February 2002

Using PGRs on Plugs By Roger Styer

Here it is, the middle of the plug season, and plug growersare wondering how to keep their plugs from stretching or flopping. With shortdays and low light conditions in much of the country during this time of theyear, 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 weretold to put your foot on the gas to make the car go and to take the same footoff the gas and put it on the brake to make the car slow down or stop. Asgrowers, we tend to “keep the petal to the metal” while trying toput on the brake. This occurs because many plug growers fail to understand whatmakes a plant grow. As temperature increases between 50 and 80° F, bothshoot and root growth increase. Below or above this range, growth slows downdramatically. When light levels on the leaf are 3,000 ft. candles,photosynthesis is maximized, and both roots and shoots get enough food. Withlower light levels, the shoots get first priority on the food. With driergrowing conditions, root growth is improved, and under higher humidity, shootgrowth stretches. Feeding plugs with fertilizers high in ammoniacal nitrogen(NH4) and phosphorus (P) will cause more shoot growth and stretching, whereasfertilizers high in nitrate nitrogen (NO3) and calcium (Ca) promote tone androot 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 canminimize the amounts of chemical growth regulators used and still produce abetter 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 onplugs. One of the easiest to work with is B-Nine. This chemical is sprayed torun-off and takes a long time to get into the plant (leaves wet for up to eighthours). It enters plants through the leaves and stems but not the roots. B-Nineworks on a wide range of crops (see Table 2 page 41) and works best in coolerweather where plugs do not grow as fast. Rates generally range from 2,500-5,000ppm. B-Nine can be more effective when used with Cycocel in a tank mix, whichwill be covered later in this article. Too many applications of B-Nine or toohigh of a cumulative concentration tend to delay flowering and reduce flowersize in some crops, particularly petunia and pansy. Avoid using B-Nine withinone week of using copper fungicides, as phytotoxicity can occur.

Cycocel is labeled for a wide range of crops but works beston geraniums, begonias and dianthus (See Table 2 page 46). The best use ofCycocel is as a tank mix with B-Nine. Cycocel, like B-Nine, takes a long timeto get into plants (up to eight hours). It enters plants through leaves andstems 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 aconcentration will produce a leaf yellowing or halo effect, a form ofphytotoxicity. Spray Cycocel as a drift onto dry foliage and when plants arenot under stress. Make sure to note weather conditions to ensure the chemicalwill stay on the plant long enough for absorption.

A-Rest works much better than B-Nine or Cycocel alone and issafer to use than Bonzi or Sumagic on many plug crops (See Table 2 page 46). Itcan be applied by spray, sprench or drench and is absorbed quickly (within 30minutes), entering plants through leaves, stems and roots. Spray ratesgenerally 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 applicationis insignificant when compared to ease of application, plant safety andperformance.

Bonzi and Sumagic are similar chemicals and work the sameway. Both chemicals are labeled for a wide range of crops; enter the plantquickly (within 30 minutes) through stems and roots; and can be sprayed,sprenched or drenched. Since both Bonzi and Sumagic are very strong, overdosingis likely during cool weather or with slow-growing varieties. Common sprayrates 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 thesechemicals is the application method, not the rate. Growers must be careful toapply Bonzi or Sumagic consistently each time and avoid drifting onto sensitivecrops such as begonia and dusty miller.

Florel is an ethylene-producing chemical used for heightcontrol, branching and disbudding. Florel is labeled for a wide range of cropsand is most commonly used with vegetatively-propagated material to replacepinching and improve branching. Florel can be applied as a spray but takes along time (up to eight hours) to get into the plant through the leaves andstems. Spray rates range from 250-500 ppm. Water pH of the spray tank aftermixing in Florel should be 4.0-4.5 for best activity. Avoid spraying plantswhen under stress, as Florel will exaggerate the stress and turn leaves yellow.Florel has been successfully tested on pansy plugs to improve branching aftertransplanting during warm weather.

