Kimberly Jane Gibson
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
- Author: Rachael Freeman Long
- Author: Amber Vinchesi-Vahl
A question came up about managing root-knot nematodes in processing tomato and lima bean rotations. Root-knot nematodes are tiny worm-like soil dwelling pests that cause root galling on plant roots, resulting in significant yield and quality losses. Symptoms of severe root-knot infestations include patches of chlorotic, stunted, necrotic, or wilted plants. These nematodes also predispose plants to other soilborne pathogens that cause root rot and wilt diseases. For example, a bean variety resistant to infection by the Fusarium wilt pathogen will become susceptible to this disease if infected with root-knot nematodes.
What is the link between nematodes in tomatoes and limas? Dr. Phil Roberts, Nematologist at UC Riverside shared the following response:
There are several root-knot nematode species and they differ in their response to resistance in tomato and various bean crops. Most common in our Sacramento Valley area are Meloidogyne incognita and M. javanica. These nematodes are normally controlled by Mi-1 gene based resistant tomatoes, but there are resistance-breaking populations so that could be the reason for the infection on tomato (unless the tomatoes grown were not actually resistant). A further possibility is that the species is M. hapla, which is not controlled by the tomato resistance. M. hapla tends to induce smaller pearl-like galls on tomato roots and is not common in the Sacramento and northern San Joaquin Valleys.
As to rotating with lima beans, limas are susceptible to these root-knot species but there are resistant varieties available. Beja Flor baby lima has strong root-knot resistance. It was bred to contain three resistance genes that do a good job of blocking M. incognita and M. javanica. It yields well with the caveat that Steve Temple (former UCCE legume specialist) used to remark that it is more Lygus bug susceptible than some varieties, so if a grower went with UC Beja Flor they would need to keep up on the Lygus management. UC Luna baby lima has no root knot resistance. Other lines carrying M. incognita (but not M. javanica) resistance are the large limas White Ventura N and UC92.
If root-knot nematodes are present in a field with a history of Fusarium wilt, choose varieties that are resistant to root-knot nematodes as well as to the particular Fusarium wilt race present when possible. Another option is to rotate with root-knot nematode resistant cowpeas (blackeyes) instead of limas. Based on host-range tests, some varieties of cowpea have more root-knot nematode resistance than tomato. For example, some root-knot nematode races are virulent and highly pathogenic to Mi-1 gene based resistant tomatoes but not to nematode resistant cowpeas.
Have you ever wondered about this damage to garbanzo beans where there's a hole clipped in the pod and the seed is missing (see photo)? In this case, the damage is from pesky ground squirrels that were foraging in and around our garbanzo research plots at UC Davis this spring. However, other culprits could include field mice or voles, rats, and pod borers such as corn earworm. If you suspect caterpillar worm pests, you should be able to find them easily enough in the plant canopy. Sometimes corn earworms move from corn fields into garbanzos, so watch for infestations from nearby corn fields. Field mammals are more elusive, though ground squirrels are active during the day and easy to spot.
Generally, garbanzos have few pests because the plants (including seed pods) are covered with tiny glands that secrete acids that help repel pests. These acids are strong enough to cause skin rashes and damage clothing. However, ground squirrels don't seem bothered at all by these plant acids as they thrived on our garbanzo seeds, green and dried alike! Looking back, we should have paid more attention to where the field trial was located, avoiding places where ground squirrels thrive, such as a nearby ditch bank. We also should have controlled them as soon as they were active.
Ground Squirrel Control. Various methods can be used to control ground squirrels around fields, including fumigation, trapping, and toxic baits. Of critical importance is the timing for control. Effective management depends heavily on understanding the unique life cycle and behavior of the California ground squirrel. Baiting with treated grain is effective in summer and fall because squirrels primarily feed on seeds during this period. Burrow fumigation is most effective in spring, when moist soil helps seal gasses in the burrow system. Fumigating at this time is also more effective in reducing ground squirrel numbers since squirrels die before they can reproduce. More information on ground squirrel management can be found on the UC IPM website for ground squirrel control at http://ipm.ucanr.edu/PMG/PESTNOTES/pn7438.html.
