Subtropical Fruit Crops Research & Education
University of California
Subtropical Fruit Crops Research & Education

Posts Tagged: fruit

Blueberry Gall Midge?

Several Florida blueberry growers have recently reported flower bud damage and corresponding fruit loss, in some cases up to 50% on certain affected cultivars. These reports have focused primarily on Emerald, Farthing and Meadowlark, although other cultivars may have also been affected to some degree. There could be multiple reasons for flower bud damage and the resulting fruit loss, including hydrogen cyanamide and freeze damage. However, in several cases this year it is believed that this type of damage has been caused by blueberry gall midge.

High populations of blueberry gall midge in blueberry can result in significant flower bud injury and reduce fruit set and yield. Females lay eggs in floral and vegetative buds just after bud swell. Gall midge larvae then feed on developing leaf and floral buds. Affected floral buds develop a dry, shriveled appearance and will often disintegrate (Figure 1). Damaged leaf buds are characterized by misshapen leaves and blackened and distorted shoot tips (Figure 2). When the terminal bud on a shoot is injured or killed, shoot elongation growth may be inhibited with excessive later branching occurring just below the damage terminal bud. Weather may impact the density of gall midge populations, with warmer temperatures > 60o F resulting in early emergence. Furthermore, re-infestation of previously infested areas is common if management action is not taken when gall midge injury is observed.

Growers should be aware of the possibility of gall midge damage in their fields this season, resulting in floral bud death and lower fruit set. Dr. Oscar Liburd, University of Florida blueberry entomologist, is preparing a bulletin to be released very soon with current gall midge management recommendations to be implemented after this season's harvest is complete. Until this extension bulletin is ready to be published, growers can view pesticide recommendations for gall midge in The Blueberry News magazine.

High populations of blueberry gall midge can result in significant flower bud injury and reduce fruit set and yield, Phillips points out. The following are his scouting tips for this pest.

Blueberry gall midge bud damage

Blueberry gall midge bud damage
Photo by Craig Roubos

  • Females lay eggs in floral and vegetative buds just after bud swell. Gall midge larvae then feed on developing leaf and floral buds. Affected floral buds develop a dry, shriveled appearance and will often disintegrate.

Symptoms of blueberry gall midge leaf damage
Photo by Craig Roubos

  • Damaged leaf buds are characterized by misshapen leaves and blackened and distorted shoot tips. When the terminal bud on a shoot is injured or killed, shoot elongation growth may be inhibited with excessive later branching occurring just below the damage terminal bud. Weather may impact the density of gall midge populations, with warmer temperatures (greater than 60°F) resulting in early emergence. Furthermore, re-infestation of previously infested areas is common if management action is not taken when gall midge injury is observed.

Is this something that California growers should be concerned about?  To my knowledge these midges have not been reported in California.  We also don't use hydrogen cyanamide which may be contributing to the problem. With plant material and people moving around, though, it might show up and be a problem.  I never thought blueberry rust would show up in California, but as the crop has become more widespread, it has showed up.  Ever alert.


Alert from UF/IFAS Blueberry Extension Coordinator Doug Phillips:


 Photo: Blueberry Gall Midge, Dasineura oxycoccana

blueberry gall midge
blueberry gall midge

Posted on Friday, April 6, 2018 at 8:12 AM
Tags: blueberry (7), dmage (1), fruit (18), infestation (1)

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

For more information about ground squirrels, download the free UC IPM Best Management Guidelines or UC IPM Pest Note

And there's more on rats in the orchard:



roof rats
roof rats

Posted on Friday, March 16, 2018 at 7:14 AM
  • Author: Pam Kan-Rice
Tags: avocado (290), citrus (339), damage (24), fruit (18), Norwegian (1), rats (2)

Hot Mandarins. What to Look forward to After a Fire

Mandarins, also known as “zipper skins” and “easy peelers” can have very fragile peels/skins/rinds/exocarp that make them easily subject to more damage than most oranges and lemons. Some are a bit tougher skinned than others, but some are so fragile that any rough handling often prevents them from going through conventional packing operations.

