Growing Irrigated Potatoes
AE-1040 (Revised) March 1999
Thomas F. Scherer, Agricultural Engineer,
NDSU Extension Service
Dave Franzen, Soil Science Specialist, NDSU
Extension Service
James Lorenzen, Associate Professor, Department
of Plant Science
Art Lamey, Professor, Plant Pathologist, NDSU
Extension Service
Dwight Aakre, Agricultural Economist, NDSU
Extension Service
Duane A. Preston, Area Extension Agent –
Potatoes, Extension Service, NDSU-University of Minnesota, East
Grand Forks, MN
Production Considerations
Planting Season
Varieties
Production and Cultivation Practices
Fertilization
Pest Control
Irrigation Management
Harvest Considerations
Groundwater Protection
Economic Analysis
Additional Sources of
Information
Production of irrigated potatoes requires specialized
equipment and a substantial capital investment. Before investing
in this enterprise, the following questions must be considered:
- Is your soil type suitable for irrigation?
- Is there an adequate supply of good quality water for
irrigation?
- Can a water permit be obtained for the potential
irrigable land?
- What potato production and irrigation machinery will have
to be purchased?
- Do you have potato production experience? Irrigation
experience? If not, do you have potato production or
irrigation consulting services available or a business
partner with experience?
- Do you know how to market your potatoes (which can
include forward contracts, an adequate sales outlet,
trucking and transportation, storage, and a potato
broker)?
- Have you determined the profitability of the other crops
in your irrigated cropping rotation?
Before going into irrigated potato production, you should not
only be knowledgeable about the cultural aspects of potato
production, but equally knowledgeable about the economic aspects,
which include fixed investments, labor and operating capital
requirements, price risk, potential annual costs and returns,
market grading criteria, storage requirements, delivery
expectations and marketing alternatives.
The planting season for potatoes extends from about April 15
to June 15, though planting on light textured soils in
southeastern North Dakota may be as early as the first week of
April. In general, late varieties used for processing and early
maturing varieties for the fresh market should be planted first.
Early maturing table varieties destined for storage may be
planted in late May or early June.
Potato yield response to irrigation will vary depending on
whether short season or long season varieties are wanted. In
general, the full season varieties will show the greatest
response to irrigation. Most varieties that have performed well
under dryland conditions also perform well under irrigation.
Market demand will generally dictate the selection of a variety
or varieties to grow.
There are three types of potatoes grown under irrigation:
smooth red skinned varieties (used primarily for the fresh
market), smooth white skinned varieties (used in processing;
chips and dehydrated products), and russet skinned varieties
(used for the fresh market, french fries and dehydrated
products). Within each of these types there are early and late
maturing varieties.
A desirable characteristic for potatoes used in processing is
the percentage of total solids (mostly starch). This trait is
variety-dependent and typically ranges from 17% to 23% (Table 1).
The percentage of total solids is often one to two points lower
under irrigation than under dryland conditions, and may be
further reduced by excess nitrogen. The most important varieties
for production of french fries are Russet Burbank, which has good
yields, high solids, and stores well, and Shepody, which can be
harvested earlier with acceptable yield and solids content.
Another important processing trait is the percentage of reducing
sugars that influence browning during the fry process. NorValley
and Snowden are somewhat resistant to the increase in reducing
sugars that comes with storage at colder temperatures.
Table 1. Potato yields of
commonly grown varieties in irrigated trials from 1994 to 1996.
----------------------------------------------------------------
Yield (cwt/acre) Typical
------------------ Percent
Variety Color Maturity2 1994 1995 1996 Solids
----------------------------------------------------------------
Goldrush Russet ME 365 424 448 20.5
Russet Norkotah Russet ME 411 385 394 20.5
Russet Burbank Russet L 416 406 484 22.0
Shepody White1 M 345 384 400 21.5
Atlantic White ML 444 427 414 23.0
Norchip White ME 352 396 350 21.5
NorValley White M 366 467 474 21.5
Snowden White L 467 342 367 23.0
Nordonna Red M 401 365 377 18.5
Red Norland Red E 450 359 389 18.5
Red Pontiac Red ML 481 374 509 18.0
----------------------------------------------------------------
With a high percentage of total solids, good storage
characteristics, and appropriate shape, the Russet Burbank
variety is the most popular variety grown under irrigation.
