Subtropical Fruit Crops Research & Education
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Subtropical Fruit Crops Research & Education

Posts Tagged: damage

Valley Lemons?

What about Planting Lemons in Kern County?

By Craig Kallsen, UC Cooperative Extension Advisor, Kern County

     Kern County is located at the southern end of the San Joaquin Valley of California. Over the past couple of years, I, as the citrus Farm Advisor for the University of California Cooperative Extension in Kern County, have received an increasing number of enquiries about the feasibility of growing lemons here. The answer is “yes” we can grow lemons here and according to the latest Kern County Agricultural Commissioner's Report (2017) we have 4010 acres of bearing and 10 acres of non-bearing lemons in the county.  Those 10 acres of non-bearing lemons indicate that fairly recently someone decided lemons were the way to go.

    These inquiries as to the feasibility of growing lemons are understandable. The price and demand for lemons in the U.S. and worldwide is increasing.  Depending upon where you get your statistics the retail prices of lemons was something like $1.50 per pound from 2011- 2013 to something like $2 a pound from 2015 – 2017.  The statistics show 2018 was even a better year for selling lemons.  Consumption of lemons in the U.S. was less than 1 million metric tons in 2011 to about 1.25 million metric tons in 2017.  Worldwide consumption has increased from about 4.5 million metric tons in 2011 to 5.5 million metric tons in 2017.  If you add in other factors such as a heat wave, which, for example, hit Ventura County production hard in July 2018, or extreme winter freeze events, and sometimes-erratic supplies from other lemon producing areas of the world, prices can skyrocket 40% or more in a month. Being able to sell a carton of lemons for excess of $55 can be very attractive to prospective growers. Not surprisingly, if you compare the cost and returns of growing lemons with those of oranges, a person might wonder why anybody would choose producing navels over lemons (see https://coststudies.ucdavis.edu/ ).

     Planting lemons is riskier. In the San Joaquin Valley, the major consideration is the greater frost sensitivity of lemons as compared most other citrus crops.  Not only do lemons freeze at a higher temperature, so do its branches.  A freeze, which can spoil orange or mandarin production for a year, can devastate lemon production for three years due to increased damage to the lemon canopy and the older branches of that canopy. If your tree freezes back to the major scaffold branches, you are out of business for a while. An important question is how often does it cold enough to destroy my lemon production capacity for three years or more?  Industry wide, for the last 30 years we have had three freezes where lemon leaf canopies, even in the warmer areas of Kern County, were severely damaged –  December 1990- January 1991, December 1998, and January 2007.  Not to be an alarmist but, in looking at these dates, it would appear that we may be overdue for an extreme freeze.  We flirted with one in early December of 2013.  Over the years, I have noticed that as the time interval increases from the previous frost event, citrus orchards move further and further down onto the valley floor, only to retreat to higher ground after the next severe event.

      Well, what about global warming?  Shouldn't Kern County be getting to be a safer place to grow lemons?  In answer, predictions can be difficult, and according to baseball legend Yogi Berra, this is especially so if they are about the future. Winter air temperatures have been climbing over the past 30 years in the southern San Joaquin Valley. With our Mediterranean climate in the SJV, most of our rain falls during the fall and winter.  Drought years, which means drought winters, have become more common. The higher winter temperatures are good news for citrus growers, but the droughts have been bad news in that dry air in not conducive for fog formation.  Fog, historically, is our winter blanket, that holds temperatures above freezing when conditions are ripe for rapid drops in temperature associated with clear, windless nights following cold fronts that move into the valley from Alaska and other points north.  

