This week’s hot and humid weather was quite a contrast to the cool weather we had which only got into the low 70s the week before. It seems to get the hottest and most humid when it’s time for bailing hay. There was a lot of that going on throughout Delaware County this past week.

Rainfall varied significantly throughout Delaware County. According to the National Weather Service forecast, the roller coaster ride will continue for the rest of June as they are calling for cooler than normal temperatures with rainfall about average for this coming week. Normal for this time of year is ¾ to 1.25 inches.

Fertilizer Certification Meeting

We will be having a Fertilizer Field Day on July 14 to get the last batch of farmers certified to apply fertilizer. If you apply over 50 acers of fertilizer, not counting the start-up fertilizer that you run through your planter, you need certified. This is mandatory through the Senate Bill 150 in 2014 for all of Ohio.

The last day according to the regulation you can get certified is Sept. 30. Come get certified on July 14 so that you do not have to test for certification. We will be discussing weather and climate trends with OSU Extension’s Climatologist and the relation of nutrient loss with weather. We will also discuss current Phosphorus research being done in the county, the current state of water quality in Ohio, and touch on Nitrogen management.

This 3-hour course will satisfy the ODA regulation to apply your fertilizer as well as teach you some nutrient loss prevention concepts. It will be held July 14 at 9 a.m. to noon at Glenn and Kelly Harsh’s, 4926 David Road, Delaware, Ohio.

Predicting Leaf Development in Corn using Accumulated Heat Units

Some parts of the county experienced hail and quite a lot of rainfall this past week. When estimating yield losses in corn due to hail and other types of plant injury, it’s essential to note the stage of plant growth at the time damage occurred. It’s also important to know corn stage of development in order to apply post-emergence chemicals effectively with minimum crop damage. According to Peter Thomison, OSU Extension State Specialist — Hort and Crop Science, counting leaf collars to determine the vegetative stage is feasible until the lower leaves can no longer be identified. At about the V6 (six leaf collar) stage, increasing stalk and nodal growth combine to tear the smallest lower leaves from the plant. This results in degeneration and eventual loss of lower leaves which makes it difficult to locate the lower leaves (especially the first rounded leaf). When identification of specific leaf collars on plants is not possible, how can the leaf stage of development of a field be estimated? Thomison says:

Given an understanding of corn leaf stage development and heat unit (growing degree day, GDD) calculation, a grower can estimate what leaf stage of development a particular field is at given its planting date and temperatures since planting.

Corn leaf developmental rates may be characterized by two phases. Purdue University research indicates that from VE to V10 (ten leaf collars), leaf emergence occurs approximately every 82 GDDs accumulated (Nielsen, 2014). From V10 to tasseling (VT) leaf collar emergence occurs more quickly at approximately one leaf every 50 GDDs accumulated. Iowa State University findings (Abendroth et al., 2011) relating leaf appearance to GDD accumulation are similar — from VE to V10 a new collared leaf appears every 84 GDDs accumulated and from V11 to VT, each leaf appears at approximately every 56 GDD accumulated.

Example: (from Nielsen, 2014): “A field was planted on April 28, but you do not know exactly when it emerged. Since planting, approximately 785 GDDs have accumulated. If you assume that the crop emerged in about 120 GDDs, then the estimated leaf stage for the crop would be about V8. This estimate is calculated by first subtracting 120 from 785 to account for the estimated thermal time to emergence, then dividing the result (665) by 82 (equal to V8.1).”

Growth-limiting stresses and conditions (soil moisture deficits, nutrient deficiencies, compaction, etc.) affect the accuracy of these predictions. Nevertheless, this method may be useful in timing when plants will reach an approximate stage of growth.