CSU RESEARCH UPDATE
By James E. Klett, Ph.D., CSU Professor & Extension, Landscape Horticulturist; and Ronda Koski, CGG, Research Associate, Colorado State University
In the production of container-grown herbaceous ornamental plants, “weeds” can be a perennial problem! Weedy plant species compete with ornamental species for moisture and nutrients, and can quickly take over containers, resulting in ornamentals with reduced growth and poor aesthetics. Hand weeding is one management option; however, this is labor intensive and costly. Application of pre-emergent herbicide products is another management option that can keep the containers weed-free for several months. However, not every pre-emergent herbicide product currently on the market is safe for use on every herbaceous ornamental.
The IR-4 Project (http://ir4.rutgers.edu) coordinates evaluations of herbicides and other agrichemical products for efficacy and safety on ornamental horticultural crops. Based on the accumulated results of numerous researchers throughout the U.S.A., labels of herbicides and other agrichemical products are periodically updated so as to provide plant nursery managers with up-to-date ornamental crop safety information.
For over three decades, Colorado State University has evaluated the effects of various agrichemicals on container-grown ornamentals. During this time, numerous pre-emergent herbicide products have been evaluated for crop safety. The following pre-emergent herbicides inhibit seedling development of numerous grasses and small-seeded, broad-leaved species; they will not control established weeds. The summary listed below is based on years of research conducted at CSU. Plant nursery managers may want to include these products in their weed management programs.
| 1) Biathlon: Oxyfluorfen + Prodiamine | |
| Formulation | Granule |
| Safe for use on | Berlandiera, Calamagrostia, Coreopsis, Helianthus, Lobelia, Pachysandra, Rudbeckia, and Sedum |
| Can damage and/or stunt plants of these genera (especially when applied at a higher rate) | Ageratum, Crassula, Dianthus, Echeveria, Echinacea, Osteospermum, Petunia, Salvia, Scabiosa, and Zinnia |
| 2) Dimension: Dithiopyr | |
| Formulation(s) | Many, including emulsifiable concentrate and granules; several products in combination with fertilizers |
| Safe for use on | Acalypha, Achillea, Ajuga, Anthrrhinum, Aquilegia, Arabis, Begonia, Callistephus, Celosia, Centaurea, Cerastium, Chyrsanthemum [some], Coleus, Coreopsis, Dianthus, Delosperma, Delphinium, Echinacea, Echinops, Erianthus, Fustuca [some], Gaillardia, Galium, Gazania, Heliotropum, Hemerocallis, Hosta, Iberis, Impatiens [some], Iris, Kniphpfoa, Lantana, Liatris, Lilium, Liriope, Mandevilla, Miscanthus, Monarda, Narcissus, Osteospermum, Pachysandra, Pelargonium, Pennisetum [some], Petunia, Phalaris, Plumbago, Portulaca, Rudbeckia, Salvia, Sedum [some], Senicio, Tagetes, Tulipa, Vinca, and Viola |
| Can damage and/or stunt plants of these genera (especially when applied at a higher rate) | Begonia, Chrysanthemum / Dendranthemum [some], Deschampsia, Eragrostis, Festuca [some], Guara (Oenothera), Impatiens [some], Lysimachia, Muhlenbergia, Pennisetum [some], Sedum, Phlox, Physostegia, Polemonium, and Viola |
| 3) Freehand: Dimethenamid-P + Pendimethalin | |
| Formulation | Granule |
