Dipping Poinsettia Cuttings to Reduce Whitefly 101: 2020 Edition

 

Although we’ve been talking for years here in Canada about dipping your poinsettia cuttings in low-risk pesticides, some growers have yet to take the plunge.

This preventive technique improves efficacy of BOTH biocontrol and pesticide programs for Bemisia, since it lowers your starting pest pressure.

If you’re still unsure of how or when to apply cutting dips, check out the rest of this post.  

 

WHY Dip?

This is an easy one to answer. Because it gives you a chance to reduce your Bemisia whitefly problem AS SOON AS CUTTINGS COME IN THE DOOR.

Figure 1, below, shows that dips by themselves can significantly reduce whitefly issues. Because the products used for dipping are soft on bios, you can also combine dipping with biocontrol for a pesticide-free poinsettia season.

Overall, dipping provides MANY benefits, including:

• Dipping cuttings in a combination of insecticidal soap (e.g. Kopa) and BotaniGard WP can reduce final whitefly populations by 70% (see more here) if used in combination with biocontrol (see Fig. 1). 
• If you don’t want to use soap, BotaniGard by itself  reduces whitefly nymph survival by ~40-50% compared to a control (water) or a soap-only treatment (see Fig. 2, below).
• Even when using a chemical control program, by reducing the initial whitefly pressure, dips can decrease the amount of pesticides needed on poinsettias by 50%, according to Dr. Rose Buitenhuis.
• Given the reduce-risk products used, dips are 100% compatible with whitefly biocontrol programs.
• Dips may also benefit whitefly biocontrol by helping to rinse off pesticide residues, allowing for better survival of natural enemies like Delphastus.
• Dips pose little risk in spreading the poinsettia pathogen Erwinia, though other pathogens (e.g. Pythium) have not been tested.

More information on the Vineland Research and Innovation Centre’s research on dips (including rates) can be found in this magazine article and in this scientific article.

WHEN to Dip:

Cutting dipping should be initiated as soon as cuttings start to come in (e.g. early July; see Fig. 3 below). For best results, cuttings should be dipped soon after receipt.  Once dipped,  cuttings should be allowed to dry before sticking and placing on the misting bench.

However, some growers have also been trialing dipping ROOTED cuttings (more on this below).  So, if  even if you’ve already received and stuck all your poinsettias, there could still be time to add dipping to your program!

WHAT to Dip:

CANADIAN label registrations include BotaniGard WP  (see the most current label by clicking the registration number for BotaniGard WP here) and Kopa insecticidal soap (here), both for whitefly nymphs.  Together, BotaniGard + soap is the most effective treatment for whitefly (see Figs. 1 and 2 above).

Suffoil X was also recently registered for whitefly on greenhouse ornamental cuttings in general (see label here). This product can be highly effective (see Fig. 2 above).

However, rates given on the label are MUCH HIGHER than have been reported by VRIC researchers to be SAFE for most plant cuttings.  To avoid phytotoxicity to poinsettia, reduce rates to 0.1% Suffoil (1ml/L water). Rates higher than this can cause burn when used as a dip, and simply aren’t necessary when it comes to killing Bemisia.

For our readers in the United States, BotaniGard WP is registered for dips there, as are Rootshield and Rootshield plus, which some growers add to their dip solution to help control disease in poinsettia, such as Pythium.

HOW to Dip:

Dipping UNROOTED cuttings:

To make sure your dipping program is successful, below are a few tips for dips, including a video on proper dipping technique:

• Dip rates are lower than spray rates for soap and oil to prevent phytotoxicity. But always test a small batch of cuttings of any new poinsettia variety before committing to a full dip program, just to be on the safe side.
• Place unrooted cuttings in a mesh immersion tray with a lid for dipping.  Total coverage of the foliage is required for dips to be effective. Do not pack the cuttings too tightly.
• Verify that there are no dry surface areas on rooted or unrooted cuttings after dipping to make sure your technique is effective.
• Good sanitation is essential. Research has shown that the risk of disease transfer through the dip solution is low, but pathogens may still build up.  Don’t re-use dipping water over several poinsettia shipments.  Ideally, dip water should be changed every 4 hrs.
• Don’t use on weak or stressed cuttings, and don’t expose the dipped cuttings to full sun.

Fig. 1. This video housed on Greenhouse Canada Magazine can help walk you through the dipping process:

Dipping ROOTED cuttings:

If you’re thinking of trialing dips of rooted cuttings, this is done while the cuttings are still in trays.  Cutting trays should be turned upside-down in the dip tank, and held under the solution for a good 3 seconds (with light swishing) to ensure thorough and even contact.

NOTE: contact of the dip solution with the root area SHOULD BE AVOIDED.  Though soap and Beauveria dips have been shown few negative effects on many poinsettia varieties , some varieties have shown cutting losses of up to 20% if roots are immersed in the dip solution (e.g. Prestige red) .  This is why variety testing is always important when you are trying a new technique. Dipping rooted cuttings in oils is likely to carry even more risk, so make sure to test a subset of ALL varieties grown if you’re going with this dip product.

Dipping rooted cuttings may be chosen over dipping unrooted cuttings for 2 reasons:

1. Growers sometimes find that dipping unrooted cuttings slows down sticking, which can effect cutting quality. Dipping cuttings AFTER rooting gets around this logisitical problem, while still applying a preventative treatment early on in production (a win-win!).
2. Although untested as of yet, this approach MAY help decrease whitefly numbers even more. Why? Because you’re likely to get better, more consistent coverage of the dip solution by immersing whole trays of upright plugs, rather than submersing a stack of layered, unrooted cuttings.

It remains to be seen whether dipping cuttings as early as possible (upon receipt) or waiting until rooting ends up being the better strategy in terms of whitefly control. But NOT dipping is definitely depriving yourself of a chance to get ahead of your Bemisia problems from the beginning.

Happy dipping!