Control Of Buttercups In Indiana fields

The Short Story

There are several buttercup species found in Indiana.  The buttercups are toxic plants and can cause poisoning in grazing animals; however, buttercups are reported not to be toxic in hay.  In the most frequently encountered buttercups, the flowers are yellow.  These plants can be problematic in no-till crops, gardens, pastures, wheat, and waste areas.  Fall or early spring applications of glyphosate + 2,4-D; Autumn (iodosulfuron) [corn only]; Princep (simazine) + 2,4-D [corn only]; and Canopy XL (sulfentrazone + chlorimuron) + 2,4-D [soybean only] have provided excellent control of smallflower buttercup (90 to 100% control).  However, triazines alone have not controlled all buttercups.  In grass pastures, Cimarron (metsulfuron), 2,4-D, and Crossbow (2,4-D + triclopyr) will provide good to excellent control of most buttercups.  Control of buttercups with dicamba products has been more variable, but can range from fair to excellent.  In winter wheat, Osprey (mesosulfuron), Olympus (propoxycarbazone-sodium), and Harmony Extra (thifensulfuron + tribenuron) provide excellent control of smallflower buttercup.

The Longer Story

The word ‘buttercup’ is a common name that is associated with a fairly large group of plants, which are predominantly in the genus Ranunculus spp.  Plants in the buttercup family (Ranunculaceae), are also called the crowfoot family.

In Indiana, there are approximately 16 species in this group of plants called the buttercups (Table 1).  However, other buttercup species can be found in the Western US and Canada, and in the Southern US.

 

Table 1. Ranunculus species that have the name ‘buttercup’ associated with them in Indiana.

 

Buttercups can often be found in no-till row crops, wheat fields, pastures, and neglected areas (Figure 1).  Dense populations of small flower buttercup have been observed in our no-till studies in Southeast Indiana at the Southeast Purdue Agricultural Center.

 

Identification

Typically when thinking of buttercups many think of single yellow flowers with five petals.  In some cases that would be correct, but buttercup flowers can have a variable number of petals within the same species and some flowers can be white or pink.  However, in Indiana they are most often bright to light yellow.  In some species the petals are waxy in appearance.  One characteristic of the flowers that is consistent is that there are many reproductive structures within a flower.  The many female components of the flower are born on a cone like structure in the center and the many male components surround the cone.

These cones in the middle of the flower will eventually become the fruit of the plant.  The fruit of the Ranunculus resembles a raspberry-looking structure (Figure 2).  The seeds are an achene that always have a notch or described as a beak in Britton and Brown’s “An Illustrated Flora of The Northern United States” (Figure 2).  This ‘beak’ is often an identifying character of the species in question; it can be an indiscreet bump to a curled hook.

The leaves are variable even within a specific species¹.  They range from entire to many types of lobbing.  Some are finely divided and others, as in the case of the basal leaves, can be rounded or kidney shaped.  For simplicity sake, we will give identifying characteristics of only five buttercup species that we may often encounter in agriculture.

• Smallflower buttercup [ parviflorus]² – This is an annual and can reach a mature height of 6 to 10 inches.  Stem and petioles can be hairy.  Basal leaves have long petioles and round leaves which are more or less 3-cleft and approximately 1 inch in diameter.  The upper stem leaves are either short petioled, or sessile (attached to the stem without a petiole) and lobed into 3 to 5 linear to oblong lobes.  Flowers are yellow and tiny, measuring 0.06 to 0.2 inches wide.  Close inspection of the flower will show small oblong petals a little longer than the calyx (the whorl of sepals below the flower, the ‘flowers cup’).  The fruit is round and approximately 0.17 inches wide.  The seed is an achene that is flat and has a sharp beak about 0.25% of its length.  The surface of the achene has tiny bumps, but this will require a magnifying glass to see.  Generally blooms in the summer months.
• Tall buttercup [ acris]² – This buttercup is a perennial and can reach a height of 2 to 3 feet tall.  This buttercup is also hairy.  The upper portion of the stems can branch.  The basal leaves are tufted; divided 3 to 7 lobes and the margins of the lobes can be further indented.  The upper leaves have short petioles and are divided 3 times.  Flowers are bright yellow with a waxy appearance and about 1 inch wide.  The petals are 2 to 3 times longer than the calyx and round.  The fruit is bulbous and 0.5 to 0.6 inches wide.  The achene has a short sharp beak.
• Harvey’s buttercup [R. harveyi]² – This buttercup is also a perennial.  It is branched and can reach a height of 8 to 18 inches tall.  Harvey’s buttercup does not have any hair; it is ‘glaborous’.  It tends to branch as you move up the stems.  The basal leaves are on long petiols and round or slightly kidney shaped.  They have rounded ridges on the margins (crenate) or can be slightly lobed and are 0.4 to 1.5 inches wide.  Like smallflower buttercup, the upper leaves are sessile or have small petioles and are deeply cleft about 3 times.  Flowers are bright yellow, with 4 to 8 petals and are 0.5 to 0.75 inches wide.  In this case, the petals are 4 to 5 times longer than the calyx.  The fruit is 0.17 inches in diameter and the achene is tipped with a small straight beak.
• Littleleaf buttercup [ abortivus]^{3, 4} – Annual or biennial, this buttercup is slightly hairy, branches from the base of the plant, and is 6 to 20 inches tall.  Basal leaves are round with margins similar to Harvey’s buttercup and are on long petioles.  Upper leaves have short petioles and are divided into 3 to 4 leaflets.  The flowers are yellow and have 5 small oblong petals.  Petals are close to the same size as the sepals.  Achenes have a small hooked beak.  Generally blooms March to June
• Creeping buttercup or corn buttercup [ repens]^{2, 5} – This buttercup can be distinguished at first glance by having stolons that root at the nodes.  This perennial can spread forming colonies.  This plant can be hairy to sparsely hairy.  Basal leaves and upper leaves have 3 leaflets.  In the upper leaves two leaflets are sessile while the center is extended on the petiole.  Flowers are bright and shinny having a waxy appearance and are approximately 1 inch wide.  Petals are round and are longer than the sepals.  Fruits are 0.3 inches wide and the achene has a short thick and slightly bent beak.

