Wednesday, May 18, 2016

How long can we continue to plant corn in 2016?

With average growing conditions corn planted after June 1 to June 5 in northern and central Wisconsin and after June 10 to June 15 in southern Wisconsin, will probably not mature with reasonable grain yield and moisture content, even with very early hybrids. However, corn silage from shorter-season hybrids may still have acceptable quality when corn is planted until June 20. Corn planted after June 20 will likely contain little or no grain, and only stover (stems and leaves) will be produced. Table 1 lists alternate hybrid Relative Maturities for delayed planting dates for the standard Relative Maturity belts shown in Figure 1.

Figure 1. Relative maturity zones (in days and Growing Degree Units - GDUs) for full-season corn hybrids planted before May15. (click to enlarge)

Table 1. Relative maturity of adapted corn hybrids for different planting dates and relative maturity zones. Derived from UWEX A3353 - Corn Replant/Late-Plant Decisions in Wisconsin. (click to enlarge)

Pest Control

It is usually easier to control weeds in late corn plantings than in early plantings. Late tillage kills many germinated weeds and crop seedlings are more competitive due to warmer temperatures. For replant situations, weed control must take into account any previous herbicide applications. If herbicides were applied pre-emergence or pre-plant incorporated, their effectiveness may be reduced by the time corn is replanted, especially if the field is tilled before replanting.

Insects normally are a greater threat to late plantings than weeds. Later plantings may have more feeding from second-generation European corn borers, and silk feeding by corn rootworm beetles may also be more severe. Soil rootworm insecticide will need to be applied if the field was tilled since the initial planting application.

Effects of Early Freeze on Yield Potential

Earlier than normal autumn frosts can devastate late-planted corn. Yield is decreased if late-planted corn does not reach physiological maturity before plants are damaged by a freeze. Grain from corn plants killed by a freeze before maturity may be slow to dry down, and it tends to be brittle after artificial drying -- making it more likely to break during handling. Test weight also will be lower when corn is prematurely killed.If late-planted corn does mature ahead of frost, grain will be wetter and probably have to dry down in weather less favorable for drying. The following lists grain characteristics and appropriate management considerations for corn killed at various growth stages:

Corn Killed in Dough Stage
 Kernels contain about 70% moisture. About one-half of mature kernel dry weight accumulated. Grain will unlikely achieve maximum yield potential unless stalk, ear and some lower leaves survive. Corn can be used for good quality silage, but entire plant must be allowed to dry to about 65% moisture.

Corn Killed in Dent Stage
 In early dent, kernels contain about 55% moisture; are 3 to 3.5 weeks from maturity; and about half of mature dry weight has accumulated. In late dent, kernel moisture is decreasing and yield is within 10 percent of final mature dry weight when kernels are past half milkline. Corn will make good silage when harvested at a whole plant moisture content of 65%. Can be harvested for grain after long field-drying period. Grain yields will be reduced and test weights low. If plant is only partially killed or the crop is close to physiological maturity before the freeze (kernel milk line half-way or closer to tip), yield loss will be only 5 to 20 percent, and test weight will be lower.
Corn Killed When Physiologically Mature (Black Layer)

Kernel moisture is 28 to 35% depending on hybrid. Killing freeze will not affect grain yield or quality. Dry-down rate of grain depends on hybrid and environment.

Crop Choice 

If planting is delayed past the time acceptable corn production can be expected, consider planting an alternative crop. Compare the relative yield potential and current price of an alternative crop for a given date with that of late-planted corn.

For example, corn yield potential of a late planting declines at a faster rate than the yield potential loss of soybeans. After June 1, it may be advantageous to plant soybeans, instead of corn, if this fits your rotation. Sunflowers and buckwheat are other grain crops that can be planted very late. Forage sorghum, sorghum-sudan crosses or sudangrass can help boost forage supplies and be planted into July. You must consider prior herbicide and fertilizer applications, desired rotation, livestock feed requirements, and the possibility of erosion on slopes when you are choosing a crop to plant late. For more information on herbicide rotational restrictions, see UW Extension publication A3646 -- Field crops pest management in Wisconsin.

