David Doll0 commentsApril 17, 2020Weeds

Herbicide Drift: PPO Herbicides

Protoporphyrinogen oxidase (PPO) enzyme inhibitors are a common class of herbicides used within almonds. They include the active ingredients oxyfluorfen and carfentrazone-ethyl. These compounds are reasonably effective in managing broadleaf weeds. Due to their limited translocation within the plant, they are often referred to as contact herbicides even though they can also provide residual control at higher rates. Off-target drift by these herbicides can damage almonds. Generally, however, the effects are more short-term due to the contact nature of these products on foliage. The reduced medium- to long-term effects of herbicide drift is useful when utilizing these chemistries on young trees. Even so, drift should be avoided as this can cause leaf spotting and loss, reducing photosynthetic area. More information on PPO herbicides and drift can be found here. PPO herbicides have a distinctive pattern when drifted onto almond leaves. At the location where the droplet lands, syptoms occur relatively rapidly. The lesion typically has a yellow outer-halo, a purple middle-halo, and a brown lesion in the center. These lesions fall out of the leaves in 2-3 weeks, giving the appearance of shot-hole fungus.

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David Doll0 commentsApril 17, 2020Diseases, Weeds

Glyphosate Drift on Almond

Glyphosate is a very effective herbicide due to the stability of the chemical once it enters the plant. Off-target drift of this herbicide onto almond, however, can cause reduced, stunted growth, and if in high enough concentrations, tree death. Drift symptoms are usually very obvious and appear similar to severe zinc deficiency. In some cases, the only way to determine the possible cause is to make a foliar application of zinc – if the symptoms are alleviated, it was a deficiency. If not, the damage was from glyphosate. After the appearance of the symptoms, it could take 2-3 months for the tree to begin to grow normally. Applying glyphosate at any time of the year can injure the tree, including dormancy. Therefore, care must be taken to reduce drift and the subsequent effects by using properly calibrated spray equipment, drift reducing surfactants, and reduced winds at the timing of application. The pictures below show the effects of dormant applied glyphosate drift onto almond 2 months after the application. The second photo shows the recovery of the limb and was made 10 weeks after the herbicide application. Once drift damage occurs, there is nothing that can be done besides to wait for recovery. Applying foliar nutrients does not expedite recovery. This has been demonstrated in multiple field demonstrations and trials. Prevention is the best cure.

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David Doll2 CommentsMay 26, 2019Weeds

Newly Planted Orchards: Weed Management

Managing unwanted vegetation is difficult in newly established orchards. Weeds grow fast due to the amount of water, fertilizer and sunlight that is available. Temperatures in the spring and summer often favor weed growth, which can quickly overgrow trees, reducing nutrient and water availability. Furthermore, control is difficult due to the sensitivity of the tree to herbicide damage. These factors make weed control one of the most challenging aspect when developing a new orchard. Most operations rely on post-emergent (aka burn-down) materials for control of weeds in newly planted trees. These products kill the plants that they contact by a number of mechanisms. Burn-down materials, however, have risk in use as drift can damage or kill young trees. This is especially true with glyphosate (e.g. Round-up) which is a systemic herbicide that can persist for a long time within a plant. To reduce this risk, glyphosate should be avoided, and operations should rely on contact materials (e.g. paraquat, oxyfluorfen) for the first growing season. Contact post-emergent products aren’t as effective as systemic products. These materials will require multiple applications through the year as they only kill the top part of the plant. Usually within 2-3 weeks, the plant begins to regrow, and follow-up sprays will be needed. Further management challenges exist for weeds that are “hairy” or have a waxy cuticle. These features prevent the full contact of the herbicide with the plant surface, reducing kill. To manage these variations within the population, coverage is critical. Utilize the upper limit of the label rate of the primary herbicide and make use of any water conditioners to improve efficacy. Increase the volume of water to provide more thorough coverage. This often means that applications are in the 30-50 gal/acre range. Check and replace worn nozzles and perform the required maintenance on

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Brand Hanson0 commentsDecember 20, 2017Weeds

Glyphosate formulations – What’s the difference (and what the heck is a “salt”)?

