Using PGRs on Plugs

March 1, 2002 - 11:45

Knowing which chemical to use under which circumstances can mean the difference between a successful crop and a waste of time and money.

Here it is, the middle of the plug season, and plug growers
are wondering how to keep their plugs from stretching or flopping. With short
days and low light conditions in much of the country during this time of the
year, small seedlings want to stretch while the roots take their time growing.
And, once the weather warms up, many of the plug crops will really take off,
catching growers by surprise.

To control plug growth, you need to understand the
“gas v. brake” concept. When you learned to drive a car, you were
told to put your foot on the gas to make the car go and to take the same foot
off the gas and put it on the brake to make the car slow down or stop. As
growers, we tend to “keep the petal to the metal” while trying to
put on the brake. This occurs because many plug growers fail to understand what
makes a plant grow. As temperature increases between 50 and 80° F, both
shoot and root growth increase. Below or above this range, growth slows down
dramatically. When light levels on the leaf are 3,000 ft. candles,
photosynthesis is maximized, and both roots and shoots get enough food. With
lower light levels, the shoots get first priority on the food. With drier
growing conditions, root growth is improved, and under higher humidity, shoot
growth stretches. Feeding plugs with fertilizers high in ammoniacal nitrogen
(NH4) and phosphorus (P) will cause more shoot growth and stretching, whereas
fertilizers high in nitrate nitrogen (NO3) and calcium (Ca) promote tone and
root growth. Increasing carbon dioxide (CO2) levels above ambient, 1,000 ppm,
will promote both roots and shoots (see Table 1 page 43).

When plug growers control the above factors, they can
minimize the amounts of chemical growth regulators used and still produce a
better quality plug. However, chemical growth regulators will still need to be used on many crops. The key is to understand which growth regulator works best on which crop, under what circumstances and at which levels. Knowing when to apply the right chemical for a particular crop is usually learned by painful trial and error. Varieties may react quite differently to the same chemical.

Available Chemicals

There are a number of chemical growth regulators for use on
plugs. One of the easiest to work with is B-Nine. This chemical is sprayed to
run-off and takes a long time to get into the plant (leaves wet for up to eight
hours). It enters plants through the leaves and stems but not the roots. B-Nine
works on a wide range of crops (see Table 2 page 41) and works best in cooler
weather where plugs do not grow as fast. Rates generally range from 2,500-5,000
ppm. B-Nine can be more effective when used with Cycocel in a tank mix, which
will be covered later in this article. Too many applications of B-Nine or too
high of a cumulative concentration tend to delay flowering and reduce flower
size in some crops, particularly petunia and pansy. Avoid using B-Nine within
one week of using copper fungicides, as phytotoxicity can occur.

Cycocel is labeled for a wide range of crops but works best
on geraniums, begonias and dianthus (See Table 2 page 46). The best use of
Cycocel is as a tank mix with B-Nine. Cycocel, like B-Nine, takes a long time
to get into plants (up to eight hours). It enters plants through leaves and
stems and can be used as a drench but rates (and cost) are prohibitively high.
Spray rates commonly used on plugs range from 250-1,500 ppm. Too high of a
concentration will produce a leaf yellowing or halo effect, a form of
phytotoxicity. Spray Cycocel as a drift onto dry foliage and when plants are
not under stress. Make sure to note weather conditions to ensure the chemical
will stay on the plant long enough for absorption.

A-Rest works much better than B-Nine or Cycocel alone and is
safer to use than Bonzi or Sumagic on many plug crops (See Table 2 page 46). It
can be applied by spray, sprench or drench and is absorbed quickly (within 30
minutes), entering plants through leaves, stems and roots. Spray rates
generally range from 1-15 ppm. A-Rest works very well on pansy, vinca, salvia,
snapdragon and dianthus but is not effective on impatiens. Cost per application
is insignificant when compared to ease of application, plant safety and
performance.

Bonzi and Sumagic are similar chemicals and work the same
way. Both chemicals are labeled for a wide range of crops; enter the plant
quickly (within 30 minutes) through stems and roots; and can be sprayed,
sprenched or drenched. Since both Bonzi and Sumagic are very strong, overdosing
is likely during cool weather or with slow-growing varieties. Common spray
rates for Bonzi range from 1-30 ppm, and for Sumagic from 1-15 ppm. Generally,
for Sumagic, rates are 1/5-1/2 that of Bonzi. The main problem with these
chemicals is the application method, not the rate. Growers must be careful to
apply Bonzi or Sumagic consistently each time and avoid drifting onto sensitive
crops such as begonia and dusty miller.