Tank Mixes

Many plug growers are experimenting with tank mixes,combining two growth regulators to achieve a greater effect than eitherseparately or to lessen negative effects of a particular chemical. The most commontank mix is B-Nine and Cycocel. Spray rates are usually set to control theCycocel halo effect, with the B-Nine rate adjusted for best control. Tank mixrates can Á start at 250 ppm Cycocel plus 500 ppm B-Nine and go up to1,500 ppm Cycocel plus 2,500 ppm B-Nine during the warmest weather and onvigorous varieties. Table 2 page 46 shows a list of crops that benefit fromthis tank mix. This tank mix will control height more than either chemicalseparately, so avoid using rates that are too high. Since both chemicals take along 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-Ninewith A-Rest. Rates generally range from 3-10 ppm A-Rest, combined with1,250-5,000 ppm B-Nine. This mix works well on pansies, petunias and someperennials, as well as other crops. Advantages include less cost for A-Restalone, less total B-Nine going into the crop to reduce flowering and lessoverdosing likely. The difficulty lies in the fact that B-Nine takes a longtime to get into the plant, whereas A-Rest doesn’t. Use of this mixduring warm, dry weather may not give results as good as A-Rest alone.

B-Nine can also be combined with Bonzi to lessen thenegative effects of higher rates of Bonzi and the flowering delay of too muchB-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 isstill a factor. This tank mix works well on petunia, dianthus, celosia and someperennials, as well as other crops. Again, use of this mix during warm, dryweather 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 aspray, sprench or drench whereas B-Nine, Cycocel and Florel are only applied asa spray. A sprench is a combination spray and drench that uses spray or boomwater equipment to apply a volume higher than a spray, obtaining more of adrench effect. Volumes can vary but might be 2-4 times that of a spray.Sprenches are typically done right after seeding and before germination isfinished and cotyledons have totally expanded. The goal is to get the earlyroots to take up the chemical and control early hypopcotyl stretch. Crops suchas cosmos, marigold, zinnia and tall varieties of celosia and snaps willbenefit the most from an early sprench. You can use A-Rest at 1-7 ppm, Bonzi at1-5 ppm or Sumagic at 1/2-3 ppm. When covering seed with coarse vermiculite, itmay take a higher concentration or more volume to get past the vermiculite.

Sprays are most commonly done on plugs when height controlis needed. Typical volume is 2-3 quarts per 100 sq. ft. Optimum chemicalconcentrations are highest in sprays, and there may be some sprenching effectwith A-Rest, Bonzi and Sumagic when leaves do not totally cover the plug mediasurface. B-Nine and Florel are sprayed to run-off; Cycocel is sprayed toglistening; and A-Rest, Bonzi and Sumagic need to be more carefully monitoredfor volume and area covered. Generally, the first growth regulator sprays willbe done when first true leaves have emerged and repeated every 7-14 days. Whenspraying Bonzi or Sumagic, not all crops need the same concentration (See Table3 page 46). Adjust your concentration or speed of application (which affectsvolume of chemical applied) to account for different plug crops.

When plugs are fully grown, it is more difficult to spraysuccessfully 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 ÁA-Rest, Bonzi or Sumagic may work better than a spray. A drench is anapplication in a large volume of water applied directly to the top of the mediato get through the whole plug cell. If the volume increases, the chemicalconcentration should decrease. You want the plug to grow out within 2-3 weeksafter applying the drench. This delay will allow successful holding, as well asdelaying spray applications after transplanting. Rates for an A-Rest drenchrange from 1/2-3 ppm, for Bonzi 1/4-2 ppm and for Sumagic 1/8-1 ppm. Conductyour own trials before drenching on a broad scale to make sure the plugs growout when you want.

Special Situations

When reusing plug trays, growers need to take into accounthow 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 besoaked 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 sprayinggrowth regulators. Try to group crops together that need Bonzi or Sumagic toavoid drifting onto sensitive crops. It is impossible to safely spray adjacentplug crops that have widely varying sensitivity to Bonzi or Sumagic (See Table3, 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 samerate. For instance, grandiflora petunias grow faster than multifloras. Inaddition, not all colors grow at the same rate. White petunias grow faster thanpink, which is faster than red. Plug growers need to take into account thesedifferences when spraying growth regulators. Know which varieties are slow andwhich are fast, and group them together in the greenhouse.