Currently, it is the industry standard for french fry potatoes.
However, other varieties were higher yielding on irrigated potato
trials.
Yield Potential
The major advantages of irrigated potato production are higher
yields, earlier production and drought protection. Yields of
potatoes grown under irrigation in North Dakota have averaged
about double that of dryland potatoes.
Irrigated potato variety trials have been conducted on light
textured soils (sands and loamy sands) in various areas of North
Dakota since 1941. The first trials were begun at the Williston
Research Center. From 1975 through 1986, the trials were
conducted at the Karlsruhe irrigation site where the 12 year
average for all varieties was 294 hundredweight/acre (cwt/ac).
Irrigated variety trials have been conducted at the Oakes
Research Test Area since 1987 and at the Carrington Research
Extension Center since 1989. Yield results from several common
varieties grown at the Oakes Field Trials Site for the 1994, 1995
and 1996 growing seasons are shown in Table 1.
Marketing
It is important to establish a marketing plan before planting
potatoes. This may mean contract growing for a processor, an
arrangement to sell through a marketing association or broker, or
gambling on the open market at the end of the growing season.
The major markets for potatoes are the process potato market,
the fresh market and for seed. Seed production is the most
technically demanding because of the need to meet rigid disease
free standards for certification.
In recent years, the main demand for irrigated potatoes has
been for french fries, where processors prefer the Russet Burbank
variety. Proper irrigation management can produce a uniform
potato shape which is long and consistent in size. Also, the
total solids or potato density can be maintained such that high
quality french fries can be produced with minimum waste.
A large portion of the potatoes used for processing are grown
under contract, which reduces the risk involved in marketing but
also limits the possible profit. Without a contract, there is a
risk of not finding a market after incurring costs of around
$1100/acre. From 1992 to 1997, North Dakota potato prices paid to
producers fluctuated from a low of $2.30/cwt in June of 1992 to a
high of $7.75/cwt in April and May of 1994. Price fluctuations of
this magnitude emphasize the need for managing price risk through
some type of forward contract before incurring the large capital
investment required for irrigated potato production.
Production and Cultivation Practices
Seed bed preparation before planting will be determined by the
previous crop. The soil should be loose at planting with a
minimum of preplant tillage.
Seeding Rate and Depth
The amount of seed needed for planting depends on variety,
distance between rows, the spacing within rows and the size of
the seed pieces (Table 2). Seed pieces should be cut from tubers
no larger than 10 ounces for round varieties and 12 ounces for
Russet Burbank. Seed pieces cut from smaller tubers are more
uniform in size, give better plant stands and usually more tubers
per hill.
Table 2. Quantity of seed potatoes needed to plant an
acre of potatoes
with different seed piece sizes and spacing (cwt).
---------------------------------------------------------
Distance Distance ------ Average Seed Size -------
between between 1� 1� 2 2�
rows seed pieces ounces ounces ounces ounces
(inches) (inches) (cwt) (cwt) (cwt) (cwt)
---------------------------------------------------------
36 8 20.4 23.8 27.2 30.6
10 16.3 19.0 21.8 24.5
12 13.5 15.8 18.1 20.4
38 8 19.3 22.6 25.8 29.0
10 15.5 18.1 20.6 23.2
12 12.9 15.0 17.2 19.3
40 8 18.4 21.4 24.5 27.6
10 14.7 17.2 19.6 22.1
12 12.3 14.3 16.3 18.4
---------------------------------------------------------
A healthy 1.5 to 2 ounce seed piece is considered best to
establish a vigorous plant. Plants from seed pieces smaller than
1.5 ounces are generally slower to emerge and have less vigor.
