er ARC research report 3-
S3Dover ARC Research Report DOVb3-1
AGRICULTURAL RESEARCH CENTER
INSTITUTE OF FOOD AND AGRICULTURAL SCIENCES
UNIVERSITY OF FLORIDA
STRAWBERRY FIELD DAY PROGRAM
E. E. Albregts and W. E. Waters, E itors
February 2, 1983 \ '
\- .R.S1 "J- -:
W. E. Waters, Center Director (AREC-Bradenton)
A. J. Overman, Nematologist (AREC-Bradenton)
J. F. Price, Assistant Entomologist (AREC-Bradenton)
J. W. Prevatt, Area Extension Economist (AREC-Bradenton)
J. P. Gilreath, Assistant Horticulturist (AREC-Bradenton)
S. P. Kovach, Assistant Extension Water Specialist (AREC-Bradenton)
Robert Wilder, Extension Agent I, Hillsborough County
C. M. Howard, Plant Pathologist (ARC-Dover)
E. E. Albregts, Soil Chemist (ARC-Dover)
Robert Wilder, Hillsborough County Extension Agent I moderator
Assembly and Registration
Dr. W. E. Waters, Welcome and Introduction .............. ......... 2
Mrs. A. J. Overman Nematode Control in Strawberries ............... 3
Mr. J. W. Prevatt Florida Strawberry Production Costs .............. 4
Dr. J. F. Price Insects on Strawberries
4:15 Dr. E. E. Albregts
4:30 Tour of Strawberry
Current Field Studies in Entomology .............
Twospotted Spider Mlte Control on Strauberries ..
- Weed Control in Strawberries ...................
Water Management in Strawberries .................
Strawberry Varieties and Diseases
Test for Spread of Wilt (Anthracnose) ...........
Strawberry Breeding .......................******
Description of Strawberry Diseases ..............
- Strawberry Nutrition and Culture
Strawberry Variety Trials .......................
Planting Date and Chilling of Transplants .......
Potassium Rate for Strawberries .................
Soil Fertility and Plant Storage ................
Foliage Application of Fertilizer ..............
Influence of Runners on Plant Development .......
Optimum Leaf Number for Strawberry Transplants ..
Research Plots (Field Map of ARC-Dover)
WELCOME AND INTRODUCTION
W. E. Waters, Center Director
On behalf of the faculty and staff, I extend to each of you a most cordial
welcome to the Agricultural Research Center here in Dover. The Center was
initiated in 1927 as a one-man operation located southeast of Plant City.
In 1963 the Center was moved to its present location and the programs were
expanded. This Center, with affiliated Agricultural Research Centers located
in Bradenton and Immokalee, Florida, is a Research and Education unit of the
University of Florida's Institute of Food and Agricultural Sciences.
In Dover and Bradenton we have 5 research scientists and 3 extension special-
ists who participate in the'strawberry programs. Each research scientist
also holds a joint appointment with his subject matter department at the
University of Florida. This combination of a broad base of research
disciplines, industry contacts and an excellent faculty makes the interdisci-
plinary cooperative team approach to research problems far more productive
than could otherwise be accomplished with limited investment in independent
The overall mission of these Centers deals directly with the strawberry
industry in Florida through research.programs in (1) genetics, breeding and
variety development and evaluation; (2) biological, chemical and mechanical
pest control; (3) production efficiency, culture, fertilization, management
and environmental stress; (4) alternate energy sources, and energy conserva-
tion and engineering; (5) mechanization, harvesting, handling, and post-
harvest physiology; (6) food quality, safety and utilization practices; (7)
water management and conservation; (8) advancement of basic knowledge of the
various scientific disciplines represented by the faculty; and (9) assistance
to the cooperative extension service, departments in the College of Agri-
culture and other Research Centers with extension, educational training and
cooperative research programs for the benefit of producers, consumers and
Information presented in this publication summarizes the active research and
extension projects under way this season on strawberries. We sincerely
appreciate your interest and support of these programs and continuously
solicit your suggestions for improvement and ideas of industry needs from
our research and extension programs.
Title: NEMATODE CONTROL IN STRAWBERRIES
Location: Field 1
Researchers: A. J. Overman and C. M. Howard
Objective: Use of two nematicides, Vydate L and Nemacur 15G, for control of
nematodes associated with strawberry production.
Plot No. Nematicide ; Lb ai/acre Application
2 Nemacur 15G 6 broadcast incorp.
3 Nemacut 15G 12 broadcast incorp.
4 Vydate L 8 broadcast incorp. + F.S.*
5 Vydate L 8 broadcast incorp. + F.S.*
*F.S. = foliar sprays at rate:of 1 or 2 lb ai/100 gals/A applied for 4
consecutive weeks starting when berries reach 1/2" diameter size
in first heavy bloom.
