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The P&PDL Picture of the Week
for 29 March 2004

 


Purple, Yellow and White

Glenn Nice, Weed Diagnostician, Department of Botany & Plant Pathology, Purdue University

Spring has often been associated with the return of the Robin, but to a weed scientist and many producers, the start of the season and the warmer temperatures are celebrated with the colors purple, yellow, and white. These are the colors of the flowers of several winter annual weeds that can bloom in the spring. In recent springs comments have come to me about fields in the southern part of the state turning yellow, but I also hear about purple. Below are some of the winter annual weeds that can be found broken out by flower color.

Purple

Purple flowers can be seen on two of the most notorious winter annual weeds in Indiana. Henbit (Lamium amplexicaule) and purple deadnettle (Lamium purpureum) (figures 1 and 2). These closely related plants are often mistaken for one another. They are both mints, so they have the characteristic square stems. They both are low lying plants not getting much taller than 10 inches. The trick to telling the two plants apart is by looking at that the leaves in the upper portions of the stem. Towards the top of the stem the leaves will be attached directly to the stem in henbit. In purple deadnettle, the upper leaves will have short petioles.

Henbit Control, Purdue University Fall Applied Study 2003

Treatment Before Corn % control
2,4-D (1 pt) 99*
2,4-D + Roundup WeatherMax (20 oz) 99*
2,4-D + Sencor (5 oz) + Python (1 oz) 99*
2,4-D + Princep (1 qt) 96*
2,4-D + Basis (0.5 oz) 92*
2,4-D + Princep + Basis 96*
   
Treatment Before Soybean % control
2,4-D (1 pt) 64*
2,4-D + Roundup WeatherMax (16 oz) 81*
2,4-D + Roundup WeatherMax + Canopy XL (1.3 oz) 98*
2,4-D + Canopy XL (2.5 oz) + Express (0.15 oz) 98*
2,4-D + Sencor (4 oz) + Python (1 oz) 97*
2,4-D + Backdraft 85*
Treatments were applied Nov. 8th, 2002 at the Pinny Purdue Research Farm. Weed control ratings were taken April 1, 2003.
* Values with an asterisks beside them are not significantly different in the treatment before corn or treatment before soybean.


Purple deadnettle does not respond well to 2,4-D. In the 2004 Weed Control Guideline for Ohio and Indiana we give henbit a 8 out of 10 for efficacy, but purple deadnettle gets a 4.

Yellow

Cressleaf groundsel (Senecio glabellus) is often mistaken for a mustard due to its prominent yellow flowers and pinnately divided leaves (figure 3). However, at closer inspection, it is actually a composite. This annual can paint a field yellow. It has a hollow stem that can get 1 to 3 feet tall. Its 6 to 12 petal-looking ray flowers distinguish it from being a mustard. Cressleaf groundsel belongs to a group of plants that are considered toxic to cattle and horses. The toxic compounds in Senecio species causes “seneciosis” or “pictou desiease”, due to liver damage. The toxins are found in the plant highest when the plant is bud to flower. Fortunately, cressleaf groundsel is not very palatable and under typical grazing conditions, it is unlikely that animals will consume amounts to cause poisoning. The toxins are still present in the making of hay.

Control: Mowing can reduce cressleaf groundsel infestations by reducing seed production. Mow in the spring from bud to flower. In grass pastures when plants are small in the fall (October or early November) or spring (March or early April) 2,4-D (1 qt/A) can be effective. If plants are larger it is recommended to add dicamba (Banvel/Clairity/Sterling) to the 2,4-D. Desirable legumes will be damaged or killed.

In alfalfa, Sencor (1.3 lb/A) or Velpar (2 to 3 qt/A) are effective when used late February while alfalfa is still dormant. Both Sencor and Velpar can be used in established fields only. Pursuit can give some suppression when applied at 2.16 oz/A in the fall when plants are less than 3 inches tall.

Control of cressleaf groundsel in winter wheat can be done by using a mixture of 2,4-D and dicamba or Harmony Extra in the early spring when the rosettes are small.

In corn or soybean the use of glyphosate and 2,4-D can be used late October or early November. If used in the spring 2,4-D can be used at 1 pt/A 7 days before planting soybean. If more than 1 pt/A is used most labels require that you wait 30 days. (M. Loux, W. Shulaw, J. Stachler. “Cressleaf Groundsel” http://vanwert.osu.edu/ag/Cressleaf%20groundsel%20article%20-%20pictures%20text.pdf accessed March 29th, 2004)

Mustards, such as wild mustard (Brassica kaber) and yellow rocket (Barbarea vulgaris) also have yellow flowers, but with close inspection, these flowers only appear to have 4 petal-looking sepals.

