- Author: C. Scott Stoddard
- Posted by: Gale Perez
August 7, 2021
Bindweed is a headache not only for its persistent and pernicious growth habit and ability to reduce tomato yields, but also because it can physically stop a processing tomato harvester in the field. Vigorously growing vines can become entangled around the shaker and conveyor belts, requiring the equipment operator to shut down and manually clear out the foliage.
Several years ago, myself and other UC researchers conducted herbicide trials evaluating field bindweed control -- with marginal success. In a given year and location, most of the registered herbicides in tomatoes gave only temporary suppression – about 40 – 80% bindweed control at 8 weeks after transplanting. Best results were observed where herbicides were stacked: trifluralin (Treflan) pre-plant incorporated followed by rimsulfuron (Matrix) post. Glyphosate helped in situations where the bindweed emerged early and could be applied before transplanting (Figure 2).
Earlier this year, I was asked to summarize the effects of weeds on processing tomato yield. This made me go back and look at this work, but with a slightly different emphasis: impact of weed control (or really, lack of weed control) on yield. To increase the size of my dataset, I also included data from trials done at UC Davis. Where I had data for both yield and weed control in good, replicated trials, I performed a regression analysis comparing % weed control and % relative yield (relative yields remove the year-to-year and location variability). In the end, I used 4 trials from 2012-13 (Table 1).
Surprisingly, these data suggested that where bindweed dominated, it did not have a big impact on processing tomato yield. Even with just 50% control 8 weeks after transplanting, potential yield was 88-95%. This may have occurred because bindweed does not shade out the tomato canopy nearly as much as some of the common annual weeds. However, when tall broadleaf weeds dominated, such as pigweed, nightshades, and lambsquarters, yields dropped rapidly. I had some plots with a 99% yield drop if these weeds were allowed to grow all season. In this situation, the weeds towered over the tomato canopy.
Literature cited:
Van Wychen L (2019). 2019 Survey of the most common and troublesome weeds in broadleaf crops, fruits & vegetables in the United States and Canada. Weed Science Society of America National Weed Survey Dataset. Available: https://wssa.net/wp-content/uploads/2019-Weed-Survey_broadleaf-crops.xlsx
- Author: O. Adewale Osipitan
- Author: Brad Hanson
- Author: Matthew Fatino
- Author: Mohsen Mesgaran
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Branched broomrape (Phelipanche ramosa), a weedy parasitic plant that can cause devastating damage to many economically important wide range of broadleaf crops including tomato, cabbage, potato, eggplant, carrot, pepper, beans, celery, peanut and sunflower has recently re-emerged in fields in Central Valley counties in California. This weed utilizes a modified root, called haustorium, to fuse into a host plant root and extract nutrients and water which can greatly reduce productivity or even kill the host depending on the level of infestation, susceptibility of the host, and environmental conditions. Tomato is highly susceptible to branched broomrape. In the United States, California accounted for over 90% of the 12 million tons of tomatoes grown in 2018. Studies in Israel showed that at extreme infestation levels broomrape can cause processing tomato yield losses as high as 70%. The annual losses in tomato due to broomrapes in Israel and Turkey are estimated at $5 and $200 million, respectively. Up to 80% crop loss due to branched broomrape has been reported in tomato in Chile which is highly concerning given the similarity in production systems and broomrape species with California.
Branched broomrape is currently classified in California as an “A” pest, that is, “an organism of known economic importance subject to California State enforced action involving: eradication, quarantine regulation, containment, rejection, or other holding action”. As a potentially severe economic pest and as a California “A-list” pest, establishment and spread of a branched broomrape in California tomato production regions could cause severe consequences for individual growers and for the entire tomato industry. Currently, discovery of broomrape in a commercial tomato field leads to a hold order and crop destruction without harvest. In addition to branched broomrape, several fields have been reported with infestations of Egyptian broomrape (Phelipanche aegyptiaca), a Q-listed species (that is, having a temporary “A” classification pending determination of permanent rating by California State), causing similar industry and grower concerns.
A severe infestation of branched broomrape in the Sacramento Valley in 1959 prompted an intervention that involved soil fumigation with methyl bromide to target the soil seedbank; this was as an industry-led effort funded through a legislative marketing order program. Branched broomrape became a less significant problem after that effort which involved research, intensive field surveys, and fumigation of infested fields and equipment from 1973 to 1982 that cost over $1.5 million. However, this parasitic weed has recently been detected in several tomato fields in Yolo, Solano (Egyptian broomrape) and San Joaquin Counties. The cause of the re-emergence of the problem remains unclear, although re-introduction or recurrence from long-dormant seed in the soil and subsequent spread have been speculated.
