Brand Hanson4 CommentsOctober 29, 2012Weeds

Glyphosate-Resistant Weeds in Orchards – Recent UC IPM Publications

Last winter, I particpated in a series of seven half-day workshops in California, Oregon, and Washington on herbicide-resistant weeds.  These workshops were organized by Kassim Al-Khatib from the Univeristy of California Integrated Pest Management (IPM) Program and had a special focus on glyphosate-resistant weeds in tree and vine crops. In preparation for these workshops, we wrote a series of extension publications that I wanted to share today.  The publications and resulting presentations were prepared by weed scientists from various Universities, Cooperative Extension, and USDA-ARS and included various aspects of herbicide resistance in permanent crops.  Even as somone who thinks about herbicide resistance every day, I found the bulletins and presentations to be tremendously informative.  These included: Selection Pressure, Shifting Populations, and Herbicide Resistance and Tolerance by Brad Hanson, Albert Fischer, Anil Shrestha, Marie Jasieniuk, Ed Peachey, Rick Boydston, Tim Miller, Kassim Al-Khatib. PPT slide handouts available here: Glyphosate Stewardship: Keeping an Effective Herbicide Effective by Tim Miller, Brad Hanson, Ed Peachey, Rick Boydston, Kassim Al-Khatib Preventing and Managing Glyphosate-Resistant Weeds in Orchards and Vineyards by Ed Peachey, Rick Boydston, Brad Hanson, Kassim Al-Khatib Managing Glyphosate-Resistant Weeds in Glyphosate-Resistant Crops by Kassim Al-Khatib, Brad Hanson, Tim Miller, Ed Peachey, Rick Boydston These bulletins are being published by UC-IPM and the near-final versions are available right now  at this link.  Or at: http://www.ipm.ucdavis.edu/IPMPROJECT/glyphosateresistance.html. Take care, Brad Read more orchard weed management blog posts at UC Weed Science

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Brand Hanson0 commentsOctober 4, 2012Weeds

Evaluation of pre-emergence herbicides in California almond orchards

by Andrew Johnson, Marcelo Moretti, and Brad Hanson; UC Davis Weed Science (Article originaly posted at UC Weed Science) Several field experiments were conducted to evaluate the performance of pre-emergence herbicides, herbicide rates, and tankmix combinations at different locations in the Central Valley of California and to compare the efficacy of burndown herbicides in mixture with different pre-emergence herbicides. The same treatments were used in three studies located in Fresno, Merced, and Colusa counties. Only data from the Merced county site is presented due to low weed densities at the Fresno and Colusa county sites.

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David Doll1 CommentJune 21, 2011Weeds

Glyphosate resistant weed control

Hairy Fleabane (Conyza bonariensis)  After the meeting last week, there were quite a few growers staying after to talk with Brad Hanson (UC Davis/AES Weed Specialist) about glyphosate resistant weeds, especially fleabane.Here are a few of their questions with answers:How do I control these weeds that are missed by glyphosate?Post-emergent materials including Rely (Glufosinate), 2-4,D, and Treevix (Saflufenacil) work well on glyphosate resistant fleabane. These tend to work a lot better on small plants but not so well on large established plants that are flowering. Paraquat works pretty well usually but there are some populations of fleabane that are resistant to paraquat in the San Joaquin Valley. Growers with serious infestations should consider making a pre-emergent herbicide application this coming winter. These residual type herbicides control emerging seedlings, killing the weed before it becomes established. Depending upon your requirements for ground water protection, consider a winter application of rimsulfuron (Matrix), simazine (Princep), indazaflam (Alion), norflurazon (Solicam), or penoxsulam and oxyfluorfen (Pindar GT). Kurt Hembree’s (Farm Advisor, Fresno County) weed susceptibility charts provide more information on controlling these weeds. There seems to be major growth flushes of fleabane, is this correct?Fleabane has two major flushes – on in late fall and another in early spring. I’d estimate that 40% emerge in the fall, 40% in the spring, and the other 20% is scattered throughout the year. What about glyphosate resistant grasses – in particular ryegrass?Post-emergent options include sethoxydim (Poast), clethodim (Select Max), and glufosinate (Rely). Pre-emergents include eptc (Eptam), napropomide (Devrinol), oryzalin (Surflan), pendimethilin (Prowl H2O). More information can be found on Kurt Hembree’s weed charts for almonds. What else should we consider when attempting to manage this weed?Treat weeds before they go to seed! This helps reduce the population within the orchard.Rotate your herbicide post-emergent chemistries and consider rotating in

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David Doll2 CommentsApril 25, 2011Diseases, Weeds

Herbicide Drift or Fungal Disease?

