Weeds problematic as summer ends

Published on Saturday, 14 September 2013 22:38 - Written by Chad Gulley Extension Agent

As we are ending the summer months and heading to fall, many people are noticing weeds in their lawn and garden areas. Chamberbitter, Virginia Buttonweed, and grassbur are three weeds homeowners are noticing in their landscape.

Chamberbitter (Phyllanthus urinaria), also known as Gripeweed, leaf flower or little mimosa, is a warm season, broadleaf, small tropical annual herb growing up to 2 feet tall. It grows upright, has a well-developed fibrous root system and resembles a mimosa seedling.

Leaves are arranged in two rows on the branchlets and are alternate. The petioles are very short and the blades are papery, oblong, egg-shaped, thin and nearly linear. The greenish-white flowers appear in mid-summer. Its fruit is very small, wart-like, greenish-red, and found under every pair of the feathered leaves. Seeds are small globe-shaped capsules that have reddish blotches.

Virginia Buttonweed (Diodia virginiana) can be one of the worst weeds in homeowner lawns. It grows in a dense matt that can cover large areas in a quick amount of time. It is easy to identify by its white star shaped flowers with four petals. It grows so thickly that it can often choke out our desirable turf species such as St. Augustine.

The plant has an extensive root system and develops underground rhizomes. Buttonweed reproduces by seed, roots and stem fragments. Its prostrate growth habit enables Virginia Buttonweed to survive low mowing. The seeds are spread by wind, wildlife, lawn care activities, plus the seeds have the ability to float and are often carried by water in heavy rain.

The plant is hard to control by hand pulling. Any portion of the plant that breaks below ground has the potential to form a new plant. Because of its persistent nature, there are no effective pre-emergence herbicides. Therefore, control strategies must focus on prevention, early detection, and proper herbicide applications.

Ah, the grassbur, everyone’s favorite grassy weed species right? The grassbur (Cenchrus spinifexis) may be referred to as field sandbur, sandbur, or just plain grassbur. Many people do not realize they even have grassburs until they see the actual bur. At that point it is too late. The bur is the next crop of grassbur as this contains the seed head. Once the seed head is present, control is often ineffective. Field sandburs can also become a problem in pastures and hayfields.

The grassbur is well adapted to dry, sandy soils but may also grow well in other soil types as well. The grassbur is generally not a problem in well maintained turfgrass areas. With proper fertilization, mowing and regular irrigation, your turf can become dense enough to prevent grassburs from becoming a problem.

No matter which weed species you have, control methods will vary from hand pulling to selective use of herbicides. If using a herbicide, be sure to read and follow all label instructions making sure the product you purchase is labeled for control of the desired weed species you are targeting. Also, be sure the labeled product is safe to use on the type of lawn grass you have. Some grass species are more sensitive to certain herbicides.

In weed control, it is also important to make sure the weeds are actively growing in order to obtain an effective control. In home lawns where many people can water their grass species, weeds are probably actively growing. In areas where watering is unavailable, due to the hot, dry conditions lately, some weeds may be in ‘dormant’ stage waiting on rainfall so control will be less effective in this situation.

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