Paraquat
Trade Name: Gramoxone
Registration status: This herbicide is registered for use on established trees in tender fruit orchards as a directed spray under trees.
When to suspect injury: Applications should avoid green bark, leaves or fruit – if misapplication occurs, injury may appear wherever the spray contacted. Injury may occur from drift up into trees from under-tree applications, or from neighbouring fields under windy conditions. If you notice symptoms of leaf yellowing, wilting or necrosis, look carefully at neighbouring fields, and at weeds in the treated area.
Herbicide Information: Knowing how the herbicide works will help to determine the likelihood of injury from either direct application or drift. Consider how the herbicide works in plants, behaves in soils and what symptoms are common in other plants.
Chemical Family: Bypyridylium
Site of Action/WSSA Group: Photo system I - electron diverters – (WSSA Group 22)
General Symptoms in Plants
- Within a few hours, in full sunlight, the plant wilts and dries out
- In 1- 3 days complete foliar necrosis occurs
- Injury from drift appears as spots of dead tissue where spray droplets land
Symptoms in Fruit Trees
- Small round, yellow spots that may turn brown but do not fall out
- Spots of dead leaf tissue wherever there is contact by spray droplets
- New growth is normal
- Fruit develop reddish brown patches where the herbicide contacts their surface
- Trunks of newly planted trees can show brown spotting if the bark is still green when sprayed. These injuries may allow infection by cankers
Uptake and Translocation
- Absorbed by foliage and green bark
- Little or no translocation
Persistence
- Highly persistent but residues are tightly adsorbed and unavailable in the soil
- Essentially no residual activity in soil
- Half-life in field: 1000 days
If you suspect herbicide injury, laboratory analyses of herbicide levels in plant tissue are necessary to confirm the presence of herbicides, although symptoms may be helpful in diagnosing which herbicides caused the problem
Both damaged and healthy plant tissues should be analyzed, because comparison levels are not readily available for many herbicides. Contact your lab for instructions on which plant parts should be sampled, how to handle and ship the sample, and what costs are involved to ensure an accurate and timely diagnosis.