       The risk in growing lemons can be mitigated. As with any real estate endeavor, the three most important factors governing the value of a prospective lemon property are location, location and location. When we are talking about cold temperatures, we are talking about nighttime low air temperatures. Daytime winter temperatures, once we get into mid-morning, usually, are more than warm enough to keep lemons from freezing.  The major mitigation factor under human control is to plant lemons in the areas of Kern County that have the warmest nighttime temperatures.  These areas tend to be on the lower slopes of the foothills on the eastern and southern areas of the SJV.  Cold air is much heavier than warm air and runs like a river downslope. Good cold drainage is necessary.  If lemons are planted too far out onto the valley floor, they end up at the bottom of a lake of cold air during late fall and winter freeze events. The area where citrus is grown, often, is referred to as a belt along the lower foothills of the SJV.  Not only is this belt characterized by more fog than higher up in the foothills, but also it is close to the atmospheric inversion layer that forms in the SJV during the winter. The SJV is at the bottom of a large deep bowl formed by surrounding mountain ranges, and the depth of this bowl makes the air more difficult to disturb by wind. This still air, on cold, clear nights during the winter, allows heat radiating into the sky from the ground to warm a layer of air, usually located from 500 to 1000 feet above the valley floor. The idea of using wind machines successfully is to move this layer of warm air down to the trees on the ground.  If you are down on the valley floor, on most nights the warmer air is way too high up to bring it down to the ground with wind machines.  If an orchard is 500 feet above the valley floor on the side of a foothill, you might already be in the inversion layer and won't even need to start your wind machines, or at worst, the inversion layer is close enough to bring that warm air down to the trees with wind machines.  Unfortunately, the amount of land winter-warm enough for growing lemons in the foothills is very limited, and, currently, is occupied by other crops, probably citrus. We cannot grow lemons too high up in the foothills, because these areas are above the inversion layer and winter temperatures there will always be too cold for lemons.  Kern County, in general, appears to be colder than its neighbor Tulare County to the north, and usually suffers more in terms of fruit and tree losses during extreme frost events.

    Those bold enough to grow lemons appear to have more choices on which lemon to grow now than in the past. Some newer seedless or lower-seeded lemon varieties are available (https://citrusvariety.ucr.edu/ ). The Lisbon lemons, of which there are several selections, is an old Kern County standby, and appears to have better frost tolerance than the Eureka, commonly grown in the central and southern coastal areas. The Improved Meyer lemon is a hybrid, apparently, with citron, mandarin and pummelo heritage, and has excellent frost tolerance.  However, the fruit does not hold up well on the tree, in storage or ship very well, and few commercial groves exist. It remains a very popular and successful backyard tree for homeowners.

     With the threat of the Asian Citrus Psyllid (ACP) and the Huanglongbing disease it spreads, the feasibility of growing citrus under protective screens (CUPS) is under investigation.   These protective screens, in addition to keeping ACP out, would likely provide additional frost protection as well.

      The other obvious concern related to the number of enquiries I have received, is that even if lemons are not widely grown in Kern County now, worldwide demand suggests that there are likely many new acres of lemons in the ground now or in advanced planning stages in other locations in California, Arizona and the world.  In the past, we have seen the acreage of a number of crop commodities rise and fall with the laws of supply and demand. We have planted and then pulled lemons in Kern County before based on market conditions.  At some point, even unfrozen lemons will not sell if there are too many out there.

Figure 1.  Frozen mature lemon trees in photo background, after the 1998 freeze in the Edison area of Kern County.  Juvenile, undamaged navel orange trees in foreground (photo by Craig Kallsen).

 

Posted on Friday, June 21, 2019 at 7:13 AM
Tags: citrus (323), cold (5), damage (24), freeze (10), frost (19), lemon (99)

Why O Why, One Tree???

It's winter time and avocados and other subtropicals are prone to frost damage.  Little trees especially that haven't developed a canopy that can trap heat are the most prone.  So it gets cold and all the orchard looks fine, but there's one tree that doesn't look right and in a couple of days it really stands out.

Here's an example of a year old tree that turned brown and it actually looks like it was doing better than the trees surrounding.  It's bigger and has a fuller canopy..... or at least it did. 

But there's all the symptoms of frost damage - bronzed leaves and dead tips.

A week after the cold weather, there is already sunburn damage on the exposed stems.  See the brown spots on the upper fork?  That will soon turn all brown and dry up.

This is still a healthy tree with green stems, in spite of the burned leaves. Now is the time to protect the tree from sunburn damage.  This is what can kill the little tree.  Time to white wash it.

Why did it happen to this one tree?  Maybe it was a little bigger and needed more water than the surrounding trees. Maybe sitting on a rock and didn't have enough rooting volume for water. Maybe a touch of root rot (although the roots looked pretty good even for winter time).  And there were ground squirrels in the area.  Easy to bklamne them.