Recently, I received a call about a blackeye bean field in the San Joaquin Valley with a lot of bean pods that did not fill out at the tips (photo). I contacted the UC Riverside blackeye bean breeders Drs. Phil Roberts and Bao Lam Huynh and they shared that this problem is primarily caused by heat, which affects pollen viability and thus fertilization. Here's their response:
It [lack of pod fill] is the typical male-sterility symptom [lack of pollen viability] associated with extreme temperatures (heat or cold). Based on the planting date you gave, we just checked the temperature in Denair, CA [farm location] and noted that it was quite warm (~100) during the flowering time (40-50 days after planting) and recently during the pod filling stage, so heat must have been a main cause. The symptom could also be more severe if water is limiting.
Always be prepared with good irrigation management practices for all crops going into heatwaves, like the one we're having now. The minimum seasonal irrigation needed to produce a blackeye bean crop being managed for full yield from one pod set is 16 to 18 inches. This estimate includes a pre-irrigation of 4-inches, and irrigations of 4-inches when floral buds first appear, and 8 to 10 inches during 5 to 6 weeks of flowering and pod filling. If additional irrigations are needed during the vegetative stage, one could increase the total irrigation requirement to 20 or more inches. Irrigating for a second flush of pods could require an additional 8 to 12 inches of water. Irrigation requirements are further increased by any water required to leach salts or to compensate for an inefficient irrigation system.
Additional water may need to be applied during extreme heat events which drive plant transpiration rates to the limit. Make sure to check the soil moisture in the top 12 to 24 inches of the soil profile and apply additional water if the soil is dry. If in doubt about how much additional water is needed, check the reference evapotranspiration (ETo) and make sure to irrigate to replace at least 120% of your daily ETo in your area. The current (mid to late August) daily ETo in the San Joaquin Valley ranges from 0.25 to 0.30 in/day; make sure your applied irrigation replaces 120% of these values.
More information on growing blackeye beans can be found in the publication, UC ANR Blackeye bean production in California, http://beans.ucanr.edu/files/226601.pdf.
In May, I looked at a lima bean field in the Sacramento Valley that showed poor seedling emergence scattered throughout the field (photo 1). I sent samples to the UC Davis Plant Pathology lab and the main pathogen consistently recovered from the roots was Fusarium root rot, a fungal disease caused by Fusarium solani f. sp. phaseoli. This pathogen is specific to beans and field peas and will not infect other field crops. A few bean seedlings also had Rhizoctonia and Pythium (also fungal pathogens).
Finding Fusarium root rot in a lima bean seedling field was a surprise because this disease is most commonly encountered in established fields during mid- to late season, where it is one of the causes of early maturity ("cut out"). Rhizoctonia and Pythium can cause seedling damping-off in dry beans. However, plants usually outgrow these pathogens, particularly if the seed is treated with a fungicide and conditions favor rapid emergence.
Fusarium solani attacks underground stems and roots of plants. In established plants, early infection is characterized by elongated reddish streaks on the roots. As the disease progresses, these eventually form reddish-brown lesions that will surround the entire root, causing decay. The above ground plant symptoms of affected plants included yellowing, wilting, stunting, and dieback. On seedling plants in the affected field, I observed dieback of the growing point, stems that were a bit swollen, and roots that were brownish and not well developed (Photo 2, diseased roots on left, healthy on right).
Fusarium root rot causes little damage to healthy plants, but under conditions of plant stress due to drought, poor nutrition, or oxygen-stressed, waterlogged soils, Fusarium root rot can cause plant dieback and yield losses, particularly in fields with a long history of bean production. In this particular lima bean field, soil moisture was lost, causing plants to be extremely water stressed. Crop rotation, use of seed treatments, and closely watching field conditions to ensure plants are not stressed will help manage Fusarium root rot. This disease tends to be a problem in fields with a long history of bean production. More information on diseases in dry beans can be found on the newly revised UC IPM guidelines for dry beans.