We had a lovely crop of blueberries this year, and in fact some of the bushes are still producing. However, Tom and I noticed that something was going very, very wrong on one of the plants. The leaves were looking like this:
First, only one plant was affected, and I went ahead and cut it to the ground, fearing a disease or infection. However soon an adjacent bush began showing the same symptoms. Then I got worried. I wracked my brain for blueberry information. I did a lot of online research. And I still couldn’t figure it out. So, I wrote to our local branch of the Master Gardeners (here, affiliated with the University of California system) and sent them a picture. The MG’s have a vast library with lots of resources and lots of experts with whom to consult. I wasn’t sure I’d get an answer, but yesterday I received a very excellent reply which totally blew me away. Here it is:
“Hello Elizabeth,
Thank you for contacting the UC Master Gardener Program Help Desk and for sending us photos. It sounds as though the management of your blueberries has worked well in the past, and has not changed recently. I understand you lost a blueberry bush to a similar-appearing ailment, and now a second bush is affected. It does not look like a virus, and most likely is a fixable problem. There is one less likely but potentially serious problem I will also address.
The pattern on your leaves is called marginal necrosis. The simplest problem causing this is inadequate water. Drip systems can clog up over time, and our weather has been very hot recently, causing more water loss than usual. Gently dig down several inches into the adjacent soil and make sure it is moist. If the organic component to the soil has broken down over the years, it may be draining too fast. You are an experienced gardener and may have checked this already. If the drip system is not working, I would try unclogging the outflows or replacing the tubing.
I discussed your problem with one of our “blueberry expert” Master Gardeners. He also had a good crop this year, yet his leaves are showing a similar pattern to yours. He thinks the most likely problem is either a watering issue, or a problem with the soil, which I will discuss below. Also, has the afternoon shade increased too much, due to tree growth? Blueberries are finicky and this might affect the leaves too.
There are several potential issues with the soil. Marginal necrosis can be caused by high soil salinity, high chloride, high boron content, magnesium deficiency, or potassium deficiency. Typically, the older leaves are more affected. Also, there is general agreement among us that even though you had a good crop, the soil may not be acidic enough. As you probably know, the pH needs to be 4.5 - 5.5, and is very hard to maintain for plants in the ground. Typically you need to acidify the soil at least annually. All these factors can be checked with lab-based soil testing (see pdf link). This will provide lots of good information and is well worth the price.
The less likely but most serious problem to be addressed is whether or not this is a fungal infection, such as verticillium wilt. This is suspicious because you lost one plant with a similar condition, although blueberries tend to be resistant to pests and diseases. This disease comes up through the soil, gets into the canes, and then spreads to the leaves. Typically one or a few shoots will be affected first, often the younger ones, unlike with soil chemical problems. If you cut through one of the canes with affected leaves and look at the cross-section, you may see browning or blackening of the water conducting system of the plant (the xylem). This fungus lives in the soil, is easily transported through water splashes or contaminated tools or shoes.
There are no sprays available that will kill this fungus. Make sure you completely remove the other affected plant, including the roots. I do not think you need to get rid of this current plant until we know for sure what this is. In the meantime, do not cross-contaminate your other plants – wash your hands and shoes well, and disinfect your tools using a 10% bleach solution. Soil solarization (clear plastic over the adjacent soil) may reduce the quantity of fungus, and that’s something cheap and easy you could do now with little harm done. A cutting could be sent to a lab for diagnosis; I will include a link below.
Finally, has a neighbor been using herbicides, such as Round-Up, near your plants? These can get carried on the wind and damage nearby plants, causing marginal necrosis.
Marginal necrosis
http://ipm.ucanr.edu/PMG/GARDEN/ENVIRON/marglfnecrosis.html
Tobacco Mosaic Virus
http://ipm.ucanr.edu/PMG/GARDEN/VEGES/DISEASES/tobaccomosvir.html
Soil testing labs – see attached pdf file
Verticillium Wilt
http://ipm.ucanr.edu/PMG/GARDEN/PLANTS/DISEASES/vertwilt.html
Plant testing lab
https://www.cdfa.ca.gov/plant/ppd/plantpath.html
Please contact us again if you have further concerns or questions.”
Isn’t that something? I was amazed.
So, today, Tom and I did our due diligence and performed inspections. We had forgotten that I had cleared a huge patch of parsley out, which had been next to these two affected plants. When I did that, I moved the irrigation line closer to the blueberries. Inadvertently, it turns out I had turned it off at the same time. DOH! Then, when we ran the drip system, another low sprinkler was in a place where it was covered in leaves, so the water was just dripping right below it instead of spreading out over the whole blueberry patch. So, with those two irrigation lines running correctly again, I’m hoping that solves the problem. We also discussed the fact that we had pruned a large branch off the tree above the blueberries about a month ago. Both removing that, and removing the parsley, had allowed more direct sun on the bushes, as well as allowed more evaporation around the bushes. With that plus the water deficiencies, the bushes were unable to keep the old leaves healthy and green, so the plant sacrificed them.
I also noticed that the soil below the bushes was hard, compact, and dry. Regular water should fix that up, but I also did as the MG’s suggested and added an acid fertilizer and watered it in. In the fall, when we spread compost everywhere, I’ll be sure to add several inches to this area so that the blueberries have better water retention.
So there you have it! Another reliable resource to contact if you have any burning questions not answered by your own knowledge or research. I’m so grateful to the MG’s for answering my question so thoroughly. They are all volunteers and I’m just amazed at this service!
Now I’m casting a more critical eye on other areas of my garden that have been looking peaked lately, and wondering if the drip is working in those areas. Tom and I check the veg beds every year, but we often just assume everything is working right elsewhere unless we see a problem. I think we’ve learned a lesson here, that we need to be more thorough.