NPSOT Logo
npsot_bluebonnet_full_color

Boerne Chapter

Malta Starthistle—A Really Bad Actor

By Delmar Cain

Growing up in East Texas I hated sandburs. You have probably seen the kind that I am referring to. Since it is a grass (Cenchrus echinatus), it hides in a yard until it matures in the late spring or early summer. Then it extends a long stem that has several seeds at the end, each enclosed in a bur about the size of a pencil eraser. Each bur has spines so sharp you can hardly grab it without getting a painful stab. Sandburs put a real crimp in my barefoot summer-romps in the yard.

But the native sandburs or grassburs are easily controlled, especially if a yard has a well-maintained turfgrass area. Keeping a healthy stand of grass with regular watering and an appropriately high setting on the mower, spells doom for the sandbur.

Field of wildflowers behind fence post
Malta starthistle choking out wild flowers along Old No. 9 Trail at Plant Street in Boerne.

Unfortunately there is a new “Darth invader” on the block and it is not so easily controlled. In Texas the problem is the Malta starthistle (Centaurea melitensis), a member of the Sunflower family, which is a winter annual and occasional biannual. I can find only two good things to say about it. First birds eat (but also spread) its seeds. Second it is not quite as bad as its cousin, the yellow starthistle (Centaurea solstitialis), which has infested millions of acres of parks, croplands, rangelands, open fields and roadsides, mainly in California

But Malta starthistle is definitely a bad actor. Control methods for the two are similar and equally frustrating. Malta starthistle was introduced in California in the late 1700’s and with human help has now moved across Arizona, New Mexico (in both states it is listed as a noxious weed), across West Texas and as far east as Ellis County. Considering that it has moved across tough growing areas, know that it demands respect.

Tall thistle alongside road
Malta starthistle out competing other plants along the road. Broad leaves of Texas thistle at lower right.

The plant begins in winter with a basal rosette. At this stage it can appear similar to an Indian blanket. In the spring one to several flower stems with narrow smooth edged leaves grows quickly, reaching a height of 3 feet. The leaves are glisten with whitish hairs and there are resinous glands overlaid with finer hairs. Each flower head is a half-inch or less, surrounded by sharp spines and at maturity opens at the top with a yellow thistle-like flower. Each plant can produce from 1 to 100 flower heads with up to 60 seeds in each head. That is a potential 6000 seeds per plant by my calculator.

Are you ready now for the really bad news? The plant is extremely difficult to control. It is also highly competitive and (according to the USDA) “often develops, dense, impenetrable stands that displace desirable vegetation.” In addition “the threat of injury from spines on the seed heads diminishes recreational opportunities, livestock grazing and other values.” Whether along the road in front of your house, in your pasture or in your yard, this is not a plant to ignore.

An even larger problem is that in addition to spreading rapidly, mowing probably makes it worse. Chemicals can be effective if applied at exactly the right time of the year. Pulling it by hand is time consuming and costly. Large infested areas may require tilling followed by a fallow time. When it has taken over an area, it requires a three-plus year effort to recover what was there before “Darth invader” arrived.

Roots of a plant
Three seed heads below cut level of a mower.

It is definitely here in Kendall County and I personally can attest that the plant is not easily controlled. I first noticed it about three years ago on the street by my house. I found out what it was and decided I wanted no part of it. I started taking a trash bag with me on my walks and pulled the plants by hand, usually getting a part of the taproot as well. I wore gloves because in addition to the spines, to me, the plant has an unpleasant odor.

Last year I didn’t see many plants. This year there were a few less that the first year, but there were still a lot of plants. The farther I got from my house the more plants I found, even though I had pulled plants on the main road as well. It dawned on me that along the right of way that had been mowed (an absent owner was trying to sell the home), the plants had multiplied.

The problem is that when mowed the plants still produce seed heads below the cut line, some as low as one-half inch from the soil level. Most other plants are controlled by the cut. But the Malta starthistle multiplies and then chokes out the competition. The seeds can be transported by road maintenance equipment and on the undercarriages of cars. Ranchers, neighbors or businesses, which regularly mow their right of ways for reasons of aesthetics or of safety, are unintentionally contributing to the problem. Their mowers are not be set low enough to get all of the seed heads. Mowers, passing vehicles and drainage along the ditches will spread the mature seeds, which may remain viable for several years.

Close up of a seedhead
Seed head with spines.

I am not the one to give advice on how to eliminate this invader on your property. But it should not be casually mowed or simply ignored. Learn to recognize the plant and get your yard workers to help keep it out of your yard. Also get advice from the local County Extension Agent on what the state recommends. Or you might want to check out the recommendations on: www.texasinvasives.org/

However you proceed, please remember that Malta starthistle is different from our native Texas thistle. Our native thistle has stickers on the leaves, but does not cover the ground with spiny burs when it dies. A weed eater easily controls our native thistle, which provides seeds for many birds and nectar for butterflies. As for the Malta starthistle, a plant pulled in time prevents six thousand.

Receive the latest native plant news

Subscribe To Our News

Subscribe to emails from the Native Plant Society of Texas.

Receive emails when new posts are added 4-6 times per month, or receive an email once a month.

Or join us on social media

About the Region

New Braunfels, the location of our Fall 2024 Symposium, straddles both the Edwards Plateau Ecoregion and the Blackland Prairie ecoregion. Interstate 35 divides the city of New Braunfels; its path through the city closely parallels the boundary of these two ecoregions, with the Edwards Plateau on the west side and the Blackland Prairies region to the east. The Edwards Plateau area is also called the Hill Country; however, this general term covers a much larger area extending farther north. Spring-fed creeks are found throughout the region; deep limestone canyons, rivers, and lakes (reservoirs) are common. Ashe juniper is perhaps the most common woody species found throughout the region. Additional woody species include various species of oak, with live oak (Quercus fusiformis) being the most common. Sycamores (Platanus occidentalis) and bald cypress (Taxodium distichum) border waterways. This area is well known for its spring wildflower displays, though they may be viewed in spring, late summer, and fall, as well. According to Texas Parks and Wildlife, average annual rainfall in the Edwards Plateau ranges from 15 to 34 inches.

The Blackland Prairie extends from the Red River south to San Antonio, bordered on the west by the Edwards Plateau and the Cross Timbers, and on the east by the Post Oak Savannah. Annual rainfall averages 30 to 40 inches, with higher averages to the east. This region is dominated by prairie species. The most common grass species include little bluestem (Schizachyrium scoparium) and Indian grass (Sorghastrum nutans) in the uplands and switchgrass (Panicum virgatum) in the riparian areas and drainages. Common herbaceous flowering plants include salvias, penstemons, and silphiums. This area has suffered greatly from overgrazing and agricultural use. Few intact areas remain, though many of the plants can be found along county roadsides throughout the region.

Our four host chapters (New Braunfels, Lindheimer, Guadalupe, and the Hill Country chapters) are located in one or both of the ecoregions above. However, the eastern portion of Guadalupe County also falls within the Post Oak Savanna ecoregion. Annual rainfall averages 35 to 45 inches, with higher averages to the east. A wide variety of hardwood trees are found, including several species of oaks, elms, and in the Bastrop area, loblolly pine (Pinus taeda). Grasses and forbs dominate in the open savannas, with most common grass being little bluestem. Ranching, agriculture, and fire suppression have allowed woody species to encroach on the once-open savannas.

Source: Wildflowers of Texas by Michael Eason