2010 Disease Advisory

Flower development and blind wood problems with Big Red; Phomopsis; and a promising, new way of managing Oak root rot - by Guido Schnabel, Edgefield, SC - April 9, 2010

Flower damage on BigRed
Blind wood on BigRed
The 'walking tree'
hyder Planting trees on berm

Otherwise healthy looking 1-year old shoots aborted flower buds on BigRed. The flowers were missing the Pistil in the flower (see picture above). Most flowers were aborted at the top of the shoots, the last 10-15 cm. It is unclear if competition between the fruit becoming a major sink (end of July) and shoot development may have caused a problem or if a micronutrient (e.g. Boron) imbalance may have been responsible. Blind wood was observed on the same trees. Blind wood is last years shoots but no leaf or flower buds have developed in the center of the shoot. 

Walking trees (roots excavated; see picture above) seem to be a great way to manage Oak root rot. Preliminary results from two experimental sites show that those trees survive significantly longer on replant sites compared to trees planted at regular height. In one experiment 41% of all control trees have died after 4 years of planting but none of the 'walking trees' has died. Some growers are already taking advantage of this discovery by planting trees on berms (see picture above) followed by root collar excavation after 2 years. Click here for more information or contact Dr. Schnabel (Schnabel at clemson.edu) if you want to discuss implementation of this system.

Phomopsis was again a big problem in some orchards.  Severe infection and shoot loss was found in one region. This disease is not easy to manage. Check out the article on page 6 of the peach newsletter Phomopsis twig blight authored by Schnabel and Lalancette, which contains state-of-the-art management information.

There was also a significant amount of bacterial canker killing scaffold limbs and entire trees. This disease has likely taken advantage of the rainy and mild winter we had in 2009/2010. The foul smell of the affected bark was very prevalent. The disease is often associated with the ring nematode. Guardian rootstock, although not immune, is -compared to Lovell and especially Nemagard- relatively tolerant to bacterial canker. To learn more about this pathogen, check out Dave Ritchie's bulletin. Also, in the absence of effective chemical control options all aspects of PTSL management apply. I recommend to be extra careful to not spread the disease during winter and summer pruning. Prune healthy blocks first. In blocks with cankers, dip loppers and saws in a 10% bleach solution not only between blocks but also between trees.