UMass Extension Landscape Message #8 - 2004

Scouting Information by Region

Environmental Data

The following growing degree day (GDD) and precipitation data was collected from April 15 through April 21, 2004. Soil temperature and phenological indicators were observed on April 21, 2004. Accumulated GDDs represent the heating units above the 50° F. baseline temperature collected via our mini-computers since the beginning of the current growing season. Please note that this data is particularly useful for pinpointing pest development at any time during the season.

Regional Notes

Cape Cod - General conditions: The weather turned more spring-like over the past week. While temperatures were quite warm off-Cape, we stayed in the mid-60's to mid-50's over the three day weekend. Lawns are greening up and plant material is beginning to develop green buds. Corylopsis paucifolia, the Buttercup Winterhazel, is a bright spot in the landscape. 'April Morn' Azalea is also in bloom. Daffodils and early spring bulbs are colorful. Pests/problems: Winter damage continues to be the main question coming in to the office. Warmer temperatures produced the first hatching of winter moth caterpillars. These tiny, eyelash sized caterpillars are just under bud scales of maples, crabapples and other deciduous trees. Lily leaf beetle adults are now feeding on emerging foliage of Asiatic lilies. Ants are active in weak turf areas. Termites are swarming indoors. Adult deer ticks are quite active; do tick checks after working outdoors.

Southeast - General conditions: Spring came quickly. Most of the accumulation of GDD occurred between Sunday and Monday of Patriot's Day weekend when the temperatures were in the 80's. Red maple, Cornus mas, pussy willows, Abeliophyllum distichum (white forsythia), Pieris japonica, Pieris floribunda (Mountain Pieris), Pieris 'Brouwer's Beauty, Leonard Messel Magnolia, Cornus mas (Corneliancherry dogwood), Helleborus orientalis, Corydalis solida, Omphalodes, Dutchman's breeches, bloodroot, vinca, daffodils, Pulmonaria, violets, and crocus are in full bloom. Helleborus niger and Iris reticulata are past bloom. Turfgrass has started to green up. This is the first year that Helleborus foetidus did not overwinter. Pests/problems: Winter moth caterpillars emerged on Patriot's day and were found inside developing apple buds. Larch casebearer, carpenter bees, mosquitoes, ticks, and eastern tent caterpillars are all active. Violets and dandelions are in full bloom. The Hanson office continues to receive calls relating to winter injury on a wide range of plant material, especially rhododendrons. Skunks are digging up lawns, and the orange jelly-like galls of cedar apple rust are present on eastern red cedar.

East - General Conditions: Warm and "springlike" other than on Patriot's Day when the thermometer reached 86° F. for the runners in the Boston Marathon. The Magnolia soulangiana greeted them with their full splendor.

Central - General Conditions: No report. Pests/Problems: No report.

West - General Conditions: The landscape has awakened after a warm weekend, with temperatures on Patriot's Day soaring to 91° F. Nights are still cool, however, and the days have been breezy. There has not been much in the way of precipitation since the last report. Forsythia is in full bloom. Turf continues to green up gradually, and dandelions are beginning to show up in many turf areas. Bees and ants are active. Pests/Problems: Winter damage continues to be evident on many broadleaf and needled evergreens on the UMass Amherst campus. Ticks are active.

Berkshire - General Conditions: Temperatures reached 90° F. on Monday, April 19. That pushed the growth of many plants. By mid week, temperatures returned to near normal. The biggest concern was high winds that accompanied the cold front that followed the two day heat wave. This resulted in breakage of many tree limbs. The winds also hastened the drying of soils and organic debris on the ground. The potential for fire in forests and grasslands is high. Landscapers considering burning of brush should be aware of local restrictions on burning. Where open burning is permitted, it should be done with great care. Pests/Problems: With warmer weather, some of the effects of the cold winter are becoming apparent. Signs of winter desiccation of broadleaf and needled evergreens is more and more noticeable as spring progresses. The death of marginally hardy plants, such as lavender and zone 5 (or above) roses has been observed.

