Floriculture Greenhouse Update

Plants at many greenhouses appear to be a little ahead. If you are thinking about holding plants using growth regulators, review the message: Using Plant Growth Regulators to Hold Finished Plants. A proper hold rate using growth regulators should give enough control to hold a mature plant under hot weather for 2-3 weeks but low enough that the plant will recover and grow for the consumer. Spray treatments carry less of a risk of overdose than drench treatment, especially when the root-active PGRs are used.Monitor for powdery mildew on gerberas. A good short video on the subject is available from Floricast by Margery Daughtery, Cornell University.Spider mites continue to be a problem on crops such as ivy geraniums and mandevilla and on perennials such as salvia, monarda, nepeta and perovskia. Spider mite injury on ivy geraniums looks like oedema, so be sure to monitor carefully with a hand-lens. See photos of oedema vs spider mite damage.

See message: Managing Two-spotted spider mites  Spider mites are very successful at surviving over the winter in their resting stage. The can hibernate in any crevices in the greenhouse so growers having problems last year are likely to have problems this year.Finally, when sunshine turns to clouds and rain, avoid wet foliage, reduce humidity by heating and venting and monitor for Botrytis. See messages: Heating and Venting and Botrytis

Leanne Pundt, University of ConnecticutTina Smith, University of Massachusetts

Many growers are reporting that mums are shorter and are flowering earlier this season. Cool temperatures,cloudy and rainy weather have been the norm this summer. Take advantage of sunny days to fertilize plants.

Premature budding Chrysanthemum flower buds initiate easily and develop rapidly, especially if plants are stressed in any way. Lack of adequate fertilizer and cool nights are causes for premature budding. When grown outdoors, we are relying on natural daylength and temperature to control the timing of the crop. Chrysanthemums are short-day plants. Both flower initiation and development of the flower buds occur more rapidly under short days than in long days. However, temperature has a greater influence than daylength on flowering of garden mums. With several cool nights in a row, garden mums can initiate many buds prematurely which results in early flowering of plants.

Short plants. Again, short plants are a result of plants setting bud too early. In chrysanthemums, flower bud initiation marks the end of vegetative growth. Garden mums initiate leaves rapidly. Cool weather early in the growing season will reduce the number of leaves formed on each shoot, thereby, resulting in plants with fewer nodes and shorter plants. Another reason for smaller, harder plants may be due to lack of nutrients. Frequent rain made it difficult to keep plants fertilized. As a result, nutrients were leached and plants stopped growing.

How growers responded. Some growers pinched buds off of plants (in July) and fertilized more often with higher rates (350 ppm) to allow plants to grow larger and flower later. This may not work for very early and early flowering varieties that are programmed to flower early.

Some growers left buds on plants and fertilized with up to 400 ppm nitrogen of 20-10-20. Some growers even included ammonium forms of nitrogen (20-20-20) in their fertilizer program. The theory being that vegetative growth would by-pass the budded growth. In some cases this has worked while for most it resulted in uneven plants with short, budded or flowering plants surrounded by some tall growth, but not enough to fill out the plant, creating two-tiered plants. Growers also reported that the plant’s response has varied according to the variety.

At this time, mums should receive constant feed of 300 ppm nitrogen from fertilizers like 20-10-20 to promote vegetative growth. Reapply up to 400 ppm after each rain to keep sufficient nutrient levels. Note that root health should be monitored.  Diseased roots will not take up fertilizer.

Final note: Some growers have asked about using Fascination [a cocktail of two plant hormones, gibberellic acid (GA4+7) and benzyladenine (BA) in equalproportions] to increase plant height. Fascination increases height by stretching the distance between the leaves. Trials using Fascination on poinsettias have shown that it will stretch soft tissue about an inch per application. Response is quick, within one week of application you will know how much additional growth the treatment produced.  Application can be repeated as needed but results are best when shoot growth is still soft and several of the upper internodes have not yet expanded. Once stems harden they will be less responsive to treatment and late treatments may just cause the flower buds to stretch above the foliage. Trials using Fascination on garden mums has been minimal at this time but preliminary results show increased stem length with a 10ppm spray application. 

