Somehow April flew by without me reminding you to apply fungicide sprays to Austrian and Ponderosa pines that have had problems with Sphaeropsis tip blight in the past. I’ve also received several scotch pine samples in the office to diagnose for pine wilt nematode. While there is no cure for pine wilt, I recommend to take a 6” long, 1-2” diameter sample of a dead branch to your local Extension office for diagnosis before cutting down the tree. Pine wilt affects Austrian (long needles groups of 2) and Scotch pines (short needles in groups of 2) as they are non-native trees while the nematode is native. Since ponderosa pines (long needles in groups of 2 and 3) are native to Nebraska, they don’t seem to be affected by pine wilt nematode.
Pine wilt is caused by beetles carrying pine wood nematodes vomiting them into the water-carrying vessels of the tree (xylem). The tree senses the nematodes and essentially blocks water to those branches. Often you will observe a branch then perhaps a side of the tree and eventually complete death of the tree within 6-9 months. While I have diagnosed many samples of pine wilt, more often when I visit homeowners the tree problems are due to fungal diseases which occur on the needles. If you look closely at your needles and observe dark bands or rings on them followed by death of the needle either direction from the band, the tree problem is most likely due to a fungal needle blight like dothistroma in Austrian and Ponderosa pines or brown spot in Scotch pines. They can all be prevented by spraying a fungicide containing copper sulfate in the spring.
With everything about 3 weeks early this year, now is the time to spray Ponderosa and Austrian pines for needle blight and spruce trees that have had problems with needle cast or shoot blight where the new growth has died in the past. In early June spray for needle blight problems in Scotch pine and cercospora blight on cedars. If you have a windbreak of combinations of these trees and don’t want to spray twice, I recommend at least spraying in early June to catch all of them. Increasing air flow by cutting out some trees is another way to reduce fungal diseases on your trees.
Also watch trees for bagworms as you may be able to tank mix a fungicide/insecticide application in early June if needed. We would recommend picking the bags off trees and burning them, but that’s just not feasible in windbreak situations. To know when to spray, take a few of the bags off the tree, place them into a plastic ziplock bag, and place outside on the south side of your house. When the larvae emerge from the bags, check your trees to see if larvae can also be observed on them. Pyrethroid insecticides are recommended for managing bagworms because they cause an irritation that makes the larvae leave the bags and allow them to be exposed to the pesticide.
Great brochure! Evergreen Diseases