Onion and Garlic
Agricultural pest management
Special Weed Problems
(Reviewed 1/07, updated 6/08)
YELLOW SWEETCLOVER and WHITE SWEETCLOVER. These clovers are difficult to control in onion and garlic because none of the registered herbicides will control them. Avoid growing onion or garlic crops in fields known to be heavily infested with these weeds.
NUTSEDGE. Nutsedge is a serious weed in spring- and summer-planted crops. Yellow and purple nutsedge are perennial weeds that reproduce from underground tubers, which can survive for several years in the soil. Each tuber contains several buds that are capable of producing plants. Only one bud germinates at a time to form a new plant; however, if that bud or plant is destroyed by cultivation or an herbicide, then a new bud is activated. Control is best achieved by continuous cultivation during a summer fallow period or by rotating to crops where effective herbicide and cultural control methods can be used. Deep plowing with moldboard plows to bury tubers 10 to 12 inches can be used to significantly reduce the population. Dimethenamid provides partial control of this weed if applied before emergence of the nutsedge.
ANNUAL BLUEGRASS. In the lower Colorado River desert, annual bluegrass can reach very high plant populations in a field and become difficult to control. In this area, some fields can no longer be used to grow onions because of annual bluegrass. One reason for this is the regular use of selective grass herbicides (sethoxydim and fluazifop) that do not control annual bluegrass. Herbicides that control annual bluegrass in the San Joaquin Valley and coastal valleys (DCPA and bensulide on onions and pendimethalin on garlic) do not effectively control annual bluegrass in the low desert area. Clethodim does control annual bluegrass.
DODDER. Dodder is a parasitic weed that can build up in onion fields in the San Joaquin Valley and coastal valley growing areas. Avoid fields with a known history of this weed. DCPA (onion and garlic) and pendimethalin (garlic only) suppress and/or control this weed.
UC IPM Pest Management Guidelines: Onion and Garlic
R. Smith, UC Cooperative Extension, Monterey County
Acknowledgment for contributions to Weeds:C. E. Bell, UC Cooperative Extension, San Diego County
D. W. Cudney, Botany and Plant Sciences, UC Riverside
G. J. Poole, UC Cooperative Extension, Los Angeles County