Phenology

The phenological indicators are a visual tool for correlating plant development with pest development:

• CAPE COD REGION - Roberta Clark, Horticulturist for Barnstable County, Barnstable.
• SOUTHEAST REGION - Deborah Swanson, Horticulturist for UMass Extension in Plymouth County, Hanson.
• EAST REGION - James R. Allen, Horticulturist and Greenhouse Manager for UMass Biology Department, Boston.
• CENTRAL REGION - Joann Vieira, Superintendent of Horticulture, Tower Hill Botanic Garden, Boylston.
• PIONEER VALLEY - Dan Gillman, Plant Pathologist, Urban Forestry Diagnostic Lab, UMass, Amherst.
• BERKSHIRES - Ron Kujawski, Specialist, UMass Extension Landscape, Nursery & Urban Forestry Program, Amherst.

Woody Ornamentals

Insects

Winter injury to broad-leaf evergreens (rhododendrons, holly, mountain laurel, etc) continues to be extremely noticeable as affected foliage dries and turns brown. In most cases, buds remain alive. Pruning can wait until the full extent of injury is known. In much of the state, it is now too late for the application of dormant oil sprays. Monitor plant development (growth) carefully if applications of this product are desired. A much increased risk of phytotoxicity now exists.

Caterpillars

In general, products containing Bacillus thuringiensis (B.t. kurstaki) are very effective against the younger free-feeding caterpillars in the Lepidoptera only. Products that contain Spinosad are generally very effective against caterpillars in the Lepidoptera and the Hymenoptera (wasp-like as adults). There are also many chemical insecticides that are labeled for caterpillars, which are pyrethroids, organo-phosphates, carbamates, and other classes.

Lepidoptera (moths):

• Winter Moth eggs began hatching last weekend (April 18, 2004) and continues. New larvae are entering buds (foliar and flower) by crawling in between bud scales. Recent warm weather has accelerated bud opening which should reduce the amount of potential injury. However, the caterpillars will be free feeders on foliage for many weeks to come.
• Eastern Tent Caterpillar and Forest Tent Caterpillarare expected to be in large numbers again in SE Massachusetts, at least. Monitor now for new silken webs (ETC) that are appearing in branch crotches. Currently they are 2-3" in diameter. Small infestations can be removed and destroyed by hand while the caterpillars are still within the webs or treat with one of the recommended biorational pesticides. FTC will be hatching very soon.
• Larch Casebearer Caterpillars caterpillars are beginning to migrate out onto the branches and the buds. They will feed on the needles as they emerge. B.t. kurstaki or a Spinosad product works well against feeding caterpillars.
• Gypsy Moth caterpillars, although limited this year in numbers, will begin to hatch within the next couple of weeks (90-100 GDD). Last year's wet spring and summer contributed greatly to the spread of the fungus, Entomophaga maimaiga which is very effective, naturally, at killing this caterpillar.

Hymenoptera (sawflies):

• European Pine Sawfly - Although still early, begin to monitor such pines as mugo for the rows of yellow eggs in the needles that appear in neat, blocky rows. Prune out and destroy when found.

Beetles

In general, products containing Spinosad are effective against the larvae (at least) of many free-feeding beetle species. However, there are also many chemical insecticides that are labeled for caterpillars, which are pyrethroids, organo-phosphates, carbamates, and other classes.

Leaf Beetles:

• Lily Leaf Beetle - Adults of this bright red beetle are now emerging from winter dormancy. Monitor for their appearance on true lilies, fritillaria and Solomon seal. NEEM products are effective but need to be reapplied every 10-14 days as long as this pest is active.

Scarab Beetles:

• Grubs in lawns in lawns will be moving up into the top layer of soil soon. Refer to the Turf Insect Section below for specific details.

Piercing-Sucking

In general, imidacloprid applied systemically is very effective on most, with the exception of spider mites. Horticultural oil or insecticidal soap, especially against the immature stages, is usually very effective.

Lacebugs: It is still too early for the emergence of these pests on trees and shrubs.