Florel is an ethylene-producing chemical used for height
control, branching and disbudding. Florel is labeled for a wide range of crops
and is most commonly used with vegetatively-propagated material to replace
pinching and improve branching. Florel can be applied as a spray but takes a
long time (up to eight hours) to get into the plant through the leaves and
stems. Spray rates range from 250-500 ppm. Water pH of the spray tank after
mixing in Florel should be 4.0-4.5 for best activity. Avoid spraying plants
when under stress, as Florel will exaggerate the stress and turn leaves yellow.
Florel has been successfully tested on pansy plugs to improve branching after
transplanting during warm weather.

Tank Mixes

Many plug growers are experimenting with tank mixes,
combining two growth regulators to achieve a greater effect than either
separately or to lessen negative effects of a particular chemical. The most common
tank mix is B-Nine and Cycocel. Spray rates are usually set to control the
Cycocel halo effect, with the B-Nine rate adjusted for best control. Tank mix
rates can Á start at 250 ppm Cycocel plus 500 ppm B-Nine and go up to
1,500 ppm Cycocel plus 2,500 ppm B-Nine during the warmest weather and on
vigorous varieties. Table 2 page 46 shows a list of crops that benefit from
this tank mix. This tank mix will control height more than either chemical
separately, so avoid using rates that are too high. Since both chemicals take a
long time to get into the plant, try to keep foliage wet as long as possible.

Another tank mix that some growers are using combines B-Nine
with A-Rest. Rates generally range from 3-10 ppm A-Rest, combined with
1,250-5,000 ppm B-Nine. This mix works well on pansies, petunias and some
perennials, as well as other crops. Advantages include less cost for A-Rest
alone, less total B-Nine going into the crop to reduce flowering and less
overdosing likely. The difficulty lies in the fact that B-Nine takes a long
time to get into the plant, whereas A-Rest doesn’t. Use of this mix
during warm, dry weather may not give results as good as A-Rest alone.

B-Nine can also be combined with Bonzi to lessen the
negative effects of higher rates of Bonzi and the flowering delay of too much
B-Nine. Rates range from 5-20 ppm for Bonzi and 1,250-5,000 ppm for B-Nine.
Chemical costs are less than using the separate chemicals, but spray volume is
still a factor. This tank mix works well on petunia, dianthus, celosia and some
perennials, as well as other crops. Again, use of this mix during warm, dry
weather may not give results as good as using Bonzi alone.

Application Method and Stage of Development

A-Rest, Bonzi and Sumagic can be applied to plugs as a
spray, sprench or drench whereas B-Nine, Cycocel and Florel are only applied as
a spray. A sprench is a combination spray and drench that uses spray or boom
water equipment to apply a volume higher than a spray, obtaining more of a
drench effect. Volumes can vary but might be 2-4 times that of a spray.
Sprenches are typically done right after seeding and before germination is
finished and cotyledons have totally expanded. The goal is to get the early
roots to take up the chemical and control early hypopcotyl stretch. Crops such
as cosmos, marigold, zinnia and tall varieties of celosia and snaps will
benefit the most from an early sprench. You can use A-Rest at 1-7 ppm, Bonzi at
1-5 ppm or Sumagic at 1/2-3 ppm. When covering seed with coarse vermiculite, it
may take a higher concentration or more volume to get past the vermiculite.

Sprays are most commonly done on plugs when height control
is needed. Typical volume is 2-3 quarts per 100 sq. ft. Optimum chemical
concentrations are highest in sprays, and there may be some sprenching effect
with A-Rest, Bonzi and Sumagic when leaves do not totally cover the plug media
surface. B-Nine and Florel are sprayed to run-off; Cycocel is sprayed to
glistening; and A-Rest, Bonzi and Sumagic need to be more carefully monitored
for volume and area covered. Generally, the first growth regulator sprays will
be done when first true leaves have emerged and repeated every 7-14 days. When
spraying Bonzi or Sumagic, not all crops need the same concentration (See Table
3 page 46). Adjust your concentration or speed of application (which affects
volume of chemical applied) to account for different plug crops.

