- Author: Alejandro Del Pozo-Valdivia
We are happy to announce that the diamondback moth capture data, presented as maps, is now housed in our own University of California Cooperative Extension Monterey website.
To access to these maps, simply click on the link below:
These maps use the closest town or landmark where the traps are located to show moths per trap per day. Moth captures are presented as yellow bubbles. The bigger the bubble, the larger the population of moths is.
On the same page, you will also find the overall population fluctuations of these moths in the Valley, as a series chart.
We also stored the overall fluctuation of aphids and thrips numbers, captured in yellow sticky cards in our UCCE Monterey website. To access to these bar charts, click on the link below:
If you would like to learn more about these three monitoring programs happening in the Salinas Valley, do not hesitate to contact Alejandro Del-Pozo at email@example.com or 831-759-7359.
- Author: Alejandro Del Pozo-Valdivia
We continue the effort of monitoring diamondback moth (DBM) across the Salinas Valley using sex pheromone baited traps, as shown in the picture above. We have been adding additional traps to cover a larger area along Highway 101. We have daily moth capture data from Castroville to Greenfield. The chart below summarizes these daily captures from our pheromone traps.
As stated in a previous blog post, higher numbers of DBM have been usually recorded in Castroville. It seems like we just passed a generation of adults during late March to early April. Currently, DBM capture numbers are going down. Lower adults in the system could be paired with more caterpillars feeding on several host plants.
We have set up yellow sticky cards to track the overall population of winged aphids and thrips. These sticky cards are in the same locations as the pheromone traps. At this point, data for aphids and thrips is not broken down at the species level.
From the chart above, there was a flight of aphids during late March to early April. Some PCAs mentioned to me that foxglove aphid started to show up in their fields during that time period. It seems now that winged aphid numbers are going down. However, it does not mean that numbers of aphids in our crops are decreasing. We might be facing higher population of wingless aphids in our crops right now.
We need to keep an eye on population dynamics of thrips in the Valley. The ultimate goal is to be better prepared this season to manage those creatures and reduce the incidence of INSV virus. The chart below shows captures of thrips in our sticky cards.
It seems like thrips populations had a spike two weeks ago. Currently, thrips numbers are going down. I believe that keeping track of the fluctuation of thrips numbers in our Valley would help us detect large populations of this pest. There is a need to alert PCAs when the front of a 'thrips wave' would happen.
If you are interested in getting more information on this monitoring effort, please do not hesitate in contacting Alejandro Del-Pozo at 831-759-7359 or firstname.lastname@example.org.
- Author: Shimat Villanassery Joseph
A series of laboratory and field studies were conducted to determine if the insecticides coated lettuce seeds are an option to control key lettuce pests in the Salinas Valley: springtail (Protaphorura fimata; Fig. 1A), leafminers (Liriomyza spp.; Fig. 1B) and western flower thrips (Frankliniella occidentalis; Fig. 1C). In addition, a laboratory test was conducted to determine if “primed” lettuce seeds reduced springtail feeding damage.
Springtails. Springtail (P.fimata) is soil dwelling primitive arthropod primarily attacks germinating lettuce seeds, reducing the plant vigor or death, which cause patchy or area-wide stand loss. Most springtails possess a forked organ (furcula) in the rear-end, which is extended forward and backward to jump; hence, the common name, springtail. However, the springtail species, sampled from lettuce fields causing the stand loss, does not have furcula. This means it cannot jump.
The head lettuce seed ‘Regency' was coated with clothianidin, thiamethoxam, and spinosad (Table 1). The seeds were coated by Dr. Alan Taylor at Cornell University and coating technique mirrored commercial seed coating procedure. Laboratory studies were conducted in containers with springtail (P. fimata) infested soil. The data show that all three insecticides spinosad, clothianidin and thiamethoxam treated seeds significantly reduced the incidence of springtail feeding injury when compared with untreated seeds. Among insecticides, superior performance in efficacy was noted in the following order: clothianidin > thiamethoxam > spinosad (Fig. 2). Two field trials were conducted against springtails using the same seed treatments, however, the springtail pressure was so low that conclusive data were not obtained. Clothianidin (NipSit) in particular, is now registered on head lettuce and could be used for springtail control. This is an important information in that springtails attack the germinating seeds of lettuce especially in the spring time. During spring, we get some rain showers and the wet conditions in the field after planting makes insecticide application along seed line almost impossible. If the insecticide coated seeds are planted, the grower or PCA could avoid at-plant insecticide application which is typically targeted toward springtails. Application of insecticides such as neonicotinoids and pyrethroids along the seed line will protect the germinating seeds from springtail feeding. More field studies will be conducted in the following years to validate these results in the field.
Studies were also conducted to determine if there are any varietal effects exists (Table 2). The much needed attribute for springtail control is faster seed germination so that the springtail would not get sufficient time to feed and cause seed mortality. “Primed” lettuce seeds are used for uniform and a quick germination (cut short 2 to 3 days than “unprimed” seeds). “Primed” and “unprimed” seeds were evaluated to determine if the quick seed development would reduce springtail damage. Data show that germinating “primed” seeds were impacted with springtail feeding affecting their germination and were not different from the “unprimed” seeds when the springtail pressure was moderate to high (Fig. 3). The seeds used for this experiment were from same seed lot (“primed” and “unprimed”) for a lettuce variety. Also, there was no clear variety difference in springtail feeding damage.
