Greenhouse Canada

Looking ahead to 2023

Preparing for spring crops

December 23, 2022  By Dr. Sarah Jandricic and Dr. Chevonne Dayboll

You can reduce pressure from thrips and other arthropod pests that come in on spring cuttings with dips. Photos by OMAFRA

It’s hard to believe, but as the first snow hits the ground here in Niagara, that means it’s time to think about spring crops again. This article gathers some of the most important things to plan and prep for in the greenhouse, including ordering inputs, preventative maintenance, and your pest control program. Think of this as your “to-do” checklist for successful spring crops.

Spring Crop CheckList

1. Make sure all your inputs are ordered
We can’t emphasize this one enough. Supply chain issues are still causing product shortages and shipping delays that are affecting many industries, including greenhouses. Make sure you order potting mixes, plastic trays and pots, fertilizers, and production inputs well ahead of when you will need them. Consider ordering into your summer and fall crops as well, and storing the materials, if you can. And, if you are planning on doing greenhouse upgrades in between seasons make sure you confirm delivery and installation timelines with your contractors. Many of them are facing delays, too!


2. Get your preventative maintenance done
Before your spring crops go in is a good time to schedule preventive maintenance for your boiler, irrigation and shading systems. Make sure that all motors and alarms are working before you need to rely on them. No one wants to find out that their temperature alarm failed on a cold February morning! Ensure you are getting the pressure you expect all along your irrigation system. If you rely on propane heaters for early spring production, make sure they are venting properly. Damage from improper venting can present as stunted growth or leaf burn.

Heat loss from an older (left) and newer, more efficient boiler (right).

Also take some time to inspect the greenhouse for wear and tear. Repair cracked poly and broken glass to keep heat from escaping. Make sure old torn energy curtains are replaced. A heat sensitive camera can help to identify areas of energy loss (see Fig. 1) and help you plan for energy efficient upgrades in the future.

3. Sanitize NOW, THEN plan your disease management program
Several key spring crops, like Calibrachoa, Pansy and Petunia are highly susceptible to black root rot (Thielaiviopsis), and we’ve seen more Fusarium root rot pop up in the last few years on crops like salvia, gerbera, echinacea and lavender. These pathogens are everywhere in the environment and can easily be brought in on cuttings, rooted lines and even on workers’ boots or via equipment.

More importantly, spores of these diseases can hide in nooks and crannies of benches while less-susceptible crops are growing, then pounce when conditions are right. Once black root rot or Fusarium get hold, it can be almost impossible to control them with fungicides. When it comes to these diseases, a good clean-out of your spring crop propagation and growing areas is as close to a “silver bullet” solution as we are going to get. This includes:

  • Scrubbing down your benches. This removes all the soil particles etc., where fungal spores might be hiding. It also allows sanitizers to work better, since they can get trapped by organic matter. Use a hose, scrub brush and a product like “Strip-It” to make sure everything is as clean as possible.
  • Sanitize benches and drip lines, where organic matter, biofilm and disease spores can accumulate. Use peroxide (e.g. Virkon) or quaternary ammonium (e.g. KleenGrow) products at the recommended rates for the material you’re sanitizing. If cleaning drip lines, make sure to always thoroughly flush your watering system several times before plants go in to prevent any potential phytotoxicity.
  • Use new plug trays. This may be more costly, but it’s something you’ll wish you did if you develop a problem. Pot/tray cleaners aren’t perfect, and trays can act as a ready source of inoculum for resting spores. If you are cleaning your trays, use the same process as for benches: first clean, then sanitize!
  • Control fungus gnats and shoreflies, as they can spread disease spores. Fungus gnat larvae can also chew on plant roots, making them more susceptible to disease.

To help you plan your disease management program beyond just sanitation, check out the GrowON webinar, “Root rots: What you can’t see can hurt you,” by Dr. Mary Hausbeck of Michigan State University. You can find this video on under “Recorded Webinars” on the blog. It’s full of tips about prevention and products to use if you do develop a problem. Other good refresher videos include “Fusarium basics” with Dr. Ann Chase of Chase Horticultural, and “Cultural controls for managing disease,” by Dr. John Lea-Cox from the University of Maryland, both of which are housed on the digital Greenhouse Canada website, under the “Webinars” tab.

4. Monitor pH For Optimal Nutrient Uptake
Keeping the pH of your crops in an ideal range can help with a host of issues. To avoid common nutritional issues such as iron deficiency, it’s best to keep crops at a pH in the range of 5.5 to 5.8. Iron deficiency can be difficult to distinguish from other issues (like black root rot), but it typically leads to yellowing of new growth. Leaves may only show chlorosis between the veins, or it may be spread throughout the leaf. This is different from nitrogen deficiency where yellowing occurs in the oldest leaves. If iron deficiency occurs, adding a chelated form of iron is best for uptake.

A lower pH can also significantly inhibit black root rot. Aim for a pH between 5.0 and 5.5. Regularly monitor the pH and EC of your feed water and crops using the pour-through method.

