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How to Manage Pests

UC Pest Management Guidelines


Yellow nutsedge flowering plant.

Potato

Special Weed Problems

(Reviewed 8/07, updated 8/07)

In this Guideline: More about weeds in potato:

NIGHTSHADE. The best strategy for controlling nightshades is to plan a crop rotation sequence that prevents populations from building up. Choose alternate crops, such as corn, sorghum, cereals, or sugar beets, that can be managed with herbicides that kill nightshades. Nightshades are prolific seed producers; once a nightshade population builds up, it may take several years' rotations to reduce infestations significantly. Tillage, a combination of two or three different herbicides, or multiple herbicide applications may be necessary to control nightshade infestations in potatoes.

NUTSEDGE. Nutsedge is very serious in the Kern County area and must be carefully managed at harvest to prevent quality losses: it reduces potato quality by penetrating tubers. Yellow nutsedge does not tolerate shade; once potato vines have closed over, further nutsedge growth is usually suppressed. In early season areas, herbicides may not be necessary if potato vines cover the ground before nutsedges begin to emerge. Where nutsedges emerge before vines close, use a preemergent application of EPTC before March 1 to prevent nutsedge growth until vines have closed; if necessary, apply EPTC again after about 1 month.

Before harvest, thoroughly apply vine-killing agents to suppress nutsedge growth after vine death and to help prevent tuber damage. Several herbicides can be used to control or suppress nutsedge in rotation crops; some very effective herbicides are available for grains or alfalfa. It is not possible to eradicate nutsedge, however, even when weed control is used during fallow periods.

QUACKGRASS. Quackgrass is a problem in the potato-growing areas in northern California. Its rhizomes may penetrate potato tubers, reducing their quality. It can be controlled, but not eradicated, with a preplant application of EPTC. Work the area to be treated thoroughly to cut quackgrass rhizomes into small pieces before applying the herbicide. Mix EPTC into the soil by discing 6 inches (15 cm) deep in two directions. This usually controls quackgrass for one season and reduces rhizomes. Fall treatments with EPTC may provide additional control.

Before potatoes are planted, use glyphosate to control actively growing quackgrass. Apply glyphosate to quackgrass that is at least 8 to 10 inches tall. For complete control, repeated applications may be necessary. Wait at least 5 to 7 days before preparing seedbeds. After planting, if quackgrass is a problem, sethoxydim (Poast) may be used. Two sequential treatments may be necessary.

[Precautions]

PUBLICATION

[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Potato
UC ANR Publication 3463
Weeds
J. Nuñez, UC Cooperative Extension, Kern Co.
H. Carlson, UC Cooperative Extension, Siskiyou Co.
Acknowledgment for contributions to the weeds section:
W. E. Bendixen, UC Cooperative Extension, Santa Barbara Co.

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