In an eight-year study soon to be published in Agriculture Ecosystems and
Environment we found weeds to be the most difficult and costly pest problem
to deal with in organically-managed row crops of Northern California,
specifically processing tomato and field corn. Disease and nematode
problems were almost absent, arthropod pests were occasional problems but
could be handled relatively efficiently and economically, but weeds were
costly to manage and escaped control in several years. High weed abundance
was the only pest variable associated with reduced crop yields in the
organic systems.
Weed management in the organic tomato system relied on the use of
transplants to give the crop a head start, mechanical cultivation, and hand
hoeing. This approach has been reasonably effective but resulted in pest
management costs that were 50% greater than those of the conventional
system, which used herbicides. Over the eight years the organic system had
average yields that were 10-15% lower than the conventional system and weed
competition appears to have accounted for part of this difference (nitrogen
availability also played a role). However, with the current high premium
prices for organic processing tomatoes, organic growers can spend the extra
money on hand hoeing and still be as profitable as conventional growers (or
even more profitable). Without premium prices, however, such increased costs
may not be justifiable in a system in which weed management expenses account
for over 20% of total operational costs.
The situation with corn was quite different than that of tomato because the
economic costs of organic pest management were less than conventional pest
management. And pest management costs in general comprised a small fraction
of total operational costs for both management systems. Cultivation
generally proved to be more cost-effective than herbicide use but the modest
use of herbicides did improve average yields (as in the low-input system)
because of occasional weed escapes. Average organic corn yields were about
5% less than conventional yields (again nitrogen played a big role here).
We are currently evaluating several additional organically-acceptable weed
management practices for tomato including flaming, weeder geese, and a
reduced tillage mulch system.
At 11:41 AM 11/18/97 +0000, you wrote:
>Dear Sanetters,
>
>Organic farming is a fast growing-industry in the UK. There are now some 870
>organic producers, farming a total of approximately 50,000 ha, or 0.3% of the
>total UK agricultural area (UK Soil Association figures). Overall if subsidies
>and the premium prices paid for organic produce are taken into account, the
>profitability of organic farming is equivalent to the conventional system.
>
>Weeds are the greatest challenge to profitable organic farming facing the UK
>industry. Perennial weed problems in particular are increasing and in many
>instances have been the cause of complete crop failure. Integrated weed
>management using mechanical, crop suppression and rotational methods is
>accepted methodology but this system is not able to effectively control all
>weeds.
>
>We will be carrying out some research into these weed problems with the aim of
>improving systems and techniques for control of annual and perennial weeds. I
>would value your input on the methods you have found to be most effective for
>the control of weeds and especially perennials. What is the place of
>suppressive crop cultivars in weed control? Are they more likely to be damaged
>than less suppressive cultivars if used in conjunction with mechanical control
>methods? Which mechanical methods are most effective and how much does soil
>type influence your choice of control method (and crop planted)? Any other
>ideas you may have on the subject?
>
>Thanks in advance for your help, I will compile a list of all the ideas I
>receive and post it on Sanet later.
>
>Geoff
>- ------------------------------------------------
>
>Geoff Seavers
>IACR-Long Ashton Research Station
>Department of Agricultural Sciences
>University of Bristol
>Long Ashton
>Bristol
>BS18 9AF
>
>Email Address : geoff.seavers@bbsrc.ac.uk
>Telephone : (+44) (0)1275 392181
> Fax : (+44) (0)1275 394007
>
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>
M. Sean Clark
Research Manager
Sustainable Agriculture Farming Systems Project
Department of Agronomy and Range Science
University of California
Davis, CA 95616
(916) 752-2023
msclark@ucdavis.edu
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