This is a public-interest archive. Personal data is pseudonymized and retained under GDPR Article 89.

Re: Propagation Tools/Misters

    Paper 12.     This copy was prepared with a scanner.  It is possible
that errors could of been introduced.  Therefore the copy should be
considered for educational use only.  Please obtain an actual copy before
doing any experiments.
                                                 HORTSCIENCE 30(7):1413 -
1416. 1995.
                                                    Aluminum Amendment of
Potting Mixes
                                       for Control of Phytophthora
Damping-off in Bedding Plants
                                                                      D.M.
Benson
                                    Department of Plant Pathology, North
Carolina State University,
                                                                   Raleigh,
NC 27695-7629
     Additional index words. Phytophthora parasifica, exchangeable
aluminum, Antirrhinum majus, Catharanthus roseus, Petunia xhybrida, disease
suppression
     Abstract. Control of preemergence damping-off caused by PhytopAthora
parasitica Dastur was investigated on three bedding plant species in a 1
peat: 1 vermiculite medium (v/v) limed at 3 kg m-3 and drenched with
aluminum at 10, 25, or 50 meq Al/100 cm3 medium. Aluminum as Al2(SO4)3 was
applied as a drench at 0.75, 1.9, or 3.75 g/150 ml water to the surface of
infested medium in 650-cm2 plug trays (1300-cm3 tray volume). All
concentrations of aluminum were effective in controlling preemergence
damping-off of snapdragon (Anfirrhinum majus L.) and vinca (Catharanthus
roseus G. Don, Madagascar periwinkle), but only 50 meq Al+3/100 cm3 medium
was effective for petunia (Petunia xhybrida Hort. Vilm.-Andr.). At 4 days
after seeding and drenching with aluminum sulfate, exchangeable aluminum
was 0, 0.5, and 2.03 meq Al+3 /100 g medium, respectively, for the three
concentrations used.  Control of damping-off of snapdragon and vinca with
10 meq Al+3/ 100 cm3 medium with no detectable exchangeable aluminum 4 days
after application suggests that P. parasitica was suppressed by aluminum
early in the host-pathogen interaction, whereas petunia was susceptible to
damping-off for a longer period before seedling emergence. Aluminum was not
phytotoxic to vinca, snapdragon, or petunia grown in a limed medium.

     Damping-off caused by Phytophthora parasitica Dastur, Pythium spp.,
and Rhizoctonia solani Kuhn is an important disease problem of bedding
plants for many growers. Traditionally, damping-off has been controlled by
the use of soilless mixes, sanitation, manipulation of the environment, and
fungicides that suppress development of damping-off pathogens. In previous
studies, Thielaviopsis basicola (Berk. ~ Broome) Ferraris, cause of black
root rot of burley tobacco (Meyer and Shew, 1991), and P. parasitica Breda
de Haan var. nicotianae (Dastur) G.M. Waterhouse, cause of black shank of
tobacco (Deluca and Shew, 1988), were suppressed by aluminum. Recently,
Benson (1993a) demonstrated that drenches of aluminum sulfate to a peat:
vermiculite medium controlled preemergence damping-off of C. roseus caused
by P. parasifica. In a nonlimed peat: vermiculite medium at pH4.4, as
little as 17 meq of Al/100 cm3 medium controlled damping-off; however, when
the medium was limed to pH 5.8, as much as 100 meq of Al/100 cm3 medium was
needed for disease control (Benson, 1993a). Differences in amount of
aluminum needed forcontrol at pH values appropriate for bedding plant
production was correlated with exchangeable aluminum in the medium. In
general, as the pH of a medium increases the amount of exchangeable
aluminum (Al+3) decreases, such that there is very little exchangeable
trivalent aluminum at pH 6 (Tisdale et al., 1985).
     The objective of this research was to determine the rate of aluminum
needed to control preemergence damping-off caused by P. parasitica on three
bedding plant species in a soilless medium limed for adequate plant growth.
