Treatments. The treatments are all listed on blog posting from August 27. But I'll list them again here.
- Untreated check
- SA-20 disinfectant @ 1 teaspoon per gallon on May 5
- Daconil @ 3 pints per acre on May 5
- Dithane @ 1.5 pounds per acre on May 5
- Kocide @ 3.5 pints per acre on May 5
- Kocide applied twice on May 5 and May 19
- Kocide on May 19
- 3% bleach solution on September 25
- Kocide on September 25
All treatments were made with a backpack mistblower except for the 3% bleach solution which was applied with a high pressure sprayer.
How we did it. Taking ratings was hard. After all, some trees don't appear to get algae at all -- whether because of their position in the landscape, their proximity to other trees, or resistance is anyone's guess. So we first looked to see if the trees had algae on older needles. The trees with algae on older needles are the only trees we counted in the data. Then we looked specifically at 2009 growth and gave it a rating of 0 to 4 where 0 = none, 1 = very light, 2 = light, 3 = moderate, and 4 = heavy. We examined 15 trees in each treatment.
Results. The results are to the right. Remember that we only counted trees that had past algae. So, the higher the pecentage of trees with no algae in 2009, the better the product was working. And obviously the lower the algae rating, the better the product worked.
The best controls were with SA-20 disinfectant and Kocide applied May 5. The Kocide applied later in May didn't work as well. Nothing worked in the fall. Again, these materials will prevent algae from developing, not cure it.
These treatments were applied to a single row and the treatments are in order going up the hill (all except for the check row which was between the Daconil and the Dithane). There was definitely more algae the farther up the hill you went, and so that may be why SA-20 disinfectant worked well. That's also why the fall applied treatments had more algae than the check.
What next? I'd like to look further at Kocide and perhaps some disinfectants next spring. I'll also be looking for some growers who will be interested in trying the Kocide. Unfortunately it looks like if you want to control algae, you need to treat for it the last 2-3 years before harvest every spring. Once it occurs, there is nothing you can do about it. Treatments will be harder to make on large trees growing together, and in fact this is where we find the most algae. So keeping a good spacing between trees is important.