Purpose
This page explains the current UC chemigation program built around Matrix SG, how timing works, and what should be treated as current guidance versus active research.
Required Under the Current Compliance Agreement
For high-risk fields, the field management program must use the Board-recommended growing degree day model to develop a scouting and rogueing plan. The same model can also be used to help time chemigation, but chemigation itself is not required under the current compliance agreement. Any chemigation that is used must be carried out in accordance with the current Special Local Need label and all applicable chemigation requirements.
UC Recommended Practices
Matrix SG through subsurface drip chemigation is currently the only approved herbicide program for broomrape management in California processing tomato. UC guidance is clear that foliar applications, the traditional Matrix SG label for processing tomatoes in California, do not provide effective broomrape control. For this problem, the herbicide must be injected through the subsurface drip system so it is placed in the soil surrounding the tomato roots, where broomrape germinates and attaches.
The current label-based program is three applications of 1.33 ounces per acre, for a total of 4.0 ounces per acre per season, applied at about 30, 50, and 70 days after transplanting. In some UC experiments, earlier applications, around 20, 30, and 40 days after transplanting, improved control of the earliest germinating cohort. Matrix should be injected into the chemigation system around the midpoint of the irrigation set, or during the last third of the set, depending on the system, so the soil is already wetted, the herbicide can move through the tomato root zone, and sufficient clean water can follow to flush the lines. The exact injection period and amount of flush water will vary with the irrigation system and soil conditions, but the goal is uniform distribution through the root zone without pushing the herbicide beyond it.
The growing degree day calculator is a practical companion to the chemigation program because it turns transplant date and field location into management windows growers can use for chemigation, scouting, and rogueing. In high-risk fields, UC strongly recommends use of the Matrix chemigation protocol, and UC also strongly encourages its use in tomato fields within the Designated Zone to reduce establishment risk. Outside the Designated Zone, growers may also consider Matrix chemigation as a prophylactic treatment where introduction risk is a concern.
Related links or companion pages
- Growing degree day worksheet and calculator