Cultivar: Dover (ARC nursery)
Method of Operation:
1. Field was sampled for nematode assay.
2. Nematicides were broadcast and rotary tilled in 3 replicates of 30'
3. Beds were constructed, 9 lb/100 ft of row of fertilizer composed of
S-coated urea, IBDU, and sludge applied mid-bed 2" deep in single
1. Dover transplants dug the same day were set into the middle 25' of
2. Routine weekly maintenance pesticide sprays were begun.
1. Plots were sampled for nematode assay.
2. First of 4 weekly foliar spray applications of Vydate L was made.
Results: Nematode populations per 150 ml soil in cultivated field prior to
Paratrichodorus (stubby-root) 2
Belonolaimus (sting) 11
Tylenchorhynchus (stunt) 9
NOTE: No rootknot nematodes were recovered from the samples, although
the field has a history of rootknot on strawberry.
Comments: Berries from these plots will be frozen and submitted for pesticide
residue analysis in order to support an IR-4 request for release of the
nematicide for use in production fields.
Title: FLORIDA STRAWBERRY PRODUCTION COSTS
Researcher: J. W. Prevatt
Analysis and Comments: The 1982-83 crop year appears to be another year of
belt tightening and corner cutting for strawberry producers. Presently, it
is'something less than a secret that things are tough, and without some
drastic improvements in the economy, they will remain tough this year.
However, the prospects of a moderate economic recovery during 1983 offer some
encouragement for an improvement in the demand for agricultural products.
Regardless of what economic conditions develop, an enterprise budget is a
prerequisite for equipping oneself with the necessary information about his
operation for making decisions. Estimating strawberry operating and owner-
ship costs is a necessary management tool that will aid growers when making
financial decisions. The development of this information enables growers to
estimate cost projections which may be used to plan credit needs before
planting the crop. Expected yields and production costs can be used to evalu-
ate marketing alternatives and break-even prices. A grower can compare pro-
jected costs to records from previous crops to determine business performance
and aid in planning future crops. In addition, enterprise budgets are
extremely useful when identifying cost items that may be reduced and/or more
Florida strawberry production acreage has fluctuated greatly during the last
two decades (Table 1). Currently, the total area planted to strawberries in
Florida for commercial production is among the highest ever. Resulting from
the increased number of acres being produced and the research and technologi-
cal advances that have been realized in yield, the total number of flats
produced during 1981-82 surpassed 8.million (Figure 1).
The value of Florida strawberries exceeded $52 million during the 1981-82 pro-
duction season. The average value per flat during the last decade has varied
between .approximately $4 and $7. (Figure 2).
The estimated operating and ownership costs per acre for strawberry production
in west central Florida during 1982-83 are reported in Table 2. This infor-
mation was developed with the assistance of participating growers, extension
specialists and researchers. Although an effort was made to insure that the
budgets are reasonably accurate, the fact remains that individual producers
can do things differently (sometimes substantially). Because of the wide
variation of alternative inputs, locations and production systems, it is
important for each grower to develop his own budgets and understand how to
utilize them when making management decisions.
Estimated break-even prices to cover operating, ownership and total costs
were calculated -fo~y: production during 1982-83, as shown in Table 3. These
break-even prices were computed by dividing the appropriate costs by the
estimated saleable yield. The break-even prices describe the price per flat
necessary to cover the various production costs associated with a particular
level of yield. Growers that estimate production costs and yield will have
the information necessary to make timely financial decisions and evaluate
marketing alternatives as they develop.
Table 1. Strawberries: acre, production, and value, Florida,
1960-61 through 1980-81.*
Crop Acreage per per Total
year planted harvested acre Production. flat value
---- (Acres)------ (Flats).** 4,000 Flats) -($)- ($1,000)
1960-61 1,900 1,800 400 820 3.75 2,812
1961-62 2,000 1,900 592 1,280 4.06 4,740
1962-63 2,100 2,000 692 1,492 3.95 5,683
1963-64 2,800 2,700 667 1,983 4.06 7,455
1964-65 3,400 3,300 692 2,134 3.78 7,678
1965-66 2,400 2,300 757 1,742 3.97 6,918
1966-67 2,100 2,000 734 1,467 3.95 5,790
1967-68 1,900 1,900 667 1,267 3.46 4,378
1968-69 1,600 1,600 833 1,333 3.91 5,216
1969-70 1,800 1,800 667. 1,200 5.53 4,234
1970-71 1,600 1,600 917 1,467 4.19 6,142
1971-72 1,600 1,600 1,042 1,667 3.79 6,320
1972-73 1,400 1,400 1,125 1,575 5.16. 8,127
1973-74 1,300 1,300 1,128 1,467 4.57 6,706
1974-75 1,200 1,200 1,375 1,650 5.08 8,375
1975-76 1,400 1,400 1,250 1,750 5.06 8,862
1976-77 1,500 1,500 1,211 1,817 4.93 8,960
1977-78 2,000 2,000 1,209 2,417 6.89 16,646
1978-79 2,400 2,400 1,333 3,200 6.92 22,157
1979-80 2,500 2,500 1,583 3,958 7.06 27,930
1980-81 3,200 3,200 1,750 5,600 4.98 27,888
1981-82 5,000 5,000 1,625 8,125 6.44 52,358
* Source: Florida Agricultural Statistics: Vegetable Summary, Florida Crop
and Livestock Reporting Service.
