Efficacy of paclobutrazol drench treatments To petunia and impatiens is affected by application Method and irrigation method

Abstract

Paclobutrazol is used to control size of annuals and other greenhouse crops and is often applied as a drench to the media surface. Previous research indicates that paclobutrazol binds to the organic components and slowly moves down through the media profile. The use of subirrigation systems is expanding, but the movement of paclobutrazol within the growing substrate in subirrigation is not fully understood. Given this information, a set of experiments were carried out with Impatiens wallerana and Petunia ×hybrida to determine the efficacy of paclobutrazol when application is to the media surface or applied through the bottom of the container (bottom application) and subsequent irrigation is either overhead or by subirrigation. For petunia in 12.5-cm pots using a peat-based media, paclobutrazol in bottom application treatments had greater efficacy when followed by subirrigation compared to irrigation from above. When paclobutrazol was applied as a drench to the media surface, irrigation method had little effect on efficacy. For impatiens in taller, gallon containers, greater efficacy was found when subsequent irrigation was in the same direction as the paclobutrazol application. When paclobutrazol was coated on vermiculite and placed in the middle of the container, there was greater efficacy with subirrigation compared to overhead irrigation. These results illustrate that both application technique and irrigation method can affect paclobutrazol efficacy.