Rain, cold weather frustrating corn progress

Late March and early April weather seems to have a Dr. Jekyll/Mr. Hyde complex. The last couple of days has gotten much colder. Just how long this back and forth warm/cold weather occurs remains to be seen.  When it comes to our corn crop, should I be concerned?  First, let me share where these temperatures “stack up” against the last ten to eleven years and address the potential impact the rest of the season.  Just notice the chart of growing degree day accumulation (GDD) from a hypothetical emergence of Mar. 10th every year from 2011 to 2022.  The embedded table on the top left of years and yield are stacked according to the warmest year to the coolest.  Notice that the yield of each year varies considerably with no discernible connection to the order of GDD accumulation. Indeed, the average yield of years with a warmer early growth period vs the average yield of the years with cooler GDDs is ~ 3 bushels per acre.  I am using this data to show that while corn is a determinate plant, the yield is complex and is affected by more than just a small window of time and management period.  In other words, we have a long way to go and therefore, need to pay attention to the crop age and external stresses.

Overall, some corn growers are still trying to get their planned corn crop in the ground, particularly in the southern half of the state while cold, rainy conditions continue to interrupt that process.  Currently, we have corn from just emerging to the V5+ stage. Fortunately, we still have time in the southern half to get the crop established and definitely in the Upper Coastal Plains and Piedmont.  Growers in the northern portions of the state are still in good shape except land preparations have been slowed by the wet conditions.

Temperatures in south-Georgia to mid-Georgia over the next few days will progressively get warmer from the lows in the mid-30s to 60 and the highs from mid-70s to the mid-80’s.  This means that the crop will move much faster as GDD’s rise rapidly.  You may very well see some hybrid differences in recovery from the cooler temperatures due to the differences in stress tolerances. Returning to normal growth can vary some between hybrids. Differences in soils, crop residue and age will also play a factor in how your crop responds. It is most important to remain diligent in managing the crop to match its growth and development and not get behind as the plant begins to change from vegetative production to a reproductive phase.

Second, I will point you to Dr. Eric Prostko’s traditional statement on weed control in early corn vs cold temperatures. Generally, a summary goes like this: “Regarding the potential spraying of corn over the next few days for those have corn from emerging to V-5.  I strongly encourage you to proceed with caution due to the potential injury from herbicide applications during cold weather.  I’ve seen damage over the years and it can be quite frustrating.”  He reminds us that “ the good news is that field corn generally recovers from this injury and final yields are NOT reduced by recommended herbicides sprayed at a 1X rate. “. I will say this, there is always a first time for everything so please heed his warning.  I will also point you to his blog post.  His articles are very good and timely, https://ugaweedscience.blogspot.com/ .

Another input which is critical at the V-3 to V6 stage is nitrogen management. Proper timing of nitrogen is critical to achieving your yield goal in corn.  Generally speaking, the V4-V6 stage are the critical growth stages to having enough nitrogen on corn to ensure that it isn’t a limiting factor in the early ear development phase. The amount of nitrogen topdressed during this time depends on your management plans and what the environment has been since you planted (wet and with some colder conditions).  If you have less than 50 to 75 lbs N per acre available going into the transition phase (between vegetative and reproductive), I suggest starting your topdressing by V4 and no later than V5. Having a greater amount of N available earlier allows you a little more time to apply your topdressing but not much.   It is important to be finished by V6-V7 if you cannot inject nitrogen through your pivot and have to finish all of your N applications by ground equipment.

If you have irrigation, injecting N through the pivot is the most efficient and effective method of applying nitrogen in corn.  Dribbling nitrogen (both liquid or dry) by the row is the next preferred method as it keeps the majority of N closet to the root system early in the growth phase and ear development phase.  Broadcasting N is an efficient application but may not be the most effective as some N will be captured in the whorls of leaves causing some burning of tissue.  It will require rainfall or irrigation to get that which does fall into to whorls dissolved in solution and ultimately in soil solution by washing off the plant and onto the soil.  In addition, nitrogen in the middle of the row is far enough away that it takes time for roots to reach the area where the nitrogen is available and can negatively impact the yield potential if you don’t have enough nitrogen closer to the row.

The general nitrogen recommendation ranges from 1.0 to 1.2 lbs of nitrogen for every bushel in your yield goal depending on your soil type.  For example, if you believe your farm and management style has the capacity to produce 250 bushels per acre then it would take 300+ lbs of N per acre.  Yes, corn is and can be more efficient and produce a bushel for every 1.0 pound of nitrogen per acre however in sandier, coarse soils with low CEC, it is better to error on the high side.  If you have the capability to apply N though your pivot, divide your total N supply into increments and apply every 10 to 14 days, finishing up at tassel.  Given current N prices, it isn’t a bad strategy to start with a 1.0 lb per bushel yield goal plan, and add an additional 30 to 40 units at the R1 stage if you see the crop is showing signs of N deficiency.

In a year with good pricing but very high input cost, the challenge is to be most effective with every input and make every dollar count.  Getting behind in corn does cost yield and reduces your returns on your investment.  Think through your choices carefully.  Take extra time to know exactly what stage of growth the crop is in as you plan your inputs so as not to get behind. Scout your fields routinely and look for diseases, insects and other stresses. IF POSSIBLE, eliminate the stress immediately. Corn is a very responsive crop and the earlier you reduce stress the more the crop pays back in yield.

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