Originally published 2005, updated May 2008
Tips for Staging Corn with Severe Leaf Damage
R.L. (Bob) Nielsen
Agronomy Dept., Purdue Univ.
West Lafayette, IN 47907-2054
Email address: rnielsen
t is not uncommon for young corn plants to suffer severe leaf damage from frost, freezing temperatures, or hail. Such weather-related events usually leads to debate in the local coffee shops as to how to identify the age of a corn plant that has recovered from rather severe leaf damage.
Some may wonder why this topic is worthy of vigorous debate. The reason lies with the fact that a number of post-emergence corn herbicides can only be applied to corn up to a label-specified leaf stage (Loux et al., 2008). Growers and applicators obviously need to be able to accurately stage corn plants, even if damaged, to determine whether application of a such herbicides will still be within label restrictions.
Unfortunately, dead leaf tissue does not resurrect itself and will eventually slough off as the plants continue to grow. The hotly debated question is whether the leaf stage of a recovered plant begins anew with the healthy leaves or whether the dead leaves (which may no longer be visible) should be counted. In other words, should a 5-leaf plant that has lost four leaves to frost injury now be considered a 1-leaf plant?
The simple answer is: A 5-leaf plant is a 5-leaf plant no matter how many lower leaves are damaged, dead, or otherwise missing. As long as the dead lower leaves remain attached to the plants, leaf staging is reasonably simple. Count the dead leaves and any additional ones with visible leaf collars (Nielsen, 2008a).
The challenge occurs when the dead lower leaves slough off and decompose or blow away. Now how do you count leaves if you are not sure whether the lowermost remaining leaf is #2 or #3? This problem is easily solved when staging V7 or older corn because one can then split stalks to identify the 5th node and its respective attached leaf (Nielsen, 2008a). Because stalk development is essential nil for corn plants V5 or younger, this strategy for staging corn does not work for younger plants.
Here are two alternatives for staging damaged young corn:
1) Walk damaged and recovering fields soon while dead lower leaves of damaged plants are still attached. Mark ten consecutive plants with plot flags or garden stakes. Identify & record the leaf number of the lowermost healthy leaf (one likely to remain attached for some time) of each plant. Mark each such leaf by simply ripping off a third or half of the leaf. To simplify future leaf staging, mark the same leaf number on each of the 10 consecutive plants. When you come back in a week or later to stage the plants again, find the marked leaf on each plant and continue counting the number of leaves with visible leaf collars.
2) Predict leaf stage development based on thermal time (growing degree days or GDDs) from planting or emergence (Nielsen, 2008c). The relationship between corn development and temperature is reasonably strong. Emergence requires 100 to 120 GDDs from planting and leaf collar emergence (up to about leaf #10) requires about 82 GDDs per leaf. Current year GDD data for various areas of Indiana are available at the Indiana State Climate Office data archive located online at http://www.agry.purdue.edu/climate/data_archive_v3.asp (URL accessed 5/7/08). At this Web site, you can search for temperature data from the automated Purdue weather stations located at a number of outlying Purdue Ag. Centers, cooperative weather stations maintained by the National Weather Service, and airport weather stations also maintained by the National Weather Service. Also, the weekly Purdue Pest & Crop Newsletter lists accumulated GDDs for selected sites across the state based on various start dates.
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Loux, Mark, Anthony F. Dobbels, Jeff Stachler, Bill Johnson, Glenn Nice, & Tom Bauman. 2008. 2008 Weed Control Guide for Ohio and Indiana (WS-16). Table 7: Rainfast Intervals, Spray Additives, and Maximum Crop Size for Postemergence Corn Herbicides. Purdue Univ. & Ohio State Univ. Coop. Ext. Services. [On-Line]. Available at http://www.btny.purdue.edu/Pubs/WS/WS-16/CornRainfast.pdf (URL accessed 5/8/08).
Nielsen, R.L. (Bob). 2008a. Determining Corn Leaf Stages. Corny News Network, Purdue Univ. [On-Line]. Available at http://www.kingcorn.org/news/timeless/VStageMethods.html (URL accessed 5/8/08).
Nielsen, R.L. (Bob). 2008b. Heat Unit Concepts Related to Corn Development. Corny News Network, Purdue Univ. [On-Line]. Available at http://www.kingcorn.org/news/timeless/HeatUnits.html. (URL accessed 5/8/08).
Nielsen, R.L. (Bob). 2008c. Use Thermal Time to Predict Leaf Stage Development in Corn. Corny News Network, Purdue Univ. [On-Line]. Available at http://www.kingcorn.org/news/timeless/VStagePrediction.html. (URL accessed 5/8/08).
Purdue Pest & Crop Newsletter. 2008. Purdue Univ. Pest Mgmt. Program. [On-Line]. Available at http://extension.entm.purdue.edu/newsletters/index.html. (URL accessed 5/7/08).