Table 2, Estimated operating and ownership costs per acre for strawberry
production, west central
.. Price/unit Price/
Item IMonth Unit Quantity of material Gross acre
I. Operating Costs
Sorghum seed June
Lay off rows Sept
Press beds Sept
Fumigant (UC-33) Sept
Captan (36 appl.)
Bealate (16 appl.)
Dibrom (6 appl.)
Plictran (6 appl.)
Phosdrin (12 appl.)
Remove plastic (labor) May
Irrigation (elec.) Oct-Apr
Packing shed labor
Marketing charge** Jan Apr
II. Ownership Costs/A***
Continued on next page
* The estimated operating and ownership costs described in this table repre-
sent a rationalization among sampled growers, extension specialists and
researchers. Individual growers should estimate their operating and owner-
ship costs, since these costs differ widely among operations.
** Marketing charge is based on handling cost per flat which was approximately
10% of the market price.
***Ownership costs include depreciation, insurance, repairs, taxes and
interest on land and equipment for strawberry production.
Table 3. Estimated breakeven prices to cover operating and ownership costs
for strawberry production, west central Florida, 1982-83.
Saleable Harvest & operating Ownership Total
yield/AC Preharvest market costs costs costs
:Flats* -----------------Dollars per flat ($/flat)----------------
1400 2.51 2.85 5.36 0.99 6.35
1600 2.20 2.85 5.05 0.87 5.92
1800 1.95 2.85 4.80 0.77 5.57
2000 1.76 2.85 4.61 0.69 5.30
*A flat is composed of 12 pints (12.00 lbs).
60-61 65-6 70-71
S 1' 5,000 .
Figure 1. Florida Strawberries: Harvested Acreage and Production
Source: Florida Agricultural Statistics: Vegetable
Summary, Florida Crop and Livestock Reporting
Florida Strawberries: Value 1955-56 1980-81.
55-6 60-61 65-6 70-71 75-6
Source: Florida Agricultural Statistics: Vegetable Summary,
Florida Crop and Livestock Reporting Service
Title: CURRENT FIELD STUDIES. IN ENTOMOLOGY
Location: Field 18
J. F. Price
Objective: To evaluate miticides for twospotted mite control on-strawberries.
A new formulation of Omite
(Water sprayed check)
Method of Operation: 'Dover'. strawberry plots for miticide trials are
established. Twelve chemical treatments will be applied for control of
twospotted spider mite outbreak as 'these occur in late winter. Treatments
will include comparisons among the older chemicals, more recently registered
chemicals and chemicals presently being developed. All treatments will be
replicated four times.
Comments: Efficacy for mite control, plant phytotoxic reactions and yields
will be recorded.
Title: UPDATE ON TWOSPOTTED SPIDER 1ITE CONTROL ON STRAWBERRIES IN THE
PLANT CITY, FLORIDA AREA
Researcher: James F. Price
Discussion and Comments: The twospotted spider mite (Tetranychus urticae
[Koch]) is the arthropod pest of strawberries most frequently requiring
chemical control in the Plant City area. Sometimes in February through
April, hard-to-control outbreaks of this mite occur on strawberry farms.
These circumstances often lead growers to consider alternatives to their
normally used miticides. The question then arises, "What is available and
will it do the job?"
This report lists1 all the miticides known by the author to be registered
for use in Florida on strawberries for twospotted spider mite control. The
report also presents information concerning the usefulness of each compound
for the Plant City area strawberry industry.
Strawberries are set each year in the early fall and fruit are harvested
about twice weekly from January through April. Although the twospotted
spider mite is present in the crop environs throughout the entire season,
this mite usually remains at low densities in strawberries until late in
February. The warm, dry days following February are conducive to rapid in-
creases in mite densities.
Initiating a crop with plants free of mites and maintaining good weed control
throughout the strawberry farm are important for reducing losses to mites in
the late winter and early spring. When mite densities begin to increase, 2
or more miticidal applications at 3-5 day intervals may be required. Thorough
miticide coverage on the undersides of lower leaves is essential.
There are 15 products registered for twospotted spider mite control in Florida
(Table 1). However, only a few are practical for control under our circum-
stances. Factors limiting the usefulness of some available miticides include
limited efficacy of some products and the occurrence of mite outbreaks when
fruit are being harvested every 3-4 days.
