SEPTEMBER
2008

 

 

 

By
B. Rosie Lerner
 
Purdue
Extension
Consumer Horticulturist

 

 

 

 

 

09-05-08

Question and Answer

Q. We discovered fire blight on one of our apple trees this summer. We cut all the branches with symptoms (withered leaves and the crook at the end) and burned them. We have seen no sign of any further damage. Do we still need 
to spray next spring as directed by the product we bought from our local nursery?

A. Fireblight is a bacterial disease that affects over 70 members of the Rose Family (Rosaceae), including ornamental and fruiting apples and pears. Cultural practices can help prevent further spread of the disease. When removing diseased limbs, you should prune only in dry weather and make cuts at least 12 inches below the infection so that the cut is made in healthy tissue. These cuts should be delayed late enough into summer that the new growth has completed for the season. Be sure to sterilize your pruning tools between cuts. Delay any major pruning jobs until late winter while trees are dormant. There are some helpful photos and description of the symptoms at http://www.ppdl.purdue.edu/PPDL/weeklypics/Weekly_Picture5-14-01-3.html.

Since your tree has a history of infection, you may want to apply a copper-based fungicide, such as Bordeaux mix, before bud break next spring. There is an anti-bacterial product called streptomycin that can be applied while plants are in bloom, but one must be very judicious in its use so that the bacteria do not develop resistance. Additional fungicides can be applied to prevent spread after bud break, as listed in Purdue Extension Bulletin BP-30, available online at http://www.extension.purdue.edu/extmedia/BP/BP-30-W.pdf.

Q. I hope you can help us with a problem we have with our evergreens. We noticed a brown cone-shaped form about an inch long covering our Arborvitae and various pine trees. There appears to be a worm inside of each cone. The cone seems to be made of the greenery of the tree. There are hundreds of them covering the entire arborvitae. The trees have masses on one side. The trees look like they are dying as a result of this infestation. We sprayed the trees with Sevin garden spray but it is unclear whether or not this will have any impact. What can we do to save our trees?

A. That sounds like a perfect description of the common insect pest known as bagworm. As you've described, the pest is a caterpillar that lives inside a spindle-shaped bag that it forms from pieces of foliage from the host tree. So heavy populations can cause serious defoliation, especially on young trees.

Handpicking the bags is a very effective control strategy for small populations of the pest and for plants that are easily reached from the ground or a short ladder (Do you know any neighborhood kids looking for a summer job?) You can drop the bags into a bucket of sudsy water.

For larger pest populations, an insecticide might be helpful, but it is too late to apply this year. The best time is around mid-June, just after the eggs have hatched into caterpillars. Sevin (carbaryl) insecticide can be effective then, but there are other products that are less harmful to bees and other beneficial insects that are a better choice.

You'll find further information about this pest, courtesy of the Purdue Entomology Extension folks at http://www.ppdl.purdue.edu/PPDL/weeklypics/7-29-02-1.html and in Purdue Extension Bulletin E-27 http://extension.entm.purdue.edu/publications/E-27.pdf.

Q. I'm having a problem with Japanese Beetles. I've combated them on my roses and other plants with great success in previous years with a product for roses. Unfortunately, this year they have attacked my cherry tree -- and this product is much too expensive for this application.

Our tree is large, about 20 feet tall, and probably 20-25 years old. In the two weeks we were on vacation this July, these beetles have eaten almost all of its leaves. Those that are left (20%) are a much lighter green than those on my neighbor's cherry tree -- and the beetles have moved to her tree now. Our tree's trunk also seems to sway in place when my husband or kids climb on it.

Is there any hope in saving this tree? What can I do to treat an infestation in the future and/or prevent it in the first place? Ironically, the beetles are leaving our apple trees alone, but have gone after a plum tree near the cherry.

A. Japanese beetles are a problem every year to some extent, but some years seem to have higher outbreaks than others and vary among geographic areas. There are over 300 different species of plants known to fall prey to the Japanese beetle, but they seem to most favor linden, grape, corn silks, smartweed, flowers of all kinds and foliage of plants in the rose family, which includes cherry, apple, plum and peach. Adults lay eggs that develop into grubs in mid-summer in lawns, gardens and other cultivated land where they will feed primarily on roots of grasses. They overwinter as grubs, emerging as beetles in mid-June. The adults can fly long distances up to 2 miles to feed on leafy plants and lay eggs and the cycle begins again.

Control strategies depend on which plants are primarily being damaged. If trying to control grub damage in the lawn, products should be applied just after the eggs hatch into grubs. If adult feeding is the problem, as in your case, the applications should be made to the foliage of the plants when the adults are active, typically twice during the peak adult flight period. Some years you might be able to just handpick the beetles to keep the damage to a minimum, so by waiting to spray until the damage is beginning to become intolerable, you can minimize the use of pesticides.

More information on the life cycle and control of Japanese Beetles can be found in Purdue Extension Bulletin E-75 http://extension.entm.purdue.edu/publications/E-75.pdf.

 

Writer: B. Rosie Lerner
Editor: Olivia Maddox,