Invertebrate pest management in rice

Numerous species of invertebrate animals are found in rice fields. These species are adapted to utilize the short-term aquatic environments of a typical rice field.  The quickly changing nature of a rice field, i.e., dry, followed by flooded, quickly developing plant material and finally drained with senescent plants, require specialized life histories in the invertebrates.  Insects, spiders, crustaceans, and other groups comprise the invertebrates.  Grigarick and co-workers (1990) sampled about 60 different species of arthropods in a survey of a California rice field.  

Most of these invertebrates inflict no damage to rice plants, whereas about ten species can hinder rice productivity and yield.  Rice is most susceptible to damage during the first six weeks after seeding.  A couple of species of insects and also of crustaceans hinder seedling establishment.  During the vegetative growth phase, a few species potentially can be problematic by feeding on foliage, but populations are generally low.  Invertebrate pests in California are rare during the grain-filling period.  Fortunately, the stink bug pests that severely impact grain quality of southern U.S. rice are absent in the California system.  Similarly, leafhopper and planthopper species (and associated virus diseases they transmit) that severely impact Asian rice production as well as stem borers also do not occur in California.

Another segment of the invertebrate complex in rice fields is the mosquito population and the natural enemies that feed upon aquatic mosquito eggs, larvae, and pupae.   These individuals have no direct impact on rice plant productivity but rice production practices can impact the mosquito populations and management.  This area is gaining increased importance with the recent upswing in mosquito-vectored diseases.

A rice field is a definite “agroecosystem”.  Management actions intended to facilitate seeding establishment, weed control, plant growth (fertilization), etc. have effects on populations of invertebrates.  These effects could be positive or negative on levels of these invertebrates.  Discussions of management of invertebrate pests will be divided into three portions of the growing season, 1.) seeding to 4-5 leaf stage (0 to ~30 days after seeding), 2.) 5-leaf stage to heading and flowering stage (30 to ~90 days after seeding), 3.) heading to harvest.

Seeding to 4-5 Leaf Stage
Tadpole shrimp, crayfish, seed midge, and rice leafminer all hinder rice seedling establishment and early-season growth.  In addition, rice water weevil adults feed during this period; however, the primary damage is done later in the growing season by the rice water weevil larvae.  Insecticidal management of this pest is targeted toward the adults so it is appropriate to consider this pest in this section.

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