A VEGETABLE CROPS EXTENSION PUBLICATION
VEGETARIAN 04-01 JANUARY 2004
PLANTING DATE AFFECTS EARLY SEASON FRUIT YIELD OF STRAWBERRY IN A SUBTROPICAL ENVIRONMENT
A study was conducted to determine the effect of planting date on the fruit yields of strawberry (Fragraria xAnanassa Duch.) transplants grown in a winter annual hill
production system. Bare-root and plug transplants of 'Sweet Charlie' and 'Camarosa' from a high latitude or high elevation nursery were planted each week during
October 1999 and 2000 at Dover, Fla. Planting date had a significant effect on December yield, with transplants planted in early October generally having higher
December yields than transplants planted in late October. Planting date also had significant effects on January, February, and March yields, but these effects were
not consistent across years or cultivars.
The annual hill production system is used in west central Florida and other subtropical areas, such as southeastern Queensland, Australia and north central
Argentina, to produce strawberry fruit during late fall and winter. Fruiting fields are reestablished each year by planting fresh dug or plug transplants in October
(northern hemisphere) or April (southern hemisphere). These plants usually start producing a few flowers within three to six weeks of planting, and this flowering
continues until spring. Flowers typically develop into ripe fruit within 30 days. In Florida, acceptable total season yields have been obtained when transplants are
planted anytime during October, but in previous studies with locally propagated transplants, the highest early season yields were obtained when transplants were
planted in early October (Albregts and Howard, 1977; Albregts and Howard, 1980; Chandler et al., 1991). Growers should be able to benefit financially by taking
steps to increase their early season yield, particularly their November/December yield. November/December production amounted to only 10% of the total crop yield
in Florida during the ten-year period 1991-2001 (Florida Agricultural Statistics, www.nass.usda.gov/fl), but that production was valuable. It returned the highest
average value per 5.4 kg flat, $16.25, compared to $12.86, $10.13, and $7.00 for January, February, and March respectively.
Currently, the majority of Florida's 2800 hectares of strawberries (>95%) is planted using bare-root, non-defoliated transplants from high latitude ( 42 N) or high
elevation (> 900 m) nurseries. The remaining acreage is planted with plug plants that are also from high latitude or high elevation nurseries. Growers prefertransplants from
these areas because they tend to have fewer disease problems and begin to flower sooner than locally produced transplants. Bare-root transplants are produced in open
fields where daughter plants remain attached to the mother plant and are allowed to root into the soil. Plug plants are produced by removing and placing young daughter
plants in standard transplant trays, misting them until sufficient roots are formed, and allowing them to grow and develop in the trays for four to six weeks (Durner et al.,
2002). This may be done in greenhouses or open fields. Relatively low cost and ample supply make bare-root plants an attractive option for growers. Water savings at
establishment and potentially earlier yields make plug plants desirable (Hochmuth et al., 2001); however, their cost can be twice as much as that for bare-root plants.
The objective of this study was to determine the effect of planting date on fruit yields of strawberry transplants from high latitude/high elevation nurseries.
Materials and Methods
Bare-root and standard (75 cm3) plug transplants of 'Sweet Charlie' and 'Camarosa' were obtained from a commercial nursery in Nova Scotia, Canada and western
North Carolina, respectively. Transplants were dug (in the case of the bare-roots), packed, and immediately shipped by refrigerated truck to Florida so that they
arrived at the Gulf Coast Research Center Dover three days before the intended planting date. Transplants were planted on Oct. 1, 8, 15, and 22 in 1999, and Oct.
2, 9, 16 and 23 in 2000. Four replications of each of the 16 treatments (two cultivars x two transplant types x four planting dates) were arranged in a randomized
complete block design. Each plot contained 16 plants on two-row raised beds, with plants spaced 30 cm apart within and between rows. Micro-overhead irrigation,
applied intermittently, was used for 10 days to establish the plots of bare-root transplants, while no overhead irrigation was used to establish the plug transplants.
After the establishment period, drip irrigation was used to meet the plants' water requirement. University of Florida Cooperative Extension Service recommendations
for fertilizer and pest management (Maynard and Olson, 2000) were followed throughout the season. Berries were harvested, graded, and weighed twice weekly
beginning on 3 Dec. 1999 and 15 Dec. 2000. Data for bare-roots and plugs were analyzed separately (by analysis of variance, SAS Institute, 2001) because the
bare-roots were propagated in a different location than the plugs, and nursery location has been shown to have a significant effect on the fruit yield of strawberry
transplants in west central Florida (Stapleton et al., 2001).
