Description of the Pest
The most common crayfish in rice fields is the red crayfish, Procambarus clarkii, but Orconectes virilis, an olive-green colored crayfish, may also be found in canals and streams associated with rice fields. Crayfish reproduce once a year. Mating takes place anytime between spring and autumn. Eggs hatch in fall or following spring. Young crayfish usually remain in the mother's burrow until they molt three times. After leaving the burrow, they molt six to seven more times before reaching maturity. Adult crayfish may live up to 2 years and molt two to four more times, growing to a length of 3 to 4 inches. Their burrows are scattered along ditches, levee banks, and in the field. The crayfish may excavate their water-filled burrows to a depth of 3 feet. When the field is drained, crayfish retreat to their burrows or migrate. If the burrows remain moist, crayfish can survive at least until the next season and maybe longer.
Crayfish are of serious concern because their burrowing in ditches and levee banks may disrupt the irrigation network. Burrows near head gates and weir boxes often make it impossible to maintain an acceptable water head. Crayfish burrowing and swimming may also muddy the water, reducing photosynthesis in submerged plants. Soil forced up around burrows by crayfish after the field is drained may be picked up by harvesting machinery and contaminate harvested grain.
Crayfish occasionally eat rice seeds and seedlings, and their digging may uproot seedlings as well. Floating leaf parts caused by crayfish may resemble feeding by the tadpole shrimp but crushed or macerated, submerged rice seed is unique to crayfish. Extensive injury of this sort has not been a frequent or widespread problem and is mainly associated with fields that are in rice several consecutive seasons.
Cultural practices, such as fallowing or temporarily draining fields, are the key methods available for crayfish control. Pesticides are not registered.
Check the irrigation system for crayfish damage all season long. Repair damage to levees, field weir boxes, and major irrigation structures as soon as possible to prevent accidental draining of the field.
If rice plant stand drops below acceptable levels (25–30 seeds or seedlings per square foot) during the first 2 weeks after flooding and damage caused by crayfish is evident, you can temporarily drain the field to drive the crayfish into their burrows until the rice seedlings are well established. This does not kill the crayfish, but the seedlings are not as susceptible to injury when older. A decision to drain must take into consideration negative aspects such as fertilizer loss, encouragement of weeds or interruption of weed control procedures, interruption of pesticide drainage requirements, and the economics of irrigation.
Leaving fields fallow for a year or more will deter crayfish populations, but the time of fallowing required and crayfish survival may vary depending on the water table, degree of cultivation, and other factors.
Organically Acceptable Methods
Drainage and fallowing, as described above under cultural controls, are organically acceptable management methods.
No chemicals are registered for crayfish control.