 

Listen to the sound of winter frost control

https://www.youtube.com/watch?v=rwTJveN8cIE

 

And when freeze damage gets extreme

https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=16448

 

 

 

Posted on Wednesday, January 23, 2019 at 6:22 AM
Tags: abiotic (13), avocado (280), citrus (323), damage (24), freeze (10), frost (19), subtropical (2), winter (6)

Herbicide Injury in Avocado

Although the main objective of herbicide use in avocado orchards (and all crops) is to manage weed populations, sometimes unintentional injury of the crop itself can occur when herbicides are incorrectly applied. Herbicide injury in avocado can reduce yield, decrease fruit, reduce plant vigor, increase susceptibility to diseases and pests, and sometimes result in plant death. Common situations resulting in injury include spray drift, tank contamination, application of the wrong herbicide or rates, and herbicide carryover from a previous crop. The extent of herbicide damage on avocado can vary widely according to factors such as herbicide mechanism of action (MOA) and application rate, route of exposure, plant size and growth stage, soil properties, and weather.

Herbicide injury can be difficult to diagnose properly and is often confused with disease, insect damage, nutrient deficiencies, and other environmental stresses. It is recommended that trained researchers or Pest Control Advisers, who may utilize plant tissue, make diagnoses or soil samples along with plant symptoms, injury progression, and other plant species affected, orchard herbicide use history, weather conditions, and other factors to confirm or rule out injury from herbicides or other causes.

Where the injury occurs can also be an indication of herbicide injury. For example, if injury is on just one side of a tree or trees near another field, it may be an indication of spray drift. If it occurs only along the edge of the skirts, it may be a hint that an uneven ground spray was applied.

The majority of herbicides for use in avocado orchards in California fall into eight MOAs as defined by the Weed Science Society of America. MOAs describe the specific biological processes that are disrupted by a group of herbicides. These processes control the growth and development of plants and when interfered with, can result in plant injury or death.

Table 1: Common herbicides used in avocado, their mechanism of action, and possible injury symptoms

WSSA Group

Mechanism of Action

MOA description1

Example herbicides

Possible injury symptoms1

1

Acetyl CoA Carboxylase (ACCase) Inhibitors

Inhibits lipid creation in grasses, preventing production of plant cell membranes

Fluazifop-P-Butyl (Fusilade DX), Sethoxydim (Poast)

Chlorosis, necrotic spots, leaf crinkling, leaf distortion

3

Mitosis Inhibitors

Inhibits cell division in germinating seedlings and lateral roots

Oryzalin (Surflan)

Thickened, shortened lower stems and small, crinkled leaves

5

Photosystem II Inhibitors

Prevents the transfer of energy generated during photosynthesis, causing a buildup of reactive molecules that damage chlorophyll and cell membranes

Simazine (Princep 4L)

Chlorosis, necrosis progressing from leaf margins toward the center of the leaves, foliar applications will appear as leaf burn

9

Enolpyruvyl Shikimate-3-Phosphate (EPSP) Synthase Inhibitors

Inhibits the production of three aromatic amino acids and the enzymes and proteins built from them

Glyphosate (Roundup)

Leaves of trees and vines become chlorotic 3 to 7 days after exposure, and margins of new leaves become necrotic

12

Carotenoid Biosynthesis Inhibitors

Inhibits production of carotenoid pigments, which harvest light and protect chlorophyll from reactive molecules

Norflurazon (Solicam DF)

Plant foliage turns white and appears bleached

 

14

Protoporphyrinogen Oxidase (PPO) Inhibitors

Blocks the production of chlorophyll and causes a buildup of reactive molecules that damage existing chlorophyll, carotenoids, and cell membranes

Oxyfluorfen (Goal 2XL), Carfentrazone (Shark EW), Flumioxazin (Chateau)

Drift injury will appear as speckling on leaf tissue. The necrotic spots are sometimes surrounded by a reddish colored ring. Injury from soil applications or residues appears as a mottled chlorosis and necrosis.

21

Cellulose Inhibitors

Inhibit cell wall synthesis and plant growth

Isoxaben (Gallery 75 DF)

Chlorosis, necrosis, leaf crinkling, leaf distortion, purpling of the leaf, and stunting

22

Photosystem I Inhibitors

Disrupts photosynthesis, forming reactive molecules that destroy cell membranes

Paraquat (Gramoxone SL)

Drift injury will appear as speckling or necrotic spots on leaf tissue

1Not a complete list. Symptoms listed are likely for established orchards. For detailed descriptions of MOAs and injury symptoms, as well as a searchable database of specific injury images (e.g., “chlorosis, necrosis, stem swelling, etc.” visit http://herbicidesymptoms.ipm.ucanr.edu.

