How to Manage Pests
UC Pest Management Guidelines
Irrigation Management Impacts on IPM
(Reviewed 3/17, updated 3/17)
In this Guideline:
Irrigation management is a major component of an IPM program. Standing water prevents vigorous high-yielding alfalfa growth (alfalfa does not like wet feet). Root diseases and nematode infestations are often the direct result of poor water infiltration or lack of drainage. Irrigation management affects diseases, insects, rodents, and weeds. It can also affect the environment, including natural waterways due to off-site movement of pesticides carried in water or on particulates.
Approximately 82% of California's alfalfa is flood irrigated (check-flood or bedded alfalfa), 15% is sprinkler irrigated (wheel-lines and pivots), and perhaps 2 to 3% is drip irrigated. Each of these systems impact on pest management.
KEY IRRIGATION CONSIDERATIONS
Standing water and tail end crop damage
Flood-irrigated alfalfa often results in standing water, particularly at the ends of fields. This can kill plants, cause diseases, and result in weed intrusion, particularly water- loving weeds such as nutsedge and summer grasses. Virtually all flood-irrigated fields have some field-end alfalfa damage due largely to standing water. Reduce tail-water damage with better system design (slope, drain design), automated methods of water shutoff, and drainage ditches to reduce tail-water effect. Be careful when using return water because pathogens and nematodes can be carried in recirculated irrigation water.
Scald is plant death due to standing water in flood-irrigated systems under high temperatures (e.g., over 104º F). Since respiration continues at high temperatures, and oxygen is displaced by water, the plant suffocates and dies. If possible, only irrigate during cool periods or at night, or reduce the irrigation run length in flood systems so the water moves more quickly across fields.
Offsite pesticide movement
Pesticides, particularly organophosphates, can move in solution with irrigation water. Minimize irrigation runoff to protect water quality. Methods to prevent off-site tailwater impacts include: tail-water return systems, managing irrigation water carefully to minimize runoff, and improved irrigation methods such as drip irrigation. For more information on reducing offsite pesticide movement, see Controlling Offsite Movement of Agricultural Residues: Alfalfa, UC ANR Publication 8459.
Soil erosion and particulates
Soil sediments are considered a pollutant in surface waters. While alfalfa is not a major contributor of sediments to surface waters, erosion can occur at the tail ends of fields moving sediments into natural waterways. Careful water management as well as techniques such as vegetated drainage ditches can help minimize soil erosion.
Estimating evapotranspiration to apply an accurate amount of water
Too much water results in a lack of oxygen to the root system, diseases, and plant death resulting in stand loss and weed intrusion. Monitoring evapotranspiration (ET), and irrigating according to crop needs maintains good plant health and saves water. Watching evapotranspiration is particularly helpful with sprinkler and subsurface drip irrigation where it is easier to monitor and adjust application rates.
Soil moisture monitoring
Soil moisture monitoring is an effective method to indicate whether too little or too much water has been applied, and should be used along with evapotranspiration estimates to schedule irrigations accurately and in a timely fashion.
Redesigning surface systems
The use of shorter check flood systems, drip irrigation, laser leveling to remove low spots in the field, and automation of surface water delivery systems will help reduce alfalfa damage from standing water.
Effective use of sprinkler systems and effects on foliar diseases
These can greatly reduce off-site water movement compared with flood irrigation. Sprinklers are particularly useful for stand establishment. However, sprinkler irrigation may encourage foliar diseases such as downy mildew, leafspot, spring blackstem, and sclerotinia. With heavy plant canopies, less frequent irrigations to allow the crop to dry between irrigations may be beneficial.
Subsurface drip irrigation system effects on weeds and rodents
Drip irrigation in alfalfa can result in greatly reduced weed pressure due to dry soil surfaces. However, gophers and other rodents can be extremely damaging in drip-irrigated fields than in surface-irrigated fields due to feeding on the subsurface drip lines, impacting water delivery. If possible, have a check system in place in subsurface drip fields to allow for flood irrigation to help reduce gopher and ground squirrel populations if needed.
Flood irrigation impacts on rodents
Though tail-water in surface-irrigated fields is difficult to manage, flood irrigation nearly eliminates ground squirrels and can significantly decrease gopher numbers.
UC IPM Pest Management Guidelines:
D. H. Putnam, Plant Sciences, UC Davis