Tank-Mixing PGRs

B-Nine and Cycocel tank mixes have been effectively used by growers for many years. However, there are still many growers who have not yet taken full advantage of this useful tool. The primary advantage of the B-Nine/Cycocel tank mix is that it provides a medium-activity product, comparable to A-Rest, that is easy to apply. In other words, the tank mix usually has a higher activity than B-Nine or Cycocel used alone and is easier to apply than the higher-activity products, Bonzi and Sumagic. (We haven't experimented with Topflor yet, but you can find extensive Topflor research on page 48.)

During spring 2002, we applied six different B-Nine/Cycocel combinations to 12 different bedding plants. The three tank mix rates used are all a 3:1 ratio (B-Nine:Cycocel). Á There is not a magic ratio of B-Nine and Cycocel, but a 3:1 ratio provides a broad range of rates that typically avoids phytotoxicity (foliar chlorosis or damage). A fixed ratio also allows growers to apply a high concentration to one crop, then dilute the tank mix with water to provide a lower concentration to another crop.

We received 288 plugs from Raker's Acres and transplanted them into 6-0-6 bedding plant flats. The first PGR applications were made five days after transplant. Plants were re-evaluated one week later (Day 12 after transplant). If plants looked like they would benefit by receiving another application, one was made. This process was repeated one week later (Day 19 after transplant), thus the different species received one, two or three applications of the same B-Nine/Cycocel combination. The tall, upright species typically received the most applications. We applied the growth regulators until run-off.

Interpreting the Results

Table 1, page 46, displays the relative results of our spray trials. Excessive growth regulation, or stunting, did not occur. The responses can be grouped into a few different categories.

Celosia, coleus, dianthus, salvia, snapdragon and vinca are examples of plants that were responsive to both B-Nine and Cycocel. The tank mix provided the beneficial additive effect of the two PGRs. These species are the best candidates for using B-Nine/Cycocel tank mixes.

Ageratum, petunia and begonia are examples of plants that were primarily responsive to one product, but not the other. As a result, the tank mixes were effective. However, this response could be attributed to just one product in the mix. Ageratum and petunia were primarily responsive to B-Nine, while begonia was primarily responsive to Cycocel. Thus, the individual growth regulators would be the more logical application rather than the tank mix for these species.

Impatiens and pansies are examples of plants that did not significantly respond to the individual growth regulators, but showed some beneficial response to the higher rates of the tank mixes. Stronger growth regulation would require multiple applications. If you have experience applying the higher-activity PGRs, consider using Sumagic on impatiens and Bonzi on pansies. If you do not have experience with these products, the B-Nine/Cycocel tank mix provides a safer option, although chemical costs will likely be higher.

Growers should view these data as a starting point from which to develop their own test trials before making applications to commercial crops, since different climates, seasons, spray techniques and varieties will impact the results.

"Hold" versus "grow-on" rates

Growth regulators can be used for different purposes. Ideally, a growth regulator is used at a relatively low rate to "tone" growth. Á Multiple applications are made to maintain toned growth. However, sometimes crops require a higher rate to put the brakes on a little stronger. Obviously, growers must avoid stunting the plants, but weather or sales can dictate that a crop needs a stronger growth regulator application. In Table 1, below, we would interpret the single asterisk as a toned appearance, while three asterisks represent plants that have been slowed considerably, but without the stunted effect that can occur with higher-activity growth regulators such as Sumagic and Bonzi.

Side Effects

Growth regulators will not only reduce stem elongation, but they frequently delay flowering. The following data refers only to the 4,500 ppm B-Nine and 1,500 ppm Cycocel tank mix. Although 'New Look' celosia is a variety that does not require a flower to sell, flowering was delayed by 28 days. B-Nine significantly intensified the bronze coloration of the foliage. Flowering of salvia, vinca and zinnia were delayed by one week. This is particularly significant during spring production when turning the bench space is critical. One additional production week represents a 25-percent increase in production time on vinca, which required only four weeks without any growth regulator and five weeks with one tank mix application. Dianthus flowering was delayed by five days, and petunia flowering was delayed three days. The remaining species did not experience a delay in time to flower.

Phytotoxicity commonly occurs on foliage or flowers following a PGR application. Typically, the symptoms are minor, and new growth will cover up the discolored or damaged foliage. Nonetheless, caution should be exercised. In this study, ageratum showed some phytotoxicity in response to the 1,000- and 1,500-ppm Cycocel treatments, while begonia leaves were less bronze (more green) with the B-Nine applications. B-Nine also altered the color on the coleus variety used in this study. Whether this should be considered positive or negative is a matter of personal taste. Impatiens showed some phytotoxicity on the foliage in response to the 1,500-ppm Cycocel treatments used alone or in combination with B-Nine.

Summary

The primary benefit of tank mixes is that a higher degree of growth regulation can be achieved compared to applying individual products. This does not suggest that something magic occurs when the two products are mixed. Rather, a small dose of one product added to a small dose of another product provides a moderate dose when mixed together.

For bedding plants, different species will have different sensitivities to different growth regulators. The beauty of a tank mix is that you can choose a tank mix rate that has a moderate effect on multiple species even though one species is responding more strongly to one product than the other. Thus, you can prepare a particular tank mix, make an application to a few species, then dilute the tank and make applications at a lower rate to more responsive species or plants that need less growth regulation. This can simplify your growth regulation program.

Our study suggests that B-Nine alone is the best choice for 'Blue Danube' ageratum and 'Madness Burgundy' petunia, while Cycocel alone is the best choice for 'Cocktail Gin' begonia. 'Accent Red' impatiens and 'Magestic Giants' pansies may require multiple tank mix applications at the higher rates, thus other PGRs may provide more cost-effective growth regulation. New Look celosia, 'Black Dragon' coleus, 'Telstar Crimson' dianthus, 'Vista Red' salvia, 'Montego Red' snapdragon, 'Cooler Red' vinca, and 'Dreamland Rose' zinnia benefited from tank mix applications of B-Nine and Cycocel. Your own trials will determine the best rates to use at your location and climate.

The authors would like to thank Raker's Acres and Uniroyal Chemical/Crompton Corp. for their support of this project.