For more information (and photo) of Fascination on mums: GroLink July Newsletter

Tina Smith, University of Massachusetts Rich McAvoy, University of Connecticut

Pesticide phytotoxicity on plants can often be distinguished from pest problems by the pattern and timing of symptom development. Although the damage may take up to several days or more to occur, pesticide damage symptoms often occur all at once and have a regular distribution on the crop. Symptoms caused by pathogens usually develop over an extended period of time in random or grouped patterns. Pesticide phytotoxicity can be expressed by a number of different symptoms, including leaf speckling, cupping and twisting and other leaf distortions or plant death. Pesticides with hormone-type activity such as the insect growth regulator Distance and herbicides containing 2,4-D tend to produce leaf cupping and twisting. Other pesticides that have caused twisted growth include Judo applied to dracaena plugs and Botanigard ES applied to tomato plants.

Phytotoxicity can also be caused by the solvents in a formulation (EC formulation vs WP), impurities in spray water, using a higher rate of pesticide than is listed on the label, tank-mixing or inadequately mixing the spray solution. Environmental conditions such the temperature, humidity, and light can also influence phytotoxicity. High temperatures can speed up pesticide degradation and volatilization, but may also result in increased phytotoxicity for some products. Plants that are stressed are more susceptible to pesticide injury.

Growers can prevent pesticide damage to plants by applying pesticides during the cooler part of the day such as the early morning or evening. Treatments made in the early morning allow foliage to dry before temperatures reach 85-90°F. Take special precautions when using oils. Treat when conditions allow plants to dry quickly. Other suggestions to prevent burning plants with pesticides include:

• Add surfactants only when recommended on the pesticide label.
• Never use a sprayer for insecticides that was previously used to apply herbicides.
• Do not apply pesticides to plants that are under moisture stress.
• Avoid using more than one emulsifiable concentrate in a tank mix.
• Do not apply pesticides with fertilizers unless the label states otherwise.
• Never use broad-leaved weed killers and brush killers around the greenhouse.

To prevent injury due to pesticides, be sure to follow label directions exactly. See the company's website to read any technical bulletins about the product or call the company's technical representative before using a product for the first time.

If minor phytotoxicity is suspected from foliar applications of an insecticide, miticide or fungicide, watch the new growth as it emerges. Plants will often grow out of one-time spray damage. As plants grow, the damage will remain on the oldest leaves and the new growth will appear healthy.

Photos Plant Growth Regulator Overdose Judo injury on dracaena plugs and ivy geraniums (See technical bulletin for list of crops for which Judo should not be used) Distance injury on poinsettia BotaniGard injury on tomato plants, 2 Herbicide injury on tomato and geranium

Tina Smith, University of Massachusetts

As garden mums continue to arrive at greenhouses, growers are asking about using Florel. The following information from Rick Yates, Griffin Greenhouse and Nursery Supplies Inc. provides some good details on using Florel.

Florel can be used to replace mechanical pinching when applied as a thorough foliar spray at 500 PPM (1.6 oz./gal.). Typically this is done one week before you would hand pinch. Even though your cell pack mums are pinched when you receive them, they will benefit from an application of Florel applied as soon as possible after they arrive. While this initial spray to pinched cuttings does not increase branching, it does reduce premature budding by getting the plants under the influence of Florel as early as possible. Repeated at two week intervals, Florel helps to keep plants vegetative as well as providing more breaks per plant when compared to hand pinching. Florel also reduces internode elongation, reducing or eliminating the need for other growth regulators later in the season. Labor savings are significant and greatly appreciated! Using more than 1 pinch and 2 Florel treatments (counting the one applied when you received the pinched cuttings) is not usually desirable. So many branches are produced that stem strength is reduced and the plants may pull apart at flowering. Most growers report great results from one application upon arrival, and one more 14 days later. You can also "time" your crop with Florel, since it delays flowering. Make your last Florel application before July 1st to avoid delaying the natural season flower date. CAUTION: Highly alkaline water may need to be treated in order for Florel to be effective. When Florel is added to your spray tank it must be able to drop the pH of that solution to between 4.0 and 5.0 to work properly. Distilled or acidified water may be needed in some cases. Using pHase5 to adjust the pH of the spray water to between 5.5 and 6.0 before adding the Florel will allow the final solution to be in the correct range.

Sample Program (normal season flowering)

• Pinched cuttings arrive about June 10th and are sprayed upon arrival with Florel @ 500 ppm
• Two days later (allows for 48 hr REI for Florel) cuttings are potted into 8 x 5 or 9 x 6 mum pans.
• Reapply Florel @ 500 ppm two weeks after the first treatment (~ June 24th)

Fact Sheet: Garden Mums from Cell Packs (PDF) by Rick Yates, Griffin Greenhouse and Nursery Supplies, Inc.

