The key to controlling weeds, just as in controlling insects and diseases, is proper identification. According to the North Carolina State University (NCSU) Flue-Cured Tobacco Guide, common weeds that affect tobacco crops include nutsedges, morningglories, common ragweed, pigweed and horsenettle. Growers need to identify the types of weeds that are present and should consult their Extension agents or state’s field manual for more information.
Yellow nutsedge and purple nutsedge are two typical weeds found in many production areas. Purple nutsedge has a seedhead that’s reddish-purple to brown and contains tubers in chains connected by rhizomes. Yellow nutsedge has a yellow seedhead with a single tuber on each rhizome. Purple nutsedge is typically more difficult to control than yellow nutsedge.
Morningglories are another problematic weed for flue-cured growers. Morningglory vines wrap around tobacco leaves and stalks, disrupt harvesting and comingle with cured leaves as foreign matter, and growers don’t currently have many chemical choices that provide good control.
Ragweed may lead to a higher incidence of Granville wilt because the bacteria causing Granville wilt can live on its roots. The NCSU guide recommends paying attention to ragweed control in rotational crops, skip-rows and field borders to help reduce populations of the soilborne bacteria that cause the disease.
Redroot pigweed/Palmer amaranth pigweed can grow as high as tobacco and interfere with harvest. In some cases, an additional application of an herbicide may be justified to help control these aggressive weeds. Most herbicides can’t control Palmer amaranth post-emergence, however, so growers often must plan for a pre-emergence application if needed. Some herbicides can control Palmer amaranth, but growers must apply these in such a way that the herbicide doesn’t touch the tobacco, and these types of applications must occur prior to lay-by or after first harvest.
Horsenettle is also known as ball brier. Unfortunately it provides an excellent host for tobacco mosaic virus, but the 2011 NCSU flue-cured guide reports that so far no herbicide labeled for tobacco can effectively control the weed. Instead, the guide recommends controlling horsenettle in a rotational crop such as corn before planting tobacco to help reduce the potential for tobacco mosaic virus.
Category: Diseases & Pests