Di-Syston and Morestan cannot be applied at all during the fruiting period
(Table 1), therefore, are of limited usefulness. The pre-harvest waiting
period for Diazinon, Metasystox-R, Parathion and Systox are too long (Table 1)
to be practical under our harvesting practices.
Recent tests at the Dover ARC have shown that Dibrom and Phosdrin are not
adequate to control a mite outbreak (Price, unpublished data). Although
Malathion has not been evaluated recently for mite control on strawberries,
this product is not generally regarded as a highly effective miticide under
Trithion and Tedion have not been evaluated in recent years for twospotted
spider mite control in Florida, however, Poe (1972a) found Trithion to be
only moderately effective. Wolfenbarger (1968) similarly found Tedion to
lack effective control properties.
For a long period prior to the early 1970's Kelthane provided excellent con-
trol of mites in Florida's strawberry crops. However, by 1972, Poe (1972b)
had shown that Kelthane was no longer effective. The new miticides, Plictran
and Omite, were registered and largely replaced Kelthane as the standard mite
control product on strawberries. Recent data (Price,-unpublished data)
indicate that Kelthane now effectively controls twospotted spider mites
when applied to populations that have not been subjected to chlorinated
hydrocarbon pesticides for many years.
In addition to Kelthane, 3 other useful products remain. Of these, Omite
and Plictran have -been used for twospotted spider mite control on strawberries
for several years. Both have been effective. Vendex, a compound related to
Plictran, has been registered recently for twospotted spider mite control on
strawberries. This product has been used successfully in Florida for several
years to control twospotted spider mites on ornamentals. Growers should find
Vendex to be comparable to Plictran in ability to control mites.
Twospotted spider mite control programs on strawberry farms of the Plant City
area should include rotating uses of the chlorinated hydrocarbon, Kelthane:
the sulfite, Omite: and the organotin compounds, Plictran and Vendex. Such
programs, based on scouting and applying miticides when conditions warrant,
should provide excellent twospotted spider mite control and prolong the
useful life of each of the miticides.
IThe list was compiled through searches of product guides provided by many
chemical companies. An effort has been made to include all registered
products (not formulations of product combinations, however), but the
author recognizes.that some registered products may have been overlooked.
Poe, S.L. 1972a. Evaluation of chemicals for control of spider mite
populations on Florida strawberries. Proc. Fla. State Hort. Soc. 85:121-123.
Poe,:S.L. .1972b. Management of spider mite populations on Florida straw-
berries. Univ. of Fla., IFAS, Bradenton AREC Res. Rept. GC1972-6. 6pp.
Wolfenbarger, D.O. 1968. Mite control tests on strawberries. Proc. Fla.
State Hort. Soc. 81:173-175.
Table 1. Miticides registered for use in Florida on strawberries.
liticides Waiting period Other.selected
Trade name Common name (days) to harvest label restrictions
A. Miticides for nursery plants only or having long waiting period:
1. Di-Syston disulfoton N/A Treat propagation
plants only Do
not eat fruit from
2. Morestan oxythioquinox N/A Do not treat after
the first bloom
Do not apply more
than 2 times per
B. Hiticides recently shown to be unsatisfactory to control an outbreak:
1. Dibrom naled 4
2. Phosdrin mevinphos 2
C. Miticides with unknown or doubtful ability to control an outbreak:
1. Malathion malathion 3
2. Trithion carbophenothion 3
3. Tedion tetradifon 3 Do not apply more
than once in any
D. Miticides expected to provide satisfactory control when used wisely:
1. Kelthane dicofol 2
2. Omite propargite 3 Do not apply more
than 3 times per
Do not apply more
than 3 times per
Title: WEED CONTROL IN STRAWBERRIES
Location: Field 5
Researchers: J. P. Gilreath and E. E. Albregts
Objective: To evaluate herbicides for use on strawberries in the fruit
production and nursery areas.
Introduction: In the past 2 years herbicide research has been conducted at
the Dover ARC in both fruiting fields and nurseries. In fruiting fields,
preemergence herbicides have been applied to the beds prior to application
of mulch film to determine phytotoxic effects (if any) of various promising
chemicals. Several postemergence herbicides have also been evaluated by
application over the plant row. Although herbicides are not generally used
on plant beds in fruiting fields, application in this manner allows selection
of only the most non-toxic herbicides for use in row middles. This affords
the grower greater latitude in application by providing him with materials
which can be applied when wind conditions are not favorable for application
of contact materials such as paraquat. Plant nursery research has focused on
identifying those herbicides which can be used repeatedly over the top of the
nursery plants without producing injury or decreasing daughter plant pro-
duction. In both areas, there is still work to be done. The remainder of
this report will concentrate on outlining fruiting field research available
for you to see today.
