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The Spring, The Bugs, The Persistence by Mike H.

As we approach the end of the calendar year we find ourselves planning and hopefully looking forward to the next growing season and spring fundraiser. Growing successful crops is the result of planning, scheduling, and discipline. While plants are predictable (much of what they do is stored in their genetics) many things surrounding and affecting their cultivation are not.

The spring crop for next year begins immediately after this year’s crop is sold. At this point, you need to begin to set that stage by cleaning out the greenhouse and making notes for the next year. What sold well? What didn’t? What were the challenges and problems that you faced and what can you do to prevent them from reoccurring? Did I order enough supplies? What varieties grew well and which ones did we struggle with? What are we wanting to grow next year? Make your notes concerning all these issues and stash them in a safe place until late summer or early fall when they can then be brought out and focused on.

It is now early December and all spring supplies and plants should be ordered for next year. Your crop plans should be finalized and all orders reviewed and double-checked to make sure nothing is missing. The greenhouse should be clean and ready to be filled with pots and baskets prior to plant material arriving. This is all the direct result of the notes made soon after last spring’s crop.


Once supplies arrive, seeds are sown, pots are filled, plants arrive and are immediately planted, watered in and fertilized. They then settle in to their new home and begin new growth as the sun shines. The kids are excited and all is looking good while fundraiser details are finalized. This sure seems like such a perfect scenario and all really feels good at this point. But something very sinister and quiet is missing, or at least seems to be.

Bugs (catch-all term for any life form with an exoskeleton that we don’t want in the greenhouse) are typically dormant or move very slowly during these winter months. They can hide under the rims of pots, in cracks on the floor, old rubber boots, etc. Short days, cooler temperatures and relatively small populations at this point make them almost undetectable. But they are there. Whitefly, aphids, thrips, fungus gnats, the heavy hitters……waiting……


Now is when you should also be planning your strategy for controlling these pests. If you methodically set up a plan and follow through with it, you’ll thank yourself later, I promise. If it sounds like I speak from experience, indeed I do. How many times have you walked the greenhouse a couple of weeks before your sale, notice the beautiful baskets overhead draped with color only to reach up, bring one down, and notice aphids and their husks all over your calibrachoa? Or thrips running rampant on your geraniums and gerberas while scarring up the flowers from their rasping and feeding? Or when you take a closer look at your tomatoes and peppers only to inhale a cloud of whitefly or discover the lines of yellow aphids running up and down the stems, it’s indeed a sickening feeling.

But, these populations did not just materialize overnight. As I’ve repeated many times before, bugs are omnipresent. They will be with us forever. They are and will always be a force to be reckoned with. Pest Control can be done either by reacting to situations similar to the above or by preventing these outbreaks before they become an issue. Prevention is the best strategy and starts before the new plants even arrive. Many growers take an IPM approach to controlling insects which is both effective and safe for students, staff, customers and the environment.


IPM (Integrated Pest Management) is an environmentally safe, sustainable and effective means to keep pest populations below tolerable levels while minimizing risk to people, environment, and non-target organisms.

This does require some planning and effort but is not really that difficult to implement in the school greenhouse environment. If you follow the strategy below you can discourage and prevent pest populations in your greenhouse. And when they do appear, as detected through your monitoring practice, they can be safely treated with safer chemicals in most cases. So how do we start?

Cultural Methods – Providing a Clean, Healthy Growing Environment

Sanitation is important to minimize friendly environments for insect pests to live. Algae, puddles, wet floors, weeds, dirty gravel, lack of airflow as well as lack of air exchange all set the stage for diseases and pests to establish and flourish. These can all be avoided with minimal effort.

Make sure that you don’t have any weeds in the greenhouse. Check along the edges, cracks in the sidewalk, etc. Random weeds are perfect resting places for bugs during the off season and serve as sanctuaries for all stages of insect pests. They’re just waiting for greener pastures which will come their way when you fill your benches.

Make sure, if you have a gravel floor, that you don’t have potting soil resting on top. Rake it out and sprinkle some fresh rock over the old to cover any organic material and improve aesthetics at the same time. Fungus gnats just love these little peat bogs and the algae that grows here.

Before each crop make sure you have disinfected benches, floor, etc. Greenshield, Physan 20 and other disinfectants work well. This is best done with the greenhouse empty.

Keep watering wands off the ground by resting them in hooks or on anything that will prevent them from making contact with the greenhouse floor. Here they can pick up all kinds of unwanted pathogens which can then be spread when watering. This will also extend the life of both valves and water breakers which don’t appreciate spending their idle moments underfoot.