| Safe for use on | Agastache, Anemone, Angelonia, Armeria [some], Astilbe, Catharanthus, Chelone [some], Chrysanthemum, Coleus, Dianthus, Echinacea [some], Gaura, Gazania, Gladiolus, Hemerocallis, Heuchera, Ipomoea, Iris, Lavandula, Lantana, Liriope, Lobelia, Lobularia, Oenothera, Pachysandra, Petunia, Phlox [some], Portulaca, Salvia [some], Sedum, Senicio, Solidago [some], Tagetes [some], Verbena, and Zinnia |
| Can damage and/or stunt plants of these genera (especially when applied at a higher rate) | Amsonia, Aquilegia, Armeria [some], Asclepias, Campanula, Chelone [some], Coreopsis, Chrysogonum, Echinacea [some], Echeveria, Gazania, Impatiens, Helianthus, Lamium, Lobelia, Matthiola, Phlox [some], Plumbago, Rudbeckia, Salvia [some], Scabiosa, Solidago [some],Tagetes [some], Teucrium, Veronica, Vinca, and all ornamental grasses |
| 4) Tower: Dimethenamid-P | |
| Formulation | Emulsifiable concentrate |
| Safe for use on | Agapanthus [some], Angelonia, Caladium, Calla, Celosia, Chrysanthemum/Dendranthema, Clematis, Coleus, Delosperma, Gomphrena, Hemerocallis, Hosta, Ipomaea, Lantana, Lilium, Liriope, Narcissus, Nepta, Petunia, Salvia [some], Tagetes, and Zinnia |
| Can damage and/or stunt plants of these genera (especially when applied at a higher rate) | Agapanthus [some], Aquilegia, Asclepias, Begonia, Berlandiera, Calamagrostis, Catharanthus, Dendranthema, Deschampsia, Echeveria, Echinacea, Epilobium, Festuca, Iberis, Impatiens, Miscanthus, Muhlenbergia, Pennisetum, Phalaris, Rudbeckia, Salvia [some], Sedum, and Teucrium |
| 5) Snapshot: Isoxaben +Trifluralin | |
| Formulation | Water dispersible granules |
| Safe for use on | Achillea, Anthirrhinum, Argyranthemum, Artemisia, Asparagus, Aster (Symphotrichium), Begonia, Berginia, Bidens, Brachycome, Callistepheus, Carex, Catharanthus, Chrysanthemum, Clematis, Corepsis, Cuphea, Dahlia, Delosperma, Descampsia, Dianthus, Erianthus, Erigeron, Erysimum, Eustomia, Festuca, Gaillardia, Gaura, Gazinia, Geranium, Geum, Gypsophila, Hakonechloa, Helichrysum, Hemerocallis, Heuchera, Hosta, Hymenoxys, Hypericum, Impatiens, Iris, Liatris, Limonium, Lobelia, Lobularia, Liriope, Lysimachia, Matthiola, Miscanthus, Monarda, Oenothera, Osteospermum, Pachysandra, Pelargonium, Pennisetum, Penstemon, Pentas, Perovskia, Petunia, Phalaris, Ratibida, Rudbeckia, Salvia, Scutellaria, Sedum [some], Tagetes, Verbena, Vinca and Zinnia |
| Can damage and/or stunt plants of these genera (especially when applied at a higher rate) | Acanthus, Ajuga, Arenaria, Brassica, Dicentra, Digitalis, Echinacea, Euphorbia, Geranium, Gypsophila, Iberis, Phlox, Pulmonaria, Sedum, Vinca, and Yucca |
| 6) Gallery: Isoxaben | |
| Formulation | Dry flowable |
| Safe for use on | Achillea, Argyranthemum, Asparagus, Aster (Symphotrichium), Begonia, Berginia, Bidens, Brachycome, Callistepheus, Carex, Catharanthus, Chrysanthemum, Corepsis, Cuphea, Dahlia, Delosperma, Descampsia, Dianthus, Erianthus, Erigeron, Eustomia, Evolvulus, Festuca, Gaillardia, Gazinia, Geranium, Geum, Gypsophila, Hakonechloa, Helichrysum, Heliotropium, Hemerocallis, Heuchera, Hosta, Hymenoxys, Hypericum, Impatiens, Ipomoea, Iris, Kniphofia, Liatris, Limonium, Liriope, Lysimachia, Matthiola, miscanthus, Oenothera, Osteospermum, Pachysandra, Pelargonium, Pennisetum, Penstemon, Pentas, Perovskia, Petunia, Phalaris, Phlox, Ratibida, Rudbeckia, Salvia, Scutellaria, Sedum [some], Tagetes, Verbena, and Vinca |
| Can damage and/or stunt plants of these genera (especially when applied at a higher rate) | Ajuga, Brassica, Echinacea, Euphorbia, Iberis, and Sedum [some] |
