Agriculture: Cole Crops Pest Management Guidelines

Special Weed Problems

Burning Nettle

Burning nettle is a winter annual in the San Joaquin Valley and southern desert and grows throughout the year in coastal areas. This broadleaf produces abundant seed. Its irritation of skin on contact makes thinning and weeding work difficult and slow, increasing the cost of labor. Preplant applications of oxyfluorfen or trifluralin will control it.

Common Chickweed

Chickweed is a winter annual weed that is very competitive with cole crop seedlings. Preplant incorporated applications of napropamide control chickweed.

Common Groundsel

Common groundsel is a winter annual broadleaf in most of California but can grow throughout the year in coastal areas. It is not a problem in the southern desert.

Use cultivation to bury viable groundsel seed a few inches below the soil surface. Groundsel seed can only emerge if within ½ inch of the soil surface.

Rotate to a crop for which registered herbicides provide effective control. Before planting, irrigate to germinate seed, then shallowly cultivate as close to planting as possible to reduce groundsel emergence in the crop. Throw dry soil as a dust mulch along the seed row during the first cultivation to reduce subsequent emergence of groundsel.

Common Purslane

Purslane is an annual broadleaf that grows rapidly in spring and summer. In addition to applying an effective preemergence herbicide, be sure to remove from the field uprooted plants where the soil surface is wet. Otherwise, uprooted purslane will reroot, continue to grow, and produce numerous seed.

Cruciferous Weeds

These include but are not limited to weedy mustard species, London rocket, and shepherd's-purse. They are very difficult to control with herbicides because they are in the same plant family as cole crops. If these weeds are abundant, rotate to a crop where they can be easily controlled with herbicides.

Little Mallow

Also known as cheeseweed, little mallow is a winter annual broadleaf and occasionally a biennial or short-lived perennial. It is very competitive in cole crops and is common in coastal areas and in the southern desert. It germinates 1 to 2 inches deep in the soil, which allows it to escape preemergence herbicide applications.

Nitrogen fertilizer surface applications are very effective when applied to cheeseweed plants in the cotyledon to two-leaf stage. A pretransplant treatment of oxyfluorfen is effective against this weed. Applications of capric and caprylic acid can also be effective if applied to emerged mallow either during the fallow period, or if applied with hooded sprayers after the crop has emerged.

Nutsedges

Nutsedges are herbaceous perennials in the sedge family that superficially resemble grasses. Moist soil and warm, sunny conditions favor their growth. Nutsedge infestations can increase or spread via both seeds and tubers. However, in many regions, nutsedges do not produce viable seed, and tubers are the main source of increased or persistent infestations. Tubers are easily moved with soil, contaminating farm equipment.

Use specialized moldboard plows (such as Kverneland) to bury nutsedge tubers 16 inches deep. This can reduce nutsedge numbers by 95 to 98%. Tubers must be left deeply buried for at least 2 years for before deep plowing again, otherwise this method will not be effective.

No herbicides are available to control nutsedge in cole crops. In infested fields, plant cole crops during cool weather, when nutsedge does not actively grow; during the summer, plant other crops in which nutsedge can be somewhat controlled with herbicides, such as beans, peppers, or tomato. In coastal areas, rotate to a crop that receives preplant fumigation, such as strawberry. Fumigation with metam products will control yellow nutsedge but will only partially control purple nutsedge.

Cultivation is the only method for removing nutsedge after planting cole crops. Cultivate nutsedge before it has four true leaves (before tuber production). Cultivating when plants are larger allows more tubers to form. Tubers persist in soil for long periods of time, and when the soil is warm, they sprout and produce aboveground growth that may interfere with subsequent crops.

Prickly Lettuce

Prickly lettuce is a common winter annual or biennial broadleaf in the Central Valley and southern desert. It germinates after fall irrigations or winter rains. Napropamide and oxyfluorfen herbicides control prickly lettuce.

Sowthistles

Sowthistle is a common winter annual that germinates throughout most of the year in coastal areas and from late fall to early spring in other locations. Napropamide and oxyfluorfen herbicides control this weed. Preplant cultivation can also provide some control. If this weed is not completely controlled early in the season, it can grow above the crop and produce and disperse seed later in the crop cycle.

Text Updated: 10/19