Irrigation Rates Affect Plant Pests and Grower Profits

Issue: Improvements in irrigation equipment and application technologies have resulted in significant increases in irrigation efficiency. Furthermore, irrigation models such as the PET program have allowed producers to schedule irrigations based on crop water use and not time intervals between irrigations. Unfortunately, most of the research on irrigation efficiency and crop water use efficiency has been conducted in the absence of disease and insect pests. When a plant is infected with a disease, the plant's water use efficiency is reduced. Likewise, severe insect infestations can alter normal water use patterns in cultivated crops. Both situations can undo the economic benefits of increased irrigation.

What has been done/discovered: Over the last three years, Texas A&M researchers have studied the effects of various PET-based irrigation levels on corn, sorghum, sugar beet, and wheat yields; water use efficiency; and disease development. They found that with all grain crops, irrigating at 75 percent PET instead of 100 percent PET typically resulted in equal or greater potential profit to growers because of reduced input costs (cost of seed plus cost of water to irrigate). Irrigating at 75 percent PET also conserved water, reduced energy costs and reduced the incidence and severity of several plant diseases and insect populations. Irrigating less often reduced the incidence and severity of many soilborne plant pathogens because the soil had a chance to dry to the point where the pathogen was less able to move through the soil to new infection sites on the host plant. Conversely, at 100 percent PET-based irrigation, soil conditions favored pathogen movement and increased disease incidence and severity. Most significantly, the research showed that producers could not irrigate crops growing in pathogen-infested soils in the same manner as crops growing in pathogen-free soils because soilborne plant pathogens adversely affected the efficiency of how crops used water.

Impact: The cost of irrigating has risen dramatically over the last year and it now costs approximately $7.50 to pump water an acre-inch, which is the equivalent of an inch of water spread over an acre. At this cost, sorghum growers in 2000 applying 75 percent PET saved approximately five inches of water and $37 per acre in reduced irrigation costs. For corn at 75 percent PET, growers saved seven inches of water per acre and $52 per acre in pumping costs. If this was applied to all irrigated corn and sorghum produced in the upper 21 counties in the Texas panhandle, it could save farmers approximately 200 billion gallons of water and $56 million.

Funding Sources: Texas Corn Producers Board, Texas Sorghum Producers Board, Texas Wheat Producers Board and Texas Agricultural Experiment Station

Contact:
Charlie Rush
Professor
Plant Pathology and Microbiology
Texas A&M Agriculture Program
Phone: (806) 354-5804
Fax: (806) 354-5829
cm-rush@tamu.edu
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