There are a number of pests that are active this time of year, before the temperatures warm up a lot.  A few of these are slugs, spruce spider mites, and the lily leaf beetle.  I’ll say a little bit about each one of these, provide links to more information, and also put in some photos.  I have been seeing slugs on my Hosta.  I was out looking at them right after a rain and they were out during the day due to the extra moisture.  Slugs are usually nocturnal.  They become active as soon as the ground thaws in the spring.  There are a number of control measures for slugs including:  Reduce humidity in the garden by allowing space around the plants; trap slugs by placing a board on the ground supported by small stones overnight and drowning the slugs in soapy water; barriers around susceptible plants such as pine needles, crushed egg shells, diatomaceous earth, or copper wire (shocks them); or use beer traps, containers of beer sunken into the soil.  Non-alchoholic beer is effective.

 

Slug photo from www.noematic.org.

Unlike some of the other mites, the spruce spider mite is most active at cooler temperatures and does most of its damage in spring and fall.  Symptoms may be noticed some time after the damage has occurred.  Mite feeding results in a stippled spotting of the needles and gives them a bronze appearance.  Hosts include spruces, arborvitae, dawn redwood, Douglas-fir, hemlock, juniper, larch and pine.  Dwarf Alberta spruce is quite susceptible.  Check for spruce spider mites by tapping a few branches firmly over a piece of white paper or cardboard.  Mites will be about the size of a period in this text and will move slowly.  Natural enemies of spider mites often keep their numbers in check so chemical controls are recommended only if mites are numerous.  Horticultural oils or insecticidal soap are effective.  Predators of the spruce spider mite include lacewings, predatory mites (these move faster than the plant pests on paper), lady beetles and predaceous midges. 

Photos: Close-up of spider mite feeding symptoms on arborvitae (Penn State), Symptoms on dwarf Alberta spruce (Penn State) and an adult spruce spider mite (Univ. of  Maryland). 

The striking red lily leaf beetles are feeding now and will be laying their eggs from June into July.  Larvae will also feed on lily leaves during late July and early August.  They then drop to the ground, pupate, and emerge as bright red adults to feed until cold weather.  They overwinter as adults.  Adults can live for two years, so it is possible to see them from April through October.  The lily leaf beetle feeds and lays eggs on true lilies including Asiatic, Oriental, tiger and hybrid lilies but not daylilies.  Control of these beetles can be achieved using handpicking or insecticides labeled for this pest.  Read and follow all pesticide label instructions carefully.  This pest is a non-native insect thought to have arrived in the US on lily bulbs from Europe.

 

Adult lily leaf beetle (www.maine.gov) and larval stage (www.uoguelph.ca).

JA