Results and Discussion
For bare-root transplants, which are by far the most important type of strawberry transplant in Florida, planting date significantly affected December yield (Table 1).
Transplants planted during the first week of October had higher December yield than transplants planted during the third and fourth week of October, and transplants
planted during the second and third week of October had higher December yield than transplants planted during the fourth week of October. In fact, the transplants
planted during the third and fourth week of October produced only 64% and 32%, respectively, of the December fruit yield produced by transplants planted in the first
week of October. Production after December was also affected by planting date, but the influence of planting date was not consistent across years or cultivars
(Table 1). 'Camarosa' transplants planted during the third week of October had significantly higher January yield than 'Camarosa' transplants planted during the first
week of October, but a significant planting date effect on 'Sweet Charlie's January yield was not detected. Beyond January, the effect of planting date on the yield of
bare-root transplants was minimal.
The effects of planting date on the December and January yield of plug transplants appears to be similar to that obtained with bare-root transplants (Table 2). Plug
plants planted in early October tended to have higher December yields than the plug plants planted in late October. In terms of December yield, the second and third
weeks of October were the best weeks to plant 'Sweet Charlie', while the first and second weeks were the best weeks to plant 'Camarosa'. However, 'Camarosa'
transplants planted during the first week in October 1999 had lower January yield than the transplants planted later in October (data not shown). This association of
high yield one month with low yield the next has been noted in other strawberry field trials in west central Florida (Bish et al., 2002; Chandler and Kemerait, 2002). The
February yield of 'Sweet Charlie' plug plants planted during week one, two, and three were similar, while the plug plants planted during week four produced
significantly less fruit than those planted during week two (Table 2). The February yield of 'Camarosa' plug plants was not affected by planting date.
The 1999-2000 season had a higher monthly air temperature in October, November, December, January, and March, but a lower monthly air temperature in
February, than did the 2000-2001 season (http://fawn.ifas.ufl.edu). These differences in air temperature could have contributed to the year x planting date
interactions detected in this study.
The influence of planting date on the high latitude/high elevation transplants in this study was similar to the influence of planting date on the locally propagated
transplants used by Albregts and Howard (1977 and 1980) and Chandler et al. (1991). For both high latitude/high elevation and locally propagated transplants,
planting date had a consistent effect on early season yield, but its effect on late season yields was variable.
Based on this study, growers in west central Florida should plant transplants during the first or second week in October to obtain the highest possible December
yields. High December yields may result in lower January yields during some years, but this tradeoff is probably acceptable considering the value of December fruit.
The Florida strawberry industry uses over 100 million transplants each year, and it would be virtually impossible for the nurseries to dig, grade, pack, and ship all of
these plants to growers so they would arrive (fresh) within the first two weeks in October. Equipment, labor, and weather are factors that limit how fast this operation
can be accomplished. Also, even if all the transplants could be obtained in the first two weeks of October, growers in Florida probably would not be able to obtain
enough labor to plant all of the transplants, which, currently, are totally set by hand. But, in view of the fact that transplants delivered to growers in late October are
likely to have relatively low December yields, there might be justification for adjusting the price of transplants according to delivery date. In other words, growers may
be justified in paying more for transplants that are delivered to them in early October and less for transplants that are delivered to them in late October.
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(John R. Duval, Craig K. Chandler, and Elizabeth Golden GCREC-Bradenton -Vegetarian 04-01)
VIRUS IN YELLOW SQUASH IN HILLSBOROUGH COUNTY
In October 2003 in Hillsborough County, a field of 'Gentry' yellow crookneck squash was severely affected by the watermelon strain of papaya ringspot virus (PRSV-
W) (Fig. 1), formerly called WMV-1. PRSV-W infects cucurbits almost exclusively but does not infect papaya. It is the most important of the aphid-transmitted viruses
affecting cantaloupe, watermelon, and squash in central and south Florida. The virus is spread in a nonpersistent manner by over 20 species of aphids. Aphids do
not retain the virus for very long but can acquire and transmit it in very brief probes of the leaf surface.