Toxicity:

Buttercups are problematic in pastures.  The buttercup family includes several toxic plants.  This family also contains the larkspur and staggerweed (Delphinium spp.) which are other well-known toxic plants.  The whole plant is toxic to livestock.  Cursed crowfoot (R. sceleratus) is reported to be one of the most toxic⁶.  The toxic component is an acrid volatile substance called anemoral and an irritant called protoanemonin, which is also reported to be a plant produced anibiotic^{6, 7}.  All buttercups have various amounts of these or related compounds.  Symptoms of poisoning are drooling, diarrhea, increased heart rate, behavior changes such as weakness and depression, bleeding, and convulsions^{6, 8}.  Protoanemonin has been reported to cause irritation to the skin in humans.  Amounts of plant tissue required to be dangerous depends on species of plant.  In the article “Poisonous Pasture Plants and Livestock” by Dwight Lingenfelter and Bill Curran of Pennsylvania State University, approximately 1 to 3% of body weight could cause poisoning⁹.  Toxicity does not appear to carry through in the hay, possibly due to the rapid break down of the toxins involved⁶.

Control:

There may be differences between specific species and herbicide efficacy research done on one species may not mean that the same treatment will be successful on all species.  Much of the work done in the Midwest has focused on smallflower buttercup.  Products that are reported to be effective on smallflower buttercup may not be as affective on all buttercups, especially for tall buttercup which is a perennial^{10, 11}.

In studies done at Purdue University¹⁰, smallflower buttercup was controlled above 95% and higher with 2,4-D [1 pt/A], glyphosate [0.5 to 0.75 lb ae/A], Autumn [0.3 oz/A and up], chlorimuron plus 2,4-D, and fall applications of 2,4-D [1 pt/A].  Glyphosate plus 2,4-D can be used as a fall or early spring burndown in corn or soybean.

In winter wheat, Osprey, Olympus, and Harmony Extra provided excellent control of smallflower buttercup^{10, 12}.  Osprey and Olympus can be applied in the fall or early spring before jointing.  Harmony Extra can be applied in the fall or spring after the 2-leaf stage and before jointing.

Buttercups in grass pastures can be an increased concern due to the toxicity posed to grazing animals.  The products Cimarron Plus, Cimarron Max, and Crossbow have excellent (> 90% control) of most buttercups you will encounter.  Other products that have good control of buttercups are 2,4-D, Curtail, Milestone, and Forefront.  Dicamba may provide fair to good control but appears to be a little more variable than 2,4-D.

References:

1. Menadue Y and RK Crowden (1989) Leaf Polymorphism in Ranunculus nanus Hook. (Ranunculaceae). New Phytologist 114(2):265-274.
2. Britton N and Brown A (1913)  An Illustrated Flora of the Northern United States and Canada.  Vol. II.  Dover Publications Inc., New York.  pp. 104-115.
3. Wax LM, Fawcett RS, Moshier LJ, Meggit WF, Wyse DL, Haderlie LC, Messersmith CG, Bendixen LB, Arnold WE, Doll J, McCarty MK, Dorschner KP, and Lund HR (1981) Weeds of the North Central States.  University of Illinois. pp. 82-83.
4. Anonymous.  Missouri Plants. com; Ranunculus abortivus.  Accessed May 21, 2020. http://missouriplants.com/Ranunculus_abortivus_page.html.
5. Uva RH, Neal JC, and DiTomaso JM (1997) Weeds of the Northeast. Comstock Publishing Associates, Cornell University Press.
6. McCain JW, Goetz RJ, and Jordan TN (1985) Indiana Plants Poisonous to Livestock and Pets. Cooperative Extension Service, Purdue University.  pp. 42-63.
7. 7. Blasco R, Mallavarapu M, Wittich R, Timmis KN, and Pieper DH (1997) Evidence that formation of protoanemonin from metabolites of 4-chlorobiphenyl degradation negatively affects the survival of 4-chlorobiphenyl-cometabolizing microorganisms.  Applied and Environmental Microbiology 63(2):427‐434.
8. Majak W (2001) Review of Toxic Glycosides in Rangeland and Pasture Forages. Journal of Range Management 54: 494–498.
9. Lingenfelter D, Hall M, and Curran B (2015) Poisonous Pasture Weeds. PennState Extension. https://extension.psu.edu/poisonous-pasture-weeds. Accessed on May 21, 2020.
10. Johnson, B (2008) Purdue Integrated Weed Management Annual Research Report. 2007-2002. http://www.purdueweedsci.com/research/.
11. Becker R, Miller D, and Salmela T (1999) Tall buttercup (Ranunculus acris L.) control in 1999 following fall herbicide application in 1998 Woodland, MN – Kanabee Co. University of Minnesota Extension Service. https://appliedweeds.cfans.umn.edu/sites/appliedweeds.cfans.umn.edu/files/99mis04.pdf Accessed May 21, 2020.
12. Krausz RF and Young BG (2007) Grass and broadleaf weed management in winter wheat. NCWSS PROC. Vol. 62:92.
13. Annonymous. Pest Facts Sheet: Ranunculus repens L. North American Plant Protection Organization.