Make sure that your ventilation fans are running at full capacity. Old or loose fan belts can cause slow rotation or excessive noise. Your HAF fans should be running well also. Air movement is much more important to plants than many realize. Air should be moving around the plants at all times.


Make sure your shade is off the greenhouse or rolled up for the winter months. Every ounce of available sun is needed for best plant growth.    

Make sure that your fertilizer injector is working and that the filter is clean. Also know what ppm you’re feeding your plants. You want to make sure you’re keeping plants well fed to make them grow as well as they can. A constant liquid feed each time you water (200- 250 ppm) is best for this. Please don’t judge this by the amount of blue dye you see in the irrigation water. You need to know exactly how much you’re feeding your plants.

Use a good soil mix. Test it first to make sure the wetting agent is still good if you’ve had this soil for over six months. Also make sure you space your plants as they start to grow into one another. Sun and space are two of the best growth regulators. Stronger plants will be the result.

The above strategies will make plants more resistant to pests and diseases. A good growing environment does this with good light, a good fertilization program and air flow. It is also important to exchange the greenhouse air even in cold winter months by “burping” the old, humid air out of the greenhouse and replacing it with fresh air from outdoors. Hopefully your greenhouse is set up to do this safely. Your heaters may run a bit more but the plants will be much better for it.

Physical Methods

We can also take steps in preventing pests from entering our greenhouses. Some will inevitably make their way in but if we can sure take steps to keep many of them out.

Prevent access into the greenhouse vents with insect screening. This is best done when building your greenhouse but can also be added later. In the image below a framework holds screening in place to where all insects are prevented from making their way in the vents and louvers. Various size screens are available and one wants to make sure that this is small enough for thrips prevention. If you’re planning to build or retrofit a greenhouse in the near future please consider adding this option.


Please do not overwinter pet plants. These are safe havens for so much that you really don’t want in your greenhouse. Many bugs are kept in hiding here until they jump over to your benches in late Feb and March in a very similar way to how they’ll jump over from any weeds as well.

Do your best to inspect incoming plant shipments. Again, bugs are impossible to totally eradicate and even professional propagators struggle to keep their operation clean. Aphids are the easiest to see on the newest growth and if you grow a poinsettia crop please inspect under the leaves for various stages of whitefly.

Use yellow sticky cards for both monitoring and catching some of the flying stages of these pests. It’s not a cure-all but does help. We’ll discuss this more in just a bit.

How do we actually implement an IPM plan and make it work?

***Start by reviewing and following through with everything listed under the Cultural Methods – Providing a Clean, Healthy Growing Environment section above. Please set this stage before planting your crop.***


Monitoring for pests

This is crucial for successful pest management. To detect and treat populations at low levels early in the season is much easier than treating later at much higher levels in April and May. “The best time to pull a weed is when it’s small”. Think of bugs in the same way.

We must understand that a greenhouse completely void of bugs is not a reality. There are no detrimental effects from having small populations of insect pests as long as they remain small. This is referred to as the “economic threshold level” where “the insect’s population level or amount of crop damage at which the value of the crop destroyed exceeds the cost of controlling the pest.” Put simply, it is basically the level at which the insect population or damage is tolerable until plants are sold. After they’re sold, they’re taken outside where the forces of nature will quickly make them go away. Sun, air movement and natural predators will quickly make these pests history and both the plants and their new owners will enjoy the summer without them.

The key to achieving a low population level is by scouting for pests. Think of this as a potential class project that can be implemented early in the growing season and followed through to a successful end.

You can make this scouting project very simple or complex depending on the amount of work or resources you have to invest into it.

On any level, the following is what is needed for this to be effective.

  • Some training to know ID of insect pests is imperative. One needs to know the life cycle of aphids, whitefly, and thrips, especially as they are the most problematic. All of this can easily be found on-line.
  • Here are some brief facts about each:
    • Aphids target newest growth/Bear wingless female young that then bear their own within a week/Growth rate is exponential once established/Very important to catch when young. Obvious signs are the husks (molted skins) that they leave behind.
    • Thrips are just as devastating and less noticeable/Hide in flowers and buds/Voracious (over time caused me more damage and grief than the other pests combined)/Growth rate is similar to aphids. These are easy to detect by shaking the plant over a piece of white paper to see what falls out. They’ll be gold to yellow in color and scrambling against that white paper. You can also exhale into the flowers and the CO2 in your breath will irritate them and bring them out where you can see them.
    • Whitefly are less of a problem but still something to be watched/easiest to see/larvae & eggs under the leaves.  They are easy to identify as they look like white gnats.

