The Application of a Mathematical Model to Extrapolate Study Results to Other Locations

Environmental models are used to simulate or reproduce real world conditions and how those conditions change due to varying input. Modeling enhances our ability to extrapolate results from intensively-studied test sites to other potential use sites. These models are used by industry and governmental organizations alike to support scientific analyses.

Input will vary based on the model being used and conditions the modeler would like to simulate, but it can include changes in land use, land management techniques, weather data, etc. The model ArcSWAT 2009 is being used to simulate conditions at the Maryland sites and to show how the incorporation of BMPs (i.e., adding compost to the soil and using a lawn seed mixture containing microclover) affects runoff.

Specifically, ArcSWAT is currently being used to model runoff characteristics from the Clarksville, Maryland test and control sites. ArcSWAT is an interface between Esri’s ArcGIS Geographic Information System and the SWAT model (Soil and Water Assessment Tool) developed by Dr. Jeff Arnold of the USDA Agricultural Research Service. SWAT is a physically-based model, which means it relies on soil, elevation, land use, and weather data to simulate water and sediment movement as well as nutrient cycling within a watershed. Therefore, it allows one to examine how various management methods affect runoff. Subbasins of the watershed are divided into hydrologic response units (HRUs), which are areas of similar elevation, land use, and soil data. Ultimately, the model simulates loadings from each HRU to the stream on a daily, monthly, or annual time step.

The Clarksville test and control sites’ watersheds have been delineated using ArcSWAT. We are currently working on refining input variables in order to accurately simulate water, sediment, and nutrient movement at each site. Once the input is complete we will be able to run the model and compare the modeled results with the results of the on-going monitoring. Ultimately, when the model is appropriately calibrated, the results will be extrapolated to other sites throughout the Chesapeake Bay watershed. 

Herbicide safety on microclover: Results from University Park

by Peter Landschoot, Dept. of Plant Science, Penn State

As the use of microclover in lawns gains interest among homeowners, questions will surface on how this species responds to routine lawn care practices such as mowing, fertilization, and weed control. Weed control practices are of particular concern due to the widespread use of herbicides that may injure microclover. A recent study by McCurdy et al. (2012) at Auburn University revealed that several common herbicides used in lawns effectively control clover species, including atrazine, dicamba, clopyralid, 2,4-D, triclopyr, metsulfuron, and trifloxysulfuron. However, these authors found that 2,4-DB, imazethapyr, and bentazon did not cause significant injury to clover, and suggested they may be suitable for weed control in scenarios where clover is a desirable species. Information is needed on the tolerance of microclover cultivars to broadleaf and annual grass herbicides used to control lawn weeds in the Chesapeake Bay watershed.

An experiment designed to examine tolerance of microclover to different broadleaf and annual grass herbicides was initiated at the J. Valentine Turfgrass Research Center in University Park, PA during the summer of 2012.  The experiment area was seeded on 7 June with a mixture of “Faith” tall fescue at 8 lb/1000 ft² and “Pirouette” microclover (2 lb/1000 ft²) using a drop spreader. The tall fescue/microclover stand was mowed several times before the first herbicide treatments were applied. 

Fig. 1. Seeding Pirouette microclover into experiment area.  

Treatments included three postemergence broadleaf herbicides [Weedar 2,4-D Amine (3.8L); Aceto 2,4-DB Amine (2.0L); and Rhomene MCPA (3.7L)] applied at two or three different rates on September 6, 2012 and September 8, 2013 (Table 1).  Also, five preemergence herbicides [Gallery 75DF (isoxaben) applied at three different rates; Pendulum 60WDG (pendimethalin); Barricade 65WG (prodiamine); Dimension 1.0EC (dithiopyr); and Balan 2.5G (benefin)]; and one postemergence nutsedge herbicide [Basagran T/O 4.0L (bentazon)] were applied on May 7, 2013 (Table 2). 

All treatments were applied using a backpack sprayer at 40 psi with a dilution rate equivalent to 1 gallon water/1000 ft². The experimental design was a randomized complete block design, and each treatment was replicated three times. Plot size was 30 ft². 

Criteria for evaluating herbicide tolerance included visual ratings of foliar injury using a scale of 0-10, with 0 indicating no injury, and 10 representing complete desiccation of clover.  After the final injury rating was taken during the 2012 and 2013 experiments, visual assessments of percent clover cover were made.

