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.

Fig.1. Characteristic window panning injury from Diamondback larva feeding on a broccoli leaf.

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.

Fig. 2. Dark colored insecticide-poisoned and dead Diamondback larva collected from an insecticide treated broccoli field.

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.

Celebrate National Honey Bee Day by brushing up on your knowledge of bee protection—check out the newly revised Best Management Practices to Protect Bees from Pesticides and Bee Precaution Pesticide Ratings from UC IPM. These resources will help you strike the right balance between applying pesticides to protect crops and reducing the risk of harming our most important pollinators.   

The best management practices now contain important information regarding the use of adjuvants and tank mixes, preventing the movement of pesticide-contaminated dust, and adjusting chemigation practices to reduce bee exposure to pesticide-contaminated water. The Bee Precaution Pesticide Ratings have also been updated to include ratings for 38 new pesticides, including insecticides (baits, mixtures, and biological active ingredients), molluscicides (for snail and slug control), and fungicides.

Most tree and row crops are finished blooming by now, but it is a good idea to learn about bee protection year-round. Visit these resources today to choose pesticides that are least toxic to bees and learn how you can help prevent bees from being harmed by pesticide applications.

Since last week, I have been receiving samples with “red” aphids to get the identification. It turned out that this time, most of these ‘reddish' aphids were identified as the lettuce aphid, Nasonovia ribis-nigri (Fig. 1). To me, they look more red-orange; however, their distinct black marks on the abdomen and short cauda (finger-like, short appendage at the end of the abdomen) are some key ID features. These features help to differentiate the lettuce aphid from the other “red” aphid, the potato aphid Macrosiphum euphorbiae (Fig. 2). Yes, we do have two different species of red aphids!

Fig. 1. Lettuce aphid.

Fig. 2. Potato aphid.

More samples for aphid ID are still coming into the UC Cooperative Extension office. The pattern is still similar to last week. There are mostly lettuce aphids on the submitted samples. I was also able to notice that some samples have mixed populations between the lettuce and the potato aphids, where all the specimens were red.

We have several trial locations where we are scouting for aphids. So far, fields in Soledad have the largest number of aphids documented, as both alates (with wings, collected from yellow sticky cards) and wingless (collected from lettuce samples). If you need further information about the other scouting locations, or would like to double check your aphid ID, please contact or send samples to Alejandro Del-Pozo (adelpozo@ucanr.edu, 831-759-7359).

We have been scouting for Bagrada bug on wild host plants at two sites in the San Ardo area since middle of May. We selected San Ardo as our most southern scouting point for the Salinas Valley. Every other week, we have performed plant visual counts and collected yellow sticky cards to document the presence of these bugs. So far, we have not found any Bagrada bug in the San Ardo area.

Four additional sites, along Highway 101, were added today to the Bagrada bug scouting route. These sites, from south to north, are located: 1) near King City, 2) south of Greenfield, 3) south of Soledad, and 4) north of Soledad. Today, we were able to document the presence of Bagrada bug adults (Fig. 1), on shortpod mustard (Fig. 2), in two of the four additional scouting sites. Bagrada bug adults are currently located north of Soledad and near King City. From our observations, there are no nymphs nor eggs on the shortpod mustard. Adults were observed mostly mating. Early instar nymphs will be expected in the next couple of weeks.

Figure 1. Bagrada bugs mating on shortpod mustard

Figure 2. Shortpod mustard along Highway 101 near Soledad

We will be increasing the frequency of the scouting for this bug to weekly visits, and we will be adding two additional sites near Gonzales, one in Chualar, and another one south of Salinas. Adding more sites will help to document if Bagrada bugs are present in other places besides Soledad and King City. Are these bugs isolated and resident Bagrada populations? We plan to answer this question setting up more scouting sites across the Salinas Valley.

Today, we also noticed that the most of the shortpod mustard plants are senescing. It would be expected that Bagrada bug females might disperse from unsuitable wild host plants to recently planted cole crops in the surrounding areas. Dispersing and mated females may lay their eggs on these crops. I would suggest to PCAs to check recently planted or young cole crops in the surrounding areas of Soledad and King City during this week. Early detection of potentially migrating females will help everybody to successfully manage this pest.

We will continue to visit our scouting sites for Bagrada bug in the Salinas Valley. If you have any further question about the situation of this pest in your area, please call or email Alejandro Del-Pozo at 831-759-7359 or adelpozo@ucanr.edu.