1 Hand weeded check --
2 Lasso 1 pretransplant
3 Lasso 2 pretransplant
4 Nortron 2 pretransplant
5 Nortron 4 pretransplant
6 Blazer 0.5 postemergence**
7 Tackle 0.5 postemergence
lb ai/acre = Ib active ingredient/acre
**postemergence = posttransplant after plants well established and
postemergence to broadleaf weeds
Cultivars: Dover (South end of each plot), Tufts (north end)
Method of Operation: Preemergence treatments were applied to the bed, then
the soil was covered with plastic mulch.- At the beginning of each plot a
5 ft section of mulch was removed to subject the herbicide to the extreme
leaching conditions found in row middles. This and remaining area under
plastic will provide comparative weed control and plant injury information.
Postemergence herbicides were applied over the top of the row.
Experiment Design: Randomized complete block
Row width: 4 ft on 2 ft beds
Plant spacing: 1 ft in 2 rows 1 ft apart
Date planted: October 15, 1982
Comments: Pretransplant treatments were applied October 14, 1982.
emergence treatments were applied November 10, 1982.
Title: TUE USE OF A TAILWATER RECOVERY SYSTEM TO REDUCE WATER NEEDS FOR
Location: Strawberry farm owned by ir.'Jeff Dankert. (Rt. 2, Box 70A
Researchers: E. E. Albregts, Fedro Zazueta, Steve Kovach, Dalton Harrison,
Sydney Feinberg, and Bob Wilder
Objectives: A. To determine the amount-of irrigation water returning to-a..
pit in a "closed-irrigation.pit system".
'B. To determine the effect that recycling irrigation water has
on water quality.
Introduction: Fruiting strawberries are generally irrigated with the use of
well water in Florida. Irrigation is mostly overhead sprinkler. Plants are
irrigated from October to establish plants and during freeze periods to pro-
tect the flowers and fruit. Irrigation during other times depends on the pan
evaporation rate. Itis not uncommon to use 100 acre inches to grow a crop
The use of pits as a source of irrigation water has been' a'limited practice
for many years among growers of strawberries and vegetables. -Generally, the
applied water does not return directly to the pit from which it was pumped.
Water in the pit comes from surface drainage, from the shallow aquifer and,
if necessary, from a well pumping into the pit when irrigation is not being
applied to the fieid. '
The use of pit water which is recycled during irrigation is being promoted
as a way to conserve water. The question remains as to how much water is
conserved and what happens to the water quality when recycling is practiced.
In order to answer the questions concerning water conservation and quality
when recycling of irrigation water is used, a research project was designed
and established on a commercial strawberryfarm.
Method of Operation: A triangular weir with a water level recorder is being
used to measure the amount of water returning to the recycling pit via sur-
face runoff. Another water level recorder located down-stream of the weir
was installed to measure the subsurface drainage water returning to the
recycling pit via Hancor Drain Tubing.
In order to monitor water quality, water samples are,-being taken from the
recycling pit, surface and'subsurface drains. The,water samples are moni-
tored for levels of soluble salts, nitrates, ammonium,.potassium.and,pll.
A diagram of the layout is given in Figure l .
Results: Findings from the demonstration will be made available when
Fig. 1. Layout of Tailwater Recovery Project
Hancor Drain Tubing
Water Level Recorder
PVC Pipe 6"
Water Sampler Hose
Junction Box for Subsurface Drain Tubing
,- ,- -l
- --- -
2 2 /
S- Recycling Pit
Title: TEST FOR SPREADOFWILT (AITIRACOSE) IN THE FRUIT PRODUCTION FIELD
Location: Field 4
Researcher: C. M. Howard
Objective: To determine if there may be spread of the wilt phase of
anthracnose in the fruit production field.
Method of Operation: During the very warm fall of 1982 it appeared that
there might be some spread of the wilt anthracnosee) pathogen from plant to
plant in the fruit production field. A few anthracnose lesions were found
on runners in some fields as late as December. In this trial on December 22,
daughter plants were pinned beside dead or wilting plants. A stake was
placed in the holes where the daughter plants were pinned. Each stake was
coded to show the approximate length of time the original plants had been
DL indicates that the original plant had been dead approximately 4 to 6
D indicates that the original plant had been dead approximately 2 to 4
W indicates that the original plant was wilting when the daughter plant
was pinned in the hole.
Comments: After each daughter plant was rooted, the runner was cut and the
daughter plants are being observed for wilt.
Title: STRAWBERRY BREEDING
Location: Fields 2, 3, 6
Researcher: C. KI. Howard
Objective: To develop new strawberry varieties that are specifically adapted
to Florida growing conditions.
