When it comes to pest management, the best place to start your program is from the beginning, so start with propagation. If your starter plants are not clean, it’s going to be an uphill battle.
If you grow your own stock plants, keep them clean. This can be challenging because these plants are often allowed to grow large and dense to produce many cuttings. Getting good spray coverage on plants with dense growth can be difficult. Often pest populations seem to be under control, but their numbers are frequently just knocked back. In these situations, systemic insecticides can be useful, but remember they may not control all pests present. Make sure your target pest is on the product label after making a positive identification.
Once cuttings have been taken (or when you buy them in), conduct a thorough inspection to check for potential problems. You may see large adult insects, but the tiny eggs and immature insect stages can easily slip by. When cuttings are shipped in, they often arrive in large volumes, and frequently it’s a race against the clock to stick them. This rush may not leave time for adequate inspections.
Try pre-treating the new cuttings before sticking them. Researchers in Canada have been looking at immersing cuttings in treatments of hot water, Safer Insecticidal Soap (potassium salts of fatty acids 2.0 percent) or Landscape Horticultural Oil (mineral oil 99 percent). The chance of developing resistance to these products is slim, which helps preserve the viability of other chemical controls.
Stop pest problems at the start of the production cycle,
and plants will be cleaner through finish. Photo: Suzanne Wainwright-Evans.Canadian researchers studied chrysanthemums and poinsettias. They found hot water can be an effective way to help control western flower thrips (WFT). Hot water demonstrated a high mortality (more than 80 percent) of second-instar larvae and adult WFT. These results were obtained at 102°F for 30 minutes or 104°F for 15 minutes. Insecticidal soap treatments at 40 ml/L provided low mortality of adult WFT, less than 75 percent. But the most effective control was the horticultural oil treatments, resulting in 100 percent mortality of WFT adults and 64-82 percent mortality of both the first and second-instar larvae.
For sliverleaf whiteflies, hot water provided low mortality of the eggs (less than 16 percent). Insecticidal soaps also had low morality with less than 14 percent of eggs killed, but horticultural oil (5 ml/L) did the best controlling whitefly eggs, resulting in 83 percent mortality.
This does not mean you should immediately run out and start dunking your cuttings to control pests. Testing must always be done to make sure there are no phytotoxic effects from these treatments and the viability of the treatments. Woody and perennial growers should replicate this test to develop the proper program for these crops.
If cuttings are being taken onsite, keep your tools clean to prevent the spread of problems (mainly diseases). Use alcohol dips or chorine treatments. This may not have to be done between each cutting, but if plants are prone to disease issues or there are signs of disease present, make sure to keep those tools clean. When production is between crops, take the time to disinfect benches, walkways and walls.
Clean cuttings do not ensure that pests will not arrive on their own. One of the easiest things to do is use sticky cards. The yellow cards will attract most flying insects including fungus gnats, shore flies, thrips, winged aphids, whiteflies and others. Blue cards work well for thrips. But sticky cards will not help you monitor for mites, because mites do not fly.
A mist system in propagation helps reduce spider mite pressures. Research has shown that overhead irrigation greatly reduces the populations of these pesky mites. But once the rooted plants are removed from the mist and potted up, populations can explode.
If pests do arrive in the propagation cycle, they can’t always be treated the same as those in a regular nursery setting with more mature plants. If you drench cuttings with a systemic pesticide, the plants can’t take it up because of the lack of a root system. As cuttings mature and root out, they will be able to take up systemic pesticides, but not at first. For a foliar application, the misting irrigation may result in the pesticides being washed off before it has an opportunity to kill the target pests. This is where stickers can help. Stickers are products designed to help the pesticides “stick” to the leaf surface.
On the other hand, beneficial nematodes will not be washed away by irrigation. Beneficial nematodes control fungus gnats, which feed on the roots of cuttings, and shore flies, which feed on algae and bacteria. Although nematodes work well in propagation, not all biologicals do, so be sure to check with your biologicals supplier.
Controlling pests early is key to a successful pest management program. Starting clean will help make the rest of the growing process a lot easier. If you don’t start with a clean crop, you may be setting yourself up for a Sisyphean battle the rest of the season.
Opit, G. P., G.K. Fitch, D.C. Margolies, J. R. Nechols, and K. A. Williams. 2006. Overhead and Drip-tube Irrigation Affect Twospotted Spider Mites and their Biological Control by a Predatory Mite on Impatiens. HortScience. 41(3):691-694
W. Romero, c. Scott-Dupree, G. Murphy, T. Blom and R. Harris. 2010. Reduce Risk Control Methods for Insect Pests on Cuttings. Poster.