Alion label changes for California orchard/vineyard crops

Cross post from the UC Weed Science blog 11-21-14Effective this fall (2014) there will be a fairly significant change to the Alion herbicide label for California orchard and vineyard crops.  Growers and PCAs will want to be aware of this as you're planning your dormant-season herbicide programs now that many areas of the state are getting some rain.The use patterns for Alion (active ingredient: indaziflam) has been modified for tree nuts, grapes, stone fruit, pome fruit, and olive (citrus uses were not changed).Most important changes include:

• Maximum use rates now have a restriction based on soil organic matter (OM) contentGrapes: if soil less than 1% OM, max rate is 3.5 oz/A (0.045 lb ai) and if over 1% max rate is 5 oz/A (0.065 lb ai)Nuts, Pome, Stone, Olive: if less than 1% OM, max rate is 3.5 oz/A; If 1-3% OM, max rate is 5 oz/A; if OM above 3%, max rate 6.5 oz/APreviously there was a 6.5 oz rate max for all crops except grape which had a 5 oz max rate.  Although it presents another thing to think about when writing recommendations, a soil OM restriction is not unusual.  Because of the charge characteristics of organic matter (as clay particles), soil OM content can greatly affect the proportion of herbicide in "soil solution" - that is, herbicide that is not bound to soil.  Rate refinements based on OM can avoid the situation where lighter soil is over treated and also should increase the margin of crop safety because light or coarse soils do not hold herbicides in the surface zone (where the weeds are) as well.
• The label now restricts Alion use in flood-irrigated orchards.  It also prohibits irrigation within 48 hrs after the applications. This is designed to ensure crop safety by giving the herbicide sufficient time to bind to surface soils before a large amount of water is intentionally applied.  It should also help maximize weed control because any residual herbicide that is moved too deeply into the soil is likely to lose some efficacy on some weeds - this is especially true for herbicide like Alion that primarily affect weeds as they first germinate but have less of an impact on established weeds.
• The manufacturer has also offered some best use guidelines for this herbicide that are very positive (in my opinion):-  Use the highest rate for local conditions for best performance-  Consider tank mixes with other PRE herbicides such as Matrix, Chateau, Goal, GoalTender (this is good for both broadening the weed spectrum and managing selection of herbicide resistant weeds)-  Tanks mix with burndown herbicides if emerged weeds are present (this was always the case as Alion as almost no activity on germinated weeds)-  Apply from Nov-Jan, avoid spring applications for best weed control (good idea also to increase crop safety and get the greatest performance out of this chemistry)-  Soil should be free of large trash and clods at application (this is true for best performance of ANY of our PRE herbicides)-  For best weed control, rainfall or sprinkler irrigation within 3-4 weeks is ideal.  If irrigation is used to activate, 0.5 inch of water is ideal (the idea is to incorporate the herbicide into the surface inch or so, where the weeds germinate, but not go too deeply.  This is also pretty true for all PRE herbicides).

In my opinion, the prohibition on use in flood irrigation orchards is probably the most important change as those sites simply cannot use the herbicide - these growers will have to use other products.   The soil OM restriction is much less of a problem and may actually be beneficial from  both a product stewardship and resistance management standpoint if growers use tankmixes and good integrated strategies.  I had several trials with a range of Alion rates in 2014 and we  observed very good weed control with the reduced Alion rates in most instances but control at 2.5 or 3.5 oz/A was definitely more dependable and long-lasting when a tankmix partner (selected based on field scouting) was used in the management program.Check out the updated Alion label on your favorite herbicide label source.Take care,Brad