Plantbugs:

• Honeylocust Plantbug will hatch from eggs, that are embedded in the shoots, around the time of bud-break on the host plant. Monitor at that time by gently shaking branches over a white piece of paper and inspecting with a hand lens. If deemed necessary, apply an application of insecticidal soap, or one of the registered chemical insecticides.

Aphids:

• Balsam Twig Aphid (BTA) is now active (prior to bud break of the host; mostly balsam and Frasier fir). The stem mothers feed a bit and then produce a multitude of offspring. These will feed on the newly emerging needles and cause distortion. BTA produce much honeydew. In the nursery (Christmas tree plantations as well) Chlorpyrifos works well once the insect is active; monitor closely. Carefully timed and applied horticultural oil sprays are also helpful. Many other chemical insecticides are labeled for this pest.

Adelgids:

• Hemlock Woolly Adelgid can still be treated with horticultural oil but monitor plants carefully for their stage of development. Avoid oil sprays on newly emerging tender foliage. There is evidence that much winter mortality occurred (perhaps as high as 80-90%) and inspections should be made prior to applications to determine if they are necessary.

Other Piercing-Sucking Insects:

• Spider Mites - Several growth regulator products are available that offer high levels of control; mostly for population numbers that are low to moderate in size. Most are so specific that they kill spider mites but not the beneficial predatory mites. Some even posses ovicidal (egg-killing) qualities. Horticultural oil sprays can also be very effective. Many insecticides and miticides are specifically labeled for spider mites as well.
• Spruce Spider Mite will resume activity very soon. Inspect by gently shaking branches over a white piece of paper and then inspecting with a hand lens. Monitor weekly to establish if population numbers increase significantly. Treat if necessary.

Eriophyid Mites:

• Hemlock Eriophyid Mite (not a spider mite). This tiny, peg-shaped, four-legged mite feeds openly upon needle surfaces. Inspect for its presence. Plants with high levels of infestation become chlorotic. Treat with a horticultural oil spray when necessary.

Root and Shoot Feeders

• White Pine Weevil adults have been active for many weeks. The vast majority of their egg-laying in terminal shoots has now occurred in much of Massachusetts. Monitor and treat, if needed; but it may be too late for effective controls.

Leafminers

• Birch Leafminer - Hang yellow-sticky cards in the branches of the host plant now as bud break is starting to occur in warmer parts of the state; monitor for adult activity. Treat with a registered insecticide when the adults appear, to break the cycle of re-infestation.
• Inkberry Leafminer is active within the mines as a larva. Pupation will occur shortly. Monitor for the adults with yellow sticky cards in mid-late May. Inspect plants now for the brown mines to gauge the levels of infestation. Treatment is aimed at the adult flies when they emerge. However, much winter injury has occurred to foliage of inkberry and may currently mask infestations.

Scale Insects

In general, horticultural oil sprays work well against most armored scale species, especially when they are in the crawler stage. Imidacloprid does not work well on armored scales but is much more effective against many soft scales.

Armored (hard) Scales:

• Monitor for Pine Needle Scale on mugo and Scots pines, in particular.
• Monitor junipers for Juniper Scale.
• Monitor different euonymus for the Euonymus Scale.

It is now too late for dormant oil sprays. Therefore, monitor each at the appropriate time of the season for crawlers and treat again at that time, if necessary.

Soft Scales:

• Monitor taxus and certain hollies for the Cottony Camellia Scale (aka: Cottony Taxus Scale). Treat the over-wintering nymphs with an oil spray.
• Begin to monitor azaleas for the Azalea Bark Scale. Inspect inner branches for nymphs and sooty mold. Treat with an oil spray if necessary.

Gall Formers

• Eastern Spruce Gall Adelgid and the Cooley Spruce Gall Adelgid are still exposed at the base of healthy buds (Norway and white spruce for ESGA and Blue Spruce of CSGA). Monitor for population size and last year's level of injury. Treat with a dormant oil spray if necessary. (Reminder: oils cause blue spruce to turn green for several months, which may be unacceptable to some clients). Also, monitor plant growth stage carefully. In some cases now, it's too late for dormant oil sprays.