Here it is, the middle of the plug season, and plug growersare wondering how to keep their plugs from stretching or flopping. With shortdays and low light conditions in much of the country during this time of theyear, 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 weretold to put your foot on the gas to make the car go and to take the same footoff the gas and put it on the brake to make the car slow down or stop. Asgrowers, we tend to “keep the petal to the metal” while trying toput on the brake. This occurs because many plug growers fail to understand whatmakes a plant grow. As temperature increases between 50 and 80° F, bothshoot and root growth increase. Below or above this range, growth slows downdramatically. When light levels on the leaf are 3,000 ft. candles,photosynthesis is maximized, and both roots and shoots get enough food. Withlower light levels, the shoots get first priority on the food. With driergrowing conditions, root growth is improved, and under higher humidity, shootgrowth stretches. Feeding plugs with fertilizers high in ammoniacal nitrogen(NH4) and phosphorus (P) will cause more shoot growth and stretching, whereasfertilizers high in nitrate nitrogen (NO3) and calcium (Ca) promote tone androot 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 canminimize the amounts of chemical growth regulators used and still produce abetter 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 onplugs. One of the easiest to work with is B-Nine. This chemical is sprayed torun-off and takes a long time to get into the plant (leaves wet for up to eighthours). It enters plants through the leaves and stems but not the roots. B-Nineworks on a wide range of crops (see Table 2 page 41) and works best in coolerweather where plugs do not grow as fast. Rates generally range from 2,500-5,000ppm. B-Nine can be more effective when used with Cycocel in a tank mix, whichwill be covered later in this article. Too many applications of B-Nine or toohigh of a cumulative concentration tend to delay flowering and reduce flowersize in some crops, particularly petunia and pansy. Avoid using B-Nine withinone week of using copper fungicides, as phytotoxicity can occur.

Cycocel is labeled for a wide range of crops but works beston geraniums, begonias and dianthus (See Table 2 page 46). The best use ofCycocel is as a tank mix with B-Nine. Cycocel, like B-Nine, takes a long timeto get into plants (up to eight hours). It enters plants through leaves andstems 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 aconcentration will produce a leaf yellowing or halo effect, a form ofphytotoxicity. Spray Cycocel as a drift onto dry foliage and when plants arenot under stress. Make sure to note weather conditions to ensure the chemicalwill stay on the plant long enough for absorption.

A-Rest works much better than B-Nine or Cycocel alone and issafer to use than Bonzi or Sumagic on many plug crops (See Table 2 page 46). Itcan be applied by spray, sprench or drench and is absorbed quickly (within 30minutes), entering plants through leaves, stems and roots. Spray ratesgenerally 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 applicationis insignificant when compared to ease of application, plant safety andperformance.

Bonzi and Sumagic are similar chemicals and work the sameway. Both chemicals are labeled for a wide range of crops; enter the plantquickly (within 30 minutes) through stems and roots; and can be sprayed,sprenched or drenched. Since both Bonzi and Sumagic are very strong, overdosingis likely during cool weather or with slow-growing varieties. Common sprayrates 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 thesechemicals is the application method, not the rate. Growers must be careful toapply Bonzi or Sumagic consistently each time and avoid drifting onto sensitivecrops such as begonia and dusty miller.

Florel is an ethylene-producing chemical used for heightcontrol, branching and disbudding. Florel is labeled for a wide range of cropsand is most commonly used with vegetatively-propagated material to replacepinching and improve branching. Florel can be applied as a spray but takes along time (up to eight hours) to get into the plant through the leaves andstems. Spray rates range from 250-500 ppm. Water pH of the spray tank aftermixing in Florel should be 4.0-4.5 for best activity. Avoid spraying plantswhen under stress, as Florel will exaggerate the stress and turn leaves yellow.Florel has been successfully tested on pansy plugs to improve branching aftertransplanting during warm weather.

