Glyphosate Herbicide Injury
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Excerpt and photos from Nelson's (2008) "Glyphosate Herbicide Injury to Coffee"
See the complete publication at: https://www.ctahr.hawaii.edu/oc/freepubs/pdf/PD-56.pdf Glyphosate is a chemical compound that is the active in- gredient in some herbicide products. It is a non-selective, systemic herbicide that is absorbed through plant leaves and green stem tissues. It can be injected into stems or applied to stumps of trees to kill them. Glyphosate applications are mainly used to kill perennial weedy plants in agricultural fields. They are broadcast or used in cut- |
stump treatments to kill undesirable plants in forests. Glyphosate initially was mar- keted by Monsanto under the trade name Roundup®, but it is no longer under patent pro- tection. It is manufactured and applied in a number of formulations for different plant or crop uses.
Glyphosate inhibits the activity of certain plant enzymes and key amino acids that are necessary for protein synthesis and plant growth. It is effective in kill- ing a wide variety of plants, including grasses, broadleafed, and woody plants. Other woody dicots (e.g., macadamia) can express disease symptoms similar to coffee plants. Contact with leaves, stems, or exposed young roots can damage the plants.
Primary disease symptoms:
Symptoms of glyphosate injury can negatively affect plants or persist for many months, up to one year or more on coffee in Hawai‘i, depending on the dosage and exposure points on plants.
The principal negative effects of glyphosate injury to coffee plants include stunting and arrested growth of plants, nutritional deficiency symptoms (foliar yellow- ing), poor coffee bean yields, and predisposition to other diseases such as Cercospora leaf spot and berry blotch. Banana moth injury to coffee verticals after pruning, and root rots in wet soils after severe coffee pruning, also cause plant damage and slow re-growth of new vertical branches.
Management practices to avoid glyphosate injury to coffee
Glyphosate inhibits the activity of certain plant enzymes and key amino acids that are necessary for protein synthesis and plant growth. It is effective in kill- ing a wide variety of plants, including grasses, broadleafed, and woody plants. Other woody dicots (e.g., macadamia) can express disease symptoms similar to coffee plants. Contact with leaves, stems, or exposed young roots can damage the plants.
Primary disease symptoms:
- abnormal stem proliferation (also known as witches’ broom)
- leaf narrowing, production of strap-like leaves
- reduction in leaf size
- leaf chlorosis (yellowing), complete or between veins
- leaf distortion (curling, wrinkling)
- retarded vertical stem re-growth after pruning
- plant stunting.
Symptoms of glyphosate injury can negatively affect plants or persist for many months, up to one year or more on coffee in Hawai‘i, depending on the dosage and exposure points on plants.
The principal negative effects of glyphosate injury to coffee plants include stunting and arrested growth of plants, nutritional deficiency symptoms (foliar yellow- ing), poor coffee bean yields, and predisposition to other diseases such as Cercospora leaf spot and berry blotch. Banana moth injury to coffee verticals after pruning, and root rots in wet soils after severe coffee pruning, also cause plant damage and slow re-growth of new vertical branches.
Management practices to avoid glyphosate injury to coffee
- Train herbicide applicators to mix and apply herbicides in accordance with herbicide label instructions (the label is the law).
- Avoid herbicide contact with foliage, green stems, exposed, non-woody roots, or fruits of coffee.
- Use a spray shield to help contain overspray.
- Encourage non-climbing, low-growing nitrogen-fixing ground covers around coffee plants.
- Apply composts and mulches around coffee plants to inhibit weed growth (but keep mulches and composts away from contact with coffee stems).
- Use weed-feeding animals such as geese or cattle in coffee fields to inhibit weeds.
- Use mobile chicken containers (“chicken tractors”) to control weeds in coffee fields.
- Use string-trimmers or mowers to control weeds, or weed the fields by hand where possible.
- Grow coffee plants under shade trees such as monkey- pod, koa, avocado, and mango to inhibit weed growth, or grow coffee in a diverse multi-level agroforestry cropping system with other plants of agricultural or aesthetic value.
- Discourage grassy weeds where possible.
- Use alternative herbicide products, or organic mixtures, or less injurious chemicals.
- Do not exceed the recommended dosage of glyphosate in spray applications.
- Apply glyphosate before pruning coffee plants, not immediately after pruning them.
- If climbing or tall weeds cover coffee plants, do not spray the plants with glyphosate; remove them byhand.
Prune low-hanging coffee branches away from the
ground before applying glyphosate to coffee rows. - Grow coffee organically (do not use herbicides).
- Avoid mixing glyphosate in spray equipment used to apply other pest-control chemicals or foliar nutrient sprays to coffee plants.
- Avoid over-irrigation of plants injured by glyphosate to minimize the development of root rot.
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