Growth hormone type herbicide injury causes leaf feathering, cupping, stem twisting and sometimes produces compressed growth resembling a cobra’s head (also called fiddlenecking). Tomatoes (see photo left) are particularly susceptible but other vegetables can also be affected (eggplant photo right).
2,4-D is commonly used for spraying dandelions and other broadleaf weeds. Ester forms are more likely to vaporize and be carried by wind than amine forms. Vapor clouds can drift for surprising distances depending on weather conditions. Granular formulations rarely volatilize.
High temperatures above 85 F during or immediately following applications increase the possibility of vaporization. Spraying earlier in spring, during cooler periods in summer and at cooler times of day is recommended. Follow label directions dealing with temperature.
Sprays should be adjusted so droplet size is large because fine sprays have a greater potential to drift. Use lower pressures or sprayers with large orifice nozzles that increase the average droplet size. Mind wind movement and chose calm days for spraying. Use spray shields when using products such as glyphosate (Roundup and other brands) near gardens. Do not apply insecticides with a sprayer used for weed killers.
Another way herbicides can reach vegetable gardens is in residues on straw used for mulch or through manures dug in as soil amendments. Clopyralid can be moved this way. This herbicide is not used for broadleaf weed control in landscapes but is used in pastures, crop production and rights-of-way among others.
Clopyralid is very persistent in manures, composts and soil. It can damage sensitive vegetable plants in extremely small amounts. Sensitive plants include those in the bean family (beans, peas), sunflower family (lettuce, endive, globe artichoke), and especially the tomato/potato family including eggplant and peppers.
Know your source or try imported straws and manure on a test plant in a pot before using in your whole garden.
Photo credit: Tomato and eggplant herbicide injury - both Carl Wilson