California Ag Network

Tag: Weed Control

  • Weed Control in Lettuce

    Weed control in lettuce and other crops is a key issue this time of year. Purslane is particularly problematic and is adapted to warm conditions and can grow very rapidly especially during July and August. At times growers and PCA’s are disappointed with the efficacy of Kerb on this weed. Kerb is effective in controlling purslane but it is readily leached and, if applied at planting, it can be moved below the zone of germinating weed seeds with the germination water. For instance, 6-8 hours of sprinkler water (1.5 to 2.0 inches) are commonly applied in the first germination water which can move the Kerb below the upper 0.5 inch of soil which is the zone where the weed seeds germinate; the movement of Kerb with the germination water is particularly problematic on sandy soils. Prefar does not leach and thus provides most of the purslane control when the two materials are tank mixed (Figure 1). However, Prefar does not control shepherd’s purse or nightshades which can also be problematic in lettuce fields. Therefore, it would be advantageous to optimize the efficacy of Kerb to maximize the control of purslane as well as other weeds.

    In the desert, the use of delayed applications of Kerb has been used for many years. Due to the large amounts of water that are applied in their hot conditions, Kerb is applied in the 2nd or 3rd germination water, approximately 3-5 days following the first germination water, just prior to the emergence of the lettuce seedlings. This technique can also be utilized in the Salinas Valley. We have looked at this technique over the years and have found it to improve the efficacy of Kerb (Figure 2).  These data illustrate the loss of control of purslane by Kerb when applied before the 1st germination water, as well as the improvement in efficacy that results when applied following the 1st germination water. It also illustrates the role that Prefar plays in the control of purslane when the efficacy of Kerb is lost by leaching. It should be mentioned that the label states that the maximum amount of Kerb that can be applied through the sprinklers is 2.5 pints/A and the amount used in this trial was for experimental purposes only. Clearly there is benefit from applying the Kerb later in the 2nd or 3rd germination water, however, we observed that applying the Kerb at the end of the 1st germination water also provided improved efficacy of Kerb. Clearly, anything that helps to keep the Kerb in the top 0.5 inch of soil improves its efficacy.

    Here are some details that need to be considered regarding the application of Kerb later in the germination phase of the crop: There is a need to use an injection pump and tank. We have typically used a tank with a circulating mechanism to keep the Kerb in suspension while the injection was occurring. The material needs to be injected into the mainline in a location where proper mixing can occur before it begins to flow down the laterals. The most difficult issue that growers face is the compatibility of the injection with surrounding crops. This is probably the greatest challenge and must be carefully thought through before attempting an application.

    Another idea that we explored last year was the use of an additive to help retain the Kerb in the upper portion of the soil where it can be most active. However, we did not see improved efficacy in two 2018 trials (data not shown).

    Many growers now are now using drip irrigation to germinate lettuce. Grower may apply the same amount of water with drip germination as with sprinklers, but the movement of the water is different which affects a surface applied material differently. With this method of germination, there are a couple of interesting dynamics that occur: 1) Kerb is not pushed too deep by this germination method and effectively reduces weed populations whether injected into the germ water (currently not a registered method of application) or sprayed on the soil surface and activated by the drip germination water (Table 1); and 2) fewer weeds emerge with drip germination than with sprinklers, regardless of the herbicide program.

    By: Richard Smith 

    Figure 1. On left: Kerb at 3.5 pints/A applied at planting; On right Kerb at 3.5 pints/A + Prefar at 1.0 gallon/A applied at planting. The main weed is common purslane which was not controlled by Kerb because it was pushed below the zone of germinating weed seeds by the germination water

     

     

  • Managing Weeds is Key to Improving Yields & Orchard Health

    Almond Board of California — Weeds are a seemingly constant issue in the orchard. If not managed properly, they can create competition among young trees, clog micro-irrigation systems, use and generate uneven irrigation and contribute to a messy orchard floor during harvest. Good weed management, then, starts with identifying the weeds in your orchard, which requires constant, attentive monitoring.

    The University of California’s (UC) Integrated Pest Management (IPM) guidelines recommend the following actions for monitoring weeds:

    • Survey your orchard for weeds in late fall and again in late spring.
    • Monitor the orchard in a thorough fashion. Include the entire orchard as well as field margins, ditch banks and irrigation canals in your survey.
    • Examine all areas that are susceptible to weed infestation, like areas of high moisture. Collect important information such as weed species, location in the field, degree of control achieved with current program, and herbicides applied.
    • Record observations on a survey form that includes a map so the infested sites can be revisited for weed control. Pay particular attention to perennial weeds and other problem weeds and note their location on the map.
    • Record weeds found in rows and middles separately. Weeds in tree rows must be managed, but annual weeds in row middles — i.e. cover crops — may have some benefit as an orchard floor cover.

    Once you know what you’re dealing with, look to select herbicides or other control techniques based on what kinds of weeds are actually present in the orchard. The UC IPM website provides a comprehensive list of common and scientific names of weeds, along with photos and descriptions of each. You can find that list here.

    In the late spring, the most important invasive weeds to look out for are perennial weeds. These weeds can be a pervasive problem for almond growers, so weed management practices should be geared toward preventing their growth in the rows or row middles of the orchard. Common perennial weeds you’ll see are Bermudagrass, Johnsongrass, Dallisgrass, Nutsedges and White Clovers. Also, tufted perennial grasses such as threespike goosegrass are especially problematic during the beginning years of tree nut establishment due to their ability to reduce three growth by competing for water, nutrients and sunlight. Once the almond trees reach their fourth leaf, established plants can reduce harvest efficiency by making it more difficult to recover nuts from the orchard floor at harvest. The UC IPM website provides a late-spring weed survey form to help you identify these pests as June approaches.

