In recent years, the University of California Division of Agriculture and Natural Resources has augmented research efforts on growing grain and silage sorghum [Sorghum bicolor (L.) Moench] in California. The purpose of the Delta Sorghum Seeding Rate Trial was to better understand optimal seeding rates for grain sorghum grown in the Sacramento-San Joaquin River Delta. While such information exists for Midwest sorghum production, applied information is lacking for California, and more specifically for the Delta – a unique agricultural region known for its organic soils, shallow groundwater, and cooler climate conditions. This information is important because sorghum has similar growth habits as corn and is sometimes grown as a substitute for corn because of its tolerance of drought and low-input conditions. In the United States, sorghum is used in a wide array of feedstocks for biofuels, pet foods, dairy, cattle, pork and poultry feed, and more recently as a gluten-free cereal grain for human food systems.

The trial took place during the 2016 and 2017 growing seasons on Tyler Island in Sacramento County. The 2016 trial was planted on May 20^th, and the 2017 trial was planted on May 25^th using a John Deere cone planter. Seed was planted approximately 2 inches deep. We used the grower's varieties, which were Eureka Seeds 3292 in 2016 and Eureka Seeds 3325W in 2017. Both varieties were white sorghum varieties, had 16,000 seeds/lb, and 85 percent germination, according to the labels. Five seeding rate treatments (5, 6, 9, 12, and 15 lbs/acre) were tested. Each plot consisted of four rows (30-inch row spacing) that were 45 feet in length in 2016 and 50 feet in length in 2017. The fields were managed similarly in both years. Site characteristics, cultural practices, and statistical procedures are described in the full report.The plots were harvested on November 14, 2016 and October 12, 2017 using an Almaco research combine, harvesting the center two rows from the four-row plots. Trial results are presented as plant establishment characteristics (Table 1), plant maturity characteristics (tables available in the full report), and yield (Figure 1). The tables and figure present mean values for the four (2016) or five (2017) replicates. Differences among treatments are indicated by different letters following the mean.

The seeding rates are expressed as plant populations in Table 1. The number of sorghum seeds/lb is highly variable across varieties. For this reason, when determining seeding rates, growers should first determine their desired plant population. A worksheet in the full report provides equations for calculating seeding rate based on desired plant populations and percent germination for the variety. Stand counts were made as the number of plants/10-foot row length approximately two weeks and one month after planting. The counts were scaled up to plants/acre. Across both years, stands generally decreased from the first count date to the second. Stand counts were lower in 2017 compared to 2016, but this did not translate into lower yields. Weeds were also counted in the month after planting (data not shown), but overall weed pressure was very low in both years.

Table 1. Plant establishment characteristics of the 2016 and 2017 UCCE Delta sorghum seeding rate trial.

While there were no statistical differences in yield across treatments in either year, the take-home message of the trial is that there appears to be no benefit to planting the highest seeding rates. In both years, the trend was for the 15-lb seeding rate to have the lowest yield. In 2016, there was a lot of variability in the data. There was a trend for the 9-lb treatment to have higher yields; however, we suspect this was due to the experimental design. In 2016, by random chance, there were several 9-lb treatment plots next to the sub-irrigation ditches, which were exterior to the experiment on both sides. For this reason, the 9-lb treatment may have been inadvertently favored with better moisture conditions. To correct for this, the experimental design was changed in 2017 in order to better control field variability. The 2017 yields were consistent across treatments, around 7000 lbs/acre. The 2017 results best illustrate how planting the higher seeding rates provided no yield benefit, yet would incur a higher seed expense. We recognize that growers will need to consider site characteristics, like weed or wireworm pest pressure, when determining optimal seeding rates; nevertheless, this research indicates that good yields can result from seeding rates of 5 or 6 lbs/acre (estimated plant populations of 80-96,000 plants/acre), and that planting higher plant populations would not only cost growers more in seed expense but could also cost them in yield.

Figure 1. Yield at 13 percent moisture of UCCE Delta sorghum seeding rate trial. There were no significant differences among treatments in 2016 (P = 0.1278) or 2017 (P = 0.2419).

In summary, it is important to study sorghum cultural practices in the Sacramento-San Joaquin Delta region, and in California at-large, because currently, most applied information comes from the Midwest. California growers need information on sorghum cultivation because sorghum may be grown as a lower-input substitute for corn. Sorghum seeding rates were studied to assist growers with determining optimum rates for the Delta environment. The results indicate that there is no yield benefit to planting seeding rates greater than 6 lbs/acre (estimated plant population greater than 96,000 plants/acre), and that planting higher rates is just added expense for the grower. Future research should investigate these plant populations on narrower row spacing. Special thanks go to growers, Steve and Gary Mello, and to UC Kearney Research and Extension Center Director, Jeff Dahlberg, for providing equipment and information for the success the trial.

Happy New Year! Hopefully the holidays were a time to rest and revive. We now enter "meeting season". The new year brings several opportunities for continuing education, including UC Cooperative Extension grower meetings, the California Plant and Soil Conference, and the Rice Technical Working Group Conference. Please see below for more information. The agendas are attached at the bottom of this posting.

1. UC Cooperative Extension will host the SJC and Delta Field Crops Meeting on Friday, January 12, 2018 from 8:00am to 12:00pm. The meeting location is the Cabral Agricultural Center in Stockton (2101 E.Earhart Ave., Stockton, CA 95206). Lunch will be provided, so please RSVP by calling 209-953-6100 or emailing cesanjoaquin@ucdavis.edu. (If you email us, please indicate your first and last names, how many people you are RSVPing for, and whether any of those people are vegetarian.) Those who RSVP will receive a lunch ticket when they arrive at the meeting. Due to budgetary considerations, we cannot guarantee a lunch to those who do not RSVP. Continuing education credits for DPR (2) and CCA (3) certifications will be available.

