Tuesday, April 19, 2011

Herbicide Injury to Tomatoes

"Classic" Glyphosate Symptom

Recently, the clinic has received several tomato plants with symptoms of herbicide damage. Glyphosate (found in products like Roundup) causes very distinctive yellowing symptoms at the base of tomato leaflets.  Broad-leaf weed killers (2,4-D type herbicides) cause stunted and deformed new growth, and whipping and curling of the leaves.  
2-4 D Type Injury 

Tomatoes are very sensitive to herbicide injury and damage can be severe.  In extreme cases, simply touching tomato plants with herbicide-contaminated hands or clothing can cause injury. 

Spray drift is an important source of herbicide damage. Sometimes symptoms appear in a gradient pattern, with plants closest to source being more affected than those further away. 
Be careful to prevent herbicide drift into home gardens, farms, or greenhouses where tomatoes are growing. To reduce the chances of spray drift, do not apply herbicides near these areas on windy days.  

Glyphosate Drift in Greenhouse
Some herbicides are formulated to provide season-long protection against weeds. Planting sensitive crops too soon after using one of these herbicides can cause injury. Check the product label to see when it is safe to replant following herbicide application.

Glyphosate Injury
Sometimes farmers and home gardeners report problems in vegetables and flowers after applying hay, manure, grass clippings, compost, or other amendments to soil.   Symptoms include poor seed germination, twisted, cupped, and elongated leaves, and misshapen fruit. Young plants may die and yields may be reduced in mature plants.  This damage can be traced to herbicide carryover in the soil amendment.  For more information on herbicide carryover in soil amendments, click here.