Tina Smith

Growers sometimes need to hold plants in check once they reach or approach the final size. This is especially true when weather conditions dictate that plants be held longer than anticipated. Under these circumstances, a spray or drench application of one of the more root-active compounds (A-Rest, Bonzi, Sumagic, Topflor) can do the trick. The danger here is that an overdose can have a long residual effect and if over done the plants may not perform in the garden for the consumer. For a proper hold, select a concentration in the upper half of the normal recommended range for that crop. You can even go 50% higher than the rate recommended for slowing growth during the grow-out stage. For instance, the normal spray rate for A-Rest on Ageratum in flats during grow-out is 10-15ppm, but a rate of 15-26ppm is recommended to hold this crop. The same principle would apply for the other PGR compounds. Note, I would not recommend Cycocel for this purpose since the spray rates required would be so high that phytotoxic injury would be likely to occur.

If you don't have experience with using PGRs to put a hold on growth, start with the high end of the normal recommended rate. You can always do a second treatment if the first is not enough. A proper hold rate should give enough control to hold a mature plant under hot weather for 2-3 weeks but low enough that the plant will recover and grow for the consumer. Spray treatments carry less of a risk of overdose than drench treatment, especially when the root-active PGRs are used.

Photos: Plant Growth Regulator Overdose, 2

2007-2008 New England Floriculture Guide: About Growth Regulators

Fact Sheet: Growth Regulators for Bedding Plants

Rich McAvoy

A grower sometimes must deal with PGR overdose situations. Overdosing with PGRs can happen in several ways including miscalculation during mixing, applying specific chemicals to ultra-sensitive species, selecting a PGR rate that is too high for the species, stage of development or prevailing environmental conditions, or applying a PGR too frequently. In addition, inadvertent spray drift and inadvertent overlap during treatment can also result in overdose.

Once an overdose is suspected, a grower has a number of options to mitigate the effects. If an overdose spray of Cycocel or B-Nine (or the generic equivalents of these compounds) is applied and the mistake is discovered before the spray dries (usually within 30 minutes of initial application), the material can be washed off with a hose and the damage avoided. This is not an option with materials like Bonzi, Sumagic, Topflor or A-Rest. If the range of overdose is only modestly high, for example 25-50% too high a rate, then environmental conditions that minimize stress may be enough to allow the plant to recover without further intervention. In this scenario, adequate sunlight combined with increased temperatures, increase fertilization, and reduced water stress will all favor rapid growth and allow the plant to out grow the adverse effects of the overdose. In circumstances where the dose is too high to mitigate in this way, a gibberellic acid treatment can be used to reverse the effect of the PGR. Remember, growth retardants (Cycocel, B-Nine, Bonzi, Sumagic, Topflor & A-Rest) inhibit gibberellic acid (GA) activity in the plant. Therefore applying GA products such as Fascination (or the generic equivalent) will produce a plant response just the opposite of the PGR.

For bedding plants, spray Fascination as soon as the error is discovered. Use a starting rate in the range of 1-to-3 ppm (but rates as high as 25 ppm may be needed). Evaluate plant response after 5-to-7 days. Then adjust the application rate based on observed plant response, and reapply as needed at this time. The full effect of a single application should be evident within 1-week.

Photos: PGR Overdose and Florel drift

Rich McAvoy, University of Connecticut

For more information 2007-2008 New England Floriculture Guide: About Growth Regulators Fact Sheets (PDF)

Another complicated situation in spring is how does one handle growth when different species are mixed in the same container. Again the grower faces two complicated situations (1) plants in the same container have widely different vigor and require different PGR control and (2) the growth regulation objectives vary for plants in the same container. . For example in the first case we may have a dwarf banana or naturally dwarf angelonia that requires no PGR control in the center of a container surrounded by an extremely vigorous petunia cultivar that requires aggressive PGR control. In the second case, we may want to increase branching on an ornamental millet plant in the center of the mixed container but also control vigor of sweet potato vines planted along the margins.

In both of these cases it is obvious that we can't apply single PGR treatment to the mixed container and achieve the desired result. The solution requires that we treat individual plants in the mixed container without affecting the others in the same planting.

