Importance of H2O and PGRs
Agua. H2O. L’eau. Acqua. In any language, water is necessary to ensure successful application of plant growth regulators (PGRs) in the commercial horticulture market.
To account for the amount of water available to their plants, growers have to be prepared to make decisions to tweak programs in response to changing conditions and market timings. PGRs play an integral part of both the overall plan and all adjustments that have to be made during production.
Figure 1. Individual PGRs at three concentrations (low, medium and high recommended rates for each product) were added to reverse osmosis (RO) carrier water adjusted to four pH (5.3, 6.2, 7.2, 8.2) levels or added to tap carrier water adjusted to four bicarbonate concentrations (40, 86, 142, 293 mg.L-1 of CaCO3).
To help expand growers’ collective understanding of PGR best practices, as well as efficient use of various products, Fine Americas asked university researchers who work regularly with growth regulators to give their perspectives and expert advice in various areas of PGR usage. One area that causes issues with efficiency and efficacy of the PGRs applied is the water used for spray applications. Water quality plays a key role in determining how successful PGRs and other commonly used products are. This article, the third and final in a series, addresses water and tank-mix issues that may affect the results observed from a PGR application.
PGR water/tank-mix issues
Roberto Lopez, Michigan State University
Agronomic crop studies have indicated that water quality affects herbicides and insecticides, but there’s little research detailing how the pH or alkalinity (presence of bicarbonates and carbonates) aspects of water quality influence PGRs in horticultural crops. Recent research indicates PGR spray solution water quality—particularly pH and alkalinity—can play a role in efficiency.
Growth regulator solutions made with high pH carrier water (>7.0) or highly buffered [>100
mg•L−1 calcium carbonate (CaCO3)] may reduce effectiveness depending on the particular PGR used individually or tank-mixed. Water used in U.S. greenhouse production facilities traditionally comes from ground water wells. Of the top 15 floriculture producing states, Florida, Illinois, Michigan, Ohio, Texas and Southern California are in regions of high alkalinity water. Thus, the potential for reduction of effectiveness of some PGRs (by mixing with carrier water of high pH and alkalinity) could result in a large impact in product performance. Previous surveys of U.S. growers indicated that less than 50% had a water treatment system in place, such as acid injection, to lower pH and neutralize bicarbonates.
A Michigan State University study conducted helped to quantify the effects of carrier water pH, bicarbonate concentration and PGR concentration on the final spray solution pH of 11 PGRs commonly used by the floriculture industry: ancymidol (Abide), benzyladenine (Configure), chlormequat chloride (Cycocel), daminozide (B-Nine), ethephon (Florel), dikegulac-sodium (Augeo), flurprimidol (Topflor), gibberellic acid (Florgib), gibberellic acid/benzyladenine (Fresco), paclobutrazol (Piccolo) and uniconazole (Concise). Three concentrations of each PGR (low, medium and high recommended rates for each product) were added individually to carrier water. The final solution pH (carrier water + PGR at the different rates) was then compared to the recommended pH range for optimum PGR performance as indicated by manufacturers or the Optimum Pesticide Spray Water pH using the Indicate Guide from Griffin (www.ggspro.com/new/pdfs/Opt-Pest-Spray.pdf).
Figure 2. Tap water and reverse osmosis water are being adjusted to the various pH levels and bicarbonate concentrations.
Michigan State research determined that for several PGRs, the final spray solution pH was outside of the recommended pH range. When added to high pH or high bicarbonate carrier water, the weak acid PGRs, such as chlormequat chloride, gibberellic acid, benzyladenine and gibberellic acid/benzyladenine resulted in a final solution pH above the maximum recommended pH of 6.5. The relatively strong acid ethephon, when added at low concentration to high bicarbonate water, had a final solution pH >5, also exceeding the recommended range for this PGR. Uniconazole, when added to carrier water with moderate to low pH and low bicarbonate, resulted in a final solution pH <5.5, the minimum recommended pH for this PGR.
To summarize, most of the 11 PGRs evaluated affected final solution pH when mixed with carrier water, varying widely in pH level and bicarbonate concentration. This research encourages growers to periodically check and adjust the bicarbonate concentration, as well as carrier water pH, as it can influence the efficacy of individual and tank-mixed PGR applications.
In conclusion
PGRs provide great tools for growers to prevent excessive growth/stretch, increase branching and stage/time plants for shipment to customers. However, paying attention to both the water source and the water quality will help to better predict PGR application results and prevent frustrations of inconsistent performance, as the H2O used can significantly impact the performance of PGRs.
Rates will vary by the plant type and cultivar, so growers should refer to recommendations that are provided by the plant breeder for the correct rate. When making applications of PGRs, growers always should read and follow label directions for the product(s) they are applying. For additional information on PGRs, contact your local Fine Americas sales representative
