- Author: Whitney B Brim-Deforest
- Posted by: Gale Perez
This year brings several new chemical tools to California rice. With many herbicide-resistant species as well as emerging problematic weed species, the new chemistries are a welcome tool for managing resistance and preventing the selection of resistant biotypes.
Cliffhanger™ (benzobicyclon) was just registered in 2024, and is a new formulation of a previously-registered granular product already widely in use in California rice. Since it can be applied as a foliar product, it expands the timing that benzobicyclon can be applied in the flooded system. It can also be applied as a direct-stream application into the water. It is an HPPD-inhibitor, providing a good option for rotation. It controls sprangletop, ricefield bulrush and smallflower umbrella sedge. Additional tank-mix testing will be occurring this season to determine if it might be a good partner in combination with other herbicides for added late-season watergrass control.
The last product recently registered is Zembu™ (pyraclonil). Zembu™ is a granular formulation of pyraclonil, applied pre-emergence or at day-of-seeding into a flooded field. It provides control of smallflower umbrella sedge and broadleaf weeds, and provides suppression of watergrass. As a PPO-inhibitor, it is a new mode of action for watergrass, as the only other PPO-inhibitor registered in California rice only has activity on sedges. It will provide a great rotational option for growers at the beginning of the season, as well as a great partner product (for added control) with other granular into-the-water products.
As always, the label is the law, so make sure to read and follow the current labels for each of these herbicides (found on the manufacturers website or at the Department of Pesticide Regulation's website). Also check in locally with your Agricultural Commissioner's office for training information and any other county-specific requirements.
With these three new options, as well as the currently-registered products, rice growers in California should have a great suite of tools available this year, both for resistance management as well as to prevent the selection of future resistance. For help planning a weed management program, please reach out to your local Rice Farm Advisor.
Original source: UC Rice Notes newsletter • April 2024
- Author: Gale Perez et al
These are notes from Central Valley nut and grape advisors, but the comments are valid for most citrus situations. As we all know, follow pesticide labels and make sure the material is valid/legal for your situation.
- Author: Mick Canevari
- Author: Brent A Holtz
- Posted by: Gale Perez
The 2023 post-harvest season is upon us and it's time to prep for your fall/winter weed control activities. The long-range forecast is calling for another wet winter, and November is the ideal time to plan your early winter weed control program, to check that your spray equipment is functioning properly and calibrated, and to clean your orchard floor of nuts and debris.
There are a variety of herbicides available today for our tree and vine production systems. No one herbicide will control all the weeds present, but choices exist to achieve excellent control for almost every weed combination. However, it takes patience and persistence to win the weed war. Before programs are decided, the following key questions should be discussed with your pest control adviser (PCA). Tree age, root stock, soil composition (sand, clay, gravel), irrigation design and practices, water source and quality, cultural practices used, a list of weed species present, and whether they are annual, biennial, or perennial weeds, your spray nozzle design, spray volume required, and if there are sensitive crops nearby. Discussing these questions early will provide the basis for your PCA to make the best recommendations possible while allowing your applicator to minimize the risk of crop injury or drift issues.
Advantages of early weed control
The advantage of implementing an early pre-emergent herbicide program, “before leaf fall occurs” is to get a jump start on winter germinating weeds at a time when they are just emerging and susceptible. Applying a pre-emergent ahead of a rain, or by activating with sprinklers, will control millions of weed seeds and provide a clean tree row for 4-6 months into spring. Applying a pre-emergent ahead of leaf drop also eliminates an additional operation of sweeping or blowing leaves after leaf drop has occurred. Weed control is enhanced and herbicide efficacy is extended when the herbicide is already in place before leaves cover the soil. A leaf barrier after an application inhibits weed germination and improves herbicide efficacy. As more orchards and vineyards turn to drip irrigation, relying on rain events to set herbicides becomes critical. A weed management program applying soil active herbicides early in the fall (November/December), and repeated in spring while rain events are still forth coming (March/May), will provide good weed control into summer. Orchards with sprinkler irrigation have more flexibility in timing their applications and selecting herbicides.
Pre-emergent herbicide use is also a recognized strategy to manage herbicide resistant weeds that have become established. We hear complaints every year that post-emergent herbicides are failing to control the same weeds they used to; and that higher application rates are needed to achieve the same level of control. Some of our more frequently used herbicides are developing weed resistance in the field: they include; glyphosate, paraquat, sethoxyodim, clethodim, rimsulfuron and other related acetolactate synthase (ALS) inhibiting herbicides.