These skins were recently put to the test in the recent fires in Ojai. There was a mix of different varieties - ‘Pixie', ‘Gold Nugget', ‘W. Murcott', ‘Yosemite Gold', ‘Tahoe Gold' and others. Some of them were more sensitive than others, some were closer to the fire, all were affected by smoke to some degree. In Matilija Canyon where smoke was present for many more days than in the east of the Ojai Valley and possibly more ash, the trees have started flowering sooner. That might be temperature difference, either cooler or warmer, so it is hard to say how much effect the smoke has had versus, the ash and/or heat. Smoke has many different gasses in it, one of which is ethylene which is a naturally occurring ripening agent. Smoke not only has gasses, but it occludes the sun so less or more or altered light might have an effect on these fruit. It's not a controlled experiment, so some little scientist is going to have to come along and wriggle out these different effects. Whatever. Fire and smoke have an effect on mandarins as we have seen in other crops, such as cherimoya, avocados and other citrus.


Heat damage. Fruit facing the fire.


Ash effects on fruit coloring. Fruit was covered with ash for several days until rain washed it off. Might be a pH effect (ash is alkaline), temperature effect, uneven light radiation, or other…….


Same sort of uneven coloring, that actually looks like an ashy color, but the ash has washed off the cluster by rain


And here's something interesting where fruit facing the fire is much lighter colored than fruit facing away from the fire. Here are two pieces of fruit, one from the side directly facing the fire, and the other from the other side of the tree. The side of that fruit facing the fire was also lighter colored. So, it had an effect through the canopy (small tree). The canopy was otherwise intact, unaffected heat or flames.


Oh yeah, and there is the characteristic fruit drop from either the heat, smoke gases, water stress or ….


And then there's the fruit that looks like it had actual embers on the skin.

If the tree survives and keeps its green leaves, sometimes the fruit is affected in ways that don't appear for a while. The peel may be affected, but in many cases the fruit is just as sweet as it could be. It just looks terrible. That might even be a selling point. "Here have a wonderous piece of history that braved the horror of the Ojai fires."

Posted on Wednesday, March 7, 2018 at 6:38 AM
Tags: abiotic (13), citrus (339), damage (24), fire (30), fruit (18), heat (6), mandarins (5), postharvest (4), smoke (2), stormy (1)

Citrus Brown Rot Lookout

No rain for several years may have let citrus growers think that brown rot control is not important.  But it still is and it's just coming out after a few inches of rain earlier this January.  This is not the brown rot of stone fruits caused by Monilina fungus but a pathogen, completely different – Phytophthora spp.

Symptoms appear primarily on mature or nearly mature fruit. Initially, the firm, leathery lesions sometimes have a water-soaked appearance. Lesions are tan to olive brown, have a pungent odor, and may turn soft from secondary infections. Infected fruit eventually drop. Occasionally, twigs, leaves, and blossoms are infected, turning brown and dying.

Brown rot is caused by multiple species of Phytophthora when conditions are cool and wet. Brown rot develops mainly on fruit growing near the ground when Phytophthora spores from the soil are splashed onto the tree skirts during rainstorms; infections develop under continued wet conditions. Fruit in the early stage of the disease may go unnoticed at harvest and infect other fruit during storage.

Brown rot management primarily relies on prevention. Pruning tree skirts 24 or more inches above the ground can significantly reduce brown rot.

One spray of copper fungicide between October and December before or just after the first rain may provide protection throughout the wet season. When rainfall is excessive, you may have to repeat the spray in January or February. Spray the skirts to about 4 feet above ground. Spraying the ground underneath the trees also reduces brown rot infections. In addition to copper, other products effective against brown rot include the phosphonate and phenylamide fungicides. Phosphonates are applied as foliar and fruit or soil treatments, whereas phenylamides are applied as soil treatments for brown rot control. For soil applications, microsprinkler irrigation applications may be used.

Recently, oxathiapiprolin (Orondis®) was registered for use on citrus in California.  Orondis® is an outstanding alternative for Phytophthora control that may be applied as chemigation or foliar application.  However, foliar applications are preferred for preventing brown rot.

Postharvest Packinghouse Treatments to Prevent Fruit Decay

Potassium phosphite fungicides may be applied in aqueous dilutions to fruit alone or in combination with other postharvest fungicide treatments to manage nonvisible infections that occurred before harvest or protect fruit from brown rot infection after harvest during storage, distribution, and marketing. Use high-volume flooder or dip treatments for maximum coverage of fruit. Heated (125–136°F) fungicide solutions optimize performance of the potassium phosphite treatment. 

