I was recently contacted by a PCA who was observing armyworm feeding in Delta rice fields. Over the last two years, both locally and in the Sacramento Valley, armyworms have been striking rice fields earlier in the season and in greater numbers. This has been described by farm advisors in the UC Rice Blog. Armyworms are generally a summer pest of rice, spending spring and early summer months on other plants, but over the last two years, armyworm feeding has been detected in June. Armyworms generally only have one generation in rice later in the season, but last year, earlier infestations caused concern for there to be two generations. This was not generally observed, but PCAs should keep this in mind again this year as they scout throughout the summer.  

Armyworm defoliation is most deleterious during stem elongation and grain formation and is observed as angular cut-outs from the leaves (Figure 1). UC IPM guidelines state that yield may be affected if defoliation is greater than 25 percent of the plant at two to three weeks before heading, and they provide the following monitoring instructions.

To sample, choose a part of the field where you have observed injury. Select a plant at random and pull it up or move all the surrounding foliage away and check for defoliation. Check the plant from the top of the leaves to the base of the plant and the water surface for armyworms. Determine if 25% or more of the foliage has been removed by armyworms; also note if you find armyworms on neighboring weeds or rice plants. Record your observations on a monitoring form. Repeat this procedure every 5 to 10 feet across a transect until 10 plants have been examined. Move to a different part of the field where feeding is evident and examine 10 more plants in the same manner. Repeat this procedure at several areas of the field until you are confident that you have an estimate of the average field condition.

It is important to monitor throughout the season in order to detect damage severity, and thus, know when to treat. Later in the season, damage may also occur on the panicle rachis. UC IPM guidelines recommend treatment when, in the vegetative stage, at least half of the plants sampled have at least 25 percent defoliation and armyworms are present. When the panicle has formed, UC IPM guidelines recommend treatment if 10 percent of the sampled panicles are damaged and armyworms are present. Armyworms are generally more apparent at night or in the cooler morning hours; thus, monitoring should occur when worms are active and apparent.

Early season management of armyworms includes weed management around the perimeter of fields. Registered chemicals are limited but include certain pyrethroids, which have not always proven efficacious, and carbaryl, which cannot be used within two weeks of a propanil application. The carbaryl label also includes precautionary language regarding bees, so it would not be recommended when rice is neighbored by insect-pollinated crops, like melons.

This year, the California Department of Pesticide Regulation has issued a crisis exemption under the US EPA Section 18 to allow for the use of Intrepid 2F (methoxyfenozide) on armyworms in certain rice growing counties, including San Joaquin County. The emergency exemption is valid until September 30, 2016. Please contact the county Agricultural Commissioner's office for more details.  

On May 20^th, we planted a grain sorghum seeding rate trial in the Delta to determine an optimum seeding rate for the unique Delta growing environment. Sorghum is a relatively new crop in the northern San Joaquin Valley and Delta region. The most recent crop reports available from the San Joaquin and Sacramento County Agricultural Commissioners' offices (2014) do not specifically name sorghum in their lists of field crops, indicating that it has not been widely planted. Anecdotally, however, I have heard that acreage is up this year as growers diversify their crop portfolios during this time of low commodity prices.

UC research on sorghum has increased over the last few years, primarily in the southern San Joaquin Valley, under the direction of Jeff Dahlberg, Director of the Kearney Research and Extension Center, and Bob Hutmacher, Director of the West Side Research and Extension Center. They have been investigating grain and silage sorghum for its adaptability under drought and low-input conditions.

Sorghum grows well in environments where corn is grown, and it has similar growth habits as corn. A grower would prepare seedbeds similarly for both crops; the vegetative appearance is similar, as is fertility management. There are, however, some differences in growth and environmental requirements between the two crops. Sorghum should not be planted in cold soils, and typically growers should wait to plant sorghum until the soil temperature is at least 60⁰F. Anecdotally, growers in this area are finishing up corn planting and then moving on to planting sorghum to allow the soils to warm. Unlike corn, sorghum tillers, and the head is a panicle of grain that is self-pollinated. The panicles develop over a period of several days, and thus, short periods of hot weather are less likely to damage sorghum pollination as it may with corn.

In our trial, we planted Eureka Seeds variety 3292, which is a white sorghum variety being grown for grain. We planted on 30-inch row spacing and about 2 inches deep. The variety label specifies 16,000 seeds per pound with 85 percent germination. The grower's practice will be to plant 12 pounds of seed per acre, based on seed representative and neighboring grower recommendations. Our trial is a randomized complete blocks design with four replicated blocks of five treatments: 5, 6, 9, 12, and 15 pounds per acre. These treatments correspond to approximate plant populations of 68,000, 81,600, 122,400, 163,200, and 204,000 plants per acre, respectively. (This takes into account the 85 percent germination.) Over the course of the season, we will evaluate the trial for stand establishment, weed pressure, and yield in an effort to determine optimum seeding rate.

The 2016 UCCE  grain corn variety trial was planted on April 27^th. The trial is located in the Delta on Tyler Island. Three replicate blocks of eighteen varieties were planted by air planter. The eighteen varieties included 16 varieties submitted by seed companies and two varieties submitted by the grower, which are presented in Table 1. Each replicate consists of four 30-inch beds on an average row length of about 1200 feet. Seed was planted two inches deep and six inches apart down the row, for an approximate planting density of 35,000 seeds per acre. The soil is a Rindge mucky silt loam with approximately 20 percent organic matter in the top 15 inches of soil. Approximately 55,600 acres in the Delta are described by the Rindge classification. Over the course of the season, we will evaluate the following parameters: stand count, days to bloom, fusarium ear rot, head smut, common smut, lodging, ear height, yield, and grain moisture at yield. Don't hesitate to contact me if you have any questions about the trial, and stay tuned to this blog for trial results at the end of the season.

