Application of Low-Volume Water Systems to the Cultural and Biological Control of Root Diseases

1989 Annual Report for LW89-013

Project Type: Research and Education
Funds awarded in 1989: $325,160.00
Projected End Date: 12/31/1991
Matching Non-Federal Funds: $141,950.00
Region: Western
State: California
Principal Investigator:
Milton N. Schroth
University of California

Application of Low-Volume Water Systems to the Cultural and Biological Control of Root Diseases


The overall goal of this project is to develop alternative approaches to the use of pesticides in the culture of tomatoes and peppers. Tomatoes and peppers are among the top ten major crops grown in the United States and the world. They are also crops that rely on heavy use of pesticides.

The approach to this research is to control pests particularly soil-borne pathogens by managing the microflora, or microenvironment, in ways that stimulate growth of beneficial organisms. This is done by water management and the application of plastic mulches which help to conserve water and regulate soil temperature.

Another approach that is being used is to treat plant transplants with beneficial organisms (biocontrol agents) at the time of planting, or to infiltrate them into the soil by adding them to irrigation water using drip irrigation methods.


(1) Manage the soil microflora by regulating water and soil temperatures with plastic mulches.

(2) Use biological control agents to reduce plant disease.

Annual Progress Report for 1992

Project Results

The following are significant findings of research completed in 1992.

Tomato fruit yields were greater in plots where plastic mulches were used compared to control plots without mulches.

More frequent irrigation also resulted in an increase in yield, and there was no difference between 25% water depletion and 50% depletion. Thus, use of less water is good up to a point. Seventy-five percent depletion of water in the soil caused a reduction in yield.

With peppers, fruit yields also were increased by use of plastic mulches but in Arizona the mulches had to be removed before high temperatures occurred. High soil temperatures cause disease to become worse.

Most important, two very serious root diseases of tomatoes corky root and Pythium root rot were reduced by the use of plastic mulches.

A Pseudomonas biological control agent significantly increased fruit yields of peppers in Arizona. This did not work on tomatoes in California, illustrating the site-specific nature of sustainable farming systems.

Dissemination of Findings

Dissemination of results has mainly been by field days at the Maricopa Agricultural Center, AZ, and Westside Field Station, CA, and via small conferences. Some of the results of the California group were described at the Ecofarm Conference held in Asilomar, CA in January, 1992, and the Soil-Root Conference (Agronomy Society of America) in Fresno, CA in February, 1992. Short presentations were made in September, 1992, to organic farmers and SARE/LISA researchers in Santa Fe, NM, and to biological control academic and industrial researchers in Estes Park, CO in November, 1992, on this project.

Additional field days will be held in 1993. And, a poster presentation will be made at the 6th International Congress of Plant Pathology in Montreal in July, 1993. Further presentations are scheduled for January and April, 1993, at the Ecofarm Conference in Asilomar, CA and Tempe, AZ at the Soil Fungus Conference, respectively. A short article is currently being prepared for California Agriculture.


This research has shown that less water up to a point can be applied to tomatoes and peppers without reducing yield. This finding can be implemented now and could conserve substantial amounts of scarce irrigation water. The research also showed that the management of microorganisms can be effected by regulation of water and the use of plastic mulches. The great reduction of corky root disease and Pythium is highly significant.

For the best economic benefits, research needs to be done on more cost effective plastics to use for mulching, such as types that degrade quickly over time. In many regions, particularly the colder areas, use of plastic mulches may be economically feasible now.

Perhaps the most significant finding is that some soil-borne pathogens can be controlled by cultural methods. These methods can be as good or better than the use of pesticides. However, this does not apply to all pathogens. Some root diseases were not affected by irrigation and plastic mulches.