Landscape Message - Landscape Nursey and Urban Forestry

Winter Moth eggs began to hatch late last week, and larvae can now be found feeding within the swelling buds of host plants: maple, crabapple, birch, apple, blueberry, and others. Controlling the caterpillars now is challenging to say the least. However, once the foliage is open, these caterpillars then feed freely and can be managed with Bacillus thuringiensis Kurstaki (B.t.K.), while they are still small, or with a product that contains spinosad, or with a registered pyrethroid product. The moisture from the earlier part of this week coupled with the projected very warm weather for the end of this week should accelerate bud opening and, hopefully, limit the damage before this serious defoliator can be treated.

NOTE on Dormant Oil Sprays: Care should be taken at this time of the year when choosing to use dormant oil sprays. In the cooler regions of the state, such as Plymouth County, which has only accumulated approximately 26 GDD to date, may still allow for dormant oil use in many cases. However, be very careful if new plant growth is occurring. Also, oil sprays should not be applied if freezing temperatures may result 24–48 hours after application. Spraying oils on evergreens, especially conifers, can result in phytotoxicity at this time of year if conditions are not correct. In central MA and the Amherst area, it may be too late for dormant oil sprays now.

Hemlock Woolly Adelgid (HWA) is rebounding from the significant winter mortality it experienced in 2005 in Massachusetts. Monitor for the new egg masses that are appearing now. HWA can be managed with oil sprays at the summer rate if the weather conditions are conducive for its application without harming plants or with systemic applications of imidacloprid. (If oil is used, avoid tender new growth or conditions that delay drying time)

Viburnum Leaf Beetle was found in MA during the 2008 growing season in several different counties. It was known to be established in Berkshire county for the past 3 years but has now been identified in Franklin, Bristol, and northern Worcester County. Many of the finds suggest strongly that this serious pest is being moved on nursery plants throughout the Northeast. Inspect now for the eggs, which were deposited on the terminal twigs last season. When found, such twigs should be removed and destroyed prior to the eggs hatching in late April–early May. Larvae will appear soon after the leaves emerge and feed until approximately mid June whereupon they will pupate. Adult beetles appear about 2-3 weeks later and feed until the first frost. Much damage can occur, especially from the larvae. For more details and preferred viburnum host species, visit: http://www.hort.cornell.edu/vlb Spinosad products work well for the larvae. Inspect viburnum twigs now for any signs of eggs; prune out and destroy if found.

Asian Longhorned Beetle (ALB) was found in Worcester, MA last August. The Regulated Area is now at 64 square miles. Approximately 21,000 trees have been removed and rendered into wood chips since January 2009. It is estimated that this population may have been in Worcester for at least 15 years. Survey work has renewed within the Regulated Area, and it is already known that many more trees are infested. Everyone must be on the lookout for this pest and report any potential finds immediately if eradication efforts are to be successful. Also, take great care when moving firewood to avoid moving this very serious killer of forest and landscape hardwood trees.

To report a potential ALB find: http://massnrc.org/pests/alb
To see “How to Recognize ALB” slide presentation: recognize_alb_ppt.pdf

Balsam Twig Aphid will be active soon. The ‘stem mothers’ can be seen with a hand lens. These pale green aphids will feed on true firs, in particular, and then produce many offspring that will feed on the new needles as they emerge from the buds causing them to twist and curl. This insect also produces much honeydew, which causes new (twisted) needles to stick together. This pest is of most concern in Christmas tree plantations but can be problematic in the landscape. If found in significant number, treat with a registered pyrethroid or with a horticultural oil if weather and plant phenology allows.

Mining Bees and Ground Bees: Many reports have been received within the past 2 weeks concerning the activity in large numbers where the soil is suitable for them to build tunnels for offspring. Dozens or more at a time can be seen flying above the ground and entering into anthill-like holes in the ground. There are numerous species, but virtually all are quite docile and rarely, if ever, sting. However, their presence usually creates alarm for some people. Their busiest time is now and will continue for the next several weeks. After that, they usually become unnoticeable. Treatments are generally not applied given that these insects are important pollinators.

Hemlock Eriophyid Mites will be active soon, if not already in the warmer regions. These tiny, yet, just visible peg-shaped and four-legged mites feed openly on the needle surfaces of hemlock. Inspect carefully for their presence. Affected trees often appear slightly chlorotic. These mites can cause harm if they occur in large numbers. They remain active until early to mid June. When found to be numerous on any particular hemlock, treat with an oil spray (weather permitting) or with one of the registered pyrethroid insecticides.

Winterkill: Many evergreen plants, especially rhododendrons, experienced winterkill this past winter. The drooping and browning foliage now was actually affected last January or February. On cold but sunny days, the foliage of rhododendrons may actually perform some photosynthesis; but when the sun sets and the night becomes very cold, the foliage cannot replace the lost water from transpiration due to the plant’s roots being in frozen ground. The result is the death of foliage. This is often seen randomly within one plant and throughout plantings due to the exact micro-climate that forms around each shoot under such conditions. Some plants will be killed while others just escape injury. Wait a couple more weeks to see exactly which shoots are dead and then prune out these killed branches.

Inkberry Leafminer: This pest overwinters as a larva within the foliage of inkberry. The characteristic brown leaf tips usually do not appear until January and, thus, get missed by many. Hold browned leaves up to the light to see if the leaf has been mined or cut into the browned area in search of the larva. If numerous mines are found, wait until mid to late May to hang yellow sticky cards on the affected plants. Once the adult flies appear, treat with a pyrethroid insecticide to kill the adults and to limit the incidence of reinfestation of the same plants. Foliage without mines but possessing browned tips may have experienced some winter injury.

Birch Leafminer: This once prevalent pest has been in diminished numbers for over a decade now in Massachusetts. However, it does appear sporadically and has the potential to damage virtually every new leaf on native white-barked birches. The adult sawfly wasps will appear around the time that the host plant leaves are about half emerged from the buds, and the females will lay their eggs within the tender new foliage. If a large population is expected in a given area, hang a yellow sticky card from a host tree branch just as budbreak starts. Then monitor these cards every day for the emergence of the birch leafminer adults. Then treat with a pyrethroid insecticide to prevent egg-laying, if necessary.

Cottony Taxus Scale (a.k.a. Cottony Camellia Scale): Inspect for sooty mold and white cottony egg sacs on the undersides of foliage. Host plants include: certain hollies, Taxus, and others. Treat with a horticultural oil spray if proper plant phenology and weather conditions prevail.

Reported by Robert Childs, Entomologist, Plant, Soil and Insect Sciences Department, UMass Extension, Amherst.

UMass Extension Landscape Message #8
April 24, 2009

DIAGNOSTIC SERVICES

UMass Extension Landscape Message #8 April 24, 2009

DIAGNOSTIC SERVICES

UMass Extension Landscape Message #8
April 24, 2009