- May 25, 2018 GROWING DEGREE DAY TOTALS FROM 5/24/18: GDD TOTAL LOCATION

Transcription

1 - May 25, 2018 Weekly newsletter compiled by Sarah Pickel, PA Department of Agriculture. This week s scouting data contributors: Jim Fogarty (Halabura Tree Farm), Nancy Gregory (University of Delaware), Karen Najda (PDA) and Cathy Thomas (PDA). GROWING DEGREE DAY TOTALS FROM 5/24/18: LOCATION GDD TOTAL Elizabethtown, Lancaster Co Indiana, Indiana Co. 416 Montoursville, Lycoming Co. 393 New Cumberland, York Co New Ringgold, Schuylkill Co * Calculation via began March 1. ELONGATE HEMLOCK SCALE Last week in Dauphin County and this week in Schuylkill County, the first few crawlers of elongate hemlock scale were found moving on needles of Fraser firs. This hard scale pest feeds on the needles of several species of conifers (Hemlock, true firs, Douglas-fir and Crawler spruces). Infestations typically begin on the lower, interior limbs of a tree and will be detected by a faint yellow speckled appearance of the upper surface of the needles and a build-up of a gray coating over the limbs. The actual scales are found along the undersides of the needles. The gray flocking is from a waxy covering that the white maturing male scales develop. Female scales are different in appearance. Their covering is typically longer, smoother and brown in color. Aside from the discolored needles, this scale can cause needle casting in heavier cases. There are different options for control strategies for this pest: use of systemic insecticide or use of a contact foliar

2 spray. Systemic control done with product such as dinotefuran (Safari), as a trunk spray or soil drench, should be applied a few weeks before bud break. This allows for enough time for the product to be drawn up into the plant tissue when scale activity resumes in mid to late May. The other control options should be applied as the crawler life stage is found moving around on the needles (which is now for parts of Central PA). The crawlers or firstgeneration nymphs are the stage that hatch from the eggs inside the female scale coverings. Scales which have already developed their tough, waxy coverings are well protected from contact insecticide sprays. Unlike some other scales which have a short time frame of when a single generation hatches, Elongate hemlock scale can have a staggered hatch over much of the growing season. This is why several applications of those contact insecticides should be made, either 3 applications with 4 weeks between each, or 4 weeks with 3 in between. Some folks have found the chemical Spirotetramat (Movento or Kontos) acts systemically and only one foliar application. THRIPS ON TRUE FIRS Scirtothrips larvae in Nordmann fir bud [Nancy Gregory, Univ. of Delaware] In the last few years, some Christmas tree farms have been found with damage to Fraser, Canaan and Nordmann firs caused by feeding from Scirtothrips, a genus of thrips which little is known about. Thrips are a tiny, slender pest with a short life cycle that are a common greenhouse pest. The Scirtothrips

3 being found on these farms are bright yellow in color. Adults have wings that rest along their backs, but the larvae stages do not. Two weeks ago, a farm in Chester County saw thrips larvae activity in the newly opening buds, but also on the ends of twigs with still unopened buds. Last week, on a farm in Dauphin County, thrips were found on last year s growth. A good scouting method for this pest is to tap the twigs over a white surface or paper plate. The yellow thrips are small but their color will help them to stand out on the plate. The thrips feeding seems to damage the new needles inside the buds, which can lead to distortion, browning and needle casting, although the casting may not occur until later in the season. To control thrips population and prevent this kind of feeding, an insecticide application should be made as the thrips are found on new buds. Several applications may be necessary. Because this is a new pest on Christmas trees, not all insecticides will have them on the label. Products used in greenhouses, like spinosad (Conserve) or abamectin (Avid) could be applied; also, bifenthrin (Talstar) or other broader spectrum products which also include flower pests will be effective on this pest. Since Fraser buds are tender when just opening, take extra precautions to avoid pesticide burn (apply early or late in the day, avoid applying on days with temps in the 90s., etc.) NEEDLE CASTS OF DOUGLAS-FIR Growers should be continuing to treat for Swiss and Rhabdocline needle casts on their Douglas-fir. With the many days of rain Pennsylvania has been experiencing, it can be difficult to get applications on with the recommended timing. If Douglas-fir on your plantation are still staggered as far as bud growth is concern, applications should continue as long as the late brakers are still expanding.

4 SPRUCE NEEDLE RUST & NEEDLE CASTS In Schuylkill County last week, the yellow and orange Spruce Needle Rust lesions had begun to rupture and sporulate on Serbian spruce. Bud break on those spruce is greater than 90% in some areas. In total, three or more applications could be needed for good control. If needles are still expanding while last season s needles with sporulating lesions are still fresh. The lesions will turn brown and needles will be cast when sporulation is done. GYPSY MOTHS This week, maturing gypsy moth larvae were found in hardwood hosts. While oak and other hard woods are their preferred hosts, they can feed on conifers. When populations of the moth are high, these larvae can move away from the tree line and into conifer plots. If clusters of the larvae are found on Christmas trees, they can do damage to the tree. Nurseries that also grow hardwoods or fruit trees near Gypsy moth larva [Jon Yuschock, Bugwood.org] Christmas trees could see larvae moving into the Christmas trees. If, in heavy occurrences, control would be necessary, a Bt product targeting caterpillars, such as Dipel or Javelin, can be used. This would allow growers to conserve the beneficial predators that are present now. Another option could be to use a more general insecticide to spot treat perimeter trees with heavy amounts of larvae. BALSAM TWIG APHIDS At this time, as the percentage of breaking buds on Fraser, Canaan and other true firs increases, the balsam twig aphids have begun to cause damage. In York County, some twisted buds were being found in areas which had damage last season. Aphids move inside the open buds and feed on the young needle, causing them to twist. In Schuylkill County, this week, there were some populations of aphids were only found this week. While some of the buds are still closed or at least farther behind, some further damage could be prevented with an insecticide application at this time. This is not ideal for getting full control. Not only will some aphids be protected from sprays inside the open

5 buds, they can also seek protective shelter inside expanding cones. In fields where aphids have been a problem, growers may want to consider bagging cones to remove from the field as they are in the process of removing them. This can remove some of the aphid pressure. LOOKING AHEAD Two common Christmas tree pests that growers should be scouting for at this time are Bagworm and Cryptomeria scale. Larvae of bagworm will be hatching from the overwintering eggs inside those cone-like cases soon, with a typical GDD range of While this hatch has not been seen yet, potentially next week, little black larvae could be found escaping the casings on strands of silk. This pest is easier to control while caterpillars are still small. Cryptomeria scale behave similarly to Elongate hemlock scale and crawler activity can begin within a range of GDD. Populations checked this week south of York City were not found to have eggs yet. There is typically a 1-2 week delay between when eggs are found and crawlers hatch.