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HERBICIDE DAMAGE



Some spots have a small brown (dead) centre. Use this to distinguish paraquat spots from downy mildew
Some spots have a small brown (dead) centre. Use this to distinguish paraquat spots from downy mildew
Photo credit: Peter Magarey
Look For Look For Notes

   LOOK FOR

    Look for in shoots
  • GLYPHOSATE
  • New shoots in the second year that are pale and stunted with shortened internodes and clustered side shoots
  • 2,4-D
  • Occasional celery-like, flattened shoots

    Look for in leaves
  • FOLIAR BURN
  • Light yellow, circular spots on leaves (at first resembling downy mildew oilspots and later powdery mildew leaf blotches)
  • A tiny dead centre in these spots (not found in young downy mildew oilspots)
  • Droplet-sized dead spots scattered on leaves of low hanging shoots
  • GLYPHOSATE
  • Fan-shaped leaves with veins crowded together
  • Rough and upward curled leaves, sometimes with yellowing between veins
  • 2,4-D
  • Fan-shaped leaves with veins growing close together
  • Fine green bubble spots dispersed evenly between veins
  • ROOT UPTAKE
  • Yellowing between the veins starting from the leaf edge. The veins remain green
  • Irregular dead patches on leaves with advanced symptoms
  • Yellowing of leaf veins. Tissue between the veins remains green
  • Whole leaves that turn yellow with severe damage

   CONDITIONS

  • FOLIAR BURN
  • Caused by spray drift, especially to lower leaves
  • FOLIAR BURN AND DISTORTION
  • LEAF BURN
  • Leaves may burn when paraquat, amitrole or gluphosinate ammonium are translocated from lower to upper parts of vines.
  • Distortion of foliage by glyphosate is typically caused by uptake in autumn.
  • GLYPHOSATE
  • Foliage and bunches show hormone-like distortions, most evident in spring. Damage from root absorption may also occur in sandy soils, particularly where there is a long-established drip irrigation system.
  • 2,4-D
  • Vines are sensitive to low doses of 2,4-D and similar hormone-based herbicides.
  • 2,4-D can drift many kilometres
  • ROOT UPTAKE
  • Simazine uptake by roots occurs more often in sandy soils
  • Symptoms from simazine and diuron occur in similar situations.
  • Symptoms can be confused with iron deficiency, but yellowing from simazine occurs mostly on older leaves.
  • Symptoms from diron and norflurazon are more common in sandy soils
  • High rates of diuron applied to frequently watered sandy soils often cause symptoms. Older leaves are more affected.

   NOTES

    FOLIAR BURN
    Root uptake of paraquat and amitrole paraquat and amitrole particularly affects vines in light sandy soils.

OTHER HERBICIDE DAMAGE IMAGES

Yellow and brown areas damaged by paraquat drift onto leaves Yellowing caused by paraquat absorbed and moved to the leaf Browning of shoots caused by paraquat Paraquat sometimes causes chlorotic ring spots Paraquat and similar herbicides taken up by roots cause burning of interveinal areas. White varieites turn yellow; red varieties turn red Paraquat and similar herbicides taken up by roots cause burning of interveinal areas. White varieites turn yellow; red varieties turn red Leaves damaged by pendemethalin are rough, curled downward and wide-angled where the leaf joins the petiole Small, fan-shaped leaves from 2,4-D or glyphosate damage 2,4-D or glyphosate damage: severe 2,4-D or glyphosate damage: mild (left) and healthy (right) Simazine causes yellowing between the vein, which remains green Mild simazine damage Various forms of simazine symptoms Bleached leaves and brown dead patches from severe simazine damage Amitrole damage from root uptake Amitrole damage, showing dead sectors of affected leaves Diuron damage shows as yellow veins but not in the tissue between Norflurazon damage shows as yellow veins but not in the tissue between Severe damage from Diuron or Norflurazon

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