Small seed pieces are also more likely to decay before the plant
becomes established. Seed pieces cut larger than 2 ounces result
in higher seed costs with little potential benefit.
Irrigated potatoes can be spaced, within the row, closer than
under dryland conditions. Seed spacing is based on varietal
characteristics such as tuber-set, resistance to hollow heart,
and resistance to the development of misshapen tubers. Wider
spacing (10 to 12 inches) is recommended for varieties with heavy
tuber-set, smooth tubers, and resistance to development of hollow
heart and misshapen tubers. Closer spacing (8 to 10 inches) is
recommended for varieties with poor tuber-set to reduce the
number of oversized tubers. Hollow heart is caused by excess
moisture and conditions that cause rapid tuber growth. Since a
potato grows from the inside out, a hollow center can result from
this rapid growth, thus the name hollow heart. Close spacing is
an effective way to reduce hollow heart.
Generally the center of the seed piece should be planted 2 to
4 inches below field level and covered with 2 to 3 inches of
soil. Shallow covering usually results in quicker emergence, less
seed decay, less blackleg and less rhizoctonia attacking the
sprouts. However, the best seed depth will vary somewhat with
soil moisture and temperature. Moist soil with temperatures
averaging from 50 to 60 �F favor wound healing in the soil with
minimum seed decay. Very deep planting may result in poor wound
healing and lead to seed decay, particularly if heavy rains
follow planting.
Growth Stages
The growth, development and water requirements of the
potato plant can be divided into the following four stages:
VEGETATIVE. After planting, this stage of
growth begins when the eyes break dormancy and produce sprouts.
This stage has a duration of 15 to 30 days and ends with tuber
initiation. Stored soil moisture and spring rains are usually
sufficient during this period to provide adequate moisture for
proper development. However, soil moisture monitoring should be
started soon after emergence. For disease control, irrigation
should be avoided between planting and emergence. If the soil is
dry prior to planting, irrigate before planting rather than
after.
TUBER INITIATION. This stage of growth begins
when tubers develop at the stolon tips. Approximate duration of
this stage is 10 to 14 days. Stored soil and spring moisture
supplies are usually adequate during this period however, soil
moisture levels should be watched closely because water stress
during this period can reduce the number of tubers produced per
plant.
TUBER BULKING. A constant rate of increase in
tuber size and weight occurs during this stage, unless a growth
limiting factor is present. This stage can last from 60 to over
90 days, depending on the length of the growing season and
presence of pathogens. Tuber size and quality is closely
related to moisture supply in this period. Research has shown
that the total yield of potatoes is most sensitive to water
stress during mid-bulking. Mid-bulking occurs three to six weeks
after tuber initiation, however, water stress any time during
this period will have an effect on the total yield. Tuber growth
is retarded by moisture stress and does not resume uniformly when
moisture again becomes available. New growth and enlargement will
take place at the top end while the other portions of the tuber
remain stunted. Thus, especially in some long tuber varieties,
constricted areas develop that are related to the stage of tuber
growth at the time the moisture stress occurred. Other
deficiencies in quality such as growth cracks and knobbiness are
also related to moisture stress followed by periods of adequate
or surplus moisture.
MATURATION. This stage of growth begins with
canopy senescence. Older leaves gradually turn brown and die.
This condition spreads throughout the vines and leaves eventually
resulting in canopy loss. Tuber growth rates are lower than
during tuber bulking. Potato plants require less water for tuber
bulking during this stage because of reduced transpiration from
the dying leaves.
Weed Control
Weeds reduce potato yields by competing for water, nutrients
and light. Also, certain weed species can cause difficulty in
harvesting, release toxins that inhibit crop growth, and harbor
insects, diseases or nematodes that may attack potatoes.
An effective weed control program includes environmentally
sound cultural, mechanical and chemical weed control methods.
