Episode 22 of Battle for the Belt is now available: https://www.youtube.com/watch?v=8KngybKmZ2E
In Episode 22, we learn about scouting for insect defoliators in soybean and western bean cutworm from Dr. Kelley Tilmon. We also learn about frogeye leaf spot identification and management from Horticulture and Crop Science PhD student, Fabiano Colet. Finally, Food, Agricultural, and Biological Engineering PhD student, Luke Waltz, gives another Tech Hub update.
In the mid-season period, we need to pay attention to defoliators. There are many insects that defoliate soybeans such as Japanese beetle, caterpillars, and bean leaf beetle. When monitoring your field for defoliation, it does not matter which insects are causing the defoliation, just the amount of defoliation that has occurred. We make recommend decisions on spraying based on how much leaf area is lost. To scout your field, start out by checking 10 locations. Ensure that these locations are not at your field edges as those are not representative of your field. At each location take a trifoliate from the top, middle, and bottom of your canopy. Then you can evaluate leaf loss. For management, the threshold of defoliation until R2 is 30% defoliation and from R3 to R5, this is bumped up to 10% defoliation. Normally when people scout, they assume a higher defoliation level than what is actually present, so to practice judging defoliation levels, we have a tool here.
The main mid-season pest in corn that we monitor is Western Bean Cutworm. This pest is a moth that lays eggs on the plant that will hatch into caterpillars and make their way to the corn ear. The pest causes damage to the ear and makes the plant more susceptible to fungal infections. To scout for this pest, examine the top four leaves of the plant, where the egg masses would be laid. Look at five different locations in the field and at each location check 20 plants in a row. If you find egg masses on 8 of your 100 plants, that is when a spray application is recommended. The treatment should be sprayed when the eggs are almost ready to hatch. The egg masses turn into a purple color when they are about to hatch. Spraying the caterpillars before they make their way into the ear or the whorl is important because the insecticide will not be able to touch them once they are hidden in this part of the plant.
Frogeye Leaf Spot
Frogeye leaf spot is an important disease in soybean caused by Cercospora sojina. The symptoms of frogeye are lesions found on younger leaves in the upper canopy. The lesions are in a circular, angular format. The center of the lesion is gray, and the margins have a reddish-purple coloration. In the last couple of years frogeye leaf spot has been showing up at R2 or R3 stages, full flower or beginning pod formation. To decide on management for this disease that can be yield-limiting, we need to think of the disease triangle: susceptible host, pathogen, and environmental conditions. The best way to manage this disease is planting a resistant cultivar, and additionally crop rotation because frogeye can overwinter as well as come in on storms. Lastly, fungicide applications can be used. However, some populations of C. sojina can be resistant to some fungicides; therefore, a product with multiple active ingredients is recommended. To decide whether an application is warranted look to see if the variety is susceptible to the disease or not, then scout to confirm the presence of the disease. Scouting the soybeans at the R2/R3 growth stage is best because fungicide applications should be made at this time. As soybeans move into R5 stage (beginning seed), fungicide applications are not recommended because you may not see a return.
Battle For the Belt Location Updates
We have begun to see raccoon damage at our Wooster and Northwest locations this week with multiple of our hybrids hitting the R3 stage (milk). The raccoons seem to favor our 100-day hybrid over all the others.
At the Wooster location, gray leaf spot has been identified in corn but has not gotten more severe with later planting dates. For soybean, there was no frogeye leaf spot at this location, but little septoria brown spot was present. The first planting date with a suitable stand, planting date three, has not yet fully canopied.
The Western location had wind damage in corn from the storms the previous weekend. The corn in planting date one reached R4 (dough stage) in some of the earlier hybrids but the majority of that planting date is at R3 (milk). At this location, gray leaf spot is still present, but it is not at high severity levels. The soybeans at this location had frogeye leaf spot show up this week. When scouting for disease we use the measurement of incidence and severity. Incidence is the percentage of plants that had symptoms of the disease, and severity is the percentage of the leaf covered by the disease. Planting date one and two in soybean were at R5 (beginning seed) and had a disease incidence of about 30% overall with a severity of 1%. Planting date three was at R3/R4 (beginning pod/full pod) and had about a 15% incidence of frogeye leaf spot and a severity of 1%. Planting date four is at R3 (beginning pod) and frogeye leaf spot was only found in one plot. Planting date five is at R2 (full flower) and had frogeye leaf spot disease in one plot.
At the Northwest location with corn, planting date one reached R4 (dough stage) with the 100-day hybrid plots, the rest of the hybrids were beginning R3 (milk). The majority of planting date two is in R3, and planting date three is generally at R2 (blister) except for the 115-day hybrid started silking this week. In planting date four, most of the plots were at R1 (silking) and being pollinated. Planting date five has not tasseled yet and is at about V13/14. The disease at this location is low within the corn and no tar spot has been found so far. The soybeans, however, do have frogeye leafspot. On planting date one, which is at R5 (beginning seed) now, there was a 50% incidence, meaning that on five out of 10 plants frogeye was found but only at a 1% severity. This was true across planting date two as well. Planting date three is at R4, meaning full pod and will begin fill seed soon, this planting date had about a 50% incidence with a 1% severity as well. Planting date four is at R3 (beginning pod) and has a 30 to 50% incidence and 1% severity rating. Lastly, planting date five is at R2 (full flower) and had a less than 10% incidence with a 1% severity where it was found.
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, https://weather.cfaes.osu.edu/.
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.