Bosc’s Mille Graines: An Emerging Weed Challenge in North Carolina Turfgrass Systems

Welcome to The Turf Zone Podcast. This episode covers Bosc’s Mille Graines – An Emerging Weed Challenge in North Carolina Turfgrass Systems. Written by Venkateswar Reddy Yelkur, Navdeep Godara, Ray McCauley – North Carolina State University. Bosc’s mille graines [Oldenlandia boscii (de Candolle) Chapman] is becoming an increasingly problematic broadleaf weed in turfgrass systems in North Carolina. Native to the southeastern United States, Bosc’s mille graines is a perennial species in the Rubiaceae family and is commonly found in moist or seasonally wet turfgrass areas, roadsides, and other disturbed habitats. It has a prostrate growth habit and can form dense, mat-like patches within the turfgrass canopy. Bosc’s mille graines can be identified by its linear to elliptic, opposite leaves; highly branched, smooth, green to reddish stems; and deep, woody taproot. The inflorescences have sepals that are visible from aboveground and produce four tiny, white petals from July through September before the plant enters dormancy during the winter months. Bosc’s mille graines can invade turfgrass rapidly because mature plants can produce more than 15 shoots, with each shoot producing multiple seed capsules containing more than 100 seeds per capsule. Consequently, weedy plants that escape control measures can contribute substantially to replenishing the soil seedbank for subsequent growing seasons. Once established, the deep taproot and prostrate growth habit allow Bosc’s mille graines to persist and regrow following routine mowing. These biological characteristics can aid in successful invasion of Bosc’s mille graines in sod production fields and lawns, where infestations can reduce turfgrass aesthetics, quality and sod marketability. Recently harvested sod fields and other disturbed areas may be particularly vulnerable because soil disturbance exposes previously buried weed seeds to light, creating favorable conditions for germination and establishment. In the past two years, several sod producers across North Carolina have reported increasing infestations of Bosc’s mille graines following sod harvest. Traditional programs utilizing a single application of synthetic auxin herbicides failed to provide acceptable control of Bosc’s mille graines in warm-season turfgrasses and led to weed seed-bank buildup following escapes. Although native to this region, Bosc’s mille graines is a relatively new weed in North Carolina turfgrass systems and its appearance can be confused with other weeds of the Rubiaceae family. Several other problematic Rubiaceae weeds common in turfgrass settings are Florida pusley, old world diamond-flower, poorjoe, and Virginia buttonweed. Among these species, Bosc’s mille graines can be easily confused with poorjoe because of their similar appearance. The two species can be distinguished by several characteristics. Bosc’s mille graines has smooth stems, whereas poorjoe has noticeable hairs on its stems and fruit. Bosc’s mille graines flower sepals are visible from above and located close to the petals, while poorjoe has smaller sepals that are positioned at the base of the flower. Misidentification can allow Bosc’s mille graines to establish, replenish the soil seedbank, and make future management efforts more challenging. Factors Affecting Weed Germination Bosc’s mille graines germination is dependent on soil temperature, soil moisture and light. Most seedlings emerge from seeds near the soil surface, where they are exposed to light. Weed germination is limited when seeds are buried more than 1 inch deep. Warm temperatures favor germination, with emergence occurring when day and night temperatures are above 77 and 50 degrees Fahrenheit, respectively, and increasing as temperatures rise. Soil moisture also plays an important role in germination. Bosc’s mille graines can germinate when soil moisture is greater than 20% of field capacity, suggesting that even relatively small amounts