Method of Operation:
First year (Field 3): Crosses are made in the greenhouse during the
winter and seeds are sown in flats in late March or early April. Seed-
lings are transplanted into individual peat pots in May or early June
and set in the nursery in late June where they form runners. In
October, clones are selected from the nursery on the basis of runner
production and resistance to anthracnose, leaf spot and leaf blight.
Four plants of each selection are transplanted into the fruiting field
where records are kept on fruit yield and other characteristics.
Specific clones are selected primarily on the basis of appearance,
ripening characteristics, yield, earliness, and fruit size. Emphasis
is also placed on selecting for long, large diameter, single fruit
stems to improve uniformity of fruit size and ease of harvest.
Second year (Field 2): The clones that have been selected are trans-
planted into the summer nursery where they are again observed for
runner production and resistance to anthracnose. In October, selec-
tions are made from this group and transplanted into 10-plant obser-
vation plots. In this trial, the clones are compared with currently
grown varieties and the fruit and plants are observed more closely
for any defects such as poor color or soft fruit. Specific clones
are selected on the basis of plant type, early and total fruit yield, ~//
fruit firmness, color, size, ripening characteristics and general
appearance. These clones are transplanted into the nursery in April
where they are again observed for runner production and resistance to
diseases (especially anthracnose).
Third year (Field 6): The most promising clones from the second year
observational trials are placed in replicated trials where they can
be thoroughly compared with varieties currently being grown in Florida.
After a clone has shown sufficient promise for at least two years in
replicated trials, a variety release committee may be formed. If the
committee, after reviewing all the accumulated data, agrees that the
specific clone should be an improvement over currently grown varieties,
then it can be named and released as anew variety. Hopefully, moe
exte sife growe~ttsting of varie candidates will b ~done i the
future even thouI manpower and tim limitations make/I very difficult
for u\to grow large numbers plants that are requ red these
Title: DESCRIPTION OF STRAWBERRY DISEASES
Researcher: C. M. Howard
Objective: Control of strawberry diseases, and to determine the cause and
importance of new diseases.
Common Diseases of Strawberries:
1. Colletotrichum fruit rot: Round, dark spots which are firm and sunken;
very severe in some fields during warm periods. This fungus also
causes anthracnose, wilt, and black leaf spot.
2. Dendrophoma fruit rot: Round, lighf pink or gray spots which are soft
and not'sunken. Small black fruiting,bodies often form in these
lesions. Very severe in some fields during some periods. This fungus
also causes leaf blight. .
3. Pestalotia fruit rot: Lesions variable. .The most typical lesion has
a round, light tan central area which is slightly sunken below the
original fruit surface and a surrounding band of soft tissue which is
definitely sunken. 'Rarely serious in commercial fields..
4. Alternaria fruit rot: Lesions round or irregular in shape and light
green to nearly black depending onthe stage of development.- Occa-
sionally severe in commercial fields.
5. Gray mold: Lesions irregular in shape, soft, and light tan at first,
changing to darker brown, then gray as many fungus spores form on the
lesion. Infected fruit eventually become covered,by the gray, dusty
spores and mummified.
6. Control of.fruit rots: Captan and Benlate remain the standard treat-
Sments for control of strawberry fruit rots. If regular spray schedules
of twice per week are maintained and good coverage is achieved, Captan
will usually give good control of all these fruit rots, but during
periods of severe disease incidence, Benlate usually gives better
control of the Collectotrichum and Dendrophoma-rots. Two new fungi-
cides, Ronilan and Topsin Mhave been registered for use on'strawberries.
Ronilan gave excellent control of gray mold. Because of the lack of
rots in the plots when Topsin was tested, it's effectiveness against
rotscould not be determined. Ronilan does not control rots caused by
Colletotrichum and Dendrophoma or foliage diseases, therefore, it must
be used in combination with other fungicides.
7. Anthracnose: In the nursery causes dark, sunken lesions first on
runners, then on leaf petioles, then invades the crown and causes
wilting and death of the entire plant (and sometimes entire nursery).
Infected plants set in the fruiting field wilt suddenly and die at
any time during the fall, winter, or spring. A new type anthracnose
fungus has generally been found in out-of state plants since about
1977. During the fall of 1982, this fungus was found for the first
time in Florida gromw plants and was isolated much more frequently
than our old anthracnose fungus.
Title: DESCRIPTION-OF STRAWBERRY DISEASES (Cont'd):
8. Control of Anthracnose: Set highly susceptible varieties (most
California varieties) in early to mid-June, use very little fertilizer
through August, and spray with fungicides at least.every other day.and
after every rain or irrigation throughout the summer until the weather
becomes dryer and cooler in mid-September. Then spray at least twice
per week until digging starts. Sprays should be continued on any part
of the nursery that will not be dug within a few days. If the weather
remains hot and wet into late September, the summer spray schedule
should be continued until digging starts. There is no known control
for anthracnose wilt in the fruiting field.
