Dover AREC Research Report DOV-1989-5
Research Highlights from the
Agricultural Research & Education Center
C. K. Chandler, C. M. Howard, and E. E. Albregts
OCT 2 21989
University of Florida
1 N ; University of Florida
Institute of Food and Agricultural Sciences- University of Florida
AGRICULTURAL RESEARCH AND EDUCATION CENTER
IFAS, UNIVERSITY OF FLORIDA
13138 LEWIS GALLAGHER ROAD
DOVER, FL 33527
Dover AREC Research Report DOV1989-5 August 1989
from the Agricultural Research and Education Center at
C. K. Chandler, C. M. Howard and E. E. Al.bregts1
The University of Florida, IFAS, faculty stationed at AREC-Dover use a
team approach to solve problems associated primarily with strawberry
production. This report summarizes recent research activities and is
divided into 3 sections: culture, pathology, and genetics & breeding.
Recycling of rain and irrigation water with a pond
Monitoring pump use, pond levels, and rainfall indicated that recycling
irrigation water and storage of rainfall reduced well water consumption by
50 to 60% on a Hillsborough County strawberry farm.
The pond capacity is about 2.5 million gallons, and is normally full in
September at the beginning of the irrigation season and nearly empty in
April at the end of the season. Accumulation and storage of rainfall
during the summer months accounts for a large share of the well water
saved. The return flow of irrigation water varies from about 20% after 4
hours of irrigation to 42% after 13 hours of irrigation.
A trial was conducted where a constant amount of liquid fertilizer (1 Ib/A
per day of nitrogen and potassium) was applied to plots containing varying
amounts of pre-plant fertilizers (0, 15, 30, 45 and 60 Ib/A of nitrogen
and potassium). The liquid fertilizer was applied through drip
irrigation, starting after plant establishment and continuing until the
end of the season. Pre-plant fertilizer rates did not affect yield.
However, the presence of pre-plant fertilizer did increase plant size, and
the absence of pre-plant fertilizer caused a slight reduction in fruit
1Assistant Professor (Plant Breeder), Professor (Plant Pathologist), and
Professor (Soil Scientist), respectively.
Controlled release fertilizers
Two new controlled release fertilizers, methylene urea and Oxamide were
tested in 1989. Both performed as well as sulfur coated urea; however it
was a warm winter which could have increased the rate of fertilizer
breakdown. We will evaluate these 2 products as well as some plastic
coated materials during the 1989-90 strawberry season.
Control of black calyx
Calcium sprays were evaluated for control of black .(necrotic) calyx. Two
sources of calcium (calcium chloride and calcium nitrate) at 2 rates were
tested. Leaves and developing fruit were sprayed every 2 weeks throughout
the season. The highest rate of calcium chloride reduced yield, probably
because of chlorine toxicity. None of the calcium spray treatments
reduced the amount of black calyx compared to the no spray treatment.
Evaluation of Leafless transplants
Some interest exists in the use of transplants that have had their leaves
partially or totally removed prior to planting. Two possible reasons for
removing leaves are a) to make the plants easier to set, and b) to reduce
water loss by the plant thus reducing the need for irrigation during the
establishment period. An experiment was conducted during the 1988-89
season in which some locally propagated plants were defoliated at the time
of digging. Compared to a non-defoliated control, defoliation caused
higher plant mortality in the fruiting field, and a reduction in
vegetative growth, fruit size, and early and total yield. In another
experiment, some Canadian propagated plants received in mid October were
also defoliated. Defoliation, in this case, didn't have much effect on
plant mortality, but it did drastically lower December yield, as well as
significantly lower total yield.
In a third experiment, locally propagated plants were cut back to a height
of 3 or 5 inches above the crown 2 weeks before transplanting. Both
treatments caused a reduction in yield throughout the season. The plants
cut back to 3 inches were more severely affected than the plants cut back
to 5 inches.
Research to date suggests that defoliation prior to transplanting is
detrimental to crop yield. This coming season we plan to test Canadian
propagated plants that have been defoliated 2 weeks prior to digging and
allowed to produce a few new leaves.
Anthracnose Crown Rot in the Fruiting Field
There are three different species of Colletotrichum fungi that cause
anthracnose crown rot of strawberries. These are C. fragariae, C.
gloeosporioides (= Glomerella cingulata), and C. acutatum. On susceptibTe
varieties, all three species cause severe frui'Trot in the fruiting field
and severe runner and petiole disease in the summer nursery. C. fragariae
and C. gloeosporioides can cause severe loss of plants from crown rot when
plants that are infected in the summer nursery are transplanted into the
fruiting field. C. acutatum seldom causes death of plants in the fruiting
field even when iTis present in the crowns of some plants.
Observations over many years indicate that there is little or no spread of
any of the three species from infected to healthy crowns in the fruiting
field. An experiment was conducted during the 1988-89 fruiting season
with 'Chandler' plants from Canada to determine if anthracnose crown rot
can spread from infected to noninfected crowns in the fruiting field and
to compare the three different species regarding their ability to cause
'Chandler' plants from Canada were set through black polyethylene mulch in
the fruiting field in October, 1988. Plants were set at spacings of 2
inches (2 plants per hole), 6 inches, and 12 inches. On Dec. 7, 1988
every other plant in each plot (one plant in each hole with the 2 inch
spacing) was inoculated by injecting.spore suspensions of C. fragariae, C.
gloeosporioides, or C. acutatum into the crowns. Sterile"Tistilled water
was injected into control plants. The plots were observed until
mid-April, and isolations were made from all noninoculated plants that
Data from this experiment are shown in Table 1. During the course of this
experiment only one plant injected with C. acutatum died. This supports
observational evidence that this species rarely kills plants in the
fruiting field in Florida even though it causes severe anthracnose of the
foliage in the summer nursery and severe fruit rot. However, there still
may be some strains of C. acutatum that cause more crown rot.
