How to Manage Pests

UC Pest Management Guidelines

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 primarily transplanted; only rarely is it 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 provide control of broadleaf and grass weeds. Trifluralin (Treflan) controls many grass weeds and broadleaves such as lambsquarters and pigweed. Broadleaf weeds can be controlled in direct-seeded celery by prometryn, which will also make the thinning operation more efficient. For transplanted celery, prometryn or linuron (Lorox) can be applied over the top of transplants.

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 fence rows 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 nonanoic 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.

For both direct-seeded and transplanted celery, a sequential application of trifluralin (Treflan) and prometryn (Caparol) will greatly enhance weed control and allow the use of lower rates of each herbicide, which in turn minimizes soil persistence. Trifluralin must be incorporated 2- to 3-inches deep before planting, which may limit its use in winter-sown celery districts because of wet soils. Trifluralin is very effective on grasses and several broadleaf weeds. Sensitive weeds include lambsquarters, nettleleaf goosefoot, redroot pigweed, purslane, burning nettle, and knotweed.

Both prometryn and linuron (Lorox) cause detectable plant injury, depending on weather conditions, but celery usually outgrows the injury without a significant reduction in yield or quality.

MANAGEMENT AT PLANTING

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. On transplanted celery prometryn can be applied before transplanting or once the plants have become established. Prometryn is very effective on broadleaf weeds, including shepherd's-purse, chickweed, nettle, common groundsel, and hairy nightshade. While it does not effectively control little mallow when applied preemergent, it does well on postemergent control of this weed.

Bensulide (Prefar) can be applied before transplanting or before direct-seeded celery emerges.

MANAGEMENT AFTER PLANTING

Once the crop emerges, closely cultivate the seedling row with precision equipment to reduce weeds. 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.

Prometryn has effective postemergent activity on several broadleaf weeds while they are still in the seedling stage of growth; it is absorbed by the roots and shoots. It can be used either on seedlings or on established transplants. Prometryn can be applied before transplanting. After transplanting, 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 of the weeds have emerged. Sprinkler irrigation should follow application after 24 hours for enhancement of weed control. An application of prometryn (Caparol) at this time also provides additional preemergent control through harvest.

If prometryn will not provide control of all the weeds present, linuron (Lorox) is registered on transplant celery for the control of broadleaf weeds. Apply it when the transplanted celery is established, or once new leaves have emerged. Sprinkler irrigation applied 48 hours after treatment will increase weed control. Because linuron has preemergent activity as well, the irrigation will also enhance preemergent weed control from this application, thus providing season long weed control. It is more selective in clay soils than sandy soils where it effectively controls broadleaf weeds such as little mallow, redroot pigweed, lambsquarters, burning nettle, shepherd's-purse, and hairy nightshade. It provides partial control of emerged yellow nutsedge.

Sethoxydim (Poast) or clethodim (Prism) can be combined with either prometryn (Caparol) or linuron (Lorox) for the postemergent control of grasses.

PUBLICATION

UC IPM Pest Management Guidelines: Celery
UC ANR Publication 3439
Weeds
R. F. Smith, UC Cooperative Extension, Monterey County
Acknowledgment for contributions to Weeds:
C. E. Bell, UC Cooperative Extension, San Diego County
W. E. Bendixen, UC Cooperative Extension, Santa Barbara County
R. J. Mullen, UC Cooperative Extension, San Joaquin County

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