To control growth of the most vigorous varieties or species without affecting the less vigorous plants, the best option is to pre-treat the transplants as needed. A "plug dip" is a useful technique for this purpose. Here the plug flat is set in a tray of PGR solution and the rooting medium of the plugs is allowed to soak up the growth regulator. Allow the plug flat to sit in the solution for at least 5 minutes, some growers will allow 30 minutes but the plug root volume should reach saturation before that much time. After soaking allow the plug sheet to sit on the bench overnight before transplanting into the final container. Only root-active PGRs such as A-Rest, Topflor, Bonzi and Sumagic (and their generic equivalents) can be used for this purpose. These chemicals can remain active in the root zone for months, and they tend not to migrate far from the treated soil. Therefore, control is conveyed to just the individually treated plugs and not the other plants in the mixed containers. For rates, use Bonzi at between 4-16 ppm, use Sumagic at 2-8 ppm, for Topflor use 3-12 ppm. If you have not tried this before and are growing in a northern climate, start with rates in the lower half of the recommended range.

With groups of plants that have different growth regulator requirements such as increased branching associated with Florel versus height control associated with growth retardants, the option again is to treat the plants separately. Here you can go two ways. Transplant the plants that require Florel into the final container & spray, and then fill in with plugs of the vigorous species that have already been treated with a root-active PGR as previously described. Alternatively, the container can be planted with the treated plugs, leaving a space for the Florel requiring plants. Grow the plants that require Florel in small containers (e.g. 4-6"pot) until the treatment schedule is complete and then drop them into the empty space. Growers will often plant an empty pot to facility the late transplant with minimal disruption to the other plants growing the mixed container.

For more information

Photos: PGRs on Bedding Plants and Combination Planters

2007-2008 New England Floriculture Guide: About Growth Regulators (pdf)

Rich McAvoy, University of Connecticut

Fact Sheets

Plant growth regulators (PGR) recommendations vary from species to species & with plant age but from a practical matter growers need to control plant growth across a wide range of material as efficiently as possible. In practice, growers face two complicated situations on a regular basis (1) relatively small plantings of many different species and varieties are in the same house at the same time, and (2) relatively small of plantings at different stages of development are present in the same house at the same time. The key complication in both cases is the small planting size. Because each small planting (for example 10-50 flats of each variety, species, or stage of development) may require the grower to mix a separate batch of PGR based on label recommendations, it would be extremely impractical to control growth in this way. The approach used by some of the more experienced growers involves using a single low concentration drench of a root-active PGR as the backbone of their program but vary the volume applied to each small block. The overall affect is that the grower is able to make a real-time decision and deliver a variable dose while moving from block to block through the house. In this way, a single formulation is used to deliver a variable dose based on the specific level of control needed for each small planting. For instance, using 1 ppm Bonzi, the grower will apply a light drench or sprench-type of treatment to flats that require light control and a heavy drench to blocks of flats that require more aggressive control. Blocks that require no control are bypassed.

For more information

Photos: PGRs on Bedding Plants and Combination Planters 2007-2008 New England Floriculture Guide: About Growth Regulators (PDF)

Rich McAvoy, University of Connecticut

Fact Sheets: Growth Regulators for Bedding Plants Controlling Plant Height Without Chemicals Subirrigating Seed Geraniums with Bonzi

During the spring crop production season growers often need to use plant growth regulators (PGRs) for a variety of reasons. Most often the purpose to control plant vigor is during the grow-out stage.

During the grow-out stage the objective it to slow stem stretch while allowing the plant to grow. Low rates of PGRs are recommended for this purpose. With low rate applications, the PGRs can be reapplied as needed to control growth. Any of the commercial PGR products can be used at this stage but of course not all species respond the same to any one material. Therefore, growers are advised to have several different classes of compounds on hand. For instance, make sure you have a triazol class chemical (Bonzi, Sumagic or Topflor) plus either Cycocel or B-Nine. Between the two, you will be able to control most of the plant species you grow.

For growers starting with plugs or rooted cuttings, growth regulation should start at or soon after transplant. If you are starting your own seed, treatments can start within 24-hours of germination.

With transplants in small containers (flats & 4" pots) materials such as B-Nine and Cycocel can be sprayed at weekly intervals. Apply the first spray as soon as new growth is evident. Use a rate at the low end of the recommended range for that species. Repeat at 7-14 day intervals as needed. Note: if you are using Florel to prevent flowering and to stimulate branching, then a growth retardant will not be needed during the early stage of development.

Triazol-class materials (Bonzi, Sumagic etc) offer more options during this stage. These materials can be applied as a soil surface spray prior to transplant (Pre-plant Soil-surface Spray or PSS), or as a Media Spray (MS) applied immediately after transplant. Note that MS applications treat both the soil surface and the plant. Triazol-class materials can also be used as traditional drenches or spray applications once the plants are established and the leaves expand to fill in the allotted space in the pot or flat.