The C. gloeosporioides isolate used in this trial killed plants more
quickTy than did the C. fragariae isolate used (Table 1). By seven weeks
after inoculation, equal numbers of plants inoculated with these two
-species at the 6 and 12 inch spacings had died but the higher death rate
caused by C. gloeosporioides was still evident at the 2 inch spacing.
Nearly all-plants injected by either species were dead within 18 weeks.
The slower death rate of plants inoculated with each of these two species
at the closer spacings was not expected. Two possible explanations for
this phenomenon are a) increased shading at closer spacings might have
reduced the temperatures of the crowns sufficiently to retard development
of the fungi within the crowns resulting in slower death of plants as
spacing became closer, and b) because fertilizer rates were not increased
to compensate for the increased numbers of plants at the closer spacings,
there could have been higher nutrient levels in the plants at the wider
spacings. Fungi may grow faster within crowns having higher nutrient
A few noninoculated plants died in all plots in which plants were
inoculated with C. fragariae or C. gloeosporioides (Table 1). At the end
of 15 weeks, 6% of the noninoculaied plants in plots that were inoculated
with C. gloeosporioides or C. fragariae had died. After 18, weeks 14% of
the noninoculated plants in these plots had died. Only 1% of the
inoculated and noninoculated plants in plots in which sterile water and C.
acutatum were used for injection had died within 18 weeks. Only tWe-
Colletotrichum species that was injected into plants in a specific plot
was isolated from noninoculated plants in that particular plot. Thus it
appears that some spread of anthracnose crown rot does occur.
Because of multiple crown formation, the inoculated and noninoculated
crowns in each hole at the 2 inch spacing were touching by mid January but
there was no more spread of crown rot at this spacing than at the 6 and 12
inch spacings. This indicates that when diseased crowns are tilled into
the soil, there is little chance of spread of crown rot from these crowns
to plants set later into this soil.
In summary, it appears that C. acutatum only rarely causes crown rot,
while C. fragariae and C. gloeosporioides cause severe crown, rot and can
spreadTo a limited extent in the fruiting field.
Alternaria Leaf Spot of Strawberry
During the 1988-89 fruiting season, unusual leaf spots developed on
'Pajaro' plants in the last 20 or 30 feet of several rows in a grower's
field near Plant City. The area affected did not seem to enlarge but the
problem was not controlled regardless of the spray schedule that was used.
Isolations from the spots yielded primarily an Alternaria species of
fungus. Since various Alternaria species grow quite well on dead plant
tissue, it was felt that probably something else had caused the spots and
that Alternaria then had invaded the dead tissue and had "crowded out" or
was inhibiting the growth of any other possible living organism that might
have originally caused the spots. Identical spots were later found on
leaves of 'Chandler' plants in a field near Dade City. Isolations from
these spots and again from the spots in the Plant City field yielded
primarily Alternaria. It was then assumed that the Alternaria probably
caused the disease. Alternaria leaf spot has been reported in Korea and
Europe but has not previously been reported in North or South America.
Experiments are in progress to determine pathogenicity of the Alternaria
isolates obtained from the spots of infected plants. It appears at
present that Alternaria is the cause of the leaf spots found in the two
Three different type spots are associated with this disease. The most
common type is round,. 1/16 to 3/8 inch in diameter with a purple border
and ash gray center. There is a faint concentric ring pattern in the gray
center of some of these spots. Minute tufts of sporophores on which the
fungus spores are borne occur on the undersurfaces of many of these spots.
The centers drop out of these lesions as the spots age giving a shot-hole
affect to the leaves. Two or more lesions near the margins of the
leaflets sometimes coalesce and form large dead areas. These leaflets
then have a ragged appearance when the dead tissue drops away. A second
type of lesion is round, 1/16 to 3/8 inch in diameter, light brown, and
does not have a colored border. The third type of lesion is round, 1/4 to
3/8 inch in diameter, without a colored border, and appears watersoaked.
Alternaria was isolated from all three types of lesions.
This disease has been a major problem in some areas of Europe for several
years. One or two very promising new varieties have been nearly abandoned
because of their high degree of susceptibility to Alternaria leaf spot.
There is a great deal of variability in susceptibility to this disease
among strawberry varieties in Europe. It is not known at this time if
Alternaria leaf spot will become a major problem in Florida. The disease
has been very difficult to control in Europe. After pathogenicity of
Alternaria has been definitely established, control practices will be
GENETICS & BREEDING
The major objective of the strawberry breeding program is to develop
strawberry cultivars that will help the Florida strawberry industry remain
competitive in U.S. and international markets. Specifically, there is a
need in Florida for several types of strawberry cultivars: 1) An
alternative to 'Selva'. This cultivar is currently the backbone of the
west central Florida industry. It is a very early yielding cultivar which
produces fruit that ships well and is relatively easy to harvest. Its
fruit usually lacks flavor, however, and the plant is highly susceptible
to spider mites. 2) An alternative to 'Dover'. The popularity of 'Dover'
has increased during the last several years -- due to a desire by some
growers to increase their February yields. 'Dover' usually produces high
marketable yields in February -- a traditionally slow month for Florida
strawberry production. Unfortunately, 'Dover' fruit can become too dark,
especially after cold storage, and the plants can produce a dense canopy
of leaves which makes locating ripe fruit difficult. 3) A highly flavored
cultivar for the home gardener and local market and U-pick sales.
