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How to Manage Pests

UC Pest Management Guidelines


Uncontrolled weeds growing in potted calla in propagation greenhouse.

Floriculture and Ornamental Nurseries

Special Weed Problems for Container Nurseries

(Reviewed 3/09, updated 3/09)

In this Guideline: More about weeds in floriculture and ornamental nurseries:

BITTERCRESS (hairy bittercress, lesser-seeded bittercress, popweed) is a small winter annual but will germinate almost any time in container-grown ornamental production areas. It grows upright when the seed stalk starts to form and is easy to hand-weed, but as a seedling it is very difficult to remove easily. It produces hundreds of seed per plant, and when the capsule matures it expels the seed some distance from the original plant. Remove this weed before it flowers to reduce seed production and new infestations. Because it is easily missed with weeding, bittercress is almost always present if an herbicide is not used. Herbicides that are effective against bittercress are those that contain oxadiazon, oxyfluorfen, or isoxaben. Sanitation is also important to reduce the spread of this weed. Because the seed of this weed adheres to soil on the outside of the pots, wash pots before reuse or if moving from an infested area. The seeds are also easily carried in irrigation water. Avoid overwatering or allowing water to runoff from an infested area to a clean one.

COMMON GROUNDSEL. Common groundsel is probably the most difficult weed to control in container nurseries in California. It is a hardy weed that grows rapidly and is tolerant to many preemergent herbicides. This weed germinates anytime during the year in container-grown nurseries, whereas in the field it usually germinates in fall and early winter. It grows in an upright manner and has a vigorous root system that makes it difficult to hand-weed. Preemergent herbicides suppress the rooting, making the weed easier to pull. Also, because the seedling is smaller after the use of a preemergent herbicide, competition with the desirable plant is not very significant. Remove this weed before it flowers, however, because its seeds are easily spread by wind. Preemergent herbicide combinations containing oxyfluorfen or isoxaben have given good control.

CREEPING WOODSORREL (Oxalis). Creeping woodsorrel is a perennial plant that grows in a prostrate manner and forms roots along its stems where nodes contact the soil. It is a prolific seed producer. When its seed pods mature, they burst open and forcefully expel seeds, which may land 10 feet or more from the plant. Because the seeds are rough, they adhere to clothing or the surfaces of machinery and are easily dispersed. The primary method of managing creeping woodsorrel is to hand-pull established plants before they set seed, being careful to remove as much of the creeping roots as possible, and to control germinating seeds with mulch or preemergent herbicides such as pendimethalin, oryzalin, oxadiazon, oxyfluorfen, or isoxaben.

CUDWEED. Cudweed is an annual that germinates in fall and grows through the winter and spring. It is a whitish, hairy plant that has small inconspicuous flower heads. Herbicide combinations containing oxyfluorfen have been effective in controlling the seedlings of this weed as they germinate.

LIVERWORT. Liverworts are nonvascular, primitive plants that reproduce vegetatively and through spores. Their flat leaf-like structure is called a thallus and their root-like structure is a rhizoid. These plants can from dense colonies in ornamental containers resulting in crop damage and reduced marketability. Preemergent herbicides containing flumioxazin, oxyfluorfen, or oxyfluorfen in combination with napropamide, oryzalin, oxadiazon, or pendimethalin provide good control of this weed. These products may not be used on every ornamental species so check the label carefully before application. At this time there are no selective postemergent herbicides available.

PEARLWORT. Pearlwort is a low-growing winter annual that roots on the stems and forms mosslike mats in the container. It reproduces by seed. If oxadiazon has been used repeatedly without rotation to other herbicides it becomes a dominant weed in the nursery. A preemergent application of oryzalin, pendimethalin, or isoxaben will give control.

SPURGE. Prostrate or spotted, and creeping spurge are low-growing annuals that grow rapidly and quickly produce seed. They are more easily removed when older but by then the seeds have usually been produced and fall off the plant into the container when the weed is removed. Mulching reduces establishment. The preemergent herbicides isoxaben, pendimethalin, oryzalin, oxadiazon, and oxyfluorfen will control spurge.

WILLOWHERB. There are at least two species of willowherb found in nursery containers, Epilobium paniculatum and E. ciliatum. Willowherb seeds profusely and the seed blows in the wind. Preemergent herbicides that have been effective in controlling germinating seeds include oxadiazon and oxyfluorfen.

[Precautions]

PUBLICATION

[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Floriculture and Ornamental Nurseries
UC ANR Publication 3392
Weeds
C. A. Wilen, UC IPM Program, UC Cooperative Extension, San Diego County
Acknowledgment for contributions to Weeds:
C. L. Elmore, Vegetable Crops/Weed Science, UC Davis

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