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 22^nd. 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.

Fig. 1. Diamondback caterpillar spotted on a secondary branch of a brassica weed by the side of Blackie Road, Castroville, CA. Photo by E. Garcia.

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).

Fig. 2. Brown barrel-like Diadegma pupa (top) and light green diamondback caterpillar (bottom) on a cauliflower leaf inside a rearing container at the UCCE Entomology lab.

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 adelpozo@ucanr.edu or 831-759-7359.

The UC Cooperative Extension is holding a Vineyard IPM Conference on Thursday, Feb. 21 in San Luis Obispo.

DPR CE and Certified Crop Adviser CEUs have been requested.

Date: Thursday, Feb. 21, 2019
Location: San Luis Obispo Veteran's Hall, 801 Grand Avenue
Cost: $100, includes morning coffee and lunch
Advanced registration is required, please register at this website: http://ucanr.edu/seminar

Agenda:

8:00 - Check in and refreshments

8:30 - CaCO3 foliar spray affecting sunburn and fruit chemistry
          George Zhuang , UCCE Fresno County

9:00 - Nematode resistant rootstocks
          Karl Lund, UCCE Madera/Merced/Mariposa Counties 

9:30 - Pierce's Disease Update
          Rhonda Smith, UCCE Sonoma County

10:00 - Maximizing effectiveness of spraying
            Lynn Wunderlich, UCCE Sierra Foothills

10:30 - Planting for root health
            Larry Bettiga, UCCE Monterey County

11:00 - Controlling ice-nucleating bacteria with copper sprays
            Glenn McGourty, UCCE Mendocino & Lake Counties

11:30 - Avoiding winter freeze damage
            Mark Battany, UCCE San Luis Obispo & Santa Barbara

12:00 - Lunch 

1:00 - Management of Vine Mealybug
          David Haviland, UCCE Kern County

1:30 - Epidemiology of Leafroll
          Kari Arnold, UCCE Stanislaus County

2:00 - Effects of GRBV on grapevine physiology
          Johann Martinez, UC Davis Viticulture & Enology

2:30 - Grapevine virus and vector management
          Kent Daane, UC Berkeley

3:00 - Adjourn

Monterey County Agricultural Center

1432 Abbott Street, Salinas, CA

Tuesday, February 26

7:45 a.m. to 12:30 p.m.

7:45         Registration (free)

8:00          Production of organic baby spinach using buried drip irrigation

Ali Montazar, Irrigation Advisor UCCE, Imperial and Riverside Counties

8:30          Mitigating pesticides and sediments in tail water using polyacrylamide (PAM): a new approach

Michael Cahn, Irrigation and Water Resources Advisor, Monterey County

9:00         Full season nitrogen management of vegetables

Richard Smith, Vegetable Crops and Weed Science Adivsor, Monterey County

9:30         Optimizing water management in celery using ET weather-based scheduling

Michael Cahn, Irrigation and Water Resources Advisor, Monterey County

10:00       Break

10:30        Region 5 water quality coalitions – demonstrating achievements in water quality

Parry Klassen, Executive Director, Coalition for Urban Rural Environmental Stewardship (CURES)

11:00        Evaluation of salinity effects on strawberry production

Andre Biscaro, Irrigation Water Resources Advisor, Ventura County

11:30        Water and nitrogen management of Asian vegetables/SWEEP and Healthy soils programs

Aparna Gazula, Small Farms Advisor, Santa Clara County

12:00       Grower Panel: Nitrogen Management in Practice

                Saul Lopez, D'Arrigo Brothers; Mark Mason, Huntington Farms; and Sal Montes, Christiansen Giannini

12:30       Pizza Lunch

CCA & DPR continuing education credits have been requested

Summary: Following the crop production season in the fall, residual soil nitrate-nitrogen (N) levels increase when N-rich residues from crops such as broccoli are incorporated into the soil. Soil temperatures in the fall and early winter are adequate to allow decomposition of crop residues, as well as mineralization of soil organic matter. The resulting pool of residual soil nitrate-N is vulnerable to leaching by winter rains. Winter-grown cover crops trap a significant portion of this nitrate in their crop biomass thereby providing a useful practice to reduce nitrate leaching during the winter fallow period; however, although growers may want to include cover crops in their rotations, conflicts with spring planting schedules and high land rents often preclude their use. Over the past two years we have conducted trials to evaluate the potential of using high carbon/nitrogen (C:N) organic amendments during the winter fallow period to immobilize (tie up) soil nitrate-N and reduce leaching. Soil microbes utilize the supplemental carbon and available soil nitrate for their growth, thereby reducing the pool of nitrate in the soil that is susceptible to leaching. On the Central Coast, fall compost applications is a common practice used by many growers. We were interested in determining whether a high C:N amendment could be substituted for compost to immobilize soil nitrate-N during the winter fallow and serve as a best management practice (BMP) to reduce nitrate leaching.

