MELeaf: A Newsletter From the Horticulture Program, June 16, 2020

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MELeaf: A Newsletter From the Horticulture Program, June 16, 2020

In this issue:

After the Hanging Baskets are Sold: Late-Season Greenhouse IPM

We’re hearing reports of brisk plant sales this spring, which is great news for many of you! If you’re nearing the end of your spring growing season don’t forget to check off the items in your end-of-season IPM to-do list. It is best to clean greenhouses as they become empty rather than to wait until you are getting ready to receive your plant shipments next spring. Summer or fall cleanup will eliminate the over-wintering sites for pests and ensure the greenhouses are ready for incoming plants next year. Here are some tips:

Pest Scouting and Management: Check any remaining plants for insects, mites and disease. Consider discarding any infested plants that managed to get through the season unchecked. Or, if you can move them outdoors, let the natural enemies clean them up. Be sure to inspect for insects and weeds under the benches too. Remove weeds now to eliminate any insect harborage or disease inoculum. Collect the blue and yellow sticky cards and make a note of any pests captured.

Update and Review your Scouting and Pest Control Records: During the busiest time of year record keeping can fall behind. Update your records now before the ink fades, clipboards are misplaced, and the pesticide containers are recycled. Downloadable record-keeping forms are available on-line, such as at the University of Vermont Greenhouse IPM website. An electronic record-keeping system such as the Greenhouse Scout mobile app ($10 on iTunes or Google Play) allows you to keep and organize pest scouting, biocontrol and pesticide records in one place.

Harness the power of your pest management records by taking a moment to review and start planning for next year:

  • What tactics worked well?
  • Which ones didn’t give the results you expected?
  • How much did you spend on biocontrols, sticky cards and pesticides? Comparing this season with previous ones can be especially helpful when assessing efficacy and costs of biocontrols.
  • Did your biocontrol program keep anticipated pests from becoming detectable? If not, contact your biocontrol vendor to see how to maximize effectiveness for your operation.

Clean and Disinfect: Begin at the top and work your way down. Sweep down walls and internal structures and sweep or vacuum the floor to remove soil, organic matter and plant debris. Disinfect the benches and potting tables. Clean and disinfect all tools and any containers you plan to reuse. Clean and flush the irrigation systems. Seal up or use any open containers of potting media. Repair tears in worn weed mat barriers or, if overly worn, replace them. It is also a good time to correct any drainage problems and low spots in greenhouses.

Properly and thoroughly closing up your greenhouse is an essential part of a successful IPM program.

Additional Resources:

Notes From the Field: Observations from Nursery and Greenhouse Inspections


Aphids were a problem on some plants earlier in the season. For the past two years we have been seeing aphids on Angel Wings Senecio, a plant that many may not think to scout for aphids due to its fuzzy leaves. Our observations indicate that this may be a preferred host for some aphids and should be scouted regularly, paying careful attention to the growing tip and checking the underside of the leaves. As the season has progressed aphid issues have faded, but thrips populations surged on some plants, especially those in the aster family. Western flower thrips are the most common thrips we see in the greenhouse, but as production shifts from the greenhouse to plants outdoors there are other thrips that may become a problem. We observed a dark colored thrips on daylilies and thrips damage on daylily leaves and flowers is commonly seen.

Broad mites were identified on thunbergia in one greenhouse. Broad mites typically cause deformed and stunted new growth. This case was interesting as all the plants of one variety showed symptoms but not another variety that was in the same area. The cause of the damage was not determined until looking at the foliage under a microscope, illustrating the need for sometimes taking a closer look.


We saw very little botrytis during inspections this spring. This could be because we did not start inspections until later in the spring and by this time the weather had become dry and sunny. We did see some minor problems with powdery mildew, but these may have been infections that began early in the spring before the weather turned drier.  

More recently we brought a sample of an ailing pachysandra to UMCE disease diagnostic lab suspected of being infected with boxwood blight. The plant turned out to be infected with volutella, but because pachysandra is an alternate host for boxwood blight it is worth a closer look at any plants with blight-like symptoms. Volutella blight of pachysandra starts as small tan spots on leaves that enlarge into blotches containing concentric line patterns. Boxwood blight symptoms on pachysandra starts as small necrotic spots surrounded by yellow halos that enlarge as disease progresses.

We included an article on impatiens downy mildew (IDM) in an earlier edition of the MELeaf and we did have two greenhouses this year that reported receiving plants from out-of-state suppliers that were infected with IDM. There was also one sample submitted to the UMCE lab earlier this spring that was confirmed to be infected and we are hearing reports of this disease from other states as well. All the evidence points to this year potentially being a bad year for impatiens. While many greenhouses have probably already sold out of impatiens by now, it may be worth brushing up what to do when this disease is found in the landscape, in case customers come to you with questions.

There is good news to report on another disease. In another issue of the MELeaf, we told you about Ralstonia solanacearum race 3 biovar 2, a serious disease of solanaceous crops, that was found in the US on geraniums that had originated in Guatemala. USDA recently announced eradication of this disease from US greenhouses.

Additional Resources:

Thrips in Flowers (University of Maryland Extension)
How to Manage Thrips in Landscapes (University of California)
Broad Mite (Tennessee Extension Fact Sheet)
Volutella Blight of Pachysandra (Missouri Botanical Gardens)
Boxwood Blight (Purdue Extension Fact Sheet)
Impatiens Downy Mildew Grower Resources

From Around the Web: Websites, Webinars and Events for the Horticulture Industry