More citrus brown rot information is at:

Packers should check the Global MRL Database for all country MRLs at

Photos of brown rot on different citrus varieties - lemon, mandarin, orange

citrus brown rot lemon
citrus brown rot lemon

citrus brown rot mandarin
citrus brown rot mandarin

citrus brown rot orange
citrus brown rot orange

Posted on Friday, January 26, 2018 at 5:35 AM
Tags: citrus (339), disease (57), fruit (18), lemon (100), mandarin (68), orange (69), Phytophthora (23), Phytophthora gummosis (2)

New Crops – Rumpa or Rumba or Copao or Copado or Eulychnia brevifolia

Growers are looking for alternative crops and drought tolerant ones are better than water intensive ones, right? So, here's a recent question from someone who wants to grow the latest, new food crop.  “What about growing a drought tolerant (in fact, it doesn't need any water) cactus fruit that will make money?”  Cool. 

My first response is that it should do no harm. That should be a mantra when it comes to food, especially in this age of hyper-food safety vigilance. People are clever, though and foods that might be dangerous are often produced so that they can be eaten by most people. We do have acorns with tannic acid that need to be leached if you don't want to get severely sick.  Olives that need to be processed to edible. Puffer fish that with a wrong slice of the knife can kill you. There are any number of other foods that people have figured out a way to safely eat. 

Rumpa is cactus fruit from Chile that has a lot going for it – high nutrient content, high polyphenolic antioxidants, high C, small seeds like kiwi and pitahaya, and tada, drought resistant for our drought prone state. So, it's a cactus, yeah, but it doesn't have the teeth crunching seeds of opuntia cactus fruit – the tunas or prickly pear – that can scare some people.  Too vigorous chomping on the wondrously flavored prickly pear fruit leads to the small, hard seeds.  Shocking, although they are safe to swallow, mostly.

There are spines, but the fine spines on the rumpa fruit surface can be removed by rubbing on an abrasive surface. Not too vigorously, though since the fruit is quite delicate. This would be the same for the tuna fruit, too.  You can get rid of those spines with rubbing, too. So, eating the rumpa should be relatively safe.

The safety issue pops up with the spines on the stems. They are wicked thorns that protect the fruit with all the defenses needed to protect fruit in a hostile environment.  This is going to be a tough fruit to harvest.  Which may add to it glamour, like puffer fish.  Although in this case, it's not the consumer who is taking the risk, but the harvester.

Or you could grow dragon fruit, which is a cactus relative, which has no spines on the fruit and a few on the modified stem/leaves. It's got entirely edible, beautiful seeds. The right variety of dragon fruit can be quite tasteful, although many are quite bland.

So back to the question posed by the grower. If it's safe to eat, do you want to grow it?

According to Francisco Meza in the link below (google translation):

“Its fruits, called rumbas, have a bitter taste similar to lemon, but less tart, which would prevent them from being consumed fresh. However, thanks to its nutritional qualities, such as a high content of vitamin C, and good flavor once sweetened, could be used in the processing of processed foods such as jams, juices and drinks. But that's not all, since according to experts it can also be used in the manufacture of cosmetics.”

So, the advantage California coastal ag has is its climate. That's the competitive advantage.  If it can be grown cheaper, processed and shipped here from somewhere else, it's not going to work competitively here.  It's hard enough competing with similar climates like Mexico's and Chile's where the shipping becomes a problem for perishables.  But that is being dealt with and it's becoming hard for out-of-season coastal blueberry growers to compete with imported fruit in the season that the coast has dominated for the last several years.

So grow rumba/rumpa/copao in Ventura commercially? It's safe to eat.  But it doesn't sound like something that you gotta have….now.  It sounds like it needs to be jazzed up, which means processing. It's hard to pick.  And the market needs to be developed.  So, it's probably not a good idea to grow it commercially on the coast.

rumpa fruit 1
rumpa fruit 1

Posted on Tuesday, November 21, 2017 at 7:06 AM
Tags: alternative crops (12), cactus (3), capao (1), fruit (18), opuntia (1), rumpa (2), specialty crops (13)

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