Protection of Rice from
Invertebrate Pests-78
 
 

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Project Leader and Principal UC Investigators

A.A. Grigarick, UC Davis

M.O. Way

F.G. Zalom

T. Esser

 

 Invertebrate pest The water weevil, armyworm, tadpole shrimp, and rice seed midges control: all received research attention during 1978. Studies determined factors that allow the buildup and movement of water weevil populations, analyzed the effect of water weevil and armyworm injury on rice yields, and evaluated pest control methods with emphasis on maintaining environmental quality.

Armyworm injury. The degree of defoliation of rice by armyworms (Pseudolita unipuncta and Spodoptera praefica) varies considerably from year to year and field to field. Injury directly to the heads is the most obvious and probably the most severe, but there is considerable question as to the effect of injury to the foliage.

An experiment to simulate feeding of armyworms on rice foliage was made on four rice varieties-late-maturing Calrose (tall) and Calrose 76 (short) and early-maturing S6 (tall) and SSS6 (short)-two to three weeks before average heading. When all of the leaves were pruned, the percent reduction in yield ranged between 65 and 76 percent of normal for the four varieties. When 50 percent of the leaves were cut, the yield was reduced to between 44 and 54 percent of normal. Considerable blanking was also noted in the pruned treatments. These results indicate that heavy armyworm infestations can cause significant yield reductions.

 

The western yellow striped armyworm defoliates rice in varying degrees from year to year and can cause significant grain yield reduction, but the insect's injury to panicles of rice probably causes more severe grain reduction than its leaf feeding.

Rice water weevil flight and ovipositon. The knowledge of movement of the rice water weevil into a rice field, within the field and from field to field in relation to oviposition on rice plants is very important for developing control procedures that are not strictly preventative. Adult weevil movement from field to field and oviposition on rice were determined by dissecting weevils collected in the paddies and determining the condition of their flight muscles and development of their eggs. The maximum egg development occurred when the weevils would be ovipositioning on three- to four-week-old rice plants. By this time the flight muscles of the weevils had degenerated to provide additional energy for egg formation.

The absence of well-developed flight muscles in rice water weevils collected from rice fields three to seven weeks following flooding indicates there is little or no movement of weevils in or out of fields during the peak oviposition period. This suggests that it may be practical to direct control efforts against adults rather than larvae.

"The 1978 results offer considerable promise for estimating potential yield losses and determining at what population level control measures should be applied."

Water weevil injury. For the first time with a natural population of weevils, a correlation was observed between number of adult rice water weevil feeding scars on the newest unfurled leaves at the third and fourth weeks of plant growth and eventual yield of the plants. Previous experiments with artificial infestations showed a good correlation between an increase in feeding scars and a decrease in yield, but tests with natural infestations in 1977 were not conclusive. The 1978 results offer considerable promise for estimating potential yield losses and determining at what population level control measures should be applied.

Chemical control of rice water weevil. Experiments with Dimilin (not yet registered) for control of rice water weevil showed it to be effective at 0.1 pound active ingredient per acre, the lowest rate tested in the greenhouse. Field studies in aluminum rings with 0.5 pounds active ingredient of Dimilin per acre indicated that it needed to be applied before the weevil infestation or within one week after the infestation. Application of Dimilin at 0.5 pounds active ingredient per acre one week after rice emergence resulted in $0 percent greater yields than untreated controls. The same rate of application at one week after emergence, followed by a second application two weeks after emergence produced 39 percent greater yields than the controls.

Sevin, Flit MLO, Bux and carbofuran treatments also were evaluated. Some of the results were inconclusive; others indicated these chemicals were not as good as Dimilin for water weevil control.

Genetic control of rice water weevil. A standardized test for tolerance to the rice water weevil with 32 lines (mostly F4 crosses) showed 17 of them to have their yields affected to a lesser degree than 1403, a cultivar previously showing considerable tolerance. Six lines showed yield reductions of less than nine percent (3.3 to 8.6 percent) when subjected to a heavy population of weevils.

"Laboratory tests for control of the tadpole shrimp showed parathion at 0.05, 0.1 and 0.2 pounds active ingredient per acre; Sevin at 1, 2 and 4 pounds; and copper sulfate crystals at 2.5, 5 and 10 pounds per acre to effectively control the shrimp at all rates."

Chemical control of tadpole shrimp. There have been a number of reports in the last three years that tadpole shrimp (Triops ]ongicaudatus) could not be controlled in certain areas with recommended chemicals.

Laboratory tests for control of tadpole shrimp showed parathion at 0.05, 0.1 and 0.2 pounds active ingredient per acre; Sevin at 1, 2 and 4 pounds; and copper sulfate crystals at 2.5, 5 and 10 pounds per acre to effectively control the shrimp at all rates. The shrimp were collected from an area where they were suspected to be resistant to these chemicals. The high level of control obtained indicates other reasons for past control failures.

Chemical control of rice seed midges. Lorsban (not yet registered) has been effective as a spray for seed midge larva. However, 1978 tests of Lorsban as a seed treatment at levels of two and four ounces active ingredient per 100 pounds did not reduce rice seed midge larvae injury to seedlings planted five days after flooding. There was an 18 to 23 percent reduction in injury when the seed was planted 10 days after flooding and an 11 to 13 percent reduction in injury when the seed was planted 17 days after flooding. In spite of these injury reductions at the later plantings, control was not adequate. It is doubtful that higher rates of Lorsban could be tolerated by the plant, as growth was retarded at the four-ounce application rate.

 

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