By John Obermeyer
- Diagnoses of a field problem requires a hunger for knowledge.
- Patience and thorough analysis may pinpoint to specific or multiple interacting factors.
- Experienced gained in challenging fields will be beneficial in the future.
“Eliminate all other factors, and the one which remains must be the truth,” Sherlock Holmes by Sir Arthur Conan Doyle. This is easier said than done when dealing with poorly growing corn in areas of a field. Symptoms often include stunting, discoloration, and leaf rolling. As one begins to investigate, the possibilities seem endless.
Still, into our second week of June, some cornfields appear to be “growing backward,” as one producer described it. Numerous samples sent to the Purdue Plant & Pest Diagnostic Lab and picture emails have revealed an assortment of corn problems, mostly linked to this spring’s challenging weather conditions. Seedling blights are still being implicated in 3-5 leaf stage corn. There are “critters” that take advantage of weak and/or dying plants. When found, they are often accused of being the culprit for a poor or uneven stand. Here is a sampling:
Millipedes are wireworm-like arthropods (like insects, they belong to the Phylum Arthropoda-means “jointed foot”), having two pairs of legs per body segment. They have become more prevalent as no-till production becomes more widespread. They are often found in large numbers, but are rarely a pest. This is because they typically feed as scavengers, feeding on dead or decaying materials often associated with seedling blights. Several pest managers have reported numerous millipedes in and around corn kernels/sprouts that have been in the ground for two or more weeks. These kernels were probably the victims of pathogens of some kind (bacteria/fungi) and opportunistic millipedes were merely acting as the “clean-up crew” and hollowing out kernels that were in early stages of decay.
Millipedes found around a "challenged" corn root.
Juvenile (“baby”) earthworms and potworms are closely related and common animals found in soils. They are small, generally colorless, and often less than 1/4 inch long. These worms feed on damaged and decaying plant remains, not live tissue. Therefore they are closely associated with the decaying plant parts and surrounding soil and sometimes wrongly accused of damaging seedlings – in fact, they usually arrive after the seed is dead. In fact, their mouthparts are incapable of causing damage to live tissue – they don’t have “teeth” and instead are specialized to suck up partially-liquefied material. The point of all this is to reiterate that pest managers should keep an open mind when diagnosing field problems. As one submitter confessed, he was so convinced that it was an insect problem and therefore looked for anything moving when he couldn’t find grubs or wireworms.
Potworms doing cleanup around a rotted seed.
Many other critters, e.g., mites, symphylans, and springtails, have been observed on or around rotting seeds/seedlings. They are small, some fast moving, and certainly unfamiliar to most. They are not causing the poor emergence/growth, but taking advantage of weak and dying plants (including dead weeds and crop debris from previous years) in various stages of decay, as well as the hospitable environment supplied by atypically wet soils.