Figure 1: What caused this damage: Herbicide drift or fungal disease? Leaf samples often appear on my desk with notes asking to identify the problem. More often than not, symptoms appear shothole-ish in nature, and growers are questioning their fungicide program (Figure 1). These symptoms, however, also appear from drifting herbicides. How can one tell the difference between three common herbicides and the fungal disease shot hole? Answer: look for fungal fruiting bodies. Shot hole infected leaves can be determined by the black fruiting body that is centrally located in the lesion on the top side of the leaf (Figure 2). Figure 2: Shot Hole affectedalmond leaf. Note the blackfruiting body in the centerof the lesions.  What about telling the difference between the three herbicides? This one is a little bit harder, but it comes down to the coloring of the leaf tissue surrounding the lesion. Kurt Hembree, Weed Management Farm Advisor in Fresno County and Brad Hanson, UC Weed Specialist, have noted the following:  lesions caused by paraquat are localized, tan in color, and remain attached (figure 3). Carfentrazone (Shark) lesions have halos that lack color (figure 4). Oxfluorfen (Goal) lesions tend to have a defined halo, sometimes purplish and/or yellow in color (figure 5).  Both of these herbicides will cause lesions to fall from the leaf. Figure 3: Shot Hole like damage caused by  Gramoxone (Paraquat). Note that the lesions do not fall from the leaf To help with the diagnosis, observe the location of the damage. Is it over the whole tree, or just lower few branches? Is it just on the outer rows? Is it across both varieties? What is the history of herbicide use? Herbicide damage tends to be found on the lower portion of the tree, with damage on all varieties within the orchard. Drift damage also tends to

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David Doll0 commentsJanuary 19, 2011Weeds

January is a good time for Pre-Emergent Herbicides

This article from last year sums up the considerations and herbicides available for pre-emergent use. Remember that pre-emergent applications must be followed by rain – usually around a quarter inch. Some other weed resources available are as follows:Almond Weed Photo Guide – With Common and Scientific Names,Susceptibility of Winter Weeds to Herbicides,and Weed Susceptibility Chart to Registered Herbicides. Also, check out the weed science blog authored by UC Weed Specialist, Brad Hanson.

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David Doll5 CommentsAugust 9, 2010Weeds

Uptake Damage from 2,4-D from a handgun application

A call to a Butte/ Padre 7th leaf orchard in the Hilmar/Livingston area provided some interesting symptoms associated with uptake from herbicides. Five days after a flood irrigation, the grower noticed that a few trees on the end of five  rows were collapsing (Figure1). The damage was occurring across varieties affecting two out of three scaffolds. The soil texture was a sand common to the Hilmar/Livingston area. Figure 1: Overview of tree collapse. Figure 2: Damaged tissue progressing from the tree roots into the trunk A closer inspection of the tree showed a sunken area on the bark, but no gumming was present. Bark removal revealed a large red canker progressing up the tree from the soil (Figure 2). Removing the soil, the damaged plant tissue was visible on the roots, but stopped about five feet from the trunk (Figure 2). At that point, the roots beyond that point appeared healthy. Leaves of the tree were yellow, maintaining green veins – similar to a few different nutrient deficiencies. Creating a cross section, it became clear that something was trans-located up the tree through the xylem – as evident by the dis-colorization of the tissue (Figure 3 and 4). This suggested that the problem was not due to a disease, but rather something chemical.  Figures 3 and 4: Bark removal and cross section of the almond tree affected by 2,4-D uptake through improper herbicide application. Speaking with the grower, we went through a variety of orchard activities that may have caused the damage.  That led to discussions about fertilizers, herbicides, and any other cultural practices. Everything seemed to be reasonable, so the conversation turned towards orchard activities that occurred prior to the flood event. The grower admitted that an herbicide application of 2,4-D was made  36 hours prior to the irrigation. 2,4-D was applied at the full label concentration and was used

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David Doll0 commentsApril 13, 2010Weeds

Glyphosate Damage on Almond

A number of calls have came in in regards to glyphosate drift damage. Drift injury from fall applications of the herbicide glyphosate (Trade names Roundup, Rodeo, Touchdown, Ranger, etc.)often appear the following spring upon the first flush of growth. The growth response from glyphosate application is very unique, with the overall tree appearing yellow (Figure 1 and 2) with deformed leaves having a “boot-lace” appearance (Figure 2), bud and limb death (Figure 3), and in severe cases, tree death. Figures 1 and 2: Almond trees showing symptoms of exposure to glyphosate. Most likely, the herbicide drifted onto the tree in the fall, with symptoms appearing the following spring. Many growers ask how a fall application of herbicide can still cause damage the following spring. Glyphosate, being a systemic herbicide, is designed to be stable once inside the plant. When glyphosate is applied to the leaves of a weed, the chemical is able to move through the leaf cuticle and enter into the phloem of the plant. From this point, it is translocated to the root, or other tissues, exits the phloem and inhibits the formation of amino acids that are critical for plant growth, killing the plant. If, however, glyphosate is applied to a woody plant (i.e. tree) entering dormancy, the chemical may not be systemically translocated, but “stuck” in the phloem tissue within the area of application. Once the plant breaks dormancy, the flow of carbohydrates from root to shoot move the herbicide into the newly formed tissues, causing deformed growth and possibly bud and shoot death. Figure 3: “Boot Lace” appearance of almond leaves is often indicative of glyphosate exposure. Figure 4: Dieback of the apical bud of a young almond shoot caused by the accidental application of glyphosate. Glyphosate damage is often confused with zinc deficiency. If

