The following is information on spider mites in greenhouses. Mites are increasing at this time.
Spider mite activity is increasing this week. We are getting reports of spider mites on lantana, verbena, dahlia, sunflower and sweet potato vine. Several growers who have mixed baskets and have verbena and tricolor sweet potato vine are finding that spider mites build up rapidly on the these plants, and then spread to the other plants in the basket. When you stick a hanging basket up in the rafters of your greenhouse where it is hot you can expect that spider mites will thrive. Several growers are putting in neonectionoids (Marathon, Flagship, Safari, TriStar) to control aphids in the baskets. This works well on the aphids but if spider mites are present it tends to encourage the build-up of the spider mite population.
Control: The problem with spider mite control in hanging baskets is that they are located in the canopy of your greenhouse and if you spray from the ground it is difficult to get the coverage needed, especially when applying to baskets that are 12 – 16 ft up in the canopy. Apply systemic miticides such as Judo would probably give you the best contact with the spider mites. If you are using contact materials such as Floramite, Akari, Mesurol or horticultural oils then you need to direct the spray into the canopy and lift the undersides of the foliage. If you have a stair set I would suggest moving them so the spray can apply to the foliage from the top and really penetrate the foliage.
Reprinted from the May 29, 2009 edition of the Greenhouse TPM/IPM Bi-Weekly Report from the University of Maryland Cooperative Extension Central Maryland Research and Education Center