When plugs are fully grown, it is more difficult to spray
successfully with Bonzi or Sumagic, as stems and roots are covered by leaves. Remember, Bonzi and Sumagic are not taken up by leaves. For plug growers who grow their own plugs and need to hold them before transplanting, a drench with Á
A-Rest, Bonzi or Sumagic may work better than a spray. A drench is an
application in a large volume of water applied directly to the top of the media
to get through the whole plug cell. If the volume increases, the chemical
concentration should decrease. You want the plug to grow out within 2-3 weeks
after applying the drench. This delay will allow successful holding, as well as
delaying spray applications after transplanting. Rates for an A-Rest drench
range from 1/2-3 ppm, for Bonzi 1/4-2 ppm and for Sumagic 1/8-1 ppm. Conduct
your own trials before drenching on a broad scale to make sure the plugs grow
out when you want.

Special Situations

When reusing plug trays, growers need to take into account
how much Bonzi or Sumagic residue is left on the surface from previous crops.
The higher the spray rates, the more residue. The standard 15-minute dip for cleaning trays will not be sufficient to remove Sumagic or Bonzi. Trays need to be
soaked for 45-60 minutes. Crops most sensitive to this residue include begonia,
pansy and dusty miller.

Placement of sensitive crops can be a problem when spraying
growth regulators. Try to group crops together that need Bonzi or Sumagic to
avoid drifting onto sensitive crops. It is impossible to safely spray adjacent
plug crops that have widely varying sensitivity to Bonzi or Sumagic (See Table
3, left). Growers need to make sure they are not trying to spray too far away.

Not all varieties of a particular crop grow at the same
rate. For instance, grandiflora petunias grow faster than multifloras. In
addition, not all colors grow at the same rate. White petunias grow faster than
pink, which is faster than red. Plug growers need to take into account these
differences when spraying growth regulators. Know which varieties are slow and
which are fast, and group them together in the greenhouse.

Here it is, the middle of the plug season, and plug growers
are wondering how to keep their plugs from stretching or flopping. With short
days and low light conditions in much of the country during this time of the
year, small seedlings want to stretch while the roots take their time growing.
And, once the weather warms up, many of the plug crops will really take off,
catching growers by surprise.

To control plug growth, you need to understand the
“gas v. brake” concept. When you learned to drive a car, you were
told to put your foot on the gas to make the car go and to take the same foot
off the gas and put it on the brake to make the car slow down or stop. As
growers, we tend to “keep the petal to the metal” while trying to
put on the brake. This occurs because many plug growers fail to understand what
makes a plant grow. As temperature increases between 50 and 80° F, both
shoot and root growth increase. Below or above this range, growth slows down
dramatically. When light levels on the leaf are 3,000 ft. candles,
photosynthesis is maximized, and both roots and shoots get enough food. With
lower light levels, the shoots get first priority on the food. With drier
growing conditions, root growth is improved, and under higher humidity, shoot
growth stretches. Feeding plugs with fertilizers high in ammoniacal nitrogen
(NH4) and phosphorus (P) will cause more shoot growth and stretching, whereas
fertilizers high in nitrate nitrogen (NO3) and calcium (Ca) promote tone and
root growth. Increasing carbon dioxide (CO2) levels above ambient, 1,000 ppm,
will promote both roots and shoots (see Table 1 page 43).

When plug growers control the above factors, they can
minimize the amounts of chemical growth regulators used and still produce a
better quality plug. However, chemical growth regulators will still need to be used on many crops. The key is to understand which growth regulator works best on which crop, under what circumstances and at which levels. Knowing when to apply the right chemical for a particular crop is usually learned by painful trial and error. Varieties may react quite differently to the same chemical.