                                                Materials and Methods
     The soilless medium used was a 1 peat: 1 vermiculite (v/v) mixture
with an initial pH of 4.1 in 1:2 CaCl2. The peat had been screened through
a 6-mm screen to remove large stem and root fragments. As the peat and
vermiculite were mixed in a cement mixer, dolomitic limestone at the rate
of 3 kg/m3 medium was incorporated. The prepared medium was used to fill 81
-cell plug trays (25.4 x 25.4 x 2.54 cm, i.e., standard 162-cell trays cut
in half). The trays were then placed on a greenhouse bench and misted for
2-min intervals five times a day. This rate of misting kept the medium
moist but not completely saturated. Trays were main tained under the mist
system for 3 days to allow partial equilibration of the lime in the medium.
After the equilibration period, the trays were seeded with 'Little Bright
Eyes' vinca (69% germination), 'Tetra RuMed Supreme Mix' snapdragon (55%
germination), or with 'Supercascade White' petunia (86% germination) by use
of a custom 81 -cell vacuum seeder (Berry Seeder Co. , Elizabeth City, N.C
. ).
     Twice-autoclaved rice grains (25 g rice/19 ml deionized water) in
125-ml Erlenmeyer flasks were seeded with two to three 7-mm diameter potato
dextrose agar disks of isolate 336 of P. parasitica (Holmes and Benson,
1994). Flasks were incubated on the laboratory bench at ambient temperature
without supplementary light. Flasks were shaken occasionally to prevent
clumping of grains. After 30 to 40 days of growth, the rice grains were
pulverized in a blender for 1 to 2 min, then screened through a sieve with
2-mm openings to select particles of uniform size. Pulverized rice grains
(0.05 g) were mixed with 150 cm3 peat: vermiculite medium for vinca or  100
cm3 for petunia and snapdragon in a 850-ml plastic bottle. Moist peat:
vermiculite medium had been reserved in shaded plastic bags on the
greenhouse bench during the 3-day equilibration period. After mixing, the
infested medium was sprinkled, through 1 -cm holes in the lid, onto the
surface of the seeded 650-cm2 trays (1300 cm3 of medium/tray). Medium
without colonized rice grains was used to cover seeds in the control
treatment. The trays were then misted twice for 2 min to settle the
covering medium.
     After misting, aluminum at 0,10,25, or 50 meq Al/100 cm3 medium
(0,10,25,50 Al) was drenched to tbe surface of plug trays by dissolving the
appropriate amount of aluminum sulfate [Al2(SO4)3] - 0, 0.75, 1.9, or 3.75
g, respectively - in 150 ml of water. Each solution was placed in a  850-ml
plastic bottle and applied evenly to the surface of the 650-cm2  plug trays
through 0.8-mm holes in the lid. The rates of aluminum chosen were based on
control of phytophthora damping-off of vinca over a pH range of 4. 1 to 6
in previous experiments (Benson, 1993a).
     Plug trays were arranged by treatment in a randomized complete-block
design with four replications. Trays were maintained under the mist system
during germination and emergence. After 16 days for vinca, and 19 days for
petunia and snapdragon, trays were transferred to a capillary-mat watering
system on a greenhouse bench. Stand counts were taken at emergence and at
=2-day intervals thereafter, until tests were complete. At 18 and 32 days
after seeding, six randomly selected seedlings in each tray were measured
for plant width in the case of petunia and snapdragon, or for length of the
first true leaf for vinca to assess aluminum phytotoxicity.
     Four days after seeding, samples of potting medium were removed at
random from each replication and composited by treatment for determination
of pH and exchangeable aluminum. Medium pH was determined in 1 :2 CaCI2
(Smiley and Cook, 1972). Exchangeable aluminum, expressed as
milliequivalents of Al+3/ 100 g medium, was determined by 1 N KCI
extraction of medium samples with a baseacid titration method that involved
sodium fluoride (Yuan, 1959).
     Forty-two days after seeding, six plugs for each plant species were
selected at random from each plug tray and transplanted into a 82cm3,
six-cell market pack of peat: vermiculite medium at pH 4.7. Immediately
after transplanting, the corresponding rate of aluminum from the initial
treatment was applied in 75 ml of water to the surface of the medium, as
described above. Plants were fertilized weekly with 100 ppm N (20:20:20;
Peters, Allentown, Pa.). At 45 and 60 days after seeding, plant height for
the six seedlings in each market pack was measured.
