Hero Image

Notes in the Margins: Agronomy and Weed Science Musings

Agronomy and Weed Science Blog
  • Wet Weather and Weeds

    The recent rain events in California have complicated crop production activities for many growers including delayed planting or harvesting and altered pest management activities (including weed control).

    Below are my thoughts about the possible impacts wet weather could have on weeds and weed suppression:

    • Rains can facilitate seed germination and seedling emergence although wet soils may delay post-emergence control activities (be they chemical or physical operations). Sarah Light, a UC advisor working in the Sacramento Valley, wrote this blog post last year about soil compaction and strategies to avoid it (https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=27421&sharing=yes) as well as this follow up article (https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=30304).
    • Sequential rain events may stimulate flushes of weeds leading to dense communities with plants that vary in size. This could complicate weed control because larger specimens may be, naturally, more difficult to manage; additionally, these individuals could shelter smaller plants from herbicide contact, requiring supplemental operations.
    • Cold, wet weather may impact crop growth resulting in an environment that isn't competitive against weed interference. Conversely, the onset of warm weather could 'kickstart' warm-season weed species in the presence of adequate soil moisture.
    • Weed seeds could move in run off water, spreading infestations within and across fields. 
    • Water-mediated erosion can remove soils treated with pre-emergence herbicides, which could result in reduced efficacy; possible crop injury could occur if the soil becomes concentrated in low areas of a field.
    • Leaching can reduce the concentration of soil-applied products in a field (especially in coarse soils with low organic matter), which could lead to control failures. Low doses of soil-applied products can act as a selective force on the weeds that do persist in that environment to find individuals that might be resistant to those herbicides.

    A similar version of this information can be found at AgNet West: http://agnetwest.com/unseasonable-rains-contribute-weed-control-issues/ 


    Attached Images:

    By Lynn M. Sosnoskie
    Author - Agronomy and Weed Science Advisor
  • Save The Date! The 3rd Annual UAV/Ag Technology Field Day on July 15th

    Mark your calendar!


    July 15, 2019


    The 3rd Annual UAV/Ag Technology Field Day

    Presented by UC Cooperative Extension, Merced County

     9am to 11:30am (CE registration begins at 8:30am)

    Bowles Farming Headquarters

    11609 Hereford Road, Los Banos, CA 93635





    UAV/Drone demonstration flights:

       -CSU Fresno 

       -UC Merced

       -Yamaha Motors - RMax

       -AeroVironment- Quantix Drone

       -Pyka Autonomous Aerial Applications (pending Certificate of Authorization)


    Other Ag Technology Representatives, Presentations and Displays:

       -Justin Metz, Bowles Farming

       -Robovator Automated Weeder

       -Ferrari Automated Transplanter

       -FarmWise Automated Weeder.

       -Naio Technologies Automated Weeder


    DPR and CCA units to be applied for


    Watch for the full agenda to be posted on our website in the coming weeks at:



    By Lynn M. Sosnoskie
    Author - Agronomy and Weed Science Advisor
  • Hail Damage and Your Cotton Crop

    May 28, 2019

    After the recent spate of storms, reports of hail damage have come in to several UCCE offices. In response, Dr. Bob Hutmacher prepared the following information (a printable pdf document is available at the end of the post):


    We have had some unusual weather so far in 2019, with repeated cool spells, thunderstorms and rain, and within the past week, some widespread locations getting hail.  While hail damage can be a fairly common late spring and early summer occurrence in many cotton production regions across the U.S., it is a much more unusual problem here in the San Joaquin Valley.  In addition, cotton has been growing more slowly than usual this year due to cloudy, generally cool conditions that have prevailed well into May, so a further set-back is not at all welcome.  In trying to decide what to consider after a hail storm hits your field, here are some recommendations to consider:

    FIRST – After a hail storm, it is likely best to wait to assess hail damage and potential impacts for perhaps 3 to 5 days after the storm.  Then, after the plants have a chance to recover a little, and the damaged leaves either fall off or the percent of plants in the field that are light damaged or more severely damaged becomes more evident, look over fields with the following questions / assessments in mind:


