Weeds Pages
Weeds reduce celery yields by competing for light, water, and nutrients, delaying maturity, and by reducing the efficiency of harvest. Weed control is especially critical in the early part of the season, to ensure a high quality crop at harvest.
The major counties where celery is grown include Monterey, Santa Barbara, and Ventura counties and to a lesser degree Santa Cruz, Orange, and San Benito counties. Within these counties, celery is in various stages of growth throughout the year; thus it encounters both winter and summer weeds. Weeds that commonly require control are little mallow, chickweed, nettleleaf goosefoot, lambsquarters, common groundsel, London rocket, burning nettle, redroot pigweed, tumble pigweed, purslane, shepherd's-purse, and annual sowthistle. Perennials weeds are usually not a major problem in the intensively farmed land used for celery, with the exception of yellow nutsedge in certain locations.
Celery is almost entirely transplanted and only rarely direct-seeded. Although transplanted celery is planted to a high density (37,000 to 44,000 plants per acre), the early stages of growth do not provide much shading of weeds. This lack of shading together with the high moisture regime required following transplanting favor weed growth.
Direct-seeded celery is usually grown on double row, 40-inch beds. Weed control in field-sown celery or seedbeds is critical because of the long germination period (21 or more days) and subsequent slow growth of the seedlings. A high moisture regime during seed germination invariably favors weed growth. The slow-developing seedling provides little to no competition with weeds. By the time the celery seedling is in the 1- to 2-true leaf stage, weeds can completely obscure the celery plant. Mechanical cultivation typically removes weeds on 80% of the bed and the remaining weeds removed chemically or by hand.
In general, weed management in celery depends on good cultural practices such as field selection, crop rotation, preirrigation followed by cultivation, in-season cultivation, and hand hoeing. Herbicides can help provide control of broadleaf and grass weeds.
Monitoring
To plan a weed management program, it is essential to know which weed species are present and the relative abundance of each. Conduct weed surveys of each field at least twice a year: the first after planting but before weeding and the second just before harvest. Records from previous crops will indicate what weeds escaped control and will likely infest the celery crop. Also examine fencerows and ditch banks, as these are other sources for weed invasion. Pay special attention to where perennial weeds such as field bindweed occur so that follow-up control measures can be taken.
Management Before Planting
An effective weed control program must take into account weed histories, soil types, celery culture, and subsequent rotational crops. Using a combination of weed management methods has the benefit of minimizing costs, while obtaining optimum weed control.
Crop Rotation
Celery is grown in rotation with either cool or warm season vegetable crops. The best crops to use in a rotational scheme are those that have effective weed management systems, such as strawberry, lettuce, or broccoli. Rotating to strawberries is especially useful in fields where yellow nutsedge is a problem; preplant fumigation helps to manage this weed. In using herbicides, always consider crop rotation schemes that allow for maximum flexibility in regards to plantback restrictions.
Field Selection and Preparation
Choose field sites that have a low weed population. If previous crops had heavy weed infestations, soil tillage practices such as plowing may reduce weed seed density. For summer-planted celery, preirrigation of preformed beds, followed by minimum tillage, will often reduce initial weed competition at seeding or transplanting. This procedure must be planned in advance to accommodate planting schedules.
Herbicides
Glyphosate (Roundup, Touchdown) and pelargonic acid (Scythe) can be used to control small weeds that have emerged before transplanting or field seeding, or to control weeds that have emerged between field seeding and emergence of the crop. Oxyfluorfen (Goal) can be applied to fallow beds up to 30 days before transplanting celery, but the beds must be thoroughly worked before planting.
Transplanted
For transplanted celery, prometryn and S-metolachlor (Dual Magnum) can be applied pretransplant.
Direct-Seeded Celery
Trifluralin (Treflan), which controls many grass weeds and some broadleaves (lambsquarters, pigweed) can be applied before planting direct-seeded.
Management At Planting
Transplanted
On transplanted celery prometryn, S-metolachlor, bensulide (Prefar), and trifluralin can be applied before transplanting. Trifluralin must be incorporated 2- to 3-inches deep, which may limit its use in winter-sown celery districts because of wet soils. S-metolachlor is effective on some broadleaf and grass weeds and is particularly useful for controlling yellow nutsedge.
Direct-Seeded Celery
Broadleaf weeds can be controlled in direct-seeded celery by prometryn, which will also make the thinning operation more efficient. For direct-seeded celery, prometryn can either be applied after seeding, or after crop emergence, and sprinkler irrigated within 48 hours. The treatment may be limited to a band application over the seed line or treating full coverage, depending upon weed history of the field and economics.
Management After Planting
For field-seeded celery, several irrigations are required to ensure germination and emergence. Following transplanting, the soil surface must also be kept moist for about 2 weeks by repeated sprinkler or furrow irrigation. The need for repeated applications of water during the period immediately following planting or transplanting limits access to the field. After celery plants are established, the irrigation interval is extended and the field becomes accessible for weeding and cultivation practices. Thinning and weeding of the celery is normally done at the three- to four-leaf stage. Hand-hoeing is essential to remove the weeds between the plants not controlled by herbicides or tillage. Depending on weed density, this practice may involve 10 to 15 person hours per acre.
Before making an herbicide treatment after planting, celery seedlings should have two to three leaves, while transplants should have new leaves developing from the crown, usually the third or fourth week after transplanting. At this time most weeds have emerged. Sprinkler irrigation should follow application after 24 to 48 hours for enhancement of weed control.
Direct-Seeded and Transplanted
Herbicide applications after transplanting can provide preemergent and postemergent weed control. They are more selective in clay soils than sandy soils where they effectively control broadleaf weeds such as little mallow, redroot pigweed, lambsquarters, burning nettle, shepherd's-purse, and hairy nightshade.
Transplanted Only
Prometryn and linuron (Lorox) provide effective postemergent weed control of many broadleaf weed seedling in transplanted celery fields. Both can be applied after transplanting over the top of transplants. Prometryn is effective on many broadleaf weeds, including little mallow when applied postemergent. Linuron provides partial control of emerged yellow nutsedge. Both prometryn and linuron cause detectable plant injury, depending on weather conditions, but celery usually outgrows the injury without a significant reduction in yield or quality. S-metolachlor can be applied as a directed or broadcast application following transplanting celery.
Both Transplanted and Direct-Seeded
Sethoxydim (Poast) or clethodim (Select Max) can be applied to control grass weeds. Carfentrazone (Shark) can be applied with a hooded sprayer to control the weeds in the furrows between the rows.