Each year fungal diseases of the foliage, stems, and pods of soybean routinely case 5 to 10% yield losses in South Carolina. In very wet years with recurring thunderstorms or hurricanes these losses can be 25% or higher. In many cases a late season hurricane can cause white, moldy seed and severely reduce the value of the crop. Foliar diseases that South Carolina growers face every year include Septoria Brown Sopot, Frogeye leaf spot, Cercospora leaf blight, and rust on leaves. On stems and pods anthracnose, Phomopsis, and pod and stem blight can cause varying levels of damage depending upon weather conditions and timeliness of harvest. Unfortunately, resistance to most of these diseases is missing in most modern soybean varieties. In many situations, where resistance is available, races or pathotypes of the fungus develop that can overcome the host plant resistance. Frogeye leaf spot is a good example of such a disease. As a result, each year growers face the dilemma of deciding whether to spray a fungicide and if they spray, which fungicide to use. Fungicides now vary widely in cost and makeup. Fungicides are now available that have up to 3 active ingredients per product. Naturally, the more active ingredients, the greater the price. However, products with 2 or 3 active ingredients now provide three or more weeks of protection from disease. In the past fungicides with one active ingredient were lucky to provide 2 weeks of protection from foliar diseases.

For the current year this project will provide growers with up to date information on the severity of fungal diseases on soybeans in their area. When coupled with an accurate weather forecast this will greatly assist growers in their spray/no spray decision. We have provided this service for the last 10 years for soybean rust. This will expand that service to other diseases that are actually more common than rust and a greater threat to produce yield losses. This project will help growers in subsequent years by providing them with direct comparisons of the efficacy of at least 6 fungicides in three categories: fungicides with 1 active ingredient (a.i.); fungicides with 2 a.i.’s; and fungicides with 3 a.i.’s. By providing growers with these comparisons in an environment relatively close to their farms they can see the yield losses incurred and determine the cost benefit of using a fungicide in each of the three categories on their farms. Fungicides cost anywhere from $10 to $30 an acre to apply, especially if application costs are included. However, when applied in appropriate conditions such as years with late hurricanes, yield increases of 5 to 10 bushels per acre are not uncommon. Depending upon commodity prices the $35 to $75 return on a $30 investment is more than worthwhile. On the other hand in a dry year there may be no economic return and a $30 investment per acre lost.

GOAL #1: Use a set of soybean varieties susceptible to specific diseases to teach growers at workshops how to accurately identify the disease present and assess its severity and probability of developing to damaging levels.

GOAL #2: Acquaint growers with the fungicides available to them and what their potential is in terms of range of diseases controlled and the duration of control provided.

Goal #3: Use each location as a case study to demonstrate to growers the effects of environmental conditions on disease development. If a grower will attend our field days and workshops or examine our results on the appropriate web site, they will be better equipped to make the spray/no spray decision that gives them the highest probability of financial return on their investment.

Specific outputs include biweekly ratings for disease incidence and severity for each of the treatments at each of the 3 locations for the fungicide trials and disease demonstration plots beginning in July. Once disease severity starts to build, we will post these results in the Clemson University Soybean Rust Newsletter so that growers will have a reference point for their area of the state to make a “spray/don’t spray” decision on their soybeans.

Soybean foliar fungal disease evaluation workshops will be held in September at each of the 3 locations for growers, county agents, and consultants. Follow up workshops will be held at each location prior to defoliation for everyone to see the efficacy of each fungicide in controlling the various fungal diseases.

Data on fungicidal effects on disease severity and incidence, defoliation, and yield will be summarized and presented at the South Carolina Corn/Soybean Meeting in December. This data will also be summarized into a bulletin and web sites on the Clemson University Agronomic Team Web site.

Quarterly reports and a final report will be submitted on time using the National Soybean Research Database platform, as defined in the RFP.

Updated April 9, 2021:
Plots will not be planted until the very end of May or early June. Disease pressure is usually higher on late planted than early planted soybeans. We have decided upon the varieties to plant, have established sites to use for field plots, and have started to accumulate the fungicides we will be using for the trials.

Updated July 15, 2021:
Fields have been planted at Edisto REC (Blackville, SC), Piedmont REC (Pendleton, SC), and Pee Dee REC (Florence, SC).
The field at the Edisto REC in Blackville is has a lateral irrigation system. As of July 15, 2021, the field has been sprayed with burndown herbicide application and the field has been disked and bedded. On April 21, 2021, 3 gallons of Telone II were applied to this field to reduce nematode populations. Soybean was planted on May 25th with Asgrow 74X8 at 130,000 seed per acre on 38-inch row spacing. PRE and POST emergence herbicides have been applied. Plots consist of 8-row plots so that we can easily spray insecticide with a plot sprayer. An additional field C8A was planted in June with strips of soybean varieties to serve as a disease nursery. These included AG59XF0, AG69XF0, AG72XF0, P53A67X, P67A28LS, and P72A21X.

