Effects of PGRs on root growth of herbaceous perennials.

Plant growth regulators, especially those applied directly to the root system, are thought to significantly reduce growth of the root systems. Various perennials were treated with uniconazole (Concise, Fine Americas, Inc.) to evaluate effects on plant height as well as shoot and root dry weights. Plant height of Lobelia cardinalis was not affected by a 1 ppm uniconazole liner dip, but shoot dry weight was reduced 52% and root dry weight 41% at 8 weeks after treatment (WAT) relative to untreated control, resulting in a root:shoot ratio comparable to the control. A 60 ppm uniconazole spray application reduced plant height of Stokesia laevis ‘Silver Moon’ over 40% at and beyond 4 WAT. Shoot dry weight of these treated plants at 8 WAT was 57% less than that of control plants while root dry weight was reduced 42%. This differential effect on shoots and roots resulted in a root:shoot ratio that was higher than that of the control plants. Reductions in root dry weight appear to correspond to reductions in shoot dry weight but the root:shoot ratio is not generally reduced. Higher root:shoot ratios are associated with better field establishment of transplants so maintenance of comparable root:shoot ratios should indicate comparable establishment rates.