August 26, 2002 Volume 11 No. 24 Update on Pest Management and Crop Development
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TRAP CATCHES (Number/trap/day)
There is increasing concern throughout the Northeast about damage done to apple trees by borers. The species of primary concern is dogwood borer, but American plum borer can be prevalent in western New York apple orchards that are close to tart cherry and peach orchards. While we do not yet fully understand the effects these borers have on dwarf trees we do know that they reduce vigor and can, in time, completely girdle and kill trees.
Over the last three growing seasons we have tested a number of insecticides against these borers. Lorsban is very effective for this use and we would strongly urge growers to take advantage of it where needed. We're also looking at some other insecticides this season but we won't be able to report on the results until control is evaluated in October.
Our tests so far have shown that borers can be controlled season-long by applying Lorsban at various times in the spring and summer (see Table 1). Fall also may be a good time to control dogwood borer. Results from this season indicate that Lorsban applied last year postharvest (my sprays went on in October 2001) controlled at least the overwintering generation, and possibly this season's generation. (Results from an evaluation conducted August 8 showed no signs of infestation, but there wasn't much in the check either. It may have been too early to detect much frass produced by this season's larvae.) Lorsban works when applied in the Fall because it infiltrates burrknot tissue and kills larvae concealed within. It is also very persistent in wood so it may continue to work into the next season against larvae that hatch in late-June. Fall application may offer growers a more convenient alternative for borer control.
Table 1. Efficacy of insecticides and white paint against dogwood borer infesting apple 2000, 2001.
Means followed by the same letter are not significantly different (p < 0.05).
In a survey we conducted recently, we observed some relationships between borer infestation and various orchard parameters such as the proportion of trees with burrknots, proximity to stone fruit orchards and presence of mouseguards. Conventional wisdom has held that borer problems are worse where mouseguards are in place. Mouseguards can contribute to increased expression of the burrknots borers invade and may shield borers from predators and insecticide sprays. This has led some growers to contemplate removing mouseguards under the premise that mice are easier to control than the borers. However, results of our survey indicate that dogwood borer larvae may be found as readily in trees without mouseguards as those with them. (American plum borer may be a different story in orchards near tart cherry or peach trees.) The orchard in which I'm conducting borer control trials has never had mouseguards and there is no shortage of dogwood borers. If mouseguards are deteriorated and no longer protect the tree, there may be some small advantage, in terms of borers, to removing them. But, in orchards where mouseguards still provide protection against rodents, removing them for the sake of borer control is probably not worth the risk. Instead, we would recommend the use of Lorsban trunk sprays to control borers. Even with mouseguards on, Lorsban will give adequate control if it is applied carefully. (i.e. a coarse, low-pressure, soaking spray with a hangun) Bottom line: as we go into Fall, consider using Lorsban after harvest to control borers, and reconsider removing mouseguards on trees where they still afford protection.
This material is based upon work supported by Smith Lever funds from the Cooperative State Research, Education, and Extension Service, U.S. Department of Agriculture. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture.
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