Artichoke is primarily grown as a perennial crop in the central coastal region of California in the major production counties of Monterey, Santa Cruz, and San Mateo. However, significant acreage of annual artichokes are also grown in the region as well as in the southern California coastal counties of Orange, San Diego, and Santa Barbara. Plantings of artichokes as an annual seeded crop have also been successful in the desert and the Central Valley. Each of these areas has specific weed problems and differences in climate and soil types that affect weed management decisions.
Transplanted annual artichokes
Transplanted annual artichokes are grown in the nursery and transplanted onto shaped beds. Plants start growing slowly, requiring from 10 to 14 days before beginning to grow rapidly enough to start to compete with weeds. Transplanted artichokes are typically planted in one seed line per bed and can be effectively cultivated while the plants are small.
Crown-planted perennial artichokes
Crown-planted perennial artichoke fields are planted in late spring. The thick fleshy crowns are separated into large chunks about 8 to 10 inches across and are planted in the field, which has previously been marked out in a grid pattern. The crowns are planted by hand with shovels and covered with 1 to 2 inches of soil. Sprinkler irrigation follows to settle the soil around the crowns and start growth.
Mature plantings are perennial artichoke stands that are at least one year old. Spring harvest is usually completed in May and is followed by mechanical cutting down of the plant to slightly below the soil level (cutback). In summer the artichoke stand is treated with herbicides or cultivated several times to remove weeds between plants. Drain ditches are established in October and November and kept in place during the rainy winter period. Following the rainy period, the drainage ditches are filled in and the area between the plant rows is cultivated for spring weed management.
Producing a uniform, vigorous artichoke stand and then maintaining it in this condition can eliminate many weed control problems. Top growth in a mature stand, when uniform and vigorous, is a very good competitor with most annual weeds. Weed problems are most common in the seedling stage and during the regrowth period each year, when the beds are open and exposed to light, and the artichoke seedlings or crown sprouts are not competitive with rapidly growing weed seedlings.
Monitor fields several seasons before planting artichokes. Keep an inventory of weeds encountered and their relative abundance in the field. Such a record can be helpful in planning which cultural techniques will be most helpful and which herbicides are most likely to be successful. Perennial weeds can be particularly troublesome in artichoke plantings. Select alternative fields to plant to artichoke if buttercup oxalis, yellow or purple nutsedge, bermudagrass, or field bindweed are present.
Cultivation and hand removal of weeds are important practices in artichoke weed management, especially following the vegetative regrowth of perennial plantings. Artichokes have been traditionally planted on a grid system that allows for cultivation in two directions. This gives good mechanical weed control, leaving weeds only in the area around the individual artichoke plant to be hand weeded. Newer plantings of artichoke have gone to a higher density planting, reducing the space between plants in the rows. The higher density limits cultivation to one direction only. Growers who wish to limit herbicide use and reduce hand hoeing costs, should retain the older system of planting so that cultivation can be done in both directions. In this manner, hand hoeing need only be done in the area at the base of the plant.
Preplant herbicides such as glyphosate (Roundup) and pelargonic acid (Scythe) can be used to kill weeds before planting. These herbicides will only kill emerged weeds.
Preemergence herbicides such as pronamide (Kerb) can be used in fields that are free of weeds. These herbicides have residual activity and kill young weed seedlings during the germination process.
When small emerged weeds are present, use diuron (Karmex, Direx), oxyfluorfen (Goal), or paraquat (Gramoxone SL). In addition to their foliar activity, these herbicides also have preemergence soil activity on emerging weed seedlings, but irrigation or rainfall is necessary for this to occur.
Sethoxydim (Poast) is used to control most annual seedling grasses except annual bluegrass. It is effective in the control of perennial grasses such as bermudagrass, but more than one application will be necessary. Its effectiveness is reduced when grasses are under moisture stress. Later growth stages of annual grasses are more difficult to control.
Combinations of herbicides are often used to enhance the weed control spectrum.
Soil residual herbicides such as pronamide and diuron are persistent and can restrict crop rotation choices. In the last two seasons of artichoke production, review labels and select herbicides such as oxyfluorfen or pronamide (lower rates), which may not be as restrictive regarding plantback crops as some of the other materials.
WEED MANAGEMENT BEFORE PLANTING
Weed management in artichokes is difficult during stand establishment, therefore it is important to begin weed management practices before planting the crop by carefully choosing and preparing the field. Choose fields that are known to be free of perennial and other problem weeds. Fallow the field for as long as possible before planting, irrigating often to germinate weeds and cultivating shallowly to destroy them. Do not cultivate too deeply because a new supply of weed seed may be brought up from deeper soil layers. A dry soil mulch will limit weed seed germination because most weed seeds germinate in the top inch of soil.