1988-89 Cultivar trials
During the 1988-89 season, 11 AREC-Dover selections and 5 cultivars
('Selva', 'Dover', 'Pajaro', 'Chandler', and 'Muir') were evaluated in a
replicated variety trial. None of the selections started producing ripe
fruit as early as 'Selva'. Several of the selections, however, produced
fruit with an appearance and flavor as good as or better than 'Selva'. In
addition, the selections appeared to be less affected by mites than
'Selva'. All of the selections have higher levels of anthracnose crown
rot resistance than 'Selva', and can be propagated easily in Florida.
One of the selections FL 79-1126 appears to be a potential alternative to
'Dover'. It has a yielding pattern similar to 'Dover', and its fruit do
not have a tendency to become overly dark. When grown at AREC-Dover, FL
79-1126 plants are usually slightly smaller and have a slightly more open
canopy than 'Dover' plants, although in commercial production, the plant
size and leaf density of FL 79-1126 is likely to depend on planting date,
seasonal weather, and fertility program.
Preliminary research (1988-89) indicates that fruit production on FL
79-1126 can be advanced several weeks by using plants propagated at
northern latitude nurseries. Northern propagated FL 79-1126 may come
close to being as early in fruit production as 'Selva'.
Another selection FL 82-1452 could possibly be a useful clone for home
gardens and local sales. It has several very desirable characteristics,
including a high sugar content in its fruit, but a fruit cracking problem
and relatively poor daughter plant production in the nursery make it
unsuitable for large scale commercial production.
The breeding program has recently been expanded in several areas:
1) Approximately 6,000 seedlings were evaluated during the 1988-89
fruiting season -- up from approximately 5,000 during the 1987-88 season.
Some further increases are anticipated in the future.
2) Genetic studies on commercially important traits have been initiated.
Traits being studied include anthracnose resistance, yield, fruit size,
and skin toughness.
3) To increase genetic diversity in the breeding population, germplasm
from California, Canada, the eastern U.S. and Israel has been used in
4) Tissue culture facilities have been established at AREC-Dover and will
be used for production of pest-free nursery stock, germplasm preservation,
cloning of seedlings for developmental studies, and in vitro selection of
The greatest cultivar need for the industry at present appears to be a
cultivar similar to 'Selva' but with better flavor. We are optimistic
that such a cultivar can be developed in the next few years. With the
recent expansion of the breeding program, there are many promising clones
in the program. The best of these are currently being progagated and will
be compared in detail with 'Selva' during the 1989-90 fruiting season.
We would like to express our appreciation to the Florida Strawberry
Growers Association for their financial as well as program support of the
Research Center at Dover.
Table 1. Strawberry plant mortality when grown at 3 plant spacings and inoculated with 3
Colletotrichum species in the fruiting field.
Numbers of plants that died after:
2 weeks 4 weeks 7 weeks 18 weeks
spacing Inoculum Inoc. Non. Inoc. Non. Inoc. Non. Inco. Non.
2 in. Sterile water 0 0 0 0 0 0 0 0
C. acutatum 0 0 0 0 0 0 1 1
CT. fragariae 0 0 7 0 18 0 25 3
T7. gloeosporioides 2 0 11 0 24 0 25 4
6 in. Sterile water 0 0 0 0 0 0 0 0
C. acutatum 0 0 0 0 0 0 0 0
t" fragariae 0 0 8 0 22 0 24 6
T. gloeosporioides 4 0 13 0 22 0 25 2
12 in. Sterile water 0 0 0 0 0 0 1 0
C. acutatum 0 0 0 0 0 0 0 0
TT fragariae 0 0 11 0 24 0 25 5
T7. gloeosporioides 7 0 16 0 23 0 25 2
There were 25 inoculated and
25 noninoculated plants in each series at each spacing.
Inoc. = inoculated; Non. = noninoculated.
irrigation, 4-row beds gave greater yields in 2 of the 3 trials, but
differences were only significant in one trial. The increased costs for
fertilizer, mulch, and plants with the use of 4-row beds were generally more
than offset by the increased yields. However, equipment costs also may be a
factor in the economic returns.
8. Albregts, E. E., and C. Ii. Howard. 1980. Fruit yield of 'Florida Belle'
strawberries as affected by rates of a resin coated fertilizer. Proc. Soil
and Crops Sci. Soc. Fla. 39:14-16.
