Hand weeding is undoubtedly the oldest method of weed control, as old as agriculture itself. The weed uprooted by hand pulling or with a hoe dies from desiccation. If a hoe were an herbicide (in reality a hoe is a pest control device), the active ingredient would be steel, and the mechanism of action would be cell collapse from lack of water. There are exceptions like common purslane and bermudagrass which will survive uprooting and can survive to re-root in a new location.
Hand weeding is an effective method of weed control, and in normal commercial practice weed control of over 90% can be achieved. If two trips are made through the field near 100% weed control can be achieved. However, hand weeding is expensive – in organic lettuce hand weeding cost exceeds $160 per acre with many fields much higher than this. There are instances in high density baby lettuce fields of hand weeding costs of >$500 per acre. Hand weeding is not a pleasant task it is tedious, dirty and involves long hot days in the field. If better paying or easier work is available than hand weeding, then the alternative work will be chosen. People work in a hand weeding crew because they need a job, not because they want to hoe. Cell phone communication among workers ensures that they know what work is available, where, and most importantly which companies pay the best wage – a true labor market which ensures upward pressure on wages. There are many other costs to hand weeding besides salaries, there are impacts of worker car caravans, CO2 emissions, and worker sanitation.
Weed control in California vegetable crops production systems is accomplished with a series of cultural, chemical and physical weed control tactics that are integrated to reduce weed competition on the crop and minimize weed seed return to the weed seedbank in the soil. In areas with valuable crops, and highly skilled growers like the Salinas Valley, it is possible to nearly deplete the weed seedbank and keep the field clean for years. However, to deplete weed seedbanks it is necessary to have a very effective weed control program that is consistently practiced, and for vegetables this means hand weeding. A reduction in hand weeding means that more weeds will escape control and reseed the field resulting weedier fields.
There are changes afoot in the farm labor pool and the California agricultural industry needs to be prepared for this change. Hand weeding involves many workers and takes a great deal of time. If one looks at the vegetable and strawberry portion of the industry there is need for laborers for hand weeding, transplanting, runner trimming (strawberry), irrigation, equipment operation, transportation and harvesting. If there are enough laborers and growers can afford them, then the system works. However, in the case of a worker shortage, as we face now, then things will change and we will need to adapt.
Most of our farm workers have traditionally come from Mexico. However, with increased border security and a developing economy in Mexico, as well as many other factors, net migration from Mexico has be zero for the past 4 years. Younger people in Mexico are more educated than their parents, making it likely they will seek higher wage careers than previous generations. Current farm workers are aging and leaving the workforce not to be replaced by younger workers. The end result is that there will be fewer workers available for hand weeding in the future.
There is a clear need to be prepared for future labor shortages by developing alternatives to hand weeding. Better and newer herbicides would seem to be the obvious answer for vegetable crops. However, the pesticide industry has little interest in developing new herbicides for high value crops. As a result most vegetable herbicides are more than 40 years old, relics from an earlier time of lower costs and more permissive pesticide regulations. The best alternative available in 2014 is to mechanize the tasks of weed removal previously done by hand weeding crews. There are good options in this area such as machine guided cultivators developed in Europe, which selectively remove weeds from the intra-row space. The trend towards mechanization is not new, with the processing tomato harvester as a prime example. A more recent example is the development of the automatic lettuce thinner which has been designed to automatically thin lettuce, by selective spray applications to remove unwanted lettuce plants. One person operating an automatic lettuce thinner can replace a crew of 20 or more workers with hoes. The automatic lettuce thinners are currently being equipped with lights and used to thin lettuce at night, something hand crews cannot do.
The question is who should pay for this increasing mechanization of weed control in California? Major US machinery manufacturers and agricultural chemical companies focus on major crops such as corn, cotton, soybeans and wheat where the market opportunities are huge compared to crops like broccoli and lettuce. Most agricultural chemical company funds that are invested on specialty crops are focused on disease and insect pests which avoid the risk of crop injury and lawsuits associated with herbicides. Because of the high cost of farm labor in Europe, machinery companies there are developing automatic cultivators for weed removal. However, those companies have little presence in the US, due to logistics, different cropping systems and uncertain demand.
There is a clear need for investment in automated weed removal systems for California vegetable crops. The question remains – who will finance the development of these systems among private and public sectors? There are public agencies, like IR-4, that facilitate the registration of pesticides on minor crops. No such agency, like IR-4, exists to facilitate pest management solutions that do not involve pesticides. I suggest that we need to develop strategies in California and the US for dealing with our mounting weed management challenges in vegetable crops.