Remember pre-harvest intervals when applying asparagus herbicides

Asparagus growers need to observe pre-harvest intervals between herbicide applications and the beginning of harvest.

April is always a hectic month for Michigan’s asparagus growers. Getting fields ready to begin harvest means working on numerous tasks all at once. Migrant housing must be made ready for occupancy, communication must be kept up with processors and packers, fertilizer needs spreading, new fields must be prepared and planted, GAP audits must be prepared for, rye cover crops need mowing and many other tasks must be completed in a very short time. During these hectic, 16-hour days, it is easy to lose track of something like the pre-harvest intervals (PHI) that must be observed for the herbicides that you are applying to your asparagus fields, but in these days of increased regulatory pressure, both from government, the food industry and consumers, it is an important thing to keep in mind.

The tricky thing about keeping within the PHIs of pre-harvest asparagus herbicides is always the weather. Most growers generally do not have a problem observing PHIs if the weather cooperates. Unfortunately three consecutive days of 80-degree weather can push asparagus through the ground very rapidly and in a matter of a couple of days you can go from ahead of the game to pretty far behind.

Unfortunately many of the most widely used herbicides that are best matched to the weed mixes found in Michigan asparagus fields have relatively long PHIs. Many have 14-day PHIs and one of the more popular ones has a 16-day PHI. Growers do not generally have a problem meeting these PHIs, but in spring with a sudden onset of hot weather plans may have to change.

Fortunately, asparagus growers have more flexibility than many vegetable commodities because they have many more herbicide choices and combinations. They also have the advantage of having a few residual herbicides with relatively short or no PHIs. These include both broadleaf and grass material. While these materials may not be perfect matches to the weeds that were scouted in the field the previous year, they do provide control or suppression of many major weeds. It is important to note however that some of them have serious side affects that may damage early asparagus pickings, so growers should read the labels carefully.

Asparagus Herbicides and Pre-Harvest Intervals (PHI)

Diuron (Karmex 80DF) (apply after mowing)
Mesotrione (Callisto 4L) (apply after mowing)
Dicamba (Clarity or Banvel 4L) 4-hours
Flauzifop-P (Fusilade DX 2E) 1-day
Sethoxydim (Poast 1.5E) 1-day
Halosulfuron (Sandea 75W) 1-day
Clethodim (Selectmax 0.97E) 1-day
Linuron (Lorox 50DF) 1-day
2,4-D amine salts (Formula 40) 3-days
Glyphosate (Touchdown or Roundup 4L) 5-days
Terbacil (Sinbar 80WDG) 5-days
Paraquat (Gramoxone Inteon2L) 6-days
Norflurazon (Solicam 80DF) 14-days
Metribuzin (Sencor 75DF) 14-days
Pendimethalin (Prowl H2O 3.8CS) 14-days
Sulfentrazone (Spartan 4F) 14-days
S-Metalochlor (Dual Magnum 7.6E) 16-days

Asparagus growers who have questions about weed control programs can consult Extension bulletin E-433 “2011 Weed Control Guide for Vegetable Crops.” This bulletin is available at Extension offices in Michigan or on the web at Please note that the bulletin is updated annually so it is important to have the current year.

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