Use preplant applications of postemergence herbicides such as glyphosate (Roundup) and pelargonic acid (Scythe) to clean up the remaining weeds and a clean, productive field is possible. Herbicides seldom control all of the weeds present. Therefore, a combination of both cultural and chemical control methods gives the best overall result.
WEED MANAGEMENT AFTER PLANTING
Weed management in perennial artichokes can be divided into two periods: stand establishment and mature plantings. Where artichokes are planted as an annual crop, weed control is similar to that during stand establishment for perennial artichokes.
Weed management during the stand establishment period is critical to maximizing the potential of the crop for the rest of its stand life. If weeds are left uncontrolled, they can compete with the developing artichoke plants and severely limit their growth, resulting in a weak, nonuniform stand. Control weeds for at least the first 8 to 12 weeks or until a heavy crop cover is established.
The type of irrigation system used is an important aspect of weed control during stand establishment. Under furrow irrigation, weed germination is limited to the moistened areas, substantially reducing weed germination problems. On the other hand, weed seed germination is enhanced under sprinkler irrigation because dry mulched areas cannot be maintained. Drip irrigation, which is increasing in popularity, allows a high percentage of the soil surface to remain dry, which reduces weed germination even further than in sprinkler-irrigated fields.
Weeds can be controlled by a combination of cultivation, hand-removal, and herbicides. For the wider-spaced planting of transplanted seedlings and for crown-planted artichokes, bidirectional cultivation is helpful in removing all but the weeds immediately around each newly developing artichoke plant. These weeds must be removed by hand, and hand removal may be necessary several times during the first 8 to 12 weeks or so in order to establish a uniform, competitive artichoke stand.
When bidirectional cultivation cannot be used because of narrower plant spacing, cultivate the furrows and shoulders of the beds as soon as transplants are 3 to 6 inches high, and then hand-remove weeds in the crop row.
Another approach is to apply pronamide (Kerb), a highly selective herbicide that is used before weeds germinate (preemergence). It can be applied either over the top of newly planted crowns, or if you are using seedlings, after transplanting. Follow an application of this material with sprinkler irrigation if rainfall does not occur. Once the surface-applied herbicide has been leached into the soil, furrow irrigation may be used.
Sethoxydim (Poast) is useful in controlling most annual seedling grasses (except annual bluegrass) after they have emerged. It is effective in the control of perennial grasses, such as bermudagrass, but more than one application is necessary. Its effectiveness is reduced when grasses are under moisture stress. Later growth stages of annual grasses are more difficult to control.
Once established, a perennial artichoke field has a stand life of 5 to 10 years. At first, newly established fields are often plagued by annual weeds. The most troublesome annual weeds include wild oats and black mustard. As time passes, perennial weeds often become a problem; these include buttercup oxalis, yellow and purple nutsedge, field bindweed, and bermudagrass.
If perennial weeds become established, they can be troublesome throughout the life of the stand by reducing stand vigor and density, and ultimately artichoke yield and quality. Perennial weeds are difficult to control culturally or chemically without injury to the artichoke stand, therefore prevention becomes a major tool in combating these weeds. Make sure that seeds, nutlets, tubers, stolons, and rhizomes of perennial weeds are not moved into clean artichoke fields with planting materials or on cultivation equipment. If spot infestations of perennial weeds are noted in the field, mark the area with flags and destroy the infestation. After the infestation is destroyed, monitor the area for at least 2 years to ensure that reinfestation does not occur.
Herbicides may be used in mature plantings of artichokes to manage both the weeds within the plant row, and the weeds between the rows and/or the winter drain ditch zone.
Pronamide (Kerb) can be sprayed over the plant row before or shortly after artichoke shoot emergence. Apply this herbicide to weed-free areas and time applications early so less than 12 inches of artichoke growth is present in order to get good soil coverage. Sprinkler irrigation or rainfall with at least one inch of moisture is necessary within 72 hours of application for best results.
Once the winter drain ditches are in place (October–November) an application of one or more residual herbicides, such as pronamide and oxyfluorfen, will provide winter weed control. It is difficult to use conventional spray equipment after the winter drain ditches are in place. All-terrain vehicles are used to allow uniform applications under these conditions. The choice of herbicide depends on the weed species present and their growth stage.