Table 1. Field corn varieties planted in the 2016 UCCE field corn variety trial.

Brand Initials	Variety Number	Brand Name	Submitted by
CP	6525VT3P/RIB	Croplan	Stanislaus Farm Supply
CP	7087VT2P/RIB	Croplan	Stanislaus Farm Supply
DKC	62-08RIB	DeKalb	Monsanto/Ag Seeds
DKC	63-07	DeKalb	Grower
DKC	63-71	DeKalb	Monsanto
ES	7514VT2P	Eureka Seeds	AgReliant Genetics
ES	7667VT2P	Eureka Seeds	AgReliant Genetics
G	6708VT2P	Golden Acres	AgReliant Genetics
G	7601VT2P	Golden Acres	AgReliant Genetics
INT	6612GSS	Integra	Wilbur Ellis
INT	6474DGVT2PRORIB	Integra	Wilbur Ellis
LG	5701VT2P	LG Seeds	AgReliant Genetics
LG	5622VT2P	LG Seeds	AgReliant Genetics
P	31N27	Pioneer	Grower
SX	5543RR	Baglietto Seeds	Baglietto Seeds
TGY	8156GT	Tech Ag	Lyman Ag Group

Wireworms are the soil-dwelling larvae of click beetles. They feed on the seeds and roots of various crops and are a particular pest of field corn in the Sacramento-San Joaquin River Delta region (Figure 1).

According to the UC IPM Guidelines, wireworms may live three or more years depending on species, conditions, and food supply. Wireworm management in corn is generally by seed treatment or soil treatment at planting. Cultural practices – like crop rotation, flooding, or cultivation – are generally not effective against wireworms. Studies have shown that neonicotinoid seed treatments are as effective at controlling wireworms as organophosphates, the latter being linked to environmental and wildlife persistence. Neonicotinoids, however, are under increased scrutiny for possible off-target effects on bees. The objective of this study was to evaluate the efficacy of a new reduced-risk product called Lumivia^™ (active ingredient chlorantraniliprole) at different rates, in combination with other products, and in combination with polymers, which are used to help hold seed treatments in place. Lumivia^™ was compared to three commercial neonicotinoid products: Cruiser^® (a.i. thiamethoxam), Poncho^® (a.i. clothianidin), and Poncho^® Votivo^® (a.i. clothianidin + Bacillus firmus I-1582). This was the second year of evaluation. Complete reports from both years are available from my website.

Two trials were conducted in 2015 – one on Staten Island and one on Tyler Island. The soil type at both trial sites is a Rindge muck, which characterizes approximately 57,000 acres in the Delta. The Rindge muck is high in organic matter and considered very poorly drained, and thus, it was a good soil for these trials because the soil stays cool and damp into late spring and early summer. Both sites have heavy wireworm pressure, according to the growers, and were planted with corn the previous year. The Staten Island trial was planted on April 15, 2015, and the Tyler Island trial was planted on June 9, 2015, both having four replicate blocks.

We evaluated growth parameters starting at about a week after planting for a period of about six weeks. Growth parameters of interest were emergence, stand count, vigor, damaged plants, dead plants, and height. Additionally, on the second week of evaluations, ten seedlings were lifted. Dead and live wireworms were counted on the seeds, roots, and surrounding soil, and the seedlings were given a visual health rating. The trials were harvested on September 30^th and October 14^th (Staten and Tyler Islands, respectively). Harvest parameters included a plant count, yield, grain moisture, and bushel weight. Additionally, at the Staten Island trial, Johnson grass plants were also counted because weed pressure was high.

Growth results are described in the online report. Yields at the Staten Island trial were highly variable, and both wireworm and weed pressure may have contributed to the variability (Table 1). Johnson grass pressure was especially high in treatments where plant stands were compromised by wireworms or birds. High weed pressure can be a consequence of poor wireworm control because stands that are compromised do not provide the consistent shading to out-compete weeds. Yields can suffer as a result. The Lumivia^™ + Cruiser^® treatment yielded the highest, and Lumivia^™ 750 yielded the worst, even lower than the untreated control. The poor result of Lumivia^™ 750 may be explained by uncontrollable factors, namely, bird damage and high wireworm pressure. The polymer treatments that were tested at the Tyler Island site showed no yield benefits over the non-polymer treatments and yielded similarly to the commercial standard, Poncho^® Votivo^® (Table 2).

The trial results illustrate that growers have several options for managing wireworms. Across both trial locations, results suggest that Lumivia^™ 250 + Cruiser^® 250, Lumivia^™ (500 or 750) in combination with bifenthrin 125, and commercial standards Poncho^®, Poncho^® Votivo^®, and Cruiser^® provide good control against wireworm in the weeks after planting when corn is in the seedling stages. While we saw few statistical yield differences, the control and resulting better stands have the potential to improve yields over non-treated seeds. The two Poncho^® products are commercially available from Bayer CropScience, and Cruiser^® is commercially available from Syngenta. Lumivia^™, a Dupont product, is not yet commercially available as a corn seed treatment in California, but if it were to become so, it would provide growers with an alternative to the neonicotinoid treatments. When making decisions on products, growers should consider their wireworm pest pressure and other soil-dwelling pests that could limit their production. Growers should also consider which seed treatments they have been using and whether those are still controlling pests. If not, rotating to a different chemistry might be a way to bring pests back under control. Integrated pest management practices recommend rotating chemistries for insect resistance management.