Dark Respiration in Corn; Corn Silage Harvest Timing; Check Your Soybean White Mold Risk

DARK RESPIRATION IN CORN

One of the topics that has come up in the last few years has been higher nighttime temperatures during the grain fill time. The old adage that warm nights, makes the corn grow or mature faster may be more relevant in the vegetative growth stage (VE-V18). However, once corn hits the reproductive growth stage Tassel/Silking (R1) to Dent (R5), you want the corn plant to cool down at night. When nighttime temperatures do not fall below 72°F the corn plant does not slow down and will keep on metabolizing sugars at a high rate. (I believe this temperature to be closer to 68°F). This rate of high nighttime metabolism, which is termed “Dark Respiration,” causes kernels to fill faster, reduces the grain fill time and makes the plant mature quicker. In my experience it can also reduce test weight.

Yield losses of 2.0 to 3.6 bushel per acre have been documented for every increase of 1°F over 72°F during nighttime hours. If a corn plant cannot produce enough energy from their leaves to fill these kernels properly, they may not fill all kernels on the ear, and may start pulling starches from the stalk, or cannibalizing the stalk, to fill the remaining kernels on the ear.

It has been my experience that corn plants that have adequate nutrients are better suited to handle the stress of Dark Respiration. These healthier plants tend to have better test weight and standability/harvestability.

CORN SILAGE HARVEST TIMING

Pollination marks a significant and critical point in time for corn plants. VT/tasseling signals the end of vegetative growth meaning fiber digestibility of the stalk has more or less been set. R1/silking immediately follows to define kernel number and potential kernel size to create starch and energy content. Successful pollination will be determined throughout the week-long pollen drop given adequate moisture falls with limited extreme weather or pest events. With this year’s cool and wet spring delaying planting until mid-May or even later, corn plants have just begun this important development period and now is the time to start planning for corn silage harvest.

To better predict the timing of corn silage harvest, know the tassel date and count 45 days into the future. Based on these key kernel growth stages, half milk line is reached at approximately the same time and often correlated to the ideal whole plant moisture of 66%. You will need to adjust harvest date based on actual stalk moisture and not just kernel maturity or number of days, but these milestones will help narrow down the range. As soon as kernels hit half milk line, whole plant moisture quickly drops off so being proactive will ensure the end of the crop is still harvested within the optimal range of 68%-64%.

You can also use tools like the Corn Growing Degree Day (GDD) Decision Support Tool, which puts current conditions into a 30-year historical perspective and offers trend projections through the end of the calendar year. Select your county, enter plant date and relative maturity for each hybrid, and the graph tracks important milestones based on your inputs.

CHECK YOUR SOYBEAN WHITE MOLD RISK

Recent rains and increased levels of humidity have created favorable conditions for white mold to begin developing. Conditions that usually create a white mold year are temperatures below 85°F and precipitation or high humidity around the time of flowering. The white mold fungus, Sclerotinia sclerotiorum, primarily infects the soybeans through senescing flowers around the R1-R3 (first flower – beginning pod) stage. The latest fungicide timing that has been shown to still have effect on white mold is R3 (beginning pod). Symptoms don’t usually appear until the R4-R6 (full pod – full seed) growth stages however, once white mold symptoms are apparent, fungicides will not be effective.

Since most of the soybeans across the area are quickly approaching the R3 (beginning pod) growth stage, now is the time to re-evaluate your risk for white mold and consider a fungicide. The most common way to assess your risk of developing white mold is to use a modeling tool like Sporecaster. Sporecaster is a free phone application that combines field information with research-based models to predict the best time for white mold treatment. If there is a risk factor above 40% during flowering, then a fungicide application should be considered. If you decide to apply a fungicide there are several options that are considered “good” and some examples are Aproach, Endura and Propulse. Other options can be found on the Fungicide Efficacy Chart from Crop Protection Network.

If you have any additional questions, please contact your Dairyland Seed Regional Agronomist.

Brian Weller Western Region 507.456.3034	Dan Ritter Central Region 219.863.0583	Branden Furseth Northern Region 608.513.4265	Mark Gibson Eastern Region 260.330.8968	Amanda Goffnett Eastern Region 989.400.3793

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