- Author: Ben Faber
- Author: Craig Kallsen
- Author: Akif Eskalen
Dry Root Rot is a pretty fantastic disease symptom that is usually seen in lemon, but can be seen in orange, as well.
Craig Kallsen, UCCE Citrus Advisor in Kern Co. comments on a disease sample:
I have seen a lot of dry root rot over the years. It usually is something that damages or weakens the root system which allows a Fusarium species to colonize the rootstock. It is very common in older lemon groves that froze at some point in their past. Also common in groves that suffered a lot of gopher damage or where the wraps got too hot in the sun burning the bark and cambium. I have also seen it in cases of fertilizer or other soil-applied chemical burn. I have no doubt that graft incompatibility could do it too.
Akif Eskalen, UCCE Plant Pathology Specialist chimes in on a disease sample submitted:
As you can see from the attached picture there is a weird callus formation and symptoms of incompatibility at the graft union which I think is the primary cause of decline. We didn't observe any discoloration in the scion, however rootstock was completely discolored where we isolated Fusarium solani the causal fungus of Dry Root Rot. Dry root rot caused by either Fusarium solani and/or Fusarium spp. When there is a disconnection at the graft union, the phloem can not transfer enough carbohydrate to the rootstock to feed feeder roots. Fusarium fungal species are present in the soil and they can attack and easily colonize on starch depleted roots and cause DRR.
We still don't know what is causing the graft incompatibility on these plants. That needs to be investigated.
It's still not clear how and why citrus becomes affected.
By: Carey Gillam, Reuters
Honey bees, critical agents in the pollination of key U.S. crops, disappeared at a staggering rate over the last year, according to a new government report that comes as regulators, environmentalists and agribusinesses try to reverse the losses.
Losses of managed honey bee colonies hit 42.1 percent from April 2014 through April 2015, up from 34.2 percent for 2013-2014, and the second-highest annual loss seen, the U.S. Department of Agriculture said in a report issued on Wednesday.
"Such high colony losses in the summer and year-round remain very troubling," Jeff Pettis, a USDA senior entomologist, said in a statement.
The 2014-15 yearly loss was down slightly from the 45 percent annual loss for 2012-2013 but well above the prior two years of annual measurements and above the benchmark of 18.7 percent that is considered economically unsustainable, USDA said.
Millions of honey bees are relied on to pollinate plants that produce a quarter of the food consumed by Americans. Beekeepers travel the country with managed hives to help the process.
But over the past few years, bee populations have been dying at a rate the U.S. government says must be addressed, and finding an answer has become a politically charged debate.
Beekeepers, environmental groups and some scientists blame a class of insecticide known as neonicotinoids, or neonics, used on crops such as corn as well as on plants used in lawns and gardens.
But Bayer, Syngenta and other agrichemical companies that sell neonic products say many factors such as mite infestations are harming the bees.
The White House has formed a task force to study the issue, and some lawn and garden retailers have been cutting use of neonics.
The Environmental Protection Agency is requiring a series of studies on neonic effects on bees and plans to issue the first of a series of assessments later this year.
The USDA report issued on Wednesday said colony losses were 23.1 percent for the 2014-15 winter months, typically the higher loss period. The 2014 summer loss of 27.4 percent marked the first time summer losses exceeded winter, and marked a surge from the 2013 summer loss of 19.8 percent, USDA said.
The results are considered preliminary and are based on survey responses from about 6,100 beekeepers managing 400,000 colonies, USDA said. Those beekeepers represent nearly 15.5 percent of 2.74 million U.S. bee colonies. A more detailed report is to be published later this year, USDA said.
There is an increasing use of high stature plastic tunnels (macro-tunnels) to grow high value crops, such as raspberries, blueberries, vegetables and flowers. This is even in relatively frost free environment, such as coastal California. More commonly tunnels are used in colder climates to produce early season crops. But along the California coast there is increasing use because of other benefits, such as improved production and reduced disease. There is estimated to be about 11,000 acres in tunnels in Santa Barbara County and even more in Ventura.
A recent, unpublished study by Mike Cahn et al with UCCE in Monterey County evaluated water use by raspberries in tunnels. They found that pan evaporation was reduced by 18% in the tunnels over the season compared to open-field grown raspberries. Also, less water was applied for the inside trial than the adjacent outside trial. Even with the reduction in applied water the soil moisture remained higher inside the tunnels than outside. The canopy was larger earlier inside the tunnel than outside even though there evapotranspiration was lower inside the tunnels. The main components of transpiration are altered in tunnels. There is less radiation because of the interference of the plastic, less wind, higher humidity, despite the warmer temperatures.
When you see dieback in an avocado it could be due to several reasons, and here are three very common causes of dieback, one of which has been especially common when there is little rain. The first major cause of dieback is an overgrown tree where there is no light that penetrates into the canopy. Branches with leaves in a darkened interior will naturally shut down and dieback, leaving these twiggy dried out branches. This is a natural process whereby the tree just gets rid of leaves that are not performing.
Another cause of dieback is our old friend Avocado Root Rot, Phytophthora cinnamomi. This causes dieback, also called “stag horning” because of the dead branches standing out from the surrounding canopy. This is normally accompanied by a thinning canopy with smaller, yellow leaves and a lack of leaf litter because of lack of energy. It's also hard to find roots and if they are found, they are black at the tips and brittle.
The third major cause of dieback is a result of water stress. This shows up with low water pressure, at the top of the hill where the most wind occurs, where a sprinkler gets clogged, when the irrigation schedule is not meeting tree's needs or when there is not adequate rainfall to get sufficient leaching. And after four years of drought, this is very common. This appears as dead spots in the canopy, a branch here and there where the leaves have died and are still hanging. It's been called “salt and pepper” syndrome, because it can have a few branches here and there that have died back while the rest of the canopy is normal, the leaves are normally sized and green. In young trees, in severe cases, the fungus that causes this blight can work its way down to the graft union and kill the tree. In mature trees, it just causes an unthrifty look to the tree. Although we have always seen this problem in avocado orchards, this has become a very common affliction in orchards these last few years
1) Lack of light dieback
2) Phytophthora cinnamomi dieback
3) Stem and Leaf Blight