Control: Shepherd’s-purse will be included in the control of the mustards. The two plants respond similarly to herbicide control. Many of the herbicides labeled for fall or spring applications are effective on mustards or shepherd’s-purse. A list of products can be seen in the 2004 Weed Control Guide for Ohio and Indiana. (http://www.btny.purdue.edu/Pubs/WS/WS-16/)

White

Shepherd’s-purse (Capsella bursa-pastoris) is a mustard with a white flower (Figure 4). Similar to the mustards mentioned above, basal leaves are highly lobed forming a rosette. This can sometimes be mistaken as dandelion in the fall when all that are present are the rosettes. To tell shepherd’s-purse from dandelion is to identify if the lobes in the rosette leaves come to points that point towards the center of the rosette. If this is the case, then you are looking at a dandelion rosette. In the spring once shepherd’s-purse starts to bloom you will see tiny white flowers with the characteristic four petal-looking sepals. The pods are triangular in shape, giving it its common name “Shepherd’s-purse”.

Control: See Mustard above.

Common chickweed (Stellaria media), also has tiny white flowers and is no stranger to Indiana (Figure 5). This annual can form a low lying green mat in fields or can be seen in the edges of the grass in our lawns. Stems can reach up as high as 16 inches. Leaves are light green, simple, ovate to broadly elliptic that come to a point. The leaves are between 2/10 to almost an inch long and 1/10 to almost 1/2 inch wide. The flowers appear to have ten petals, but the ten petals are actually 5 petals that are deeply lobed.

Control:

Chickweed control, Purdue University 2003.

Treatment Before Corn % control
  4-1 5-1
2,4-D (1 pt) 99* 99*
2,4-D + Roundup WeatherMax (20 oz) 89* 96*
2,4-D + Sencor (5 oz) + Python (1 oz) 100* 100*
2,4-D + Princep (1 qt) 99* 99*
2,4-D + Basis (0.5 oz) 83* 92
2,4-D + Princep + Basis 86* 78
     
Treatment Before Soybean    
2,4-D (1 pt) 19 20
2,4-D + Roundup WeatherMax (16 oz) 91* 83*
2,4-D + Roundup WeatherMax + Canopy XL (1.3 oz) 94* 96*
2,4-D + Canopy XL (2.5 oz) + Express (0.15 oz) 88* 91*
2,4-D + Valor (2 oz) + Express (0.125 oz) 84* 82*
2,4-D + Sencor (4 oz) + Python (1 oz) 74 85*
2,4-D + Backdraft SL (5 pt) 96* 95*
Treatments where put out Nov. 8th, 2002 at the Penny Purdue Research Farm. Weed control ratings were taken April 1, 2003.
*Values with an asterisks beside them are not significantly different in the treatment before corn or treatment before soybean.


Star-of-Bethlehem (Ornithogalum umbellatum) can form dense mats of dark green narrow linear leaves in the Southern portion of the state (Figure 6). Often a problem in lawns; however, I have also seen it in row crop fields. At first glance, this plant might be mistaken as a thick grass. But in actuality, this plant belongs to the lily family. If you dig Star-of-Bethlehem up you will see that it arises from many bulbs.

Control:
Star-of-Bethlehem is known for being non-responsive to several herbicides. In Indiana it is often a problem in no-till fields where tillage is not an option. Dr. Bryan Young of the Southern Illinois University did some work with star-of-Bethlehem in no-till soybean. Gramoxone Max + Activator 90 (2 pt + 0.25%); Gramoxone Max + Harmony GT + Activator 90 (2 pt + 0.6 oz + 0.25%); Valor + COC (2.5 oz + 1%); Authority + COC (5.33 oz + 1%); and Canopy XL + COC (6.8 oz) all controlled star-of-Bethlehem 95% or greater, 14 days after treatment. Applications were put out April 18th.

Figure 1. Henbit
Figure 2. Purple deadnettle
Figure 3. Cressleaf groundsel flowers and pinnately divided leaves.
Figure 4. Shepherd’s-purse infested field
Figure 5. Indivigual chickweed plant with deeply lobed flower

Figure 6. Tuft of Star-of-Bethlehem

Photo courtesy of Dr. Fred Fishel, University of Missouri

 

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Last updated: 29 March 2004/amd
The Plant & Pest Diagnostic Laboratory at Purdue University