Herbicide resistant weeds continue to spread across the state in different cropping systems, with the greatest occurrence in perennial orchards and vineyards. Problematic weeds include annual ryegrass, junglerice, goose grass, hairy fleabane, palmer's amaranth and horseweed or marestail with several other annual weeds close behind in developing resistance. There are several approaches to control these resistant weed species--but the best option by far is starting with a pre-emergent herbicide program early and attacking weed seeds at the point of germination.
New herbicides expected in 2023-2024
We are always anxious to share information from our various weed and herbicide research trials. But we never know for certain when a new herbicide will be registered for use in California. Two new herbicides are expected to be available this coming season, Florpyrauxifen-benzyl and a combination product with Indaziflam and Rimsulfuron.
Hulk (florpyrauxifen-benzyl) is a post emergent synthetic auxin mode of action HRAC (herbicide resistance action committee) group 4 herbicide from Corteva Agriscience. It is a foliar uptake and systemic herbicide that translocates through the phloem and xylem accumulating in meristematic tissue. It exhibits herbicidal symptoms of twisting and epinasty, typical of phenoxy herbicides. It targets many broadleaf weeds, typical of phenoxy herbicides, but with greater efficacy with certain weed species. Symptoms develop rapidly when plants are actively growing, but whole plant death may take several weeks to a month depending on the growth stage and environmental conditions. Currently, labeled crops include pome, stone, citrus and tree nuts. Grapes are being explored and may be added to the label in 2025. Tank mix partners are needed for emerged grasses which may include the use of glufosinate, glyphosate, clethodim and some ALS herbicides with post grass activity. Generally, one should avoid using contact herbicides that readily burn leaf tissue, like “paraquat” for example, since they may inhibit foliar absorption and systemic movement needed to control the weed. Check the label for specific recommendations.
Centrus (Indaziflam + Rimsulfuron) is a pre-emergent herbicide from Helena Agri company packaged with two active ingredients and modes of action herbicides in HRAC group 29 & 2. Centrus will provide long term pre-emergence control over a broader spectrum of weeds and grasses. It is labeled for tree fruit, nut, and vines for residual weed control targeting winter and summer annual weeds common in orchard and vineyards, including annual ryegrass, filarees, fleabane-horseweed, malva, shepherd's purse, willowweed, knotweed, and many more. In all cases it will be necessary to add a post emergent herbicide for emerged weeds. By combining two active ingredients with different mode of actions, it broadens weed control across more species while slowing herbicide resistance to either active ingredient. We need to be mindful of mixing different modes of action herbicides and not using the same herbicides repeatedly. By mixing different mode of action herbicides we strive to keep our products viable for years to come.
Overview of pre-emergent (before weed germination) herbicides currently registered
Craze (orthosulfamuron) HRAC Group 2 is a new 2022 broad-spectrum soil residual herbicide from Nichino America. The active ingredient in CRAZE is orthosulfamuron. This herbicide, an acetolactate synthase (ALS) inhibitor, works by inhibiting the enzyme responsible for the production of amino acids (valine, leucine, and isoleucine) essential for plant growth. CRAZE has demonstrated broad spectrum residual control of many broadleaf and grassy weeds including horseweed and fleabane and suppression of yellow nutsedge if applied in a timely pre-emergent manner. Several years of testing has demonstrated that it will fit into our Tree and Vine weed control program with flexibility and safety. In our testing, it included tank mix combinations with Alion, Chateau and Prowl which extended long-term control.
Prowl H2O and Surflan (pendimethalin & Oryzalin) are HRAC group 3 herbicides that have excellent annual grass control along with many broadleaves, especially those that germinate in the spring and summer. Surflan and Prowl are of the same mode of action and are similar in their weed spectrum and residual properties. Prowl H2O and Surflan remain stable on the soil without moisture no more than 21 days. Prowl is in the DNA family which controls weed seeds once the germination begins by inhibiting meristematic growth and plant cell division or mitosis, inhibiting seedling development. A common weed control strategy in the fall is to use a mode of action herbicide such as Chateau, Matrix, Alion, Pindar GT, Craze, and then switch to the DNA chemistry of Prowl/Surflan in the late winter or spring timing (February to May) to control summer annual broadleaf weeds and grasses. Prowl is an herbicide used for newly planted orchards because of its strong affinity of soil binding properties and safety to young trees. Prowl may be used before or after transplanting nonbearing nut and fruit crops and roots are covered with at least 2 inches of soil. Always follow the label instructions.