The field at the Piedmont REC in Pendleton, SC has a center pivot. As of July 15, 2021, the field has been sprayed with burndown herbicide application and soybean has been planted no-till behind oats. Asgrow 69XF0 was planted on July 1 on 30-inch row spacing. PRE and POST emergence herbicides have been applied. Additional strips were planted on July 1 to serve as a disease nursery. These varieties included AG59XF0, AG69XF0, AG72XF0, P53A67X, P67A28LS, and P72A21X.

The field at the Pee Dee REC in Florence, SC has no irrigation. As of July 15, 2021, the field has been sprayed with burndown herbicide application and soybean has been planted. Asgrow 69XF0 was planted on June 15th on 30-inch row spacing. PRE and POST emergence herbicides have been applied.

Fungicide applications will be made at each location as it reaches R-3. Fungicides to be applied include: 1). nontreated check, 2). Tebuzol 3.6F, 3). Headline, 4). Topguard, 5). Stratego YLD, 6). Approach Prima, 7). Priaxor Xemium, 8). Revytek fungicide, 9). Delaro Complete, 10). Miravis Neo, and 11). Trivapro Fungicide.

Updated October 15, 2021:
Plots were established at the Edisto REC, Pee Dee REC, and Piedmont REC as described in previous reports. Fungicide applications were made at approximately R3 at each of the locations. Each test consisted of 4 replications of plots that were 40 ft. long. At the Edisto REC plots were 8 rows wide and treated using a "Mudmaster self-propelled sprayer modified for plot use. At the other 2 locations plots were 4 rows wide and fungicides were applied using a back-pack sprayer with a CO2 spray system. At the Edisto REC 11 fungicide regimes and a nontreated check were established. At the Pee Dee REC and the Piedmont REC sites 6 fungicides and a nontreated check were established. Fungicides were chosen to compare products with either 1, 2, or 3 active ingredients. Fungicides applied at all locations included tebuconazole, Headline, Aproach Prima, Stratego YLD, Trivapro, and Revytek. Additional fungicides applied at the Edisto REC included Topguard EQ, Priaxor Xemium brand fungicide, Delaro Complete, Miravis Neo and Miravis Top.

Plots have been rated for incidence and severity of diseases at each location. Disease pressure has been very low. Downy Mildew has been the most common disease and is present in all plots. Frogeye leaf spot and Cercospora leaf spot were two of the primary target diseases but incidence and severity of these diseases has been low. Leaves have also been collected from each plot and examined for rust under a dissecting scope. Rust has been found at the Edisto REC and at the Piedmont REC. Rust is developing rapidly at the Edisto REC and will probably cause a 5 to 10% yield loss. Levels of rust in the check were as much as 3X that found in most of the treatments. Four of the fungicides have prevented any infection by rust.

Although we had planned field day activities at each location these were cancelled due to COVID restrictions. We did distribute materials prior to anticipated spray dates on fungicides and their applications to agents and growers via electronic media.

County strip trials and OVT plots are being used to develop a listing of varieties resistant and susceptible to particular diseases.

Updated January 19, 2022:

View uploaded report 4

Plots were successfully taken to harvest at both the Edisto and Piedmont Research and Education Centers. Eleven fungicide regimes and a nontreated check were applied at the Edisto REC and 6 fungicide regimes and a nontreated check were applied at the Piedmont REC. All plots were harvested using a modified small plot combine.

The 2021 growing season was an excellent year for soybean production, especially in the Savannah Valley. Very few foliar diseases were detected at either the Edisto or Piedmont REC locations. The most significant fungal disease observed was soybean rust. However, even it appeared too late at both locations to have major impacts on yield. Rust was first detected on September 20th at the Edisto REC. It was only 1 pustule on 1 leaf. By October 13th it was present at a mean severity of 31% across all of the leaves in the Check plots. On October 18th it was present on more than 53% of the leaves. Several fungicide regimes including Tebuzol 3.6F, Approach Prima, Revytek and Delaro Complete 458 SC provided very good control of soybean rust. Yields at the Edisto REC location were excellent exceeding 60 bu/acre in most plots (Table 3). Rust seemed to have minimal effect on yield. Yield in the nontreated check regime was 66.4 bushels. Only Topguard EQ (70.5) and Stratego YLD (69.6) appeared to out yield the nontreated check.

At the Piedmont REC Rust was present on approximately 10% of the leaves of all treatment regimes by October 6 (Table 4. On October 25th 100% of the leaves in the check plots had rust present on them with approximately 64% of the leaf area affected. All fungicide treatments reduced the incidence of rust on October 25th with Approach Prima, Revytek, and Folicur providing the highest levels of reduction in incidence. All fungicide regimes reduced rust severity on October 25th by more than 50%. Yields at the Piedmont REC were lower than at the Edisto REC with a range from 24.3 to 33.2 bushels per acre. Yield of the check was 32.1 bu/acre; no treatment appeared to significantly increase yields.

Both tests show that application of a fungicide does not automatically result in an increase in yields. Both tests had low levels of diseases such as Frogeye leaf spot, Cercospora leaf spot, and Target spot making application of a fungicide to control yield losses unneeded. In both fields levels of soybean rust were high immediately prior to defoliation. However, this disease pressure was too late in the year to cause significant yield losses.

Results from this project will allow growers to choose the most cost effective fungicides and applicaation dates for the control of foliar fungal pathogens of soybean.