Available Chemicals

There are a number of chemical growth regulators for use on
plugs. One of the easiest to work with is B-Nine. This chemical is sprayed to
run-off and takes a long time to get into the plant (leaves wet for up to eight
hours). It enters plants through the leaves and stems but not the roots. B-Nine
works on a wide range of crops (see Table 2 page 41) and works best in cooler
weather where plugs do not grow as fast. Rates generally range from 2,500-5,000
ppm. B-Nine can be more effective when used with Cycocel in a tank mix, which
will be covered later in this article. Too many applications of B-Nine or too
high of a cumulative concentration tend to delay flowering and reduce flower
size in some crops, particularly petunia and pansy. Avoid using B-Nine within
one week of using copper fungicides, as phytotoxicity can occur.

Cycocel is labeled for a wide range of crops but works best
on geraniums, begonias and dianthus (See Table 2 page 46). The best use of
Cycocel is as a tank mix with B-Nine. Cycocel, like B-Nine, takes a long time
to get into plants (up to eight hours). It enters plants through leaves and
stems and can be used as a drench but rates (and cost) are prohibitively high.
Spray rates commonly used on plugs range from 250-1,500 ppm. Too high of a
concentration will produce a leaf yellowing or halo effect, a form of
phytotoxicity. Spray Cycocel as a drift onto dry foliage and when plants are
not under stress. Make sure to note weather conditions to ensure the chemical
will stay on the plant long enough for absorption.

A-Rest works much better than B-Nine or Cycocel alone and is
safer to use than Bonzi or Sumagic on many plug crops (See Table 2 page 46). It
can be applied by spray, sprench or drench and is absorbed quickly (within 30
minutes), entering plants through leaves, stems and roots. Spray rates
generally range from 1-15 ppm. A-Rest works very well on pansy, vinca, salvia,
snapdragon and dianthus but is not effective on impatiens. Cost per application
is insignificant when compared to ease of application, plant safety and
performance.

Bonzi and Sumagic are similar chemicals and work the same
way. Both chemicals are labeled for a wide range of crops; enter the plant
quickly (within 30 minutes) through stems and roots; and can be sprayed,
sprenched or drenched. Since both Bonzi and Sumagic are very strong, overdosing
is likely during cool weather or with slow-growing varieties. Common spray
rates for Bonzi range from 1-30 ppm, and for Sumagic from 1-15 ppm. Generally,
for Sumagic, rates are 1/5-1/2 that of Bonzi. The main problem with these
chemicals is the application method, not the rate. Growers must be careful to
apply Bonzi or Sumagic consistently each time and avoid drifting onto sensitive
crops such as begonia and dusty miller.

Florel is an ethylene-producing chemical used for height
control, branching and disbudding. Florel is labeled for a wide range of crops
and is most commonly used with vegetatively-propagated material to replace
pinching and improve branching. Florel can be applied as a spray but takes a
long time (up to eight hours) to get into the plant through the leaves and
stems. Spray rates range from 250-500 ppm. Water pH of the spray tank after
mixing in Florel should be 4.0-4.5 for best activity. Avoid spraying plants
when under stress, as Florel will exaggerate the stress and turn leaves yellow.
Florel has been successfully tested on pansy plugs to improve branching after
transplanting during warm weather.

Tank Mixes

Many plug growers are experimenting with tank mixes,
combining two growth regulators to achieve a greater effect than either
separately or to lessen negative effects of a particular chemical. The most common
tank mix is B-Nine and Cycocel. Spray rates are usually set to control the
Cycocel halo effect, with the B-Nine rate adjusted for best control. Tank mix
rates can Á start at 250 ppm Cycocel plus 500 ppm B-Nine and go up to
1,500 ppm Cycocel plus 2,500 ppm B-Nine during the warmest weather and on
vigorous varieties. Table 2 page 46 shows a list of crops that benefit from
this tank mix. This tank mix will control height more than either chemical
separately, so avoid using rates that are too high. Since both chemicals take a
long time to get into the plant, try to keep foliage wet as long as possible.

Another tank mix that some growers are using combines B-Nine
with A-Rest. Rates generally range from 3-10 ppm A-Rest, combined with
1,250-5,000 ppm B-Nine. This mix works well on pansies, petunias and some
perennials, as well as other crops. Advantages include less cost for A-Rest
alone, less total B-Nine going into the crop to reduce flowering and less
overdosing likely. The difficulty lies in the fact that B-Nine takes a long
time to get into the plant, whereas A-Rest doesn’t. Use of this mix
during warm, dry weather may not give results as good as A-Rest alone.