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David Doll0 commentsMarch 22, 2010Weeds

Drift Management to Avoid Herbicide Damage

Written by Kurt Hembree (UCCE Fresno County) Reducing spray drift is necessary to prevent crop injury, both within the field being treated and off-site. Environmental conditions (air temperature inversions, wind velocity, etc.), applicator awareness, type of spray equipment, nozzle selection, spray boom operating pressure, water volume discharge, and other factors affect the degree of drift that may occur during any application. While spray shields do not guarantee drift will not occur, they can greatly minimize the risk of drift, especially in open fields or where young vineyard and orchard plantings are being treated. The following steps should be taken to minimize the risk of drift from ground sprayer equipment: 1. Don’t spray when it’s windy: Do not spray in winds above 6 – 10 mph. 2. Be cautious on calm days: Do not spray under dead calm conditions in early morning, evening, or the night. Calm conditions are often associated with temperature inversions which can result in long-distance spray drift (1 mile or more). Burning brush on calm days can give an indication on the presence of temperature inversions (refer to local regulations on restrictions for obtaining a burning permit). 3. Check the buffer zones: Refer to the product label to determine adequate buffer zones outside of the field treated. Do not spray if the wind is blowing towards a nearby sensitive crop, garden, waterway, or other sensitive area. 4. Use a shield: Consider equipping your sprayer with a protective shield. A number of designs are available that can reduce drift between 35 and 75%. Avoid spraying trunk-to-trunk with unshielded spray booms. 5. Use a spray drift retardant: Spray drift retardants are available that can be added to many products to help reduce off-target drift. 6. Check the formulation: Use amine formulations of 2,4-D when possible. Use special care when

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David Doll0 commentsJanuary 12, 2010Weeds

Organic Weed Control in Almond Orchards

Weed control within organic blocks is more critical than in conventional blocks. Weedy orchards can compete for the high value organically certified nutrients, decreasing yields and/or increasing fertilizer input costs. Organic weed control methods are also not as effective and more costly than conventionally available materials. Therefore it is important for growers to use multiple strategies to reduce weeds to a level that is economically acceptable. This entry will focus on several methods available for organic almond production weed control. These methods may also be useful in conventional orchards that have multiple areas of herbicide resistant weeds. Mulches: Plastic or fabric mulches block light, preventing weed germination or growth. These materials are often placed in the row strip before planting. Upon planting, a hole is made at the planting location so that the tree can be planted. Placing the mulches post planting can also be done. These materials control most weeds effectively while they are still intact. Materials do degrade over time due to UV light and temperature. Weed seeds that land on top of the mulches can germinate and grow. These types of materials are expensive ($250-$300 treated acre) and post-use disposal can be problematic since they are currently are not able to be recycled. Organic mulches (straw, newspaper, wood chips) can be used for early season weed management, but often interfere with harvesting practices. Organic mulches are most effective when they are at least four inches thick. Use on non-bearing age trees may be feasible. Remember, these mulches MUST be organically certified to be used. Cultivation: This is the most widely used organic weed control method. Cultivation uproots and buries weeds. This tends to work better on smaller, shallow rooted weeds. Deep cultivation is not advisable since it can damage tree roots. Usually, a mix of a tractor

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David Doll4 CommentsDecember 28, 2009Weeds

Managing Resistant Weed Populations

Over the next couple of weeks, I will be presenting information regarding weed control in an orchard system. Since herbicide resistant weeds are becoming more prevalent in the San Joaquin Valley (think Hairy Fleabane, Horseweed/marestail), it is becoming more important for growers to utilize practices that reduce the chance of herbicide resistance. Herbicide resistance is defined as the inherited ability of a plant to survive and reproduce following an exposure to a dose of herbicide that would normally kill the wild type (Think: “We used to get good control of this weed with this herbicide…”). This is different than herbicide tolerance, which is the ability of a species to survive and reproduce a herbicide treatment with no implied selection or genetic manipulation that would make the plant tolerant (Think: “We’ve never gotten dependable control of this weed with this herbicide…”). Since 1980, cases of herbicide resistant weeds within California has increased from 0 to 21 reported cases. This is mainly due to the change in tillage and herbicide use practices within agriculture. In perennial crops, growers have shifted away from orchard tillage and have become more reliant on herbicide “burn downs” to control weeds in the tree rows. Glyphosate is one of the most widely used herbicides for this practice, and, until recently, has provided good control. The formation of herbicide resistant weeds is an evolutionary process that occurs due to the application of herbicides. Since most herbicides are reliant upon a single site mode of action, it only takes a minor mutation within the plants genome to become resistant. Furthermore, the high genetic diversity of weed populations provides the opportunity for weeds to contain a mutation, thus yielding an “escape.” Once the weed is unable to be controlled by the herbicide, it produces progeny that is also resistant. These

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