Root Inhibiting Herbicide Injury on Processing Tomatoes

Oct 18, 2021

By Amber Vinchesi-Vahl

Root-inhibiting herbicides (like pendimethalin or trifluralin) are soil-applied and pre-plant incorporated as a standard practice for conventional processing tomatoes in the Sacramento Valley.

inhibiting herbicides

Earlier this year, I visited a young processing tomato field with herbicide injury on a significant amount of plants. The plants had the swelling I've seen with trifluralin injury on tomatoes and no/very little root growth above the root ball/transplant plug. They were also very brittle and easily snapped in half which can be characteristic of pendimethalin injury. Some of the affected plants had snapped at the weakened area likely from the north winds over the previous weekend. More plants were affected in the sandier pockets of the field, where less herbicide is tied up compared to clay soils. There was new root growth in some areas, specifically in areas with better soil moisture.

trifluralin and pendimethalin

Pendimethalin was applied pre-plant, a common practice for this particular grower, but never with this result. So the question remained, “how did this happen?” If the herbicide was only in the top two inches of soil and the transplant plug/root ball is inches below that, how did the plant take up the herbicide to cause this damage?

Both trifluralin and pendimethalin are root-inhibiting herbicides used to target small early-season weeds. They can cause brittle stems and swelling at the soil line on broadleaf plants. Though these herbicides are not generally translocated, they can be taken up by roots and stems. I reached out to Brad Hanson, UC Davis CE Weed Specialist, and he suggested that since there was some new root growth, the concentration of herbicide deeper in the profile was likely lower and the problem was in the shallow layers, which led to the stem damage. The question still remains, why was injury worse this year than in previous years?

I was told similar injury (not from pendimethalin specifically but similar herbicides) had been seen more in 2021 on tomatoes than usual, possibly because of the low water at planting.

Source : ucanr.edu

Video: Dicamba Returns for Georgia Farmers: What the New EPA Ruling Means for Cotton Growers

After being unavailable in 2024 due to registration issues, dicamba products are returning for Georgia farmers this growing season — but under strict new conditions.

In this report from Tifton, Extension Weed Specialist Stanley Culpepper explains the updated EPA ruling, including new application limits, mandatory training requirements, and the need for a restricted use pesticide license. Among the key changes: a cap of two ½-pound applications per year and the required use of an approved volatility reduction agent with every application.

For Georgia cotton producers, the ruling is significant. According to Taylor Sills with the Georgia Cotton Commission, the vast majority of cotton planted in the state carries the dicamba-tolerant trait — meaning farmers had been paying for technology they couldn’t use.

While environmental groups have expressed concerns over spray drift, Georgia growers have reduced off-target pesticide movement by more than 91% over the past decade. Still, this two-year registration period will come with increased scrutiny, making stewardship and compliance more important than ever.