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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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 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 Doll1 CommentJune 9, 2009Weeds

Herbicide drift damage to a Butte/Padre almond orchard by 2,4-D

May is the time of the year for the herbicide injury to almonds. High winds, fast growing weeds, and too many orchard tasks to complete in a day are the typical causes of herbicide drift. Herbicide drift can be prevented by following a few simple principles:1). Avoid windy days when applying herbicides,2). Apply the correct herbicide that targets the correct weed,3). and apply the herbicide at the proper rate. A field call in mid-May by a grower yielded a case of typical 2,4-D injury to almond. The 2nd leaf orchard was 50% Butte and 50% Padre on nemaguard rootstock. The orchard was situated in sandy soil with microsprinklers used for irrigation. The grower reported multiple trees showing dieback of new growth. He was uncertain of the cause and thought verticillium wilt may be affecting his orchard. Picture 1 shows the overall symptoms of an affected almond tree. Picture 1: Overall tree symptoms caused by 2,4-D herbicide drift. Note tip dieback and odd growth. Overall, the distribution of the symptoms were found throughout a large percentage of the block. Many trees where showing a “shepherd’s crook” of the new growth indicating either a wilt disease or herbicide/salt issue. Picture 2 shows the severity of the symptoms on the new growth of the almond tree. Picture 2: Branch tip dieback due to 2,4-D herbicide drift. Leaves at the tip of the crook were crispy, indicating a fast wilt. Shoots with contorted growth were found throughout the canopy. Pictures 3 and 4 are of these symptoms. Picture 3: Branch damage from 2,4-D herbicide drift. Branch is showing the “shepherd’s crook” symptom, typical of vascular wilt pathogens or salt/chemical damage. Picture 4: Contorted growth of new growth caused by exposure to 2,4-D herbicide. With the exception of the contorted growth, symtpoms expressed by the

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