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UCCE Weed Specialist Brad Hanson
<p>University of California Cooperative Extension Weed Specialist Brad Hanson explains herbicide trial studies at UC Davis.</p>

Label change for Alion herbicide in California

Changes are now in effect Updated labels available online Changes affect tree nuts, grapes, stone fruit, pome fruit and olives.

California regulators recently released a fairly significant label change to the Alion herbicide label for California orchard and vineyard crops. Those changes are now in effect and growers and PCAs will want to be aware of this as they plan dormant-season herbicide programs now that many areas of the state are getting some rain.

The use patterns for Alion (active ingredient: indaziflam) was modified for tree nuts, grapes, stone fruit, pome fruit, and olive. Citrus uses were not changed.

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Most important changes include:

Maximum use rates now have a restriction based on soil organic matter (OM) content.

  • Grapes: if soil less than 1 percent OM, max rate is 3.5 ounces/acre (0.045 lb. ai) and if over 1 percent max rate is 5 ounces/acre (0.065 lb. ai)
  • Nuts, Pome, Stone, Olive: if less than 1 percent OM, max rate is 3.5 ounces/acre; if 1-3 percent OM, max rate is five ounces/acre; if OM above 3 ounces, max rate 6.5 ounces/acre.

Previously there was a 6.5 ounce rate max for all crops except grape which had a five ounce 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.

Also important: the label now restricts Alion use in flood-irrigated orchards. It also prohibits irrigation within 48 hours after the applications.

Crop safety

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 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 burn down herbicides if emerged weeds are present (this was always the case as Alion has 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 three-four 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 tank mixes 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 ounces/acre was definitely more dependable and long-lasting when a tank mix partner (selected based on field scouting) was used in the management program.

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