    Once weeds are properly identified and the correct herbicides are applied, it’s vital to control herbicide resistance by using a variety of weed-control strategies. Failure to do so can result in the rapid loss of an herbicide’s effectiveness — and there are very few new herbicide technologies in the pipeline.

    Detecting resistance is the second step in preventing resistance. Patterns of herbicide resistance include patches of dense weeds with less dense populations radiating out from the central patch and weeds that have escaped control, scattered throughout the field.

    To combat resistance and reduce weed seed spreading, the UC IPM recommends the follow steps:

    • Rotate herbicides that have different modes of action and Weed Science Society of America (WSSA) group numbers.
      • Drew Wolter, UCCE Junior Specialist Horticulture Intern under Brad Hanson recently published an article on herbicide performance that helps demonstrate the importance of rotating applications.
    • Monitor for weed survival after an herbicide application.
    • Include non-chemical weed control methods such as cultivation or hand weeding.
    • Clean equipment after working in weed-contaminated orchards to prevent the spread of weed seeds.
    • Control weeds suspected of herbicide resistance before they can produce seed.
    • If weeds escape treatment, use shovels, hoes, and other hand tools to cut the plants below the soil surface to prevent flowering.
    • Use a pre-emergent herbicide before weeds appear. When the weeds emerge in fall and spring, consider splitting applications to meet the multiple emergence windows.

    Weed management is vital to a successful growing season and — with the right steps — can improve the yield and growth of established trees.

    For more resources regarding weed management, please visit the follow links on the UC IPM website:

  • Using the Sun & Agricultural Waste to Control Pests

    Biosolarization Shows Promise for Conventional & Organic Farmers

    By Diane Nelson

    Farmers spend a lot of time and money controlling weeds and other pests, and often have to turn to chemical fumigants to keep the most destructive pests at bay. Farmers also wrestle with what to do with low-value byproducts of crop production, such as skin, seeds and hulls from fruit, vegetable and nut processing.

    What if those agricultural waste streams could generate alternatives to chemical fumigants and make farming more productive, profitable and environmentally friendly?

    Maybe they can. Researchers at the University of California, Davis, are encouraged by early results from collaborative experiments with “biosolarization,” a process that combines the sun’s heat with soil amendments to manage weeds and other soil-borne pests.

    “It looks promising,” said food science and technology professor Christopher Simmons, who is testing biosolarization with various crops and working with farmers throughout the state. “We still have a lot of work to do, but biosolarization is showing real potential as a safe, sustainable way to control pests while improving crop quality and yield.”

    Strengthening solar power   

    Many backyard gardeners know the power of solarization. When you lay a clear plastic tarp over moist soil, you can trap solar radiation and heat the soil enough to kill weeds and other soil-borne pests. It’s effective, but can take four to six weeks, which is often too long for commercial fields to lay fallow.

    Biosolarization can accelerate and improve the process. Simmons and his team are adding organic amendments such as grape and tomato skins or ground nut hulls to the soil before they tarp it, which promotes growth of beneficial bacteria. The helpful microorganisms compete with pests and temporarily make the soil more acidic and therefore less hospitable to weeds and other pests.

    Together, the soil-heating and microbial activity can reduce the treatment time to days, not weeks.

    “And by activating beneficial microbes in the soil, biosolarization has the potential to improve soil health over the long term,” Simmons explained.

    Testing under commercial conditions

    Chemical fumigants are expensive, and many have been identified as carcinogenic by state and federal regulatory agencies. But when it comes to killing soil-borne pests, they are very effective.

    “Fumigants are broadly biocidal, meaning they affect beneficial microorganisms along with the pests,” Simmons said. “Biosolarization allows more innocuous and beneficial microorganisms to persist in the soil.”

    But for farmers to adopt biosolarization as an alternative to chemical fumigants, the treatment must be effective, predictable and economical. So the team is testing biosolarization with a wide variety of crops, amendments and soils against different pests in various locations at commercial scale throughout the state.

    “We have field trials underway with lettuce, tomatoes, melons and various cover crops,” Simmons said. “And we have a long-term, 10-acre trial with almonds at a conventional orchard in Chico.”

    In Chico, Simmons and his team are collaborating with almond grower Rory Crowley at Nicolaus Nut Company with funding support from the Almond Board of California and the Western Center for Agricultural Health and Safety. They are one year into a 25-year experiment to see if almond-processing residues and the sun can boost soil health and reduce weeds and other soil-borne pests. So far, Crowley is impressed.

    “It’s been great for the soil,” Crowley said. “Using biosolarization and a mustard cover crop, we’ve increased organic matter by 1.25 to 1.75 percent, which is a huge jump. That’s good for carbon sequestration and the overall health of the soil.”

    It’s too soon to tell if the soil improvements will translate to greater crop yield, but Crowley thinks biosolarization could become a good pest-management tool and a valuable use for what would otherwise be agricultural waste.

    “We need to find a home for the co-products of almond processing, so why not see if we can use them to improve soil health while controlling pests?” Crowley asks.

    Field tests continue

    Simmons and his team are testing biosolarization on several annual and cover crops in plots on the UC Davis campus using agricultural waste streams from tomato and wine processing. Soon they will begin tests with strawberries, which are commonly treated with fumigants each season as farmers plant berries anew.

    Simmons’ hope is to demonstrate to farmers that biosolarization can be effective and economical under a wide range of conditions against a broad number of pests.

    “We’re making significant ground,” he said. “We’re hopeful biosolarization can help farmers return food and agricultural waste back into the system to control pests and improve crop production.”