Chateau EZ (flumioxazin) is now in a new liquid formulation. Fortunately, the use rates and product rates for the new formulation remain the same, so the conversion from granular to liquid also remain the same. It is HRAC group 14, a long-lasting pre-emergent herbicide used for tree, nut, and vine crops. Applied between 8 -12 ounces per treated acre, Chateau enhances burndown of small broadleaf weeds and provides long residual control of difficult to control weeds such as fleabane and horseweed (marestail), malva, willow weed, filaree and a host of other winter weeds. Its broad-spectrum control of winter annuals makes it an excellent herbicide for use in the fall and early winter timing during the dormant period. Chateau at lower rates (6-8 ounces) has become a popular tank mix with other pre-emergent herbicides to extend control of more grass species and slow herbicide resistant issues. New Plantings: Chateau EZ provides early protection of new plantings from weeds. It can be applied immediately after planting according to label guidelines. Trunk protectors are required.
Matrix (rimsulfuron) HRAC group 2 is an ALS inhibitor pre-emergent herbicide active on many winter and summer weeds including fleabane, willow weed, and marestail, barnyard grass, jungle rice, crabgrass. Its broad-spectrum activity on grasses and broadleaf weeds, make it a good fit for an early fall application timing in November or December. It has become a popular herbicide to manage glyphosate resistant ryegrass pre-emergent and is effective post emergent on small emerged ryegrass. We have observed nice broad spectrum weed control when other pre-emergent herbicides are combined with Matrix. A post emergent herbicide should be added when weeds are emerged. Matrix is safe on young trees and a popular tank mix with Prowl or Trellis.
Mission (Flazasulfuron) is a HRAC group 2, an ALS inhibitor in the same family as rimsulfuron, orthosulfamuron (Matrix, Craze) with a similar weed spectrum. Our research has shown that Mission increased post emergent activity on certain weeds at a rate of 2.14 ounces per acre. Research from other Farm Advisors suggests improved yellow nutsedge activity when applied ahead of emergence with adequate water for soil incorporation. Use a post herbicide as a tank mix partner when weeds are up.
Alion (indaziflam) is a broad spectrum pre-emergent soil active herbicide registered in tree nuts and vines. It is a long-lasting soil residual herbicide exceptional in controlling many grasses and broadleaf weeds. It is effective on both winter and summer annual weeds, including fleabane, marestail, sowthistle, and willow weed, shepherd's purse, chickweed, and most grasses. At least 1/4 inch of water is needed to set and activate Alion as a soil residual. Since it is strictly a pre-emergent herbicide, it requires a tank mix with a post herbicide for emerged weeds, typically Rely, Matrix, Shark, Goal, Roundup, Venue, Treevix and Gramoxone are all compatible. Alion has shown to be an excellent tank mix partner with other pre-emergent herbicides to increase its weed spectrum, especially for malva and knotweed. Since it does not control weeds already germinated or just under the soil surface (called white phase) it should be tank mixed with herbicides that will control weeds just prior to emerging (Matrix, Mission, Pindar Gt or Goal are some popular choices).
Pindar GT (oxyfluorfen and penoxsulam) HRAC group 14 & 2 is a premix with two active ingredient herbicides. It combines both a pre- and post-emergence punch for many broadleaf weeds used in tree nuts and fruits but not registered in vineyards. An excellent herbicide for winter applications beginning in November to January, that can provide residual control lasting into spring and early summer. It is especially effective on fillaree, malva, henbit, willow weed, sowthistle, fleabane and marestail among others. If weeds have emerged, it is still recommended to combine it with a post emergent herbicide such as Roundup, Rely, or Gramoxone. If heavy grass pressure is anticipated in the orchard, an addition of Prowl, Matrix or Alion will extend long term grass control into spring. Within 14 days of application, a half-inch of water is needed to set and activate the herbicide.
Trellis (isoxaben) HRAC group 21 is registered for use in tree nut and fruit crops and for non- bearing newly planted orchards (check label for specific timing). It is a pre-emergent herbicide controlling only broadleaf weeds, therefore consider using another herbicide for grass control. Applied in the fall and winter timeframe, Trellis will provide 4-5 months of broadleaf control. It has no post-emergent activity; therefore, it must be tank mixed with the commonly used post emergent herbicides Trellis' mode of action is unique; it inhibits cellulose development making it a good rotational herbicide to manage weed resistance. If grass weeds are an issue, the addition of herbicides with grass control activity such as Prowl, Matrix, Alion, or Surflan are needed.
