The nearly ideal planting conditions followed by extensive rains statewide have led to some unusual crop emergence problems for corn and soybeans in Ohio.
Peter Thomison reported several instances of somewhat unusual corn emergence issues.
?Often the problems were associated with corn seedlings leafing out underground and it?s likely weather and seedbed conditions were responsible for the occurrence of the abnormal growth. Seedlings exhibiting abnormal emergence may have a twisted appearance because internal leaves start expanding before the seeding has elongated. ?Corkscrewed? mesocotyl/coleoptile development may occur when the coleoptile encounters resistance (like soil crusting or a dense soil surface) as the mesocotyl elongates. Several factors (or combination of factors) may be responsible for this abnormal growth. These factors may be characterized as environmental, chemical, or mechanical. Environmental conditions associated with underground leafing include light penetration, cold soils, or heavy rains soon after planting. When plants unfurl below the soil surface, they usually turn yellow and die,? Thomison wrote in a recent CORN Newsletter.
There can also be issues in cloddy fields with uneven sunlight warming the soil and, as was the case this spring in some fields, heavy rains can cause surface crusting and challenging corn emergence conditions. Herbicides can also cause some similar issues, Thomison said.
?Certain herbicides, such as cell growth inhibitors like acetochlor, and various premixes that contain their active ingredients can show similar symptoms (i.e. twisting, abnormal growth) when excessive rates are applied pre-emergence. Besides excessive rates, improperly closed seed furrows can allow the pre-emergence herbicide to come in direct contact with the seed,? Thomison said. ?Prompt treatment with a rotary hoe, weeder, spiketooth harrow or cultipacker may help break the crust and improve emergence. However, even when used carefully, these salvage operations can cause some damage to seedlings, which are emerging normally. To minimize poor seedling emergence due to unfurling below the soil surface, watch for cloddy seedbeds, open seed furrows, and crusting surface soils after rains.?
Ohio State University Extension plant pathologist Anne Dorrance points out that, in many ways, the situation in early May was a perfect storm for soybean problems.
?For most of these situations we have the following scenario: PPO herbicides (flumioxazin, sulfentrazone, saflufenacil) included as a component of the preplant burn down, fields planted seven days later with fungicide treated seed, followed by one to two weeks of suboptimum growing conditions between 40 to 50degrees F for two weeks, and greater than two inches of rain. These conditions are very conducive to both Pythium damping-off and PPO injury,? wrote Dorrance and Extension herbicide specialist Mark Loux in a recent CORN Newsletter. ?Some of the reports from the field were with seedlings that have already croaked. Wispy skeletons of soybean seedlings could be found on or below the surface. These are most likely from Pythium, it moves fast under these conditions. Other seedlings had black at the hypocotyl hook with a reddish brown on the underside of the cotyledon. These could be PPO injury.?
In some of the severe cases, it may be difficult to tell the cause of the problem.
?There is still much to learn from this unusual weather pattern, but if the soybean plants are slow to get out of the ground they are exposed to the herbicide/cold temperatures for a much longer period of time. In addition, with soybeans and cold soil temperatures, they are stressed and leak nutrients ? signal compounds which attract seedling pathogens. If they are stressed they may also be more vulnerable to PPO injury,? Dorrance and Loux wrote. ?How to tell the difference between pathogen, flooding, and PPO injury is not going to be easy this year as all three may be present in the field at the same time.?
If the plant dies from a pathogen, it will have soft tissue and consistent browning on the bottom of the seedling. With flooding injury there will be a smell from the anaerobic conditions in the field. For severe cases, there may also be algae on the soil surface and the seedlings may have gray roots on the outside with white inside the roots, Dorrance said. If the problem was PPO injury there will be necrosis on the emerging shoot, variable rate of emergence, possibly some growth distortion, and failure to emerge or plant death if severe, Loux said.
No matter what the problem, the warm, sunny conditions that followed in the third week of May helped, if it was not already too late.
