The common name “spider weed” refers primarily to Cleome viscosa, a persistent annual weed. This species is known for its widespread distribution in tropical and subtropical regions globally, aggressively colonizing disturbed areas. Understanding the specific characteristics of Cleome viscosa is the first step toward effective management.
Identifying the Plant
Cleome viscosa is an erect annual herb that can reach up to 120 centimeters in height. The stems and leaves are covered in glandular hairs, giving the entire plant a sticky or “viscid” texture.
The foliage is compound, typically forming palmate leaves with three to five leaflets. These leaflets are elliptic or obovate with entire margins, arranged alternately along the stem. When handled, the plant releases a noticeable, aromatic odor.
Flowering occurs as solitary, bright yellow blooms in the upper leaf axils, each featuring four free petals. After flowering, the plant produces its namesake fruit: a cylindrical, elongated capsule or pod. This fruit is covered with glandular hairs and opens by two valves to release numerous small, reddish-brown seeds. The long, thin appearance of the mature seed pod earns the plant the “spider” moniker.
Growth Habits and Spread
Cleome viscosa is an annual plant that completes its life cycle within a single growing season. It is classified as a ruderal species, thriving in disturbed sites such as roadsides, waste areas, and agricultural fields.
The weed demonstrates a strong preference for sunny locations and lighter soil types, including sandy or calcareous substrates. Its ability to grow well in both seasonally dry and consistently moist conditions allows it to establish itself across a wide range of environments. Reproduction relies entirely on the successful dispersal of its prolific seed production.
The seeds are released from the elongated capsules once they dry and open. This reliance on seed dispersal means that established populations can quickly re-infest the same area year after year, especially when the soil is disturbed by cultivation. Its rapid growth rate contributes to its status as a noxious weed in various regions.
Controlling and Removing Spider Weeds
The most effective management strategy involves preventing seed set. Mechanical control methods are highly successful, particularly hand-pulling or hoeing, when performed before the plant begins to flower and produce its capsules. Due to its shallow taproot system, the plant is easily removed when small.
For larger infestations or in agricultural settings, cultivation techniques provide good control. Repeated shallow tillage can disrupt the germination of new seedlings and bury any plants that have already emerged. Cultural controls, such as applying a thick layer of organic mulch, can also suppress new growth by blocking sunlight and inhibiting seed germination.
When chemical control is necessary, several types of herbicides have been shown to be effective, especially when applied early in the plant’s growth cycle. Foliar-applied herbicides like MCPA and 2,4-D, as well as paraquat, have proven successful for post-emergent treatment. Additionally, some soil-applied pre-emergent herbicides, including trifluralin and atrazine, can be used to prevent seedlings from emerging in the first place. Timing is important for chemical applications, as the rapid growth of Cleome viscosa means it should be controlled early in the season.