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 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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