LABORATORY EVALUATION OF A DIATOMACEOUS EARTH AND PYRETHRIN INSECTICIDE AGAINST DM LARVAE, 1996:

R. F. L. Mau and L. R. Gusukuma-Minuto
University of Hawaii
Dept. of Entomology
3050 Maile Way, Rm. 310
Honolulu, HI 96822
Phone: (808) 956-7063

 

HEAD CABBAGE: Brassica oleracea L. 'C-G Cross'

Diamondback moth (DBM); Plutella xylostella (Linnaeus)

Three rates of Organic Solutions 0.2% were compared against a treated check, Xentari, and an untreated check. Test insects were obtained from laboratory colonies initiated from field collected insects. DBM eggs were collected from the colonies and hatched in plastic containers 10 days prior to the start of the bioassay. Larvae were fed fresh cabbage leaves daily and were in the late second to early third instar at the start of the bioassay. The head cabbage variety ‘C-G Hybrid’ was used as the test plant. Seeds were planted in community pots and kept in the greenhouse until ready to use. At the time of the bioassay, the plants were in the 8-10 true leaf stage. A cabbage leaf with a diameter greater than 5 cm was removed and infested with 10 DBM larvae. Each spray mix as aggitated vigorously and placed in a spray aerosol apparatus. The leaf containing the larvae was sprayed for 3 seconds or until the leaf was thoroughly coated. The treated leaf and larvae were placed in a ventilated petri dish. Each treatment was replicated ten times. Mortality was assessed at 24 hour intervals. Larvae were counted as "dead" when there was no movement in the larvae when probed.

Organic Solutions at 5.0 lb. rate produced the highest mortality 3 DAT. However, it did not compare to the treated check (Xentari). Lower rates of Organic Solutions did provide some control but surviving larvae continued to feed producing damage comparable in size and quantity to the untreated check. The product did not provide adequate DBM control and probably would not provide economic levels of control under field conditions.

 

                                                                    _______Mean % Mortality (DAT)______  
Test material     Concentration
(lb/100gal)
    1     2     3
Organic Solutions 0.2%     3.0 lb.     12.3+4.6c     23.3+4.4bc     34.1+5.2bc
Organic Solutions 0.2%     5.0 lb.     40.0+10.2b     47.0+10.5b     50.0+10.5b
Organic Solutions 0.2%     6.0 lb.     26.5+3.7bc     36.8+4.9b     44.5+5.3b
Xentari     1.0 lb.     78.5+5.4a     96.1+2.2a     100.0+0.0a
Untreated check     ---     6.3+2.3c     12.4+5.8c     16.7+6.1c

Numbers in the same column followed by a different letter are significantly different (P<0.0001 Tukey's studentized range test SAS Institute version, 6.08). Data was subjected to arcsine transformation prior to analysis. Untransformed number are presented.

 

 

Trade Composition\Common name     Formulation         name     Source
Organic Solutions     WP         ------     Organic Solutions
                       
Xentari     ME         B. thuringiensis     Abbott