The groundwork
The Groundwork for Sero-X's label claim against Verticillium Wilt was laid between 2016 and 2019, spearheaded by Dr. Karen Kirkby and her team at the NSW Department of Primary Industries. Initial Lab trials in 2016-17 showed Sero-X inhibited microsclerotia at all application rates. Comprehensive field trials from 2017-2019 confirmed Sero-X effectively suppressed microsclerotia formation, limiting increases or reducing soil inoculum levels. These results, using a Propagule Per Gram of soil testing method secured an APVMA approval, validating Sero-X's efficacy in managing Verticillium dahliae and establishing its role as another tool alongside crop rotation.
Transition to DNA testing:
With a goal to understand the rate response and most effective timing, trial work evolved from labor-intensive propagule counting to DNA abundance measurement. The GPS located sampling technique employed in this trial showed significant drawbacks for assessment of levels over time, due to high variability in the data. Statistical analysis showed substantial variance at each GPS location and across sample dates, with some points exhibiting a 10-fold range in DNA abundance within a single treatment. This extreme variation, coupled with potential inconsistencies in exact sampling locations due to GPS float (5-30m), made it challenging to draw conclusive results from GPS-located data points. The scale-dependent nature of the variability, where higher average abundance levels corresponded to greater variation, further complicated data interpretation. Consequently, the analysis focused on the broad sampled points (50 cores spread across each treatment replicate) as a more reliable and representative measure of treatment effects over time.
Summary of Key findings:
Effectiveness across application rates: All tested Sero-X treatments showed reduced Verticillium dahliae DNA levels compared to the untreated control, with risk reduction ranging from 26.44% to 97.89%. Optimal application: The label rate (3 x 2L/ha) proved most effective, reducing pathogen exposure by 97.89%, showcasing Sero-X's potential to significantly mitigate the risk of Verticillium Wilt. Flexible options: Lower rates, including half-label rate and a low-rate application, also showed substantial efficacy, once regulatory approval has been achieved this will provide growers with alternatives that still offer significant disease management benefits. Long-term impact: The trials revealed Sero-X's ability to inhibit microsclerotia formation, breaking the disease cycle and reducing inoculum buildup in the soil over time. Integrated approach: While Sero-X demonstrated strong efficacy, and significantly reduced the risk in the cotton season, Fallowing the field also dramatically reduced all treatments after 12 months. Crop rotations Fallow management including the Trial Highlight While there is no single solution to eliminate Verticillium Wilt from cotton production, Sero-X offers a significant advancement in risk mitigation. Management Practices Integration of Sero-X into management practices, particularly when combined with strategies like fallow management, presents a robust approach to combating the disease.
1. Rate and timing:
The trial was sucessful in hibiting microsclerotia. The label rate (3 x 2L/ha) proved most effective, reducing pathogen exposure by 97.89%. Lower rates also showed significant efficacy, with half-label and low-rate applications reducing risk by 70.94% and 73.46% respectively. A single defoliation application (2L/ha) showed the least effect but still reduced risk by 26.44%. These results provide clear guidance on optimal application strategies for Verticillium Wilt management.
2. DNA as a diagnostic tool:
DNA abundance measurement as a diagnostic tool for assessing Sero-X's mode of action yielded mixed results. While more efficient than PPG counting, its detection of all pathogen stages (including hyphae and conidia) initially obscured Sero-X's specific impact on microsclerotia. This lack of specificity is a drawback compared to propagule counts, which directly measure microsclerotia. However, the study demonstrated that over time, as DNA from hyphae and conidia degrades, DNA abundance can eventually reflect Sero-X's impact on microsclerotia formation. This time-dependent approach allows for the assessment of treatment effects, albeit with a delay compared to more specific methods. The efficiency of DNA testing must be balanced against its initial lack of specificity when evaluating Sero-X's effectiveness in inhibiting microsclerotia.
3. Data for statistical analysis:
The study successfully provided enough data points from replicated and randomized treatments for statistical analysis. The shift to taking multiple samples per GPS location (3 data points per GPS location, 4 GPS locations per treatment, plus a broad sampled point) in later sampling dates (SD3-SD5) significantly increased the number of data points. This approach yielded 195 data points per sampling date, providing a robust dataset for statistical analysis.
4. Spatial variability:
While efforts were made to minimise the effect of spatial variability across the paddock, this aim was only partially achieved. The high variability observed in GPS-located samples presented significant challenges. In the end the analysis relied on on broad sampled points (50 cores across each treatment replicate), which proved more effective in managing spatial variability. This adjustment aligns with SARDI's recommended sampling techniques for research blocks and demonstrates the importance of flexible methodologies in field trials.
Silver Bullets?
Fallowing your field, coupled with good farm hygiene, or crop rotations with recommended crops will always remain a crucial part of your strategy to keep this disease in check There is no silver bullet that is going to make Vert disappear from our industry. It is now a vital and ongoing part of your IPM strategies. We can't announce new label rates yet but we CAN say is that these trials demonstrated, no matter what rate of Sero-X you use, it WILL decrease your risk. The label rate remains the the most effective at mitigating an explosion of verticillium wilt next season, but we will continue to work hard to have label changes made so (no matter your budget) you can take meaningful steps to manage the problem. The best time to start using Sero-X to manage Verticillium Wilt in your cotton crop was last season - the next best time is the 2024/25 season.