Controlling Cleome Height By Jim Barrett and Carolyn Bartuska

Cleome is fast growing and can have a very short crop time in production. It also can produce large, colorful garden displays rapidly. In the University of Florida's 2006 variety trials, the vegetatively propagated 'Spirit Appleblossom' and 'Senorita Rosalita' were recognized as two of the best new varieties in the trials. While this fast development can be an asset, cleome grow so fast that height control can be a problem if they have to be held for some time either in production or at retail.

This winter and spring, we conducted a series of studies to look at growth regulator usage on these two cleome varieties in 1-gal. containers. Some liners were pinched one week after planting and others were left unpinched. In the warmer spring period, crop time for unpinched plants was only four weeks and five weeks for pinched plants.

Comparing Applications

We first compared spray and drench applications of paclobutrazol on 'Senorita Rosalita'. The paclobutrazol product used for this work was Bonzi, but there are several others on the market that can be used as well. Spray applications up to the relatively high rate of 100 ppm had only a slight effect on plant height. Drench treatments at 5-20 ppm, however, provided better control.

It is not unusual in vigorous crops to find that growth regulator drenches give better performance than spray treatments. We did not evaluate higher paclobutrazol rates. Measures that may provide better activity with sprays of PGRs such as paclobutrazol, which work better as a drench, include using higher rates, heavier spray volumes and/or multiple applications.

In subsequent studies, we compared making the drench application at 2-4 weeks after planting. We found that the paclobutrazol drench provided better control and at a lower rate if applied two weeks after planting (see Figure 1, opposite). A benefit to the earlier applications was that less chemical was needed and there was little effect on flowering time. We also found that the single early application provided adequate control and a second application was not needed.

Increasing Rates

For both varieties, we found a strong response to increasing paclobutrazol drench rates. 'Spirit Appleblossom' is a little more sensitive compared to 'Senorita Rosalita' and higher rates caused more delay in flowering in 'Spirit Appleblossom'. The optimum paclobutrazol drench rate at two weeks after planting was 21Ú2-5 ppm for 'Spirit Appleblossom' and 5-10 ppm for 'Senorita Rosalita'. These trials were all done in Florida, and generally, optimum PGR rates are lower in other parts of the country with lower production temperatures.

More recently, we have looked at sprays of a tank mix of B-Nine (daminozide) and Cycocel (chlormequat). This spray at 2,500-ppm B-Nine and 1,500-ppm Cycocel applied one week after pinching has greater effect than a paclobutrazol spray. However, the amount of control with the tank mix spray does not last as long as the paclobutrazol drench. If more control is needed, a second spray or a paclobutrazol drench could be applied at 2-3 weeks after planting depending on how much control an individual grower desires.

Cleome is like other fast-growing crops in that making the PGR application early is important to control growth before the plants are too tall and too much chemical is needed. While fast growing, cleome is sensitive and responsive enough to the PGRs that size control is not difficult.

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Jim Barrett and Carolyn Bartuska

Jim Barrett is professor of floriculture and Carolyn Bartuska is a biological scientist at the University of Florida, Gainesville, Fla. Barrett can be reached at [email protected]

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