5. Prevent Pests Where Possible
Cutting dips aren’t just for whitefly on poinsettia anymore! Research from Dr. Rose Buitenhuis’ BioControl Lab at the Vineland Research and Innovation Centre has demonstrated that dips can be an important weapon for reducing thrips, whitefly and spider mites in chrysanthemums and potentially other spring crops (once label registrations are achieved for crops other than chrysanthemum). Dip registrations are currently available for the following products: BotaniGard WP, Kopa Insecticidal Soap, Landscape Oil, and Suffoil X. 

The first step in successfully incorporating dips into any IPM program is phytotoxicity testing. Testing at Vineland demonstrated just how differently certain plants react to different products. For example, although Landscape Oil at 0.5% is safe for hardier crops like potted chrysanthemums, ivy geraniums, ipomea, impatiens and mandevilla, it can cause significant phytotoxicity on sensitive crops, like zonal geraniums, petunia and mini roses. Variety can also play a role, even crops where dips are already registered, like chrysanthemums. This highlights why on-farm testing of a small batch of all varieties should always be done before you incorporate preventative dips on a wide-scale. You can see a summary of the plants and products tested by Vineland on Always read the product label for appropriate rates and allowable crops.

The second step in incorporating dips into an IPM program is deciding which products will best tackle your specific pest problem. Vineland’s BioControl lab also researched the efficacy of different products against the most common pests, which can co-occur on cuttings. In general, oils have the highest efficacy (>70%) against all three main greenhouse pests (thrips, whitefly and spider mites). Soaps were generally only effective for whitefly, whereas BotaniGard (by itself) was generally only effective for thrips. However, soaps and BotaniGard also pose the least risk to plants when it comes to phytotoxicity. Striking the right balance between efficacy and phytotoxicity is why testing like this is a must.

6. Plan Your Biocontrol Program
Advanced planning can help you decide where you’re spending your dollars, and where you can potentially cut back based on last year’s performance. It can also help you plan for contingency issues (i.e. what are you going to do if your planned biocontrol program isn’t working?).

Making a table like on p. 24 for your own greenhouse can help you remember which plants are likely to get which pests each year, so you can focus where to spend your IPM dollars. For example, spring crops like zonal geraniums, begonias, torenia, fushia, vinca, petunia and sunpatiens are unlikely to get thrips, so why waste applications of predatory mites here? Similarly, Rieger begonias are unlikely to get other pests besides broad mites. A “one and done” application of an effective miticide can allow you to focus your attention on more challenging crops. The list was originally compiled by Mark Crossley of Western Michigan IPM, but has been tweaked for what we commonly see here in Ontario.

For the more common pest issues we see in spring crops, here are some further tips to help you have a successful spring:

  • Hanging baskets: thrips can be tricky in these crops, since they tend to get hung up and forgotten about. If your baskets contain any thrips-magnet crops (see table on p. 24), then your best strategy is to use long-duration sachets here. These products have a higher chance of ensuring mites are present in the baskets for eight to 10 weeks, without needing to add a second sachet. Make sure to nestle them within the foliage, as placement has a big effect on sachet performance. As with thrips, aphids can be a major problem in hanging baskets, especially those containing calibrachoa or pansy. Work from Cornell University demonstrated that parasitoids don’t control aphids on calibrachoa, which means pesticides are your best bet. Beleaf (flonicamid) has been the go-to for a while, but Altus (flupyradifurone) may provide an alternative. Both work best when applied as a preventative drench sometime in early March.
  • Chrysanthemums and gerbera: Using dips on both will make your life easier, as these popular crops can arrive already infested with insecticide-resistant pests that may move to other attractive crops.
  • Verbena: Use thrips-sensitive crops like verbena to assess whether your current strategy is working, or if you need to add things like twice-weekly sprays of Beauveria-containing microbial pesticides.
  • Impatiens, begonia, and other crops prone to broad mites: Although spider mites can generally be controlled with releases of Persimillis when outbreaks occur, broad mite and cyclamen mites are much harder. In some crops, high releases of Amblyseius cucumeris will keep populations in check enough to get you to sale. Where broad mites tend to be your only problem (and insecticide residues aren’t an issue) preventative applications may be the best option. Fujimite (fenpyroximate) and Forbid (spiromesifen) are registered for broad mites, but Pylon (chlorfenapyr) or Avid (abamectin) are likely your best bets if spider mites are also a crop concern.
  • All crops: Mass trapping is your friend in the spring, as temperatures above 10°C mean thrips can potentially fly in from outside (including the usual Western flower thrips and onion thrips). Large sticky cards also help prevent thrips from migrating from source crops to sensitive crops.  

More information can be found on the blog version of this article. Questions about spring plant production and pest management can currently be directed to Dr. Sarah Jandricic (OMAFRA’s Greenhouse Floriculture IPM Specialist) at Dr. Chevonne Dayboll will return to her position as Greenhouse Floriculture Specialist in March 2023.

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