A resin-coated slow-release fertilizer called Osmocote is used extensively in
strawberry (Fragaria X ananassa Duch.) fruit production to reduce fertilizer
leaching, but only limited data are available as to the effect of Osmocote
rate on fruit yield with sandy soils. Rates of 700, 1050, and 1400 kg/ha of
a 16-2.2-13.3 Osmocote were evaluated during two seasons with overhead
sprinkler irrigation and during one season with drip irrigation. Several
fertilizer placements were used. Soil tests taken prior to fertilizer
application indicated high levels of P and K in the soil. The soil organic
matter content was rated as low. Total yield, fruit weight, plant size, and
foliage color were not different because of Osmocote rates or placements with
either overhead sprinkler or drip irrigation. Soil soluble salts were above
yield limiting levels and tended to increase with increasing rates of
9. Albregts, E. E., and C. M. Howard. 1980. Effect of pre-transplant chilling
and planting date on growth and fruiting response of the 'Dover' strawberry.
Proc. Fla. State Hort. Soc. 93:239-241.
'Dover' strawberry (Fragaria X ananassa Duch.) plants were given either 0, 15,
or 30 days of pre-transplant chilling at 2C and set in the fruiting field on
or near October 1 and 15 and November 1 for two seasons. During the third
season, plants were chilled either 0 or 15 days and set on October 22 and
November 1 and 15. Chilling reduced January fruit yields, increased April
fruit yield, and increased daughter plant production. Delaying the planting
date generally reduced January yield. The highest April yields were from
plants set on October 15, and seasonal yields were generally reduced if plants
were set on November 1 or later. The most desirable date for highest early
yields and lowest daughter plant production appeared to be October 1.
10. Albregts, E. E., and C. M. Howard. 1981. N, P, K composition of and accumula-
tion by strawberry plant organs from transplanting through fruit harvest.
Proc. Soil and Crops Sci. Soc. Fla. 40:30-33.
Plants of 3 strawberry (Fragaria X ananassa Duch.) clones were analyzed for
N, P, and K during two seasons at transplanting, initial flowering, initial
harvest, middle of harvest season, and end of harvest season. The N, P, and K
concentrations in the roots and crowns decreased during each fruiting season.
The N concentrations in all plant organs other than the fruit decreased during
the fruiting season while only the P concentrations of the leaves and petioles
decreased during the same period. The leaves accumulated more N, P, and K than
the roots and crowns throughout the growing and fruiting season. Once fruit
harvest began, the fruit accumulated more N, P, and K than all other plant
organs combined. The roots and crowns appeared to be under the greatest
nutrient stress during the fruiting period.
11. Albregts, E. E., and C. M. Howard. 1982. Response of fruiting strawberries
to micronutrient fertilization. Proc. Soil and Crops Sci. Soc. Fla. 41:158-
Strawberries (Fragaria X ananassa Duch.) were grown for two fruiting seasons
on a well drained fine sand which had not been fertilized for at least 12
years. Each season micronutrients were applied pre-plant as 1) fritted trace
elements (FTE 503) at 45 kg/ha, 2) as a mixture of micronutrients in the
oxide form applied at the rate of 680 g B and Cu, 4050 g Fe, 1690 g Min, and
1580 g/Zn/ha, 3) the oxide form of micronutrient applied at double the
proceeding rate, and 4) a control. There were no significant differences in
fruit yields, fruit quality, and elemental composition of the fruit because
of treatment. Treatment differences were obtained for Mn, Cu, and Zn content
of the leaf blades and the Zn content of the soil. The B content of the leaf
blades was in the deficient range with all treatments the second season, but
no foliage or fruit deficiency symptoms were evident.
12. Albregts, E. E., and C. M. Howard. 1982. Effect of fertilizer rate on number
of malformed strawberry fruit. Proc. Fla. State Hort. Soc. 95:323-324.
'Dover' and 'Tufts' strawberry (Fragaria X ananassa Duch.) plants were
fertilized at 65, 130, and 195 ib.N/acre with isobutylidene diurea and
evaluated for number of malformed fruit of marketable weight. Phosphorus
and potassium were supplied to all treatments at 27 and 162 lb./acre,
respectively. The percent of the fruit malformed increased with increased
nitrogen rate. The effect was most noticeable in the March and April
harvests. A greater percentage of the 'Tufts' than of the 'Dover' fruit were
malformed. Leaf N and soil N03-N increased with increasing rates of applied
N. Foliage color was darker green and plant size was larger with higher rates
of applied N.
13. Albregts, E. E., and C. M. Howard. 1984. Boron application to strawberries.
Proc. Soil and Crops Sci. Soc. Fla. 43:(In Press).
Experiments were conducted for two seasons, 1980-81 and 1981-82, using the
annual hill culture system for strawberries (Fragaria X ananassa Duch.) on
a well-drained Scranton adjunct fine sand (a siliceous, acid, thermic, Typic
Psammaquent) at the Agricultural Research Center, Dover, Florida. During the
first season, treatments we e solubor applied to the foliage in five monthly
applications of 112 g B ha- each, borax incorporated into the plant bed It
1.12 kg B ha -1, dolomite incorporated into the plant bed at 2.24 .g ha "-
and an untreated check. During the second season two additional foliar
application rates were used, 56 and 224 g B ha- per application. The
'Dover' cultivar was used first season and the 'Dover' and 'Tufts' cultivars
were planted the second season. Foliage application at 112 g B ha-1 monthly
gave the highest total marketable fruit yields during both seasons. Dolomite
application reduced the fruit yield the first season, but not the second.
Yields were more highly correlated with fruit number than with fruit weight.
The dolomite and the check treatments increased the percent malformed fruit
during both seasons. Soil application of boron resulted in the highest
concentration of B in the foliage and in the soil saturated extract.
