If you are a grower of tree or vine crops in California, I'm sure you are aware by now that Surflan production for the 2001 season will be significantly impacted.

According to Dow AgroSciences, a recent explosion near their southern manufacturing facility has halted production of one of the more popular tree and vine pre-emergence herbicides. As a result, amounts available to growers will be extremely limited this coming season. Therefore, your current stock of Surflan herbicide will most likely be all that is available.

Surflan has been very effective at controlling a wide-array of annual grasses (like annual bluegrass, barnyardgrass, foxtails, etc.) and a select number of broadleaves (like chickweed, lambsquarters, purslane, and pigweeds). It is routinely tank-mixed with a broadleaf pre-emergence herbicide (usually Goal) to provide broad-spectrum weed control. Single or split applications are often made to obtain season-long control.

While it would be nice to say that there are plenty of alternatives and you have nothing to worry about, this is obviously not the case. Because growers are left with limited options, it will be very important that growers carefully select the most appropriate course of action to control their weeds. Certain considerations should be taken when deciding on which alternatives are the "best."

Know your weeds The best starting point is to have a full understanding of which weeds you expect to have in your field. If you have a whole host of weeds that require something other than Surflan for control, this is a good opportunity to look towards other options. If you are unsure of your weed spectrum, start looking for winter annuals as the temperatures begin to decline in the fall and the summer annuals in late winter or early spring.

While pre-emergence herbicides will not control the emerged weeds, it will give you a better understanding of what weeds you do have. You still have the option at that point of controlling them with a timely postemergence treatment (Roundup Ultra, Gramoxone, Touchdown, etc.).

Once you do know which weeds you are battling, you can select from the list of currently registered pre- and/or postemergence herbicides that best fit your needs. The herbicide labels are pretty clear as to the specific weeds each will control. If unsure about the identity of certain weeds, contact your local farm advisor, PCA, or manufacturer representative for assistance.

In many instances, you may have to use combinations of pre- and postemergence treatments to meet your goals. See table I for a list of herbicides that are registered in selected tree and vine crops in California.

Of the herbicides currently labeled, Devrinol or Solicam may offer the closest control when compared to Surflan and are registered in a majority of the tree and vine crops. However, it is important to understand that they will not work for all weed types or field conditions. For example, Devrinol must be incorporated within four to seven days or the efficacy will decline.

Time the treatment just ahead of a storm with a predicted rainfall of at least one-half inch. Leasing additional spray equipment to get the done on time or using a custom applicator may be needed where large acreage is a concern. Keep in mind, Devrinol tends to break down rapidly under wet conditions, especially in the spring and summer under frequent low-volume irrigation. Follow-up sprays with postemergence herbicides also may be required.

In addition to the weeds Surflan controls, Devrinol will also control cudweed, filaree, prickly lettuce, pineappleweed, sowthistle, and others. Devrinol can be tank-mixed with other pre- and postemergence herbicides for broader weed control.

Solicam is perhaps a little weaker on the annual grasses, compared to Surflan, but is very effective at suppressing nutsedge. It is also effective on the mustard species, cudweed, and nightshade and will suppress filaree, groundsel, horseweed, and flaxleaved fleabane. Solicam can be tank-mixed with other pre- and postemergence herbicides for broader weed control.

One of the major weaknesses of Solicam is its performance under light soil conditions and frequent low-volume irrigation. Solicam is fairly soluble in water and can be readily leached into the root zone, causing bleaching of the desirable crop foliage. Caution must be used to avoid possible phytotoxicity. It is important to adjust the rate based on your particular soil texture. Please consult the appropriate label for recommended rates under varied soil types.

Contacts, systemics Finally, we do have a good selection of contact and systemic postemergence herbicides available. They are very effective at controlling most of the annual weeds you will encounter, but must be applied in a timely manner to keep them under control.

If you choose to move towards a more postemergence approach to weed control, keep in mind that the weeds should be treated before they become hairy or mealy or prior to setting seed. For flaxleaved fleabane or horseweed control, it is best to treat when they are no more than four inches tall and before they begin to bolt. Some weeds like spurge can produce a large amount of seed rapidly (in less than 20 days after emergence), so timing of postemergence sprays is critical to reduce the future population. Additional sprays or spot treatments will likely be needed near sprinkler emitters where weed flushes tend to be great.

If entering wet fields is not an option for you in the winter, consider one of the pre-emergence herbicides, followed by timely postemergence treatments as access becomes available.

Several people and commodity groups are pursuing a Section 18 for the use of Visor in almonds. It is not known at this time whether it will be approved, but if approved, will not likely be available until after the first of the year. So in the meantime, look at the other options as a possible solution to the Surflan shortage. If in doubt of your options, contact your local farm advisor, PCA or industry representative for assistance.