Herbicide Injury in Fruit Trees and Grapevines

Herbicides applied to control weeds in orchards and vineyards sometimes cause injury to the trees and vines we are trying to protect from weed competition.

Three common orchard herbicides - glyphosate, Ignite and 2,4-D, represent three different modes of action.

• Glyphosate is a systemic herbicide, which means that it moves through the vascular system of the tree.

• 2,4-D is a hormone herbicide, controlling the plants growth and forcing excessive cell division.

• Ignite is a contact herbicide, causing a burn/blast injury on any green tissue it touches.

The symptoms caused by these herbicides can be related to these three different modes of action. Recognizing these symptoms will allow you to make adjustments to reduce future damage.

Glyphosate

Glyphosate (Credit, Factor, Glyfos, Renegade, Roundup (also Transorb and Weathermax), Touchdown iQ, Vantage, Vision)

Uptake and translocation: Absorbed through foliage and translocated throughout the plant. In spring, translocation is toward the growing tips, and in late summer/fall, translocation is toward roots.

Mode of action: Inhibits enzymes needed for growth.

Symptoms: Causes growth to stop immediately, then general yellowing of tissue, especially in the growing tip (meristems). In trees, where sub-lethal doses have penetrated into the woody tissue, new growth has thin, strappy leaves. This symptom may appear for several years after application.

Figure 1. Glyphosate injury on fruit trees the year after application.
Note the thin strappy leaves, often pale and thickened.

Figure 2. Gumming on trunk of cherry tree caused by Roundup injury. Note that the entire trunk is girdled, blocking the flow of nutrients and water through the trunk.

Figure 3. Decline of peach tree caused by gumming in trunk from glyphosate application. Avoid applying glyphosate to first year trees, and 2nd year trees if bark is still green.

Ignite

Ignite (glufosinate ammonium)

Uptake and translocation: Requires a 4 hour rain-free period to be absorbed by tissue. Absorbed through the foliage, with minimal translocation through the plant. No root absorption as it is quickly broken down by soil microorganisms.

Mode of action: Inhibits glutamine synthatase, which allows ammonium to accumulate in the cells, which destroys them.

Symptoms: Chlorosis and wilting generally shows up on green tissue in 3 to 5 days, and tissue death (necrosis) in 1 to 2 weeks. Green shoots and leaves on trees and vines will show spotting where spray droplets touched them, followed by yellowing and dying leaves, twigs and canes.

Figure 4. Ignite injury on soybeans, with similar symptoms to tree leaves.

2,4-D

Uptake and translocation: Absorbed through leaves or roots. Translocated to rapidly growing tips (meristem) of shoots or roots.

Mode of action: Stimulates growth, causing uncontrolled cell division and growth, which destroys vascular tissue. Essentially plants grow themselves to death.

Symptoms: Leaves show bending, twisting, leaf cupping and curling. The shape of leaves and veins is abnormal, with grapes described as fan-like. Plants generally take 3-5 weeks to yellow, wilt and die.

Figure 5. 2,4-D injury on grape leaves, showing twisted growth.

Related Links

• Preventing Herbicide Drift and Injury to Grapes, Oregon State University Extension Service

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