Roof rats are running rampant in California orchards this year, according to UC Agriculture and Natural Resources scientists.

“In pistachio and other nut orchards, roof rats are burrowing and nesting in the ground where they're chewing on irrigation lines, causing extensive damage,” said Rachael Long, UC Cooperative Extension advisor. “They are also nesting in citrus trees, feeding on the fruit and terrifying field workers when they jump out as people are picking fruit. The chewing pests are also girdling citrus limbs, causing branch dieback.” 

Rats like to eat fresh avocados.

 

The wet winter of 2017 led to lots of weed seeds for rats to eat. “Last season, rats were also nibbling on pomegranates, avocados, and other fruit and nut crops, rendering them unmarketable,” Long said.

Holes in the ground around the base of pistachio trees throughout a Yolo County orchard puzzled the grower.

“We looked for ground squirrels, but never saw any,” Long said. “We set up game cameras, but only got birds and rabbits. We put rodent bait in the holes, but the digging didn't stop.”

Long, the pest detective, cracked the case by consulting Niamh Quinn, UC Cooperative Extension human-wildlife interactions advisor based in Irvine. “She informed us that the damage we were seeing was from roof rats.”

Burrowing roof rats sounds like an oxymoron. While roof rats generally don't burrow in urban environments, their country cousins have been known to burrow.

“It's not true that they don't burrow,” Quinn said. “When I worked as staff research associate for Roger Baldwin, UC Cooperative Extension wildlife specialist, that is mostly what we studied, burrowing roof rats in orchards.”

Roof rats are nocturnal animals that climb in trees and burrow underground.

 

Control measures

Baldwin said, “It seems to be a good year for rats in a number of different areas and crops throughout the state. I've received more questions and comments about rats this year than perhaps the last 10 years combined. As for bait application, putting bait down burrow systems for rats doesn't usually work too well, so I'm not surprised that approach didn't work. Growers will likely have better luck with bait stations in the trees.”

Because the rats climb, Baldwin suggests attaching bait stations to tree branches.

“In addition, elevating the bait stations will eliminate access to bait for many protected mammal species, such as kangaroo rats,” Long said. “The bait diphacinone grain can be purchased from some ag commissioners' offices. This is what Roger Baldwin said they tested and it worked.”

As for the bait stations, they should be designed so that there isn't any spillage for nontarget animals to eat, Long said. 

When roof rat outbreaks occur, rodenticides are often needed to prevent crop damage. However, timing is critical as diphacinone use is highly restrictive and not allowed during the growing season, which is beginning as the weather warms. 

“Check the product label for application instructions,” Long reminds growers. “It's the law.”

Because roof rats climb, UC Cooperative Extension wildlife specialist Roger Baldwin recommends attaching bait stations to tree branches.

 

Identifying the pest

Roof rat holes are typically 3 to 4 inches in diameter.

 

One way for growers to identify whether they have roof rats is by the size of the burrows. The nocturnal pests are active above ground in trees and below ground.

“Roof rats can forage away from their nest, so you won't likely find signs of their activity, such as rat droppings outside their burrow, to help identify them,” Long said.

Ground squirrels are active during the day, so they are more likely to be seen, dig holes about 4 inches in diameter and forage above ground near their burrows. Vole and mouse holes are 1- to 2-inches in diameter. Roof rat holes are typically 3 to 4 inches in diameter and might have nut shells in front of them, for example pistachio or almond shells. Rabbits will feed on seedling crops, but do not dig burrows.

Ground squirrels are active during the day and their burrows are 4 inches or more in diameter.

 

Roof rats are prolific breeders that reproduce year-round, according to Baldwin. Females typically have three to five litters per year with five to eight young, enabling their populations to rapidly increase. The omnivores feed on a wide variety of plant and animal materials, allowing them to adapt to any environment, including urban and agricultural lands.

“Rats are sneaky and hard to spot,” Long said. “If you see damage, including digging in the soil but no wildlife, suspect rats.”

For more information on controlling roof rats, download Quinn and Baldwin's free UC ANR publication 8513, Managing Roof Rats and Deer Mice in Nut and Fruit Orchards at http://anrcatalog.ucanr.edu/Details.aspx?itemNo=8513.

For more information about ground squirrels, download the free UC IPM Best Management Guidelines http://www.groundsquirrelbmp.com or UC IPM Pest Note http://ipm.ucanr.edu/PMG/PESTNOTES/pn7438.html.

And there's more on rats in the orchard:

https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=26570

https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=24581

https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=19525

PULLMAN, Wash. Soil pathogen testing - critical to farming, but painstakingly slow and expensive - will soon be done accurately, quickly, inexpensively and onsite, thanks to research that Washington State University scientists plant pathologists are sharing.

As the name implies, these tests detect disease-causing pathogens in the soil that can severely devastate crops.

Until now, the tests have required large, expensive equipment or lab tests that take weeks.

The soil pathogen analysis process is based on polymerase chain reaction (PCR) tests that are very specific and sensitive and only possible in a laboratory.

