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Section V Biological & Cultural Controls

COLORADO POTATO BEETLE CONTROL USING BIOLOGICAL CONTROL VERSUS STANDARD CONTROL METHODS, 1993 Nancy A. Matteson and Robert L. Stoltz P. O. Box 1927, Twin Falls, ID 83303-1827 208/736-3600

Two fields located approximately a mile apart were established near Castleford, ID. Field 1 was approximately 5 acres in size and was managed for organic potato production using biological control strategies. An area of equal size was used in Field 2 which was managed using standard insecticide control methods. On a weekly basis beginning on 25 June both sweep net and DeVac samples were taken from both the standard control and biological control fields. Sweepnet samples consisted of five sets of 25 sweeps per field. DeVac samples consisted of five sets of 50 suctions per field. In addition to these sampling systems, whole plant inspections, five sets of five plants, were made visually for Colorado potato beetle (CPB) egg masses, larvae and adults. The standard control field had a single treatment of Phorate (3 lb ai/A) at planting for the control of CPB. There were no control measures used in the biological control field. Sampling results are presented as total number of insects per 125 sweeps or 250 suctions for both field 1 and field 2. CPB, green peach aphids and thrips are listed with other insect pests that included potato aphids, lygus and looper. The total number of beneficial insects are listed which included nabids, orius, bigeyed bugs, lady beetle adults and larvae and lacewing adults and larvae.

Counts in the standard control field remained low for CPB adults and larvae for the entire sampling period (25 June to 23 August) using both sampling methods. Although green peach aphid counts were higher this year than in the preceding two years, they were still below economic thresholds. CPB adults and larvae were observed in greater numbers in the biological control field but were not considered great enough to warrant controlling. In general the biological control field had increased numbers of other pest species as compared to the standard control field. This trend is also observed for beneficial insect species counted.

In a comparison of sweepnet sampling versus DeVac sampling we found that the DeVac appeared to be more efficient, collecting 1.5 to 15 times more beneficials than with sweep nets. In the early season the DeVac samples included an average of three times more beneficial and pest species than the sweep net samples. This ratio increased later in the sampling period. As beneficial populations increased in the field as observed with both sampling systems, the ratio of DeVac (D) to Sweepnet (S) sampled beneficials increased by a factor of over 7x (33:9 to 629:24, D:S). The data also indicate that other insects such as lygus and loopers can exist in potatoes without causing serious problems. Their presence may help support beneficial populations which in turn help suppress CPB and green peach aphid. Biological Field (#1)

6/25 111 7/9 7/19 7/27 8/2 8/10 8/17 8/23 l z Insect S D S D S DS D S D SD S D S D S D

CPB Adults 2 1 8 0 7 1 7 0 1 0 1 0 1 0 7 0 3 1 CPB Larvae 1 0 23 2 8 10 41 57 14 16 31 11 7 17 14 11 9 8 GP Aphid 0 0 1 4 13 45 1 0 3 5 9 78 6 77 0 14 0 8 Thrips 0 0 0 1 0 0 0 5 43 65 56 165 65 145 17 130 25 90 Other Insect Pests 30 118 99 288 94 178 84 227 74 744 202 2028 153 2397 103 1241 96 759 Beneficial Insects 9 34 10 39 10 33 8 40 20 69 7 132 22 528 16 497 24 629

Standard Field (#2)

6/25 111 7/9 7/19 7/27 8/2 8/10 8/17 8/23 1 Insect SD S D S D S D SD S D S D S D S D

CPB Adults 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 CPB Larvae 0 0 0 0 0 0 0 0 0 0 0 0 6 0 0 2 2 0 GP Aphid 0 0 0 7 0 0 1 0 0 1 5 22 7 49 1 16 3 11 Thrips 0 0 0 0 0 0 0 25 87 115 60 175 145 110 69 145 92 130 Other Insect Pests 7 23 4 41 8 20 11 31 16 64 27 99 76 201 53 228 32 201 Beneficial Insects 0 15 0 9 4 14 4 22 5 19 11 29 41 126 21 142 22 195

1Sweep= Total#/125sweeps 2DeVac = Total#/250 Suctions

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