2. UC Cooperative Extension will host five meetings for rice growers. The meeting details are as follows:

Woodland: Tuesday, Jan. 16, 1:30pm, Cracchiolos Banquet Hall, 1320 E. Main Street, Woodland

Richvale: Wednesday, Jan. 17, 8:30am, Evangelical Church, 5219 Church St., Richvale

Willows: Wednesday, Jan. 17, 1:30pm, Glenn County Office of Education, 311 South Villa Avenue, Willows

Colusa: Friday, Jan. 19, 8:30am, Colusa Casino Resort, 3770 Hwy 45, Colusa

Yuba City: Friday, Jan. 19, 1:30pm, Veterans Hall, 1425 Veterans Memorial Circle, Yuba City

Time: Doors open at 8:00am, and meetings start at 8:30am at Richvale and Colusa. Doors open at 1:00pm, and meetings start at 1:30 pm at Woodland, Willows, and Yuba City. DPR and CCA continuing education credits will be offered.

3. The California Chapter of the American Society of Agronomy will hold its annual Plant and Soil Conference on February 6-7 in Fresno, California. Program information and registration are available from the conference website. The keynote address will be given by Karen Ross, Secretary of the California Department of Food and Agriculture. DPR and CCA continuing education credits will be offered.

4. The University of California is pleased to welcome the 37th Rice Technical Working Group Conference to Long Beach California from February 19-22, 2018. Registration is now open. Session topics include rice culture, pest management, and plant breeding. Continuing education (DPR) will be available. Please see the conference website for more information.

On Friday, January 12th, I hosted the annual SJC and Delta Field Crops Meeting in Stockton, CA. The presentations from that meeting have now been posted to my website and are available here. Also available from my website are full reports of local research trials, including the Delta sorghum seeding rate trial and field corn variety trial.

UC statewide specialists make their research results available through the Agronomy Research and Information Center (RIC) website. At the meeting, we had a presentation that referenced the small grains variety selection tool, which was developed using trial data from across the state. 

We hope you will find this information useful, and we hope you will share your feedback with us so that we may best serve your interests for research and outreach.

I have received a couple inquiries from Pest Control Advisors about wheat that is showing leaf tip yellowing and burning (Fig. 1). Their suspicion is frost injury, and with the weather we have experienced over the last several weeks, their suspicion is likely true. 

Fig. 1. Yellowing and tip burning of wheat from frost injury. (Photo courtesy of PCA.)

There isn't a hard-fast rule of when frost injury will occur because several factors influence its occurrence and severity. The factors include the temperature but also the duration of cold exposure, the plant growth stage, and the growing conditions. The UC Small Grains Production Manual (see page 101) states that injury may occur with temperatures at or below 35⁰F and that even just a couple hours of exposure is enough to cause injury.

Below (Fig. 2), I present temperature data from the last month from a few local CIMIS stations. Remember that in early-February, daytime highs were getting above 70⁰F. By mid-February, however, minimum temperatures were low enough to cause frost injury, and hourly data (which I am not showing but is available from the CIMIS website) shows that temperatures below 30⁰F often spanned several hours over many nights in late-February.

The plant stage of development is critically important to how a crop may be injured from frost and how it may overcome injury. At tillering, leaf yellowing and tip burning will be the obvious symptoms. At this stage, however, yield impact will likely be slight, if any. That is because the growing point of the tillers is close to the soil and protected from the cold. When warmer weather resumes, the plants may be able to continue tillering, particularly in thin stands where there is space to fill, and overcome the injury. In the jointing stages, in addition to the leaf yellowing and tip burning, some leaf or stem lesions may be apparent. There could be moderate impacts on yield if the growing points of the tillers have been injured. Look for a chlorotic or dead leaf in the whorl. Also, try splitting the stem with a razor blade at the growing point. This picture from Texas A&M University shows how to do this. If the growing point (at the arrow) appears white, brown, or water-soaked, then there has been frost injury. Once the crop gets into the reproductive stages of growth, it becomes more sensitive to injury with bigger repercussions for yield, but luckily, I think most of the fields in our region aren't yet to these later stages of development.

Fig. 2 Recent temperature data from three San Joaquin County CIMIS stations

Keep in mind that there are field and other growth conditions that may lessen or worsen the severity of frost. Low parts of the field where cold air settles will likely show more injury. Fields that were planted earlier in the fall, or earlier-maturing varieties, that are in a later stage of growth will likely show more injury. Crops that have had good moisture and nutrient conditions may also show more injury. With one of the inquiries I received, the field had been fertilized about a month ago, and given the warm daytime temperatures we had at that time, those plants were likely resuming growth and probably got hit by the frost all-the-more. Crops that have been moisture stressed, however, may have been hardened and not show as much injury.

So, what now? Again, growers and consultants with crops in the jointing stages who are seeing leaf tip yellowing may wish to split some stems to observe whether there has been injury to the growing points. If this has occurred, there is nothing that can be done to “save” those tillers, but it might provide some insight into potential yield impact. If stem lesions appear, be on the look-out for disease infections but also lodging later in the season. Unfortunately, the most telling symptom will appear after heading when grain doesn't fill. Don't hesitate to reach out to me or your local farm advisor if you have questions about frost injury.