends on both temperature, duration of low temperature, and growth stage of the plant. The soil can provide some temperature buffering capacity, especially if soil is wet. Water is approximately 4x more resistant to temperature changes than air or dry soil, and thus will buffer the soil from experiencing large temperature changes as air temperatures drop. Deeper planted seeds may also be more resistant to large temperature swings.

Imbibitional chilling. Imbibitional chilling may occur in corn and soybean seeds if the soil temperature is below 50°F when the seed imbibes (rapidly takes up water from the soil, usually 24 hours after planting). Imbibitional chilling can cause reductions in stand and seedling vigor. If seeds were planted into soil at least 50°F (and have imbibed), the drop in temperature is not likely a problem if the plants have not yet emerged from the soil.

Corn after germination. The growing point of corn is below the soil surface until the V6 growth stage, and therefore is protected from low temperatures to some extent. However, if the soil temperature falls below 28°F, this can be lethal to corn. Temperatures between 28 to 32°F may result in frost damage, and both the temperature and duration will affect the severity of damage. Between May 9 and May 10, the minimum soil temperature at a 2-inch depth was 38°F at the Northwest Agricultural Research Station in Wood County, 44°F at the Ohio Agricultural Research and Development Center in Wayne County, and 58°F at the Western Agricultural Research Station in Clark County.

Soybean after germination. The growing point of soybean is above the ground when the cotyledons are above the soil surface. If damage occurs above the cotyledons, the plant will likely recover. If damage occurs below the cotyledons, the plant will die. Look for a discolored hypocotyl (the “crook” of the soybean that first emerges from the ground), which indicates that damage occurred below the cotyledons.

Assessing your fields. It is best to assess damage to plants or seeds 48 to 96 hours after the drop in temperatures, as symptoms may take a few days to appear. Additionally, cold temperatures slow GDD accumulation and may further delay crop emergence. For corn, recent work suggests 50% emergence can be expected following accumulation of 130-170 soil GDDs (using soil temperature to calculate GDD rather than air temperatures) from planting, which may take 5-7 days to accumulate under normal weather conditions.

Stalk Quality Concerns

Source: Peter Thomison, Pierce Paul, OSU Extension

2019 may be an especially challenging year for corn stalk quality in Ohio. Stress conditions increase the potential for stalk rot that often leads to stalk lodging (Fig. 1).  This year persistent rains through June caused unprecedented planting delays. Saturated soils resulted in shallow root systems. Corn plantings in wet soils often resulted in surface and in-furrow compaction further restricting root growth. Since July, limited rainfall in much of the state has stressed corn and marginal root systems have predisposed corn to greater water stress.

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Corn Grain Test Weight

Source: R.L. Nielsen, Purdue Univ. (edited)

Among the top 10 most discussed (and cussed) topics at the Chat ‘n Chew Cafe during corn harvest season is the grain test weight being reported from corn fields in the neighborhood. Test weight is measured in the U.S. in terms of pounds of grain per volumetric “Winchester” bushel. In practice, test weight measurements are based on the weight of grain that fills a quart container (37.24 qts to a bushel) that meets the specifications of the USDA-FGIS (GIPSA) for official inspection (Fig. 1). Certain electronic moisture meters, like the Dickey-John GAC, estimate test weight based on a smaller-volume cup. These test weight estimates are reasonably accurate but are not accepted for official grain trading purposes.

The official minimum allowable test weight in the U.S. for No. 1 yellow corn is 56 lbs/bu and for No. 2 yellow corn is 54 lbs/bu (USDA-GIPSA, 1996). Corn grain in the U.S. is marketed on the basis of a 56-lb “bushel” regardless of test weight. Even though grain moisture is not part of the U.S. standards for corn, grain buyers pay on the basis of “dry” bushels (15 to 15.5% grain moisture content) or discount the market price to account for the drying expenses they expect to incur handling wetter corn grain.

Growers worry about low test weight because local grain buyers often discount their market bids for low test weight grain. In addition, growers are naturally disappointed when they deliver a 1000 bushel (volumetric bushels, that is) semi-load of grain that averages 52-lb test weight because they only get paid for 929 56-lb “market” bushels (52,000 lbs ÷ 56 lbs/bu) PLUS they receive a discounted price for the low test weight grain. On the other hand, high test weight grain makes growers feel good when they deliver a 1000 bushel semi-load of grain that averages 60 lb test weight because they will get paid for 1071 56-lb “market” bushels (60,000 lbs ÷ 56 lbs/bu).

These emotions encourage the belief that high test weight grain (lbs of dry matter per volumetric bushel) is associated with high grain yields (lbs. of dry matter per acre) and vice versa. However, there is little evidence in the research literature that grain test weight is strongly related to grain yield.

Hybrid variability exists for grain test weight, but does not automatically correspond to differences in genetic yield potential. Grain test weight for a given hybrid often varies from field to field or year to year, but does not automatically correspond to the overall yield level of an environment.

Similarly, grain from high yielding fields does not necessarily have higher test weight than that from lower yielding fields. In fact, test weight of grain harvested from severely stressed fields is occasionally higher than that of grain from non-stressed fields, as evidenced in Fig. 2 for 27 corn hybrids grown at 3 locations with widely varying yield levels in Kansas in 2011. Another example from Ohio with 22 hybrids grown in common in the drought year of 2012 and the much better yielding year of 2013 also indicated no relationship between yield level and grain test weight (Fig. 3).

Conventional dogma suggests that low test weight corn grain decreases the processing efficiency and quality of processed end-use products like corn starch (U.S. Grains Council, 2018), although the research literature does not consistently support this belief. Similarly, low test corn grain is often thought to be inferior for animal feed quality, although again the research literature does not support this belief (Rusche, 2012Simpson, 2000Wiechenthal Pas et al., 1998). Whether or not low test weight grain is inferior to higher test weight grain may depend on the cause of the low test weight in the first place.

Common Causes of Low Grain Test Weight

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