1998 will go down as a year of extremes. The forecasted effects of El Nino came true as an unusually mild winter and early spring was experienced. The summer featured extended dry periods, bouts with severe weather that recently included baseball sized hail in Niagara Falls.
The growing season began early and for much of the year crops were well ahead of schedule. Unfortunately the same mild weather that promoted plant growth also encouraged pest problems.
Epidemic levels of insects including gypsy moth, viburnum leaf beetle and the fungus disease tar spot affected parts of Niagara County in 1998. Dry conditions in late summer encouraged rust on lawns and leaf scorch on trees. Damage from chinch bugs, grubs and diseases such as Fusarium and summer patch have been noted on turf.
Tar Spot - This fungus disease of Maples is well established in Niagara County and other parts of New York. The following article summarizes some current information on the problem and indicates it is more severe to our east.
Table of ContentsThe current season has brought with it an incredible attack of foliar pathogens on Norway maples in the Ithaca area. Residents of the town are understandably alarmed to see hundreds of large trees with hardly a live leaf left and foliage dropping as it normally would in September. As one views treed hillsides from a distance, the crispy brown Norway maples stand out in stark contrast to the lush green of other species. While the ultimate fate of the trees remains of concern, the situation is reminiscent of a similar episode in New Hartford (just south of Utica) in the mid-1980's. There, virtually all affected trees survived, and we're hoping for a similar outcome this time around. A major contributor to the damage on the Norway maples is, unquestionably, the tar spot pathogen, Rhytisma acerinum. This fungus is native to Europe where it commonly attacks Norway and sycamore maples. It was apparently introduced to North America in late 1930s with the first official report of its occurrence appearing in 1941 from a site in northeastern Ohio. The disease didn't cause enough damage to warrant concern then for 45 more years, until the outbreak in New Hartford came to our attention. That episode, presumably triggered by favorable weather conditions for both host and pathogen, subsided in subsequent years, and the town has not seen a repeat.
In 1986, a survey of Norway maples throughout the Northeast indicated that only those in the Utica/New Hartford area and in East Aurora, NY were affected with tar spot. However, within a few years the disease was found in about a 20 mile wide band from Jamestown to Albany. It was conspicuously absent from Binghamton, Elmira, Corning and other Southern Tier Communities, and remains at low levels in those cities today. Meanwhile, the disease has also spread to southern Vermont and New Hampshire, western Massachusetts, and down the Hudson Valley to northern New Jersey and Long Island. Several diseased trees were also found in State College, PA in 1996 (it has presumably increased since then) and we have had several frantic calls from neighbors to the west in Ohio and Michigan. Observers in southern Quebec also report occurrence of the disease.
From the first report of a tar spot on Norway maple, we have wondered how that fungus might be related to a fungus by the same name commonly found on red and silver maples in North America. Recently, using host range observations. Microscopic characters, and DNA sequence comparison, we have concluded that Norway maple pathogen is, indeed, the true Rhytisma acerinum described by Elias Fries in the mid 1800s. The pathogen on red and silver maples is a different fungus, which we have named Rhytisma americanum. R. americanum is occasionally collected from red or silver maples in Europe, but it seems to have been transported to that continent from North America.
Despite the conspicuous presence of tar spot on Norway maples in Ithaca this year, it is obvious that it is not the only fungus involved in the death and premature drop of leaves. At least two other fungi - both yet to be conclusively identified - are apparent on the shriveled leaves. One is apparently related to the group of fungi that cause anthracnoses while the other makes spores in submerged, flask-shaped bodies and thus is a member of another group. Our best guess at this time is that the massive tar spot infections predisposed the leaves to attack by the other two fungi, and they are responsible for actual leaf death. In some cases, we find conspicuous lesions on leaf petioles as well as blades. The petiole infections can result in leaf death long before the blades are colonized by pathogens.
Insofar as the prognosis of the trees is concerned, we are cautiously optimistic that this year's victims will rebound next year not too much the worse for wear. Deciduous trees typically maintain enough stored food reserves to survive at least one complete defoliation, and we expect our Norway maples to be no different. However, if the disease(s) repeat their attack with equal severity in 1999, then we could begin to see death of some large and valuable specimens.
Is there anything to be done now or next year to help trees cope with the present crisis? For the short run, it is advisable to be sure that managed trees have adequate access to water. Despite seemingly endless rainfall earlier in the year, we are not into our second week without significant rainfall, and if this should persist for another week, watering of the trees would be worthwhile. Water is not only necessary for maintenance for turgor and conduction of basic life processes, but it is also important for production of defensive barriers against other pathogens. Water stressed trees are much more likely to be attacked by opportunistic organisms.
In a normal year, we would also recommend raking and destroying diseased leaves. However, with so much infection on so many trees, anything less than a total cleanup of all leaves is likely to be for naught. On the positive side, we expect that most, if not all, of the leaves killed before mid-August probably won't make spores to infect next year's leaves. Thus, the premature death of many leaves should actually lead to reduced inoculum loads and reduced disease in 1999.
