After a mild winter, there usually are scattered reports of volunteer potatoes growing in wheat and corn fields. This is especially true when the ground doesn't freeze more than a couple of inches or not at all. Besides potentially greater insect problems such as Colorado potato beetle, aphids and European corn borer, and maybe sand chafer, a problem may develop with respect to volunteer potatoes in rotation crops. Potatoes can act like weeds, competing for resources -- light, nutrients and water. Volunteer potatoes may act as hosts for early and late blights, leaf roll and other viruses, and, if from an infected tuber, may act as a source for all of these. Volunteer potato tubers can survive and continue to propagate for several years.
Although many potato growers rent and do not own the land on which potatoes are grown, neighbors whose land is being used may want to know how to deal with a potential volunteer potato problem. So in the interest of a good neighbor policy, here are some suggestions.
Studies in the U.K. show that as much as 150,000 tubers per acre may be left in the field after harvest and that as many as 10% of these (15,000/acre) may remain viable after a mild winter (Lutman, 1977). In Washington studies, 95,000 tubers of Russet Burbank per acre have been reported to be left behind after harvest and 5,700 tubers per acre may be as much as six inches deep (Figure 1; modified after Eberlein et al., 1997).
Full plowing can bury tubers even more deeply, protecting them from freezing. It is best to disc fields after harvest to bring up to the surface and chop any tubers left behind. Short season cultivars like Russet Norkotah tend to leave fewer tubers behind and these tend to decay due to warmer temperatures in the afternoons. In dry soil, tubers won't freeze until the ground around them is below 25 F. To eliminate tubers left behind in the field, winter needs to freeze the ground at least six inches which is common in many northern States and Provinces but not always true every year. For example, Nebraska usually freezes sufficient to eliminate tubers left in the field but this did not occur in the winter of 1999-2000 (Table 1).
The obvious first step to minimizing volunteer potatoes is to minimize the amount of tubers unharvested and to destroy those left behind. Some useful manufacturing practices are narrowing pitch chain spacing and post-harvest shallow tilling. Some commercial growers apply MH30 (maleic hydrazide) toward the season end for sprout inhibition; apply no later than two weeks before vine desiccation. MH30 application has been reported to lower volunteer potato population by 70-80%.
Cultivating in a non-potato field with volunteer potatoes having about 5-10 leaves or one to two weeks after their emergence works well when done in combinations with herbicide applications. Note, however, that the efficacy and/or phytotoxicity of some herbicides may change when followed by cultivation. Also, be careful to the damage the crop being cultivated.
Competitive crops to plant after potatoes are small grains especially winter wheat. Sugar beet, dry bean and onion do not compete well against volunteer potato and should be avoided following a warm winter. Planting small grains after potato, therefore, is recommended.
SMALL GRAINS
When small grains are planted, there are a number of herbicides that may be used against volunteer potato (Table 2; modified after Eberlein et al., 1997). Bronate and Buctril burn down potato foliage sufficiently to allow small grains to grow and be competitive. Banvel, Curtail, Harmony, and other plant growth regulators herbicides injure potato causing stunting and leaf mal-formation but not kill the plant. The most effective is Roundup but it should only be used in commercial grains not those grown for seed. It should be applied after the hard-dough stage when grain moisture is less than 30%. Potato plants should be killed before grain harvest. Aim, a new herbicide, may be useful in controlling potatoes in wheat and barley.
CORN
In corn, herbicide application should be used with conventional tillage. Recent studies report that cultivation plus a sequence of atrazine applied pre-emergence followed by post-emergence application of 2,4-D plus Banvel is the best treatment program (Table 2). Substituting atrazine with Bladex is acceptable but there may be more second generation tubers. However, using Bladex avoids atrazine-related crop rotation problems. Tough with crop oil and Liberty have also been mentioned as giving good control. Starane has Section 18s ('emergency use') in Oregon and Washington, but misses some weeds. It is also more expensive than 2,4-D plus Banvel. New herbicides that may be useful for control of volunteer potatoes in corn are Aim and Calisto.
LATE CROPS
For late-planted crops when volunteer potato may emerge before planting, application of Roundup (glyphosate) is suggested to kill emerged sprouts. New sprouts could emerge a few weeks later and small tuber could be produced before the season ends.
OTHER CROPS
For row crops in which herbicides can not be used, a minimum of four cultivations are usually needed starting when potato plants are three to six inches tall.
CULL PILES
Another place for volunteer potato is in cull piles that did not thoroughly freeze. Even buried piles as deep as 18 inches can produce volunteer sprouts. Cull piles can be designated as non-crop areas and thereby allow the use of several broadleaf herbicides (Table 3; modified after Eberlein et al., 1997).
GLYPHOSATE
There is more information available about glyphosate (Roundup) for control of volunteer potato then other herbicides. With cultivation, it is the most effective treatment in most cases. Although most effective when applied in June or July, it is effective in April and May. Low temperatures, <50F, will lower its absorption by potato plants (Masiunas and Weller, 1988); light intensity does not affect efficacy. The stage of growth of the potato at the time of application does not play a role in efficacy either (Smid and Hiller, 1981). Glyphosate is effective when applied about ½ to 1 lb/ac. It translocates throughout the plant and directly lowers sprout viability; for example, approx. 1 lb glyphosate/a lowered viability of green-house grown tubers from 85% to 3% sprouting (Lutman and Richardson, 1978).
REFERENCES
- Eberlein, C.V., R. Boydston, and M. Thornton. 1997. Volunteer Potato Control. U. Idaho CIS # 1048.
- Lutman, P.J.W. 1977. Investigations in some aspects of the biology of potatoes as weeds. Weed Research 17:123-132.
- Lutman, P.J.W. and W.G. Richardson. 1978. The activity of glyphosate and aminotriazole against volunteer potato plants and their daughter tubers. Weed Research 18:65-70.
- Masiunas, J.B. and S.C. Weller. 1988. Glyphosate activity in potato (Solanum tuberosum) under different temperature regimes and light levels. Weed Science 36:137-140.
- Smid, D. and L.K. Hiller. 1981. Pytotoxicity and translocation of glyphosate in the potato (Solanum tuberosum) prior to tuber initiation. Weed Science 29:218-223.