Poinsettia Pest Management Pointers: Early Production 2023

Hopefully you’ve read our previous post on pest management in propagation. Now it’s time to cover poinsettia IPM during early production.

This post will cover the first signs of root rots, as well as whitefly and Lewis mite monitoring and management. As healthy plants are better able to defend themselves from pests and diseases, we’ll also give a quick nutrient refresher.

(Note: For all pests, click the link in the title for more helpful information!).

Here’s what you should be doing in August/September:

Monitoring for Root rots:

Early August is when you might start seeing the beginning of root rot issues in plug trays or at potting up (especially Pythium, but also RhizocontinaPhytophthora and even Fusarium). Although these won’t kill the rooted cutting outright, these diseases will proceed slowly and potentially cause large die-offs mid Fall.  So make sure you’re regularly inspecting plants to determine if you should treat now, to head off problems later.

Evidence of root rots include:

  • Poor rooting
  • Stunted growth
  • Discoloured (black or brow) roots
  • Loss of lower leaves
  • Cankers on stems.

If you see these, then get the disease identified by the Guelph Lab Services so you can apply the appropriate chemical fungicide in propagation to help knock it back. Follow this with an application of an appropriate microbial fungicide like (like Actinovate, PreStop, Rootshield Plus, Taegro or Trianum; check the label) to boost root growth and continue to fight disease in susceptible cuttings. Continue applications of microbial fungicides at potting, to support the plants as long as possible.

Monitoring for Whitefly:

Given that bios need time to work, and pesticide applications should be delayed at least 2 whitefly life cycles (ca. 6 weeks) after cutting receipt to avoid resistance issues, scouting for whitefly should start in earnest in August.

Scouting poinsettia for whitefly. Score plants as “with”or “without” whitefly.

The following technique is quick, but gives you a sense of the whitefly pressure across your whole farm, including in different varieties:

  • To save time/effort,  record presence/absence of whitefly per plant only to get a percent infestation rate  week by week.
  • To do this, pick up 15-20 plants per bench on at least 50% of the benches in your compartment.  This may sound like a lot, but the process goes quickly.
  • A good rule of thumb is to make sure you sample 100 pots total.
  • Hold them above your head or in a way so you can see the undersides of as many leaves as possible and score the whole plant as “With Whitefly” or “No Whitefly”. This includes sightings of ANY whitefly life stage (nymphs, pupae or adults; you’re unlikely to notice eggs without a hand lens).
  • Plants with “very high” whitefly numbers should be noted (and flagged), as should the variety, as these can attract whitefly differently.
  • Every week, add up the number of plants that had whitefly on them and divide this by the total number of plants you sampled (or do this by variety).  Then multiply that number by 100 to get the % infested plants.
  • For example, if I sampled 20 plants per bench in a compartment with 30 benches, and found a total of 55 plants with whitefly, then my % infestation rate would be: (55/(20×30))x100 = 9.1%.
  • Check out this post on how to use this number to make pest management decisions based on crop stage: https://onfloriculture.com/2021/09/01/the-whitefly-tipping-pointand-testing-pesticides-in-poinsettia/

If you want to see a video on monitoring in poinsettia, here’s an excellent one from the Vineland Research and Innovation Centre and Agriculture and Agri-Food Canada.

Starting Whitefly Control:

By now, your Bemisia biocontrol program should be planned out, with natural enemies added either in propagation or about to be added at potting. But if you’re a little behind, or need a refresher, check out these resources:

This video from Vineland and AFFC is a quick guide to the basics of Bemisia IPM in poinsettia:

But if you need more in depth information, check out this video from the Greenhouse IPM 101 Course (run by OMAFRA and EcoHabitat Agriservices) starting at the 24 minute mark:

Monitoring for Lewis mite: 

Although Lewis mite come in on cuttings, they are impossible to notice at low densities in June/July.  Preventative predatory mite applications are possible (see here), as is a single application of a miticide on cuttings (e.g. Forbid (spiromesifen), Floramite (bifenzate), or FujiMite (fenpyroximate)).  But, pesticide use early in the crop runs the risk of interfering with your whitefly bio program.  

As Lewis mite only seems to be an issue in random years, the better option is to regularly walk the crop, looking for the characteristic stippling symptoms, to figure out if you have it.  Mite populations build up enough to show damage as early as August, so it’s a good idea to start now. If you don’t see anything by October, you should be good. 

Lewis mite damage looks similar to spider mite damage on other crops. Look for yellowing of leaves in a stippling pattern, and webbing at high mite densities.

Keep an Eye on Your Nutrient Levels:

Common deficiencies are more likely to appear in mid-fall, but to head them off, it’s important to keep track of your E.C. and pH levels starting in August

For best results, maintain a feed E.C. between 1.0 and 2.5.   Higher E.C. values will allow salts to accumulate, which will inhibit nutrient uptake.  High E.C. can also cause young roots to burn – which provides an entry point for root rot problems.  An optimal pH is in the range of 5.8-6.2.  A pH greater than 6.5 will stunt growth, and iron deficiencies will eventually occur.  Also remember that an unhealthy, stressed plant is more likely to succumb to pest and disease issues.

Bi-weekly testing of these indicators and keeping good fertility and spray records can help you to understand what type of corrective action to take if a problem arises.  More descriptions of specific nutrient deficiencies in poinsettia can be found here , herehere and here.

Ok, that’s all I’ve got until mid September! Unitl then, you also might want to check out a previous post on other production tips from 2021 that’s still highly relevant!

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