Caterpillars Active in Cut Flowers Caterpillars Active in Cut Flowers

Earlier this season, a commercial cut flower grower sent in a picture of a caterpillar feeding on cut flowers. It was a geometrid caterpillar, commonly called a looper. If you just find one or two caterpillars active in your cut flowers, I would not get really concerned. If the population is much higher than you like, try using either Bacillus thuringiensis (Bt) or Spinosad (Conserve is one of the trade names). Both are bacteria that control caterpillars, but have minimal impact on beneficial organisms in your cut flower plots.

Fighting Fungus

With the unprecedented amounts of rainfall growers across North America are experiencing, likely as a result of human-caused climate change, plant diseases such as botrytis are increasingly common. A bio-fungicide called BotryStop was recently introduced by BioWorks and seems to be showing great promise when rotated with standard fungicides. This is an organic formulation developed specifically for the control of pathogens such as Botrytis cinereaSclerotinia sclerotiorum, and Monilinia spp. BioWorks claims that BotryStop provides protection to blossoms, fruit, and plant tissues. The active ingredient is Ulocladium oudemansii strain U3. If you are using this material, we would love to hear what you think on how efficacious it has been in your operation.

Speaking of Botrytis

Cool and wet weather sets the stage for botrytis blight in cut flower production. Lilies can be especially vulnerable to leaf spot and leaf blight caused by two botrytis species, B. elliptica and B. cinerea. These fungi are excellent saprophytes, meaning they survive on colonized dead plant debris, and produce masses of gray spores which can easily move through air currents. Cultural practices that make the environment unsuitable for infection are critical for managing botrytis diseases.Keeping leaf surfaces as dry as possible is key to disease management. 

Increasing plant spacing and keeping weeds under control both serve to increase air circulation around the plant canopy and encourage quick drying of wet foliage. If plants are irrigated, using drip irrigation reduces leaf wetness. If overhead irrigation must be used, watering early in the day allows for rapid drying of foliage after an irrigation event. Removing old fallen leaves, dead stems, and other plant debris around the lily planting will help reduce the stockpile of fungal spores near the planting. For more detailed information on managing botrytis blight in cut flower production, refer to this fact sheet from the University of Massachusetts: greenhouse-floriculture/fact-sheets/botrytisblight-of-cut-flowers

Four-lined Plant Bug

We have received reports of four-lined plant bug nymphs feeding on ornamental plants such as native pussytoes (Antennaria sp.), lyreleaf sage (Salvia lyrata), new foliage of panicle hydrangea (Hydrangea paniculata), Japanese anemone (Anemone x hybrida), and catmint. As they feed, the insects inject a toxin into the plant that causes the tissue to collapse and go necrotic. You end up with a series of small roundish dead spots on the foliage. Once the damage is present, there is not a lot to do about it. There is one generation per year early in the season. Some other host plants include herbaceous perennials like chrysanthemum, Chinese lantern, liatris, and Shasta daisy; herbs like mint and basil; woody ornamentals including azalea, dogwood, forsythia, viburnum; and flowering annuals such as zinnia and marigold.

This four-lined plant bug nymph is causing damage to catmint (top right) Photo: Marie Rojas, IPM Scout, Four-lined plant feeding causes necrotic spots on leaves of pussytoes (bottom right) Photo: Christa Carignan, UME-HGIC.

Stanton Gill

Extension Specialist in Nursery and Greenhouse IPM

Stanton Gill is Extension Specialist in Nursery and Greenhouse IPM, Central Maryland Research and Education Center, University of Maryland Extension and Professor with the Landscape technology Program, Montgomery College. Contact him at [email protected]