Crop rotations, cultivation and the use of different herbicides
help avoid the buildup of resistant weed species. Certain
herbicide residues from previous years can damage potatoes. Use a
planned weed control program and avoid herbicides that will
injure or reduce growth of subsequent crops. Always read the
pesticide label for information on crop rotations and intervals.
Tillage and herbicides are the two primary means of
controlling weeds in potatoes. Cultivators, harrows and rotary
hoes are commonly used. The first tillage operation after
planting is usually a "blind" cultivation or harrowing
before the crop emerges. The number of tillage operations will
vary, but three cultivations and two harrowing operations are
common.
After emergence, inter-row cultivation is used to control
weeds and to form a ridge or hill over the seed-piece and
developing tubers. Besides controlling weeds, the ridge or hill
helps protect tubers from sunburn (tuber greening), late season
frosts, excessive rainfall or irrigation, and reduces the amount
of soil to be moved at harvest. One danger of excessive
cultivation and deep cultivation of potatoes is root pruning.
Potatoes are a shallow rooted crop, with roots growing laterally
10 to 18 inches and downward to a maximum depth of 3 feet. Root
pruning may be a problem with late cultivations, reducing the
overall growth potential of the potato plant.
Herbicides labeled for injection into irrigation systems and
recommendations for use in the control of weeds in potatoes can
be found in NDSU Extension Circular W-253 (Revised), the current
years Agricultural Weed Control Guide, and in the current year's
NDSU Crop Production Guide.
A potato crop makes a large demand on the soil for nutrients.
The amount a 300 cwt/ac crop of potatoes will utilize depends on
potato variety, climate, soils, and irrigation system management.
The average nutrient content is:
Nitrogen -- 200 lbs.
Phosphorus (P205) -- 60 lbs.
Potassium (K20) -- 300 lbs.
One-third to one-half of these nutrients are found in the
vines and returned to the soil. The remainder is removed with the
harvested tubers and must be replaced. The partitioning of
nitrogen in a potato plant as it occurs during the growing season
is shown in Figure 1. Phosphorus, potassium and other nutrients
are seldom deficient in North Dakota soils for potatoes unless
the soil is very sandy or the pH tests above 8.0. Land that has
been leveled can be deficient in zinc. Soils with a DTPA extract
zinc level below 0.5 parts per million (ppm) are more likely to
show a response to zinc fertilization.
Figure 1. Uptake of nitrogen
for Russet Burbank potatoes using an emergence date of June
1. (Adapted from Sultanpour, American Potato Journal, Figure
7, Vol. 46: 111-119, 1969.) (5KB b&w
graph)
Mechanical application of sulfur may not be needed when
irrigating with water containing high sulfate (30 ppm or greater)
concentrations. Response to sulfur is likely only when soil
sulfur levels are low and sulfur contained in irrigation water is
not adequate.
Soil Testing
The best way to determine the amount of fertilizer to apply is
by a soil test. Fields should be tested every year for
nitrate-nitrogen and every two to four years for phosphorus and
potassium. Recommendations for nitrogen, phosphorus and potassium
based on soil test results are shown in Table 3.
Table 3. Nitrogen, phosphate and potash recommendations
for potatoes with yield goals.
Source: Dave Franzen, EB-65, North Dakota Fertilizer Handbook.
-----------------------------------------------------------------
Soil Phosphorus Test (ppm)1
Soil Test ------------------------------------
N Plus Method VL2 L M H VH
Yield Fertilizer Bray-1 0-5 6-10 11-15 16-20 21+
Goal N Olsen 0-3 4-7 8-11 12-15 16+
-----------------------------------------------------------------
cwt/ac lbs/ac-2' --------- P2O5 lbs/ac ---------
200 80 90 65 40 10 0
300 120 135 95 55 15 0
400 160 180 125 75 25 0
500 200 225 155 95 30 0
-----------------------------------------------------------------
Soil Test Soil Potassium Test (ppm)
