PGR`s - PLANT GROWTH REGULATORS (man made)/ HORMONES (natural)
THIS IS WHAT WHERE WHEN........
Plant growth regulators (PGRs) are chemicals that are designed to affect plant growth and/or development. They are applied for specific purposes to affect specific plant responses right?
Although there is F@#k load of scientific information on using PGRs in the greenhouse, it is not an exact science. Achieving the best results with PGRs is a combination of art and science - science tempered with a lot of trial and error and a good understanding of plant growth and development.
Selecting and Using Plant Growth Regulators on Floricultural Crops
Authors: Original is by Joyce G. Latimer, Extension Specialist, Greenhouse Crops; Virginia Tech Publication Number 430-102, November 2001, i have summarized most of it.
index:
Optimizing Results
Read the Label
Plant Growth Regulators for Height Control
Plant Growth Regulators for Lateral Branching
Plant Growth Regulators for Flowering Application Guidelines
Treat All Recommendations as Starting Rates for Your Own Trials
Recordkeeping
Costs of PGRs
Conclusions and Rate Recommendations
Recommended Resource
Appendix. Helpful conversions
Optimizing Results
1. For best results, PGRs should be handled as production tools, like water and fertilizer.
2. They should not be used as crutches for poor management of other cultural practices.
3. PGRs should be an integrated part of your crop production cycle.
4. They are most effective when applied at the appropriate times to regulate plant growth or development. In other words, growth retardants cannot "shrink" an overgrown plant. They must be applied before the plant is overgrown to avoid plant stretch.
THINGS YOU CAN ACHIEVE:
1. Do you want to reduce the growth rate of the plant, improve its color and general condition (toughness)? If so, you probably want a growth retardant such as B-Nine, Cycocel, A-Rest, Bonzi, or Sumagic.
2. Do you want to increase plant branching for enhanced cutting production, or for a more bushy potted plant or hanging basket? If so, you probably want to use a branching agent or "chemical pincher" such as Atrimmec, FlorelÆ Brand Pistill (Florel), or Off-Shoot-O.
3. Do you want to enhance flower initiation or synchronize flowering? If so, you probably want to use Cycocel, Florel, NAA, GibGro, or ProGibb.
Answering these questions will indicate which type of PGR you need to use to accomplish your goal. It also will determine the most appropriate timing of the application. Then you will need to select a specific PGR in that class and determine the appropriate dosage and the appropriate application method for the selected application. THESE are many Indsutry brands which I intend on useing at some point. As well as the pure forms mentioned in thread.
Read the Label
Plant growth regulators are classified as pesticides so use with care...
- Is the chemical labeled for the crop you wish to treat? Most of the PGR labels have undergone recent revisions that apply to a broad range of similar crops not specifically listed on the label, with the user taking responsibility for determining appropriate rates. This provides label permission to use the compound on these crops without the manufacturer accepting the responsibility for the rate selection.
- Look for information on the effectiveness and on the side effects (phytotoxicity) of the chemical on your specific crop. B-Nine is considered to be a safe, short-term growth retardant with few phytotoxicity problems. However, it has little effect on growth of petunias and may burn treated leaves of kalanchoe. Begonias are extremely sensitive to Bonzi and Sumagic, and the label warns you to avoid overspray or drift on these crops.
- Notice any label warnings regarding the PGR's effect on plant flowering. Many branching enhancers delay flowering. Florel causes flower bud abscission prior to enhancing branching; therefore, it is not recommended within six to eight weeks of Croping.
Plant Growth Regulators for Height Control or SOG
Most of the PGRs used in the greenhouse are used to regulate shoot growth of bedding plants, garden mums, and other containerized crops. These PGRs are referred to as "growth retardants." Typical growth retardants are B-Nine, Cycocel, A-Rest, Bonzi, and Sumagic . These PGRs reduce plant height by inhibiting the production of gibberellins, the primary plant hormones responsible for cell elongation. Therefore, their effects are primarily on stem, petiole and flower stalk tissues. Lesser effects are seen in reductions of leaf expansion, resulting in thicker leaves with darker green color.
Other benefits of using these PGRs in plant production include improved plant appearance by maintaining plant size and shape in proportion with the pot. Plant growth retardants also increase the stress tolerance.
Remember, growth retardants do not reduce plant size. They reduce the plant's growth rate. You must apply the growth retardant prior to the "stretch." Look for recommendations on the PGR label for time of application. These recommendations will be given in terms of plant development or plant size as opposed to production time. For example, the Sumagic label specifies that pansies should have attained a minimum height of four inches prior to application. The Bonzi label says that bedding plant plugs should be treated at the one to two true leaf stage and bedding plants (after transplanting) at two inches of new growth or when the plants reach marketable size.