B-Nine can also be combined with Bonzi to lessen the
negative effects of higher rates of Bonzi and the flowering delay of too much
B-Nine. Rates range from 5-20 ppm for Bonzi and 1,250-5,000 ppm for B-Nine.
Chemical costs are less than using the separate chemicals, but spray volume is
still a factor. This tank mix works well on petunia, dianthus, celosia and some
perennials, as well as other crops. Again, use of this mix during warm, dry
weather may not give results as good as using Bonzi alone.

Application Method and Stage of Development

A-Rest, Bonzi and Sumagic can be applied to plugs as a
spray, sprench or drench whereas B-Nine, Cycocel and Florel are only applied as
a spray. A sprench is a combination spray and drench that uses spray or boom
water equipment to apply a volume higher than a spray, obtaining more of a
drench effect. Volumes can vary but might be 2-4 times that of a spray.
Sprenches are typically done right after seeding and before germination is
finished and cotyledons have totally expanded. The goal is to get the early
roots to take up the chemical and control early hypopcotyl stretch. Crops such
as cosmos, marigold, zinnia and tall varieties of celosia and snaps will
benefit the most from an early sprench. You can use A-Rest at 1-7 ppm, Bonzi at
1-5 ppm or Sumagic at 1/2-3 ppm. When covering seed with coarse vermiculite, it
may take a higher concentration or more volume to get past the vermiculite.

Sprays are most commonly done on plugs when height control
is needed. Typical volume is 2-3 quarts per 100 sq. ft. Optimum chemical
concentrations are highest in sprays, and there may be some sprenching effect
with A-Rest, Bonzi and Sumagic when leaves do not totally cover the plug media
surface. B-Nine and Florel are sprayed to run-off; Cycocel is sprayed to
glistening; and A-Rest, Bonzi and Sumagic need to be more carefully monitored
for volume and area covered. Generally, the first growth regulator sprays will
be done when first true leaves have emerged and repeated every 7-14 days. When
spraying Bonzi or Sumagic, not all crops need the same concentration (See Table
3 page 46). Adjust your concentration or speed of application (which affects
volume of chemical applied) to account for different plug crops.

When plugs are fully grown, it is more difficult to spray
successfully with Bonzi or Sumagic, as stems and roots are covered by leaves. Remember, Bonzi and Sumagic are not taken up by leaves. For plug growers who grow their own plugs and need to hold them before transplanting, a drench with Á
A-Rest, Bonzi or Sumagic may work better than a spray. A drench is an
application in a large volume of water applied directly to the top of the media
to get through the whole plug cell. If the volume increases, the chemical
concentration should decrease. You want the plug to grow out within 2-3 weeks
after applying the drench. This delay will allow successful holding, as well as
delaying spray applications after transplanting. Rates for an A-Rest drench
range from 1/2-3 ppm, for Bonzi 1/4-2 ppm and for Sumagic 1/8-1 ppm. Conduct
your own trials before drenching on a broad scale to make sure the plugs grow
out when you want.

Special Situations

When reusing plug trays, growers need to take into account
how much Bonzi or Sumagic residue is left on the surface from previous crops.
The higher the spray rates, the more residue. The standard 15-minute dip for cleaning trays will not be sufficient to remove Sumagic or Bonzi. Trays need to be
soaked for 45-60 minutes. Crops most sensitive to this residue include begonia,
pansy and dusty miller.

Placement of sensitive crops can be a problem when spraying
growth regulators. Try to group crops together that need Bonzi or Sumagic to
avoid drifting onto sensitive crops. It is impossible to safely spray adjacent
plug crops that have widely varying sensitivity to Bonzi or Sumagic (See Table
3, left). Growers need to make sure they are not trying to spray too far away.

Not all varieties of a particular crop grow at the same
rate. For instance, grandiflora petunias grow faster than multifloras. In
addition, not all colors grow at the same rate. White petunias grow faster than
pink, which is faster than red. Plug growers need to take into account these
differences when spraying growth regulators. Know which varieties are slow and
which are fast, and group them together in the greenhouse.

About The Author

Dr. Roger C. Styer is President, Styer’s Horticultural Consulting, Inc., Batavia, Ill. He can be reached by phone at (630) 208-0542 or E-mail at carleton@voyager.net

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