Unusual growth patterns were observed in a newly emerging baby lima field in Colusa County that were planted in late April, prior to a cold snap. The grower planted the field into baby limas at 70 lbs of seed per acre. The field was planted on April 28^th in 3-4” row spacing at a 1.5 to 1.75 inch seeding depth. Soil temperature at planting was 57 degrees. The grower applied a pre-plant mix of Brawl (S-metolachlor) and Sonalan (ethalfluralin) at labeled rates. In the two weeks after planting, when beans were germinating and emerging, there was a cold spell, with a low of 37F.

The grower and PCA observed unusual growth patterns in seedlings including twisted and u-shaped stems, plants emerging and then growing back into the soil, stunting of the leaves and new shoots, swollen hypocotyl, and rusty red lesions on stems near the soil line. Some plants appeared to have hollow stems. About 20% of the plants did not emerge or died.

Plant samples were collected on June 1^st and taken to the UC Davis Plant Pathology lab. At the lab it was observed that the lesions and abnormal vascular tissue, which often indicate disease, were not active infection sites. The tissue was not rotting or necrotic with some damage appearing more callous where damaged tissue had a clear end, and healthy tissue began (lesions did not extend into the stem tissue as one would expect from an infection). This type of damage is usually abiotic (not caused by a pathogen). Overall, diagnostic tests confirmed that there was no evidence of a pathogen and concluded that damage was caused by abiotic factors.

Seedlings grow more slowing in cool conditions and the baby limas had more residence time in the soil following germination because of the cool weather conditions. This led the bean shoots to absorb some of the pre-plant herbicide mix in the moist soils. Herbicides are designed to modify plant growth and the symptoms observed match expected symptoms from the tank mix that was applied.

Sonalan is MOA 3 (mode of action) and inhibits root growth. Brawl is MOA 15 and inhibits seedling shoot growth. Both in combination lead to stunted malformed plants with swollen stems and stubby roots as we saw in the field. Increased exposure from cold weather in wet soils along with a bit of soil crusting due to high magnesium levels in the soil led to unfortunate injury. Fortunately, plants will typically fill in and grow out of this type of abiotic damage as the season progresses.  In the end, the field yielded well, over 3,500 pounds per acre (uncleaned).

We look forward to hosting the UC Dry Bean Field day next Tuesday at UC Davis. This is just a reminder that, due to Covid-19 safety precautions, pre-registration is required. There is no registration fee. Please visit https://tinyurl.com/ucbean21 to register. The agenda is pasted below, and a downloadable version is available from the registration page. CCA continuing education credits (2.0) have been approved. Thank you, and we hope to see you next week!

Agenda:

9:00 am   General Introduction, Paul Gepts, UC Davis

9:10 am   Improving Both Productivity and Nutritional Quality in Beans, Christine Diepenbrock, UC Davis

9:20 am   Garbanzo Drought Tolerance Genetic Study, Claire Spickermann, UC Davis

9:30 am   Applying Novel Sensor Technology to Studying Lygus Interactions in Lima Bean, Kimberly Gibson, UC Davis

9:40 am   Green cotyledon and Growth Vigor Research, Varma Penmetsa, UC Davis

9:50 am   Lima Bean Breeding and Cooperative Dry Bean Nursery, Antonia Palkovic, UC Davis

10:00am  Dry Bean Research Update: Seed Treatments, Plant Growth Regulators, USDA Garbanzo Variety Trials, Rachael Long UC Cooperative Extension

10:15am  Nitrogen Fertility in Common Beans following Whole Orchard Recycling, Michelle Leinfelder-Miles, UC Cooperative Extension

10:30am  Travel to Agronomy Field Headquarters

10:40am  Release of New Bean Varieties with Heirloom-like Seed Patterns, BCMV Resistance, and Improved Yields, Travis Parker, UC Davis

10:50am  Post-emergence Herbicide Options for Broadleaf Weed Control in Blackeye-beans, Jose Luiz Carvalho de Souza Dias, UC Cooperative Extension