References:

Al-Khatib, K. 2015. University of California Integrated Pest Management Herbicide Symptoms. http://herbicidesymptoms.ipm.ucanr.edu (accessed 09/05/18)

Faber, B.A., C.A. Wilen, B.D. Hanson. 2016. Weeds. Pages 107-124 in University of California Integrated Pest Management Guidelines for Avocado. http://ipm.ucanr.edu/PMG/selectnewpest.avocado.html (accessed 09/05/2018)

Sosnoskie, L.M., B.D. Hanson. 2013. Understanding herbicide mechanisms (modes) of action and how they apply to resistance management in orchards and vineyards. UC Weed Science Blog Post. //ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=9383 (accessed 09/05/2018)

Weed Science Society of America. Summary of Herbicide Mechanism of Action

According to the Weed Science Society of America. https://wssa.net/wp-content/uploads/WSSA-Mechanism-of-Action.pdf (accessed 09/05/2018)

Photo: Sometimes weeds are tasty, like amaranth and purslane

organic herbicide live
organic herbicide live

Posted on Monday, October 15, 2018 at 6:51 AM
  • Author: Travis Bean
Tags: avocado (280), damage (24), herbicides (18), injury (1), weeds (32)

Hot Avocados Dont Ripen Right

California avocados often are exposed to high temperatures after harvest, either in the field or during preconditioning (ethylene treatment), especially in summer. It's been known that long periods of high temperatures can delay ripening time and reduce fruit quality, but a new study indicates pronounced effects after only short periods of high temperature following harvest. Authors of the study concluded that it's important to maintain avocados at temperatures below 25°C following harvest and that the ideal temperature to ripen the fruit is 20°C. The authors also found that ripening below 20°C resulted in significantly longer ripening times and resulted in poorer coloration of the ripened fruit.

Mary Lu Arpaia, UC Cooperative Extension specialist, Jim Sievert and Sue Collin, staff research associates (retired) in the Department of Botany and Plant Sciences at UC Riverside, working with David Obenland, research physiologist with the USDA Agricultural Research Service, Parlier, studied for two seasons holding avocados from multiple harvest times for the first 24 or 48 hours of the ripening period at high temperatures (20°C to 35°C), with and without ethylene. In the third season, they made a detailed assessment of ripening temperatures (15°C to 25°C) on ripening time and fruit quality.

Results from the first two seasons showed that even a 24-hour exposure to temperatures of 25°C and above inhibits ripening and increases postharvest disorders such as stem end rot and body rot. In season 1, the incidence of stem end rot increased from 9.7% at 20°C to 32.3% at 35°C, and body rot increased from 3.9% to 20.2% for the same treatment comparison. Ethylene applied during the exposure period was ineffective in preventing the disorders.

In the third-season trial, temperature was also shown to be critical. Fruit ripened below 20°C took slightly longer to ripen. Additionally, the authors found that the ripened fruit at either 15°C or 18°C remained more green then fruit ripened at the higher temperatures. Avocados ripened above 20°C were more likely to develop pink discoloration in the mesocarp. Ripening temperature had no effect on overall likeability, or ratings of grassy or rich flavor.

Arpaia ML, Collin S, Sievert J, Obenland D. ‘Hass' avocado quality as influenced by temperature and ethylene prior to and during final ripening. Postharvest Biol Tec. 2018. 140:76-84.

Photo:  Damaged fruit from the recent heat wave was more than 24 hours of overheating on  the tree

 

avocado fruit hot
avocado fruit hot

Posted on Wednesday, October 10, 2018 at 5:56 AM
  • Author: Jim Downing , UC Agriculture and Natural Resources Lucien Crowder, UC Agriculture and Natural Resou
Tags: avocado (280), damage (24), heat (6), postharvest (4)

Roof Rats, O MY!!

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

 

 

roof rats
roof rats

Posted on Friday, March 16, 2018 at 7:14 AM
  • Author: Pam Kan-Rice
Tags: avocado (280), citrus (323), damage (24), fruit (18), Norwegian (1), rats (2)

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