     Stand counts among treatments, plant widths, leaf length, and plant
height measurements were compared by analysis of variance (ANOVA) with the
PROC ANOVA procedure of PC SAS (SAS Institute, Cary, N.C.). Mean separation
was by Waller-Duncan k  ratio t test, k = 100, P = 0.05. Experiments were
repeated three times and representative data from one experiment presented.
                                                                         
Results
     Vinca. Stand counts of vinca seedlings were lower (P = 0.05) in the
infested, nontreated control due to preemergence damping-off caused by P.
parasitica compared to the noninfected control (ck) at 11 days after
seeding (Fig. 1). Based on stand count in the noninfected control,
preemergence dampingoff caused by P. parasitica was 56.2% in the infested
control. When drenches of aluminum at rates of 10 to 50 Al were applied to
infested medium seeded with vinca, stand counts were different (P < 0.05)
from the infested, nontreated control but the same as counts in the
noninfected control (Fig. 1). Preemergence damping-off was 9.5%, 0%, end 0%
for 10, 25, and 50 A1, respectively, based on stand count for the
noninfected control.
     Snapdragons. No damping-off of snapdragons occurred in medium amended
with 25 or 50 Al, respectively, and stand counts were not different (P >
0.05) from the noninfected control (Fig. 1). Preemergence damping-off in
snapdragons not drenched with aluminum averaged 48% in the infested control
with P. parasitica.  At 10 Al, damping-off was 21%, but stand count was not
different (P > 0.05) from the noninfected control (Fig. 1).
     Petunia. In petunia, 10 and 25 Al did not control preemergence
damping-off (29% and 20% diseased plants, respectively), compared to the
infested control  (0 meq) and stand counts were similar to that of the
noninfected control (Fig. 1). Damping-off in petunia was 58% in the
infested control without aluminum amendment. At 50 Al, damping-off of
petunia averaged only 2.4% and stand count was greater than (P < 0.05) the
infested control (Fig. 1).
     pH. Medium pH ranged from 5.5 to 5.6 in composite samples from
treatments without aluminum amendment 4 days after seeding (Fig. 2).  As
the rate of aluminum amendment increased from 10 to 50 Al, medium pH 
dropped from 5.5 to 5.1, respectively, 4 days after seeding (Fig. 2).
     Exchangeable aluminum. Four days after seeding, exchangeable aluminum
from composite samples across crop species was 0 and 0.13 meq/ 100 g medium
in the infested control (0 meq) and noninfected control (ck), respectively
(Fig. 3). No exchangeable aluminum was detected in samples from medium
drenched at 10 Al.  Exchangeable aluminum was 0.5 and 2.03 meq/100 g medium
in samples from media drenched with 25 and 50 Al, respectively, at 4 days.
     Plant growth. Eighteen days after seeding,  lengths of the first true
leaves of vinca were similar (P > 0.05) among treatments (range 8.6 to 9.7
mm). At day 32, however, first true leaves in the infested control were
shorter (P = 0.0001) than in treatments with aluminum or the noninfected
control (Table 1). Heights of vinca seedlings at day 45 (range 47 to 68 mm)
and day 60 (range 101 to 159 mm) after seeding were similar (P > 0.05)
among treatments.
     At day 45, snapdragon seedlings in the infested control and in medium
amended with 50 Al were shorter (P = 0.036) than seedlings in medium
amended with 25 Al (Table 1). At day 60, no differences in height of
snapdragon seedlings (range 148 to 235 mm) were detected among treatments.
Plant width at day 18 and day 32 (range 33 to 42 mm) after seeding was
similar for all treatments.
     At 32 days after seeding, petunia seedlings in the noninfected control
and medium drenched with 25 Al were larger (P < 0.005) than seedlings in
other treatments (Table 1). No differences in heights of petunia seedlings
were detected at 45 and 60 days (range 202 to 255 mm).
                                                                    
Discussion
     Drenches of aluminum to a peat: vermiculite medium at 10 to 50 Al were
effective in controlling preemergence damping-off; but differences existed
among bedding plants tested. Damping-off of vinca and snapdragon was
controlled at all rates of aluminum tested, whereas only the 50 Al
treatment completely controlled damping-off of petunia.