New Disease of Strawberries:
:1. Black leaf spot: Spots are round and vary in diameter from about the
size of the period at the end of this sentence to 1/16 inch (occas-
Sionally up to 1/8 inch). They are usually black, but may remain
light gray in color. Spots become very numerous on some leaflets
without killing them. Black leaf spot is often present in areas of
nurseries where typical anthracnose of runners and petioles is severe.
howeverr, it is often found before symptoms can be detected on runners
or petioles. It can, therefore, serve as an early warning that the,
anthracnose fungus is present in the nursery and has infected some
-plants. At the first sign of black leaf spot, all possible efforts
for control of anthracnose should be-initiated.
Title: STRAWBERRY VARIETY TRIALS
Location: Field 6
Researchers: E. E. Albregts and C. IM, Howard
Objective: To evaluate all
for earliness, yield, fruit
promising breeding lines and out-of-state varieties
size, ripening characteristics, and plant growth
Set on October 14, 1982
Title: STRAWBERRY VARIETY'TRIALS (Cont'd)
Results: Yields of marketable fruit in 1981-82 trials
Variety Yield (flats/A) Avg. fruit
or line January February March April Total Jan. +Feb. wt (g/fruit)
78-3Y 91 1,036 889 146 2,163 1,127 14.29
74-6 249 851 1,093 175 2,367 1,100 13.99
78-27Y 203 1,081 899 276 2,459 1,284 15.82
78-137 261 1,033 738 316 2,346 1,294 14.18
77-163* 432 1,081 769 419 2,702 1,513 14.57
77-169* 301 1,076 857 274 2,507 1,377 15.07
77-198* 217 1,053 962 177 2,408 1,270 15.10
76-264 202 1,198 515 199 2,114 1,300 13.37
77-313 435 996 431 348 2,210 1,431 12.73
77-332 190 780 359 205 1,534 970 12.06
76-624 215 937 510 296 1,958 1,152 14.39
77-672 54 922 1,139 312 2,426 976 13.39
76-802 320 768 500 159 1,747 1,088 12.45
77-869* 379 990 778 291 2,438 1,369 13.38
77-873* 314 902 1,476 294 2,986 1,216 16.45
79-1119* 80 1,047 1,263 201 2,591 1,127 14.29
79-1120* 483 1,211 892 193 2,780 1,694 13.57
78-1124 255 889 718 229 2,091 1,144 12.67
79-1125* 329 832 682 315 2,157 1,161 13.58
79-1126* 297 910 955 321 2,483 1,207 14.46
79-1164* 256 924 815 222 2,217 1,180 15.56
78-1268* 384 855 690 156 2,084 1,239 15.14
78-1558 327 850 853 168 2,198 1,177 12.20
Douglas* 353 435 1,273 423 2,483 788 17.14
Pajaro* 277 352 1,224 366 2,219 629 16.48
Tufts* 316 619 1,265 389 2,589 935 14.91
Dover* 495 1,076 779 171 2,522 1,571 14.22
*Placed into 1982-83 variety trial. A more detailed summary is available in
Research Report: Strawberry Variety Trial 1982 by E. E. Albregts and C.
M. Howard. Dover ARC Research Report DOV-1982-4. 6 pp.
Title: PLANTING DATE AND CHILLING OF NEiWYORK & NORTH CAROLINA TRANSPLANTS
Location: Field 13 and 14
Researcher: E. E. Albregts
Objective. To'evaluate the effect of planting date and plant chilling in the
nursery on strawberry growth and fruiting response.
I. New York transplants (Field 13)*
Plot No. Planting date
1 September 29
2 October 01
3 October 08
4 October 14
5 October 21
6 October 29
Plot No. Cultivars
*The later the planting date, the more chilling the plants received.
II. North Carolina transplants (Field 14)*
Plot No. .Planting date
1 September 16
2 October 01
3 October 15
4 October 29
Plot No. Cultivars
A Douglas :
Plot No. Days chilling in phytotron
*The later the planting date the more chilling the plants received.
Results: Removal of foliage from the New York plants on October 1 and 8
retarded plant growth.
Title: POTASSIUM RATE FOR STRAWBERRIES
Location: Field 7
Researcher: E. E. Albregts
Objective: To evaluate effect of potassium soil rates on fruit yields, fruit
quality and plant growth.
1 100 lbs/acre of potassium
2 -,200 Ibs/acre of potassium
3 300 lbs/acre of potassium
A Dover, south end of each plot
B Florida Belle, middle of each plot
C 77-169, north end of each plot
Method of Operation: Nitrogen and phosphorus applied at 200 and 50 ibs/acre
of N and P205, respectively. Pesticides and.moisture applied as needed.
Results: No results yet.
Title: SOIL FERTILITY AUD PLANT STORAGE ON GROWTH AND FRUITING .