Both foliage and fruit symptoms observed in 'Gentry' were severe. The leaves of the plants were distorted and mottled, with the newer leaves reduced in size and
very narrow laciniatee or filiform). The squash were knobby instead of smooth with green veining over the fruit. Yield was greatly reduced. In this field, you could see
where the virus had first infected squash on the north side where an old abandoned orange grove overgrown with weeds was present. It was easy to tell that the
plants next to the grove had been infected at an early age. By the time of harvesting, the plants on this side of the field were severely stunted and were distorted with
little to no fruit. The fruits present were small and gnarled with much green veining. The spread of the virus through the field appeared to follow the prevailing winds.
As you moved south across the field away from the grove, symptoms were milder. More distant plants had normal lower leaves and fruit with only the upper portion of
the plants and youngest fruit distorted, indicating that these plants had been infected later than plants near the grove.
The grower noticed no aphids on the plants but it is unlikely that he would have noticed transient winged aphids without using yellow sticky traps or yellow pan traps to
monitor their presence. To transmit the virus, the aphid does not have to be settling down to feed on the squash but can be merely probing the surface of the leaf to
determine if the plant is a suitable host. In the process, it can acquire virus from an infected squash plant and move it to another or transmit a virus that it may have
already acquired. Most insecticides do not act quickly enough to prevent transmission. Many of the aphid vectors are transients coming from weeds and do not
reproduce on cucurbits. Melon aphid, which does reproduce on squash, can transmit the virus but may not be an important vector because it does not move as
readily as aphids looking for other host plants.
Samples were collected from the field and tested by ELISA for nine viruses known to infect cucurbits. Of 39 samples, 38 were positive for PSRV-W. The sample not
infected with PRSV-W had severe viral symptoms. We were able to reproduce the symptoms by rubbing the sap from the ground sample onto squash seedlings in
the greenhouse. Further tests are being done to determine what this virus might be. Nine samples of the predominant weed in the abandoned grove, balsam apple,
(Momordica charantia), were also tested (Fig. 2). The vines of this weed almost covered some of the old trees. All of balsam apple samples were positive for PRSV-
W, although no sample had obvious symptoms. This weed and another, creeping cucumber (Melothria pendula), have been shown in the past to be important
sources of PRSV-W.
The grower also had three varieties of zucchini squash ('Dividend', 'Cash Flow', and 'Payroll') growing just east of the block of yellow squash. The zucchini did very
well all season. Only at the very end of the season were mild virus symptoms seen on 'Dividend' and 'Cash Flow'. None was seen on 'Payroll'. According to Rogers
(Syngenta Seeds), 'Payroll' has tolerance to zucchini yellow mosaic virus (ZYMV) and watermelon mosaic virus (WMV-2) (also found in Florida), 'Dividend' has
tolerance to these two viruses and cucumber mosaic virus (CMV), and 'Cash Flow' has tolerance to ZYMV. No claim is made for tolerance to PRSV-W, although in
this case it appears that these varieties may not develop severe symptoms when infected. However, no samples of the zucchini varieties were tested.
Fig. 1. PRSV-W symptoms in squash.
Pholo credit: Gary Simone
Fig. 2. Balsam apple growing on a dilchbank in southwest
Pholo credit: Warren Adlerz
(Alicia Whidden Hillsborough Co. ext. agent II & Susan Webb assoc. prof., Ent. and Nem. Dept. Vegetarian 04-01)
Extension Vegetable Crops Specialists
Daniel J. Cantliffe
Professor and Chairman
Assistant Professor. strawberry
Assistant Professor. vegetable production
Elizabeth M. Lamb
Assistant Professor. vegetable production
Assistant Professor. soils
Donald N. Maynard (retired)
Stephen M. Olson
Professor. small farms
Mark A. Rilenour
Assistant Professor. postharvest
Steven A. Sargent
Assistant Professor and EDITOR. vegetable nutrition
William M. Stall
Professor. ,eed science
James M. Stephens (retired)
Professor. vegetable gardening
Charles S. Vavrina
James M. While
Associate Professor. organic farming
Assistant Professor. hydrology
University of Florida
Institute of Food and Agricultural Sciences
Horticultural Sciences Department
Florida Cooperative Extension Service
North Florida Research and Education Center Suwannee Valley
Gulf Coast Research and Education Center Dover