Generally, growth retarding PGRs should be applied just prior to rapid shoot growth. This is usually one to two weeks after transplanting a plug, after the roots are established and as the plant resumes active growth; on pinched plants, it is after the new shoots are visible, just starting to elongate. This is where the art of plant growth regulation is most important. You must learn how your crop grows and when to intervene to obtain the desired results. Remember to note details of crop development in your records of PGR treatments. For example, due to the weather conditions, next year you may need to treat at seven days after transplanting instead of at the ten days after transplanting that you used this year. Gauge when rapid elongation will likely occur and treat to counter it.
Many growers use multiple applications of growth retardants to better control plant growth. A single application at a high rate early in the plant production cycle may be excessive if growing conditions are not as good as expected. An early application at a lower rate provides more flexibility, but the tradeoff is in the additional labor involved with a second application if it becomes necessary. Some growers improve crop uniformity by using multiple applications of lower rates to affect small corrections in plant growth.
Be careful to avoid very late applications, especially of Bonzi or Sumagic as they may delay flowering .
Plant Growth Regulators for Lateral Branching
Another group of PGRs used in floricultural crops are those that enhance branching, including Florel, Atrimmec and Off-Shoot-O . These PGRs are frequently called "chemical pinchers" because they generally inhibit the growth of the terminal shoots or enhance the growth of lateral buds, thereby increasing the development of lateral branches. They can be used to replace mechanical pinching of many crops. Often this increased branching also will reduce the overall height of the plant. The ethylene released inside the plant by Florel also inhibits internode elongation, keeping treated plants more compact than untreated plants. Florel also affects flowering (see below). If you are looking for enhanced branching, you must have sufficient growth on the plant to allow for sites of lateral development. They cannot enhance lateral branching if there are no laterals on the plant. Again, read the label for details of when to apply for optimum response.
You may need to consider combinations of PGRs. For example, if you apply Florel to enhance the branch development of 'Wave' petunias in a hanging basket, you will probably need to follow up with a treatment of a plant growth retardant like Bonzi to control the elongation of those new laterals. Always consider the side effects of treatments. As mentioned in Tables 1 and 2, some of these PGRs affect flowering which is critical to the successful production of floricultural crops.
Plant Growth Regulators for Flowering
Plant growth regulators can be used to enhance flowering (GibGro) or to remove flowers (Florel). To improve flowering, GibGro, which contains the growth promoter gibberellic acid, can be used to substitute for all or part of the chilling requirement of some woody ornamentals typically forced in the greenhouse, including azalea. [A broad use label was submitted for EPA approval in 2001 for Pro-Gibb (Valent USA) which would include camellia, hydrangea, and a variety of other floricultural crops.] Special attention must be given to the stage of flower bud development for successful treatment. In addition to overcoming dormancy, these compounds can improve flowering and/or bloom size of camellia, geranium, cyclamen, spathiphyllum, statice, and calla lily (see product labels for specific uses). Again, timing is critical since late applications, or excessive rates, may cause excessive plant stretching resulting in weak, spindly stems. Cycocel used to control stem height of hibiscus and geranium also improves early flowering.
Flower removal is especially desirable for stock plants maintained for cuttings of vegetatively propagated ornamentals, like geraniums, fuchsia, begonias, or lantana. Florel (ethephon) is the primary compound used for flower removal. Once ethephon is absorbed by the plant it is converted to gaseous ethylene, a natural plant hormone effective in many plant processes. Ethylene is the primary hormone responsible for flower senescence and fruit ripening. It is the "postharvest" hormone. With proper rates and timing, it will remove unwanted flowers from stock plants or from plugs or young bedding plants.
Flower removal diverts more energy into vegetative growth, increasing the number of laterals available for cuttings on stock plants, and promoting increased branching of plugs and finished plants, which increases fullness in hanging baskets or other containers. Early flower removal also allows synchronization of flowering of a container for a more dramatic appearance or for flowering on a specific marketing date. Since initiation and development of flowers requires time, Florel should not be used on crops within six to eight weeks of marketing.
Application Guidelines
Spray Applications. The pesticide label not only contains information on restrictions but also much information on using the product effectively. The label will identify the target tissue for that PGR - B-Nine is only effective as a foliar spray whereas Bonzi and Sumagic sprays must reach the stems or roots. When making spray applications, look at the physiological development of the plant to see that there is sufficient plant material at the correct stage of growth to make the treatment effective and to accomplish your goal. Generally, there should be sufficient foliage or stems to absorb the PGR. Uptake and effectiveness of a PGR also depend on selecting the application technique that will ensure proper coverage of the target tissue. B-Nine is not soil active and is fairly mobile in the plant. Therefore, a foliar spray application, wetting most of the foliage, will provide a fairly uniform reduction in growth of sensitive crops.
