Abstract:
Relay strip-cropping combines two vegetation management tactics, under-sowing
and strip-management. In this study conducted from 1994 though 1997, a
cover crop seed-mixture containing oats (Avena sativa L. var. "Monida"), common
vetch (Vicia sativa L.), red clover (Trifolium pratense L.), annual ryegrass (Lolium
multflorum Lam.), and buckwheat (Fagopyrum esculentum Moench) was
broadcast over established broccoli (Brassica oleracea L.) 32 days after planting.
The broccoli was planted, under-sown, and harvested in sections alternated with
strips of cover crop. The cover crop relay provided tillage and pesticide refuges
for beneficial insects without taking land out of broccoli production. Relay strip-cropping
increased the abundance and diversity of ground beetles (Coleoptera:
Carabidae), spiders (Araneae), harvestmen (Opiliones: Phalangiidae), lady beetles
(Coleoptera: Coccinellidae), and damsel bugs (Heteroptera: Nabidae) in the
cropping system; however, this did not always result in increased natural enemies
in the broccoli. Arthropod species varied significantly in their propensity to leave
the non-crop vegetation and move into the broccoli. Movement of the lady beetle
Coccinella septempunctata L. from the cover crop strips into the broccoli may have
depressed aphid populations in 1996. The non-crop vegetation may have served as
a sink rather than a source for Nabis species and appeared to reduce their density in
the broccoli growing nearby. There was no evidence that background vegetation
surrounding the broccoli reduced colonization by winged aphids. The density of the
cabbage flea beetle Phyllotreta crucferae Goeze was lower in the broccoli relay
compared with the clean-tilled broccoli. The number of third instar imported cabbage worm Pieris rapae (L.) and cabbage looper Trichoplusia ni (Hubner) was
reduced on broccoli leaves and harvested buds in the relay strip-cropping system
compared with the clean-tilled system. The number of diamondback moth Plutella
xylostella (L.) pupae was higher in the clean-tilled broccoli; percent parasitism of
the pupae was similar in the two cropping systems. Although reduction in broccoli
contamination associated with relay strip-cropping was significant, the residual
insect contamination was unacceptable for commercial broccoli production. Relay
strip-cropping may be useful for preventing soil erosion and protecting water
quality. Relay strip-cropping may be a useful component of an integrated pest
management program.
