Agriculture: Rice Pest Management Guidelines

Crayfish

  • Crayfish: Faxonius (=Orconectes) virilis, Procambarus clarkii
  • Description of the Pest

    The most common crayfish in rice fields is the red crayfish, Procambarus clarkii, but Faxonius virilis, an olive-green colored crayfish, may also be found in canals and streams associated with rice fields.

    Red crayfish reproduce once a year. Mating takes place anytime between spring and autumn. Eggs hatch in fall or the following spring. Young crayfish usually remain in their mother’s burrow until they have molted three times. After leaving the burrow, they molt six to seven more times before reaching maturity. Adult red crayfish may live up to 2 years and molt 2 to 4 more times, growing to a length of 3 to 4 inches. Their burrows are scattered along ditches, levee banks, and in the field. Red crayfish may excavate their water-filled burrows to a depth of 3 feet. When the field is drained, they retreat to their burrows or migrate. If the burrows remain moist, crayfish can survive at least until the next season.

    Damage

    Crayfish are of serious concern because their burrowing and tunneling into 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. Floating leaf debris caused by crayfish feeding may resemble feeding signs caused by tadpole shrimp. Crayfish damage is distinguishable by the presence of crushed or macerated rice seed that is submerged, which 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 for several consecutive seasons.

    Management

    Cultural practices, such as fallowing or temporarily draining fields after initial flooding, are the key methods available for crayfish control. No pesticides are registered.

    Cultural Control

    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 the number of rice plants in a stand drop below acceptable levels (12 seedlings per square foot) during the first 2 weeks after flooding, and damage caused by crayfish is evident, temporarily draining the field will drive crayfish into their burrows until the rice seedlings are well established. This doesn’t kill the crayfish, but the seedlings are not as susceptible to injury when older.

    The decision to drain has negative aspects to consider, such as fertilizer loss, encouragement of weeds or interruption of weed control procedures, interruption of pesticide holding requirements, and the economics of irrigation.

    Leaving fields fallow for a year or more will deter crayfish, but the duration of fallowing required and rate of crayfish survival may vary depending on the water table, degree of cultivation, and other factors.

    Organically Acceptable Methods

    Use drainage and fallowing, as described above under cultural controls, in an organically certified crop.

    Treatment Thresholds

    No pesticides are registered for crayfish control.

    Text Updated: 04/24
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