New Tools for Managing Volunteer Potatoes
in Carrot Production
Carrot Country
Spring 2007
Carrot was most sensitive to weed
interference of 25 crops reviewed by
Van Heemst (1985). Weeds in carrot
reduce yields, impede proper root formation
and interfere with harvest operations.
Volunteer potato is difficult to manage as
a weed in many areas where potatoes are
grown in rotation. In regions with mild
winters, potato tubers left in the soil after
harvest often escape exposure to lethal
cold temperatures and become a weed in
the following crop. Densities of volunteer
potato emerging in the spring in Washington
are as high as 93 plants per 100 square feet
(Thornton et al. 2001).
Herbicides registered for use in carrot
production are limited, and until recently,
none suppressed volunteer potato. Costly
hand-weeding and limited cultivation are
the primary methods of controlling volunteer
potato in carrot. High crop seeding
rates and narrow rows restrict mechanical
cultivation to furrows between beds. Growers
also utilize soil fumigation to suppress
volunteer potato, especially if nematode
presence warrants fumigant use. Fumigation
with as low as 38 lb ai/a of 1,3-dichloropropene
or 86 lb ai/a of metham sodium
(about half the labeled rate of each product)
significantly reduced potato tuber viability
in lab and field studies (Boydston and Williams
2003).
One aspect of volunteer potato management
should include reducing or eliminating
daughter tuber production. Surviving tubers
can overwinter and cause losses in yield or
quality of rotational crops including field
corn, green peas, onion, snap beans, and
sweet corn. Moreover, volunteer potato is
a host to serious pest of potato including
insects, nematodes, and diseases.
Researchers at USDA-ARS and Washington
State University conducted field
trials near Prosser, WA to: (1) quantify the
effect of volunteer potato density on carrot
yield, (2) determine the critical time for
volunteer potato removal in carrot, and (3)
determine the response of volunteer potato
and carrot to various treatments of Nortron
and Caparol. Results of these studies have
recently been published (Williams and
Boydston 2005, 2006)
Volunteer Potato Density Study
Carrot yield was nearly eliminated by
volunteer potato at relatively low weed
densities (Figure 1). A 5 percent carrot
yield loss was observed with as few as
0.6 volunteer potato plants per 100 square
feet. A density of 74 plants per 100 square
feet reduced carrot yield by greater than 80
percent. Volunteer potato produced many
daughter tubers even at low densities. For
instance, a volunteer potato density of 0.6
plants per 100 square feet produced from
nine to 13 tubers. Control measures that
allow survival of even very few volunteer
potato plants can result in daughter tubers
capable of causing substantial losses in
subsequent crops.
Time of Volunteer Potato
Removal Study
Increasing the length of time for volunteer
potato to compete with carrot before
removing them resulted in sharply lower
carrot yields. Carrot tolerated volunteer
potato well for only a week or two after
crop emergence, and yield dropped rapidly
beyond about four weeks. Five percent
yield loss occurred when carrot had 4.5
leaves and 10 percent yield loss was
estimated for 6-leaf carrot. Consequently,
volunteer potato should be removed early in
carrot to prevent yield loss. Volunteer potato
height at the time of removal was a good
predictor of carrot yield loss (Figure 2). If
volunteer potato was removed before reaching
12 inches tall, yield loss was minimal.
In addition, early removal of volunteer
potato reduces the number of daughter
tubers produced, which prevents problems
in subsequent crops.
Volunteer potato was able to produce
many small tubers relatively quickly while growing in carrot. Each volunteer
potato
plant produced about five daughter tubers
by approximately four weeks, exemplifying
the need to deploying management tactics
early in the season.
Additional factors come into play when
deciding when to remove volunteer potato.
Not all potatoes emerge simultaneously and
if growers remove them too early, another
weeding may be necessary to remove later
emerging plants. Removing plants too early
also increases the chance of leaving the
maternal tuber in the ground, which could
give rise to new shoots.
Suppression of Volunteer Potato with Nortron
Nortron, active ingredient ethofumesate,
was labeled for use in carrot grown in
Oregon and Washington in late 2006.
Nortron is also registered for use in
sugarbeet and grass seed production for
control of annual grass and broadleaf
weeds. Nortron may be applied
preemergence (PRE) at or soon after carrot
planting and may also be applied early
postemergence (POST) when carrot has two
to four leaves.