Tank Mixes

Many plug growers are experimenting with tank mixes,combining two growth regulators to achieve a greater effect than eitherseparately or to lessen negative effects of a particular chemical. The most commontank mix is B-Nine and Cycocel. Spray rates are usually set to control theCycocel halo effect, with the B-Nine rate adjusted for best control. Tank mixrates can Á start at 250 ppm Cycocel plus 500 ppm B-Nine and go up to1,500 ppm Cycocel plus 2,500 ppm B-Nine during the warmest weather and onvigorous varieties. Table 2 page 46 shows a list of crops that benefit fromthis tank mix. This tank mix will control height more than either chemicalseparately, so avoid using rates that are too high. Since both chemicals take along 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-Ninewith A-Rest. Rates generally range from 3-10 ppm A-Rest, combined with1,250-5,000 ppm B-Nine. This mix works well on pansies, petunias and someperennials, as well as other crops. Advantages include less cost for A-Restalone, less total B-Nine going into the crop to reduce flowering and lessoverdosing likely. The difficulty lies in the fact that B-Nine takes a longtime to get into the plant, whereas A-Rest doesn’t. Use of this mixduring warm, dry weather may not give results as good as A-Rest alone.

B-Nine can also be combined with Bonzi to lessen thenegative effects of higher rates of Bonzi and the flowering delay of too muchB-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 isstill a factor. This tank mix works well on petunia, dianthus, celosia and someperennials, as well as other crops. Again, use of this mix during warm, dryweather 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 aspray, sprench or drench whereas B-Nine, Cycocel and Florel are only applied asa spray. A sprench is a combination spray and drench that uses spray or boomwater equipment to apply a volume higher than a spray, obtaining more of adrench effect. Volumes can vary but might be 2-4 times that of a spray.Sprenches are typically done right after seeding and before germination isfinished and cotyledons have totally expanded. The goal is to get the earlyroots to take up the chemical and control early hypopcotyl stretch. Crops suchas cosmos, marigold, zinnia and tall varieties of celosia and snaps willbenefit the most from an early sprench. You can use A-Rest at 1-7 ppm, Bonzi at1-5 ppm or Sumagic at 1/2-3 ppm. When covering seed with coarse vermiculite, itmay take a higher concentration or more volume to get past the vermiculite.

Sprays are most commonly done on plugs when height controlis needed. Typical volume is 2-3 quarts per 100 sq. ft. Optimum chemicalconcentrations are highest in sprays, and there may be some sprenching effectwith A-Rest, Bonzi and Sumagic when leaves do not totally cover the plug mediasurface. B-Nine and Florel are sprayed to run-off; Cycocel is sprayed toglistening; and A-Rest, Bonzi and Sumagic need to be more carefully monitoredfor volume and area covered. Generally, the first growth regulator sprays willbe done when first true leaves have emerged and repeated every 7-14 days. Whenspraying Bonzi or Sumagic, not all crops need the same concentration (See Table3 page 46). Adjust your concentration or speed of application (which affectsvolume of chemical applied) to account for different plug crops.

When plugs are fully grown, it is more difficult to spraysuccessfully 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 ÁA-Rest, Bonzi or Sumagic may work better than a spray. A drench is anapplication in a large volume of water applied directly to the top of the mediato get through the whole plug cell. If the volume increases, the chemicalconcentration should decrease. You want the plug to grow out within 2-3 weeksafter applying the drench. This delay will allow successful holding, as well asdelaying spray applications after transplanting. Rates for an A-Rest drenchrange from 1/2-3 ppm, for Bonzi 1/4-2 ppm and for Sumagic 1/8-1 ppm. Conductyour own trials before drenching on a broad scale to make sure the plugs growout when you want.

Special Situations

When reusing plug trays, growers need to take into accounthow 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 besoaked 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 sprayinggrowth regulators. Try to group crops together that need Bonzi or Sumagic toavoid drifting onto sensitive crops. It is impossible to safely spray adjacentplug crops that have widely varying sensitivity to Bonzi or Sumagic (See Table3, 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 samerate. For instance, grandiflora petunias grow faster than multifloras. Inaddition, not all colors grow at the same rate. White petunias grow faster thanpink, which is faster than red. Plug growers need to take into account thesedifferences when spraying growth regulators. Know which varieties are slow andwhich are fast, and group them together in the greenhouse.