Invertebrate Pest
Control - 85

 

 

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Project Leader and Principal UC Investigators

A.A. Grigarick, Dept. of Entomology, UC Davis

 

Objective

The objectives of the invertebrate pest control project are 1) to gain a better understanding of the physical and biological factors chat cause fluctuation and movement of pest populations and result in economic injury to rice and 2) to determine the most effective control of these pests without injuring the environment.

Rice Seed Midge

Studies were continued for the third year on the effects of seed coating on rice seedling midge injury. Seedlings from coated and uncoated dry seeds were compared with those from soaked uncoated seeds. Plantings were made at five different intervals spaced three days apart following flooding.

Seedlings from the soaked uncoated seeds grew faster than seedlings from the dry coated and dry uncoated seeds, but midge injury, which was quite variable, showed no significant differences among the seed treatments.

The 1985 results did not support the observations made in previous years that delayed seeding after flooding increased midge injury. Midge injury appeared to be less when seedling growth was most rapid.

Water Management Effects on the Rice Water Weevil

Research literature reports that draining water from rice fields after a water weevil attack decreases populations. Greenhouse studies over the last three years suggest some egg susceptibility to drainage.

In 1984 no egg survival differences were found in drainage periods ranging from one to seven days. The 1984 studies were repeated in 1985 and again, there was no relationship between the number of larvae recovered and the number of days eggs were exposed to the drained condition. It does not appear that water management by drainage up to seven days will be a reliable method for controlling water weevil eggs.

Population Trends by Light Trap Studies

Light trap collections are being used to gather information on peak flight periods so population trends can be understood. A small population peak of rice water weevil occurred from April 16-24 followed by a major flight from May 16-25. The first armyworm moth flight occurred April 18-24, a smaller peak May 3-8 and a major flight June 20-22. This last flight is believed to be the generation that oviposits on rice and causes the major defoliation.

Chemical Control of the Rice Water Weevil

Surface and lightly incorporated carbofuran granules applied before flooding for rice water weevil control were compared at 1/2 and 1 lb ai per acre. There was no difference between the two methods of application, but 1 lb ai/acre was the more effective rate. One-half and 1 lb ai/acre of flowable carbofuran were sprayed on the soil surface before flooding. The 1 pound rate significantly reduced larvae populations, but the 1/2 pound rate did not.

Carbofuran granules also were used as a post-flooding treatment applied about three weeks after planting. A series of water levels were compared starting with no standing water, 1/4 to 1/2 inch deep, 1 to 2 inches deep and 3 to 5 inches deep. The water was contained within metal rings in a field being drained for herbicide treatment. Adult water weevils were added to the rings. Counts made later showed that only the completely drained rings had significantly fewer larvae than the untreated check.

Alsystin was studied as a spray treatment for rice water weevil control applied after the rice had emerged through 4 to 5 inches of water. The spray treatments were made at 1/3 lb ai/acre four and seven days after rice emerged and a double treatment was applied four and ten days after rice emergence. All treatments had significantly fewer larvae than the untreated check when counts were made 21 to 37 days after treatment.

Genetic Tolerance for Rice Water Weevil Control

A breeding program for rice plant tolerance to the water weevil has been in progress for a number of years. One of the most promising selections showed only a 17 percent yield reduction under a very heavy population of water weevils, compared with the variety M-9 which showed a 68 percent yield reduction. The degree of tolerance appears to be related to plant vigor during tillering and the potential for regrowth following water weevil injury.

Chemical Control of the Rice Seed Midge

A field experiment compared rice seeds coated with the insecticide mesurol at 8 and 16 oz ai/ 100 lbs of seed for control of midge larvae. No significant differences were found between the two treatment rates or between treated seeds and untreated controls. Mesurol does not appear to be an effective midge control insecticide.

Chemical Control of the Tadpole Shrimp

The herbicides Ordram and Bolero, Kocide and copper sulfate were used in laboratory trials for control of tadpole shrimp. Ordram and Bolero were not effective, but Kocide and copper sulfate were equally effective at the 10 pound rate per acre. Both also were effective at the 5 pound rate, but Kocide was somewhat slower acting. The 2 1/2 pound rate for Kocide was too slow for effective control.

Lycosid Spiders Reduce Certain Insect Pests

Lycosid (wolf) spiders reduced nymph and adult populations of the aster leaf hopper and adult seed midge populations. Other pests such as the rice leafminer and mosquitos might also be reduced, but they were not abundant enough for an adequate evaluation.

Field tillage, straw burning and pesticides can reduce spider abundance. Carbofuran (5G) did not affect spider abundance. Methyl parathion (4EC) was moderately suppressive and carbaryl (80W) had a devastating negative effect on the spiders. The no-tillage fields had spider densities 20 to 50 times greater than conventionally tilled fields during the early part of the season.

Effects of water management on invertebrate pests

(Funded by the University of California Integrated Pest Management Project)

Objectives

  • Determine the effect of water depth and drainage on rice water weevil oviposition as related to plant age and infestation levels.
  • Determine the effects of field drainage on rice seed midge and tadpole shrimp development as related to rice and weed growth and determine the effect of water depth on midge development.
  • Demonstrate the practicality of monitoring rice water weevil adult leaf scars at three weeks as a method for determining the need for treating with carbofuran after drainage for weed management.
  • Demonstrate the effect of water depth and drainage on the infestation level of the rice leafminer.

Summary of Results

Rice water weevil infestations in the test area were light to moderate. No relationship was found between infestation levels and water management. Although the rice midge was present in greater numbers than in previous years, there was no relationship between crop injury and water management. However, significant differences were observed in the number of midge larvae among water management treatments. The greatest number of larvae were in early drained and shallow water treatments.

No tadpole shrimp were observed in these plots.

Leaf miner activity was greater in deeper water treatments, but the differences were not large and not statistically significant.

Studies to date have not led to water management recommendations for controlling these rice pests.

 

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