14. Albregts, E. E., and C. M. Howard. 1984. Effect of three slow release
fertilizers on fruiting strawberries. Proc. Soil and Crops Sci. Soc. Fla. 43:
Slow release N fertilizers are included as part of the fertilizer mix to reduce
N leaching during the production of fruiting strawberries (Fragaria X ananassa
Duch.). Sludge (heat dried sewage sludge), ureaformaldehyde, a 1:l mixture of
sludge and urea-formaldehyde, and organiform were evaluated for fruiting
strawberries as the only source of N. Two rates of N (146 and 219 kg/ha) were
applied. Treatments in which the nitrogen was derived from sludge produced
highest March, April, and total fruit yields, highest NO3-N and NH4-N in the
soil :solution, and highest total N in leaf tissue during December. In addition
these plants were larger and foliage greener in January and February. Total
fruit yields were higher with the highest N rate.
15. Albregts, E. E., and C. M. Howard. 1979. Nutrient accumulation by strawberry
plants. Fla. Agr. Expt. Sta. Res. Report SV-1979-1. 5 pp.
The strawberry grower is vitally interested in his production costs.
Fertilizer is one of the larger items in cost of strawberry production, and
the price of fertilizer has increased considerably in the last few years. To
hold down production costs the grower needs to be aware of the changes
occurring in the fertilizer industry. Some of the changes are the greater
availability of many slow-release fertilizers, the greater awareness of the
role of micronutrients in cropping, and others. In this report we will discuss
plant nutrient accumulation and the use of one slow-release fertilizer.
16. Albregts, E. E., and C. M. Howard. 1980. Effect of plant chilling prior to
transplanting and planting date on growth and fruiting response of strawberry
clones in Plant City area. Fla. Agr. Expt. Sta. Res. Rept. SV-1980-1. 9 pp.
Strawberry growers harvest plants from the strawberry nursery at various times
during the fall season. The plants are handled in various ways and may or may
not be stored in coolers before transplanting in the fruiting field. How
transplants are handled from the time they are removed from the soil at the
nursery until transplanting will have a direct affect on the transplant's
growth and fruiting response.
This report will be concerned with two of the many variables encountered in
this interval between plant harvest and transplanting.... (1) The length of the
chilling period given the plants from time of removal from the nursery until
transplanted in fruiting field and (2) the date transplants are set in the
17. Albregts, E. E., and C. M. Howard. 1980. Effect of poultry manure on straw-
berries. Fla. Agr. Expt. Sta. Res. Rept. SV-1980-2. 7 pp.
To evaluate the effect of poultry manure on strawberries, a study was conducted
for 4 seasons using the 'Dover source. poultry manure. The manure was
incorporated into the top 6" of the soil about one or two weeks prior to
fumigation at the rates of 0, 4, 8, 16,. and 32 tons per acre for each of the
first 3 seasons. 'Florida Belle' strawberry plants were set each year into the
plots. Although no manure was applied the 4th season, 110 lbs/acre of urea
were applied to all plots except the zero treatment.
18. Albregts, E. E., and C. 1I. Howard. 1981. Micronutrients for strawberries. Fla.
Agr. Expt. Sta. Res. Rept. Dover ARC SV-1981-6. 7 pp.
% vany strawberry growers apply micronutrients annually to their soils. Growers
believe this is a good investment since the cost of micronutrients are
relatively low. any growers believe that most of the applied micronutrients
are either taken up by the plant or lost from the soil since deficiencies often
occur. However, it has been shown that, except for boron, leaching is not a
serious problem. In addition, the amount of micronutrients needed to grow an
acre of fruiting strawberries is very small. Grower application rates to the
soil are generally ten times those needed to grow a crop. Of course, only that
amount in the fruit is taken from the field which makes the application rates
appear higher yet; therefore, for maintenance purposes only small quantities
are needed. Additional amounts of micronutrients are supplied to the plants
with the application of some fTuzin idsa .' However,, large am.nUts.of .:i.cro-
nutrients may be supplied to the soil and micronutrient deficiencies can still
occur. The problem is either that leaching removed them from the root zone or,
more likely, they are not available to the plant root for uptake because of
physcial or chemical reasons.
19. Albregts, E. E., and C. M. Howard. 1982. Effect of stress on strawberry
transplant growth and fruiting response. Dover ARC Research Report DOV-1982-3.
Since most strawberry transplants set in the fruiting field in Florida are not
dormant, they are more subject to stress. Transplants are removed from the
soil in the nursery, placed in small bundles, and handled in various ways until
set in the fruiting field. Some transplants are set in the fruiting field
immediately after removal from soil, while others are placed in coolers for an
indefinite period before transplanting. Occasionally, growers will bury the
plant roots in the nursery soil for periods ranging from one to five hours.
Some plants are occasionally left on the soil surface, either in the nursery
or fruiting field, for lengthy periods. Transplants are also placed under
stress between time of running the blade under the plants in nursery until
irrigation is started on transplants after setting in the fruiting field.
Because the weather is very warm during plant harvest, excessive wilting of
plants can occur with some harvesting, storing, and setting procedures. If
defoliation of non-dormant plants occurs, plant growth, development, and
fruiting may be delayed.
1. Albregts, E. E., and C. M. Howard. 1981. Weed control in strawberry nursery.
Proc. Fla. State Hort. Soc. 94:132-133.
