Pacific Pests, Pathogens & Weeds - Mini Fact Sheet Edition

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Tomato - residual herbicide (379)

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Photo 1. Stunted tomato plant grown in land previously treated with glyphosate, Mount Hagen, Papua New Guinea.

Photo 2. Stunted, twisted plant with cup-shaped leaves, Port Vila, Vanuatu.

Photo 3. Plant showing twisted terminal growth and small, bunched leaves, Port Vila, Vanuatu.

Summary

• Unknown distribution. In Oceania, symptoms of toxicity recorded in Fiji (possibly), Papua New Guinea, Vanuatu. On tomato. Possibility of residual herbicide.
• Damage: twisting of leaves, bunching of terminate growth, stunting of plants.
• Reasons for residual herbicide and toxicity include: i) soils (sandy, low clay) that fail to retain glyphosate; ii) frequent applications; iii) applications at high concentrations; iv) applications of phosphorus fertilizer (competing with glyphosate for soil binding sites); v) addition of other herbicides to increase residual activity.
• Control:
  • Avoid land where glyphosate applied frequently and/or at high rates, or wait at least 40 days between last application and planting
  • Make sure product only contains glyphosate, i.e., no other chemical present to increase residual activity in soil.
  • READ THE LABEL CAREFULLY.
  • Alternatively, carry out a bioassay (see below). 
  • Transplant test seedlings across area prior to planting entire crop. Inspect for toxicity after 7-14 days.

Common Name

Tomato - residual herbicide effects.

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