Several fungicides are registered for control of tar spot on maples, and timely application of one of those next spring can do much to reduce disease incidence. However, because most Norway maples worth saving are growing around and near highly populated areas, efforts to apply sprays to them may meet with some resistance. Both triadimefon and mancozeb have proven to be effective. We'll be testing injectable fungicides in 1999 to try to cope with problems associated with drift and non-target contamination.
As landscape managers begin to select future generations of trees, Norway maple is probably not a good choice…at least not until tar spot resistant individuals are identified and propagated. Be advised that we have also found the disease on hedge maples in Ithaca. Defoliation is not nearly as severe as it is on Norway, but the spots are conspicuous.
Table of ContentsA rapacious leaf beetle is chewing its way through ornamental bushes in western New York, Cornell researcher warns. Two years ago, the viburnum leaf beetle (Pyrrhalta viburni), a pest with an appetite for certain ornamental bushes, was found in upstate New York along the Lake Ontario shore. Since then it has been chewing its way steadily south, and now a Cornell University entomologist says the pest has been found in Geneva, New York.
'The damage is very striking. The beetles devour the leaves of the viburnum and totally skeletonize the leaves,' says E. Richard Hoebeke, associate curator of the Cornell entomology collection. 'There's nothing else that attacks vibrunum like that.'
In early June Hoebeke issued an alert to Cornell Cooperative Extension (CCE agents throughout New York State asking them to be on the lookout for reports from homeowners and nurseries of viburnum damage.
'This alert is meant to introduce you to this new pest situation,' said Hoebeke in his message. 'More importantly, if there are other inquiries from homeowners, landscapers, and arborists coming into the county (CCE) offices, I would like to know about it.'
Hoebeke first discovered the viburnum leaf beetle in the area on July 5, 1996, at Fairhaven Beach State Park in northern Cayuga County along the shore of Lake Ontario. That summer he also found the pest in Monroe, Orleans, Niagara, and Jefferson counties. Now, two years later, the counties of St. Lawrence, Oswego, Ontario, Wayne, and Genesee have joined the list.
The insect was first discovered in the United States in 1947, although Hoebeke believes the beetle first entered the country from Europe on nursery plants around the turn of the century. It was not seen in North America again until 1955 at Font hill, Ontario. The insect then went undetected for 31 years, until it was found again in Ottawa, Ontario, and Hull, Quebec. Scientists have kept track of its movement since.
Hoebeke says that the leaf beetle caused severe defoliation of ornamental viburnums in the Ottawa-Hull region in 1978. The beetle attacked the popular European highbush cranberry viburnum or Guelder rose (Viburnum opulus), as well as arrowwood viburnum (V. dentatum complex), American highbush cranberry viburnum (V. trilobum) and mapleleaf viburnum (V. acerifolium)
The beetle is extremely difficult to see, resembling a small dark-brown blotch, about the size of the head of a large, kitchen match-stick. Its effects are unmistakable: Shrubs reduced to leaf veins and branches.
The larvae of the beetle are equally as destructive to ornamental plants as are the adults. Beetle larvae hatch from eggs in early May and feed on the viburnum leaves throughout the larval period, which lasts 8 to 10 weeks. Biyearly to mid-July, the adults begin to appear and continue feeding on what remains of the leaves. They then mate and lay eggs on the shrub's twigs.
Homeowners or landscapers should contact their county CCE office if they suspect the presence of the beetle on their ornamental viburnum tree or bush.
The Ontario Ministry of Agriculture, Food, and Rural Affairs (OMAFRA) runs an informative web site on the pest. The address is: http://www.gov.on.ca/OMAFRA/english/crops/facts/vlb.htm. Cheryl Frank, Editor, Electronic Information Services, Cornell
Table of ContentsThe influential Dutch Bulb Program in the United States has moved to Cornell University from Raleigh, N.C. The selection announcement noted that the move is a tribute to Cornell's extremely long and prestigious horticultural tradition.
The announcement was made by the Dutch Wholesalers Association for Flowerbulbs and Nursery Stock and by the North American Flowerbulb Wholesalers Association, made up of representatives from the Dutch and U.S. flower-bulb and greenhouse industry.
In recent years the bulb program has been headed by August A. De Hertogh, who is retiring as professor of horticultural science at North Carolina State University in Raleigh. The program in North America was established three decades ago by the Dutch association and it was instrumental in developing techniques for commercial greenhouse bulb producers to precisely force flower bulbs to be ready for the holidays and other market opportunities.
The selection announcement also noted that New York State has various climate zones that are available for research and that Cornell is situated in a part of the country with a rich tradition in flower bulb horticulture.
'This gives Cornell visibility and unique strength in plant materials,' said Thomas Weiler, Cornell Professor and chair of floriculture and ornamental horticulture. 'Plant materials are one of our core interest areas and one of scientific opportunity.'
Cornell has selected William B. Miller of Clemson University to direct the bulb program. He has joined the Cornell faculty in late July as a professor of floriculture and ornamental horticulture. Miller earned his doctorate from Cornell in 1986. Since joining Clemson in 1991, he has taught several courses and developed a major research program on flower-bulb forcing and physiology. With collaborators and students, he has published more than 30 major scientific papers on bulbous plants and other floricultural crops, and a book, Easter and Hybrid Lily Production, published by Timber Press.
