How to Manage Pests

UC Pest Management Guidelines

BITTERCRESS (hairy bittercress, lesser-seeded bittercress, popweed) is a winter annual but will germinate almost any time in container-grown ornamental production areas. It has an upright growth 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 as 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 pre- emergent 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 rootstock as possible, and to control germinating seeds with mulch or preemergent herbicides such as pendimethalin, oryzalin, oxadiazon, oxyfluorfen, or isoxaben.

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, 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.

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.

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.

PUBLICATION

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

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