WEED CONTROL in GARLIC Harry S. Agamalian Farm Advisor Monterey County Garlic Is Grown in Three Different Climatic Zones of California

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WEED CONTROL IN GARLIC Harry s. Agamalian Farm Advisor Monterey County Garlic is grown in three different climatic zones of California. It is produced in the central coastal.area (Monterey, Santa Clara, and San Benito Counties), the San Joaquin Valley (Fresno and Kern Counties) and the low desert areas, namely Imperial County. It is one of the few annual crops that is planted by the use of cloves. The production of garlic requires precise cultural operations. Consequently it is sensitive to any force that may alter its normal growth, resulting in good bulb formation.

The weed problems in the three distriets are somewhat similar, espe cially in the garlics early stages of growth. Since garlic is normally planted in the fall, the winter weeds (I.c:>ndon rocket, shepherd's purse, stinging nettle, goosefoot and cheeseweed) are extremely competitive in the cloves early stages of growth. The current herbicide program is based on the use of Dacthal (DOPA) or Furloe (chlopropham) as a preemergence treatment. These two herbicides are effective when used in this manner under sprinkler irrigation. The use rate for Dacthal is 10 lbs/A Ca.i.) and Furloe 4 lbs/A (a.i.). Dacthal appears to have a greater degree of tolerance to garlic under sandy soils than Furloe. When growing the crop on sandy soils a lesser rate of Furloe is suggested, 2-3 lbs/A Ca.1.). Dacthal is less effective on weeds in the ·mustard family. Furloe is very effective on ahepherd 1e purse, London rocket, burning nettle and volunteer cereals.

Since the garlic cloves may take three to four weeks to emerge, a preemergence weed oil, dinitro or paraquat application may be made after escape weeds have germinated through Dacthal or Furloe treatments. The other basic herbicide used in garlic is (Dow selective or Sinox selective), dinoseb. This herbicide is normally applied after the garlic has two true leaves and a waxy bloom has developed. The use rate is 1 to 1.5 lbs/A (a.i.). The addition of 2-3 lbs. of Ammonium Sulfate per 100 gallons of water will often times increase herbicide effectiveness.

Although the above herbicides have been used in garlic production for several years there is a definite need for additional postemergence herbicides and the extension of the preemergence herbicides for lay by weed control in this long season crop. In the coastal area it may be in the soil for 10 months. 114

At the present time extensive trials are being conducted with bromoxynil, linuron, and nitrofen. All three of these herbicides exhibit varied degrees of selectivity to garlic. Bromoxynil (Buetril1 Brominal) offers control of the mustard family of weeds with no soil persistence. Thia herbicide is being evaluated at )29 l, and 2 lbs/A (a.1.). Linuron (Lorox) will control mustard type weeds and cheeseweed and leave some risidual for late germinating weeds. Experimental trials are being conducted in all production areas at )29 l, 2 and 4 lba/A (a.i.). Nitrofen (Tok-WP) will not control the mustard family of weeds, but would be effective on cheeseweed, stinging nettle and pigweed. Tok-WP is being evaluated under preemergence and postemergence conditions using 4 and 8 lbs/A (a.i. ). Additional studies are being made to determine the advantages of midseason applications of Dacthal and Furloe. The additional treatment of these two products would definitely enhance summer grass control. Based on resistant weeds to Dacthal and Furloe either Lorox or Buxtril/Brominal would greatly improve the weed control program throughout the production districts. One could speculate that Tok-WP would be of limited benefit, because of its weakness to the mustard family of weeds. This would of course depend on the weed population and the time of usage. Other herbicides that have shown tolerances to garlic include oxa diazon (Ron.star) chloroxuron (Tenoran) methazole (Probe) and pronamide (Kerb). Since garlic falls in the category of a miaor crop, the current cooperative research program expects to utilize a IR-IV registration pro cess for either linuron or bromoxynil. At this time Tok-WP is being de veloped by the parent company. In summary garlic weed control programs are highly dependent upon selective herbicides. At the present time the grower continues to utilize hand and mechanical methods for weed control in addition to herbicides. It is most important that the crop not only be free of weeds during its growth cycle, but be free of weeds for mechanical harYest. 115

DISCUSSION SESSION (Edited Summary)

1. Have onions been taken off the Norex label? Mr. Harold Kempen indicated that Norex is not labeled for use on onions and probably would not be in the future. 2. Will Devrinol be labeled for use on tomatoes and peppers as surface applied and sprinkler incorporated rather than power-driven i.Jlcorporated? Mr. Bill Fischer indicated his work with sprinkler incorpo ration of Devrinol was less effective pound-for-pound than when power-driven incorporated. Further, Mr. Ken McA:fee stated that Stauffer Chemical Company was recommending only the power-driven incorporator at this time; additional re search is needed on preemergence applications. 3. What is the future of new herbicides being registered for use on min.or vegetable crops? It was the consensus of the panel members that very few or no herbicides would be registered for use on minor vegetable crops in the near future. The basic reasons given were as follows: (l) companies' reluctance to re~ister herbicide on high-liability crops with low acreage, (2) more required re search and expense to register product on crops, and (3) a degree of grower reluctance to accept responsibility for prob lems that can arise when herbicides are used.

It was suggested that future weed control research in minor crops should be directed to increasing our knowledge on the most effective use of herbicides presently registered.