Miller was a founding academic director of the Southeast Greenhouse Conference, in Greenville, S.C., a 6-year-old program that has grown into the second-largest floriculture industry meeting in the United States.
Table of ContentsTrade names used herein are for convenience only. No endorsment of products is intended, and no criticism of unnamed products is implied.
The product 'X-Gnat' is one you may want to try for fungus gnat larvae control. This is a tough pest to control and 'X-Gnat' may be helpful. 'X-Gnat' utilizes naturally-occurring, beneficial insect predators known as nematodes (steinernerma feltiae) to provide effective control of fungus gnat laveae in greenhouses and nurseries. It is naturally-occurring, user-friendly, and exempt from EPA Requirements of Registration [(FIFRA, Section 25(b)(1)], does not carry Worker Protection Standard (WPS) and REI labeling. Workers can enter and exit the greenhouse without any time restrictions, and posting is not required.
Formulated in water-dispersible granules, the nematodes in 'X-Gnat' enter the fungus gnat larvae's body and release a bacterium that results in death of the target insect. Millions of nematodes are present in each container of 'X-Gnat'.
Table of Contents[Editor's note: The summer months are an excellent time to clean up the greenhouses that were used during the last several months. The elimination of all trash, old plants and weeds are essential if a neat, sanitary greenhouse is to be used for later plantings. To help growers choose the appropriate herbicide we provide the following information for your use. This taken from the 1998 Recommendations for the Integrated Management of Greenhouse Florist Crops: Management of Pests and Crop Growth.]
Weeds such as creeping wood sorrel (Oxalis corniculata), hairy bittercress (Cardamine hirsuta), prostrate spurge (Euphorbia humistrata), and others are persistent problems in greenhouses. Not only do these weeds detract from the perceived quality of plants produced, but some also are known to harbor insects, such as whitefly, mites, and thrips. Therefore; the removal of weeds from greenhouse pots, benches and floors is important for aesthetic and pest management reasons. There are a number of options available to the greenhouse manager for controlling these pests.
The first and most important control measure is sanitation. Keeping weed propagules out of the greenhouse by using sterile media, introducing only clean plant materials, and weed control outside of the greenhouse. Where possible, screening vents and windows will limit the introduction of wind blown seed as well as insect movement. Concrete or mulched floors will also limit weed establishment. Some weeds will get into the greenhouse. These should be removed manually or by herbicide treatments before going to seed.
If the weeds are already established in the greenhouse they can be killed by (1) manual removal, (2) emptying the range and allowing the weeds to dry up, (3) emptying the range and fumigating (see Appendix Table 3, Cornell Recommendations), or (4) using a postemergence herbicide (see Table 1 below). Each method (except fumigation) will only remove the vegetation that is present but does nothing to prevent reestablishment from seed which will be present. Continuous removal is expensive and time consuming. Currently there are no residual herbicides labeled for greenhouse use. Where weeds are a continual problem, clean up the area, removing the soil or covering it with a mulch. Geotextile fabrics covered by gravel (or other mulches) have been successfully used in many greenhouses. Only under extremely rare circumstances would fumigation be recommended for weed control.
Table 1. Herbicides labeled for greenhouse weed control
Trade names used herein are for convenience only. No endorsment of products is intended, and no criticism of unnamed products is implied.
Reward (diquat) is a postemergent contact type, non translocated weed killer. It is good for killing small annual weeds. Large weeds will be burned but not killed. Reward is very toxic. Always use the recommended safety equipment when spraying Reward. Chief advantages include rapid kill of seedling weeds, it may be used when a crop is present in the house, cost, and small amounts of spray drift will cause cosmetic damage to the crop but will not translocate to kill entire plants. The chief disadvantage is the relatively high mammalian toxicity.
Sharpshooter (salts of fatty acids) is also a contact type, non-translocated herbicide which controls small seedling weeds. Sharpshooter works better when air temperatures are relatively high (greater than or equal to 80°F). Large weeds will be burned but not killed. Chief advantages include lower toxicity (compared to Reward) and it may be used while a crop is in the house. Also, Sharpshooter is the only herbicide that can be used to control weeds growing in woody plant production benches, such as rose benches.
In all applications, avoid contact with desirable vegetation. (The other herbicides are for use only under benches, in walkways, or around the foundation.) Chief disadvantages of Sharpshooter are cost and it is somewhat less effective than Reward on larger weed seedlings. Additionally, the odor can be persistent and offensive to some people.
In contrast, Roundup (glyphosate) is a systemic weed killer which kills annual and perennial weeds. It is much safer to use than Reward. However, when applying any pesticide in a closed environment, like a greenhouse, one should wear protective clothing, eye protection, and respirator. The chief advantages are the systemic kill of annual and perennial weeds and low mammalian toxicity. The chief disadvantage is that small amounts of spray drift can severely injure greenhouse crops. Therefore, it is recommended that Roundup be used only in empty geeenhouses (between crops) with the fans off. If drift occurs, six hours after treatment wash the sides of the house; otherwise, condensation containing Roundup may drip on plants.
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