The first thing to realize when looking at algae control is that the best you can do is prevent more algae from developing. It's hard to cure algae once it's already there. It develops primarily on last year's foliage -- not this year's. It appears that it comes in the June time-frame. Therefore in these spray trials, we were looking at algae development on last year's growth -- that is 2009 growth. For the most part, we didn't do anything to reduce discoloration on 2008 growth (which developed the summer of 2009) or earlier. Still, if you can go to market with 2 years of good green color, it should be good enough.
We applied different materials for algae control this spring before bud break at 2 sites -- one in Mitchell and one in Avery. Thanks to Jeff Vance and Jerry Moody for help in finding locations to work in and spraying the materials.
All applications were made with a backpack mistblower. At both sites, an untreated row was left between each treated row to reduce cross contamination of treatments.
At the Mitchell County site, treatments were made on rows of 10 trees. There were 3 replications. Applications were made on April 29 using one of the following materials:
- Kocide 3000 at 3.5 pound per acre. This is a copper based material which is made up of 30% copper. Kocide label.
- Dithane at 1.5 pounds per acre. The active ingredient of Dithane is mancozeb. Some Jackson county growers were seeing some control of algae in the fall when this material was applied. However last year, I didn't see very good results from this. Review of last year's work.
- Daconil at 3 pints per acre. The active ingredient of daconil is chlorothalonil.
In Avery County we didn't replicate, but instead treated a long row with 30 or more trees. Original treatments were made on May 5 using either Kocide, Dithane or Daconil at the treatment rates described above. Addition treatments were as follows:
- Cosan, an organic disinfectant, at 2 teaspoons per gallon
- SA-20 disinfectant at 2 teaspoons per gallon. This product is made of 10% dimethyl benzylammonium chloride and 10% dimethyl ethybenzyl ammonium chloride. It is used to disinfect pots, greenhouse areas and tools.
- Kocide applied twice -- on May 5 and again on May 19
- Kocide applied once on May 19
Jerry, Doug Hundley and I looked at the Avery County treatments yesterday, and Jeff Vance and I looked at the Mitchell County treatments this morning.
There appeared to be more algae developed at the Avery than the Mitchell County site. This surprised me as the Mitchell County site was much worse last year. (This photo, taken in Mitchell County, shows a shoot from an untreated tree with algae on last year's growth).
All treatments appeared to have some effect on the algae. The Dithane and Daconil didn't work as well as the other products. Kocide appeared to work best. Applying it twice seemed to work a bit better, and applying it later in May also seemed to work some better.
This photo is of a shoot from a treated tree. Note that there is no discoloration on 2010 or 2009 growth. If the treatment hadn't worked, you would see discoloration on 2009 growth. The material didn't reduce the discoloration already present on 2008 growth.
This is typical of any fungicide. They prevent disease from developing. They don't cure disease. Therefore a successful treatment will keep algae from developing the year it is applied. But that's similar to all of our pests. When you treat for twig aphids or spider mites, you don't do away with the damage you already have. Instead you cover it up with new, undamaged foliage.
I would like to repeat this next year, applying materials with either a high pressure sprayer or backpack mistblower. I suspect that the high pressure sprayer will give better control, but that most growers will prefer the speed of the mistblower. I also hope to try out some Kocide this fall to see if it will help "cure" some of the algae. I don't think it will, but since I didn't try it last year, I want to make sure.
Take home message: It looks as if Kocide and perhaps some other materials will reduce and in some instances prevent algae from developing when applied in the spring. In fields where algae development is expected because of woods or the trees are growing close together, a preventative treatment is required starting the year before sale and continuing until all the trees are harvested.
A big thanks goes to Kelly Ivors and Gary Chastagner for their help in identifying possible treatment windows and materials.