Our research demonstrated that Nortron
applied PRE at 1.5 lb ai/a or more can delay
emergence and growth of volunteer potato
and often results in deformed and stunted
growth of volunteer potato plants. Nortron
applied POST at 2 lb ai/a causes crinkled,
epinastic growth of potato leaves and
shoots. Nortron applied PRE followed by
POST or two sequential POST applications
has consistently suppressed volunteer potato
growth and reduced potato tuber mass
(Table 1). Nortron treated potato may still
produce a fair amount of small daughter
tubers. The maximum allowed Nortron rate
for a single application in carrot is 2 lb ai/a,
and rates should be adjusted for soil type
and for plants under stress as injury to carrot
is possible. Nortron also controls a number
of annual grass and broadleaf weed species.
Suppression of Volunteer Potato with Caparol Caparol, active ingredient prometryn, also suppresses volunteer potato selectively in carrot. Caparol is registered for use in cotton, celery, pigeon peas and carrot grown for seed. Caparol registration in carrot is expected in 2008. In studies conducted by researchers at Washington State University and USDA-ARS near Prosser, Wash., single or sequential POST applications of Caparol at 2 lb ai/a, were safe on carrot and frequently controlled volunteer potato simila rto the hand-weeded treatment.
Caparol
applied POST initially caused chlorosis to
potato leaf margins followed by necrotic
lesions and stunted growth within one week
of application. In 2002, the most effective
treatments were the sequential applications
of Caparol and Caparol plus an adjuvant
(Table 2). All Caparol treatments reduced
volunteer potato tuber production. Caparol
reduced the size (mass) of daughter tubers
to a greater extent than the number of
tubers.
Carrot tolerance to Caparol has been
similar to that of Lorox and only minor
and transient injury symptoms have been
observed. Carrot yields were similar to
hand-weeded controls when Caparol was
applied POST twice at 1 lb ai/a or POST once at 2 lb ai/a plus adjuvant. Follow
up studies conducted by Syngenta in
2006 demonstrated that an early POST
application of Caparol at 1 lb ai/a plus
crop oil concentrate followed by another
POST application at 1 lb ai/a with crop
oil concentrate or a single application of
Caparol at 2 lb ai/a was safe on carrots.
Caparol also controls numerous annual
broadleaf weeds.
Both Nortron and Caparol offer benefits
to integrated weed management systems in
carrot, particularly where volunteer potato
is problematic and may help reduce or
eliminate hand-weeding costs. Prowl H20,
active ingredient pendimethalin, was also
recently labeled for weed control in carrot,
but does not have activity on volunteer
potato.
Integrated Management of
Volunteer Potato in Carrot Rotations
•Where allowed, treat potato crop with
maleic hydrazide prior to harvest to
reduce sprouting of tubers left in the
field.
•Limit the tubers left in the fi eld
after potato harvest through use of
proper chain size, proper blade depth,
digging speed, fi eld conditions, etc.
•Do not perform tillage operations that
bury tubers deeper where they are
more likely to escape killing temperatures.
•Utilize rotation crops that are competitive
with volunteer potato and
which include numerous cultivation
and effective herbicide options (i.e.
field corn).
•Fumigate with metham or 1,3-dichloropropene
if nematode and disease
problems warrant.
•Delay planting of carrot in fields
where volunteer potato is expected
to be a problem and control early
emerging potatoes with cultivation or
herbicides.
•Utilize new herbicide options of Nortron
and/or Caparol (not yet labeled)
to suppress volunteer potato in the
carrot crop.
•Hand-weed and/or cultivate volunteer
potato escapes to prevent daughter
tuber production.
Literature Cited
Boydston, R. A. and M.M. Williams II. Effect
of fumigation on volunteer potato (Solanum
tuberosum) tuber viability. Weed Technol.
17:352-357. 2003.
Thornton, R. E., g. d. Newberry, D. Joy, G. Hyde,
and T. Schotzko. 2001. Potato volunteer project.
Pages 189-239 in Progress Reports 2001.
Moses Lake, WA: Washington State Potato
Commission.
Van Heemst, H.D.J. 1985. The infl uence of weed
competition on crop yield. Agric. Syst. 18:81-93.
Williams, M. M. II and R. A. Boydston. Alternatives
to handweeding volunteer potato (Solanum
tuberosum) in carrot (Daucus carota). Weed
Technol. 19:1050-1055. 2005.
Williams, M. M. II and R. A. Boydston. Volunteer
potato (Solanum tuberosum L.) interference in
carrot. Weed Science 54:94-99. 2006.
© 2007
Columbia Publishing