Results

Late summer applications of 2,4-D amine at 2 and 3 pt/A caused noticeable injury and reduced cover of microclover when compared to the untreated control in 2012 and 2013. Injury from the 3 pt/A treatment was more severe than the 2 pt/A treatment in both years, resulting in an approximate 50% reduction in microclover ground cover in 2012 and 20% reduction in 2013. The 2 pt/A treatment resulted in about 20% less microclover relative to the control in 2012, and a 15% reduction in 2013, 3-4 weeks after treatment. The 2,4-DB treatments (2 pt/A, 4 pt/A, and 6 pt/A) did not produce visible foliar injury in 2012 or 2013, but the 6 pt/A treatment resulted in a slight reduction (8%) of microclover cover in 2012 compared to the control 1 month after treatment. No reduction in cover was observed with any 2,4-DB treatment in 2013. 

Fig. 2. Thinning of microclover in plot (on right) treated with 2,4-D.

No significant visible injury to microclover foliage was observed with the 0.5 and 1.0 pt/A rates of MCPA in 2012.  However, a slight reduction (8%) in microclover cover was detected with the 0.5 pt/A treatment in 2012.  In 2013 the 1.0 pt/A treatment showed some minor foliar discoloration following the late summer application.  Neither of the MCPA treatments resulted in microclover cover reductions in 2013.

Although some significant reductions of microclover were observed with 2,4-D applications in both years, the clover fully recovered during the spring of the following year. 

Table 1. Influence of herbicide treatments on Pirouette microclover following applications on September 6, 2012 and September 8, 2013 at the J. Valentine Turfgrass Research Center in University Park, PA.

					Clover	% Clover		Clover	% Clover
			Product		Injury§	Cover		Injury	Cover
Treatments			Rate		9/21/2012	10/7/2012		9/16/2013	9/30/2013
2,4-D Amine (3.8L)			2 pt/A		3.7 b¥	72 c		4.0 b	81 b
2,4-D Amine (3.8L)			3 pt/A		6.7 a	45 d		6.3 a	75 b
2,4-DB Amine (2.0L)			2 pt/A		0 c	92 ab		0 d	97 a
2,4-DB Amine (2.0L)			4 pt/A		0 c	85 ab		0 d	97 a
2,4-DB Amine (2.0L)			6 pt/A		0.3 c	83 b		0 d	95 a
MCPA (3.7L)			0.5 pt/A		0.7 c	83 b		0 d	97 a
MCPA (3.7L)			1 pt/A		0.7 c	87 ab		1.0 c	95 a
Control					0 c	91 a		0 d	98 a

^§Foliar injury visually assessed using a scale of 0-10, with 0 indicating no injury, and 10 representing complete desiccation of clover. 

^¥Data means within the same column and followed by the same letter are not significantly different as determined by Fisher’s Protected Least Significant Difference test at P=0.05.

 

None of the preemergence annual grass herbicides used in the spring 2013 trial (Pendulum 60WDG, Barricade 65WG, Dimension 1.0EC, and Balan2.5 G) resulted in any visible injury or thinning of microclover.  However, all three rates of Gallery 75DF showed considerable injury, leading to thinning of the stand.  The only postemergence nutsedge herbicide used in the 2013 spring trial (Basagran T/O) did not produce visible injury symptoms or thinning. 

Based on results of the spring 2013 trial, Gallery 75DF should not be used in stands of microclover.  This trial will be repeated in 2014. 

Table 2. Influence of preemergence herbicide treatments and one postemergence herbicide (Basagran) on Pirouette microclover following applications on May 7, 2013 at the J. Valentine Turfgrass Research Center in University Park, PA.

			Product		Injury§	Injury
Treatments			Rate		5/14/2013	17-May-13
Gallery 75DF			0.66 lb/A		2.0 ab¥	5.3 ab
Gallery 75DF			1.00 lb/A		2.3 ab	4.3 ab
Gallery 75DF			1.33 lb/A		3.7 a	5.3 a
Basagran T/O (4.0L)			2 pt/A		0 c	0 c
Pendulum 60WDG			3.4 lb/A		0 c	0 c
Barricade 65WG			1 lb/A		0 c	0 c
Dimension 1.0EC			2 qt/A		0 c	0 c
Balan 2.5G			60 lb/A		0 c	0 c
Control					0 c	0 c

^§Foliar injury visually assessed using a scale of 0-10, with 0 indicating no injury, and 10 representing complete desiccation of clover. 

^¥Data means within the same column and followed by the same letter are not significantly different as determined by Fisher’s Protected Least Significant Difference test at P=0.05.

 

References:

McCurdy, J.D., J.S. McElroy , and M.L. Flessner. 2013. Differential response of four Trifolium species to common broadleaf herbicides: Implications for mixed grass-legume swards. Weed Technology, 27(1):123-128.