C.O.R.N. Newsletter: 2022-22

The Ohio State University at Lima will be the host of a drainage installation field day on Tuesday, August 9^th. Field demonstrations by the Ohio Land Improvement Contractors of America (OLICA) will begin at 9:00 a.m. in an open house style format and continue throughout the day.

Registration will be in a tent on Lot G which is accessible off Biddle Drive, and south of the Life and Physical Sciences Building. Campus maps are available online at lima.osu.edu/aboutus/campus-maps-and-directions.html. Parking is free and shuttles will be running to the field site where the demonstrations will be held between 9:00 a.m. and 3:00 p.m. Contractors will be available on-site to help answer any questions about the tile installation process.

There will be a free lunch provided at noon for those who pre-register. After lunch, Bruce Clevenger will make a presentation on the economic benefits of systemic drainage tile. Register for the lunch and learn by emailing schroeder.307@osu.edu or calling 419-879-9108 before August 1^st.

Tar spot is relatively easy to diagnose based on visual symptoms. So as the crop develops you should begin scouting fields to determine: 1) if tar spot is present, 2) estimate how much is there, 3) determine whether it is increasing over time, and 4) decide whether you should consider making a fungicide application. Walk down about 25-ft-of-row at 10 to 15 locations across the field and examine a pair of plants at every 10 steps for the present of tar spot. Make a note of the total number of plants examined and the total number with tar spot symptoms. Divide the last number by the first and multiply by 100 to estimate tar spot incidence. Repeat these steps every 5-7 days, particularly of conditions are wet and rainy, to determine if the disease in increasing over time.

INCIDENCE = (number of plants with tar spot/total number of plants examined) x 100

However, it may be difficult for untrained eyes to tell tar spot apart from a few other diseases. Yes, tar spot, as the name suggests, is characterized by the presence of raised, black, tar-like spots called stromata predominantly on leaf blades (A). However, not all raised, black, tar-like spots on a leaf are tar spot. Two other diseases that produce raised, blackish spots on leaves are southern rust (B) and common rust (C). Yes, it is true that rusts, as the name suggests, give leaves a typical yellowish-orangish rusty color, but this is the color of urediniospores, one of several types of spores produced by corn rust fungi. As the crop begins to dry down and temperatures drop, the rust fungi will produce a different type of spore called teliospores, and these develop in raised, blackish, structures called telia. Insect poop (frass) and dirt may also be confused with tar spot.  

Here are a few tips to help you tell the difference between tar spot, rust telia, and insect frass. Tar spot stromata do not rupture the leaf or have a split on the top. In addition, they cannot be easily broken or rubbed away with your fingers like rust or insect frass. Rust telia usually break or rupture the upper surface of the leaf tissue (D), and if rubbed, the spores are released, leaving your finger with a dark-rusty to blackish tinge.

Strong storms the week of July 4^th have led to some downed corn fields in parts of the state. Much of the yield penalty in corn is dependent on the stage the corn was at the time of the storm, as well as if the damage is root lodging (plants tipped over but stalk is intact) or stalk damage (greensnap/ brittlesnap or bent) (Fig. 1). Root lodging is easier for plants to recover from and will lead to less yield loss than stalk damage if occurring at the same rate.

Figure 1: Greensnap of corn stalks (A,B) and root lodged corn (C) after strong storms in Ohio in 2012. Photo courtesy of Peter Thomison.

Internode elongation in corn continues through tasselling (VT), so if root lodging occurs between V10 and VT, there is a good chance the corn will correct to upright growth to some degree. In Ohio research trials where severe root lodging was imposed, yield losses were 5% or 22% when lodging occurred at the V10 or V14 growth stage, respectively, compared to non-lodged controls. In these cases, most plants were able to recover and regain upright growth. When root lodging was imposed at VT/R1, minimal recovery of upright growth was seen and yield losses were closer to 40-45% due to poorer/uneven pollination and more barren plants.

Greensnap can be more detrimental to yield than root lodging or stalk bending. Reports from Nebraska suggesting 1.5-1.8 bu/ac loss for every 1% greensnap incurred. In Ohio, data from 2012-2013 suggested losses closer to 0.5-0.8 bu/ac per 1% greensnap, though it is possible losses could be greater as greensnap incidence in plants was primarily less than 40% of plants. Yield losses due to greensnap would be influenced by the crop stage and which nodes is broken. For example, greensnap occurring in nodes above the primary ear would result in lower yield losses relative to plants broken at nodes below the primary ear as long as some plants in the field retain their tassels to facilitate pollination.

If the recent storms came through and fields were less than V10, the major issue we’ve seen is “floppy” corn (Fig. 2). Rootless or floppy corn are plants that look normal from above-ground, but their root systems are underdeveloped due to a myriad of factors (e.g., hard/compacted soils reduce rooting ability, warm/dry soils affecting root elongation, shallow planting depths limiting root formation). When strong storms move through, rootless corn plants are unable to withstand the winds as the soil softens from added rain due to the poor root system and the plants fall over. It is rare that these plants will re-root and recover, and some stand losses can be expected as the rootless plants die off. The good news is that the remaining corn plants can compensate to some degree for slightly lower stands and will help minimize yield losses from the slight stand reduction. Replanting the field at this point is not a likely option as more yield will be lost because of poor planting date than gained from adding plants back into the field. If stands are reduced substantially and plants are still small, producers may want to consider other crop options for this season (planting a small grain this fall).

Figure 2: Image of a rootless corn plant lodged after July 5 storms in Northwest Ohio in 2022. Photo courtesy of Alex Lindsey.

Additional past work from Ohio on strong storm damage to corn is discussed in this factsheet: https://ohioline.osu.edu/factsheet/ac-1054. Information includes crop defoliation (sometimes seen with strong winds and hail), stand reduction, and more details on root lodging and greensnap research. The yield losses reported in this article show very severe cases, and it is possible yield losses will be lower than those mentioned in the article.

Regardless of the damage, there is a good chance much of the fields will experience partial recovery. Best practice is to wait a week to return to the field and conduct an assessment of damaged areas and consult with your crop insurance agent to discuss options moving forward. Keep in mind if plants do recover, there is often lateral displacement (rows shift over some, bent plants) which can make future field operations challenging. If fungicides are planned for this year, consider aerial applications to reduce likelihood of further plant damage.

References:

Elmore, R.W., and Ferguson, R.B. 1999. Mid-season stalk breakage in corn: hybrid and environmental factors. Journal of Production Agriculture 12:293-299. https://doi.org/10.2134/jpa1999.0293

Lindsey, A.J., Carter, P.R., Thomison, P.R. 2021a. Impact of imposed root lodging on corn growth and yield. Agronomy Journal 113:5054-5062. https://doi.org/10.1002/agj2.20848

Lindsey, A.J., Geyer, A.B., Minyo, R., and Thomison, P.R. 2021b. Seeding rate impact on root lodging and greensnap in corn. Crop, Forage and Turfgrass Management 7:e20112. https://doi.org/10.1002/cft2.20112.

Ortez, O. A., McMechan, A. J., Hoegemeyer, T., Ciampitti, I. A., Nielsen, R. L., Thomison, P., Abendroth, L. J., & Elmore, R. W. 2022. Conditions potentially affecting corn ear formation, yield, and abnormal ears: A review. Crop, Forage & Turfgrass Management, 8, e20173. https://doi.org/10.1002/cft2.20173