11:00am  UC Blackeye Variety Trial Updates, Sarah Light, UC Cooperative Extension and Bao-Lam Huynh, UC Riverside

11:10am  Travel to Campbell Tract Field 

11:20am  Physiological Breeding for Drought Resilience in Common Bean, Tom Buckley, UC Davis

Monitoring insect populations in crop fields is important for managing pests and diseases. Sweep nets have been the main tool for this task but new sensor technology is being developed to conduct continuous real-timing monitoring. This summer, the Gepts Lab at UC Davis is hosting 5 such sensors from the Danish start-up company, FaunaPhotonics, in collaboration with Dr. Emily Bick, who earned her Ph.D. in Entomology from UC Davis in 2019 and is currently a Postdoctoral Fellow at the University of Copenhagen.

These sensors operate by shining LEDs at 2 specific wavelengths into a conically shaped volume of approximately 30 liters extending about 2 meters out from the sensor. As insects fly through the beams, light bounces off of them and is returned to the sensor. From this returning light, 30 different data points are collected including wing-beat frequency, body-size to wing-size ratio, color, and speed. With a trained model, analysis of these data can identify insects by species, sex, age, and mating status. With an untrained model, a cluster analysis can be conducted to determine the overall diversity of the insect population.

Model-training datasets are created by flying pre-identified populations of insects in a black neoprene cage equipped with a sensor. A disadvantage of this technology is that it only monitors flying insects. While most pests and beneficial insects do fly as adults, nymphs and larva do not fly.

The sensors are mounted on posts positioned about half a foot above the crop canopy. Two portable solar panels connected with a car battery enable the sensors to run continuously. While wireless data transfer is possible for live monitoring, the sensors can also store data on memory cards for future study. Each sensor is equipped with a small external weather station which monitors temperature and humidity.

Past studies have used these sensors to study a variety of insects in olives, alfalfa, canola, apples, strawberries, corn, soy, winter wheat and other crops. While only a handful of sensors are currently in existence, one can envision a future in which permanent installations of this technology provide routine monitoring for various crops.

Our California research project with the sensors is focused on monitoring lygus bugs L. hesperus in lima beans. Currently, all five sensors are installed over lima beans. Four are positioned in unsprayed strip plantings of UC 92, UC Haskell, UC Beija Flor, and Henderson Bush respectively. The fifth sensor is located in a sprayed strip planting of UC 92. The collected data will inform our research on the specific mechanisms of Lygus-tolerance in lima bean. We also hope to gain insight into the interactions between Lygus and various beneficial insects that prey on or parasitize Lygus including big-eyed bugs, Geocoris spp., Peristenus relictus, a parasitoid wasp, and minute pirate bugs, Orius spp.

By monitoring insect presence and abundance continuously over the course of a season, these sensors have the potential to provide researchers, plant breeders, and farmers more detailed data than the snapshot measurements provided by sweep nets. Researchers may be able to identify the specific mechanisms of plant tolerance to an insect pest. For example, in my study, the sensor data may reveal differences among lima bean lines in attracting or repelling Lygus; or may reveal which lines more successfully attract beneficial insects. With a better understanding of the specific mechanisms of plant insect tolerance, plant breeders will be able to more successfully select new resistant varieties. The sensors are not yet publicly available but eventually they may be used by farmers to monitor pest populations and make management decisions.

The Gepts Lab will be showcasing these sensors at the UC Davis Dry Bean field day on August 31, 2021.  We are mindful of the on-going Covid-19 pandemic and are following safety precautions to keep everyone safe. Therefore, pre-registration for the event is required. There is no registration fee, but the registration survey will help us in the event there is a need for contact tracing. Please visit https://tinyurl.com/ucbean21 to register. This link also provides directions to the dry bean field site. Thank you for your cooperation, and we look forward to seeing you later this month.  A full agenda can be found at:http://beans.ucanr.org/?blogpost=50265&blogasset=91063