Broadworks (mesotrione) HRAC group 27 is registered in almond, walnut, pistachio and certain fruit crops. It is primarily a pre-emergent herbicide to control only broadleaf weeds hence the name Broadworks. We have observed some post activity on small broadleaf weeds (fleabane marsetail) when actively growing but to be safe will still require a post emergent herbicide partner for complete burn down control. Broadworks controls some of the more difficult broadleaf weeds in orchards but will need a pre-emergent tank mix partner that controls germinating grasses. We have observed a general reduction in bindweed populations when spring applications of Broadworks are used ahead of emergence.
Goal (oxyfluorfen)HRAC group 14 is a PPO (Protoporphyrinogen oxidase) post-emergent broadleaf herbicide with a soil residual of 1-3 months depending on the rate. Goal has been a mainstay in broadleaf weed control for decades and is especially useful in our fall orchard and vineyard programs as a burn down of broadleaves. It is regulated for application use due to its co-distillation (lift off in warm temperatures) issues subject to drift. Goal Tender is a different formulation of oxyfluorfen which reduces volatility issues associated with the 2XL formulation. Under our fall/winter conditions and weed species Goal is very good on malva, burning nettle, henbit, sowthistle, prickly lettuce and many more broadleaf annuals. It is weak on grass species and does miss some broadleafs as well. We encourage tank mixes with other pre-emergent herbicides of different HRAC groups for extending soil residual control.
Post-emergent herbicides (when weeds are up)
Embed Extra (2,4-D) HRAC group 4 post-emergent herbicide is registered on almonds, pistachios, walnuts, pecans and certain tree fruit. It controls a long list of broadleaf weeds, both winter and summer annuals, and broadleaf biennials and perennials including marestail, bindweed, fleabane and malva. Embed Extra is a new post-emergent phenoxy herbicide, containing choline formulation of the active ingredient 2,4-D which reduces the risk of volatility (soil lift off) while minimizing drift. The systemic action of Embed Extra provides a more thorough kill down to the roots of larger broadleaf weeds, that many contact herbicides struggle with. Embed Extra translocates at a slower pace in weeds than contact herbicides. A grower won't see immediate visible burn, since its mode of action is systemic, mimicking the action of the plant growth hormone affecting cell division and slowly twisting until dead. Embed Extra can be tank mixed with other post-emergent herbicides, such as glyphosate and glufosinate. It can also be tank mixed with many “residual”-type herbicides.” Our trials on spring treated larger plants of fleabane, marestail and willow weed showed excellent results.
Rely (glufosinate ammonium) a HRAC group 10 herbicide has become a mainstay for growers needing a broad spectrum burn down herbicide to control tough broadleaf weeds and grasses; willowweed, barnyardgrass, junglerice, crabgrass and glyphosate resistant fleabane and marestail. In recent years, the development and spread of glyphosate resistant weeds has shifted our growers to use more glufosinate herbicide in combination with other post emergent herbicides. Rely does not translocate totally like glyphosate, so the key to success is good coverage and smaller weed size. It is a popular tank mix with any of the pre-emergent herbicides. We have found that glufosinate plus other foliar herbicide combination to be very effective across most emerged weeds.
Treevix (saflufenacil) HRAC group 14 is a PPO (Protoporphyrinogen oxidase) post-emergent broadleaf herbicide with a short soil residual of approximately 30 days. It is registered in tree nut and fruit crops. It is recognized as an excellent post emergent herbicide for some of our toughest emerged broadleaf weeds. However, it is mostly effective on broadleaf weeds, and should be mixed with another herbicide to control emerged grasses. Like all post contact herbicides, treating small weeds, 1-6 inches tall and using a 20-40 gallon per acre (GPA) rate and thorough spray coverage is important. Treevix is excellent in controlling young fleabane, marestail, malva, willowweed, sowthistle, nettle, henbit, prickly lettuce, especially in cool conditions from fall through spring. It is not considered a long soil residual herbicide, so it should be mixed with a pre-emergent herbicide for soil residual control.
Shark, Venue (carfenthrazone, pyraflufen ethyl)are group 14 PPO herbicides. They are all post emergent herbicides especially effective on broadleaf weeds having little soil residual. Theyprovide a tank mix addition to pre-emergent herbicides to control emerged broadleaf weeds. They also work well with other post herbicides glyphosate and glufosinate (Roundup and Rely). A rule for these and all post-emergent herbicides, "Spray when weeds are small for better coverage and control!"
