Mount Vernon Northwestern Washington Research and Extension Center

Vegetable Research and Extension

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WSU Extension Research Report
Control of Corn Root Worm in Green Peas

Carol A. Miles, Chuhe Chen, Caitlin Blethen, Richard Carr, and Mark Amhrein
360 NW North Street, Chehalis, WA  98532, 360-740-1295, milesc@wsu.edu

Background

We have been studying root insects in Southwest Washington since 1996. From February through May 1996, we monitored overwintering cucumber beetles (Diabrotica undecimpunctata undecimpunctata) in the area. In mid-July, cucumber beetle populations increased by over 400%, likely due to emergence of the first generation. In 1997, we sampled a pea field in Curtis and found corn root worm (CRW), the larval stage of the cucumber beetle, and pea leaf weevil (PLW) (Sitona lineatus) in pea-root soil samples. In 1998 and 1999, we began testing control options for CRW and PLW in green peas.

1998 Control Study

In 1998, we isolated and quantified PLW larvae and CRW in a pea field in Curtis. Four pesticides, diazinon, Di-syston, Fipronil, and imidacloprid (Admire) and one biological control, an entomopathogenic nematode, Steinernema feltier, were tested to evaluate efficacy for reducing pea root damage. Fipronil and imidacloprid are both not registered for use in peas. Plot design was a randomized complete block design with four replications. Peas were planted May 4 and harvested July 21. Chemical treatments were applied in a pre-plant incorporated broadcast spray, and the nematode was applied as a broadcast spray approximately 3 weeks after pea emergence. Soil samples along with 2 – 3 plants and their root systems were collected from each plot on three dates, June 10,  June 30, and July 14. Peas were harvested from an area of approximately 7 ft2 per plot and yield data was measured.

Insect Counts

PLW larvae and CRW were isolated from soil samples using the Berlesse-Tullgren funnel technique. The treatments of Diazinon and Di-syston had the lowest number of PLW larva in the July 14 sampling (Table 1). Di-syston and the nematode, Steinernema feltier, treatments had lower numbers of PLW larvae than the check in the first two samplings. Di-syston had the highest number of CRW at all three sampling dates, and the treatments Fipronil and imidacloprid had high numbers of CRW and PLW larvae at all sampling dates. However, none of these differences were statistically significant.

Table 1
Effect of treatments on number of PLW larva and CRW per plant on June 10, June 30 and July 14 in a pea field in Curtis, SW Washington in 1998.

    No. PLW Larva No. CRW
Treatment 10-Jun 30-Jun 14-Jul 10-Jun 30-Jun  14-Jul
Di-syston 0.1 3.3  0.6 bº 0.20 1.3 0.9
Diazinon 0.3 4.0  0.2 b 0 0.4 0.3
Fipronil 0.1 6.7 2.2 a 0  0.9 0.5
Imidacloprid 0 7.0 0.9 ab 0 0.5  0.7
S. feltier 0.2 2.7 0.9 ab 0 0.5 0.5
Check  0.4 4.5 1.1 ab 0 0.8 0.1
Significance NS NS * NS NS NS

 º Means of the treatments with different characters are significant at P < 0.05 level (Duncan's multiple range test)

NS Not significant

Root damage was recorded using microscope-mounted digital movie technology and a 35mm microscope-mounted camera. An electronic video of CRW on a pea root can be viewed on the web at http://vegetables.wsu.edu/crw.

Yield

At harvest, theabove-ground portions of plants were weighed and separated into plants and marketable pods. The weight of 50 pods and weight of 30 peas were also measured. Plant and pod yields tended to be higher in plots which received  imidacloprid or Fipronil however these differences were not statistically significantly (Table 2). The entomopathogenic nematode appeared to cause a slight decrease in pea productivity though again this decease was not significant.

Table 2
Effect of treatments on weight (g) of whole plant (plant + pods), plant only, marketable pods, 50 pods and 30 peas.

Treatment Whole Plant Plant Only Mrkt. Pods 50 Pods  30 Peas
Di-syston 1130 520 531 192 12.52
Diazinon 1055 535 453 177 12.31
Fipronil 1160 545 559 212 12.28
Imidacloprid 1250 570 583 193 11.96
S. feltier 1000 500 442 181 12.87
Check 1135 540 537 195 12.55
Significance NS NS NS NS NS

NS Not significant

1999 Control Study

In 1999, we continued tosample, isolate, and quantify PLW larvae and CRW in a pea field in Curtis. The plot design was a strip plot, a procedure developed for on-farm tests using large conventional equipment (Wuest et al., 1994). Treatments were applied to one long strip in the field and the strips were then divided into four equal areas. Data was collected from these areas and were treated as replicated plots. This experimental design procedure was used because the large equipment which we used to plant the trial and apply the chemical treatments was not conducive for small randomized plots. Six pesticides and three biological controls were tested to evaluate efficacy for reducing pea root damage. The six chemical treatments were diazinon, Di-syston, Fipronol, imidacloprid (Admire), Lorsban, and Malathion. The three biological treatments were entomopathogenic nematodes Steinernema carpocapsae, Steinernema feltiae, and Heterorhabditis bacteriophora. Fipronil, imidacloprid, and Lorsban are not registered for peas.