However, the triazoles, Bonzi and Sumagic, are absorbed primarily by stem tissue and then translocated upwards in the plant. Therefore, consistent and complete coverage of the stems is necessary for uniform effects. In other words, if the stem of one lateral receives an inadequate amount of spray, it will grow faster than the others, resulting in a poorly shaped plant, most noticeable in potted crops like poinsettia or chrysanthemum. The triazoles also are very "soil active" which means they may be adsorbed to particles in the media and become available to the plant through root uptake. Therefore, drenching is a very effective application method for these chemicals in crops where it is economically feasible (see How to Apply Drenches below).
The label will provide a recommended application volume for sprays or drenches, especially for chemicals that are soil active. All foliar applications of PGRs should be applied on an area basis, i.e., uniformly spray the area where the plants are located with the recommended volume of solution. Do NOT spray individual plants or spray to reach a subjective target like "spray to glistening." Since every applicator will have a slightly different definition of these goals, there will be no way of recommending appropriate rates or obtaining predictable results. For soil active PGRs, dosage equals the concentration of the solution multiplied by the volume applied in the treated area. Therefore, to improve predictability, the label-recommended spray application rates are generally set at 2 qt. finished spray per 100 sq.ft., a comfortable walking pace for applicators with hand-held sprayers.
Since Bonzi and Sumagic are soil active, precautions should be taken to avoid over-application with sprays. Spray applications require more attention to detail, because overspray material lands or drips onto the medium. Remember that dosage equals concentration times volume. Figure 1 shows the effect of Sumagic application volume on growth of vinca (Catharanthus roseus) at four weeks after treatment. A 1 ppm spray solution of Sumagic was applied at the label recommended volume of 2 qt. per 100 sq. ft., at 3 qt. per 100 sq. ft., or at twice the label rate, 4 qt. per 100 sq. ft. This high volume application was comparable to the amount of spray you might apply "to runoff." These vinca plants were effectively treated with 0, 1, 1.5, or 2 ppm Sumagic (dose = concentration x volume).
Recognizing that stem coverage is necessary for the triazoles, you may need to apply a higher than recommended volume to large or dense plants to obtain adequate coverage. In fact, the Bonzi label recommends 3 qt per 100 sq.ft. for "larger plants with a well developed canopy." Adjust the concentration you apply accordingly. This suggests the importance of record-keeping (see below).
Spray Equipment. To assure proper spray volumes, your compressed air sprayer should be equipped with a pressure gauge and regulator and you should consistently use the same nozzle for all PGR applications. Your sprayer should be calibrated by determining the output of the chemical with the selected nozzle at the selected pressure within a specified time period. Using this information, you can apply a known amount of material to a known area. Spray droplet size also affects response with smaller droplet sizes providing better coverage, but only up to a point. Mist or fog type applicators do NOT provide adequate volume for coverage of plant stems and have not been effective when used with compounds like Bonzi and Sumagic.
The way I tested was to capture your spray for a certin period.
Applying Drenches. Drenches have several advantages over sprays. Drenches generally have less effect on flower or bract size and tend to provide longer lasting growth regulation than sprays. Drenches are easier to apply uniformly than sprays because the drench volume is easily measured, and when applied to moist media, it is easy to obtain good distribution of the PGR in the media. Therefore, the resulting growth regulation is frequently more uniform. The label specifies the recommended volumes for drench applications to different size pots or types of media. Read the label. In general, 4 fl. oz. of drench solution is applied to a six-inch "azalea" pot, and that volume is adjusted up or down with pot size to obtain a volume where about 10% of the solution runs out the bottom of the pot when the media is moist.
Remember that the amount of active ingredient applied to plants using soil-active PGRs is a product of the concentration (ppm) of the solution and the volume applied. Label recommendations for drench applications give solution rates (in ppm) and volume recommendations. In some cases, drench application recommendations are given in terms of milligrams of active ingredient (mg a.i.) per pot. For Bonzi, the label provides mixing directions for mg a.i. solutions for Bonzi, or, you can use the NC State University "PGR Calculator" (See Resources below) to obtain solution directions for drench recommendations using this format.
Other methods of applying PGRs directly to the media have been developed and labeled. For example, Bonzi and A-Rest are labeled for chemigation or application through the irrigation system. These are generally limited to flood (sub-irrigation) or drip irrigation, not overhead sprinkler systems. Again, rates vary with the volumes used and method of application. Bonzi applied once by sub-irrigation requires 50% to 75% of the amount of Bonzi that is applied in a typical drench application. Read and exactly follow the label for chemigation applications.