Three herbicides applied either alone or in combination and a fumigant were
evaluated for weed control, plant injury, and plant production with two
cultivars in a strawberry (Fragaria X ananassa Duch.) nursery. Weed control was
best with a combination of DCPA (dimethyl tetrachloroterephthalate) and
chloroxuron (3-4P-(P-chlorophenoxy)phenyl)-l,l-dimethylurea) at 16 and 8 Ibs
a.i./acre, respectively, and was only slightly less effective at one-half these
rate. DCPA alone, diphenamid (N,N-dimethyl-2,2-diphenylacetamide), and the
fumigant IM-33 (67% methyl bromide and 33% chloropicrin) gave poor weed control.
Daughter plant production by 'Florida Belle' was not apparently affected by
treatments. DCPA and DCPA-chloroxuron combination treatments produced fewer
large plants of 'Dover' than the hoed check. The number of 'Dover' small plants
produced was not affected by treatments. Phytotoxic symptoms were noted with
all herbicides. On a scale of 1 to 10 with a 10 rated as non-phytotoxic, the
phytotoxicity ratings of the herbicides were: dtphenamid 9.3, DCPA (low rate)
7.8 and (high rate) 6.1, and the DCPA-chloroxuron (low rate) 7.4 and (high
rate) 5.5, respectively.
2. Albregts, E. E., and C. M. Howard. 1983. Weed control in the strawberry fruit
production field. Proc. Fla. State Hort. Soc. 96:75-76.
Herbicides were applied for 2 seasons to a strawberry (Fragaria X ananassa
Duch.) fruit production field. During the first season, herbicides were
applied on October 3, 1980 in the row middles immediately after transplanting.
Treatments were napropamide (2-(a-naphthoxyl )-N,N-diethylpropionamide) at 6 lb.
a.i./acre, DCPA (dimethyl tetrachloroterephthalate) at 12 lb. a.i./acre,
chloroxuron (3-(p-(p-chlorophenoxy)phenyl)-l,l-dimethylurea) at 6 lb. a.i./acre,
and an unhoed check. Plots were evaluated and then cultivated on November 10,
December 4, and March 3. During the second season, herbicides were applied on
October 6, 1981 prior to transplanting to row middles and to beds with mulch
temporarily removed, and on December 28 to row middles only. Treatments were
DCPA at 9 lb. a.i./acre, paraquat (l,l'-dimethyl-4,4'-bipyridinium dichloride)
at 1 lb. a.i./acre, napropamide at 2 and 4 lb. a.i./acre, terbacil (3-tert-
butyl-5-chloro-6-methyluracil) at 1/8 and lb. a.i./acre, and hoed and
unhoed checks. During the first season, chloroxuron and napropamide gave best
weed control and smallest size weeds on November 10 and December 4 with no
significant yield effects. During the second season, napropamide and paraquat
gave best weed control on December 1 and December 28, and weed control was
excellent in all herbicide treatments on February 26. Herbicide drift in the
paraquat treatment the second season resulted in some plant damage which may
have reduced yields. Evening primrose (Oenothera laciniata, Hill) was the
major weed both seasons.
3. Gilreath, J. P., and E. E. Albregts. 1984. Weed control in mulched strawberry
production. Proc. Fla. State Hort. Soc. 97:(In Press).
Preplant application of 1 and 2 Ib./acre of alachlor (2-chloro-2',6'-diethyl-
N-(methoxymethyl)acetanillde) and 2 and 4 Ib./acre of ethofumesate (2-ethoxy-
2,3-dihydro-3,3-dimethyl-5-benzofuranyl methanesulfonate) and postemergence
applications of 0.5 lb./acre of two different brands of acifluorfen (sodium
5-(2-chloro-4-trifluoromethyl)-phenoxy)-2-nitrobenzoate) were evaluated for
weed control and crop phytotoxicity in mulched 'Tufts' strawberries (Fragaria
X ananassa Duch.) during the 1982-83 production season. Alachlor and
ethofumesate provided excellent early season grass and broadleaf weed control.
Acifluorfen (both brands) provided good control to carolina geranium (Geranium
carolinianum L.), but did not control grass weeds. Strawberry plant vigor was
reduced by the high rate of alachlor and both brands of acifluorfen; however,
the effect of acifluorfen was confined to the foliage present at treatment
and plants soon overcome the visible injury. None of the treatments provided
season-long weed control. Fewer fruit were produced in herbicide treated plots
than in the untreated control.
1. Ridings, W. H., and C. M. Howard. 1979. Strawberry anthracnose and crown rot
caused by Colletotrichum fragariae. Fla. Div. Plant Industry Plant Path/
Circular 198. 2 pp.
Strawberry anthracnose caused by the fungus Colletotrichum fragariae Brooks was
first described in 1931 from Florida. The fungus was initially thought to
attack only the stolons of strawberry (Fragaria X ananassa Duchesne), but later
it was shown to infect the petioles, fruits, and crowns. The crown rot phase
is of great concern to Florida growers since infected plants obtained from
nurseries and set in the fruit-producing field result in wilting and death of
2. Howard, C. M., A. J. Overman, J. F. Price, and E. E. Albregts. 1984. Diseases,
nematodes, and insects affecting strawberries in Florida. Univ. of Fla. Expt.
