Since the disease is aggravated by extended wet periods, avoid frequent irrigations of excessive duration. Allow the top foot of soil to dry out periodically to inhibit disease, enhance oxygen exchange, control annual weeds and permit harvest. If moisture is in the subsoil, alfalfa's deep root system will continue to supply adequate moisture for growth. Excessive irrigation not only saturates the soil, but runoff water carries spores of the pathogen, causing further spread of the disease. Do not allow irrigation water to stand on fields longer than two days.
Most irrigation is scheduled using plant or soil-based criteria.
Where phytophthora root rot is involved, short frequent irrigations or deep infrequent irrigations will aggravate the disease less than long frequent irrigations. Successful water management and flexibility to adjust water management depends on drainage characteristics of the soil and on prevention of flooding all or parts of the field for extended periods. Land leveling to eliminate low areas and any other methods that provide better distribution of irrigation water help reduce disease development. Alfalfa does not tolerate 'wet feet'. Fields with poor drainage probably should be planted to grasses or a grass-alfalfa mix rather than solid alfalfa.