“Dear Horticulture Talk,
We are planning to plant some asparagus crowns in the next few weeks. Can you tell me if their is a herbicide that I can use to make my summer weeding more enjoyable.
Thank you for the email regarding weed control in your asparagus patch. To be honest, my personal recommendation is to put in the manhours to pull weeds and keep the area clean. Not only is this the pure way to do it that doesn’t hurt the earth, but is also good for your health by having a bit of weed-pulling-exercise.
If you plan to do a chemical treatment, the one thing to keep in mind as you go about this is to always check with your local ag agent or extension office to make sure that the items recommended here for using as a herbicide are allowed for use in your area. Different states, counties, and municipalities have different rules for different chemicals.
To control weeds before planting, choose an area that is known to be free of perennial weeds. Fallow the area for as long as possible before planting, irrigating often to germinate weeds and cultivating shallowly to destroy them. Do not cultivate too deeply as a new supply of weed seed may be brought up from deeper soil layers.
Before planting, metham or other soil fumigants are often used to control soilborne diseases and nematodes, but these materials can also be used to control annual weeds and reduce perennial weed propagules. Take care to assure that the soil is well cultivated and moist for at least 1 week before an application of metham.
Paraquat (Gramoxone Extra) and glyphosate (Roundup) can be used as preplant or preemergent treatments to control emerged weeds before planting or before asparagus emergence. Make sure the emerged asparagus is not contacted by these herbicides or the plants will be killed.
Once the asparagus is planted, the first 2 years are very important. During the first 2 years after planting, the asparagus plants become established. Weed control is critical to the long-term well-being of the crop during this period, and it relies on both cultural and chemical controls.
Depending on the exact time you are applying your herbicide application:
STAND ESTABLISHMENT. For all three methods of stand establishment, planting beds are used and fields can be lightly cultivated several times during the season to throw soil onto the bed tops, thus keeping weed competition to a minimum.
—Direct Field Seeding. In direct seeding, asparagus is seeded into raised beds that may be cultivated during stand establishment to control weeds in the furrow and bed shoulders. The seedling asparagus is slow to emerge, requiring from 14 to 21 days. Once emerged it continues to grow slowly and is not competitive with most weed seedlings. This emphasizes the need to plant into fields that have a low soil weed seedbank or that have been fallow irrigated and cultivated to reduce the weed seedbank. If it is necessary to remove weed seedlings from the rows of seedling asparagus, this can be done with herbicides or by hand removal. Weed management at this stage is important in order to establish a uniform, competitive asparagus stand. Control weeds for the first 3 to 4 months in seedling asparagus until a heavy fern cover is established.
Linuron (Lorox) controls a broad spectrum of broadleaf and grass weeds and has both soil and foliar activity. Apply linuron as a directed spray to minimize contact with asparagus foliage when asparagus seedlings have from 6 to 18 inches of growth.
Sethoxydim (Poast) is used for controlling most annual grass species, except annual bluegrass. It is also effective in the control of some perennial grass species, however, more than one application is necessary. Its effectiveness requires that grasses not be under moisture stress. Later growth stages of annual grasses are more difficult to control.
Fluazifop-p-butyl (Fusilade) is a selective systemic grass herbicide that must be applied before grasses are 3 to 4 inches tall for best control. Asparagus seedlings are relatively tolerant of fluazifop, which can be applied as a broadcast application.
—Transplanting Seedlings. Planting of 10- to 12-week-old transplants hastens the establishment process compared to direct seeding. Transplants are planted into trenches and usually sprinkler irrigated. This procedure allows weeds to germinate within the planted area. The young asparagus seedling is a poor competitor; thus early weed management is essential for plant survival and growth. As with direct-seeded asparagus, it is necessary to control weeds until a heavy uniform fern cover is established. The same materials used for direct-seeded asparagus can be used for transplanted seedlings.
—Crown Planting. Crown planting is done when the asparagus crowns are dormant. The crowns are set into trenches and covered with 2 to 4 inches of soil, followed by rainfall or furrow or sprinkler irrigation to settle the soil around the crowns. Weed emergence soon follows, often before asparagus emergence. Rapidly growing weeds must be removed from within the planted beds. As the asparagus grows, the furrow and sides of the beds can be cultivated, which throws some soil onto the bed tops. This soil fills in around the plants and provides some weed control as small weed seedlings may be buried. As with the previous two methods of stand establishment, timely cultivations and hand removal of weeds or herbicide treatments are needed during the first season until a uniform fern cover is produced.
Paraquat (Gramoxone Inteon) is a contact herbicide that is effective against both grasses and broadleaf weeds and must be applied before asparagus spears emerge. It is most effective when applied as a broadcast application to weeds that are in the two- to four-leaf stage.
Linuron (Lorox) can be used on crown-planted seedling fields to control a broad spectrum of broadleaf and grass weeds and has both soil and foliar activity. Use linuron as a directed spray to minimize contact with asparagus foliage when asparagus seedlings have from 6 to 18 inches of growth.
Diuron (Karmex and others) may be used in the San Joaquin Delta only on high organic matter or clay content soils. It is a broad-spectrum preemergent herbicide that is useful in controlling emerging annual weeds; however, it is not very effective in the control of common groundsel, sowthistle, volunteer cereals, and wild oats.
Fluazifop may be applied for grass control after the asparagus spears have emerged. It is most effective when applied before the grasses are 6 inches tall.
