Bindweed is a deep-rooted perennial that is difficult to control once it becomes established. Herbicides are not effective against established plants. Seedlings can be easily identified from established plants by the presence of cotyledons. Established plants require cultivation for control. Field bindweed is best controlled after a cereal crop when actively growing bindweed can be treated in fall with glyphosate (Roundup) or a similar material. Rotation with cotton, corn, or lettuce has helped reduce field bindweed in some areas. The frequent cultivations used in lettuce help control this weed and in cotton, glyphosate can be applied with hooded sprayers or over the top if Roundup Ready cotton is planted. In corn, both cultivation and selective herbicides can be used to control field bindweed.
The nightshade family includes black nightshade, hairy nightshade, cutleaf nightshade, groundcherry, and several others. These annual weeds are related to eggplants and are resistant to many of the herbicides commonly used in eggplant production. Soil fumigation with metam sodium or soil solarization can be very effective if it is done properly. Cultivation is also effective. Rotating to crops where available herbicides control nightshade helps to avoid seed buildup. Roguing nightshades from the field to reduce seed deposition is effective if the weeds can be distinguished from the crop plants.
Nutsedge is a perennial that reproduces primarily through abundantly produced tubers, but can also produce viable seed. Tubers can remain viable in the soil for several years until conditions are favorable for growth. The tubers contain four to seven buds, each capable of producing a plant. Generally only one bud will germinate on any tuber; however, if the top is removed by cultivation or herbicide treatment, another bud will form a new plant. Fields infested with nutsedge should not be planted to eggplants. If this is not possible, deep plowing (9–10 inches) with a moldboard plow before listing the beds can bury nutsedge tubers to a sufficient depth so that their emergence is slowed down during the crop establishment period. The soil has to be thoroughly inverted to obtain good control. Yellow nutsedge can be particularly troublesome in Southern and Central California because it can grow through the black plastic mulch used in this area on fresh market eggplants.
Metam sodium applied before planting only delays emergence of nutsedge, especially on sandy soil, but does not provide effective control. Soil solarization may not be effective in soil heavily infested with nutsedge tubers. Halosulfuron (Sandea) provides effective control of both yellow and purple nutsedge after it emerges.
Little Mallow (Cheeseweed)
This aggressive annual and occasionally biennial weed produces seeds that remain viable in the soil for many years. It is only marginally controlled by napropamide and, as a result, is frequently present in eggplant fields. It can be removed in hand-weeding and thinning operations although the deep taproot makes this job difficult. Cheeseweed that escapes control can make harvest operations difficult.
Bermudagrass and Johnsongrass
The preplant herbicide bensulide (Prefar) effectively controls these perennials growing from seed but it will not control growth from established rhizomes.
Disk fields infested with bermudagrass and johnsongrass plants several times to cut the rhizomes into short segments. This will significantly enhance the effectiveness of clethodim (Select Max), which can be used to selectively control these two weeds in all varieties of eggplants. The grasses should be growing vigorously at the time of treatment and an oil or paraffin-based adjuvant should be added to sethoxydim. If regrowth occurs, a second application will be required.