Roundup, Rely, Gramoxone, 2,4-D & PPO (group 14 herbicides) are registered for multiple use in nut and fruit orchards year around. Growers having certain weed species may need multiple post-emergent treatments for specific weed issues or escapes. Glyphosate is moderately effective on purple nutsedge with repeated applications prior to the six-leaf growth stage. Yellow nutsedge can be controlled by using 3-4 quarts per acre of glyphosate at two sequential application timings. Sandia has shown very good results to control emerged nutsedge but is not registered on almond. Sandia is registered for use in pistachio and walnut orchards. The key to nutsedge and other perennial weeds is persistence with repeated applications as it emerges and before it can regenerate new underground nutlets or rhizomes. Problem broadleaves such as fleabane, horseweed, malva, knotweed that germinate most of the year, should be targeted early at a small growth stage and controlled before seed heads develop. Vigilance and persistence are necessary until orchards mature and reach a full canopy of shade to slow perennials and other weeds from continuous germination.
NOTE: Before using any herbicide, always check the label for any use restrictions applicable to your area, crop, or soil type. Our comments and suggestions are from years of testing herbicides in our research plots and field trials. We appreciate our grower cooperators, who let us have access to their orchards. Again, always review and follow label instructions.
- Author: Michelle Leinfelder-Miles
Rice production in the Sacramento-San Joaquin Delta region has been steadily increasing in recent years. While Delta acreage is only a fraction of that in the Sacramento Valley, Delta yields are consistent with statewide averages. I estimate that in 2023, the Delta had around 10,000 acres of rice. In this seasonal recap, I'll overview UCCE research in Delta rice, as well as provide some observations about the 2023 season.
Armyworm Monitoring: I have been monitoring armyworm populations in the Delta since 2016, in collaboration with my UCCE colleague, Luis Espino. Monitoring involves scouting for damage and deployment of pheromone bucket traps that catch the moths. We can use trap counts and Growing Degree Day modelling (i.e. a temperature measure of time) to determine whether and when to treat fields. In 2023, we were thinking we might get away with minimal pressure because the population stayed low through early July. Then, the population spiked in mid-July, later than we had ever observed (Fig. 2). We surmise this was due to the cool, wet spring and later planting season. This year, Methoxyfenozide (Intrepid 2F) was available for use under full registration.
Disease Observations: We have identified diseases like stem rot, aggregate sheath spot, and rice blast on some Delta farms. It is important to scout for these diseases at late-tillering and early-heading because treatment timing is critical for management. Fungicide treatments are most effective when applied between late-boot and early-heading. Rice blast may be exacerbated by too much nitrogen, and stem rot and aggregate sheath spot by low potassium (K). K can be limiting in some Delta soils, especially where the straw is baled. There is a loss of approximately 28 lb K/ac for every ton of straw removed. Consider leaf tissue sampling for K between tillering and panicle initiation. The Y-leaf should have a K concentration of at least 1.5%. At heading, the flag leaf should have a K concentration of at least 1.2%. On-farm consultations are a service provided by UCCE. Please reach out if I can help identify pests and provide management guidelines.
Weedy Rice: We should continue to keep weedy rice on our radars because we have observed it in the Delta. In-season management includes rogueing or spot spraying before viable seed is produced. The organic herbicide Suppress is registered for spot spraying. Post-harvest management should include straw chopping, but not incorporation, and winter flooding. This will keep seed on the soil surface, where it can potentially deteriorate over the winter.
Variety Trial: UCCE collaborates with the California Rice Experiment Station to evaluate commercial varieties and advanced breeding lines. The San Joaquin County Delta location was one of ten locations in the 2023 statewide trial. The Delta is a test site for very-early maturing varieties because it has cooler growing conditions than other rice growing regions of the state. Variety trial results will be made available in the February 2024 newsletter.
Cover Cropping: With funding from the CDFA Healthy Soils Program and CA Rice Research Board, I am collaborating with Sara Rosenburg (UC Davis graduate student) and Whitney Brim-DeForest (UCCE rice advisor) to evaluate winter cover crops. We are interested to learn whether cover cropping improves soil carbon and nitrogen dynamics in the rice system. Since rice may be grown over multiple seasons without rotation, cover crops may provide an opportunity to introduce plant diversity, including nitrogen-fixing legumes. Trials will occur from 2022-2025, and the Delta site is one of three (also in Butte and Colusa counties). The 2022-2023 winter season presented several challenges for cover cropping. At the Delta location, seasonal rainfall exceeded 25 inches, and in the ten days after planting, the site received nearly 3.5 inches of rain. In addition to saturated soils, bird predation was severe. This fall, our aim is to plant earlier, if conditions allow.
