July/August 2010
Preparing for Harvest By Bill Schaefer

Preparation for vine kill begins now

Potato plant canopies have begun to spread, the plants are looking healthy and now’s the time to begin making plans to kill all the vines, stems and leaves in anticipation of the harvest.

There are two methods of vine kill – mechanical and chemical. The advantages of a chemical application are that it provides for a greater than 90 percent leaf and stem kill within one to two weeks of application, giving time for the tuber skin to set, to avoid bruising during harvest and giving the grower a timetable for when he can begin the harvest, said Pamela Hutchinson, a specialist in cropping systems weed science at the University of Idaho’s Aberdeen Research and Extension Center.

Hutchinson said it takes from one to three weeks for tuber skin set, depending on moisture and cool weather following application of desiccants. Another reason for chemical application is to eliminate the potential for late blight transmission at the end of the season.

“It becomes more prevalent that growers use some type of chemical vine kill because the vines would die quicker and you would have less chance of the disease getting to the tuber. Then you wouldn’t have any problems with storage with the late blight manifesting itself in the tuber,” Hutchinson said.

There are basically five types of chemical applications that are currently used for vine kill.

The most efficient and fastest method is sulfuric acid, something growers have used for years. It provides 100 percent desiccation of stems and leaves in three to three days. That means that skin set begins immediately and harvest can begin in a week to 10 days.

The downside to sulfuric acid is that it can only be applied by a custom applicator and the cost has been rising with it becoming less available.

“There are three or four chemicals that work really well for vine kill,” Hutchinson said. “One that’s been around for a while is called Reglone. The common name for that is diquat.”

Reglone is a Syngenta product, with the primary ingredient diquat. It also is used for control of a wide range of broad-leafed weeds. Reglone is rainfast 30 minute after application and has a pre-harvest interval of seven days.

Another popular desiccant is Bayer CropScience’s Rely.

This past March, Bayer CropScience announced a new formulation of Rely, calling it Rely 280. The new formulation is more powerful than its predecessor, according to the company. Rely 280 contains the active ingredient glufosinate-ammonium. It is a contact herbicide, rainfast within four hours of application, with a re-entry period of 12 hours and a pre-harvest interval of nine days.

Last year Gowan, under a marketing agreement with Nichino America Inc., introduced Vida herbicide. Vida’s active ingrediant is pyraflufen-ethyl. Gowan is marketing Vida in the northern half of the United States and Nichino in the southern half. On its own it works best in warmer temperatures and greater sunlight. It can be used as a tank mix with either Reglone or Rely.

Aim herbicide, sold by the FMC Corp., is used for a variety of weed management along with vine kill. Carfentrazone-ethyl is the active ingredient. Aim is a water dispersible, granule that can be used alone or in tank mix combinations.

There is a restricted entry interval (REI) of 12 hours and a seven day pre-harvest interval following application.

Hutchinson advised growers to be aware that certain varieties, such as Alturas are late to bulk up, unlike Russet Burbanks, so you would want to apply vine kill desiccants later in the season for Alturas. Ranger Russet and Russet Norkotah-CO No. 3 are also late bulking varieties, according to a study released in 2007 by Bill Bohl and Stephen Love.

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