Agricultural pest management
Special Weed Problems
(Reviewed 11/05, updated 11/05, corrected 9/16)
All broadleaf perennial weeds pose a difficult problem for sugarbeet production because all herbicides that control such perennials also kill sugarbeets. The best approach is to control the weeds in rotational crops and only plant sugarbeet if populations of the problem weed are low.
Several annual broadleaf weeds that grow in fall and winter are not well controlled by phenmedipham plus desmedipham (Betamix), including redmaids, miner's lettuce, dogfennel, and knotweed. It is necessary to use other herbicides to control these weeds.
The most widespread problem weed in spring- and summer-sown beets is probably velvetleaf. Control this weed in rotational crops because the only herbicide registered for use in sugarbeets in California that will give more than partial control is triflusulfuron methyl (UpBeet), which requires 2 sequential applications for control. Close cultivation and hand hoeing when velvetleaf is small provides control in sugarbeets. If velvetleaf has not yet become established in a field, a program that prevents seed production should be followed.
KNOTWEEDS and SMARTWEEDS
These weeds can be a problem at times. Preemergence combinations of pyrazon (Pyramin) and ethofumesate (Nortron) early in the season can control them. Split applications of Progress or a tank-mix of Betamix plus Nortron has also provided high levels of control. Partial control of later emerging weeds can be anticipated from the Nortron.
The parasitic plant dodder can invade sugarbeets. The majority of dodder emerges from the soil from mid-March through mid-May, so close monitoring during this period is essential. None of the registered herbicides for use in sugarbeets control this weed. It is probably best to kill the individual infested sugarbeet plants rather than let the weed set seed.
Volunteer cereals are best controlled with timely application of sethoxydim (Poast) when they are young. Otherwise, applying EPTC (Eptam) during the season via water run irrigation can provide preemergence control.
Cocklebur is commonly associated with fields near rice fields and ditches where water can be used to move the seed. Cocklebur is only partially controlled with current preplant or preemergence herbicides. For effective control, apply clopyralid (Stinger) or split applications of triflusulfuron methyl (UpBeet) plus Progress when weeds are no larger than the cotelydon stage. When using Progress plus UpBeet, it is critical that both applications be made at 5-10 day intervals or control will be significantly reduced.
Postplant, preemergence treatment with ethofumesate (Nortron), pyrazon (Pyramin), or a combination of the two can give effective control of germinating weeds. Seedy plants can be controlled with combinations of Betamix plus Nortron, or the premix Progress, as split applications. Once well established, most herbicides are not effective and hand hoeing is required. Clopyralid (Stinger), however, can give partial control of established plants.
UC IPM Pest Management Guidelines: Sugarbeet
K. J. Hembree, UC Cooperative Extension, Fresno County
Acknowledgment for contributions to Weeds:R. F. Norris, Vegetable Crops/Weed Science, UC Davis