Thank you to all the growers who collaborated with us on these projects. I wish everyone a good end to the year and a great 2024.
- Author: Dr. Anthony Fulford
What is subsoil?
There are several layers (also known as “horizons” to soil scientists) that can be found when we dig deeper and deeper down into the soil. We can imagine all the individual layers of a soil stacked one on top of the other like a layer cake, this is called the soil profile. The surface soil is the uppermost layer of the soil profile, and the one we are most familiar with, because this is where most of the action takes place. Soil mixing with tillage, compost and fertilizer application, irrigation, plant root growth, and animal activity (including microbes) are mainly concentrated within the soil's surface layer. Additionally, decomposition of plant and leaf litter occurs most rapidly in the surface soil, this eventually leads to the formation of new soil organic matter. In comparison, the subsurface soil, or subsoil, is composed of one or more soil layers that lie below the influence of surface soil activities. There is not a consistent depth at which every surface soil layer changes into the subsoil layer(s), rather the subsoil occurs at a different depth from place to place depending on numerous factors, including some of the factors mentioned previously. This is the reason why it is difficult to determine where the subsoil layer begins in the soil profile.
What does subsoil contain?
What does subsoil look like?
What is subsoil used for?
In general, the subsoil is a less suitable medium for plant growth compared to surface soil because of some of the factors mentioned previously. There are properties of subsoil however that make it suitable for other uses such as a source of “fill soil” for “cut-and-fill” construction operations, as a source of clay for building materials, and as an absorption layer for on-site wastewater disposal.
What can home gardeners do to keep their subsoil in great shape year after year?
What is the substratum layer of soil? Does that layer affect gardening at all, and if so how?
What is the bedrock layer? Does that layer affect gardening at all, and if so how?
Bedrock is the bottom layer of the soil profile layer cake. The bedrock layer consists of solid rock that has not yet been exposed to the chemical, physical, and biological processes of the surface soil and subsoil. In some places, bedrock is the foundation from which the overlying soil layers developed, while in other places, the bedrock layer may have become “buried” by windblown sand or sediment. Bedrock does not directly influence plant growth, but it can determine the type of clay minerals found in different layers of the soil profile.
Dr. Anthony Fulford is the Area Nutrient Management and Soil Quality Advisor for Stanislaus, Merced, and San Joaquin Counties.
/h3>/h3>/h3>/h3>/h3>/h3>/h3>- Author: Sonia Rios
Control of weeds has always been a major economic cost in subtropical fruit production because of favorable climate that allows for weed germination and year-round growth. The use of chemical weed control has increased dramatically due to labor costs, equipment costs, product costs and availability, the shift to more narrowly spaced tree rows, and installation of low volume irrigation systems that prohibit the operation of mowing or tillage equipment under the tree canopy area (Futch 2001).
However finding herbicides that are labeled for certain subtropical crops can be a bigger challenge. UC Weed Science has updated the Subtropical Crops herbicides usage chart for California growers (2020). It also seems that preventive programs are most frequently overlooked as a method of weed control. Preventive programs entail the use of such practices as sanitation, spot spraying, or hand labor to prevent the source of weed infestation (seed and/or vegetative) from widespread dissemination throughout a given area. By removing the undesirable weed species prior to seed development, dissemination by wind or mechanical transport on equipment can be effectively delayed.
Weed control programs will vary from location to location within the state and can even vary within a given site based upon specific conditions such as soil type, variety, method of herbicide application, and the presence of specific weed species.
Before herbicide application, growers should survey the grove and determine the stage of growth and type of weeds for that given location. Many products do not provide control of emerged species, thus requiring the application of more than one product to provide both preemergence and postemergence protection. Rotation of soil-applied herbicides should also be considered to prevent the buildup of resistant annual and perennial weeds. The resistant species may not be evident initially; however, if the same herbicide and cultural program is maintained, over time their populations may build up until they infest the entire grove and become the dominant weed species.
Herbicide damage to foliage and fruit has also been noted when herbicides were applied under windy conditions or use of improper equipment allowed the materials to contact areas other than the weeds or soil. Please make sure to follow the label's direction and use caution.
Attached is a chart listing herbicides registered for avocado, citrus, date, kiwi, fig and pomegranate, along with the Big Trees' herbicides. Check out how many more are available on almond than avocado. Both start with an A.