Cross post from UC Weed Science blog 12/20/17 Glyphosate is one of the most widely used herbicides in the world and is extremely important in many of our orchard, vineyard, and annual crops as well as in non-crop and home situations. However, it can be confusing to understand some of the differences among various formulations of glyphosate herbicides. I’ll paraphrase a recurring extension question like this: “I’m trying to compare the rates and cost-effectiveness of two glyphosate herbicides. One lists the active ingredient as ‘41% glyphosate as the isopropylamine salt’ and the other as 48.7% glyphosate as the potassium salt’.  How do I compare these two herbicides?” First important point, glyphosate is a weak acid herbicide.  The various salt formulations have major impacts on how the herbicide behaves in the jug, and to some degree on how it gets into the plant.  But once in the plant, it is the glyphosate acid that binds to the target enzyme in susceptible plants and causes the herbicidal effect. What is a salt? From a chemistry perspective, a salt is simply a compound formed by ionic bonding of two ions of opposite charge.  Glyphosate acid has a weak negative charge and the salt is formed when the glyphosate acid is bound to a base that has a positive charge.  In the cartoon below, this is illustrated a little incorrectly – you can see the negatively charged glyphosate acid on the left (C3H8NO5P); however, the “salt+” tagged on the right should really be labeled  “base+” (the combined molecule is actually the “salt”).   (image from www.wheatgrowers.com)  ((the “salt” on the right should more accurately be labeled “base”)) What are some common glyphosate salts? There are several glyphosate salts currently available in the market and others have been in the past but are less common now.  Four examples (below) include:

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David Doll0 commentsJanuary 12, 2017General, Horticulture, Weeds

Dormant Practices and Wet Weather

Over the past week, a lot of rain has fallen across California. Orchard access should be limited during periods of wet soil to reduce soil compaction as well as stuck equipment. Limiting access, however, creates challenges in performing a variety of orchard operations, including the list below.   Winter Sanitation. Removal of almond mummies from trees is critical for Navel Orangeworm management (NOW). Many operations usually wait for the first rains to help with leaf drop and to help “loosen” the mummies. In wet years, however, it becomes difficult to winter shake the trees as orchard conditions remain too wet for access of shakers. Furthermore, the “window” to winter shake is limited on the late end as fruit bud loss increases as trees enter delayed dormancy and buds swell (Mid to late January, depending on location). To manage this limited access, operations should consider poling crews. If these aren’t available, and sanitation is not performed, a spring timed (usually late April through early May) insecticide can reduce overwintering NOW. This strategy is not as effective as winter sanitation, but is better than doing nothing. Insecticide sprays targeting NOW in the dormant period are NOT effective due to NOW pupae being inside of the almond mummies. Planting bare root trees. Hand planting crews have an easier time than machine planting due to limited field access. If planting delays occur, trees should be placed into cold storage at the nursery as soon as possible to reduce the risk of leaf out and weakened trees. Keep trees in cold storage until ready to plant. Unless there is no other option, do not take delivery of trees in bins or plant them in a temporary location at the farm. On delivery, check tree roots to make sure they are healthy and living (should be

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David Doll1 CommentApril 1, 2016Weeds

Planning for your summer tree nut weed control

Written by: Kurt Hembree, UCCE Farm Advisor, Fresno County Winter weeds were abundant this year, thanks to the high amount of rainfall we had. Hopefully you found time between storms and were able to get into your orchards and treat for weeds. Given moist soil conditions and warming temperatures close at hand, summer weed growth is also expected to be high. So, are you ready to go with your summer weed control program? Hopefully you already know what weeds you’ll be up against. If not, look to see if there are new ones emerging in recently-watered orchards or after the last rainfall. Note specific weeds so herbicide(s) can be selected accordingly. When it comes to herbicide selection, make sure you’re using products that are effective against your specific weeds, which often vary from field to field. Also, select herbicides and rates that are appropriate for the soil type; lower rates of preemergent products are often needed on sandier soils than heavier soils. Consider using sequential treatments where appropriate if rainfall occurs in April, which can help extend control through summer. Remember to add postemergent products to the tank if weeds are already up and growing when you treat. If glyphosate-resistant horseweed, hairy fleabane, junglerice, or ryegrass are present, and you still want to use Roundup or a similar material, be sure to add another burn-down material that is effective on those weeds. Combining Treevix or Rely 280, Lifeline, or similar product with Roundup has worked well on these and a wide variety of weeds. Be sure to treat when the weeds are small for optimum control. Don’t wait to spray when weeds are large, droughty, or dense, or herbicide coverage and performance may suffer. Use spray tips, a spray volume, and spray pressure that adequately wets the weeds, while minimizes