    1)     Is the hail damage seen in the field really severe in some areas but much lower impact in other areas?  Sometimes hail comes through as a “band” affecting a limited zone within the field, with severe plant damage (stem breakage, heavy leaf loss, severe terminal damage) limited to a small portion of the field and lesser damage in the remainder of the field.  Severity of damage can be evaluated according to the discussions below, but if the % of field affected is relatively small then decisions to abandon, replant, or modify management practices going forward can be directed just to those limited areas.  Early-season light to moderate hail damage in other field areas that is limited mostly to some shredded leaves (without much stem or terminal damage) will not have much impact on your crop's yield potential when compared to impacts of insect pressure or cold or hot weather problems.


    2)     What % of plants in the field have significant or severe terminal damage?  The “terminal” of plant is the newest forming small leaves at the top of the plant stem, representing the new growth on the main stem as well as where future vegetative and fruiting branches are initiated.  Damage to terminals can be light (just breaking of small, developing leaves) all the way to complete terminal loss, with the upper stem breaking off or killed.  Loss of the terminal part of the plant will have the greatest impact on yield potential when plants are very small (at the 2 to 4 leaf stage) since there isn't a lot of leaf area, and there will only be a couple of nodes where new vegetative branches can start to develop.  Severe terminal damage and especially terminal loss will definitely delay maturity and will produce at least moderate reductions in yield potential.  Plants will recover, regrow by pushing out vegetative buds, but will typically produce multiple vegetative branches which will have delayed fruit production.  Reduced yield potential and growth management problems associated with delayed fruiting can be a problem, but not necessarily a reason to terminate the crop.  


    3)     What % of plants have main stems that are broken off at the cotyledon or below the first main stem leaf?     These plants will likely die or will have very delayed production and low yields. If the stems aren't completely broken, are they bent and damaged enough that you think they will fall over later in the season when the fruit loads up? Again, if that level of damage is widely seen, impacts on yield potential will be significant and potential for plant recovery is greatly reduced.  


    4)     What % of plants have major leaf loss?  While the impacts of leaf damage and leaf loss can look terrible and give the appearance that your field was shredded, damage to or loss of even 50-75% of leaf area can be tolerated quite well when plants are young (maybe in the 3-leaf to 7 or 8-leaf stage) particularly if the terminal is only lightly damaged and can re-start leaf growth quickly.  Again, if the terminal is present to provide new sites for leaves to develop, recovery can be pretty quick under good weather conditions, since root systems are decently established by that time.   In some ways, impacts of early leaf damage or loss with hail can be similar to those seen with early thrips damage, where we often see good recovery, with not a lot of lasting impact on growth and only slightly reduced yield potentials. 


    5)     Is replanting a viable option to consider at this time of year?  Since most of the hail damage reported recently has occurred in the third week of May, replanting would not generally be a good option to consider for the currently-available Pima cultivars, since they were developed with full-season production in mind. Under “typical” fall weather conditions in the SJV, there is a considerable likelihood that you will run out of heat units to mature out the later-season bolls, or will have to take a chance on very late harvests for replanted fields. There are many Upland varieties with potential to set and mature out a decent crop in a significantly shorter growing season than most Pimas, but you may have to settle for lower yields and employ practices to terminate the crop earlier to avoid late-season insect pest control costs and losses.  Another consideration with replantings that occur in May or early June is that seedlings developing during warm to hot weather often exhibit very fast vegetative growth and delayed timing of first fruiting branches, making late plantings even more likely to produce late-maturing fruit.


    6)     Management practice changes with hail-damaged plants?  Particularly with small plants with fewer than 7 to 8 leaves at the time of the hail damage, plants will produce multiple (sometimes many) vegetative branches in response to main stem damage.  If weather conditions are decent, vegetative growth can be very vigorous following this type of damage.  Vegetative branches have potential to produce flowers and bolls, but bolls set on the plants will be delayed.  Under this combination of conditions, plant growth regulators may be very beneficial in helping manage growth while trying to get acceptable fruit set.    

