Tag Archives: tree defoliation

Oak Wilt Disease Spotted on Long Island

Earlier this month, the NY State Dept. of Environmental Conservation issued a press release about the first known case of oak wilt, a serious tree disease, on Long Island. In June an arborist spotted symptoms of the disease in four trees in the Town of Islip and submitted samples from them to the Cornell Plant Disease Diagnostic Clinic, where the disease was identified. No treatment for oak wilt is known to contain and kill it other than removing infected trees and surrounding host oak trees, which was done in Islip. This is the second place in New York where the disease has been seen, the first being in Schenectady County in 2008 and 2013.

owleaves1

Note different patterns of infection on the white oak leaf (A), with its round lobes, and the red oak (B), with its pointy lobes.

Oak wilt appeared in the Great Lakes Region in 1944 and has since spread throughout the eastern United States, killing thousands of oak trees each year. Caused by the fungus Ceratocystis fagacearum, the disease creates blockage in the xylem vessels (sapwood) that conduct water within trees, slowing water delivery until leaves wilt and drop off. Red oaks succumb more quickly to the disease than white oaks and typically die within a few weeks of infection.

Oak wilt spreads three ways:

  • through underground root systems
  • through beetles that colonize infected oak trees and carry oak wilt to other trees
  • through the movement of firewood within and out of areas where trees are infected

If you witness unusual leaf wilting and drop off on oak trees where you live, please call the NYSDEC Forest Health Information Line toll-free at 1-866-640-0652 to report it.

To learn more about the symptoms of oak wilt and how to submit samples of oak trees suspected of having it, click here to visit the 2016 Oak Wilt Update  on the Cornell Plant Disease Diagnostic Clinic website. This You-tube video Oak Wilt in NY (made by Dr. George Hudler in 2008 after the first outbreak of oak wilt upstate) is very helpful in walking you through how to identify red and white oaks and how to prepare plant samples to submit for diagnostic testing.

Robin Simmen is Community Horticulture Specialist for CCE Suffolk. She can be reached at rls63@cornell.edu or at 631-727-7850 x215.

How Dry Was 2015?

Last year Suffolk County experienced its driest growing season in over twenty years. Riverhead received only 21.96 inches of precipitation from March 1 to October 31, 2015, which is 9.27 inches less than the ten-year average rainfall for Riverhead. The last four years in particular have seen a steady decrease in our precipitation, averaging only 26.22 inches in comparison with the previous six year’s average of 34.58 inches. We are surely in a dry spell, but only time will tell what 2016 has in store for us.2015 Seasonal Precipitation for RiverheadSo what did last year’s dry season mean for our landscapes? For one thing, we dragged the hose around more often in an effort to keep plants alive. This was especially true for container plantings, vegetable gardens, newly planted plants, and probably your lawn. Then again, if you left your landscapes to fend for themselves last year, it’s possible you’ll notice more winter damage this spring.

New plantings and transplants, especially of larger trees and shrubs, are probably the hardest to maintain in droughty growing seasons. Keeping the soil moist is very important for establishing strong plants. During the first year of planting, be sure to water trees deeply at least once every week during dry spells; with rainfall, once every two weeks should be fine. Applying a two- to three-inch layer of mulch around them will help keep their roots moist and reduce evaporation from the ground.

During the first autumn after planting trees and shrubs, watering them once every four weeks is recommended. In their second year, these plants should receive supplementary irrigation once every four weeks in the spring, once every three weeks in summer, and once every five weeks in autumn. The key to these waterings is deep and infrequent. A plant should always enter autumn and winter with ample moisture in its system. Research has shown that mid-August through September is the most important time to prepare plants to tolerate winter stress. Once winter arrives and the ground freezes, a plant cannot replace water lost to transpiration by winter sun and wind, making it susceptible to winter injury and die-back.

Most gardeners set out a few containers and pots of plants around their yard each year. These are the plants we need to watch closely during consistently hot, dry days. The trick to watering containers is just like any of your other plants: Water deeply! Let the water run until you see it coming out of the bottom of the pot, which will encourage roots to grow longer, deeper, and ultimately healthier and more resistant to dry days. This year consider creating containers filled with such drought-tolerant species as zinnias, gazanias, salvia, lavender, and dusty miller, or design contemporary containers filled with ornamental grasses or succulents. You could also invest in some self-watering pots that take the guesswork out of when and how much to water, so you don’t have to water your plants every day to keep them hydrated.

