Rice pests: identify the damage before choosing a pesticide
In rice, name the pest first: root-feeding weevil larvae, leaf-mining flies, tadpole shrimp, armyworms and weeds each call for a different product and timing. Use the sections below to match the damage to the pest, then read the exact label for the planned use.
Rice water weevil
Rice water weevil adults are gray with a prominent beak and a dark back marking. They leave lengthwise feeding scars on emerged leaves, while the larvae move to the soil and feed on roots, which can reduce tillering and yield. Check levee margins and headlands for early infestations.
After flooding, foliar lambda-cyhalothrin and zeta-cypermethrin treatments kill adults and reduce egg deposition. Diflubenzuron sterilizes females and affects newly laid eggs less than four days old. These treatments interrupt the life cycle before the damaging root-feeding stage; they do not kill established larvae.
Base the decision on field history, nearby overwintering sites and economics. Check ditch banks, riparian vegetation and weedy canal margins. Eggs may be laid before leaves emerge from the water, so few visible feeding scars can still accompany significant risk. Time the selected label’s treatment to adult presence: an early application can dissipate before adults arrive, while a late one misses eggs and larvae already present.
Rice leafminer
Adult leafminers are olive-green flies. Pale, maggot-shaped larvae mine between the leaf layers, and the mined area can fade from light green to yellow or white as it dries. Infestations particularly affect leaves lying on the water surface; plant vigor and weather affect the injury.
Encourage emergence and upright growth through water management to reduce susceptibility. Monitor the affected crop before deciding whether an insecticide is needed.
Tadpole shrimp and early stand loss
Tadpole shrimp chew germinating rice structures, uproot seedlings and muddy the water through digging. Their shed skins may be mistaken for dead shrimp. Germinating seed is vulnerable until roots become established and leaves reach the water surface.
During germination and seedling development, inspect all field quadrants. Use a sampling cylinder or square enclosing one square foot, with sides higher than the water.
Count healthy seedlings in ten samples across the check and record shrimp abundance. Once seedlings have an anchored root system and developed spike, consider treatment when shrimp are present and the average stand falls below 25 healthy seedlings per square foot. Where the stand remains at or above that level, repeat sampling every two to three days until plants emerge above the water.
A drainage decision can affect fertilizer, weed control, pesticide holding requirements and irrigation economics. Before changing water to address a suspected shrimp problem, give the adviser the complete recent treatment history and current water restrictions.
Armyworms
True armyworm and western yellowstriped armyworm occur in California rice. White or broken panicle branches can also come from stem rot, cool-temperature blanking and rat injury, so confirm the cause before spraying.
Keep your spray records in one place. Free to start.
Larvae often hide near the water level by day and feed at night or under cloudy conditions. Natural enemies include parasitoid wasps and caterpillar diseases. For an adviser visit, provide the time of observation, species identification if known, injury type and whether live larvae were found.
Choosing herbicides for a rice farm
Build weed management around the basin and the establishment system: combine weed prevention with field preparation, rotation, tillage, fertilizer, water management and herbicides. Base the program on species, infestation and resistance history, and consider opportunities to rotate crops or fallow.
Uneven basin elevations prevent uniform water depth and can produce uneven rice and weed growth. Establishment systems include permanent flood, pin-point flood, the Leathers’ method, stale seedbeds and dry or drill seeding. A recommendation written for another establishment method may raise different timing and water questions.
Use UC IPM’s rice herbicide table for a California weed-management question. For each candidate, compare active ingredient, trade name, amount per acre, REI in hours, PHI in days, timing, method and comments, then check the full product label for the planned use. Read the label’s partner restrictions and required intervals for the exact treatment sequence.
Match the weed, rice stage and water regime to the individual formulation. In California, penoxsulam granules and suspension concentrate have different timings: Granite GR follows the two-and-a-half-leaf rice stage, while Granite SC starts at the four-leaf stage and ends 60 days before harvest. Both have a listed 12-hour REI and 60-day PHI. Granules enter water; the suspension is generally sprayed later onto exposed foliage. Avoid use on wild rice.
Propanil is a contact herbicide for susceptible watergrass, barnyardgrass and sedges, with suppression of sprangletop and other broadleaf weeds. Stam 80 EDF-CA has a listed 24-hour REI and 60-day PHI. Treatment may cause rice tip burn above 85–90°F. Keep propanil at least 14 days apart from carbamate or organophosphate applications, except for the specified low-dose mosquito-larva-control provision.
Triclopyr targets ricefield bulrush, redstem and waterhyssop and does not control grasses. Expose at least 70 percent of weed foliage for coverage. If water is lowered before treatment, wait at least 48 hours before raising it. Grandstand CA has a listed 48-hour REI and 60-day PHI. Limit applications to two per season, at least 20 days apart, and obtain current county water restrictions.
Product and site checks in California
Use the DPR services guide to reach the official product and county routes. Ask the county agricultural commissioner about current water-management restrictions.
Next step
Bring field observations and the flooding plan to the adviser. Compare candidates in the rice herbicide table and read the selected label.