y contention earlier in the week (Nielsen, 2005) that little crop injury resulted from the low temperatures on the morning of 24 April has been tempered by what appears to be minor injury to exposed corn leaves during the clear-sky early morning hours on 25 April. Even though air temperatures dropped no lower than the mid-30's Monday morning, the sky was clear and the winds calm for at least 3 to 5 hours, setting the scene for minor frost and radiational leaf cooling. The latter event is the commonly attributed cause of the so-called "silver leaf" symptom more frequently observed on older corn (Nielsen, 2004).
The leaf damage that occurred Monday morning to emerged corn was not life threatening to the plants by itself and I am confident that most affected fields could recover satisfactorily with good growing conditions. However, the continuing cool (and often cloudy) weather this week has slowed overall crop development (including leaf expansion from whorls) and has changed previously green plants to a putrid yellow-green color. Coupled with minor injury to exposed leaves earlier in the week, the upshot is that fields that were appealing to the eye nearly a week ago can most politely be described now as “crappy”.
Some growers are justifiably concerned about the prognosis for these “crappy” looking fields that also sustained low levels of leaf injury to minor frost or radiational cooling. As is often the case with crops, the prognosis depends on the weather. Most fields would snap out of their doldrums upon a quick return to warm, sunny conditions. Continuation of cool, cloudy weather will further delay crop development as well as recovery from leaf injury.
Slow crop development following emergence also translates to slow establishment of the permanent nodal root system from the crown of the plants, thus lengthening the plants’ dependence on the energy reserves of the kernels and increasing the consequences of exposure to other belowground stresses. Development of seedling diseases (Malvick, 2005) or insects feeding on the seed and mesocotyl (Steffey, 2005) prior to the successful development of nodal roots can be devastating to plant survival.
Don’t rush to replant these “crappy” looking fields. The current cool weather will delay your ability to confidently assess recovery from leaf damage. Instead of waiting the usual 3 – 5 days to assess fields, it may take a week or longer. Furthermore, growers with corn acres yet to plant the first time around should concentrate on completing that task before replanting suspect fields. Before making a replant decision, consult my worksheet-formatted replant decision guide (Nielsen, 2003).
Malvick, Dean. 2005. Corn Seed and Seedling Diseases. Illinois Pest & Crop Bulletin. Univ. of Illinois. Available online at http://www.ipm.uiuc.edu/bulletin/article.php?issueNumber=6&issueYear=2005&articleNumber=3 [URL verified 4/29/05].
Nafziger, Emerson. 2005. Return to “Normal”. Illinois Pest & Crop Bulletin. Univ. of Illinois. Available online at http://www.ipm.uiuc.edu/bulletin/article.php?issueNumber=6&issueYear=2005&articleNumber=8 [URL verified 4/29/05].
Nielsen, R.L. (Bob). 2003. Estimating Yield and Dollar Returns from Corn Replanting. Purdue Univ. Cooperative Ext. Service Publication AY-264-W. Available online at http://www.agry.purdue.edu/ext/pubs/AY-264-W.pdf [URL verified 4/28/05].
Nielsen, R.L. (Bob). 2004. “Silver Leaf” Symptom in Young Corn. Corny News Network, Purdue Univ. Available online at http://www.kingcorn.org/news/articles.04/Silverleaf-0508.html [URL verified 4/28/05].
Nielsen, R.L. (Bob). 2005. Did We Dodge a Frozen Corn Bullet? Corny News Network, Purdue Univ. Available online at http://www.kingcorn.org/news/articles.05/FrozenCornBullet-0424.html [URL verified 4/28/05].
Saab, Imad and Steve Butzen. 2005. Diagnosing Chilling and Flooding Injury to Corn Prior to Emergence. Pioneer, a DuPont Company. Available online at http://www.pioneer.com/growingpoint/agronomy/library_corn/crop_injury/flooding_injury.jsp [URL verified 4/28/05, but note that access to this article requires registering (no cost) at Pioneer’s Growing Point™ Web site.]
Steffey, Kevin. 2005. Time for Early-Season Corn Insect Pests. Illinois Pest & Crop Bulletin. Univ. of Illinois. Available online at http://www.ipm.uiuc.edu/bulletin/article.php?issueNumber=6&issueYear=2005&articleNumber=1 [URL verified 4/29/05].
Thomison, Peter and Patrick Lipps. 2005. Impact of Freezing Temperatures and Snow on Corn Survival. Crop Observation Reporting Network, Ohio State Univ. Available online at http://corn.osu.edu/index.php?setissueID=80#D [URL verified 4/29/05].
|Leaf injury from minor frost and/or radiational cooling.||"Silver leaf" symptom descriptive of leaf tissue injury due to radiational cooling.|
|Leaf injury from minor frost and/or radiational cooling.||Damaged plant that would have recovered had I not dug it out of the field. Note the putrid yellow-green tissue color resulting from days of cold, cloudy weather.|
|Frost-damaged plant that also shows early signs of disease to mesocotyl and kernel that would have eventually killed it.||Same plant as one to the left, showing closeup of disease symptoms on mesocotyl and kernel.|
|Same plant as one above, showing closeup of disease symptoms on mesocotyl.||Frost-damaged plant showing damaged whorl tissue that may restrict further leaf expansion.|
|Closer view of damaged whorl tissue that may restrict further leaf expansion.||Another example of plant with minor frost damage that will survive.|
|Closer view of the leaf elongation that occurred during 3+ days following the frost, limited due to continued cool, cloudy weather.||Closer view of healthy growing point region of frost-damaged plant.|
|Frost damage to seedling that was just emerging at time of the frost.|