It's going to be a long weed season...

Jan 28, 2019

With the rainfall we've been having every month in Southern California, there are a lot of weeds out there. For those who work in wildland management where rain is the only source of irrigation, in Southern California the growing season started in October. With the continued rains in November, December and January our hills and valleys are green with a bouquet of weeds. Last year the season began in mid-January.

As I write this, there are grasses and mustards that are in well into flower and immature fruits are starting to appear on these plants. There are also numerous tiny seedlings growing in between the larger and more sparse almost mature weeds. And in between those giant weeds and the tiny cotyledons are a variety of middle-sized weeds too. It's enough to make goldilocks' head spin. What is a land manager to do?

Unfortunately for the weeds, this means that treatments need to begin as soon as possible. Annual weeds must be stopped from producing seeds if a population is to be reduced and extirpated. Since many weeds are in flower that means ‘now' is the right time for treatments, ‘better late than never' is right around the corner, and ‘too late' will be here too soon for the big weeds. 

It also means land managers will need to be careful with what methods they choose to use to reduce their weeds. Some herbicides can take up to two weeks or longer to kill the plant. If those treated weeds are already starting to fruit and certain death will come in two weeks, it might mean that plant will have produced some viable seed before it dies. It will certainly not produce the full complement of seeds had it not been treated, and that is certainly progress. If the goal is removing all your weeds, then it might be worth investigating herbicides or tank mixes that are faster acting or switching methods.

Weeding season is far from over. With so many seedlings growing under a larger canopy of tall weeds, a single treatment is often insufficient to do the job. The tall plants will intercept most of the herbicides and the seedlings will eventually grow through the dead stalks of their weedy brethren. In most cases, since the seedlings are already growing, applying a pre-emergent herbicide now will not injure seedlings. A pre-emergent herbicide will stop any new weeds from coming up if it rains again in February or March (such as tumbleweed or goat's head aka puncturevine), but not those that have already germinated. Herbicide labels are often quite specific about which weeds can be treated as seedlings and which pre-emergent herbicides are only effective before germination.

Many land managers are switching over to mechanical or manual methods of weed control, especially since the Fall rains were not substantial enough to germinate large crops of weeds in October and November. Treating these larger weeds that are flowering will go a long way to protecting our wildlands. It's just the beginning of weeding season and many more weeding days are sure to follow. And if it rains again in February, we could have another crop of seedlings poking up through the soil!


By Chris McDonald
Author - Inland and Desert Natural Resources Advisor, County Co-Director San Bernardino