N Plus Method ------------------------------------
Yield Fertilizer Bray-1 VL L M H VH
Goal N Olsen 0-40 41-80 81-120 121-160 161+
-----------------------------------------------------------------
cwt/ac lbs/ac-2' ------------ K2O lbs/ac ------------
200 80 150 105 65 20 0
300 120 225 160 95 30 0
400 160 300 210 125 40 0
500 200 375 265 155 50 0
-----------------------------------------------------------------
1 ppm - parts per million of phosphorus or potassium in the soil test
2 VL - Very Low, L - Low, M - Medium, H - High, VH - Very High.
Subtract the amount of nitrate-nitrogen in the top 2 feet of soil
from the N figures to determine the amount of nitrogen to apply.
With a good crop rotation, a certain amount of residual nitrogen
will be carried over for use by potatoes. Potatoes following any
legume such as soybeans, alfalfa, dry beans, or clover will
benefit. Also, if sugarbeet leaves are green at harvest, some N
would also be expected to be released the following year.
Potatoes following corn or small grains may not inherit much
residual nitrogen. Soil sampling before planting will indicate
how much residual nitrogen is left in the soil but may not
reflect mineralization of residues during the year. Previous crop
nitrogen credits for different crops should be subtracted from
nitrogen required. Nitrogen credits are published in the annual
NDSU Crop Production Guide and other Extension Service
publications
Fertilizer Application
Fertilizer applied at planting should not come in direct
contact with the seed pieces. The recommended method is to place
fertilizer in two bands, each band 2 inches to the side and 2
inches below the seed pieces. Broadcasting is also acceptable.
Application of all the required nitrogen in a single preplant
operation is not a recommended practice. Fertilizing to achieve
maximum utilization of nitrogen in potatoes on irrigated sandy
ground requires split applications. A rule of thumb on medium to
heavy soils would be one-half the needed nitrogen applied
preplant and the remaining nitrogen needs applied as urea or 28%
liquid solution at hilling. On sandy soils consider applying
one-third to one-half at planting followed by one-fourth to
one-third at emergence and the remainder at hilling. Additional N
should be applied using chemigation as determined by petiole
sampling.
Additional nitrogen becomes available to the plants through
soil mineralization during the growing season. This occurs at
about 15 lbs/ac per warm season month, but varies due to soil
organic matter level and previous crop residues. Based on plant
analysis, additional nitrogen may be applied through the
irrigation system. Studies on irrigated potatoes at the Oakes
research site show little to no advantage to applying more than
200 lbs/ac of total nitrogen to reach optimum yields. The quality
of the potato for storage also declines if excessive nitrogen is
used.
All fertilizer products can be used in potato production. Dry
product blends that match soil test needs and are broadcast
applied prior to seedbed preparation offer management and
application convenience. Also, during the hilling operation, the
fertilizer is moved to the row with the soil, which concentrates
nutrients in the active root growth zone. Equal management
convenience can be obtained with a variety of fertilizer products
that are sidedress applied in bands that the root system
intercepts early in the vegetative growth stage.
Chemigation
Applying fertilizer through the irrigation system is called
chemigation. Required equipment is outlined by state law and
administrative rule. Backflow protection equipment must be
installed at all water pumps. Chemigation is a recommended Best
Management Practice (BMP) when used with center pivot or lateral
move irrigation systems, however, it is not recommended
for volume gun ("big gun") irrigation systems. Because
volume guns throw the water high into the air, the uniformity is
affected by the wind causing poor chemical application and drift.
Injection pumps which use either a piston or a diaphragm are
available. The piston pumps have a larger capacity and are
generally used for injecting liquid fertilizer. They are
available with either a single or double piston and range in
capacity from less than 1 to over 300 gallons per hour (gph). The
most common have a maximum capacity of 18 gph using a single
piston and 36 gph with a double piston. Diaphragm pumps are best
suited to injecting smaller amounts of chemicals. They can inject
chemicals with more precision than piston pumps and are commonly
used for pesticide injection.
