Integrating trap crops and entomopathogenic nematode foliar sprays to manage diamondback moth and imported cabbage worm

Authors: BUDHATHOKI, SABINA - University Of Hawaii; SIPES, BRENT - University Of Hawaii; SHIKANO, IKKEI - University Of Hawaii; Myers, Roxana; MANANDHAR, R - University Of Hawaii; WANG, KOON-HUI - University Of Hawaii

Submitted to: Horticulturae
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/10/2022
Publication Date: 11/16/2022
Citation: Budhathoki, S., Sipes, B.S., Shikano, I., Myers, R.Y., Manandhar, R., Wang, K. 2022. Integrating trap crops and entomopathogenic nematode foliar sprays to manage diamondback moth and imported cabbage worm. Horticulturae. 8(11). Article 1073. https://doi.org/10.3390/horticulturae8111073.
DOI: https://doi.org/10.3390/horticulturae8111073

Interpretive Summary: Diamondback moth (DBM) and imported cabbage worm (ICW) are destructive insect pests that attack cruciferous vegetables. Larvae of these pests feed on the leaves of host plants, reducing photosynthetic ability and marketable yield. While chemical pesticide sprays can be effective against ICW, many populations of DBM have developed resistance to insecticide treatments. To overcome this limitation, more sustainable and environmentally compatible approaches need to be developed and incorporated into an integrated pest management program. Entomopathogenic nematodes (EPNs) have been shown to suppress insect populations on a number of crop plants. However, each cropping system has different environmental conditions and intricacies such that EPN application must be optimized for each. Trap cropping is the practice of planting an additional crop in between or bordering cash crop rows. These plants attract and intercept insect populations subsequently reducing pest pressure on the desirable crop. In this study, the use of kai choi as a trap crop was examined with and without foliar sprays of entomopathogenic nematodes. Results from the field trials were variable but in general intercropping kai choi with head cabbage or kale reduced DBM and ICW populations and leaf damage. Adding an EPN foliar spray further reduced DBM populations in some instances. While complete control of DBM was only achieved in one combined treatment trial, incorporating these techniques in an integrated pest management plan can reduce damage caused by chewing insects and increase crop quality and marketable yield.

Technical Abstract: Diamondback moth (DBM), Plutella xylostella, and imported cabbage worm (ICW), Pieris rapae, are destructive pests of crucifers worldwide. Although several insecticides are effective against ICW, pesticide management against DBM is challenged by insecticide resistant populations. The objective of this study was to explore the potential of integrating foliar sprays of the entomopathogenic nematode (EPN) Steinernema feltiae with trap cropping using kai choi (Brassica juncea) planted as an intercrop for the management of DBM and ICW. Four 2 x 2 (trap crop × EPN) factorial designed field trials were conducted with 2 trials on head cabbage (Brassica oleraceae var capitata) and 2 on kale (Brassica oleraceae var acephala). In the first head cabbage trial, trap cropping reduced DBM abundance by 46% and ICW abundance by 73%. Leaf damage by DBM and ICW were reduced by 45% and 33% respectively. In the second head cabbage trial, DBM populations were reduced by 19% whereas ICW was reduced by 65%. No effects were observed on leaf damage. Trap cropping suppressed DBM abundance by 50% and DBM leaf damage by 19% in the first kale trial. No significant effects were observed on ICW. In the second kale trial, trap cropping reduced ICW leaf damage by 13%. In the first head cabbage trial, adding EPN foliar sprays further reduced DBM populations in plots with trap crops and ICW in plots without trap crops. In the second kale trial, EPNs suppressed DBM populations entirely. No effects from EPNs were observed in the second head cabbage trial or the first kale trial. It is concluded that trap cropping with kai choi did not improve the efficacy of EPN foliar sprays consistently but there was a synergistic effect at times. EPNs were most successful at suppressing DBM and ICW populations when the average pest pressure was below 0.5/plant whereas trap crops worked more effectively at insect populations above 0.5/plant. Although the use of trap cropping reduced pest abundance and leaf damage, the weight of head cabbage and kale was lower when planted 30 cm or closer to kai choi plants. This was resolved by leaving a distance of 60 cm between cash and trap crops. With further optimization, the use of trap cropping and EPN foliar sprays can be beneficial to an integrated pest management program to control DBM and ICW in cruciferous crops.