What are the first signs of root rots, as well as whitefly and Lewis mite monitoring and management? The basic assumption is that healthy plants are better able to defend themselves from pests and diseases.
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 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 plants to determine if you should treat them now to head off problems later.
Evidence of root rots include:
- Poor rooting
- Stunted growth
- Discolored (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 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 two whitefly life cycles (ca. 6 weeks) after cutting receipt to avoid resistance issues, scouting for whitefly should start in earnest in August.
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 the 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 in 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%.