Glenn Nice, Weed Diagnostician, Department of Botany & Plant Pathology, Purdue University
Last fall I received several images of dead plants in the eastern side of the state. When the dead plant material was closely inspected it turned out to be the weed prickly sida (Sida spinosa) also known as prickly fanpetals, teaweed and Indian mallow. Although prickly sida is not a stranger to Indiana, it is not one that I typically hear a lot about. However, later in the season last year it was one that I did get a string of inquiries about.
Prickly sida is a branched annual that can grow up to 3.3 feet tall. It is often a spindly looking plant with alternate leaves. Leaves have petioles and are 0.75 to 2 inches long, 0.4 to 0.75 inches wide. Leaves are simple, lanceolate to oval with serrated margins (Figure 1). Flowers are pale yellow, five-petaled and tiny (about 0.2 inches wide). Prickly sida produces a 5-chambered capsule that will split into one-seeded segments that have 2 distinctive spreading spines, or horns.
In studies conducted by Bill Johnson of Purdue University, it was reported Valor XLT (3 oz/A) or Canopy DF (3 oz/A) + 2,4-D (1 pt/A) provided over 94% control preemergence 36 days after application. The products Scepter and Sencor both have excellent activity on prickly sida. Postemergence applications of glyphosate can be variable providing approximately 70% to 90% control. If using glyphosate, use a 1.1 lb ae/A rate on prickly sida that is 6 inches tall. Basagran or Basagran + 2,4-DB can also provide good control of small plants in soybean. Ignite 280 can be used to control up to 4-inch prickly sida in Liberty Link soybean at 22 floz/A. Two applications of Ignite can be made within the labeled window at that rate.
Simazine has excellent preemergence activity on prickly sida. Although it is rated as 9 out of 10 in several weed guides, prickly sida is not listed on the label. Atrazine containing products can provide good to excellent control of prickly sida. Postemergence products labeled in corn that work well and provide good control on prickly sida are dicamba (at 0.25 to 0.5 lb ae/A on small weeds and 0.5 to 0.75 lb ae/A on established weeds), 2,4-D (0.25 to 0.375 lb ai/A), Lightning (1.28 oz/A; Clearfield corn) and Ignite 280 (22 fl oz/A; LL corn).
Click image to enlarge
Figure 1. Prickly sida leaves and capsule