- Author: Alejandro Del Pozo-Valdivia
Diamondback moth (DBM) is a persistent pest in the Salinas-Castroville area. We were able to find late instar caterpillars in several spots along Blackie road on Tuesday January 22nd. Basically, these caterpillars were feeding on brassica weeds, located along the side of the road (Fig. 1). This is an example of how insects exploit weeds as alternative hosts when there is a lack of a preferred and abundant host plant in the landscape. DBM will continue feeding on these weeds, while increasing their numbers. These DBM adults, originated from weeds, have the potential to infest any commercial cole crop during the upcoming weeks and months. Based on our observations, most of these caterpillars were close to pupate. Within the next two weeks, we might see an influx of DBM adults flying around fields and weed patches. A new generation of caterpillars may be present around mid-February in our system, depending on temperature fluctuations.
It seems like not all of these caterpillars will become adults. Approximately, 10% of the caterpillars collected from Blackie road were parasitized by Diadegma wasp. We took these caterpillars to the UCCE Entomology lab to refresh and re-introduce DBM into our colony; and we were able to spot the parasitic wasp pupae inside our rearing containers (Fig. 2).
Ideally, controlling weeds outside our fields and along the roads could be part of our strategies to manage resident pest populations. Control of these weeds will allow to reduce population of these pests cycling through the winter here in the Salinas-Castroville area. Managing these weeds could be challenging too, due to accessibility and other issues. Please, keep in mind that cole crop fields surrounded by weedy patches will have a higher chance to be infested with DBM. You could prioritize the scouting of those fields to timely detect any economically damaging DBM population in your crop.
If you would like to learn more about DBM and the research conducted by the UCCE Entomology team, please contact Alejandro Del-Pozo at firstname.lastname@example.org or 831-759-7359.
- Author: Alejandro Del Pozo-Valdivia
It has been a couple of “rough” weeks managing the diamondback moth (DBM), Plutella xylostella (Lepidoptera: Plutellidae), in the Central Coast. Based on my conversations with some PCAs, we are managing large populations of this moth, resulting in high infestations in cole crops like broccoli and Brussel sprouts. Larvae of this insect will typically feed on the underside of the leaves, rasping the epidermis and generating this characteristic “window panning” that results on perforations later on (Fig. 1). Diamondback larvae will also feed on the plant's growing points, floral stalks, and even on flower buds.
It seems like populations have been building up during early summer in our area, resulting in enough individuals, at this point, generating significant injury in cole crops. PCAs have been recommending spraying several different insecticides to reduce the infesting populations in affected fields, since damage has been beyond tolerable. For instance, after one of my field visits, I was able to spot affected larvae in treated fields (Fig. 2). Treatments are working, I believe we need to continue being ahead of future DMB infestations.
Some information to consider:
- Scout early. If you have transplants or direct seeded seedlings, pay a visit more often. We are dealing with a large DBM population right now. There will be a high chance that those fields may ended having DMB earlier than expected during this time of the year.
- Use of adjuvants. The waxy nature of cole crop leaves represents a challenge for insecticide deposition in the canopy. Make sure that you are using a spreader/sticker adjuvant to potentially reduce any pesticide “sliding off” from the waxy leaves.
- Rotate pesticides. Consider using different classes of insecticides, before using different active ingredients within the same class. For instance, using an avermectin and then a diamide, instead of using chlorantraniliprole and cyantraniliprole (two different active ingredients within the diamide class) back to back. Using different modes of actions will help to delay potential issues of developing insecticide resistance in our DBM populations.