Wood Attackers

Monitor previously stressed plants (drought, soil compaction, etc.) for signs of invasion.

• Bronze Birch Borer is one such invader. Water infested trees during drought periods. Insecticide injections may be effective in some cases.
• Conifer Bark Beetles, such as the Black Turpentine Beetle, invade stressed trees. Inspect for pitch tubes and streaks of pitch on the bark. These are a sign of an already weak tree. Water during times of drought.

Nuisance Pests

• Western Conifer Seedbugs that over-wintered in homes are still emerging from dormancy and once again becoming a nuisance in the home. Vacuum and then remove the vacuum cleaner bag afterwards. They will eventually leave the home or die. They neither bite nor sting. They feed on conifer seeds and are not threatening to plants.

Reported by Robert Childs, Entomologist, UMass Extension Landscape, Nursery and Urban Forestry Program, Amherst

Diseases

Cedar-apple rust galls on eastern red cedar (really a juniper) and Rocky mountain juniper are erupting with the orange, gelatinous telial horns in eastern and central Massachusetts. The orange, gelatinous horns release spores that infect apple and crab apple leaves at this time of the year during cool, rainy periods.

Leaf spot and shoot blight diseases were widespread last year because of the extended periods of rainy weather in the spring and again in mid-summer in many regions of Massachusetts. The recent spring rainfall has given plants a good watering; but with young leaves developing and lots of over wintering inoculum around, trees and shrubs are vulnerable to new infections at this time. It is especially the case when accompanied by temperatures of 55-75° F. This is the best time to begin protective fungicide applications to nursery and specimen woody landscape plants that are known to be susceptible to these types of diseases.

There were recent news reports about Sudden Oak Death (SOD), caused by the fungus Phytophthora ramorum. SOD is a severe disease of oak and tanoak in certain Pacific Northwest fog forest areas. In March 2004 Phytophthora ramorum was found in two large ornamental nurseries in southern California. This detection demonstrates that the pathogen is not necessarily limited to the moist coastal regions of northern California and southern Oregon. At least one of the two nurseries distributes nursery stock nationwide, including Massachusetts. To date, Phytophthora ramorum has not been found in Massachusetts, though it has been positively identified in Florida and Georgia. The Massachusetts Department of Agricultural Resources (MDAR) is monitoring this situation carefully. A number of surveys are planned by MDAR, the United States Department of Agriculture (USDA) Forest Service, and the USDA Animal and Plant Health Inspection Service nationwide and in Massachusetts to check for the presence of Phytophthora ramorum in nurseries and natural forest areas.

This pathogen has a wide range of host plants, including rhododendron, viburnum and camellia, which are potential 'carriers' of the fungus when plants are transported. The damage on non-oak hosts involves minor leaf spotting and twig dieback. However, infections on these non-oak hosts may contribute to a rapid build-up of the fungus in the environment, serving therefore as a reservoir of inoculum, which in turn infects woody tissues of oaks and tanoak trees.

Landscape, Nursery, and Urban Forestry Diagnostic Lab Report

The following are some of the interesting disease/abiotic disorder samples received at the UMass Extension Landscape, Nursery, and Urban Forestry Diagnostic Lab in Amherst during the period April 12 through April 16, 2004:

• Apple - dead branches are overgrown with gray-green leaf-like and hair like growths and there was concern they caused recent branch dieback; non-parasitic foliose (leaf-like) and fruiticose (hair like) lichens thriving in the sunny, moist conditions that developed after the branch died and the leaves were absent.
• Euonymus - pale, brown-spotted foliage on most of several established plant in a landscape; winter drying/opportunistic Pestalotiopsis leaf spots exacerbating damage.

Reported by Dan Gillman, Plant Pathologist, based in the Urban Forestry Diagnostic Lab at UMass, Amherst, Mass

Landscape Turf

Insects

Many people have been asking about options for control of white grubs during the spring. Here's the situation as I see it:

Until recently turf managers had three basic approaches they could consider for controlling white grubs in New England.

