Timely vine killing is essential for good tuber separation from stolons, tuber skin set, and efficient harvest. Tubers from immature or recently-killed vines are typically very susceptible to skinning and mechanical injury during harvest. Storage decay problems are a common result. Such tubers also tend to have relatively low starch and high sugar concentrations compared to mature tubers. Whenever possible, kill vines at least two, and preferably three, weeks ahead of harvest. Place only mature, sound, clean potatoes in storage.
Several vine removal methods are available to growers including chemical sprays, mechanical methods such as chopping and rotobeating, flaming, and sometimes frost, or combinations of the preceding. If mechanical choppers are to be used, adjust the blade height to effectively remove the tops without uncovering and injuring tubers. Flail-type shredders are typically superior to rotary blades for this purpose since exposure can be adjusted so that chains are longest between rows. Application of a chemical desiccant a few days before rotobeating is sometimes a good approach since the chemical assures a good kill while the chopper pulverizes plant debris and simplifies harvest.
Seed potatoes may require more care during vine killing. For example, regrowth of vines can lead to virus spread in seed potato crops. Therefore, an additional chemical treatment may be desirable to prevent aphid feeding. Also, many viruses are mechanically spread, casting doubt on the use of rotobeaters in seed fields.
Chemical vine killng is the leading method by far. Chemical sprays are not only more efficient than mechanical means, but also more effective in most cases. Chemical desiccants work best in warm, clear weather. Avoid spraying during very hot periods above 81oF, during rains which can wash the materials off, or when dew is heavy. Provide good mechanical agitation in the tank. Spray l0 to 21 days before harvest depending on the material used.
To avoid the risk of stem-end browning caused by too-rapid top kill:
l. Do not exceed the maximum recommended rate stated on the label. Less chemical is required as the crop matures.
2. When foliage is heavy and vigorous and the label permits, use low-dosage split applications 5 to 7 days apart.
3. When plants are actively growing and very succulent (soft) and when temperatures are high, use a slow acting vine killer.
Label recommendations change from day to day. The following rates and materials may no longer be applicable. Always follow current label directions. Labels can be obtained from the manufacturer or via websites such as CDMS--Agrichemical Database or C&P Press Greenbook. Directions for retrieving and printing labels are provided at the sites.
Treatment, Active Ingredient/Acre, and Application Comments
endothall
0.75 to 1.0 lb ai/A Des-I-Cate
Apply 10 to 14 days before harvest. Use higher rate during cool or cloudy weather or when vine growth is heavy. The addition of 3 to 5 gal/A of diesel fuel or 1 pint paraffin base herbicidal oil for each 20 gal total spray may increase speed and over all vine kill. No wetting agent or emulsifier is required since endothall will emulsify diesel fuel or herbicidal oil. A restricted-use herbicide in Oregon. Do not use high rate, diesel fuel, or other oils under low soil moisture conditions or high temperatures since stem-end discoloration may occur. ------------------------------------------------------------------------
diquat
0.25 lb ai/A or up to 0.5 lb ai/A on Russet Diquat Burbank (SLN ID-930007, OR-930018)
Make last application at least 7 days before harvest. Apply with 8 to 16 oz obtain adequate desiccation where vine growth is dense. Allow a minimum of 5 days between applications. A moderately toxic herbicide that requires protective gear for handling and application. Follow all use restrictions and precautions given on the label. Do not apply to drought-stressed potatoes. Make the last application at least 7 days before harvest. ------------------------------------------------------------------------
sulfuric acid (93%)
17 to 25 gal/A
2 to 3 weeks before potato harvest. This material is not as dependent on temperature or other environmental conditions as most other desiccants. Sulfuric acid is very caustic. Protective clothing including face shield, rubber boots, and rubber gloves must be worn. ------------------------------------------------------------------------
monocarbamide
20 gal/A diluted 1:1 with water for 40 gal/A dihydrogensulfate Enquik
No specified time; allow adequate time for skin set, preferably 2-3 weeks. Must be applied diluted. Surfactant must be added. This material is much safer to user (less caustic to skin), but is as corrosive to cotton, nylon, and some other matrials as sulfuric acid. Consult label for full directions. Do not mix sulfuric acid and urea to make this solution. Use the premixed solution.
Vine
Killing
Harvest
Production
Management
Potatoes,
General