Sta. Bull. (In Press).
Strawberry plants are grown in all months of the year in Florida in plant
nurseries during the winter, spring, summer, and early fall, and in fruit
production fields in the fall, winter, and spring. The warm humid climate of
the state that permits year-round growth of plants in the field is also ideal
for the development of a large number of pests on the crop. These pests -
fungi, bacteria, nematodes, insects, mites, and weeds occur in the
nurseries or fruit production fields as environmental conditions become
favorable for activity of each pest.
This bulletin offers causes, symptoms, and control measures for strawberry
pests that are important in Florida plantings. Since pest control
recommendations may change frequently, no specific pesticides are listed.
Consult extension or research personnel or publications to determine the
proper pesticide for control of specific pests.
3. Howard, C. M., and E. E. Albregts. 1981. An outbreak of Verticillium wilt of
strawberries in central Florida. Plant Disease 66:856-857.
Verticillium wilt of strawberries was found for the first time in central
Florida in 1981. Surveys showed that all infected plants came from two nursery
fields in Michigan. The greatest percent of wilt occurred in plants that were
grown in soil that had been in potatoes the previous year and was fumigated
with MB-C 98-2 rather than MB-C 67- 33 before setting the strawberries.
4. Howard, C. M., and E. E. Albregts. 1981. Cleistothecia of Sphaerotheca
macularis (powdery mildew) on strawberry plants in Florida. Plant Disease 66:
Cleistothecia of Sphaerotheca macularis were found in 1981 for the first time
on strawberry plants in Florida. They were found only on plants that were
grown in Maine and lichigan and transplanted into Florida fruit production
fields. Benomyl and sulfur failed to control powdery mildew on these plants.
Powdery mildew was widespread on plants that had been grown in five other
states, but no cleistothecia were found on those plants. Benomyl or sulfur
controlled the disease on plants from those five states.
5. Howard, C. 1., and E. E. Albregts. 1983. Black leaf spot phase of strawberry
anthracnose caused by Colletotrichum gloeosporioides (=0. fragaria). Plant
Since the mid-1970's, a new leaf spot of strawberries has been found in summer
nurseries in Florida. Isolations from the lesions consistently yielded a
Colletotrichum sp. identical to the original description of C. fragariae. In
inoculation tests, an isolate from a leaf lesion and an isoliae from the
crown of a wilted plant incited leaf spot and typical anthracnose symptoms
on stolons and petioles.
6. Howard, C. M., and E. E. Albregts. 1984. Anthracnose of strawberry fruit
caused by Glomerella cingulata in Florida. Plant Disease 68:(In Press).
Glomerella cingulata was isolated from anthracnose lesions on strawberry
fruits. Lesions caused by G. cingulata on fruits in the field and inoculated
fruits were indistinguishable from those caused by Colletotrichum fragariae.
Conidia of G. cingulata are slightly shorter but larger in diameter than
those reported for C. fragariae.
7. Howard, C. M., and E. E. Albregts. 1981. Anther and pistil blight of straw-
berry blossoms caused by a Rhizoctonia sp. Phytopathology 71:882.
For several years we have encountered a condition of potted strawberry plants
in the greenhouse, and occasionally of plants in the field, in which the
anthers of some flowers are black and the pistils are abnormal or totally
destroyed. Isolations from these blossoms failed to consistently yield any
specific microorganism. Observations revealed that affected flowers could
usually be detected by the presence of a pink color or brown necrotic spot
on the petals of buds several days before they opened. Isolations from anthers
or pistils of these buds yielded a Rhizoctonia sp. Flower buds were inoculated
with the Rhizoctonia sp. by placing 2 mm squares of potato dextrose agar in
which the mycelium was growing under the sepals. The plants were enclosed in
plastic bags for 3 days. As these flowers opened, all had brown necrotic
spots on the petals, all but one had black anthers, and 50% had pistil
destruction. Rhizoctonia was reisolated from the affected flowers.
8. Howard, C. I., and E. E. Albregts. 1981. Verticillium wilt of strawberries
in central Florida. Fla. Agr.'Expt. Res. Rept. Dover ARC SV-1981-4. 3 pp.
Verticillium albo-atrum Reinke & Berth., the fungus that causes Verticillium
wilt attacks a wide variety of crop plants including strawberry, tomato,
potato, pepper, okra, and eggplant. This disease has been recognized as a
serious and widespread problem in the calcareous soils of south-east Florida
since the early 1960's. It was found in the major strawberry production area
in central Florida for the first time in 1981.
9. Howard, C. M., and E. E. Albregts. 1981. Powdery mildew of strawberry in
Florida. Fla. Agr. Expt. Res. Rept. Dover ARC SV-1981-5. 3 pp.
Powdery mildew of strawberry has occurred sporadically in Florida at least
since 1967. Previous to 1981, powdery mildew was controlled quite easily by
two or three applications of sulfur or Benlate at weekly intervals. Ten to 12
applications of Benlate plus up to five applications of sulfur failed to
control mildew in a few fields during the 1980-81 season. This raises the
possibility that fungicide resistant strains of the fungus may have been
present in those fields.
10. Howard, C. LI., and E. E. Albregts. 1982. Strawberry anthracnose, crown rot,
fruit rot, and black leaf spot caused by Colletotrichum fragariae. Dover
ARC Research Report DOV-1982-2. 5 pp.