    Hail Damage on Cotton

    Attached Files:

    By Robert B Hutmacher
    Author - Cooperative Extension Specialist and Center Director, West Side REC
    By Lynn M. Sosnoskie
    Author - Agronomy and Weed Science Advisor
  • Upcoming Extension Meetings - May 2019 - UC Small Grains - Alfalfa/Forages Field Day

    University of California Small Grains - Alfalfa/Forages Field Day


    Wednesday, May 15, 2019

    UC Davis Department of Plant Sciences Field Headquarters

    2400 Hutchison Dr., Davis, CA 95616, Davis, CA

    8:00-4:30 Includes Lunch

    CEUs: TBD


    The annual UC Small Grains/Alfalfa-Forages Field Day will be held on May 15th at the University of California, Davis Department of Plant Sciences Field Headquarters on Hutchinson Road (west of Highway 113) from 8AM – 4:30PM.

    The event showcases UC efforts in breeding and agronomic research related to small grains, alfalfa and forage crops and is one of the longest running field days in the state. The small grains portion will take place from 8 to noon and the alfalfa/forages section will take place between 12:40 and 4:30. A barbecue lunch will be provided.


    7:30     Registration (no charge)

    8:00     Start of Small Grains Program

    8:00     Welcome and Opening Remarks

    8:35     Malting Barley & Oat Breeding: Alicia del Blanco, UC Davis

    8:45     Barley Breeding for Food, Feed and Forage: Allison Krill-Brown, UC Davis

    9:00     New Wheat Varieties: Oswaldo Chicaiza, UC Davis

    9:15     Breeding Triticales for Bread and Forage: Josh Hegarty, UC Davis

    9:25     Increasing Grain Size and Number: Alejandra Alvarez, UC Davis

    9:35     A New Gene Controlling Number of Grains Per Spike: Saarah Kuzay, UC Davis

    9:40     Balancing Source and Sink to Increase Yield: Jorge Dubcovsky, UC Davis

    10:00   Herbicide Programs for Barley and Wheat: small grain herbicides and maximizing efficacy for control: Lynn Sosnoski, UC Cooperative Extension

    10:20   Italian Ryegrass: Updates on Cultivation vs Herbicide Trials: resistance and methods for control: Konrad Mathesius, UC Cooperative Extension

    10:30   Warm-season legume cover crop between winter small grains: Michelle Leinfelder-Miles, UC Cooperative Extension (This project was supported by the California Climate Investments program.)

    10:45   Using Nitrogen Rich Reference Zones to Guide Wheat Topdress Decisions in the Sacramento Valley: Sarah Light, UC Cooperative Extension

    10:55   Yield and Protein Stability for Wheat and Triticale Varieties Grown under N and Terminal Drought Stress: Mark Lundy, UC Cooperative Extension

    11:05   Updates on UC Statewide Small Grain Trials: Seasonal conditions, pests and diseases, nitrogen management, and extension efforts: Mark Lundy, UC Cooperative Extension

    11:15   Comments from breeders with entries in UC Statewide Small Grain Trials

    11:30   UC Statewide Small Grain Trial Observations

    11:50   Return for lunch

    12:00   BARBEQUE LUNCH – Sponsored by CCIA – Many thanks to the staff at CCIA!

    12:40   Start of Alfalfa and Forage Portion


    12:40   Welcome and Introductions—Dan Putnam, UCCE/UCD Alfalfa Specialist


    12:50   Managing Alfalfa in a Wet Year- What are the Diseases?-How to Help your Fields Recover?  Rachael Long, UCCE Farm Advisor, Yolo County, Woodland, CA

    1:05      IPM and Managing for Weevil Resistance in Alfalfa – Ian Grettenberger, Entomology Specialist, UC Davis, CA

    1:20      Evaluation of N Stabilizers in Corn –Michelle Leinfelder Miles, UCCE Farm Advisor, Delta Region.

