Early season nursery crop disease management
April 18, 2008 - Author: Thomas Dudek, Michigan State University Extension
Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.
Bacterial blight on lilac
Nursery growers should be on a routine copper fungicide program to help reduce the spread of bacterial blight, especially when lilacs are overwintered in polyhouses. Prune out and destroy any infected shoots as soon as symptoms appear. Be sure to disinfect cutting tools between cuts. Overhead watering increases the spread of bacterial blight and condensation in polyhouses and can also spread the bacteria on to the plant.
Beware that freezing temperatures in polyhouses that have plants leafing out can also increase the risk of bacterial blight. If irrigation for frost protection is necessary, be sure to apply a copper fungicide within 12 hours prior to irrigating for frost protection.
Growers with flowering dogwood trees affected by dogwood anthracnose should begin fungicide treatments as soon as the first leaves emerge. Apply Banner Maxx every 28 days throughout the period of leaf and shoot development. Avoid overhead irrigation if possible and irrigate with drip or direct soil application.
Immediately upon arrival of new stock, remove and burn small dead twigs from the canopy. Do not allow any of the twigs to remain on the ground where stock is held. Prune off all epitomic shoots and water sprouts as soon as they appear.
Most species and hybrids of cornus are resistant to this disease except C.florida and C.kousa ‘Autumn Rose,’ ‘Moonbeam’ and ‘Wolf Eyes.’ ‘Spring Grove’ and ‘Sunset’ cultivars are resistant. Consider offering these to your customers.
Sphaeropsis blight (a.k.a. Diplodia)
This twig blight disease of two and three needle pine species will start to show up in the spring as the buds begin to break. Nurseries trying to manage this disease need to scout Austrian pine closely and just prior to bud break, make a fungicide application and two more at 10 day intervals. Options include: Spectro 90, Camelot, Protect T/O,Junction or Banner Maxx. Or apply Clearys 3336 plus a spreader sticker or apply Heritage as per label instructions.
Powdery mildew on Scabiosa
Perennial growers who grow Scabiosa (pincushion flower) in the greenhouse have noted an increase in powdery mildew over the past couple of weeks. Look for the white flour-like dust on the leaves. This disease does not require wet foliage for development. Maintain good humidity control to reduce the infection and spread. If possible, space plants as much as possible if growing a susceptible crop like this. Powdery mildew is well known for its ability to adapt and develop resistance to fungicides, and it is important to rotate among fungicides with different modes of action. Using as few sprays as possible also helps to delay the development of resistance. Fungicide options include:
* Heavy pressure: Eagle or Terraguard.
* Light pressure: Compass, Zyban, Heritage, Insignia or Strike.