Strawberry anthracnose, caused by the fungus Colletotrichum fragariae, Brooks,
has been a serious problem in summer plant production nurseries in Florida
at least since the late 1920's. The fungus is known to cause spotting and
girdling of runners and petioles, crown rot resulting in wilting and death of
plants, and fruit rot. Since the late 1970's, the anthracnose fungus has been
consistently associated with a black leaf spot of strawberry in the summer
nursery. Black leaf spot has now been shown to be caused by this fungus and
often is the first indication that the anthracnose disease is present.
INSECTS AND MITES:
1. Schuster, D. J., J. F. Price, C. M. Howard, and E. E. Albregts. 1979.
Twospotted spider mites: Control of strawberry with organotin, naphthoquinone,
and cyclopropane acaricides. J. Econ. Entomol. 72:360-361.
Efficacy of selected compounds from recently developed groups of acaricides
was evaluated in 3 winter field experiments for control of Tetranychus
urticae Koch on strawberry. The naphthoquinone, DPX-3792 (2-acetyloxy)-3-
dodecyl-l,4-naphthalenedione', and the organotin compounds, cyhexatin,
hexakis, and R-28627 (S-tricyclohexyltin 0,0-diisopropyl phosphorodithioate),
effectively reduced mites and their eggs below levels that developed on
strawberry foliage treated with water alone. Fruit yields from plants
treated with these compounds were as high as or higher than yields from plants
to which no acaricides were applied. The cyclopropane compound, ZR-856
(hexadecyl cyclopropanecarboxylate), was effective against T. urticae but
reduced yields in one experiment. The carbamates, benomyl anT-oxamyl, were
not as effective in reducing mite populations as the aforementioned chemicals
but did significantly reduce populations relative to those on plants sprayed
with water only.
2. Schuster, D. J., J. F. Price, F. G. Martin, C. M. Howard, and E. E. Albregts.
1979. Tolerance of strawberry cultivars to twospotted spider mites in Florida.
J. Econ. Entomol. 73:52-54.
Two experiments were conducted in Florida to determine the tolerance of four
strawberry cultivars to Tetranychus urticae Koch by comparing populations of
mites on plants treated or not treated with cyhexatin for mite control.
Based on percent reductions of both numbers and weight of marketable fruit in
the presence of dense mite populations, 'Florida Belle' and 'Sequoia' were
more tolerant to T. urticae than were 'Tioga' and 'Siletz'. Cyhexatin
significantly reduced mite populations on all cultivars. There were no
significant differences among cultivars in number of mites present.
1. Albregts, E. E., and C. L1. Howard. 1984. Biomass cultural evaluation for sweet
potatoes, kenaf, and sorghum. Proc. Fla. State Hort. Soc. 97:(In Press).
Experiments were conducted for 3 seasons with sweet potato (Ipomoea batatas,
'Georgia Jet' and 'Lorado'), kenaf (Hibiscus cannabinus L.), and forage
sorghum (Sorghum bicolor 'Pioneer 947') to evaluate cultural methods to
maximize biomass yield when grown as a second crop on strawberry beds.
Treatments for each crop were: season 1, (a) fertilizer rates of 0-0-0, 36-0-
24, and 56-8-40 lbs/acre NPK, season 2, (a) fertilizer rates of either 27-4-21
or 45-8-36 lbs/acre NPK, (b) either 12 or 18 inch plant spacing for sweet
potato, and either 130,000 or 260,000 seeds/acre for kenaf and sorghum, (c)
either with or without polyethylene mulch, and (d) plants were harvested
either 3 or 4 months after planting, season 3, (a) fertilizer rates of either
40-16-36 or 80-32-72 lbs/acre NPK, (b) sweet potato plant spacing of 4, 8, 12,
and 16 inches, and seeding rates of one-third, two-thirds and one million
seeds/acre for kenaf and sorghum. During the first season, the tubers of the
'Morado' sweet potato gave highest dry matter yield with the highest fertilizer
rate. During the second season, the sweet potatoes harvested 4 months after
planting gave highest dry matter yields of tubers and foliage with the 12"
spacing treatment and greater yield than plants harvested 3 months after
planting. Sorghum and kenaf produced greater dry matter yields with denser
plantings, without mulch, and with the 4 month culture. During the third
season, sweet potato dry weight yields increased with increasing plant density
and with the higher fertilizer rate. Sorghum and kenaf yields decreased with
increasing plant density, and sorghum yields increased with highest fertilizer
rate. Plant dry matter of both crops decreased with increasing plant density.
2. Howard, C. M., and E. E. Albregts. 1980. Strawberry mechanization in Florida.
Proc. Res. Workers Conference on Strawberry IMechanization, 1980. Oregon State
Univ., Ag. Expt. Sta. Bull. 645. pp 11-14.
Mechanization of bedding, soil fumigation, and polyethylene mulch application
for strawberry production in Florida as evolved over the past 20 years.
Although some of the machinery novW being used may have been adapted from other
crops, most of it has been designed and built by strawberry growers and local
metal workers. The harvest season extends continuously over a three to four
month period in Florida, and all fruit is intended for fresh market use.
Because of this, there is only little interest in mechanical harvesting of
strawberries in Florida. The only research on mechanical harvesting that has
been done in Florida has been cooperative world in which researchers from other
states have tested their machines on plot areas made available by researchers