Poinsettias are almost here! Instead of covering the whole crop cycle, this year we’re breaking posts down into 4 key growing periods: Receipt/Propagation, Early Production, Late Production, and Finishing.
This post on propagation will cover things you can do now to treat pests and diseases in your cuttings to prevent BIG problems later. And make sure to check out Dr. Chevonne Dayboll’s post from last week, on ensuring cutting quality.
A Dip in Time (At Receipt!) Saves 9 (Potential Pesticide Applications):
Ok, maybe not nine pesticide applications. But dipping cuttings in reduced-risk insecticides to tackle problems at the beginning of the crop can lower pesticide applications by 50-70%, according to Dr. Rose Buitenhuis at the Vineland Research and Innovation Centre.
And Rose isn’t the only one singing the praises of cutting dips for Bemisia control in Poinsettia. Even in the U.S., where there are a lot more chemical options for whitefly control, researchers like Dr. J.C. Chong are looking at the benefits of preventative dips. As in Canada, they are seeing an impressive reduction in whitefly, for up to 8 weeks after sticking (see Fig. 1, below). You can read about Dr. Chong’s other results in this article.
Make sure you look up registered products for dips, effective rates for whitefly, and proper dipping procedures BEFORE you dive into this technique for your whole farm, though!
Derailing Diseases in Propagation:
There are several diseases you should start scouting for NOW, under the misting bench, in order to treat problems at the first sign of trouble:
Cutting Rots:
- The bacterial rot Erwinia (now called Pectobacterium) is the one of the first diseases to appear in poinsettia. Check for soft and mushy cuttings, starting at the base of the stem and moving upwards. The cuttings will smell funky (due to the bacteria) and eventually collapse.
- Rhizoctonia can also cause problems early in the crop, and exhibit similar symptoms as Pectobacterium (without the funky smell). You may also see white fungal strands near the crown.
Proper water management can help mediate both diseases; keep mist minimal overnight and turn mist off as soon as possible. The goal is to keep the foliage wet, but with minimal wetting to the media. Think about adding a wetting agent to help the cuttings stay turgid. You can read more about poinsettia cutting rots here.
If Erwinia DOES rear it’s ugly head, Rhapsody (a biofungicide containing Bacillus subtilis strain QST ) and Phyton 27 (containing copper) are your only options for suppression. But these options will only work along side good sanitation. So, make sure to immediately rogue out any propagation strips affected by Erwinia/Rhizoctonia, as ALL cuttings in the same strip are likely to be infected.
Root rots:
Although they can start in the plug tray, root rots such as Pythium, Phytopthora, Rhizoctonia and Fusarium generally proceed slowly. Regularly inspect your cuttings between now and potting to look for any initial signs, such poor rooting, stunted growth, discoloured (black or brow) roots, loss of lower leaves, or cankers on stems.
If you see anything that looks suspicious, then you’ll want to confirm the presence of a disease using DNA analysis and/or plating of the pathogen on media (done by a diagnostic lab). This way, you can pick the best plan of attack, including appropriate fungicides.
Generally, with any root rot, here’s how to get on top of it:
- Rogue out any infected plants immediately to make sure the innoculum doesn’t spread.
- Once you’ve had your disease identified, apply an appropriate preventative chemical fungicide in propagation to help knock it back. Treating plug trays is MUCH easier and cheaper than treating plants once they are potted.
- Around 7-14 days later, follow chemical fungicides with an application of a broad-spectrum biofungicide like Actinovate, PreStop, Rootshield, Taegro or Trianum on rooted cuttings. This will help boost root growth and help fight off disease. You may even be able to drench these directly with the chemical fungicide you’re applying, depending on the chemical. Ask your rep!
- Don’t over-fertilize or over-water plants, as this can promote disease.
- Keep your greenhouse sanitary: this means no hoses on the ground, no pools of algae or potting mix on the floor that can promote pests like fungus gnats, which can spread plant disease.
- If necessary, control fungus gnats with applications of nematodes or insect growth regulators like Citation or Dimilin as soil drenches.
- Repeat up your microbial fungicide applications RIGHT at potting. This step is key in continuing the fight disease as they get placed in a bigger container.
Starting Biocontrol for Bemisia
By now, you should be thinking about what your biocontrol program for whitefly is going to look like. In Canada, growers tend to use 3 main programs for this pest (see below). At their best, these programs completely eliminate the need for pesticides. At their worst, they still play a critical role in delaying pesticide applications for as long as possible. Read how delaying pesticide applications helps overcome potential pesticide resistance in Bemisia whitefly in this blog post.
- Program 1: High rates of a mix of Encarsia formosa and Eretmocerus eremicus. Encarsia and Eretmocerus come in handy “combo” emergence cards from many suppliers, like Koppert, Biobest and BioLine.
- Program 2: Lower rates of Encarsia plus the predatory beetle Delphastus. Sometimes referred to as the “West Coast Program”, this method was pioneered by British Columbia’s Applied Bionomics, and relies on “fresh” Encarsia that are purported to have better searching ability.
- Program 3: The “kitchen sink” approach. This includes any of the parasitoids above, plus Delphastus AND mites like Swirskii or Limonicus to attack whitefly eggs. Limonicus or Swirskii can be given supplemental food such as pollen or Ephestia eggs to help their populations build up.
Many of the pros and cons (including costs and reliability) of the various programs are outlined in OMAFRA’s Greenhouse IPM 101 Course: Whitefly video (starting at around the 24 minute mark).
Regardless of which program you chose, natural enemies should be released early in the crop. This should be done either:
- A) on the misting bench. Although some growers think the bios may not do well under mist, the pests do just fine, so it stands to reason the predators and parasitoids can function under these conditions too. The only caveat is that parasitoid cards should be covered with a styrofoam cup to prevent them from rotting before all the wasps have emerged.
- B) at potting up. This strategy is most popular with growers, and it also allows the 4 week “waiting period” to pass before Delphastus can be released, as this natural enemy is extremely sensitive to residual pesticides on cuttings.
What’s Next?
Once you’ve released your biocontrol agents, you’re good to let the crop ride for a while. Scouting for whitefly and other pests like Lewis mite and Pythium will begin in August in earnest, in order to see how your pest and disease programs are doing, and if you need to step in with other measures.
We’ll be back with another post in July to tell you what to watch out for! So stay tuned.