Liquid urea-ammonium nitrate (28-0-0) is the preferred
nitrogen source for chemigation. From 10 to 30 lbs-N/acre are
usually applied during each chemigation event. To accurately
determine the amount of nitrogen fertilizer to apply, the
chemigation injection pump needs to be calibrated. Chemigation
calibration worksheets are available from county Extension
Service offices. The injection pump should be checked before each
chemigation event to ensure it is injecting the desired amount of
fertilizer.
Anhydrous ammonia should not be injected into irrigation
systems. Irrigation water with high bicarbonates (HCO3)
will generally cause an ammonium carbonate (NH4CO3)
precipitate which will plug sprinkler nozzles. Almost all
groundwater in North Dakota has high bicarbonates.
Petiole Sampling for Nitrogen Management
Petiole sampling will help determine the nitrogen status of
the potato plant during late vegetative growth and tuber bulking.
It can be an effective tool for both high yield production and
groundwater nitrate contamination protection. The petiole is that
part of the potato plant connecting the leaf blade with the stem
(Figure 2).
Figure 2. Petiole sampling
procedure for potatoes. The 4th or 5th petiole from the top
of the plant is used for tissue analysis of nitrate nitrogen.
(10KB b&w illustration)
Nitrogen demand is high during vegetative growth (the three to
four weeks after seeding). Uptake is rapid and nitrogen stored in
vegetative growth later translocates to the tubers. However,
lysimeter studies at the Oakes research site have shown that from
April to early May, 43% of yearly drainage and 37% of annual
nitrate loss takes place. Hence, preseason nitrogen fertilization
that exceeds growth needs during this period increases the risk
of drainage loss. Petiole analysis can help manage crop nitrogen
needs under high leaching potential, irrigated potato production.
Petiole samples should be taken several times during the
growing season, ideally once per week to help establish petiole
nitrate trends. Soil samples to a depth of 18 inches should be
taken in conjunction with the petiole samples and analyzed for
soil nitrate levels.
Analysis of petiole nitrate during early vegetative growth is
problematic because of early-season fluctuations, but should be
in the range of 12,000 to 22,000 ppm at the time of tuber
initiation (Figure 3). The petiole nitrate levels should be
allowed to drop slowly through the season with a measured range
from 11,000 to 15,000 ppm at mid-season and 6,000 to 8,000 late
in the season. This provides for rapid, uniform tuber growth and
still allows proper tuber maturation prior to harvest.
Figure 3.
Recommended petiole nitrate for irrigated potatoes in
North Dakota. (5KB b&w chart)
If petiole nitrate level indicates deficiency, supplemental
nitrogen can be applied in early season by side-dressing or
through the irrigation pivot at any time during early to mid
tuber bulking. Insufficient nitrogen supply can cause premature
senescence and susceptibility to related diseases, reducing yield
potential. Large fluctuations in nitrate supply can lead to
quality problems (knobs, sugar ends, etc.) and should be avoided.
Excess nitrogen fertilizer can reduce yield and specific gravity,
increase reducing sugars in the tuber (poor fry quality) and
delay maturity, which can cause excess skinning at harvest and
lead to poor storability.
Nutrient concentrations in recently matured whole leaves
(fourth leaf from the top) can also be used to diagnose nutrient
disorders (Table 4).
Table 4. Nutrient
sufficiency levels in recently matured leaves
taken 45-55 days after emergence.
----------------------------------------------------
N P K Ca Mg S
------------- Percent -------------
5.0 0.3 4.5 0.6 0.3 0.2
Fe Zn Cu Mn B Mo
----- Parts Per Million (ppm) -----
51 25 6 30 21 1.0
----------------------------------------------------
N - Nitrogen P - Phosphorus K - Potassium
Ca - Calcium Mg - Magnesium S - Sulfur
Fe - Iron Zn - Zinc Cu - Copper
Mn - Manganese B - Boron Mo - Molybdenum
Irrigation not only improves the yield and growth potential of
potatoes but also increases the number of pests that feed on
them. The timely application of water during the growing season
provides an almost ideal environment for weeds, insects and
disease organisms, so efforts to control these pests may be
greater than under dryland conditions.
