Spray Drift Affects Sensitive Crops
R. David MyersExtension [email protected]
A Vineyard Coming to a Farm Near You!
Herbicide Drift Potential
All herbicides are subject to particle drift.
Vapor drift potential varies by each herbicide’s vapor potential.
Droplet size controls both types of drift.
Wind, temperature and humidity affects drift severity.
Herbicides with High Drift Damage Potential
High vapor potential herbicides.
Herbicides that are active at very low application rates.
Herbicides that are Plant Growth Regulators (PGR’s)
WSSA Group 4Growth Regulators
Synthetic Auxins
Phenoxys Benzoic Acids Pyridines
2,4-D (many trade names)
2,4-DB
MCPA
2,4-DP (diclorprop)
2,4,5-T (no longer marketed)
Dicamba (Banvel, Clarity, Distinct, Vanquish, Status, many others)
Picloram (Tordon Grazon P&D)
Triclopyr (Garlon, Remedy)
Clopyralid (Stinger, Transline, Hornet)
Aminopyralid (Milestone, Forefront)
Herbicide Vapor Pressure mmHg @25○C (77○F)
EPTCVernam (vernolate)
Command (clomazone)
Treflan (triflualin)
Callisto (mesotrione)
Dual (metalachlor)
Prowl (pendimethalin)
Banvel (dicamba)
DCPAStinger (clopyralid)
Roundup (glyphosate)
Atrazine
2,4-D AmineClassic (chlorimuron)
Gramoxone (paraquat)
3.4X10-2 (.034)
1.0X10-2 (.010)1.4X10-4 (00014) incorporation breaking point
1.1X10-4 (00010) incorporate due to UV decomposition
4.3X10-5 (000043)
3.1X10-5 (000031)
9.4X10-6 (0000094)
9.2X10-6 (0000092)
2.7X10-6 (0000027)
1.3X10-6 (0000013)
3.0X10-7 (00000030)
2.9X10-7 (00000029)
1.4X10-7 (00000014)
4.0X10-12 (0000000000040)TLTL (Too Low to List)
Vapor pressure of selected herbicides arranged according to decreasing vapor pressure.
Note: Spray particles under 50 microns in diameter may remain suspended in the air indefinitely or until they evaporate.
In relatively dry, warm air (e.g., 30 percent relative humidity and 78°F), a 100-micron droplet quickly loses water by evaporation and becomes less than half its original diameter (one-eighth of its original volume) while falling only 2.5 feet.
By comparison, in relatively moist air (e.g., 70 percent relative humidity and 78°F), a 100-micron particle will fall 5 feet and hit the ground before evaporating to half its original diameter.
Small droplets become
smaller very quickly