Cause of uneven stand
It is established that uneven emergence in the field has a negative effect on corn yields. Evaluation of the cause of this problem is not always clear. Was it planter problems - too deep, too shallow, poor spacing? Or perhaps uneven soil preparation? Did planting get followed by prolonged cold wet weather? Soil too wet or too dry? Or was it seed quality? It is not always easy to sort out the cause or causes.
If the unevenness is occurring in consecutive plants, perhaps it is some field condition that caused the problem. Seed quality problems usually only applies to a small percentage of the seed with a lot, the bad ones scattered among many good ones. Furthermore, even the weaker seed range from being dead to potentially recovering enough to emerge a few days behind the good ones. If it is a seed quality problem, it seems reasonable to expect that these delayed plants will be mostly randomly distributed in the field. Expression of a seed quality problem is likely to be greater when there is a field stress, as well, such as cold, wet weather soon after planting or heavy soils. Dead or partially germinated seed showing only the root are most likely indications of seed quality problems.
Seedlings in the field are surrounded by microbes attracted to exudates from the new roots and the carbohydrates stored in the seed. Seed treatments do ward off some of the fungi but also the living, healthy cells actively produce defense compounds to limit potential invasion by most pathogens. However, most dead or even weakened seedlings will have some fungi such as Fusarium species, complicating the analysis of cause of the poor stand. Did the fungus cause the seedling to be weak or did the weak seedling allow the fungus to invade? More aggressive pathogen such as Pythium species, favored by cold wet soils, are more likely to attack healthy seedlings if not inhibited by a seed treatment, but Fusarium species are generally more likely secondary to poor seedling development.
It is remarkable that seed producers can provide high quality seed from genetics basically developed for carbohydrate storage to be planted in environments loaded with organisms that feed on such carbohydrates. And that growers can apply techniques to provide favorable environments for each of these seed to produce hundreds more units of the carbohydrates.
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About Corn Journal
The purpose of this blog is to share perspectives of the biology of corn, its seed and diseases in a mix of technical and not so technical terms with all who are interested in this major crop. With more technical references to any of the topics easily available on the web with a search of key words, the blog will rarely cite references but will attempt to be accurate. Comments are welcome but will be screened before publishing. Comments and questions directed to the author by emails are encouraged.