When poinsettias get problems, they always seem to hit hard and fast. Things like whitefly, Lewis mite, root rots, and nutritional issues can all quickly derail a quality crop. This is why scouting might be more important in this crop than any other.
Here’s a month by month guide on what you should be looking for to prevent small problems from becoming big issues.
(Note: For all pests, click the link in the title for more helpful information!).
What to Look for in July:
Cutting Rots: The bacterial rot Erwinia (now renamed to Pectobacterium, just to confuse you) is the one of the first diseases to appear in poinsettia, as is Rhizoctonia (a fungus). Check for soft and mushy cuttings, starting at the base of the stem and moving upwards. The cuttings will eventually collapse.
With Erwinia, cuttings will also smell funky, due to the bacteria. With Rhizoctonia, you may 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. Sanitation is also key to controlling their spread: 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: July is also when you might start seeing the beginning of root rot issues in plug trays (especially Pythium, but also Rhizocontina, Phytophthora 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 your cuttings 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.
Whitefly: Given that bios need time to work, and pesticide applications should be delayed at least 2 whitefly life cycles (ca. 6 weeks) to avoid resistance issues, scouting for whitefly should start in earnest in August to determine future pest management decisions.
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.
- 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, which can attract whitefly differently.
- Every week, add up the number of infested plants 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%.
- Look under “September” for how to interpret this number based on crop timing.
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, and as late as October. (See “October” for what you should do if you find them).
Nutrient issues: 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. 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 , here, here and here.
Height issues: Early-to-Mid Fall is the time to start looking at the height of your crop, to see if it’s on track to reach commercial standards. Research out of MSU has shown that early low-dose drenches of Paclobutrazol (e.g. Bonzi) can effectively control height for poinsettia. However, response by variety plays a big part in both the number of applications and the rate. In general, more vigorous varieties required more applications or a higher rate (details on what they found for specific cultivars is here). In general, sprays of Daminozide (e.g. B-Nine) or Chlormequat Chloride products (e.g. Cycocel) will provide shorter-term inhibition of stem elongation, which may be desirable for small height corrections or holding crops later in production.
Whitefly: Consultants who’ve been in the business for 20+ years in Ontario have developed a general rule of thumb when it comes to whitefly levels on Poinsettia, and how this affects management. If fewer than 20% of your pots are infested mid-September, then you can continue your biocontrol program. Pockets of higher infestation can likely be dealt with by releases of Delphastus. But, having more than 20% of your pots infested mid-September is a bad sign, suggesting that numbers might get out of control by sale time.
If you’re at that 20% cut off, AND if numbers per plant are generally high, AND this is affecting the major variety you grow, it’s likely time to switch to chemical controls. Drenches of Kontos (spirotetremat), Beleaf (flonicamid) or Altus (flupyradifurone) may be good choices at this point, but you’ll need to monitor after each application to determine efficacy.
Root rots: If you weren’t able to get ahead of disease issues in propagation, now is the time you’ll likely see it rear it’s ugly head in the crop. Look for rapid yellowing and sudden wilting, which could be signs of Pythium aphanidermatum or P. ultimum. The additional sign of stem cankers right at the crown indicates either Phytophthora or even Fusarium (showing up more commonly in poinsettia crops). You’ll need to get your plants tested at a lab ASAP, as depending on the disease, chemical treatments may slow the spread of the infestation (e.g. Subdue MAXX for Pythium or Phytophthora) or be completely ineffective at this stage (e.g. any applications for Fusarium). Rogue out infested plants immediately, especially if you are using flood floors/benches.
Botrytis Stem Rot: A grower can be right on track for a quality crop, only to be suddenly derailed by Botrytis stem rot (caused by the same fungi as foliar Botrytis) in October. Look for sunken cankers near stem branches and sudden defoliation/branch death on one side of the plant (above the canker).
The main culprit in Botrytis stem rot is improper spacing at the beginning of the crop, and is likely more common in 4-inch crops, where growers are trying to maximize profits. Once it appears, reduce your watering, increase ventilation, and get an application of a product like Medallion (fludioxonil) or Decree (fenhexamid) on before the canopy closes and it’s too late to penetrate the crop properly. Other chemicals can be effective but risk discolouring bracts.
Lewis mite: Often, Lewis mite populations go undetected until October, when populations build up enough to start causing noticeable damage: the upper foliage will turn brown and the mites will form unsightly webbing. If you find a spot on the bench, immediately throw out infested plants in a “circle of Love” (i.e. the centre infested plant and all those immediately touching it). You should also consider a spot spray of miticides for nearby plants (a spot spray being less likely to interfere with bios for Bemisia control). The contact insecticides listed under “August” will still be options, but If the canopy is dense, systemic miticides might be more effective (e.g. Avid (abamectin), Kontos (spirotetremat).
If you’ve made it this far with a clean crop, your future’s looking bright!
If not, it’s time to make notes on what when right, and what didn’t, so you can tweak your IPM and production programs for next year.