With both PSS & MS applications, the concentration or rate applied is higher than for a drench but less than for a typical spray. For example, the spray recommendation for Sumagic on petunia is 25-50 ppm and the drench rate is 1-2 ppm but the PSS rate is 5-7.5 ppm.

In both PSS & MS, a spray volume of 2-quarts per 100 square feet is used but because the soil surface is exposed and the chemicals are highly root-active, these applications have a mild drench-effect. This spray coverage (2-qt/100 sq ft), typically referred to as spray to glisten, is not enough to soak deep into the soil so the total dosage delivered to the root zone is less then with a traditional drench even though the concentration used is relatively high.

More information Photo: Marigold Flats 2007-2008 New England Floriculture Guide: About Growth Regulators (PDF)

Richard McAvoy, University of Connecticut

Fact Sheets: Growth Regulators for Bedding Plants (Note: See 2007-2008 Floriculture Guide for latest growth regulators) Controlling Plant Height Without Chemicals Subirrigating Seed Geraniums with Bonzi

Cooler night temperatures combined with the warm sunny days often result in plant stretch. The greater the difference between day and night greenhouse temperatures, the more stretch you will see on your crops. Some growers may be only reducing the night temperatures, to save on energy costs, with the daytime temperatures increasing due to the bright sunny days.

Many growers successfully use an early morning temperature DIP to reduce plant stretch. They reduce the temperature 30 to 60 minutes before dawn and maintain this lower temperature for the first few hours of the day.

Bedding plants may also become too tall if they are started too soon, are spaced too close together, are shaded by hanging baskets grown above them, or are grown in greenhouses with low light levels (due to old plastic) combined with poor ventilation, especially during the day.

There are no growth regulators labeled for use on herbs or vegetable bedding plants. For more information see the fact sheet: Controlling plant height without chemicals

Growth regulators may be used on many different ornamental crops including bedding plants, herbaceous perennials, and many different ornamentals to help manage plant stretch. Many growers may use multiple applications of growth regulators at lower rates to manage plant height and stretch, as opposed to one application at higher rates.

Links for more information: Growth Regulators for Bedding Plants Section D Growth Regulators In New England Greenhouse Floriculture Guide For Herbaceous Perennials and Plant Growth Regulators Go to PGR DATA in left column and Search Under Herbaceous Perennials Michigan State University, Growth Retardant Efficacy Trials on Perennials

Leanne Pundt

Some growers have reported that their poinsettias seem to be "stretching" and may become too tall before they finish. This stretch might be the result of the extended period of cloudy weather we have recently experienced and it could be made worse by close-spacing, old plastic, or dirty glass. Many poinsettia varieties are beginning to show color and some of the early ones show significant amounts of color. At this point in the season, can growth retardants be applied to poinsettias to control stretch? Poinsettias cannot be sprayed with growth retardants now because bract development may be inhibited, but the plants can be drenched with low concentrations of the paclobutrazol-containing chemicals Bonzi, Piccolo, or Paczol.

There are two approaches to applying drenches, one is called "early drench"and the other "late drench". "Early drench" was described by Jim Barrett in the July 2005 issue of Greenhouse Product News. Here 0.1 ppm (a.i.) drench solutions are applied several times as substitutes for spray treatments beginning in September and continuing through October. The number of times to drench is determined by "observation and experience" or by measuring and keeping track of height. Although it is late to start an early drench program now, growers can try 0.1 ppm drenches to control stretch; I doubt one treatment will be enough, but you can safely use 0.1 ppm repeatedly right into November. Limit your treatments if the varieties you grow are considered "short" types. On the other hand, some vigorous types like "Monet Twilight" will need repeat treatments and perhaps a higher concentration (0.2 ppm).

The "late drench" approach has been used safely and effectively by growers for some years and was trialed at UMass in the late 1990s. Right now, as the end of October nears, a late drench may be the best option. One drench of Bonzi at 1.0 ppm (a.i.) applied in late October-early November should reduce stem stretch and have no significant effects on bract development. Do not make more than two drench treatments and do not use a higher concentration than 1.0 ppm.

One final point on drenching: drenches with growth retardants are most effective when plants have healthy, well-developed root systems. Sometimes poinsettias have healthy but rather sparse root systems or the roots may be in poor condition due to disease. If either of these conditions exist, the inhibitory effects of early or late drenches may be limited because not enough chemical is being taken up.

For more information see: Growth Retardants for Poinsettias Late Season Application of Bonzi to Control Stretch of Poinsettia About Growth Regulators, 2005-2006 New England Recommendation Guide (pdf)

Doug Cox