One of the largest weed issues affecting the California processing tomato industry is the parasitic plant, branched broomrape (Phelipanche ramosa; Orobanche ramosa)

• https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=50241
• https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=47701
• https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=43342

Last week, CDPR issued a positive decision on a 24c "Special Local Needs" label request to allow application of rimsulfuron (Matrix SG) via chemigation through subsurface drip irrigation systems.   This newly-allowed use pattern should be helpful for suppression of broomrape in tomato.

The CDPR decision was posted here: https://www.cdpr.ca.gov/docs/registration/nod/nodmenu.htm and is in Report 2022-39 for the Week of September 30, 2022.  I've also attached it to the bottom of this blog post.

Rimsulfuron is widely used in tomato in California both as PRE and early POST herbicide for control of many weeds.  The 24c label simply adds a new application method that is targeted specifically at the broomrapes which are parasites that attached to the root of tomatoes and other host plants.  The new use pattern puts the herbicide right in the rootzone of the tomato plant at the time when broomrape seeds are germinating and the seedlings just attaching to the host.

The protocol for this specific use is three applications of rimsulfuron; one at early bloom and two more at 10-15 d intervals thereafter.  Each of the three applications should be 1.33 oz product (25% WDG) which equates to the yearly max allowed on the Section 3 label. 

In our field trials, chemigated rimsulfuron provided significant reductions (about 4-fold) in broomrape clusters in a highly-infested field; however, no herbicide treatments were 100% effective for this A-listed quarantine pest. This may be of interest and utility to processing tomato growers who have light infestations or fields near infested fields that may be at some risk but should be combined with other sanitation practices. 

One important note is that this SLN cannot be used with other rimsulfuron applications.   The 4 oz product per year maximum is for all uses; so, if you apply rimsulfuron via chemigation for broomrape management, you cannot also use rimsulfuron for PRE or POST control of other weeds.