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Project description

Yellow nutsedge (Cyperus esculentus) management systems for field-grown cut flowers. (00DS027)
Program UC IPM competitive research grants program
Principal
investigators 		C. Wilen, UC IPM, San Diego County
R. Smith, UCCE Monterey County
C.L. Elmore, Vegetable Crops, UC Davis
Host/habitat Flowers
Pest Yellow Nutsedge Cyperus esculentus
Discipline Weed Science
Review
panel 		Decision Support
 Start year (duration)  2000 (Two Years)
Objectives Develop and validate economically viable methods for controlling yellow nutsedge.

Develop degree-day based model for timing of preemergent weed control.

Develop phenological model for postemergent weed control.

Compare mechanical, chemical, and cultural techniques as well as combinations of these methods for yellow nutsedge control.

Final report Yellow nutsedge (Cyperus esculentus) is a perennial weed with impacts productivity and harvesting of field crops. There are a limited number of chemical controls for this weeds and their activity is often erratic. Additionally, these products are limited in their use, as they are not tolerated by a wide range of crops. We conducted trials to examine chemical and non-chemical methods of controlling yellow nutsedge. We also developed models based on phenology that can be used to improve weed control methods.

In comparisons among mechanical, cultural, and chemical control, we found that cultivation or hand-weeding early in the weed's development provided the most effective weed control. This was particularly true in the flower crop as late emerging plants were shaded out or otherwise outcompeted by the more vigorous crop. The principal problem we encountered using herbicides was the lack of crop safety for the flower crops. Halosulfuron injured all four tested species. Metolachlor was less injurious but was not very effective in controlling yellow nutsedge in 2001. Use of black or infrared transmitting plastic (IRT) mulch was moderately effective for weed control but yellow nutsedge grew in holes or slits in the plastic that were used to plant the crop. At the Soledad site where asparagus was grown, cultivation compared very favorably to the control obtained from the most efficacious herbicide, halosulfuron. In this case, there was good crop safety with the herbicides. We could not develop a model for preemergence metoloachlor application since there were no differences among treatment dates. Halosulfuron, cultivation, or hand removal of yellow nutsedge at the 5-leaf stage was the most effective method of control in these studies.

Second-year
progress 		During the second year of this two-year project, we completed two field trials to develop decision support methods to control yellow nutsedge. Treatments included timing of chemical applications to predicted emergence dates; removal of emerged yellow nutsedge plants based on number or stage of development, and use of plastic mulches. We examined these methods on rice flower and sunflower in the first year of the study. During the second year, the methods were tested on asparagus and annual cut flowers. Herbicides used were halosulfuron, metolachlor, and linuron (Soledad only). The 2001 experiments were conducted in Soledad (in asparagus) and Irvine (in cut flowers), California. Although the data has not been completely summarized, we noted that in the asparagus plots, there was clear suppression in the number of nutsedge plants in halosulfuron treatments on May and June evaluation dates and in cultivated plots in June. However, tuber counts in July were too erratic to determine if there was an early effect on tuber production by any of the treatments. There was a general trend of reduced above ground live nutsedge biomass in all treatments except metolachlor in the September evaluations. In the flower crops, we found that the best treatments, either by halosulfuron or by hand removal, were those where yellow nutsedge was removed at low threshold numbers, e.g. whenever there were 3-30 plants per 6m plot, or at developmental stages such as when the yellow nutsedge plants were 20cm tall or had five leaves. Metolachlor was not effective in controlling yellow nutsedge and black and IRT plastics were only moderately effective.

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