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 a tree is zinc deficient, the leaf symptoms will worsen, while a glyphosate damaged tree will slowly recover (if not killed!). A previous blog discussed the varying possibilities of glyphosate and zinc deficiency in almond trees.
If symptoms similar to the pictures above appear in your orchard, be sure to apply herbicides with care in order to prevent herbicide drift. Drift injury can be prevented by following precautions mentioned on the label of the herbicide used, avoiding applications during windy weather, and using proper pressures, rates, and maintained equipment. More information in regards to herbicide drift prevention can be found in a previous entry.