Once crop plants are established (2 years+), focus weed management efforts first on limiting establishment and spread of perennial weeds, which can reduce the vigor and quality of the asparagus stand, and second on controlling annual weeds to avoid competition during the cutting season.
Weed control in established asparagus is only possible during a relatively short window of opportunity that lasts about 4 months. This period begins with preharvest cultivations, when beds are tilled and shaped before the harvest season. It also includes the harvest period, when shallow cultivations can be used to control weeds; limit cultivation to the furrows, however, because cultivation on the bed tops will interrupt harvest for a period of up to 10 days. The postharvest cultivation, which is possible until the fern limits mechanical activity, is the last chance during the growing season to control weeds by cultivation; after this time the asparagus fern becomes too tall to permit cultivation. Perennial weeds can be difficult to control because of the relatively limited opportunity to cultivate.
Preemergence (When spears are not present). Glyphosate (Roundup) and paraquat (Gramoxone Inteon) may be used on established beds before spears emerge to control newly emerged annual weeds. Asparagus emerged at the time of application will be injured by these herbicides and spears will be unmarketable.
Metribuzin (Sencor) has preemergent activity and postemergent activity on newly emerged annual weeds. If the field is to be cultivated or rotovated, apply after bed preparation. Irrigation or rainfall is necessary to activate this herbicide.
Diuron (Karmex and others) is useful for the control of many emerging annual weeds, but does not control common groundsel, sowthistle, volunteer cereals, and wild oats. Apply it as a band or broadcast application to weed-free beds and incorporate it mechanically or with irrigation if rainfall does not occur. Do not use it on soils with less than 2% organic matter; use lower rates on coarse-textured soils.
Flumioxazine (Chateau) is useful for the control of a wide-spectrum of broadleaf weeds. Apply it no less than 14 days before spears emerge and before weeds emerge, or burn the weeds back with a tank-mix material. Requires 0.25 inch of rainfall or irrigation to activate.
Halosulfuron (Sandea) can be applied before the cutting season to control broadleaf weeds. Do not use an adjuvant with sprays applied before the harvest period.
Napropamide (Devrinol) is useful in the control of winter annual weeds, such as common groundsel, which are difficult to control with other asparagus herbicides. It has no postemergent activity and should be used after bed preparation before weeds emerge. Napropamide requires shallow mechanical incorporation (one to two inches deep), and if rainfall does not occur, it must be irrigated.
Trifluralin (Treflan and others) is active in the control of many grasses and broadleaf weeds with the exception of those in the sunflower, mustard, cheeseweed, and legume families. Use trifluralin before spears emerge or after cutting but before ferns develop. It has no postemergent activity on weeds and must be mechanically incorporated immediately after application two times in opposite directions with disks or rolling cultivators or one time with a power-driven incorporator. Can suppress the growth of Bermudagrass if applied at this time. Will also suppress field bindweed at high label rates.
Linuron (Lorox) can be used before harvest. Linuron has a broad spectrum of annual weed control activity. It also has both foliar and soil activity. Its residual soil activity is shorter than other residual asparagus herbicides. This makes it a better choice to use in the last season of an asparagus planting to avoid long-lasting soil residues that could affect succeeding crops. See herbicide labels for plantback restrictions.
Postemergence (After spears emerge). Dicamba (Banvel) is useful for the control of annual broadleaved weeds and troublesome perennials, such as field bindweed and swamp smartweed. It is applied immediately after spear cutting or as directed sprays to avoid spear and fern contact. Spears that are twisted or malformed as a result of treatment should be cut and discarded. Be sure to comply with all state and county regulations as to proximity to susceptible crops and other restrictions regarding their use.
Linuron (Lorox) can be applied immediately after cutting, but do not harvest within one day after application.
Halosulfuron (Sandea) can be applied during the cutting season to control broadleaf weeds. Do not use an adjuvant with sprays applied during the harvest period.
The grass herbicides sethoxydim (Poast) and fluazifop-p-butyl (Fusilade) can be used on emerged spears. Both have a one-day preharvest interval and work best on actively growing grasses.
Postharvest (Before or at the onset of the fern growth). Halosulfuron (Sandea) can be applied following the cutting season to control broadleaf weeds and yellow nutsedge. A nonionic surfactant or crop oil concentrate may be used with postharvest applications only.
Diuron (Karmex and others) can be used during the postharvest period, but care needs to be taken to not exceed the seasonal limitations.
Linuron (Lorox) can be used during the fern stage by using sprays directed to the base of the fern.
Metribuzin (Sencor) can be used following the final harvest but before spears emerge that will form the fern.
Trifluralin (Treflan and others) can be mechanically incorporated following harvest and before fern growth to suppress grasses and broadleaf weeds.
The grass herbicides sethoxydim (Poast) and fluazifop-p-butyl (Fusilade) can be used on emerged spears and both have a one-day preharvest interval. They all work best on actively growing grasses.
Glyphosate (Roundup) may also be used as a postharvest treatment when all remaining spears have been removed (clean cut). It is useful in controlling emerged annual and perennial weeds; use higher rates of application to control perennials. Direct contact of the spray with asparagus fern can cause serious injury. Glyphosate is useful for spot treating perennial weeds around the edges of asparagus fields to prevent these weed infestations from spreading into the field on incorporation and cultivation equipment.
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