Other Types of PGR Applications. Three other methods of providing a drench type application of soil-active PGRs on a more economical scale are being used by growers. One is media surface application sprays. These are spray applications made to the surface of the media of filled flats or pots. The treatment is applied at normal to high spray volumes, but since it is applied to the media surface it is activated by irrigation and is available to the plant in the root zone. Both Bonzi and Sumagic are labeled for this method of application. Rates are lower than used for sprays, but higher than used for drench applications.
A second method is called "
sprenches" which is a high volume foliar spray that results in runoff into the media, providing a drench effect. Rates are lower than those recommended for sprays.
A third technique is called "
watering in" where the PGR, A-Rest and Bonzi are currently labeled, is injected into the irrigation water and applied in each irrigation at very low rates of active ingredient.
All of these application methods use the relationship between rate and volume to provide the desired control and preferred application methods. Again, you must develop techniques that fit your production methods and your growth management preferences.
Beware of Bark. For all media applications, be aware that soil-active PGRs tend to be tied up by bark particles in the media which makes it less available to the plants. Therefore, if your media mix is high in bark you will need to compensate for this unavailability by adjusting your application rates up for any type of drench or media applications.
Growing Conditions. Look also for label recommendations on time of day or condition of the plant for optimum treatment response. Generally, a healthy, unstressed plant growing under low evaporative conditions, e.g., early in the morning or late in the afternoon, is most responsive to treatment. To maximize uptake, the chemical must remain in contact with the leaf long enough to be absorbed. This time varies for the different PGRs. Plants treated with B-Nine or Florel should not be overhead irrigated for at least 12 hours after treatment, but plants treated with Bonzi or Sumagic may be irrigated one hour after treatment. Spraying when the treatment will not dry quickly increases absorption of the active ingredients and increases the effectiveness of the treatment. Read the label for any warnings on how irrigation or environmental conditions will affect plant response to the PGR treatment.
Treat All Recommendations as Starting Rates for Your Own Trials
The multitude of variations possible in application methods, cultivar and species grown, and growing conditions make it impossible to recommend specific rates for all operations. There are a couple of general rules for using rate recommendations from other sources:
- Southern growers use higher rates and more frequent applications than Northern growers. Rates for Virginia tend be closer to the Southern rates.
- Outdoor applications usually require higher rates or more frequent applications than for plants grown inside the greenhouse.
Recordkeeping
Making notes on your application methods and the results of your PGR treatments will allow you to improve the consistency of your own application methods and establish rates and volumes appropriate to your production system. Note the concentration and the volume applied, the stage of development of the crop (number of leaves, approximate height, presence of flowers), and the environmental conditions under which the PGR was applied. It is always helpful to keep a few untreated plants for comparison, especially if you are new to using PGRs.
Costs of PGRs
Also consider the cost of the various plant growth regulators in developing your production program. You will need to add your labor and equipment costs to calculate the PGR application costs in your operation. You also will want to consider the costs of multiple applications vs. single applications when determining which PGR to use in a given situation.
Conclusions and Rate Recommendations
Plant growth regulators are valuable production tools that can enhance product quality and marketability while reducing labor for pinching and/or pruning and plant maintenance. They must be used with proper attention to other cultural practices, especially proper fertility and irrigation management. Plant growth regulators cannot correct poor production practices.
Plant growth regulator recommendations for a wide variety of floricultural crops are listed. These rates are label recommended rates and should be evaluated under your own growing conditions. For more information on rates for herbaceous perennials see VCE Publication 430-103, Using Plant Growth Regulators on Containerized Herbaceous Perennials.
Recommended Resource
For a ready resource on preparing PGR solutions, download the North Carolina State University Plant Growth Regulator Calculator from:
http://www.ces.ncsu.edu/depts/hort/floriculture/software/pgr.html
software allows growers to calculate the amounts of A-Rest, Atrimmec, B-Nine, Bonzi, Cycocel, Dazide, Downsize, Facination, Florel, Fresco, GibGro, Paczol, Piccolo, ProGibb, Sumagic, or Topflor needed to create any spray or drench solution you desire. If you enter your costs for each PGR, it will also calculate your materials cost per application as well as per plant treated. By entering plant dimensions and application rate per unit area, it will calculate the amount of active ingredient each plant received during application
Appendix. Helpful conversions.
Volume
1 gallon (gal) = 128 fluid ounces (fl oz)
1 fl oz = 30 milliliters (ml)
1 gal = 3785 ml = 3.785 liters
1 cup = 48 teaspoons
1 tablespoon = 3 teaspoons
1 fl oz = 2 tablespoons = 6 teaspoons
Weight
1 ounce (oz) = 28.3 grams (g)
1 pound (lb) = 16 oz = 454 g
Concentration
1% = 10,000 ppm
1 ppm = 1 milligram (mg) per liter
.... meaning people who dont know squat about them may be able to have a good start.... 
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