    1:35      Forage Sorghum as a Summer Option: Controlling Sugarcane Aphid in Sorghum/ Sudangrass—Nick Clark, UCCE Farm Advisor, Kings/Fresno/Tulare Counties

    1:50      Innovations in Overhead Irrigation – How that might improve Water Use Efficiency—Isaya Kisseka, UC Davis Professor, Irrigation Technology

    2:10      Fun with Drones –Detecting Pest and Diagnosing Problems with Aerial Photography—Umair Gull, UC Davis Graduate Student, Plant Sciences.

    2:25      Controlling Difficult Weeds in Alfalfa—Lynn Sosnoskie, UCCE Farm Advisor, Merced County.

    2:50      Alternative Crops Research—Kura Clover, Switchgrass, Hemp—Dan Putnam, UC Davis

    3:05      Reduced Lignin Alfalfa Varieties and Interactions with Harvest Scheduling—Brenda Perez, Graduate Student UC Davis

    3:20     Analyzing Alfalfa Varieties for Pest Resistance (Nematodes, Insects, Diseases) and other characteristics—Dan Putnam, UC Davis

    3:35      Alfalfa and Tall Fescue Breeding Programs at UC Davis –Charlie Brummer and students, UC Davis.

    3:50      Test your Weed ID IQ: Weed Identification—Brad Hanson, UC Davis

    4:15      Return to Headquarters



    IMG 0072


    Attached Files:

    By Lynn M. Sosnoskie
    Author - Agronomy and Weed Science Advisor
  • Weed Identification - Why it's important and where to go for help

    The importance of proper weed identification

    Weeds are a problem in a variety of systems, from agronomic and horticultural crops, to orchards and vineyards, to turf and ornamentals, to rangelands, and to natural areas. The first step in developing a successful weed management program is to ensure that the unwanted vegetation has been identified correctly. Not all weeds respond equally well to all treatment measures. For example, broadleaf weeds will be managed by the auxinic herbicides (WSSA Group 4) whereas grasses will not. Mowing may be more effective at suppressing upright growing species as opposed to those that are more prostrate. Shallow cultivation may control annual weed species while missing deep-rooted perennials.

    In short:

    • A successful identification provides you with the knowledge that you need to develop a successful management plan
    • Your strategy should based on the sensitivity of a target species to control measures 


    Weed identification books, phone applications and submitting samples

    There are numerous tools available to help you identify weedy species, including guidebooks (Weeds of the West, ISBN-13:0-941570-13-4; Weeds of California and Other Western States, ISBN-13:978-1-879906-69-3) and phone applications (Pl@ntNet https://plantnet.org/en/; iNaturalist https://www.inaturalist.org/).

    Local extension advisors can also help with the identification of troublesome species. Identifications can be made either from live specimens or from digital images. If submitting a fresh sample, collect several plants that are representative of the infestation. Collect as much of each individual plant as possible (including roots, flowers and seed pods). Place the samples in a sealed ziploc bag with a few damp paper towels and deliver (or ship) your specimens to your county office (the faster, the better, as fresh samples are easier to identify). Be sure to include your name and contact information, the location of where the weeds were collected (GPS coordinates, address, and description of the habitat (i.e. roadside, orchard, alfalfa field, etc)), as well as any other relevant information.

    If emailing digital images, be sure to capture pictures of the plant's leaves, stems, flowers, roots, and seedpods, as well as a photo of the specimen in its environment. Try to remove excess vegetation from around the sample so that its growth habit is apparent. Take photos of any unique structures (such as spines) that could be a diagnostic tool. Include the same contact information (name, address, etc) as listed above in your message.

    Remember, it can take several days to determine an ID and some specimens may require confirmation from additional sources, such as the staff at the UC Davis Herbarium.

    Improving your chances of a successful ID

     Figure 1. Strategies to improve weed ID success using digital images.

    By Lynn M. Sosnoskie
    Author - Agronomy and Weed Science Advisor