Monday, May 16, 2016

Frost on Corn: The Key is Patience

This past weekend significant areas of northern Wisconsin were affected by frost with temperatures below 28 F. Most corn has either not emerged or is just starting to emerge. The key management practice here will be patience. It will take some time to determine if corn was damaged by this frost.

Corn plants will not be killed by frost unless temperatures get cold enough to kill the growing point that is 3/4 of an inch below the soil surface. So corn that has not emerged typically is well insulated from frost damage. So corn that has not emerged typically is well insulated from frost damage.
Frost should not be a problem with corn until the growing point moves above-ground around V5 to V6. Farmers and agronomists usually do not worry about frost at these early stages of development. Early frost can have an impact on grain yield, but the trade-off between planting date impact on yield is greater than for frost damage impact on yield. Delayed planting further impacts profitability due to greater moisture and consequential drying costs.

Symptoms of frost damage will start to show up about 1 to 2 days after a frost. Symptoms are water soaked leaves that eventually turn brown. After 3 to 4 days watch for new green leaves emerging n the whorl. If new leaves are not emerging check the growing point for discoloration. Any deviation from a white, cream or light yellow color indicates that the growing point is killed.

To measure the impact of early defoliation on corn grain yield corn plants were clipped with a scissors. Clipping treatments were applied at V2, V4 and V6. Plants in the control treatment were not clipped. In another treatment, all plants in the plot were clipped. In another set of treatments, half of the plants were clipped in 2-, 4-, and 8-plant patterns. For example in the 2-plant pattern, the first 2 plants in the row were not clipped, the next 2 plants were clipped at ground level, the next 2 plants were not clipped, and so on.
Figure 1. Impact of clipping corn leaves at V2. Experiments were conducted in 2001, 2002, 2003, 2004, and 2005 at Arlington, WI. Treatments consisted of clipping at ground level (or not clipping) consecutive plants in 2-, 4-, 8-, and all-plant patterns.

Although these treatments do not fully simulate the frost damage, they do provide some guidance on what a frost might do that completely defoliates the plant without killing it. Figure 1 describes the impact of complete defoliation on corn grain yield at the V2 stage of development. When all plants were clipped, grain yield decreased 17 bu/A from 210 to 193 bu/A (8%). When half of the plants were clipped in various patterns, grain yield was not affected; the trend was a decrease of 8 to 9 bu/A (4%).

These data indicate that frost early in development has relatively little impact on corn grain yield. If all of the leaves are removed from every plant in the field at the V2 stage of development and plants are not killed, then the expectation is that grain yield would decrease up to 8%. If the recent frosts were hard enough to kill plants then use the publication UWEX 3353 for guidance on whether or not to keep a stand and what to look for when assessing plant health.

Further Reading
Frost effects on corn
Corn replant/late-plant decisions in Wisconsin UWEX 3353

Wednesday, May 11, 2016

To replant, or not to replant, that is the question.

Farmers are faced with replanting decisions every year. Cold temperatures, wet or crusted soils, and/or pesticide or fertilizer injury may reduce seed germination and seedling emergence. After emergence, stands may be further reduced from insects, diseases, wind, frost, hail, and/or flooding. Stands too dense or non-uniform because of planter malfunctions or variable seeding depth may warrant replanting.

The major decision facing a farmer is whether it is more profitable to keep the original stand using a full-season hybrid or replant. Replanting may result in an optimum stand, but it would be planted at a later than desired date using a shorter season hybrid.

To minimize losses, information must be collected and evaluated quickly. You'll first need to estimate three factors: stand population, plant health, and evenness of spacing. Then compare the yield potential of the existing stand to the yield potential of a late-planted stand. When deciding whether to replant, you'll also need to consider replanting costs, seed availability, rotation restrictions from previous herbicide applications, and possible alternative crops. Base your replant decision on proven agronomic facts rather than emotion.

Steps in the process:
  1. Determine plant population
  2. Evaluate plant health
  3. Assess the unevenness of stands
  4. Compare the yield of a reduced stand to that of a replanted stand
  5. Calculate replanting costs
  6. Factor in risks of replanting

Further Reading
Corn Replanting
Corn Replanting or Late-Planting Decisions UWEX Bulletin A3353
Uneven emergence in corn NCR344