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David Doll4 CommentsJune 14, 2015Weeds

Glufosinate Trunk Injury of Young Almond Trees

Glufosinate (Rely 280 and other trade names) usage has increased over the past year due to the increase supply and availability of generics. This herbicide has been shown to be very effective in controlling glyphosate resistant weeds, including fleabane, marestail, and goosegrass and has an important role in orchard weed control. One concern of glufosinate usage is plant safety. Accidental applications of glufosinate to the trunk of one to three year old almond trees can cause damage. Field observations and studies by Brad Hanson (UC Weed Specialist) have shown that gumming and a sunken canker can occur three to four weeks post herbicide application. This canker is distinctively different from Phytophthora, band canker, and bacterial canker as there is more consistency of symptoms across the field (i.e. a pattern in symptom occurrence). Within affected trees, symptoms include origination of the irregular shaped canker being above the soil line and in a similar location on multiple trees, the lack of a “sweet” smell, and amber gumming. Although the damage appears to be a severe issue, most observed damage has resulted in slightly smaller, mis-shaped trunks. Within a few years – and usually by the first harvest -affected areas appear to be compartmentalized by the enlarging trunk and are rarely visible. Tree loss has not been observed in normal drift incidences. Glufosinate is a useful tool for post-emergent weed control. As with any herbicide, its use should be used with caution around young trees. Avoid spraying in windy conditions and use the right equipment and pressure to avoid drift.

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David Doll1 CommentMarch 20, 2015Weeds

New UC IPM photo repository shows plant damage from herbicides

Written by Tunyalee Martin and Chris Laning, UC Statewide IPM Program Identifying nontarget crop and ornamental plant damage from herbicides has become much easier with the launch of a new online photo repository by the Statewide IPM Program, University of California Division of Agriculture and Natural Resources. Herbicides applied to manage weeds may move from the site where it was applied in the air or by attaching to soil particles and traveling as herbicide-contaminated soil.  When an herbicide contacts a nontarget plant, a plant it was not intended to contact, it can cause slight to serious injury.  Herbicide injury also occurs when the sprayer is not properly cleaned after a previous herbicide application.  Herbicide residue can be found in the spray tank, spray lines, pumps, filters and nozzles so a sprayer must be thoroughly cleaned after an application.  Dry herbicide particles can be redissolved months later and cause herbicide damage to plants.  Economic damage includes reduced yield, poor fruit quality, distorted ornamental or nursery plants, and occasionally plant death. Accurately diagnosing plants that may have herbicide injuries is difficult.  In many cases, herbicide symptoms look very similar to symptoms caused by diseases, nutrient deficiencies, environmental stress and soil compaction.  Plant disease symptoms such as mottled foliage, brown spots or stem death and plant pests such as insects or nematodes cause foliage to yellow and reduce plant growth similar to herbicide injury. Dr. Kassim Al-Khatib, weed science professor at UC Davis and director of the UC Statewide Integrated Pest Management Program (UC IPM), has gathered nearly a thousand photos of herbicide-damaged plants, drawn from his own and others’ research. The images are cataloged to show damage that can occur from 81 herbicides in more than 14 specific herbicide modes of action, applied in the field to demonstrate the symptoms or when known

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Franz Niederholzer0 commentsDecember 5, 2014Insects, Weeds

Time to change your sprayer nozzles?

When was the last time you replaced the nozzles on your sprayers – airblast and/or weed?  If you can’t remember, chances are it’s been too long.  If your nozzles are worn and allowing more flow per minute than manufacturer specs you could be wasting hundreds of dollars per orchard.  For example, if you apply $200/acre/year worth of insecticides, fungicides, and miticides through worn airblast sprayer nozzles that allow 5% more flow per minute than expected, then you are wasting $10/acre/year.  For a 100 acre orchard, that’s $1000/year in excess materials.  Replacing those worn nozzles will save you hundreds of dollars per year in that 100 acre orchard.  Yes, a new set of wear-resistant airblast sprayer nozzles isn’t cheap, but spraying through worn nozzles is more expensive.

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