• They could wait until problems developed and spot treat with a fast-acting material like trichlorfon (Dylox™).
• Apply a slow-acting but long lasting material like imidacloprid (Merit™) in the summer to prevent subsequent infestations, or
• Use an intermediate material in late summer.

The intermediate materials (most of which are either already gone or are being phased out) usually worked within four to seven days after application and remained active for four to six weeks. We have essentially lost the "intermediates" for many aspects of turf management, so my comments today will be restricted to the fast and the slow options.

Imidacloprid, often sold as Merit™ or under other trade names, takes two to three weeks to start working but will remain active two to six months, depending on when it is applied and how often it has been used in a given location. It is not recommended for use in the spring because field trials conducted in Ohio, Pennsylvania, Massachusetts, and other locations over the years have shown that it does not normally have any impact on the grubs that are present in the soil in the spring. (In other words, grub populations are not significantly lower in treated plots than in untreated plots.) This is a source of frustration for us in academia because many formulators of imidacloprid aggressively market it as having "season-long control", which of course implies that an application made in the spring should control grubs that are already present. University research refutes that claim.

Imidacloprid normally should be applied between late June and early August in New England to maximize its effectiveness against the various species of white grubs we experience here. (It can be applied slightly earlier if absolutely necessary, but in most cases the six week window given above is "ideal".) Such an application is in the soil as the eggs begin to hatch and the tiny larvae emerge. Note that imidacloprid is slightly less effective against European chafers than it is against Japanese beetles, and the timing of application becomes that much more critical when the primary species is European chafer. Another product that has a similar window of opportunity is halofenozide, often sold as Mach 2™. This product is a "molt accelerating compound". It is not a traditional nerve poison, like so many other turf insecticides, but instead interferes with a grub's ability to molt successfully, either from the first to the second instar or from the second instar to the third instar. Once a grub reaches the third instar, halofenozide will have no impact on the insect. So late summer or early autumn applications do not make sense because most grubs have already molted to the largest grub stage by then. Similarly, spring applications are not effective because the grubs that are present in the spring are the same large grubs that were present the previous fall. So... applications should be made just as the earliest eggs begin to hatch. That may be as early as late June for European chafers in southern New England or mid August for Japanese beetles in northern New England. (This is yet another example of why it is important to know which species of grubs you have in a given location.)

The only product that provides "after the fact" coverage for white grubs and is still available in the turf market is trichlorfon, usually sold as Dylox™. This material normally will kill grubs within one to three days after application but breaks down in seven to ten days. It is highly soluble and therefore quite mobile, so must be used with care in areas with sandy soils or shallow water tables. But the fact that it breaks down quickly usually minimizes the likelihood that the product will move to groundwater. Dylox™ can be used in the spring to "clean up" grub infestations that become apparent. Applications probably should not be made until soil temperatures (top two inches) are at least 50 °F, and it is possible that temperatures need to be even warmer than that. (I am not aware of any field trials testing the efficacy of Dylox™ in different soil temperatures, so this is a "best guess" on my part.) Late season applications can be made as late as mid to late September, particularly if the autumn is an unusually mild one.

There are two key points: First, any application made to control white grubs MUST be watered in. You should aim for at least 0.1 inch, but in general the more water follows an application, the more effective it will be - up to a point, of course. Up to a half inch of water would be fine for Merit™ or Mach 2™, while up to 0.25 inch would be good for Dylox™.

The second key point is that Merit™ and Mach 2™ normally should NOT be applied in April and May to control white grubs unless there are extenuating circumstances. (Examples of extenuating circumstances would be: a golf course dealing with black turfgrass ataenius and trying to get control of both the BTA and Japanese beetle grubs, or possibly an athletic field complex that cannot water in an application in July or August.) Spring applications of Merit™ or Mach 2™ normally will not reduce spring grub populations significantly and, because they are four to eight weeks earlier than the ideal application dates, may be markedly less effective than the July applications, particularly if the primary species is European chafer or oriental beetle.

Pat Vittum, Professor, Turf Entomology, Department of Plant, Soil & Insect Sciences, UMass, Amherst.