Last year after the first flush of spring growth, lawns quickly started gulping for rainfall. Many irrigation systems struggled to keep up with the water demand, and many homeowners without in-ground irrigation weren’t willing to set up sprinklers every day. Typically lawns require an inch of water per week, so professionals often recommend letting lawns without irrigation go dormant over the summer. The majority of lawns on Long Island are made up of cool-season grasses (Kentucky bluegrass, perennial ryegrass and fescues). These grasses look and perform their best in the cooler months of April-June and September-November and prefer to go dormant in the heat of the summer unless they are provided with adequate moisture.

Other factors besides drought last year may affect the health of our plants this year. White oaks were severely defoliated by gypsy moths in 2015. Although oaks can recover and push out a new flush of growth in the same growing season, last year’s drought while they were in recovery may be detrimental to their growth this year. Landscapes damaged by Super Storm Sandy may also be set back by the drought as sufficient water is critical to their long-term recovery. And established trees and shrubs that experienced root disturbances from new driveways, fences, pool installations, or any construction job using heavy equipment and machinery, may struggle as a result of the 2015 drought as well. How your landscape will look this year is pure speculation at this point, but bear these thoughts in mind when monitoring the health of your plants in 2016.

Sandra Vultgaggio is Horticulture Consultant for CCE Suffolk. She can be reached by email at sib7@cornell.edu or by phone at 631-727-7850 x387.

Gypsy Moth Defoliation across Long Island

After decades of very little gypsy moth activity, we are seeing “outbreaks” again this year. Many areas of Long Island have experienced extensive defoliation from gypsy moth caterpillars this summer, and other areas in New York and around the region (CT, RI, MA, PA) have also been affected. Homeowners are learning the hard way that touching the hairs on these caterpillars can be quite irritating, so minimizing contact with them is important, especially for those with sensitive skin.

Photo credit: USFWS/James Appleby

Photo credit: USFWS/James Appleby

Long Island’s NYS DEC Forester is aware of the situation, particularly since it is affecting forest areas and not just those in residential landscapes. At this point nothing can be done; gypsy-moth damage is about finished for the year. The adult moths are now active and egg masses are very obvious on tree trunks, suggesting we’re in for another round next year (there is only one generation a year). Trees that have been heavily defoliated should, however, be protected from a second wave of defoliation from other insects this summer, such as the orange-striped oak worm, which we sometimes see in August. One defoliation weakens trees, but a second one in the same season can kill them or make them more susceptible to opportunistic pests like two-lined chestnut borer. You’ll want to protect trees from defoliation next year, too, which would also weaken them. Now is a good time to examine cultural conditions around affected trees – are they getting too much or too little water? Do you see soil compaction, root competition, or root disturbance around them?

Our Horticulture Diagnostic Lab is a good place to get information on helping trees recover from gypsy moth defoliation and on management options to reduce the risk of damage next year. Call the Lab’s hot line at 631-727-4126 from 9 a.m. to noon. Options might include systemic treatment (trunk injection) where foliar pesticides aren’t an option, or foliar sprays where spray drift and getting tree adequate coverage are not problems. A fact sheet about the gypsy moth is available on our website: http://ccesuffolk.org/gardening/horticulture-factsheets/tree-and-shrub-insect-pests (Note: this fact sheet is for homeowners; CCE Suffolk has additional information for arborists and other professional applicators).

Many years ago a natural insect-killing fungus was introduced to control the non-native gypsy moth. This fungus has done a good job of regulating its population since 1988, but this year’s exceptionally dry spring probably contributed to the fungus’ limited impact this summer (we did see some evidence of it at Heckscher State Park and elsewhere). Unfortunately the fungus tends to “kick in” after some defoliation is already apparent, but when spring conditions are wet, the fungus can be highly effective in minimizing the problem the following year.

Late this summer we’ll be better able to gauge the risk for 2016 based upon counts of gypsy-moth egg masses. These counts are usually done by forest entomologists and professional foresters. The procedure is outlined in a document posted at the NYS DEC website (http://www.dec.ny.gov/animals/83118.html), providing an estimate of expected severity in the coming year. Homeowners can also check around their properties to see what might be in store locally for next year. Since the newly hatched caterpillars can blow around to other areas, infestations outside your property can also be a threat and should be taken into consideration. If you see lots of tan, felt-like egg masses in your area (including adjacent forest trees) then expect another year of significant damage in 2016.

If you have valuable, susceptible trees, you might want to plan accordingly by engaging a consulting arborist this fall or winter for spring treatment to deter risk of heavy defoliation. There are a variety of options, including some organic products and other products used as trunk injections (noted above) where spray drift or adequate coverage are issues. You can remove and destroy egg masses on trees during late summer through early spring; however since the caterpillars can migrate from other areas it doesn’t provide absolute protection in large outbreaks.

Dan Gilrein is Extension Entomologist for CCE Suffolk. He can be reached at dog1@cornell.edu or at 631-727-3595.