     Previous research with P. parasitica has shown a close correlation
between exchangeable aluminum at 4 days after seeding vinca and subsequent
development of preemergence damping-off (Benson, 1993a). Apparently, the
first few days after seeding are critical in emergence of healthy seedlings
or development of disease even though seedlings may not actually emerge
until several days later. Thus, it appears for vinca and snapdragon, where
control of preemergence damping-off was good at a rate as low as 10 Al,
that the critical interaction of exchangeable aluminum with pathogen
suppression occurs within 4 days. In addition, the amount of exchangeable
aluminum must have been very low during this period, since exchangeable
aluminum was not detectable at 4 days after seeding when applied at 10 Al.
The transitory nature of exchangeable aluminum when applied at low rates to
a peat: vermiculite medium limed at 3 kg m-3 suggests that long-term
disease control would not be effective if the crop were susceptible to P.
parasitica at other stages of growth. This situation would apply for the
phytophthora blight disease that develops on foliage of vinca as a result
of splash dispersal of inoculum to foliage of seedlings or even flowering
plants in the landscape (Benson, 1993b).
     However, for petunia, only 50 Al of aluminum was effective in disease
control where exchangeable aluminum was 2.03 meq Al+3/ 100 g medium at day 
4, suggesting that germinating petunia seed were susceptible to P.
parasitica for a longer period than snapdragon and vinca before emergence.
Therefore, exchangeable aluminum must remain at levels inhibitory to P.
parasitica for longer periods.
     In acidic soils with a pH near 4, aluminum toxicity to plant growth
can be a problem. In peat media with a naturally low pH, potential aluminum
toxicity can be corrected by adding lime. However, the natural
suppressiveness of nonlimed peat media to sensitive soilborne pathogens due
to high exchangeable aluminum is lost by liming. Amendment of peat media
with aluminum in the form of aluminum sulfate may be one way to restore
suppression to sensitive soilborne pathogens.
     Vinca, snapdragon, and petunia seedlings were not sensitive to
aluminum toxicity at rates of 10, 25, or 50 Al when the peat: vermiculite
medium was limed at 3 kg m-3.
However, Benson (1993b) found that both petunia and snapdragon emerged
poorly, and had restricted root systems and top growth when exposed to
aluminum at 100 Al in a nonlimed peat: vermiculite medium at pH 4.2.
Although only a limited number of bedding plant crops have been tested for
aluminum tolerance (Benson, 1 993b), it is apparent that even
aluminum-sensitive crops such as petunia and snapdragon can be grown at
favorable pH in environments with enough exchangeable aluminum to control
damping-off due to P. parasitica. In practice, growers could use alutninum
amendments to create levels of exchangeable aluminum in peat-based media
that were suppressive to sensitive pathogens such as P. parasitica yet
avoid aluminum phytotoxicity problems by liming the medium.
                                        Literature Cited
      Benson, D.M.1993a. Suppression of Phytophthora parasitica on
Catharanthus roseus with aluminum. Phytopathology 83:1303-1308.
     Benson, D.M. 1993b. Exchangeable aluminum in potting mixes: Effect on
control of phytophthora damping-offend growth of beddingplants. Bedding
Plants Foundation, East Lansing, Mich., no. F-052.
     Deluca, T.H. and H.D. Shew. 1988. Inhibition of growth and
reproduction of Phytophthora parasitica var. nicotianae by aluminum.
Phytopathology 78:1576.
     Holmes, K.A. and D.M. Benson. 1994. Evaluation of Phytophthora
parasitica var. nicotianae for biocontrol of Phytophthora parasitica on
Catharanthus roseus. Plant Dis. 78:193-199.
     Meyer, J.R and HD. Shew. 1991. Soils suppressive to black root rot of
burley tobacco, caused by Thielaviopsisbasicola. Phytopathology 81
:946-954. 
     Smiley, R.W. and R.J. Cook.1972. Use and abuse of the soil pH
measurement. Phytopathology 62:193-194.