Location: Field 8
Researcher: E. E. Albregts
Objective: To evaluate effect of.fertilizer level in nursery and in fruit
production field plus storage of transplants in cooler on plant growth and
1 High fertility in nursery and production field and plants stored 1 week.
2 High fertility in nursery and production field and plants set direct,
3 High fertility in nursery and low fertility in production field and
plants stored 1 week.
4 High fertility in nursery and low fertility in production field and
5 Low fertility in nursery and high fertility in production field and
plants stored 1 week.
6 Low fertility in nursery and high fertility in production field and
7 Low fertility in nursery and in production field and plants stored
8 Low fertility in nursery and:in production field and plants set direct.
Cultivars: Dover on south end of Field 8 and Florida Belle on north end of
Method of Operation:
1. Low fertility nursery plants were those not fertilized 6 weeks before
2. High fertility production treatment received 400 lbs/acre of N and K20.
3. Low fertility production treatment received 200 lbs/acre of N and K20.
Results: (1981 Season)
1. Four hundred lbs of N and K20 in the fruit production field reduced
January and February fruit yields compared to one-half that amount.
Total yields were slightly higher with the lower rate.
2. Plants from low fertility area of nursery were small in size in the
fruit production field all season.
3. lore fruit were misshapen in the high fertility treatments.
Title: FOLIAGEAPPLICATION OF FERTILIZER TO STRAWBERRIES
Location: Field 9
Researcher: E. E. Albregts
Objective: To determine if spraying fertilizer on strawberries throughout
the growing and harvest season will enhance the plant's fruiting response.
1 No soil fertilizer applied in bed + no foliar fertilizer applied.
2 No soil fertilizer applied in bed + 5 lbs of a 20-8-20 applied
every 2 weeks.
3 No soil fertilizer applied in bed + 5 lbs of a 20-8-20 applied
every 2 weeks.
4 1000 lbs/acre of 10-4-10 in bed + no foliar fertilizer applied.
5 1000 lbs/acre of 10-4-10 in bed + 5 Ibs of a 20-8-20 applied every
6 1000 Ibs/acre of 10-4-10 in bed + 5 Ibs of a 20-8-20 applied every
7 2000 lbs/acre of 10-4-10 in bed + not foliar fertilizer applied.
8 2000 lbs/acre of 10-4-10 in bed + 5 lbs of a 20-8-20 applied every
9 2000 Ibs/acre of 10-4-10 in bed + 5 lbs of a 20-8-20 applied every
Fertilizer derived from potassium poly phosphate, potassium sulfate
potassium nitrate, and urea.
Cultivars: Dover on the south end and Tufts on the north end of each plot.
Previous results: Using a 20-20-20 fertilizer derived from different
fertilizer, sources than ones presently used resulted in considerable
foliage burn with weekly applications. Foliar fertilization generally
enhanced yields with insufficient soil fertilization. However, yields
were generally below that obtained when sufficient soil fertilizer was
applied at mulching.
Title: INFLUENCE OF RUNNERS ON PLANT DEVELOPMENT AND FRUITING
Location: Field 17
Researcher: E. E. Albregts
Objective: To evaluate the effect of timing.of runner removal on plant
growth and fruiting.
Runners,removed every two weeks.
Runners removed.every four weeks.
Runners not removed.
Pegged daughter. plants and removed
Runners removed every two weeks.
Runners removed every four weeks.
Runners not removed.
Pegged daughter plants and removed
Method of Operation: For treatments 4 and 8, daughter plants pegged into same
slot with otherr plant and mother plant removed within two weeks. Mother
plants were removed on December 2 and 18 from the Dover and Tufts, respectively.
Results: No results yet.
Title: OPTIMUMI LEAF NUMBER FOR STRAWBERRY TRANSPLANTS
Location: Field 16
Researcher: E. E. Albregts
Objective: To determine optimum leaf number on transplants for growth and
1. Leaf number at transplanting
Plot No. Treatment
0 No leaves at transplanting.
1 1 leaf at transplanting.
2 2 leaves at transplanting.
3 3 leaves at transplanting.
4 4 leaves at transplanting.
5 5 leaves at transplanting.
Cultivars or Clone:
B. Florida Belle
Method of Operation: Transplants were dug, graded so each treatment (leaf
number) had equal size plants, then removed leaves with shears two inches
above crown and transplanted into beds.
Results: (One month after transplanting)
Clone 0 1 2 3 4 5
Dover 1 73 96 97 97 96
Fla. Belle 1 69 93 99 99 96
*Pajaro 94 96 90 89 96 100
Plant size (% of largest plants)
Dover 1 40 68 83 82 82
Fla. Belle 1 64 71 84 90 97
Pajaro 26 65 74 82 93 100
*Anthracnose killed some Pajaro plants.
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