Leafminers and western flower thrips. The leafminer eggs are laid within the surface layer of the leaf. The eggs hatch within couple of days and the maggots mine through the surface layer of the leaves. The egg laying and maggot mining creates stippling and mining injuries which make the leaves unmarketable. Although UC recommends few insecticides such as Agri-mek (Abamectin), Trigard (Cyromazine), Aza-direct (Azadirachtin) and Entrust (Spinosad), the management of leafminers are primarily relied upon on Agri-mek applications.
Thrips is another of the major pest of lettuce, and combination of direct feeding injury and viral disease [thrips-transmitted tospoviruses [Impatiens Necrotic Spot Virus (INSV)] can cause significant losses in lettuce production. In addition, because most of the export markets have set higher standards on prevalence of live and dead thrips in the produce, the lettuce industry is constantly battling ways to significantly reduce thrips in the produce targeted for export.
A replicated-field trial was conducted to determine the efficacy of seed coated insecticides (Table 1) on leafminers and western flower thrips incidence and their infestation. The results show that insecticide seed coating may not be an effective option for leafminers and thrips control in head lettuce (Table 3 and 4) under the conditions this experiment was conducted. There was no reduction of leafminer or thrips feeding with insecticide coated seeds compared with untreated control. Further evaluations under varying conditions might be necessary to validate the consistency of these results.
- Author: Steven T. Koike
Coastal California growers, pest control advisors, and other field professionals might be on the alert for early outbreaks of lettuce problems caused by viruses. In particular, early confirmations have been made of the Tomato Spotted Wilt Virus (TSWV) on lettuce in this region. Affected leaves have tan, brown, or blackish spots and dead areas; this necrotic tissue can resemble damage caused by pesticide or fertilizer applications (see photos below). Some leaf yellowing can also be observed. If disease is advanced, symptoms can also be found on the newer leaves near the center of the plant axis. If plants are affected early in their development, growth can be stunted. Symptoms caused by TSWV in lettuce are indistinguishable from symptoms caused by the closely related Impatiens necrotic spot virus (INSV) which in some seasons can be commonly found on lettuce in the Salinas Valley. All lettuce types (iceberg, romaine, greenleaf, redleaf, butter) are susceptible to both TSWV and INSV. Both viruses are spread by thrips, are found in hundreds of crop and weed species, and are not seedborne. In our coastal region, TSWV and INSV are spread only by the western flower thrips (Frankliniella occidentalis).
Our laboratory has confirmed TSWV on lettuce in late March, which is rather early for such developments. PCAs also report early buildups of thrips populations in lettuce and other fields. The relatively dry spring is resulting in early drying up and senescing of weeds and hillside vegetation; this early decline of surrounding vegetation very likely is driving thrips populations into fields earlier than normal. Lettuce growers should be aware of possible early problems due to thrips vectoring tospoviruses into their fields.
Lettuce with tospovirus-like symptoms can be sent for analysis to the UC Cooperative Extension diagnostic laboratory in Salinas.
Tomato spotted wilt on lettuce.
Impatiens necrotic spot on lettuce
Impatiens necrotic spot on lettuce
- Author: Steven T. Koike
Beginning in early April, 2012, the UC Cooperative Extension diagnostic lab in Salinas began to receive lettuce samples exhibiting obvious symptoms of a virus problem. Samples continued to be submitted throughout the month. All samples tested positive for the thrips-vectored Impatiens necrotic spot virus (INSV). This virus first began to cause damage to California lettuce in 2006. Since that time, INSV has occurred to a greater or lesser degree every season. However, significant INSV outbreaks usually are found beginning in late May or early June. Seeing INSV on lettuce in April is therefore unusual and growers and pest control advisors should carefully monitor these situations.
INSV-infected plants have leaves with brown to dark brown spots and dead (necrotic) areas; this necrotic tissue can resemble burn damage caused by pesticide or fertilizer applications (see photos below). Affected leaves can be distorted and twisted. Extensive necrosis can cause much of the leaf to become brown, dry, and dead. Some leaf yellowing can also be observed. Yellowing and the brown spotting tend to be observed on the newer leaves near the center of the plant’s growing point. If plants are affected with INSV early in their development, growth may be stunted. All lettuce types are susceptible, and INSV has been confirmed on iceberg, butterhead, romaine, and leaf lettuces. INSV can infect many other crops and weed species; the virus is vectored by the Western flower thrips (Frankliniella occidentalis).
Growers, PCAs, and other field personnel should exercise caution in diagnosing INSV disease because the lettuce dieback viruses cause very similar symptoms (see table below). Lettuce dieback is caused by two pathogens: Lettuce necrotic stunt virus (LNSV) and Tomato bushy stunt virus (TBSV). Infected lettuce can be severely stunted, especially if infected early in plant development. The oldest, outer leaves can be severely yellowed. Brown, necrotic spots and lesions later develop in these outer leaves. The younger, inner leaves remain dark green in color, but can be rough and leathery. LNSV/TBSV infects only romaine, butterhead, and leaf lettuces; modern cultivars of iceberg lettuce are immune. The LNSV/TBSV virus complex is a soilborne problem and no vector (insect, nematode, fungus) is known to spread these viruses.
Photos: Impatiens necrotic spot virus (INSV) on lettuce.