Research efforts are currently being made to further understand, and develop detection and control approaches for branched broomrape in tomatoes and other specialty crops in California. For more information about branched broomrape in California, please see:
http://tomatonet.org/branchedbroomrape
http://tomatonet.org/img/uploadedFiles/Broomrape/CTRI_2019_NEWSLETTER.pdf
https://www.plantsciences.ucdavis.edu/news/broomrape-eradication-high-priority-uc-researchers
- Author: Amber Vinchesi-Vahl
Weeds are one of the biggest challenges to organic vegetable production and can be expensive to manage since herbicides are not an option.
Though sub-surface drip irrigation is the most common method of irrigation in processing tomatoes in California, furrow irrigation is still used by some producers in Sutter County, particularly organic growers. Buried drip irrigation allows for dry bed tops which helps prevent weed germination among other benefits. Furrow irrigation is common among organic producers in Sutter County because it allows for more flexibility with crop rotation and tillage. Alternate furrows are irrigated to keep bed tops from getting too wet but still provide sufficient moisture to tomatoes. Irrigation is generally not needed immediately after tomatoes are transplanted due to adequate moisture from spring rains, but sprinkler irrigation is sometimes used for seedlings before switching to furrow irrigation. Organic and furrow-irrigated tomatoes are generally planted in single row to facilitate mechanical cultivation.
Mechanical cultivation is used when tomatoes are small to control weeds in the beds and seedline. The closer a cultivator can get to the seedline, the better, because it will likely reduce the need for hand weeding.
There are many different types of cultivators, two of which are the double disc opener and the finger weeder. I am currently working on a trial comparing the two for weed control efficacy in an organic tomato field. The double disc opener is a common standard cultivator, while the finger weeder is newer and gaining in popularity because it can reach the seed line to remove weeds.
To measure weed control, I am taking percent cover measurements pre- and post-cultivation in random 1m2 quadrats within plots where the double disc opener was used or where the finger weeder was used. I am measuring bare soil, tomato plants, residue (from the vetch cover crop), broadleaf weeds, grass weeds, and volunteer vetch. Examples from early May, late May, and mid-June can be seen below.
Once the tomatoes are too big for mechanical cultivation, hand weeding crews are relied upon for weed control in organic production.
UC-IPM. Pest Management Guidelines for Tomato. Integrated Weed Management. http://ipm.ucanr.edu/PMG/r783700111.html
- Author: Sara Tiffany
- Author: Dr. Martin Burger
The Solution Center for Nutrient Management brought together growers, advisors and university researchers for a breakfast meeting to discuss nitrogen management in processing tomatoes. A number of growers attended to share their experiences and learn about research including a new protocol for accurate soil nitrate sampling, and the latest updates on agricultural greenhouse gas emissions research. Cooperative Extension Specialist Daniel Geisseler also presented the CDFA-FREP website that provides Fertilization Guidelines for California's Major Crops, including tomato: https://apps1.cdfa.ca.gov/FertilizerResearch/docs/Guidelines.html
Research Highlights:
Soil nitrate sampling protocol
For maximum accuracy that can reliably predict nitrate availability in the soil, growers should sample according to the following protocol:
- For fields with 60-inch beds: soil cores should be taken at 3 lateral distances from drip tape, in at least 4 locations within a field.
- For fields with 80-inch beds: soil cores should be taken 2 lateral distances from drip tape, in at least 3 locations within a field.
click here to read full summary (or scroll down)
Research on agricultural greenhouse gas emissions in tomatoes
- The adoption of subsurface drip irrigation substantially reduces greenhouse gas emissions in tomato production (compared to furrow irrigation).
- Use of nitrification inhibitors lowers nitrous oxide emissions in tomato fields with subsurface drip irrigation.
click here to read full summary (or scroll down)
Full Summaries:
Soil nitrate sampling protocol
UC Davis researcher Dr. Martin Burger presented the results of a survey conducted by post-doctoral scholar Cristina Lazcano on pre-plant nitrate, phosphorus (Olson-P), and exchangeable potassium levels in 16 processing tomato fields in Yolo, San Joaquin and Fresno counties. The purpose of the study was to develop an economical sampling protocol that reliably predicts nitrate availability and allows growers to adjust fertilizer rates taking the residual soil nitrate into account.