Tisdale, S.L., W.L. Nelson, and J.D. Beaton. 1985. Soil fertility and
fertilizers. 4th ed. Macmillan, New York.
     Yuan, T.L. 1959. Determination of exchangeable hydrogen in soils by a
titration method. Soil Sci. 88:164-167.
     Received for publication 22 Nov. 1994. Accepted for publication 21
July 1995. This research was supported by the North Carolina Agricultural
Research Service, North Carolina State Univ., Raleigh. I thank  Billy I.
Daughtry for  his technical assistance. This publication reports research
involving an arntimicrobial substance. It does not contain recommendations
for its use, nor does it imply that the uses discussed here have been
registered. All uses of pesticides must be registered by appropriate state
and federal agencies before they can be recommended. The cost of publishing
this paper was defrayed in part by the payment of page charges. Under
postal regulations, this paper therefore must be hereby marked
advertisement solely to indicate this fact.
                                         CAPTION FOR FIGURE 1
     Fig. 1. Stand counts for vinca, snapdragon, and petunia grown in a
peat: vermiculite medium limed at 3 kg.m-3 and infested with Phytophthora
parasitica The medium was drenched wirh aluminum sulfate at 0, 10, 25, or
50 meq Al+3/100 cm3 medium. The control designated "ck" was neither
infested nor drenched with aluminum. Mean separation within species (means
of four replications) by the WallerDuncan k ratio t test, k = 100, P =
0.05.
                                              CAPTION FOR FIGURE 2
     Fig. 2. Medium pH at 4 days after seeding and drenching a limed peat:
vermiculite medium with aluminum sulfate at 0, 10, 25, or 50 meq A1+3/100
cm3 medium. Samples were taken at random from plug trays of vinca,
snapdragon, and petunia infested with Phytophthora parasitica. The control
designated "ck" was neither infested nor drenched with aluminum.
                                           CAPTION FOR FIGURE 3
     Fig.3. Exchangeable aluminum (meq Al+3/100 g medium) at 4 days after
seeding and drenching a limed peat : vermiculite medium with aluminum
sulfate at rates of 0, 10, 25, or 50 meq Al+3/100 cm3 medium. Samples were
taken at random from plug trays of vinca, snapdragon, and petunia infested
with Ph tophthora parasitica. The control designated "ck" was neither
infested nor drenched with aluminum. Mean separation (means of two
replications) by the Waller-Duncan k ratio t test, k = 100, P = 0.05.
                                          CAPTION FOR TABLE 1
     Table 1. Growth of bedding plant seedlings in peat: vermiculite medium
infested or noninfected with Phytophthora parasitica and drenched with
aluminum sulfate at O (noninfected and infested controls), 10, 25, or 50
meq Al+3/l00 cm3 medium.
                             I HAVE NOT INCLUDED THE DATA IN THE TABLE.
     (Z) Mean separation within a column by the Waller-Duncan k ratio t
test; k = 100, P = 0.05.
     (Y)First true-leaf length measured at 32 days for vinca seedlings in
plug trays.
     (X) PIant height measured at day 45 for snapdragon seedlings retreated
with aluminum at transplanting 42 daysafter seeding.
     (W) Plant width measured at day 32 for petunia seedlings in plug
trays.




----------
> From: Angelika Burles <angelika@mail.coos.or.us>
> To: seeds-list@eskimo.com
> Subject: Re: Propagation Tools/Misters
> Date: Friday, February 28, 1997 10:58 AM
> 
> Hi,
> 
> >Do I really need to mist the soil on a schedule basis and what is the
> >recommended tool? I have seen seedling misters in the catalogs
> 
> I also have a greenhouse (Northern Lights--just love it!)  Having my
share
> of starting seeds this year.  Lots of damp off.  I read that we should
> never mist our seeds from above......I'm confused.....can someone
clarify?
> ? ?
> 
> Angelika
> 
> Angelika's Knit Club for Machine Knitters
> http://www.coos.or.us/~angelika
> Located on the South Western Oregon Coast
> 2110 North Lake Road
> Lakeside, Or 97449
> Phone/Fax 541-759-3975
Other Mailing lists | Author Index | Date Index | Subject Index | Thread Index