During the winter of 2016-17 we evaluated the impact of a high C:N green waste mulch (GWM) (C:N 31.4) on nitrate-N leaching following a fall broccoli crop. No reduction in soil nitrate-N was observed with 5 or 10 tons/A of GWM. The lack of efficacy was probably due to the coarseness of the GWM particles, which were too big to provide soil microbes with sufficient carbon quick enough to utilize and effectively immobile soil nitrate-N. During the winter of 2017-18 we evaluated almond shells (C:N 70.3), ground to 0.5 millimeters in size, and applied at 5 and 10 tons/acre, as well as 2.50 tons/acre of glycerol, and 1.25 tons/acre of glycerol ₊ 5 tons/acre of ground almond shells. At the end of the winter fallow period, all these materials reduced the load of nitrate-N in the top three feet of soil by nearly half compared to the untreated control. Almond shells applied at 10 tons/acre significantly reduced the subsequent lettuce crop yield, presumably because it continued to immobilize nitrate during the cropping season. The other treatments did not significantly reduce crop yield. These data show promise for winter fallow immobilization of nitrate as a viable BMP that growers could utilize to help reduce nitrate leaching during the winter fallow without substantially changing other production practices. However, there are aspects of this practice that we still need to understand to effectively reduce nitrate leaching, safeguard yields and minimize cost differences between standard compost applications and the high carbon amendments. The costs of the high-carbon materials used in these studies ranged from $270 and $720 more per acre than the standard grower treatment; subsequent experiments will need to focus on test materials that have costs that are closer to standard compost application to be a realistic option for growers to consider and routinely utilize. In future testing of GWM, particle size will need to be small enough to allow soil microbes to obtain sufficient C to drive the immobilization process during the winter.

Methods: The trial was established in a commercial vegetable production field west of Gonzales, CA on a site with Mocho silty clay loam soil. In the 2017 production season romaine lettuce was produced in the spring through early summer and broccoli was grown from mid-summer through fall. The N content of the broccoli residues at harvest was measured on October 4. After harvest, crop residue was mowed and disced, and the land was prepared for winter beds according to standard practices in the Salinas Valley (discing, ripping to three feet deep, chiseling and land planing). Tillage was complete on October 23 and 350 lbs/acre of 6-20-20 (21 lbs N/acre) was applied on October 24, 2017. On October 28, ground almond shells (C:N 70.3, Table 1), were applied with a commercial spreading truck at three rates: 0 (untreated control), 5 and 10 tons/acre. Each plot was 20 feet wide (the width of throw of the applicator) by 100 feet long. The plots were arranged in a randomized complete block design with four replications. Following the ground almond shell application, the field was chiseled and then listed into peaked 40-inch wide winter beds. Glycerol treatments were applied to the listed beds at 1.25 and 2.50 tons/acre (240 and 479 gallons/acre, respectively) on October 30 with a commercial spray rig. Before application, glycerol was diluted with water at a ratio of 1:1. All treatments were then lillistoned into the beds. Drain Gauge G3 lysimeters from Decagon were installed in the untreated control and the 10 ton/acre almond shell treatment on October 30 after the fields were lillistoned They were capable of measuring nitrate leaching down to a depth of six feet. Sample of drainage water would have been collected after each rainfall event. However, the rainfall was insufficient to generate drainage and sprinkler pipe was installed in early February and 1.5 inches of irrigation water was applied to simulate rainfall. The lysimeters were removed on February 22, 2018 prior to planting the lettuce. Rainfall totals for winter of 2017-18 were retrieved from the Soledad CIMIS weather station (Figure 1). Soil temperature at the CIMIS station was in a range of 50 to 60 °F during the evaluation period. Soil samples were collected from the top three feet of soil each month during the fallow period from November 2017 to February 2018 and during the subsequent lettuce crop cycle (March to May 2018). Soil samples were extracted with 2M KCl and analyzed for nitrate and ammonium.

Following the winter-fallow period, iceberg lettuce was planted on March 7, 2018. The anti-crustant 6-16-0 supplied 24 lbs N/acre. Crop biomass and biomass N uptake were measured on May 9. Yield of the iceberg lettuce was evaluated on May 25 by harvesting 36 heads per plot for crop biomass and biomass N accumulation.

Results: Broccoli residue contained 188 lbs N/acre at broccoli harvest. Soil nitrate levels in the first foot was 25 ppm nitrate-N at the beginning of the trial on October 28 (Figure 2). Minimum soil temperatures at 6 inches deep ranged from 53 to 66 °F from October 1 to December 1, 2017 (Soledad CIMIS station) which was warm enough to allow mineralization of crop residues and soil organic matter; as a result, soil nitrate-N levels increased to over 40 ppm by the end of November and to over 60 ppm by early February (Figure 2) in the untreated control. Levels of nitrate-N declined in the first foot of soil after the application of 1.5 inches of water with sprinklers used to simulate rainfall and to obtain nitrate samples in the lysimeters. However, soil moisture content was not sufficient from rainfall or supplemental irrigation to obtain drainage samples. The levels of nitrate were also elevated in the untreated control in the second foot of soil until after the irrigation event (Figure 3); no difference among treatments were observed in the third foot of soil (Figure 4). The combined total of nitrate-N was higher in the top three feet of soil in the untreated control than all other treatments on February 2 (Figure 5). These results indicate that all treatments reduced the amount of nitrate-N in the soil that would be at risk for leaching. The 10 ton/acre rate of almond shells significantly reduced lettuce yield (Table 2). The plants were stunted and yellow and presumably this rate of almond shells reduce nitrogen availability to the crop. The other rates of almond shells and of glycerol did not significantly reduce lettuce yield. The high carbon amendments increased costs from between $270 and $720 per acre over the standard compost application. For this practice to be considered a realistic and recommended BMP for growers to reduce nitrate leaching during the winter fallow, additional research on more affordable materials and/or application rates will be needed