While the conversion to subsurface drip irrigation has enabled growers to precisely deliver water and nutrients close to plant roots, there is still pressure for growers to increase nitrogen use efficiency, for example to reduce the risk of nitrate leaching. Previously, the spatial distribution of macronutrients in fields under drip irrigation was not well known. One concern has been that nitrate may accumulate at the periphery of the wetted soil volume, whereas the less mobile nutrients phosphorus and potassium may be depleted near the drip tape where roots can be expected to proliferate.
According to the survey encompassing more than 1000 soil analyses, pre-plant nitrate levels in the 16 fields varied widely, ranging from 45 – 438 lbs NO3- - N per acre in the top 20 inches of soil, with higher levels of nitrate found in fields under consecutive tomato cultivation. No depletion of Olsen-P or potassium in the root feeding areas close to the drip tape was detected. The majority of the fields showed phosphorus concentrations lower than 15 ppm, which based on earlier research is the threshold below which a yield response can be expected from a P addition. In contrast, potassium levels were higher than previously reported values, ranging from 293 ppm on average in Yolo County to 468 ppm in Fresno County.
The nitrate sampling protocol was based on a Minimax analysis by selecting the minimum number of samples within the field and locations within the beds (i.e. lateral distance from the drip tape). The combination of samples with the lowest relative error across all fields (< 5% from the field average) and the lowest number of samples taken was selected as the best sampling procedure to estimate average soil NO3-N. The analysis showed that soil cores should be taken at three (60-inch beds) or two (80-inch beds) lateral distances in at least four (60-inch beds) or three (80-inch beds) locations within a field.
Table 1. Pre-plant nitrate sampling protocol for 60-inch beds in Yolo (Y), San Joaquin (SJ), and Fresno (F) County SDI tomato fields.
Table 2. Pre-plant nitrate sampling protocol for 80-inch beds in Yolo (Y), San Joaquin (SJ), and Fresno (F) County SDI tomato fields.
***The full article about this study will appear in the Oct-Nov-Dec 2015 issue of California Agriculture.
Research on agricultural greenhouse gas emissions in tomatoes
An update on agricultural greenhouse gas emissions research included results of field studies testing a nitrification inhibitor for mitigation of nitrous oxide in subsurface drip irrigated tomato.
Nitrous oxide (N2O) is arguably the most important greenhouse gas produced in the agriculture sector, with its global warming potential 300 times that of Carbon Dioxide. N2O is produced by soil microbes during N transformations. N2O is a by-product of nitrification and denitrification.
Recent studies have shown that N2O produced during nitrification can be as important as that resulting from denitrification (Zhu et al., 2013). The highest rates of N2O emissions typically occur shortly after N fertilizer applications when soils are re-wet. The main regulatory factor is the availability of oxygen since microbes use nitrate (denitrification) and nitrite (nitrification) as electron acceptors of respiration when oxygen is in short supply. Soil processes that consume oxygen, such as the presence of a carbon source, and conditions that limit replenishment of oxygen levels in the soil, such as high soil water content, promote N2O production in soil. Compacted soils lead to rapid depletion of oxygen because of the reduced air spaces and greater tortuosity of pathways of oxygen diffusion.
Although the use of the nitrification inhibitor significantly lowered nitrous oxide emissions in SDI tomato in one of the two years of the study, the reduction in absolute values is rather small (64 lbs carbon dioxide per acre) to make a significant contribution to California's greenhouse gas inventory. With the adoption of subsurface drip irrigation, tomato growers have already lowered the impact of greenhouse gas emissions from tomato production substantially as furrow irrigation generated leads to greater nitrous oxide emissions than SDI.
References
Zhu, X., Burger, M., Doane, T.A., Horwath, W.R., 2013. Ammonia oxidation pathways and nitrifier denitrification are significant sources of N2O and NO under low oxygen availability. Proceedings of the National Academy of Sciences of the United States of America 110, 6328-6333.
- Author: Jeannette E. Warnert
Despite the drought, California farmers produced a record-breaking crop of processing tomatoes in 2014, reported Dale Kasler in the Sacramento Bee.
“It's remarkable, simply remarkable that tomatoes weren't negatively impacted,” said David Goldhamer, an emeritus water management specialist with the University of California Cooperative Extension.
According to the California Tomato Growers Association, the 2014 processing tomato crop amounted to 14 million tons, 16 percent larger than last year and surpassing the old record of 13.3 million tons harvested in 2009.
The growth was attributed to processing tomatoes' increasing value. Processors agreed to pay growers $83 per ton in 2014, up from $70 per ton last year. That prompted farmers to grow tomatoes rather than lower-value crops like rice, wheat and other commodities.
The article says farmers would be unlikely to be able to match the 2014 tomato crop next year if there is another year of drought.