Application of sustainable weed management practices in agronomic crops will be one of the largest challenges farmers face in the future. Marestail (Conyza canadensis) is a problematic weed in row crops where management can be challenging. The life cycle of marestail is rather complex, and shifting emergence patterns have further complicated management. There are two central goals for this project: examine the biological nature of marestail across a broad region (KY, IL, MO and KS) to provide data on emergence timing and plant growth patterns, and to provide a regional model for managing this weed, examining a broad range of management strategies, which includes incorporating cover crops.
This project included two sectors: a field experiment in a no-till soybean system where different management strategies were applied, and a biology aspect. Within the biology portion, marestail emergence was tracked from seeds collected at various locations across the four state region. Plant growth and survival was also measured within a separate population of flagged specimens.
While data are still being analyzed, preliminary results in the biology experiment indicates that most marestail emergence in KY occurred shortly after seed rain in the fall of 2018, regardless of location where seed was collected. Initial data also shows a pattern with larger marestail rosettes being more successful at surviving winter.
For analysis, cumulative marestail emergence in the field experiment will be divided into two time intervals relative to soybean planting: cumulative mean density prior to planting and cumulative mean density post planting. Examining the data over these two periods can better track emergence and provide a clearer model for marestail management. Within the field experiment, yield data are also being analyzed. This will allow us to compare how each treatment responds to the corresponding management strategy.
Objective 1: Characterize marestail biology to better inform how cover crops can be used to manage this species. We will primarily answer the questions: when does it emerge and how well does it survive the winter?
Objective 2: Determine how well the cover crops will suppress marestail emergence and growth.
We are currently conducting a study tracking biological processes, such as emergence and over –winter survival for marestail. The methods described in this report are part of a larger set of experiments led by our group at the University of Kentucky looking at how weed management practices and changing climates will affect marestail populations. It also includes field trials at other universities.
Objective 1. Weed seed was collected in the summer of 2018 from 30 individual plants from two populations in each state. Each research site received seeds from all locations. Each university established an area in a no-till field that was not cover cropped. 8” diameter PVC pipes (rings) were inserted into the soil to isolate the seed populations. The PVC pipe extended 3” above the soil surface to prevent seed dispersal via wind and water movement from other areas. Seeds from different locations were allotted using a completely randomized design with six replicates of each seed lot for a total of 48 experimental units. Collected seeds were broadcasted into their respective ring to simulate seed rain. Six empty rings acted as controls at each site. Once the seeds were sown, marestail emergence was counted twice a week until soil temperatures reached 52 degrees Fahrenheit at 2” depth, and resumed in spring once temperatures returned to the above the base temperature. Counted plants were removed.
Soil moisture and temperature were collected hourly at 2” depth using sensors and dataloggers. Air temperature and precipitation were continually measured at a nearby weather station. The data collected will give information to answer the question: what are the temperature and moisture levels favorable for weed emergence?
To measure over-winter success, native populations were tracked by establishing one 16×32’ supplemental plot at each location. In this plot, 100 marestail rosettes were flagged (50 large and 50 small), where 1.5” in diameter divided large and small plants. Diameter of these flagged plants were measured before winter. Height and diameter measurements were taken weekly starting the following spring and summer (of 2019) until maturity. Other plant species, not of interest, were removed from the surroundings to promote an ideal growing situation. Statistical analysis of these measurements will provide answers to the following question:
- Is the size of a plant a determining factor for overwinter survival?
Objective 2. Each of the four sites conducted one experiment in a no-till soybean system that followed corn. Plots were arranged into a randomized complete block design, with four replications and ten different treatments. Within these treatments we will analyze a few different comparisons. Five treatments were planted with cover crops to be compared with the no cover cropped counterparts. Data from counting marestail will allow us to make interpretations on how well these cover crops suppress emergence.
After the cover crop was established and a fall herbicide application was applied to the corresponding treatments, two small quadrants were established in each plot. Within these quadrants, marestail emergence was counted and removed from the time the field study began to the termination of the cover crop in the spring. Cover crop biomass measurements were also collected following any herbicide application. Soybeans were planted two weeks after the termination of the cover crop, and soybean yield will be collected at harvest. Once soybean yield data is determined, an economic breakdown will be conducted to determine a cost benefit analysis on the adoption of cover crops in an integrated weed management (IWM) program.
The data collected are being used to answer the following questions:
- Do treatments affect the growth of marestail?
- Does the research site affect marestail population density or biomass levels?
- What are the economic incentives for using these management strategies and how do they compare between sites?
From a preliminary analysis, the majority of marestail emergence from simulated seed rain occurred in fall of 2018. In Kentucky, fall of 2018 was both warm and wet, potentially explaining this high volume of marestail emergence. In KY, all populations that were sown exhibited a similar emergence time, regardless of where the seeds were collected. Initial results also show that size of the marestail rosette may play a role in determining the success in over-wintering. Larger rosettes appear to be better equipped to survive the freeze and thaw of winter, again these results are preliminary. This is important for farmers considering that plants that overwinter successfully have a competitive advantage in spring.
These results will provide more clarity to how marestail can behave depending on the changing environmental conditions from year to year. No two years follow the exact same weather pattern, and it’s important to consider how environmental conditions affect management strategies.
Data from the management experiment have yet to be analyzed.
Educational & Outreach Activities
- Southern Cover Crop Conference
Presented a poster that highlighted our research
No farmers participated in this experimental design, yet there were many farmers and extension agents who had the opportunity to see our results at the Southern Cover Crop Conference at the University of Auburn in July 2019. Farmers and educators both were very aware of the competitive pressure marestail is putting on our no-till cropping systems.
As our project is still finishing up, so how our research affected agricultural sustainability is still unknown, yet will be clearer when data analysis is completed. Preliminary data shows a positive impact on suppressing marestail through the adoption of cover crops to an IWM program. Further agricultural research that attempts to show cover crops role in weed management should include a broader area of collaborators, and expand beyond only looking at marestail.
Our results provided a clear model for incorporating cover crops into their IWM programs, as well as a model herbicide program that uses a variety of chemistry in order to reduce the risk of resistant populations. Future conferences will provide an opportunity to present our data on the biological demeanor of marestail, in regards to emergence timing and winter survival.