The new methods, designed by WSU plant pathologists, are not only portable and fast, but utilize testing materials easily available to the public. A paper by the researchers lists all the equipment and materials required to construct the device, plus instructions on how to put it all together and conduct soil tests.

Responding to growers needs

"We've heard from many growers that the time it takes to obtain results from soil samples sent to a lab is too long," said Kiwamu Tanaka, assistant professor in WSU's Department of Plant Pathology. "The results come back too late to be helpful. But if they can get results on site, they could make informed decisions about treatments or management changes before they even plant their crop."

Some diseases from soil pathogens may not be visible until weeks after the crop has sprouted, Tanaka said. That could be too late to treat the disease or could force farmers to use more treatments.

Magnetic breakthrough

WSU graduate student Joseph DeShields, a first author on the paper, said it took about six months of work to get their device to work in the field. It relies on magnets to capture pathogens' DNA from the soil.

"It turns out, it's really hard to separate and purify genetic material from soil because soil contains so much material for PCR tests," said DeShields "So we were thrilled when we made that breakthrough."

Rachel Bomberger is a WSU plant diagnostician who helped with the concepts of the machine testing. She said she's impressed by what Tanaka and the team accomplished.

"We removed a huge stumbling block when it comes to soil testing," said Bomberger, one of the co-authors on the paper. "We found the missing piece that makes the testing systems work in the field without expensive lab equipment or testing materials."

Worldwide application

The system was tested on potato fields around eastern Washington, Tanaka said, but it will work on soil anywhere in the world.

"It's a really versatile method," he said. "You could use it for nationwide pathogen mapping or look at the distribution of pathogens around the country. We started small, but this could have huge implications for testing soil health and disease."

Tanaka said it was important for this discovery to be available in an open-access video journal.

"We're always concerned about helping every grower and the industry as a whole," Tanaka said. "We want everybody to look at this and use it, if they think they'll benefit from it."

###

The results were published in the Journal of Visualized Experiments, an open-access journal that includes a video showing how to assemble and used the system and a full list of materials needed to use their method.

This research is supported by the Northwest Potato Research Consortium and the Washington State Department of Agriculture - Specialty Crop Block Grant Program.

See the video here:

https://www.jove.com/video/56891/on-site-molecular-detection-soil-borne-phytopathogens-using-portable

And the article here:

https://www.jove.com/pdf/56891/jove-protocol-56891-on-site-molecular-detection-soil-borne-phytopathogens-using-portable

This article first appeared in Sacramento Valley Orchard Source

http://www.sacvalleyorchards.com/blog/almonds-blog/why-you-should-irrigate-potted-trees-directly-onto-potting-media/

Missing the Target: Why you Should Irrigate Potted Trees Directly onto Potting Media

or

Why Emitters Should be Placed on the Root Ball at Planting

Dani Lightle, UCCE Orchards Advisor, Glenn Butte & Tehama Counties

N.B. potted trees are standard commercial container grown citrus and avocado trees

Generally, when I am working with growers on a problem related to potted-tree establishment, the cause is lack of water movement into the potted media, creating tree stress. This results from the difference in soil particle size at the boundary between the orchard soil and the tree's potting soil. When you plant a potted tree in your orchard, it has a substrate – some mix of peat and vermiculite – that is very different than your soil type. The change in texture and pore size inhibits water movement from the surrounding soil into the potting media. As a result, Irrigation water applied outside the potted soil media isn't getting to the roots.

The sequence of photos in Figure 1 demonstrates this phenomenon. I set up a mock orchard condition with soil (Tehama series silty loam) next to a potted tree (potting soil) in a ½ inch wide frame. I then slowly added water to match the soil infiltration rate, similar to a drip emitter, approximately 4 inches away from the potting soil in the ‘orchard' soil.

You will see that the water does not move into the potting soil (Figure 1C & D). Two forces – gravitational pull and capillary action – move water downward and laterally in the soil. Since the potting soil is not below the orchard soil, gravity does not move water into the potting soil. Capillary action is not strong enough to move water into the potting soil because the difference in pore size is too great. So, irrigation water goes where it can easily flow – downwards and laterally into dry, native soil but not into the potting soil. More water does not solve the problem, it will just move past your newly planted trees and wet more native soil.

For about the first month of growth, irrigation emitters should be located at the base of the potted tree to ensure the potting medium receives water. Frequently check to ensure that the potting soil stays wet – not the soil somewhere else in the tree row or mound – before, after, and between irrigation sets. The best way to do this is with a small trowel and your hands. Water will need to be applied at the base of the tree until the tree roots grow beyond the potting soil and into your orchard's native soil. The time required for this to happen will vary depending on factors such as temperature, but it should take roughly a month.

Figure 1. This sequence of photos shows the movement of water applied to Tehama series silty-loam soil. Water was applied at the blue arrow, approximately 4 inches from the potting soil. Total elapsed time was 51 minutes. Water moved downwards and laterally but did not cross the boundary into the potting soil.