Peas were planted April 30 and harvested July 27. Soil samples along with three plants and their root systems were collected from each plot three times during the growing season: June 22, July 6, and July 20. On July 27, peas were harvested from an area of approximately 14 ft2 per plot and yield data was measured.

Insect Counts

PLW larvae and CRW were isolated from soil samples using the Berlesse-Tullgren funnel technique. The Diazinon and the check treatments had the lowest number of PLW larvae at the last sampling date, July 20, and Diazinon also tended to have a low number of PLW larvae at the two earlier sampling dates (Table 3). Di-syston and the check treatments had the highest number of CRW at all three sampling dates, while Fipronil and the nematodes, Steinernema carpocapsae and Steinernema feltiae, tended to have the lowest number.

Table 3
Effect of treatments on number of PLW larvae and CRW per plant on June 22, July 6, and July 20 in a pea field in Curtis, SW Washington in 1999.

    No. PLW Larva No. CRW
Treatment 22-Jun 6-Jul 20-Jul 22-Jun 6-Jul 20-Jul
Di-syston 5.0 2.8 0.3 abº 1.3 0.5  0.8
Diazinon 1.8 3.0 0 b 1.0 0 0
Fipronil 3.3 4.3 0.3 ab 0   0.3 0.5
Imidacloprid 2.8 3.5 0.8 ab  0.8 0.8 0
S.carpocapsae 1.3 3.3 0.5 ab 0 0 0.3
Lorsban 2.0 2.3 1.3 a 0.5 0.8 0
Malathion 4.0 2.8 0.8 ab 0.3 0.5 0
S. fleltiae 5.0 3.3 0.5 ab 0 0.5 0
H.bacteriophora 3.3 3.3 0.8 ab 1.0 0 0
Check 4.25 2.3 0 b 1.3 1.3  0.5
Significance NS NS * NS NS NS

º Means of the treatments with different characters are significant at P < 0.05 level (Duncan's multiple range test)

NS Not significant

Yield

At harvest,the above-ground portions of plants were weighed and separated into plants and marketable pods. Marketable pods were weighed and then 50 random pods and 50 peas were weighed. Results indicate that some treatments had more than 10% higher plant biomass and marketable pod weight than the check, however, the means did not differ significantly (Table 4). A larger plot or sample size may be needed to achieve better yield estimates.

Table 4
Effect of treatments on weight (g) of whole plant (plant + pods), plant only, marketable pods, 50 pods and 50 peas.

Treatment Whole Plant Plant Only Mrkt. Pods 50 Pods 50 Peas
Di-syston 2615 1110 1410 235 22.8
Diazinon 2610 850 1360 250 23
Fipronil 2305 965 1235 242 25.2
Imidacloprid 2280 975 1235 234 22.3
S.carpocapsae 2260 950 1141 235 23.8
Losban 2390 973 1310 261 22.8
Malathion 2665 1130 1393 258 23.6
S. feltiae 2660 1130 1385 249 22.8
H.bacteriophora 2450 1065 1265 248 21.8
Check 2360 1060 1188 246  22.1
Significance NS NS NS NS NS

NS Not significant
 

Summary

In our research we have successfully isolated and identified CRW feeding on pea roots. We have also determined that pea leaf weevil larvae are causing root damage while feeding on nodules. The data collected in the last two years indicates that Diazinon may offer the most effective and lasting control of PLW larvae in pea fields. Due to limited sampling size, we have not been able to show significant differences in yield data due to treatments. In 2000, we propose to continue to test control options for CRW and PLW larvae in southwest Washington in collaboration with Dr. Chuhe Chen, WSU Vancouver Research and Extension Center, and to investigate timing of pesticide application. We also propose to conduct laboratory studies to further document CRW and PLW larvae damage on isolated pea roots.
 

References

Wuest, S., B. Miller, J. Alldredge, S. Guy, R. Karow, R. Veseth, and D. Wysocki. 1994. Increasing Plot Lenght Reduces Experimental Error of On-Farm Tests. J. or Production Agriculture, Vol 7(2): 211-215.

Johnson, J., B. Miller, J. Alldredge, and S. Ullrich. 1994. Using Single-Replicate On-Farm Tests to Enhance Cultivar Performance Evaluation. J. or Production Agriculture, Vol 7(1): 76-80.

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