  • A magnifying Glass is very helpful as some life cycles of these pests are small, somewhat transparent and almost invisible to the human eye.
  • Scouting consists of routine inspections, ideally done weekly by the same people (for continuity). Pick several plants on each bench as well as a basket or two for each variety of plant. (Please don’t forget baskets that are hanging overhead and on automatic watering as these are often forgotten.
  • Inspect the plants from top to bottom, focusing especially on new growth (exception here are poinsettias where older leaves often hold the biggest part of the population).
  • Choose two plants per plant variety on each bench to inspect (pests have their favorites so it is best to make sure all varieties are checked).
  • Record what you find during these inspections weekly. This is also a good time to watch for nutrient deficiencies and any other abnormality that may exist. If possible do this on the same day every week and target mid-day as this is when insects are most active.
  • Yellow sticky cards are also a means by which to record populations. I would advise using the 3×5 cards and putting up new weekly after each inspection for a more accurate count. Yellow is the best color overall. 1 card per bench would work better for most school greenhouses. Place these cards a few inches above the plant canopy and with the flat side facing the wind-flow. Counts on these should be recorded weekly.

Treatments once pests are discovered

For spring crops, aphids are probably the first pest you’ll notice. Numbers will be small so, while it may sound silly, when you see these first few harbingers of spring just squish them! Remember that one can turn into ten which can then turn into 100 and so on. If you squish the first ones you’ve prevented a lot of aphids. This is not feasible on the commercial level but in the school greenhouse were you may have just 25 to 100 of a variety it is an option.

When small populations are detected they are often on the newest growth which makes sense since it is the most tender and tasty. This makes them easy to target. Neem oil, horticultural oils, insecticidal soaps can all be effective at this point. These safe, benign products are indeed effective if used before populations increase and establish themselves. As with any chemical please read the label and apply early or late in the day to avoid phytotoxic damage associated with sun exposure. Also make sure that the plants are hydrated. These treatments are safe for vegetable plants as well. Many of your stronger chemicals are not. Keep in mind that these sprays much make contact with the bugs to be effective.

If you want to take a preventative step against the buildup of pests, consider Marathon granules that can be applied to the surface of the soil in each pot. If applied correctly, this chemical will then translocate into the vascular part of the plants and provide systemic protection as days get longer and warmer and bug metabolisms kick into high gear. Systemic products have the benefit of affecting all feeding stages of the pest including adult and larvae. If you apply this early in the crop (late Feb/Early March) the potential to harm pollinators is no longer an issue once these plants find themselves in the garden and hanging on porches later on in April and May. Marathon is very effective on aphids, whitefly and, to some extent thrips. It affects what feeds from the leaves and stems rather than the flowers so is not as effective on thrips.

Again, please remember to read the label of any chemical carefully before using. There are other harsher, commercial chemicals that can also be used but in the school setting this can be difficult with REI’s and other restrictions. There are better ways.

In addition to the soaps, oils and chemicals above, considerer trying some biological controls to curb pest populations by using natural enemies to eradicate the pest target. This is a science that has come a long way. Many growers now use biologicals as a means of pest control and is best implemented when pest populations are low. The cost of these predators is relatively low and small quantities can be purchased. Some research is needed for knowing what to use and how often. These predators actively seek food and if they don’t find it they’re not going to last. If they’re blown out of the greenhouse by ventilation fans they won’t do much good either. A one-time release will not do the trick in most cases but routine scheduled releases will take you far in finishing a clean crop. As with other treatments this must be done early, before populations reach high levels.

I know this is a lot of information but if I can answer any questions or go into more detail on any of the above I would be glad to do so. Please feel free to reach out at any time.


Disclaimer!
If you’re doing something different in your greenhouse than is shared above and all is going well, please don’t change. Perhaps modify, experiment and consider but be cautious before changing a good thing. Successful growing is the result of many, many variables. Some we have control over and some we don’t. The above is only meant as a guide or checklist prior to the upcoming growing season.

Questions/Concerns?
If you need help or elaboration on any of the above topics, please feel free to contact us. If you need a source for or advice on annuals, perennials, pH or EC meters, soil or anything else, I can help you with that as well.

Happy Growing!

Mike Hellmann
Plants and Cuttings Manager

P.S. Curious about my background and how I got to Hummert? You can find out more here.

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