Bagworms are most common on evergreens. Eggs have hatched and small bagworms now range in size from about 1/4" to 3/4" and are tan to brown in color. They are moving around on host plants and can be difficult to see. When bagworms are small is the best time to apply chemical controls such as Permethrin, Carbaryl or Spinosad. In recent years, bagworms have completely defoliated Spruce and Junipers and control is recommended.
Fall Webworms are beginning to appear in trees such as cottonwood and crabapple. At this time of year, the webbed nests are small, but with time they will enlarge and become unsightly webbed nests filled with caterpillars, dead leaves, frass and worm excrement. While nests are unsightly, the caterpillars are fairly harmless to most established trees. Mechanically remove nests when feasible. Application of insecticides such as Bt (Bacillus thuringiensis), Perenthrin, or Spinosad when caterpillars first appear in July will reduce their numbers and web nest sizes.
Spruce Mite is a common cool season mite. This mite can be found on all types of conifers including spruce, pine, and juniper. This mite spends the winter in the egg stage
attached to host plants. The eggs hatch in March to April and the mites can complete development in 3 to 4 weeks.
If summer temperatures are constantly over 90°F, this mite becomes dormant and lays resting eggs. These eggs and adults resume activity in the fall when cooler temperatures return.
Conifers often react slowly to the feeding of this mite. Yellowing and bronzing of the needles may not become apparent until the heat of the summer, even though the damage may have occurred the previous fall and spring. Check for active mites before applying a chemical control at this time of year.
Spruce mites can be controlled during the dormant season (April) with dormant oil. When mites are detected in April or May and in September of October, insecticides such as horticultural oils, insecticidal soaps or Acephate are effective. A hard spray with water will help keep populations down.
Scale Insects damage plants by removing large amounts of plant sap from infested trees through their piercing-sucking mouthparts and can seriously weaken affected plants. They also excrete a shiny, sticky substance called honeydew, consisting of excess plant sugars, which drops onto surfaces below the affected plant and may be colonized by sooty mold fungi.
Oystershell Scale is a common insect pest of many woody plants. It feeds on plants by sucking plant sap. Heavy infestations can kill branches and even cause the decline and death of a plant. Oystershell scales overwinter in the egg stage. The eggs hatch in the spring and newly emerged insects attach themselves to the plant and develop the protective scale. Oystershell scales are best controlled when eggs hatch and light yellow crawlers appear, about late May. There may be a second hatch in August. Monitor plants at this time for the presence of yellow crawlers. Horticultural oils, insecticidal soaps, Acephate or Malathion are recommended controls.
Source: Horticulture Update
