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Ohio State University Extension


Battle for the Belt: Episode 21

Episode 21 of Battle for the Belt is now available:     

In Episode 21, we talk with Dr. Stephanie Karhoff, Agronomic Systems Field Specialist about scouting for tar spot in corn. Tar spot is a relatively new disease to the state of Ohio, but it can be problematic, especially in Northwest Ohio. When scouting for tar spot, visit multiple locations in your field and answer these questions:

  1. Is tar spot present?
  2. To what severity?
  3. Is it increasing over time?

The recommendation is to examine about 15 locations throughout your field. At each stop, walk about 25 feet of row and stop every ten steps to look for raised, black spots that are fungal structures called stromata (Figure 1). To calculate the disease incidence, count the number of plants showing signs of tar spot divided by the total number of plants observed, and then multiply by 100. When examining the leaves, also record the estimated amount of leaf area affected. After the initial assessment, it is important to come back every five to seven days to observe how much tar spot has progressed.

Figure 1. Tar spot stromata. Picture: Crop Protection Network.Tar spot can be easily confused with insect frass (poop), dirt, and rust telia. The key to detect the difference is to rub or scratch the area where tar spot is suspected. Tar spot is embedded into the leaf epidermis and cannot be rubbed or scratched off. If you would like to read more about tar spot please click here.

On this week’s video, we also hear from Luke Waltz, PhD Student in the Department of Food, Agricultural, and Biological Engineering as he gives a tech corner update on the use of time lapse video in the Battle for the Belt study. Results of the time lapse process across locations and planting dates will be shared later this season.

Battle For the Belt Location Updates

In each location, our earliest planting date is fully pollinated in corn and soybeans are putting on pods. Disease ratings for both corn and soybeans started at R1 in corn and R3 in soybeans. Disease pressure for our planting dates one through three is low.

Figure 2. Gray Leaf Spot. Picture: Kiersten Wise.The Western location showed evidence of gray leaf spot (Figure 2) and northern corn leaf blight in planting date one on few ear leaves, however, the disease pressure was 5% or less. There was minimal evidence of silk clipping. Planting date one is fully pollinated and at R2, while planting date two is silking with some plots still tasseling. We have four corn hybrids that are 100, 107, 111, and 115 days to maturity. This causes some of planting date one and two to be synced in the reproductive stages. Planting date three was between VT and R1 depending upon the hybrid, planting date four is V14/15, and planting date five is at V10. In the soybeans, there was no sign of frogeye leafspot or a need for fungicide application. Planting date one and two are at R4 which is full pod. Planting date three is at R3, beginning pod, planting date 4 at R2, full flowering, and planting date five at V6.

At the Wooster location, planting date one is at R1. This location had the highest level of gray leaf spot severity on the ear leaves. The incidence of this disease was between 50 to 80% with a range between 1 and 5% severity. The hybrid that had the most incidence and highest severity overall was the 100-day hybrid across planting dates. There was also more incidence of silk clipping at this location (20% incidence) from Japanese beetle than the other two locations. Planting date two, three, four, and five are at V16, V16, V10, and V6. On the soybean side, planting date one, two, and three are at R3, planting date four is at R2, and planting date five, is at V4. At this location there was little to no disease or insect pressure in the soybeans.

At the Northwest Location planting date one two and some hybrids in planting date three were at R1. Silking can last for about 10-13 days, so this stage can overlap due to the length. Planting dates four and five are at V13 and V10. This location in corn has low disease pressure with low occurrence in Northern Corn Leaf Blight and Gray Leaf Spot. The soybeans are in planting date one in R4 and planting date two and three at R3. Planting dates four and five are R2 and V11. This is the only location that has Frogeye Leaf Spot, in planting date one, two, and three, however, they are at low levels (1% severity).

Gray leaf spot can cause economic loss if there is enough leaf coverage in the two weeks before and after tasseling. To read more about scouting and disease management for gray leaf spot click here. To learn more about scouting and management for northern corn leaf blight click here.

Table 1. Planting dates one, two, three, four and five in the trial at all three locations with day of planting, soil, air temperature averages, and Growing Degree Days (GDDS). Information from CFAES Weather System,


Keep following the ‘Battle for the Belt’ this growing season to learn more and get further updates! You can  find the full video playlist of Battle for the Belt on the Ohio State Agronomy YouTube channel.

Crop Observation and Recommendation Network

C.O.R.N. Newsletter is a summary of crop observations, related information, and appropriate recommendations for Ohio crop producers and industry. C.O.R.N. Newsletter is produced by the Ohio State University Extension Agronomy Team, state specialists at The Ohio State University and the Ohio Agricultural Research and Development Center (OARDC). C.O.R.N. Newsletter questions are directed to Extension and OARDC state specialists and associates at Ohio State.