D2B-Lancaster Farming Saturday, March 11,1989 WELLSBORO (Tioga) Sugar Maple foliage throughout much of northeastern United Slates was damaged this spring by a very small insect known as pear thnps, Taeniolhrips inconsequens (Uzel). To residents of northern Pennsylvania, this damage is com mon and has been occurring for nearly a decade. Other more northerly states are experiencing their first encounter with thrips damage. Foliage damaged by thrips resembles late frost injury. Light to moderately damaged leaves are 30-50 percent smaller than nor mal, which makes the tree crown appear thin. The individual leaves have a puckered appearance and are mottled yellow to pale green. Heavily damaged leaves are reduced in size by -nearly 70 per cent and will be more severely puckered and mottled. The leaf margins have a tattered or tom appearance. The tree crown has a brownish cast to it and is noticeab ly thin. What effect is this insect having on sugar maples and what impli cations does it have for syrup pro ducers? Very little research has been conducted to measure the impact of the thrips on the health of infested sugar maples. Howev er, based on what we know about a tree’s food production system, we can make some assumptions. A tree needs foliage to produce the food it needs for both the cur COMING 500 N... WALNUT BARN & DAIRY. EQUIPMENT HCR 8QX1738 Sales & Service MIFFLIN, fk 17(158 (717) 527-2«81 Pear Thripes Are Threat To Sugar Maples rent season’s growth and some to store in the root system to fuel foliation the following spring. It is probably safe to assume that thrips damaged foliage, which is sub normal in both quality and quanti ty, will alter the food production capability of a tree. Also that repeated attacks over a number of years will result in lower overall vigor of the tree. Compound this with other stresses such as defi cient rainfall (as in 1988), frost damage, and defoliation by other insects, and the prognosis is not good. Unfortunately, there are no practical controls for this insect, chemical or otherwise. Until suit able controls for this insect become available, forest managers must attempt to control the other factors that influence a tree’s vig or. For example, tapping, cultural practices, and damage by insects are stresses that often can be mod ified. Some suggestions for stressed stands are; - Monitor trees periodically for damaging agents or signs of stress. - Identify those trees with such signs of stress as branch dieback, defoliation, reduced sap produc tion or sugar content. - Limit tapping on stressed individuals. - Forego thinning operations or operating heavy equipment in affected stands. The initial effect of thinnings and root compaction are stressful to residual trees. - Intervene when insects such as fall cankerworm or forest tent caterpillar pose a further threat to tree vigor. Work is underway to look for answers to the multitude of ques tions we have about thrips. Sever al states and the U.S. Forest Ser vice have formed the “Regional Pear Thrips Committee.” The objectives of this consortium are; 1. To gather and disseminate pertinent information about pear thrips impact, surveys, control, biology, and research action on sugar maple. 2. To coordinate training, survey methods, management recommendations, and research activities on sugar maples. 3. To identify needed research and training. In addition, research is being initiated by the states of Vermont, Pennsylvania, and Massachusetts and the U.S. Forest Service to investigate ways to survey for pear thrips and methods to control the effect of pear thrips. Investiga tion into the biology and control of pear thrips will not yield results quickly. There is only one genera tion of thrips in a year. This spe cies gives us only a fleeting glimpse of the adults, the larvae are quite small and furtive, and for about nine months of the year, they are completely secretive ,t# HsaRAU SAUES Construction ** Const _lOOO uses- per month/renta We can deliver because they are in the ground, gets and sugar bush operators arc None of these habits are condu- advised to do what they can to civc to easy observation. limit other stresses on these trees. Until we have answers to the Perhaps it will be possible to have pear thrips mysteries, forest mana- our maples and eat them too. Detective Work (Continued from Page D 27) cult. And the scientists arc looking for more than circumstantial evidence, To prove that nematodes are the vectors, Evans must demonstrate transmission by nematodes in the greenhouse. To do this, he collects nematodes from soil surrounding infected plants, a labor-intensive process. Using a microscope to see the small organisms and very fine needles to pick them up, an experienced person can collect 30 nematodes per hour on a good day. The nematodes are added to sterile soil, and plants are grown in this infected soil and watched closely for symptoms of the disease. “We’ve done this experiment twice, with 30-40 nematodes per plant, and still haven’t been able to transmit the virus,” Evans says. “To ensure infection, we need lots and lots of nematodes to carry the disease. Although 30 nematodes per plant might be the minimum threshold needed to cause disease in the field, we’ll probably need a minimum of 100-200 per plant in the greenhouse.” Evans says one of the problems in going from the field to the greenhouse is that after nematodes are disturbed, many refuse to feed. That means the disease won’t be transmitted. So Evans is now building a greenhouse nematode population in large crocks of field soil planted with Sudan grass, in the hopes of producing well above the minimum number of nema todes per plant needed to transmit the disease. While the scientists continue to investigate this unusual disease, they’re also helping soybean far mers deal with it. TTtey have iden tified soybean varieties that are most susceptible to infection by the virus - Verde, Avery and Essex. They have also identified three resistant cultivars -- HT-5203, A 5149 and Sparks - that are essentially immune to it under normal field conditions. In addition, the researchers plan ■ to experiment with crop rotation -to control dagger nematodes in the soil and thus limit the disease. By rotating soybeans with non-host plants such as com. wheat or sorg hum, they may be able to elimi nate the nematode vector. What motivates Evans and his colleagues to continue their pur suit of this disease? “We’ve shown photo slides of the infected plants at< national meetings and no one else seems to recognize the symptoms,” he says. “The disease appears to be pecul iar to Delaware and based on symptomatology, it is a new dis ease of scientific merit.” And so the detective work continues. ?V. ~h
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