Insects
The insects affecting potatoes in North Dakota are primarily
aphids, the Colorado potato beetle, the potato flea beetle,
wireworms and leafhoppers. The application of a systemic
insecticide at planting will usually control these insects
through the middle of July. If insects become a problem after the
middle of July it may be necessary to apply foliar sprays.
Insecticides can be applied by aerial application or, if labeled,
can be applied through the irrigation system.
The Colorado potato beetle has developed a high degree of
resistance to the synthetic pyrethroid insecticides, so they may
not provide reliable control. In situations where poor control
has occurred with this class of insecticides, growers are advised
to switch to another class of insecticide such as an
organophosphate or carbamate compound. More information on insect
control can be found in NDSU Extension Circular, E-881, Potato
Insect Control, and the current year's NDSU Crop Production
Guide.
Disease
High quality, healthy seed is essential to production of a
good potato crop. Use only certified seed. Sanitize knives
between seed lots and prior to cutting. Plant seed immediately
after cutting. If possible, avoid irrigation to obtain crop
emergence. Early irrigation can lead to early infection from
Verticillium and to problems with soft rot and blackleg.
Potatoes should not be grown more often than every three years
on the same piece of land. This reduces carryover of diseases
such as early blight, silver scurf, late blight, and Verticillium
wilt. Potatoes should be monitored beginning in late June for
both early blight and late blight. Early blight is common on
irrigated potatoes. Fungicide applications should begin when
early blight is beginning to show up on the lower leaves of the
plants.
Late blight can cause the greatest loss. This disease has been
common since 1992, and the new genotypes (A2 mating types) of the
fungus are more likely to cause problems in years with marginal
conditions than the old genotypes. Late blight is favored by
extended periods of cool, cloudy, foggy and wet weather. It is
also favored by the nearly continuous wet conditions near the
pivot of center pivot irrigation systems. It can spread rapidly
and is very destructive. The new genotypes actively attack stems
as well as foliage and more actively attack the tubers.
Information on the current status of late blight under
non-irrigated conditions is available on the Blight Hot Line,
1-800-482-7286. An application of fungicide should be made before
the rows close to provide protection within the canopy, with
regular applications thereafter. Once conditions favor late
blight, fungicides should be applied as recommended by the Hot
Line.
Foliar fungicides can be used to control early and late blight
by preventing entry of the fungus into the plant. To have maximum
effectiveness, fungicides must be on the foliage before the
fungus spores contact the leaves. Labeled fungicides can be
applied through the irrigation system, but coverage of foliage
may be less complete than with ground application. Information
about fungicides can be found in the current year's NDSU Crop
Production Guide or the current year's Field Crop Fungicide
Guide, PP-622. Fungicide applications should continue after first
vine kill to reduce tuber infection. Vines should be dead before
harvest to reduce tuber infection.
Soil inoculum of verticillium wilt can reach high levels in a
single season if the highly susceptible variety Kennebec is
grown. This inoculum is stable for several years. Russet Burbank
is susceptible.
Two applications of Ridomil (see label) will help protect
against Pythium leak and Phytophthora erythrospetica pink
rot. They will not protect against tuber infection from the A2
mating type of the late blight fungus.
Avoid short rotations of potatoes and dry beans. Pythium,
which causes leak in potatoes, causes a root rot in dry beans.
Pythium is favored by wet, hot soil conditions, so it is more
likely to be a problem under irrigation. Potatoes can be infected
with white mold. However, this disease is usually not a problem
except when potatoes are rotated with dry beans under irrigation
or seeded on white mold-infected sunflower ground.
[ More ]
[ Irrigation
Management ] [ Harvest
Considerations ] [ Groundwater
Protection ]
[ Economic Analysis ] [ Additional Sources of Information
]
AE-1040 (Revised) March 1999
|
